ORCID Profile
0000-0002-7816-537X
Current Organisation
Australian National University
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Photonics, Optoelectronics and Optical Communications | Nanotechnology | Nanotechnology | Materials Engineering | Materials Engineering Not Elsewhere Classified | Compound Semiconductors | Nanofabrication, Growth and Self Assembly | Optical Physics | Optics And Opto-Electronic Physics | Other Electronic Engineering | Electrical and Electronic Engineering | Photonics and Electro-Optical Engineering (excl. Communications) | Synthesis of Materials | Photodetectors, Optical Sensors and Solar Cells | Condensed Matter Physics—Electronic And Magnetic Properties; | Nanophotonics | Nanoscale Characterisation | Interdisciplinary Engineering Not Elsewhere Classified | Renewable Power and Energy Systems Engineering (excl. Solar Cells) | Microelectronics and Integrated Circuits | Manufacturing Engineering Not Elsewhere Classified | Plant Biology | Instruments And Techniques | Functional Materials | Invertebrate Biology | Engineering Design | Manufacturing Processes and Technologies (excl. Textiles) | Lasers and Quantum Electronics | Catalysis and Mechanisms of Reactions | Engineering And Technology Not Elsewhere Classified | Nanometrology | Nanomanufacturing | Plant Cell and Molecular Biology | Plant Physiology | Photonic and electro-optical devices sensors and systems (excl. communications) | Electronics sensors and digital hardware | Electronic device and system performance evaluation testing and simulation | Physical Sciences Not Elsewhere Classified
ANZSRC Socio-Economic Objective (SEO)
Expanding Knowledge in the Physical Sciences | Integrated circuits and devices | Expanding Knowledge in Technology | Physical sciences | Other | Expanding Knowledge in Engineering | Communication equipment not elsewhere classified | Emerging Defence Technologies | Integrated Circuits and Devices | Scientific instrumentation | Solar-Photovoltaic Energy | Communication services not elsewhere classified | Expanding Knowledge in the Biological Sciences | Plant Production and Plant Primary Products not elsewhere classified | Air Force | Solar-photoelectric | Other | Manufactured products not elsewhere classified | Computer hardware and electronic equipment not elsewhere classified | Technological and organisational innovation | Manufacturing not elsewhere classified | Hydrogen Production from Renewable Energy | Expanding Knowledge in the Chemical Sciences | Machinery and equipment not elsewhere classified |
Related Links
Publications
Tilted response of fishnet metamaterials at near-infrared optical wavelengths
Publisher: American Physical Society (APS)
Date: 05-03-2010
Solid-phase epitaxy of Al/sub x/Ga/sub (1-x/)As: kinetics as a function of composition
Publisher: IEEE
Date: 1996
Selective wavelength tuning of self-assembled InAs quantum dots grown on InP
Publisher: AIP Publishing
Date: 08-05-2006
DOI: 10.1063/1.2203333
Abstract: We report the experimental results of tuning the emission wavelength of InAs∕InP quantum dots (QDs) by varying either the GaAs interlayer thickness or the indium composition of the InxGa1−xAs interlayer. The InAs QDs are grown on lattice-matched GaInAsP or InP buffers and are capped with an InP layer. As∕P exchange is prominent when the QDs are grown on an InP buffer. A model is developed which considers the As∕P exchange, gallium interdiffusion, strain, and barrier height. Our theoretical and experimental results show that gallium interdiffusion and the As∕P exchange reaction are mainly responsible for the observed shifts in the QD emission wavelength. The model shows that gallium interdiffusion from the interlayer to the InAs QDs grown on a GaInAsP buffer can be utilized to selectively tune the InAs QD emission wavelength over a wide range.
Global, regional, and national incidence, prevalence, and years lived with disability for 354 diseases and injuries for 195 countries and territories, 1990–2017: a systematic analysis for the Global B
Publisher: Elsevier BV
Date: 11-2018
Artemether-lumefantrine dosing for malaria treatment in young children and pregnant women: A pharmacokinetic-pharmacodynamic meta-analysis
Publisher: Public Library of Science (PLoS)
Date: 12-06-2018
Self-Healing of Fractured GaAs Nanowires
Publisher: American Chemical Society (ACS)
Date: 18-03-2011
DOI: 10.1021/NL104330H
Spatially resolved luminescence investigation of AlGaAs/GaAs single quantum wires modified by selective implantation and annealing
Publisher: AIP Publishing
Date: 22-11-1999
DOI: 10.1063/1.125344
Abstract: Single Al0.5Ga0.5As/GaAs V-groove quantum wires (QWR) modified by selective implantation and rapid thermally annealing were investigated by spatially resolved microphotoluminescence (micro-PL). The PL from the necking region was clearly observed at room temperature. Optical properties of QWR and the adjacent quantum well structures were strongly degraded by the implantation. The recovery properties of the PL signals from all the structures were dependent on the implantation dose. A critical dose of 1×1013 cm−2 was found for the selective implantation, over which the PL from the necking region could not be recovered. Also the blueshifts of QWR and the necking-region PL peaks were observed for all the annealed s les. This blueshift is caused by the interface intermixing, which is very useful to increase the confinement of carriers in QWR region for optoelectronic device applications.
Ultrafast dynamics in ZnO/ZnMgO multiple quantum wells
Publisher: IOP Publishing
Date: 06-07-2007
Elemental diffusion during the droplet epitaxy growth of In(Ga)As/GaAs(001) quantum dots by metal-organic chemical vapor deposition
Publisher: AIP Publishing
Date: 13-01-2014
DOI: 10.1063/1.4859915
Abstract: Droplet epitaxy is an important method to produce epitaxial semiconductor quantum dots (QDs). Droplet epitaxy of III-V QDs comprises group III elemental droplet deposition and the droplet crystallization through the introduction of group V elements. Here, we report that, in the droplet epitaxy of InAs/GaAs(001) QDs using metal-organic chemical vapor deposition, significant elemental diffusion from the substrate to In droplets occurs, resulting in the formation of In(Ga)As crystals, before As flux is provided. The supply of As flux suppresses the further elemental diffusion from the substrate and promotes surface migration, leading to large island formation with a low island density.
Evaluation of a treatment protocol for anaemia in pregnancy nested in routine antenatal care in a limited-resource setting
Publisher: Informa UK Limited
Date: 2019
Band alignment and band bending at α-Ga2O3/ZnO n-n isotype hetero-interface
Publisher: AIP Publishing
Date: 11-11-2019
DOI: 10.1063/1.5126325
Abstract: Understanding the electronic structures at the interfaces of wide bandgap oxide heterostructures is crucial for the rational design of oxide-based optoelectronic devices with novel functionality and improved performance. In this work, the electronic band diagram at a ZnO/α-Ga2O3 n-n isotype heterojunction is investigated by depth-profile x-ray photoemission spectroscopy (XPS). The directly measured valence-band offset is −0.61 ± 0.1 eV and a type-I (straddling gap) band alignment is formed at the ZnO/α-Ga2O3 heterointerface. As probed by the depth profile of core-levels and VB-XPS, the formation of an interfacial layer is observed due to Ga and Zn interdiffusion, where charged interfacial states result in the downward and upward band-bending at the ZnO and α-Ga2O3 sides, respectively. The influence of band bending and band discontinuity at the interface is confirmed by the rectifying characteristics in the Au/α-Ga2O3/ZnO heterojunction with electron accumulation at its interface. Taking the thermionic-field emission and band-to-band tunneling mechanisms into account, the simulated transport properties agrees well with the reported I-V characteristics of Au/α-Ga2O3/ZnO avalanche photodiode, a further validation of the deduced band alignment of the heterostructure.
Catalyst size dependent growth of Pd-catalyzed one-dimensional InAs nanostructures
Publisher: AIP Publishing
Date: 20-05-2013
DOI: 10.1063/1.4807597
Abstract: In this study, Pd was used as catalyst to grow one-dimensional InAs nanostructures on GaAs (111)B substrates in order to explore the growth mechanism and the effect of non-gold catalysts in growing epitaxial III-V nanostructures. With detailed morphological, structural, and chemical characterizations using electron microscopy, coupled with analysis of the Pd-In binary phase diagram, it was found that size of Pd nanoparticles plays a key role in determining the growth mechanism of one-dimensional InAs nanostructures.
Retrospective Review of Documentation Practices of Hepatitis B Immunoglobulin, Birth Dose, and Vaccination at the Hospital of Birth, in Thai Nationals and Migrants in Northern Thailand
Publisher: Oxford University Press (OUP)
Date: 12-2019
DOI: 10.1093/OFID/OFZ518
Abstract: Vaccination remains the mainstay of prevention of hepatitis B virus (HBV) including birth dose and hepatitis B immunoglobulins (HBIGs). National estimates of vaccination coverage exclude migrants. The objective of this study is to investigate documentation practices of HBV-related infant vaccinations in Northern Thailand including migrants. This is a retrospective review of hospital records of women who birthed infants in 2015 at Maharaj Nakorn Hospital, Chiang Mai (CM) or on the Thailand-Myanmar border, Tak. Of 2522 women, 987 were from CM (861 Thai nationals, 126 migrants) and 1535 were from Tak (651 Thai residence and 884 Myanmar residence). In CM, documentation for the birth dose vaccine (999 of 999, 100%) and HBIG was complete. In Tak, documentation was 1441 of 1549 (93%) for birth dose and 26 of 34 (76.5%) for HBIG, with missed opportunities including home delivery, delay in obtaining hepatitis B e-antigen status, and limitations of the records. Expanded Program of Immunization (EPI) documentation of 3 follow-up vaccinations dwindled with subsequent doses and distance, and complete documentation of 3 HBV EPI vaccines at the hospital of birth was low, 41.5% (1056 of 2547), but equitable for Thai or migrant status. This review provides strong support for excellent documentation of HBIG and birth dose vaccination in urban and rural settings, and in migrants, consistent with Thailand’s vaccination policy and practice. Documentation of the 3 HBV EPI at the hospital of birth decreases with sequential doses, especially in families further away. Innovative data linkage is required to prove coverage and identify gaps.
Vivax malaria in pregnancy and lactation: A long way to health equity
Publisher: Springer Science and Business Media LLC
Date: 22-01-2020
DOI: 10.1186/S12936-020-3123-1
Abstract: The Sustainable Development Goals (SDG) call for increased gender equity and reduction in malaria-related mortality and morbidity. Plasmodium vivax infections in pregnancy are associated with maternal anaemia and increased adverse perinatal outcomes. Providing radical cure for women with 8-aminoquinolines (e.g., primaquine) is hindered by gender-specific complexities. A symptomatic episode of vivax malaria at 18 weeks of gestation in a primigravid woman was associated with maternal anaemia, a recurrent asymptomatic P. vivax episode, severe intra-uterine growth restriction with no other identifiable cause and induction to reduce the risk of stillbirth. At 5 months postpartum a qualitative glucose-6-phosphate dehydrogenase (G6PD) point-of-care test was normal and radical cure with primaquine was prescribed to the mother. A 33% fractional decrease in haematocrit on day 7 of primaquine led to further testing which showed intermediate phenotypic G6PD activity the G6PD genotype could not be identified. Her infant daughter was well throughout maternal treatment and found to be heterozygous for Mahidol variant. Adverse effects of vivax malaria in pregnancy, ineligibility of radical cure for pregnant and postpartum women, and difficulties in diagnosing intermediate levels of G6PD activity multiplied morbidity in this woman. Steps towards meeting the SDG include prevention of malaria in pregnancy, reducing unnecessary exclusion of women from radical cure, and accessible quantitative G6PD screening in P. vivax -endemic settings.
High dose Si- and Mg-implantation in GaN: Electrical and structural analysis
Publisher: Elsevier BV
Date: 05-1997
Effect of the crystal structure on the optical properties of InP nanowires
Publisher: IEEE
Date: 10-2009
Selective confinement of macroscopic long-lifetime exciton and trion populations
Publisher: American Physical Society (APS)
Date: 27-12-2011
Realization of p-type gallium nitride by magnesium ion implantation for vertical power devices
Publisher: Springer Science and Business Media LLC
Date: 19-06-2019
DOI: 10.1038/S41598-019-45177-0
Abstract: Implementing selective-area p-type doping through ion implantation is the most attractive choice for the fabrication of GaN-based bipolar power and related devices. However, the low activation efficiency of magnesium (Mg) ions and the inevitable surface decomposition during high-temperature activation annealing process still limit the use of this technology for GaN-based devices. In this work, we demonstrate successful p-type doping of GaN using protective coatings during a Mg ion implantation and thermal activation process. The p-type conduction of GaN is evidenced by the positive Seebeck coefficient obtained during thermopower characterization. On this basis, a GaN p-i-n diode is fabricated, exhibiting distinct rectifying characteristics with a turn-on voltage of 3 V with an acceptable reverse breakdown voltage of 300 V. Electron beam induced current (EBIC) and electroluminescent (EL) results further confirm the formation of p-type region due to Mg ion implantation and subsequent thermal activation. This repeatable and uniform manufacturing process can be implemented in mass production of GaN devices for versatile power and optoelectronic applications.
Effect of Auger recombination on the performance of p-doped quantum dot lasers
Publisher: AIP Publishing
Date: 17-04-2006
DOI: 10.1063/1.2193433
Abstract: Experimental results on spontaneous emission rates from InGaAs quantum dot lasers that can be explained theoretically by considering the influence of nonradiative mixed state recombinations in the quantum dot-wetting layer system are presented. Our model qualitatively explains the experimental results such as an increase in the threshold current density, temperature stability, and a narrower gain spectrum due to doping the quantum dot active region with the acceptors. Our model also predicts that moderate acceptor concentrations can improve the laser performance at higher carrier injection densities but high acceptor concentrations deteriorate the laser performance due to the nonradiative Auger recombination that counteracts the benefits of increased spontaneous emission rates.
Intermixing-induced resonance shift in GaAs/AlxOy distributed Bragg resonators
Publisher: AIP Publishing
Date: 06-1999
DOI: 10.1063/1.370616
Abstract: The effect of ion implantation-induced interdiffusion on the resonant wavelength of GaAs/AlxOy distributed Bragg reflectors is investigated. As interdiffusion becomes stronger, the resonant wavelength is seen to redshift. Shifts of more than 60 nm could be achieved for center wavelengths around 800 nm. A model is proposed to explain this behavior. This model agrees well with previous lateral oxidation studies.
Ion implantation for wavelength-shifting and quantum wire lasers
Publisher: IEEE
Date: 1996
Enrolling pregnant women in research: ethical challenges encountered in Lao PDR (Laos)
Publisher: Springer Science and Business Media LLC
Date: 12-2017
A new optical front-end compensation technique for suppression of spurious signal in photoreflectance spectroscopy using an antiphase signal
Publisher: AIP Publishing
Date: 04-2010
DOI: 10.1063/1.3368598
Abstract: A new optical front-end compensation technique to suppress the unwanted, spurious signal in photoreflectance (PR) spectroscopy is developed. In this approach an optical compensation signal, which is litude-matched to and in antiphase to the spurious signal, is introduced and directed to the photodetector. The combination of the compensation signal and the spurious signal results in a dc output from the photodetector which is thereafter suppressed by the lock-in lifier, leaving only the true PR signal to be recovered and lified. A high spurious signal suppression efficiency is demonstrated and the advantages of the technique are discussed.
Twinning Superlattice Formation in GaAs Nanowires
Publisher: American Chemical Society (ACS)
Date: 05-09-2013
DOI: 10.1021/NN403390T
Abstract: Semiconductor nanowires have proven a versatile platform for the realization of novel structures unachievable by traditional planar epitaxy techniques. Among these, the periodic arrangement of twin planes to form twinning superlattice structures has generated particular interest. Here we demonstrate twinning superlattice formation in GaAs nanowires and investigate the diameter dependence of both morphology and twin plane spacing. An approximately linear relationship is found between plane spacing and nanowire diameter, which contrasts with previous results reported for both InP and GaP. Through modeling, we relate this to both the higher twin plane surface energy of GaAs coupled with the lower supersaturation relevant to Au seeded GaAs nanowire growth. Understanding and modeling the mechanism of twinning superlattice formation in III-V nanowires not only provides fundamental insight into the growth process, but also opens the door to the possibility of tailoring twin spacing for various electronic and mechanical applications.
Crystallographically driven Au catalyst movement during growth of InAs/GaAs axial nanowire heterostructures
Publisher: AIP Publishing
Date: 04-2009
DOI: 10.1063/1.3103265
Abstract: The movement of Au catalysts during growth of InAs on GaAs nanowires has been carefully investigated by transmission electron microscopy. It has been found that Au catalysts preferentially stay on {112}B GaAs sidewalls. Since a {112} surface is composed of a {111} facet and a {002} facet and since {111} facets are polar facets for the zinc-blende structure, this crystallographic preference is attributed to the different interface energies caused by the different polar facets. We anticipate that these observations will be useful for the design of nanowire heterostructure based devices.
Room temperature photocurrent spectroscopy of single zincblende and wurtzite InP nanowires
Publisher: AIP Publishing
Date: 11-05-2009
DOI: 10.1063/1.3138137
Abstract: Simple photolithographic techniques are used to fabricate single InP nanowire devices with back-to-back Schottky barriers. Direct imaging of the photoresponse shows that the active regions of the device are spatially localized near the reverse-biased Schottky barrier. By tuning the laser excitation energy from below to well above the energy gap, photocurrent spectroscopy can illuminate the zincblende or wurtzite nature of the nanowire device even at room temperature.
Solid-phase epitaxial growth of AlxGa1−xAs alloys as a function of Al content
Publisher: AIP Publishing
Date: 08-09-1997
DOI: 10.1063/1.119904
Abstract: The solid-phase epitaxial growth (SPEG) of amorphized AlxGa1−xAs alloys has been investigated as a function of Al content (0⩽x⩽0.46). Time-resolved reflectivity and Rutherford backscattering spectrometry in combination with channeling (RBS/C) were used to determine the recrystallization kinetics over the temperature range 220–310 °C. Residual disorder was characterized with RBS/C and cross-sectional transmission electron microscopy. At a given temperature, both the average velocity and nonplanarity of the amorphous/crystalline interface increased as the Al content increased. In contrast, an Al-content dependence was not observed for residual disorder—for all compositions, single-crystal regrowth was apparent for ∼25 nm followed by the onset of twinning. The SPEG kinetics exhibited an Arrhenius-type temperature behavior with an average activation energy Eact value of 1.60 eV independent of Al content. Also, the validity of a recrystallization mechanism based on the collective reorganization of groups of atoms was verified—Debye frequency values derived from experimental Eact results were in excellent agreement with theoretical predictions.
InGaAs quantum dots-in-a-well photodetectors grown by metal organic chemical vapor deposition
Publisher: IEEE
Date: 2005
Rapid thermal annealing study of InGaAs/GaAs quantum dot infrared photodetectors grown by metal-organic chemical vapor deposition
Publisher: IEEE
Date: 2005
Air Pollution Exposure During Pregnancy and Symptoms of Attention Deficit and Hyperactivity Disorder in Children in Europe
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 09-2018
Photomodulated Rayleigh Scattering of Single Semiconductor Nanowires: Probing Electronic Band Structure
Publisher: American Chemical Society (ACS)
Date: 16-09-2011
DOI: 10.1021/NL202433G
Abstract: The internal electronic structures of single semiconductor nanowires can be resolved using photomodulated Rayleigh scattering spectroscopy. The Rayleigh scattering from semiconductor nanowires is strongly polarization sensitive which allows a nearly background-free method for detecting only the light that is scattered from a single nanowire. While the Rayleigh scattering efficiency from a semiconductor nanowire depends on the dielectric contrast, it is relatively featureless as a function of energy. However, if the nanowire is photomodulated using a second pump laser beam, the internal electronic structure can be resolved with extremely high signal-to-noise and spectral resolution. The photomodulated Rayleigh scattering spectra can be understood theoretically as a first derivative of the scattering efficiency that results from a modulation of the band gap and depends sensitively on the nanowire diameter. Fits to spectral lineshapes provide both the band structure and the diameter of in idual GaAs and InP nanowires under investigation.
Single-Step RIE Fabrication Process of Low Loss InP Waveguide Using CH[sub 4]∕H[sub 2] Chemistry
Publisher: The Electrochemical Society
Date: 2011
DOI: 10.1149/1.3532767
Measurement of the distribution of damage in ion implanted GaAs by differential reflectance spectroscopy
Publisher: Elsevier BV
Date: 03-1995
On quantifying the group-V to group-III interdiffusion rates in InxGa1−xAs/InP quantum wells
Publisher: IOP Publishing
Date: 09-05-2006
Design Principles for Fabrication of InP-Based Radial Junction Nanowire Solar Cells Using an Electron Selective Contact
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2019
Phase Perfection in Zinc Blende and Wurtzite III-V Nanowires Using Basic Growth Parameters
Publisher: American Chemical Society (ACS)
Date: 04-02-2010
DOI: 10.1021/NL903688V
Abstract: Controlling the crystallographic phase purity of III-V nanowires is notoriously difficult, yet this is essential for future nanowire devices. Reported methods for controlling nanowire phase require dopant addition, or a restricted choice of nanowire diameter, and only rarely yield a pure phase. Here we demonstrate that phase-perfect nanowires, of arbitrary diameter, can be achieved simply by tailoring basic growth parameters: temperature and V/III ratio. Phase purity is achieved without sacrificing important specifications of diameter and dopant levels. Pure zinc blende nanowires, free of twin defects, were achieved using a low growth temperature coupled with a high V/III ratio. Conversely, a high growth temperature coupled with a low V/III ratio produced pure wurtzite nanowires free of stacking faults. We present a comprehensive nucleation model to explain the formation of these markedly different crystal phases under these growth conditions. Critical to achieving phase purity are changes in surface energy of the nanowire side facets, which in turn are controlled by the basic growth parameters of temperature and V/III ratio. This ability to tune crystal structure between twin-free zinc blende and stacking-fault-free wurtzite not only will enhance the performance of nanowire devices but also opens new possibilities for engineering nanowire devices, without restrictions on nanowire diameters or doping.
Recrystallization of high energy As-implanted GaAs studied by transmission electron microscopy
Publisher: AIP Publishing
Date: 11-03-1996
DOI: 10.1063/1.115679
Abstract: Ion implantation damage and the regrowth process during thermal annealing of 2 MeV As-ion-implanted GaAs were studied by transmission electron microscopy. With low-temperature annealing, a high denisty of stacking faults was formed during the recrystallization process, but they were rarely observed with high-temperature annealing. At intermediate temperatures, a much lower denisty of stacking faults was generated at the upper interface between the buried amorphous layer and the crystal than that at the lower interface, where a higher concentration of as-implanted arsenic exists. Based on the observed experimental results, an atomic model is proposed to explain the formation of stacking faults induced by As clusters.
Passive mode locking of a self-frequency-doubling Yb:YAl_3(BO_3)_4 laser
Publisher: The Optical Society
Date: 15-03-2002
DOI: 10.1364/OL.27.000436
Abstract: We report passive mode-locking experiments with a novel self-doubling laser crystal Yb:YAl(3)(BO(3))(4) (Yb:YAB). The diode-pumped laser was mode locked by an ion-implanted semiconductor saturable absorber mirror. Far off phase matching, soliton mode locking produced pulse widths of 198 fs to 1.4 ps, with up to 660-mW output and optical efficiency of 24% at 1040 nm. The shortest pulses had a peak power of 28 kW with 440-mW average power and 16% efficiency. A few degrees off phase matching, a total of 60 mW of green femtosecond pulses was generated simultaneously. Close to phase matching, the laser produced picosecond pulses and, without infrared output, a total of 270 mW of green output, corresponding to 10% conversion efficiency (absorbed pump to green output).
Electrically-tunable solid-state metasurfaces via flash localised heating
Publisher: Research Square Platform LLC
Date: 24-05-2022
DOI: 10.21203/RS.3.RS-1665364/V1
Abstract: Metasurfaces have recently realised many revolutionary applications such as metalenses, equation solvers, beam shapers, and holographic projection.1–4 However, the conventional metasurfaces are monotask due to their fixed dimensions. Therefore, realising multitask metasurfaces for applications such as beam steering, optical switches and meta-displays, which require fast and dynamic reconfigurability, has bottlenecked. To address this technological challenge, there has been a quest to enable tunability via mechanical tilting or stretching the s les, rotating the illumination angle or the incident light polarisation, use of chemical reactions, and others.5–8 However, most of these approaches still suffer from slow tuning rate, weak modulation, and bulky or non-solid state components. Here, we introduce electrically tunable metasurfaces that offer up to 9 folds surge in transmission, i.e. 90% transmission modulation depth, with switching time µs, i.e. one order of magnitude faster than video frame rates. To realise such a breakthrough, we have driven the designed metasurface by V spiked voltage, asymmetrically, for the first time in optoelectronics.
Comparison of proton and phosphorous ion implantation-induced intermixing of InAs/InP quantum dots
Publisher: IOP Publishing
Date: 02-04-2007
Ion damage buildup and amorphization processes in GaAs–AlxGa1−xAs multilayers
Publisher: AIP Publishing
Date: 09-1996
DOI: 10.1063/1.363186
Abstract: The nature of ion damage buildup and amorphization in GaAs–AlxGa1−xAs multilayers at liquid-nitrogen temperature is investigated for a variety of compositions and structures using Rutherford backscattering-channeling and cross-sectional transmission electron microscopy techniques. In this multilayer system, damage accumulates preferentially in the GaAs layers however, the presence of AlGaAs enhances the dynamic annealing process in adjacent GaAs regions and thus amorphization is retarded close to the GaAs–AlGaAs interfaces even when such regions suffer maximum collisional displacements. This dynamic annealing in AlGaAs and at GaAs–AlGaAs interfaces is more efficient with increasing Al content however, the dynamic annealing process is not perfect and an amorphous phase may be formed at the interface above a critical defect level or ion dose. Once an amorphous phase is nucleated, amorphization proceeds rapidly into the adjacent AlGaAs. This is explained in terms of the interplay between defect migration and defect trapping at an amorphous–crystalline or GaAs–AlGaAs interface. In addition, enhanced recrystallization of the amorphous GaAs at the interface may occur during heating if an amorphous phase is not formed in the adjacent AlGaAs layer. This is most likely the result of mobile defects injected from the AlGaAs layer during heating.
Impurity-free disordering mechanisms in GaAs-based structures using doped spin-on silica layers
Publisher: AIP Publishing
Date: 31-05-2002
DOI: 10.1063/1.1484244
Abstract: We have used photoluminescence, deep level transient spectroscopy and x-ray photoelectron spectroscopy to investigate the mechanisms of impurity-free disordering in GaAs-based structures using doped spin-on silica layers. We demonstrate that VGa is efficiently converted into arsenic-antisite, AsGa, related defects (EL2-type defects) when the GaAs layer is under compressive stress. We propose that the efficient formation of EL2-type defects reduces the efficiency of impurity-free interdiffusion of GaAs/AlGaAs quantum wells.
Nutrition in transition: historical cohort analysis summarising trends in under- and over-nutrition among pregnant women in a marginalised population along the Thailand–Myanmar border from 1986 to 201
Publisher: Cambridge University Press (CUP)
Date: 26-06-2019
DOI: 10.1017/S0007114519000758
Abstract: The objective of the present study is to summarise trends in under- and over-nutrition in pregnant women on the Thailand–Myanmar border. Refugees contributed data from 1986 to 2016 and migrants from 1999 to 2016 for weight at first antenatal consultation. BMI and gestational weight gain (GWG) data were available during 2004–2016 when height was routinely measured. Risk factors for low and high BMI were analysed for ·5 kg/m 2 or ≥23 kg/m 2 , respectively. A total of 48 062 pregnancies over 30 years were available for weight analysis and 14 646 pregnancies over 13 years (2004–2016) had BMI measured in first trimester ( weeks’ gestational age). Mean weight at first antenatal consultation in any trimester increased over the 30-year period by 2·0 to 5·2 kg for all women. First trimester BMI has been increasing on average by 0·5 kg/m 2 for refugees and 0·6 kg/m 2 for migrants, every 5 years. The proportion of women with low BMI in the first trimester decreased from 16·7 to 12·7 % for refugees and 23·1 to 20·2 % for migrants, whereas high BMI increased markedly from 16·9 to 33·2 % for refugees and 12·3 to 28·4 % for migrants. Multivariate analysis demonstrated low BMI as positively associated with being Burman, Muslim, primigravid, having malaria during pregnancy and smoking, and negatively associated with refugee as opposed to migrant status. High BMI was positively associated with being Muslim and literate, and negatively associated with age, primigravida, malaria, anaemia and smoking. Mean GWG was 10·0 ( sd 3·4), 9·5 ( sd 3·6) and 8·3 ( sd 4·3) kg, for low, normal and high WHO BMI categories for Asians, respectively.
Photoconductive response correction for detectors of terahertz radiation
Publisher: AIP Publishing
Date: 09-2008
DOI: 10.1063/1.2969035
Abstract: Photoconductive detectors are convenient devices for detecting pulsed terahertz radiation. We have optimized Fe+ ion-damaged InP materials for photoconductive detector signal to noise performance using dual-energy doses in the range from 2.5×1012 to 1.0×1016 cm−2. Ion implantation allowed the production of semiconducting materials with free-carrier lifetimes between 0.5 and 2.1 ps, which were measured by optical pump terahertz probe spectroscopy. The time resolved photoconductivity of the detector substrates was acquired as a function of time after excitation by 2 nJ pulses from a laser oscillator. These data, when combined with a deconvolution algorithm, provide an excellent spectral response correction to the raw photocurrent signal recorded by the photoconductive detectors.
Anelastic Behavior in GaAs Semiconductor Nanowires
Publisher: American Chemical Society (ACS)
Date: 13-06-2013
DOI: 10.1021/NL401175T
Abstract: The mechanical behavior of vertically aligned single-crystal GaAs nanowires grown on GaAs(111)B surface was investigated using in situ deformation transmission electron microscopy. Anelasticity was observed in nanowires with small diameters and the anelastic behavior was affected by the crystalline defects in the nanowires. The underlying mechanism for the observed anelasticity is discussed. The finding opens up the prospect of using nanowire materials for nanoscale d ing applications.
Properties of In0.5Ga0.5As/GaAs/Al0.2Ga0.8As quantum-dots-in-a-well infrared photodetectors
Publisher: IOP Publishing
Date: 15-04-2009
Impact of invasive metal probes on Hall measurements in semiconductor nanostructures
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0NR04402D
Abstract: Experimental data and modelling show that invasive Hall probes lead to substantial misestimates of carrier concentration and mobility in 2D-nanostructure devices.
Author Correction: Mapping local patterns of childhood overweight and wasting in low- and middle-income countries between 2000 and 2017
Publisher: Springer Science and Business Media LLC
Date: 02-07-2020
DOI: 10.1038/S41591-020-0972-7
Abstract: An amendment to this paper has been published and can be accessed via a link at the top of the paper.
A comparative study of deep levels created by low dose implantation of hydrogen, oxygen and silicon into MOCVD grown n-GaAs
Publisher: Elsevier BV
Date: 12-1995
Room-Temperature Preperation of InGaAsN Quantum Dot Lasers Grown by MOCVD
Publisher: The Electrochemical Society
Date: 2005
DOI: 10.1149/1.1848293
Extreme absorption enhancement in ZnTe:O/ZnO intermediate band core-shell nanowires by interplay of dielectric resonance and plasmonic bowtie nanoantennas
Publisher: Springer Science and Business Media LLC
Date: 08-08-2017
DOI: 10.1038/S41598-017-07970-7
Abstract: Intermediate band solar cells (IBSCs) are conceptual and promising for next generation high efficiency photovoltaic devices, whereas, IB impact on the cell performance is still marginal due to the weak absorption of IB states. Here a rational design of a hybrid structure composed of ZnTe:O/ZnO core-shell nanowires (NWs) with Al bowtie nanoantennas is demonstrated to exhibit strong ability in tuning and enhancing broadband light response. The optimized nanowire dimensions enable absorption enhancement by engineering leaky-mode dielectric resonances. It maximizes the overlap of the absorption spectrum and the optical transitions in ZnTe:O intermediate-band (IB) photovoltaic materials, as verified by the enhanced photoresponse especially for IB states in an in idual nanowire device. Furthermore, by integrating Al bowtie antennas, the enhanced exciton-plasmon coupling enables the notable improvement in the absorption of ZnTe:O/ZnO core-shell single NW, which was demonstrated by the profound enhancement of photoluminescence and resonant Raman scattering. The marriage of dielectric and metallic resonance effects in subwavelength-scale nanowires opens up new avenues for overcoming the poor absorption of sub-gap photons by IB states in ZnTe:O to achieve high-efficiency IBSCs.
Validation of the Edinburgh Postnatal Depression Scale (EPDS) on the Thai–Myanmar border
Publisher: SAGE Publications
Date: 12-07-2017
Abstract: Postnatal depression is common and may have severe consequences for women and their children. Locally validated screening tools are required to identify at-risk women in marginalised populations. The Edinburgh Postnatal Depression Scale (EPDS) is one of the most frequently used tools globally. This cross-sectional study assessed the validity and acceptability of the EPDS in Karen and Burmese among postpartum migrant and refugee women on the Thai–Myanmar border. The EPDS was administered to participants and results compared with a diagnostic interview. Local staff provided feedback on the acceptability of the EPDS through a focus group discussion. Results from 670 women showed high accuracy and reasonable internal consistency of the EPDS. However, acceptability to local staff was low, limiting the utility of the EPDS in this setting despite its good psychometrics. Further work is required to identify a tool that is acceptable and sensitive to cultural manifestations of depression in this vulnerable population.
Influence of Nanowire Density on the Shape and Optical Properties of Ternary InGaAs Nanowires
Publisher: American Chemical Society (ACS)
Date: 21-02-2006
DOI: 10.1021/NL052189O
Abstract: We have synthesized ternary InGaAs nanowires on (111)B GaAs surfaces by metal-organic chemical vapor deposition. Au colloidal nanoparticles were employed to catalyze nanowire growth. We observed the strong influence of nanowire density on nanowire height, tapering, and base shape specific to the nanowires with high In composition. This dependency was attributed to the large difference of diffusion length on (111)B surfaces between In and Ga reaction species, with In being the more mobile species. Energy dispersive X-ray spectroscopy analysis together with high-resolution electron microscopy study of in idual InGaAs nanowires shows large In/Ga compositional variation along the nanowire supporting the present diffusion model. Photoluminescence spectra exhibit a red shift with decreasing nanowire density due to the higher degree of In incorporation in more sparsely distributed InGaAs nanowires.
Resolving Stable Axial Trapping Points of Nanowires in an Optical Tweezers Using Photoluminescence Mapping
Publisher: American Chemical Society (ACS)
Date: 14-02-2013
DOI: 10.1021/NL304607V
Abstract: Axially resolved microphotoluminescence mapping of semiconductor nanowires held in an optical tweezers reveals important new experimental information regarding equilibrium trapping points and trapping stability of high aspect ratio nanostructures. In this study, holographic optical tweezers are used to scan trapped InP nanowires along the beam direction with respect to a fixed excitation source and the luminescent properties are recorded. It is observed that nanowires with lengths on the range of 3-15 μm are stably trapped near the tip of the wire with the long segment positioned below the focus in an inverted trapping configuration. Through the use of trap multiplexing we investigate the possibility of improving the axial stability of the trapped nanowires. Our results have important implication for applications of optically assisted nanowire assembly and optical tweezers based scanning probes microscopy.
III–V Semiconductor Whispering-Gallery Mode Micro-Cavity Lasers: Advances and Prospects
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2022
Transient Rayleigh Scattering: A New Probe of Picosecond Carrier Dynamics in a Single Semiconductor Nanowire
Publisher: American Chemical Society (ACS)
Date: 19-09-2012
DOI: 10.1021/NL302767U
Abstract: Using a new technique, transient Rayleigh scattering, we show that measurements from a single GaAs/AlGaAs core-shell semiconductor nanowire provide sensitive and detailed information on the time evolution of the density and temperature of the electrons and holes after photoexcitation by an intense laser pulse. Through band filling, band gap renormalization, and plasma screening, the presence of a dense and hot electron-hole plasma directly influences the real and imaginary parts of the complex index of refraction that in turn affects the spectral dependence of the Rayleigh scattering cross-section in well-defined ways. By measuring this spectral dependence as a function of time, we directly determine the thermodynamically independent density and temperature of the electrons and holes as a function of time after pulsed excitation as the carriers thermalize to the lattice temperature. We successfully model the results by including ambipolar transport, recombination, and cooling through optic and acoustic phonon emission that quantify the hole mobility at ∼68,000 cm(2)/V·s, linear decay constant at 380 ps, bimolecular recombination rate at 4.8 × 10(-9) cm(3)/s and the energy-loss rate of plasma due to optical and acoustic phonon emission.
Enhanced photoluminescence efficiency of mid-infrared InAsSb nanostructures using a carrier blocking layer
Publisher: AIP Publishing
Date: 24-05-2010
DOI: 10.1063/1.3436562
Abstract: This paper presents a study on the emission efficiency enhancement of InAsSb nanostructures using a carrier blocking layer. InP is proposed to serve as the carrier blocking layer to suppress the thermal escape of carriers in InAsSb nanostructures and significantly enhance their emission efficiency at high temperature (good photoluminescence signal even at 330 K). However, this leads to a blueshift in their emission wavelength due to the significantly increased quantum confinement of the nanostructures. By inserting a thin InGaAs layer between InP blocking layer and InAsSb nanostructures, longer emission wavelength can be maintained. This provides an approach to achieve InAsSb nanostructures with both good high-temperature optical characteristics and long emission wavelength, which is very useful for fabricating mid-infrared emitters operating at room temperature.
Magneto-Optical Properties of Wurtzite-Phase InP Nanowires
Publisher: American Chemical Society (ACS)
Date: 08-07-2014
DOI: 10.1021/NL500870E
Abstract: The possibility to grow in zincblende (ZB) and/or wurtzite (WZ) crystal phase widens the potential applications of semiconductor nanowires (NWs). This is particularly true in technologically relevant III-V compounds, such as GaAs, InAs, and InP, for which WZ is not available in bulk form. The WZ band structure of many III-V NWs has been widely studied. Yet, transport (that is, carrier effective mass) and spin (that is, carrier g-factor) properties are almost experimentally unknown. We address these issues in a well-characterized material: WZ indium phosphide. The value and anisotropy of the reduced mass (μ exc) and g-factor (g exc) of the band gap exciton are determined by photoluminescence measurements under intense magnetic fields (B, up to 28 T) applied along different crystallographic directions. μ exc is 14% greater in WZ NWs than in a ZB bulk reference and it is 6% greater in a plane containing the WZ ĉ axis than in a plane orthogonal to ĉ. The Zeeman splitting is markedly anisotropic with g exc = |ge| = 1.4 for B⊥ĉ (where ge is the electron g-factor) and g exc = |ge - gh,//| = 3.5 for B//ĉ (where gh,// is the hole g-factor). A noticeable B-induced circular dichroism of the emitted photons is found only for B//ĉ, as expected in WZ-phase materials.
Suppression of thermal atomic interdiffusion in InGaAs/AlGaAs QW laser structures
Publisher: SPIE
Date: 25-03-2004
DOI: 10.1117/12.523517
Influence of the number and timing of malaria episodes during pregnancy on prematurity and small-for-gestational-age in an area of low transmission.
Publisher: Springer Science and Business Media LLC
Date: 21-06-2017
Direct-write non-linear photolithography for semiconductor nanowire characterization
Publisher: IOP Publishing
Date: 03-08-2012
DOI: 10.1088/0957-4484/23/33/335704
Abstract: A practical bottleneck prohibiting the rapid, confident and damage-free electrical contacting of vapour-liquid-solid grown nanowires arises from the random spatial distribution and variation in quality of the nanowires, and the contact dimensions required. Established techniques such as electron-beam lithography or focused ion-beam deposition have challenges in scaling, damage or complexity that can make a large statistical s le difficult. We present a direct laser-writing technique to allow rapid electrical contacting of nanowires on a large variety of substrates.
Engineering the composition, morphology, and optical properties of InAsSb nanostructures via graded growth technique
Publisher: AIP Publishing
Date: 21-01-2013
DOI: 10.1063/1.4789513
Abstract: Graded growth technique is utilized to realize the control over the composition, morphology, and optical properties of self-assembled InAsSb/InGaAs/InP nanostructures. By increasing the initial mole fraction of the Sb precursor during the graded growth of InAsSb, more Sb atoms can be incorporated into the InAsSb nanostructures despite the same Sb mole fraction averaged over the graded growth. This leads to a shape change from dots to dashes/wires for the InAsSb nanostructures. As a result of the composition and morphology change, photoluminescence from the InAsSb nanostructures shows different polarization and temperature characteristics. This work demonstrates a technologically important technique—graded growth, to control the growth and the resultant physical properties of self-assembled semiconductor nanostructures.
Characterization of deep level traps responsible for isolation of proton implanted GaAs
Publisher: AIP Publishing
Date: 05-03-2003
DOI: 10.1063/1.1554761
Abstract: Deep level transient spectroscopy was employed to determine the electrical properties of defects induced in metalorganic chemical-vapor deposition grown n-type and p-type GaAs during proton bombardment. Thermal stability of these defects was investigated and correlation with defects responsible for isolation of GaAs by ion bombardment was discussed. The annealing temperature region (220–250 °C) is similar to proton isolated GaAs below the threshold dose for complete isolation. At least four of the five traps observed in n-type GaAs are not simple interstitial-vacancy pairs. For p-type GaAs we have observed an unknown level with apparent energy of ∼0.64 eV.
Whispering gallery modes in indium oxide hexagonal microcavities
Publisher: AIP Publishing
Date: 27-04-2009
DOI: 10.1063/1.3126443
Abstract: We report on the use of In2O3 nanowires with hexagonal cross section as optical whispering gallery resonators. The single-crystal In2O3 nanowires were fabricated by an in situ thermal oxidation method. Whispering gallery modes (WGMs) in the visible spectral range were directly observed at room temperature. Due to the slight tapering of the nanowires, the energies and orders of the WGMs were modulated when excitations were scanned along the c-axis (length) of the nanowires. The experimental results were explained and fitted well with a plane wave interference model and Cauchy dispersion formula for refractive indices.
Measurement of the damage profile of ion-implanted GaAs using an automated optical profiler
Publisher: Elsevier BV
Date: 02-2001
Global burden of 369 diseases and injuries in 204 countries and territories, 1990–2019: a systematic analysis for the Global Burden of Disease Study 2019
Publisher: Elsevier BV
Date: 10-2020
A plasmonic staircase nano-antenna device with strong electric field enhancement for surface enhanced Raman scattering (SERS) applications
Publisher: IOP Publishing
Date: 13-07-2012
DOI: 10.1088/0022-3727/45/30/305102
Abstract: In this paper, a staircase plasmonic nano-antenna device is analysed both theoretically and experimentally. The tapered nano-antenna cavity with a grating leads to electric field enhancement factor (EF) as high as 31 close to 830 nm. The integration of a metallic grating aids the coupling of light coming from the vertical direction to the nano-antenna, increasing the electric field in the nano-antenna by a factor of 3. The smallest air gap width between the metallic regions of the fabricated nano-antenna is about 35 nm, fabricated using focused ion beam system. The small air gaps in the nano-antennas can generate very high intensity electric fields which can be used in applications in biological sensing and imaging, nanoparticle manipulations and enhancement of nonlinear effects. In this paper, to experimentally demonstrate that with the integration of a well designed grating and reflectors, the resonance inside the nano-antenna cavity is increased significantly, we exploit one application of this device: the enhancement of surface enhanced Raman scattering (SERS). The present structure can lead to SERS EFs above 1 million.
<title>Use of ion implantation for the creation of ultrafast photodetector materials and tuning of quantum well infrared photodetectors</title>
Publisher: SPIE
Date: 12-06-2001
DOI: 10.1117/12.429438
Ion-implanted In0.53Ga0.47As for ultrafast optoelectronic applications
Publisher: AIP Publishing
Date: 27-05-2003
DOI: 10.1063/1.1579565
Abstract: Undoped In0.53Ga0.47As epilayers were implanted with 2-MeV Fe+ ions at doses of 1×1015 and 1×1016 cm−2 at room temperature and annealed at temperatures between 500 and 800 °C. Hall-effect measurements show that after annealing, layers with resistivities on the order of 105 Ω/square can be achieved. Carrier lifetimes as short as 300 fs are observed for s les annealed at 500 and 600 °C. For higher annealing temperatures, characteristic times of the optical response are on the order of a few picoseconds.
Ultrathin Ta2O5 electron-selective contacts for high efficiency InP solar cells
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8NR09932D
Abstract: This work demonstrates stoichiometric Ta 2 O 5 ultrathin layer as a novel and efficient electron-selective contact for planar InP heterojunction solar cells achieving an efficiency of 19.1% and a highest ever reported open circuit voltage of 822 mV.
Third generation biosensing matrix based on Fe-implanted ZnO thin film
Publisher: AIP Publishing
Date: 27-09-2010
DOI: 10.1063/1.3496456
Abstract: Third generation biosensor based on Fe-implanted ZnO (Fe-ZnO) thin film has been demonstrated. Implantation of Fe in rf-sputtered ZnO thin film introduces redox center along with shallow donor level and thereby enhance its electron transfer property. Glucose oxidase (GOx), chosen as model enzyme, has been immobilized on the surface of the matrix. Cyclic voltammetry and photometric assay show that the prepared bioelectrode, GOx/Fe-ZnO/ITO/Glass is sensitive to the glucose concentration with enhanced response of 0.326 μA mM−1 cm−2 and low Km of 2.76 mM. The results show promising application of Fe-implanted ZnO thin film as an attractive matrix for third generation biosensing.
Recombination dynamics and screening of the internal electric field inZnO /
Publisher:
American Physical Society (APS)
Date:
15-12-2009
Publisher: American Physical Society (APS)
Date: 15-12-2009
Novel Growth Phenomena Observed in Axial InAs/GaAs Nanowire Heterostructures
Publisher: Wiley
Date: 05-11-2007
Design of Ultrathin InP Solar Cell Using Carrier Selective Contacts
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 11-2020
Ultrafast carrier trapping in high energy ion implanted gallium arsenide
Publisher: AIP Publishing
Date: 15-04-1996
DOI: 10.1063/1.115866
Abstract: Time resolved photoluminescence and electrical measurements were made on MeV As, Ga, Si, and O ion implanted GaAs to doses in the range of 1×1014–5×1016 cm−2 and subsequently annealed at 600 °C for 20 min under arsine ambient. Carrier trapping times were found to decrease with increase in implantation dose for all species studied and can be shorter than 1 ps. Sheet resistance values were found to be independent of implantation dose and were of the order of 108 Ω/⧠ for As, Ga, and O implantation and ∼2×102 Ω/⧠ for the Si case due to its electrical activation. Conductivity activation energies of 0.67–0.69 eV were observed for As, Ga, and O ion implanted and annealed GaAs, which are close to the reported activation energy for annealed low-temperature GaAs (0.65 eV).
Forecast-skill-based simulation of streamflow forecasts
Publisher: Elsevier BV
Date: 09-2014
Spin-polarized Wide Electron Slabs in Functionally Graded Polar Oxide Heterostructures
Publisher: Springer Science and Business Media LLC
Date: 25-07-2012
DOI: 10.1038/SREP00533
“I can’t read and don’t understand”: Health literacy and health messaging about folic acid for neural tube defect prevention in a migrant population on the Myanmar-Thailand border
Publisher: Public Library of Science (PLoS)
Date: 13-06-2019
Analytical expression for the quantum dot contribution to the quasistatic capacitance for conduction band characterization
Publisher: AIP Publishing
Date: 15-07-2008
DOI: 10.1063/1.2959681
Abstract: This paper demonstrates an analytical expression for the quasistatic capacitance of a quantum dot layer embedded in a junction, where the reverse bias is used to discharge the initially occupied energy levels. This analysis can be used to determine the position and the Gaussian homogeneous broadening of the energy levels in the conduction band, and is applied for an InGaAs/GaAs quantum dot structure grown by metal organic chemical vapor deposition. It is shown that the Gaussian broadening of the conduction band levels is significantly larger than the broadening of the interband photoluminescence (PL) transitions involving both conduction and hole states. The analysis also reveals a contribution from the wetting layer both in PL and modeled C-V profiles which is much stronger than in typical molecular beam epitaxy grown dots. The presence of a built-in local field oriented from the apex of the dot toward its base, contrary to the direction expected for a strained dot with uniform composition (negative dipole), is also derived from fitting of the C-V experimental data.
Large Square Resonator Laser With Quasi-Single-Mode Operation
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-2009
Modal refractive index measurement in nanowire lasers—a correlative approach
Publisher: IOP Publishing
Date: 09-2023
Arsenic implantation-induced intermixing effects on AlGaAs/GaAs single QW structures
Publisher: Elsevier BV
Date: 06-2000
Wavelength-tunable InAsP quantum dots in InP nanowires
Publisher: AIP Publishing
Date: 29-07-2019
DOI: 10.1063/1.5095675
Abstract: There is considerable interest in quantum dots incorporated in nanowires for nanolasers and quantum emitters. In this letter, we demonstrate single InAsP quantum dots embedded in InP nanowires grown by metalorganic vapor-phase epitaxy. Despite the abrupt change of growth conditions at the interface, InAsP quantum dots can be grown in pure wurtzite InP nanowires. We develop a model and analyze the effects of the thickness of InAsP quantum dots and the composition of As on the formation of dislocations. Furthermore, the InAsP/InP quantum dot nanowires show bright photoluminescence up to room temperature without any surface passivation. The emission from the quantum dots could be well tuned by adjusting the dot size either vertically or laterally. The study demonstrates the potential of this material system for optoelectronic applications.
High power CW output from low confinement asymmetric structure diode laser
Publisher: Institution of Engineering and Technology (IET)
Date: 1999
DOI: 10.1049/EL:19990078
The conduction band absorption spectrum of interdiffused InGaAs/GaAs quantum dot infrared photodetectors
Publisher: AIP Publishing
Date: 15-06-2012
DOI: 10.1063/1.4729833
Abstract: We report on a theoretical study of the relationship between interdiffusion and the conduction band optical absorption of In(Ga)As/GaAs quantum dots. Quantum dot geometries are progressively interdiffused based on Fick’s model and the quantum dot strain, band structure and optical absorption cross-section are calculated numerically. Quantifying the effects of interdiffusion on quantum dot optical absorption is important for applications that utilize post-growth techniques such as selective area intermixing.
Structural, electrical, and optical analysis of ion implanted semi-insulating InP
Publisher: AIP Publishing
Date: 29-12-2003
DOI: 10.1063/1.1633349
Abstract: Semi-insulating InP was implanted with MeV P, As, Ga, and In ions, and the resulting evolution of structural properties with increased annealing temperature was analyzed using double crystal x-ray diffractometry and cross sectional transmission electron microscopy. The types of damage identified are correlated with scanning spreading resistance and scanning capacitance measurements, as well as with previously measured Hall effect and time resolved photoluminescence results. We have identified multiple layers of conductivity in the s les which occur due to the nonuniform damage profile of a single implant. Our structural studies have shown that the amount and type of damage caused by implantation does not scale with implant ion atomic mass.
Tuning of detection wavelength of quantum-well infrared photodetectors by quantum-well intermixing
Publisher: Elsevier BV
Date: 06-2001
A Partially Depleted Absorber Photodiode With Graded Doping Injection Regions
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 10-2004
Direct Measure of Strain and Electronic Structure in GaAs/GaP Core−Shell Nanowires
Publisher: American Chemical Society (ACS)
Date: 04-02-2010
DOI: 10.1021/NL903547R
Abstract: Highly strained GaAs/GaP nanowires of excellent optical quality were grown with 50 nm diameter GaAs cores and 25 nm GaP shells. Photoluminescence from these nanowires is observed at energies dramatically shifted from the unstrained GaAs free exciton emission energy by 260 meV. Using Raman scattering, we show that it is possible to separately measure the degree of compressive and shear strain of the GaAs core and show that the Raman response of the GaP shell is consistent with tensile strain. The Raman and photoluminescence measurement are both on good agreement with 8 band k.p calculations. This result opens up new possibilities for engineering the electronic properties of the nanowires for optimal design of one-dimensional nanodevices by controlling the strain of the core and shell by varying the nanowire geometry.
Enhanced transmission of light through periodic and chirped lattices of nanoholes
Publisher: Elsevier BV
Date: 05-2009
Impurity-free vacancy disordering of quantum heterostructures with SiOxNy encapsulants deposited by magnetron sputtering
Publisher: SPIE
Date: 28-08-2008
DOI: 10.1117/12.793568
Variation of NO2 and NOx concentrations between and within 36 European study areas: Results from the ESCAPE study
Publisher: Elsevier BV
Date: 12-2012
Growth and properties of III–V compound semiconductor heterostructure nanowires
Publisher: IOP Publishing
Date: 15-12-2010
Polarity-driven Nonuniform Composition in InGaAs Nanowires
Publisher: American Chemical Society (ACS)
Date: 21-10-2013
DOI: 10.1021/NL402244P
Abstract: Manipulating the composition and morphology of semiconductor nanowires in a precisely controlled fashion is critical in developing nanowire devices. This is particularly true for ternary III-V nanowires. Many studies have shown the complexities within those nanowires. Here we report our findings of compositional irregularity in the shells of core-shell InGaAs nanowires with zinc-blende structure. Such an effect is caused by the crystal polarity within III-V zinc-blende lattice and the one-dimensional nature of nanowires that allows the formation of opposite polar surfaces simultaneously on the nanowire sidewalls. This polarity-driven effect in III-V nanowires may be utilized in manipulating the composition and morphology of III-V nanowires for device applications.
Early neonatal mortality and neurological outcomes of neonatal resuscitation in a resource-limited setting on the Thailand-Myanmar border: A descriptive study
Publisher: Public Library of Science (PLoS)
Date: 05-01-2018
Directional Lasing in Coupled InP Microring/Nanowire Systems
Publisher: Wiley
Date: 18-12-2022
Abstract: The realization of on‐chip microlasers with out‐of‐plane, controllable emission direction has been one of the core research themes in modern photonics. Traditional approaches for directional light scattering, including plasmonic nanoantennas and passive dielectric metasurfaces, are not suitable for on‐chip integration due to potential metallic contamination and reliance on external light sources. Meanwhile, achieving directional emission in active III–V microcavity lasers remains challenging due to geometrical symmetry and large free‐space coupling losses. Here, a novel approach is presented to realize directional lasing in an all‐dielectric, bottom‐up grown material system by coupling the laser emission from an InP microring cavity into a vertical nanowire at the ring center, which function as the photon source and directional antenna in the system, respectively. Efficient optical coupling is facilitated by enhanced light scattering at specific sidewall facets of the microring cavity, which can be engineered deterministically during epitaxial growth. Through Fourier imaging, out‐of‐plane laser emission with antenna‐like far‐field directivity in the coupled system is demonstrated. Furthermore, the emission directivity and side mode suppression in the coupled system can be improved significantly by tuning the geometric parameters of the system. The way for low power consumption, on‐chip microlasers with tunable emission directionality is paved here.
Ion-implanted InGaAs single quantum well semiconductor saturable absorber mirrors for passive mode-locking
Publisher: IOP Publishing
Date: 07-08-2001
The asymmetry in the characteristics of GaAs/AlGaAs quantum well infrared photodetectors
Publisher: Elsevier BV
Date: 02-2001
The effect of nitridation on the polarity and optical properties of GaN self-assembled nanorods
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8NR00737C
Abstract: After nitridation, nanorods show better optical properties, while their polarity changes from mixed-to N-polarity.
Optical transition in infrared photodetector based on V-groove Al0.5Ga0.5As/GaAs multiple quantum wire
Publisher: AIP Publishing
Date: 15-02-2001
DOI: 10.1063/1.1339857
Abstract: Photoconductors based on V-grooved Al0.5Ga0.5As/GaAs multiple quantum wires (QWR) were fabricated. The geometric structure of the QWR was carefully characterized by transmission electron microscopy and spatially resolved microphotoluminescence measurements. Infrared response at 9.2 μm is observed from the photocurrent spectrum measured at 80 K. It is attributed as the intersubband transition in the quantum wire region. Due to the effective quantum confinement from the two (111)-surfaces forming the V groove, the overlapping between the ground state in the QWR and the one in the vertical quantum well is very small. This explains the weak photocurrent signal from the QWR photodetector. Theoretical design for a better wave function overlapping and optical coupling is outlined from the analysis of two-dimensional spatial distributions of the wave functions.
Effects of strain and barrier height of thin interlayer on InAs quantum dots grown on GaInAsP/InP (100) by metalorganic chemical vapor deposition
Publisher: IEEE
Date: 2005
Influence of SiO2and TiO2dielectric layers on the atomic intermixing of InxGa1−xAs/InP quantum well structures
Publisher: IOP Publishing
Date: 20-07-2007
Proton-irradiation-induced intermixing of InGaAs quantum dots
Publisher: AIP Publishing
Date: 25-03-2003
DOI: 10.1063/1.1561153
Abstract: Proton irradiation was used to create interdiffusion in In0.5Ga0.5As quantum dots (QDs), grown by low-pressure metalorganic chemical vapor deposition. After 25-keV proton irradiation, the QD s les were annealed at two temperatures (700 or 750 °C) for 30 s. It was found that much lower annealing temperatures were needed to recover the photoluminescence signals than in the quantum-well case. Large blueshifts (120 meV) and narrowing of the photoluminescence spectra were seen. Various doses (5×1013–1×1015 cm−2) and implant temperatures (20–200 °C) were used to study the interdiffusion processes in these s les. In QD s les, much lower doses were required to achieve similar energy shifts than reported in quantum-well s les.
The influence of doping on the device characteristics of In0.5Ga0.5As/GaAs/Al0.2Ga0.8As quantum dots-in-a-well infrared photodetectors
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/C0NR00128G
Abstract: We report on a detailed analysis of the effects of doping on the main device parameters of In(0.5)Ga(0.5)As/GaAs/Al(0.2)Ga(0.8)As quantum dots-in-a-well infrared photodetectors. Due to the relatively large conduction band offset of GaAs/Al(0.2)Ga(0.8)As (167 meV) transitions from wetting layer to quantum well states are observed for the highly doped devices. Since increasing the doping concentration fills the quantum dot states, electrons are forced to occupy the one-dimensional wetting layer states and therefore have quantum-well-like properties. This has facilitated a comparative study of the effects of three-dimensional and one-dimensional confinement of electrons on device parameters such as the responsivity and dark current by studying one particular detector structure with different doping concentrations of the active region.
Polarization-sensitive terahertz detection by multicontact photoconductive receivers
Publisher: AIP Publishing
Date: 16-06-2005
DOI: 10.1063/1.1951051
Abstract: We have developed a terahertz radiation detector that measures both the litude and polarization of the electric field as a function of time. The device is a three-contact photoconductive receiver designed so that two orthogonal electric-field components of an arbitrary polarized electromagnetic wave may be detected simultaneously. The detector was fabricated on Fe+ ion-implanted InP. Polarization-sensitive detection is demonstrated with an extinction ratio better than 100:1. This type of device will have immediate application in studies of birefringent and optically active materials in the far-infrared region of the spectrum.
Removal of Surface States and Recovery of Band-Edge Emission in InAs Nanowires through Surface Passivation
Publisher: American Chemical Society (ACS)
Date: 07-06-2012
DOI: 10.1021/NL300015W
Abstract: Surface states in semiconductor nanowires (NWs) are detrimental to the NW optical and electronic properties and to their light emission-based applications, due to the large surface-to-volume ratio of NWs and the congregation of defects states near surfaces. In this paper, we demonstrated an effective approach to eliminate surface states in InAs NWs of zinc-blende (ZB) and wurtzite (WZ) structures and a dramatic recovery of band edge emission through surface passivation with organic sulfide octadecylthiol (ODT). Microphotoluminescence (PL) measurements were carried out before and after passivation to study the dominant recombination mechanisms and surface state densities of the NWs. For WZ-NWs, we show that the passivation removed the surface states and recovered the band-edge emission, leading to a factor of ∼19 reduction of PL linewidth. For ZB-NWs, the deep surface states were removed and the PL peaks width became as narrow as ∼250 nm with some remaining emission of near band-edge surface states. The passivated NWs showed excellent stability in atmosphere, water, and heat environments. In particular, no observable changes occurred in the PL features from the passivated NWs exposed in air for more than five months.
In/sub 0.5/Ga/sub 0.5/As/GaAs quantum dot infrared photodetectors grown by metal-organic chemical vapor deposition
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 09-2005
Raman probing of competitive laser heating and local recrystallization effect in ZnO nanocrystals
Publisher: The Optical Society
Date: 25-09-2012
DOI: 10.1364/OE.20.023281
Optical, structural, and numerical investigations of GaAs/AlGaAs core-multishell nanowire quantum well tubes
Publisher: American Chemical Society (ACS)
Date: 25-02-2013
DOI: 10.1021/NL304182J
Abstract: The electronic properties of thin, nanometer scale GaAs quantum well tubes embedded inside the AlGaAs shell of a GaAs core-multishell nanowire are investigated using optical spectroscopies. Using numerical simulations to model cylindrically and hexagonally symmetric systems, we correlate these electronic properties with structural characterization by aberration-corrected scanning transmission electron microscopy of nanowire cross sections. These tubular quantum wells exhibit extremely high quantum efficiency and intense emission for extremely low submicrowatt excitation powers in both photoluminescence and photoluminescence excitation measurements. Numerical calculations of the confined eigenstates suggest that the electrons and holes in their ground states are confined to extremely localized one-dimensional filaments at the corners of the hexagonal structure which extend along the length of the nanowire.
Wavelength shifting in GaAs quantum well lasers by proton irradiation
Publisher: AIP Publishing
Date: 03-11-1997
DOI: 10.1063/1.120177
Abstract: Proton irradiation followed by rapid thermal annealing was used to selectively induce layer intermixing and thus shift the emission wavelengths of GaAs–AlGaAs graded-index separate-confinement-heterostructure quantum well lasers. Up to 40 nm shifts were observed in 4 μm ridge waveguide devices irradiated to a dose of 1.5×1016 cm−2. Although the wavelength shifts were accompanied by some degradation in the lasing threshold current and differential quantum efficiency, they were still quite acceptable at moderate wavelength shifts. This technique provides a simple and promising postgrowth process of integrating lasers of different wavelengths for wavelength- ision-multiplexing applications.
Optical properties of arsenic ions implanted GaAs/AlGaAs V-grooved quantum wires
Publisher: AIP Publishing
Date: 09-2000
DOI: 10.1063/1.1287119
Abstract: Asymmetric double GaAs/AlGaAs V-grooved quantum wires, grown by low pressure metalorganic chemical vapor deposition, are studied using photoluminescence (PL) spectroscopy. The structure was selectively treated by ion implantation at different arsenic (As) doses after growth. The ion implantation strongly reduces the efficiency of the emissions from the implanted well regions or even quenches the PL emissions from certain well regions due to irradiation damage. Wire emission is clearly resolved in the s les after treatment by low dose implantation. The temperature dependence of the wire emission intensity shows an enhancement at a temperature of around 45 K. The wire emission peak with a shoulder at its high energy side at low temperatures develops into double peaks in a temperature region between 20 and 140 K, and the high energy transition component dominates the PL spectra at temperatures above 140 K. The deduced energy separation between two peaks is about 10 meV. With further increasing temperatures the wire emission related to the light hole state can be observed at temperatures above 150 K. Deduced splitting between the heavy and light states is about 35 meV in our structures.
III-V nanowires for optoelectronic applications
Publisher: The Electrochemical Society
Date: 31-08-2013
Abstract: We present an overview of our work on improving the crystal quality and carrier lifetimes of our GaAs-based nanowires. These two properties are crucial for optoelectronic device applications and which we report by showing two ex les of nanowire lasers and nanowire solar cells.
Three-Dimensional in Situ Photocurrent Mapping for Nanowire Photovoltaics
Publisher: American Chemical Society (ACS)
Date: 08-03-2013
DOI: 10.1021/NL304170Q
Abstract: Devices based upon semiconductor nanowires provide many well-known advantages for next-generation photovoltaics, however, limited experimental techniques exist to determine essential electrical parameters within these devices. We present a novel application of a technique based upon two-photon induced photocurrent that provides a submicrometer resolution, three-dimensional reconstruction of photovoltaic parameters. This tool is used to characterize two GaAs nanowire-based devices, revealing the detail of current generation and collection, providing a path toward achieving the promise of nanowire-based photovoltaic devices.
Enhanced optical properties of the GaAsN/GaAs quantum-well structure by the insertion of InAs monolayers
Publisher: AIP Publishing
Date: 04-2004
DOI: 10.1063/1.1697628
Abstract: Microstructural and optical properties of InAs-inserted and reference single GaAsN/GaAs quantum-well (QW) structures grown by metalorganic chemical vapor deposition were investigated using cross-sectional transmission electron microscopy and photoluminescence (PL). Significant enhancement of PL intensity and a blueshift of PL emission were observed from the InAs-inserted GaAsN/GaAs QW structure, compared with the single GaAsN/GaAs QW structure. Strain compensation and In-induced reduction of N incorporation are suggested to be two major factors affecting the optical properties.
InAs quantum dots grown on InGaAs buffer layers by metal-organic chemical vapor deposition
Publisher: Elsevier BV
Date: 08-2005
Quantification of the association between malaria in pregnancy and stillbirth: a systematic review and meta-analysis.
Publisher: Elsevier BV
Date: 11-2017
Empirical lessons regarding contraception in a protracted refugee setting: A descriptive study from Maela camp on the Thai-Myanmar border 1996 – 2015
Publisher: Public Library of Science (PLoS)
Date: 23-02-2017
Annealing of ion implanted gallium nitride
Publisher: AIP Publishing
Date: 09-03-1998
DOI: 10.1063/1.121030
Abstract: In this paper, we examine Si and Te ion implant damage removal in GaN as a function of implantation dose, and implantation and annealing temperature. Transmission electron microscopy shows that amorphous layers, which can result from high-dose implantation, recrystallize between 800 and 1100 °C to very defective polycrystalline material. Lower-dose implants (down to 5×1013 cm−2), which are not amorphous but defective after implantation, also anneal poorly up to 1100 °C, leaving a coarse network of extended defects. Despite such disorder, a high fraction of Te is found to be substitutional in GaN both following implantation and after annealing. Furthermore, although elevated-temperature implants result in less disorder after implantation, this damage is also impossible to anneal out completely by 1100 °C. The implications of this study are that considerably higher annealing temperatures will be needed to remove damage for optimum electrical properties.
Growth of highly strained InGaAs quantum wells on GaAs substrates—effect of growth rate
Publisher: Elsevier BV
Date: 2005
III–V semiconductor nanowires for optoelectronic device applications
Publisher: Elsevier BV
Date: 03-2011
Atomic-scale observation of parallel development of super elasticity and reversible plasticity in GaAs nanowires
Publisher: AIP Publishing
Date: 13-01-2014
DOI: 10.1063/1.4861846
Abstract: We report the atomic-scale observation of parallel development of super elasticity and reversible dislocation-based plasticity from an early stage of bending deformation until fracture in GaAs nanowires. While this phenomenon is in sharp contrast to the textbook knowledge, it is expected to occur widely in nanostructures. This work indicates that the super recoverable deformation in nanomaterials is not simple elastic or reversible plastic deformation in nature, but the coupling of both.
Nanosheets-Based Rhombohedral In2O3 3D Hierarchical Microspheres: Synthesis, Growth Mechanism, and Optical Properties
Publisher: American Chemical Society (ACS)
Date: 21-05-2009
DOI: 10.1021/JP902843P
Strain relaxation and phonon confinement in self-assembled InAsSb/InP (001) quantum dashes: Effect of deposition thickness and composition
Publisher: AIP Publishing
Date: 29-11-2010
DOI: 10.1063/1.3522889
Abstract: This paper presents a study on the strain relaxation and phonon confinement effect in InAsSb/InP quantum dashes (QDashes). The phonon mode with a frequency between that of InAs-like longitudinal optical mode and that of InP transverse optical mode is determined to be originated from InAsSb QDashes. Despite the small height of the QDashes, their phonon frequency is found to be mainly determined by the strain relaxation in the dashes. With increasing InAsSb deposition thickness and Sb composition in InAsSb dashes, the phonon mode shows an upward shift of its frequency due to the increased compressive strain.
Multiple wavelength InGaAs quantum dot lasers using selective area epitaxy
Publisher: AIP Publishing
Date: 23-04-2007
DOI: 10.1063/1.2731729
Abstract: The authors demonstrate multiple wavelength lasers fabricated from InGaAs quantum dots. Selective area epitaxy is used to grow the active region, consisting of five layer stack of InGaAs quantum dots with different band gap energies in selected regions of the substrate, for fabrication of the lasers. The mechanism responsible for engineering of the band gap of quantum dots is discussed. The performance of the selectively grown lasers is compared to the lasers fabricated from structures grown in a standard, nonselective area growth process.
Structural and Optical Properties of III-V Nanowires and Nanowire Heterostructures Grown by Metalorganic Chemical Vapour Deposition
Publisher: IEEE
Date: 08-2007
Anemia prevalence in women of reproductive age in low- and middle-income countries between 2000 and 2018
Publisher: Springer Science and Business Media LLC
Date: 10-2021
DOI: 10.1038/S41591-021-01498-0
Abstract: Anemia is a globally widespread condition in women and is associated with reduced economic productivity and increased mortality worldwide. Here we map annual 2000–2018 geospatial estimates of anemia prevalence in women of reproductive age (15–49 years) across 82 low- and middle-income countries (LMICs), stratify anemia by severity and aggregate results to policy-relevant administrative and national levels. Additionally, we provide subnational disparity analyses to provide a comprehensive overview of anemia prevalence inequalities within these countries and predict progress toward the World Health Organization’s Global Nutrition Target (WHO GNT) to reduce anemia by half by 2030. Our results demonstrate widespread moderate improvements in overall anemia prevalence but identify only three LMICs with a high probability of achieving the WHO GNT by 2030 at a national scale, and no LMIC is expected to achieve the target in all their subnational administrative units. Our maps show where large within-country disparities occur, as well as areas likely to fall short of the WHO GNT, offering precision public health tools so that adequate resource allocation and subsequent interventions can be targeted to the most vulnerable populations.
Electrical isolation of n-type and p-type InP layers by proton bombardment
Publisher: AIP Publishing
Date: 15-05-2001
DOI: 10.1063/1.1365063
Abstract: The evolution of the sheet resistance (Rs) of n-type and p-type conductive InP layers during proton irradiation and the stability of the formed isolation during postirradiation annealing were investigated. It was found that the threshold dose (Dth) to convert the conductive layer to a highly resistive one is different for n- and p-type s les with similar initial free carrier concentrations. From our results, one infers that the antisite defects and/or related defect complexes formed by the replacement collisions are the carrier trapping centers, where InP is responsible for electron trapping and PIn for the hole trapping. A time dependence of the Rs was observed after each irradiation step to doses of ≅Dth and higher. This time variation is related to metastable processes involving free carriers. The thermal stability of the isolation of n-type s les is limited to temperatures lower than 200 °C, irrespectively of the irradiated dose. For p-type s les the thermal stability of electrical isolation is extended to 450–500 °C.
Effects of a p–n junction on heterojunction far infrared detectors
Publisher: Elsevier BV
Date: 04-2007
Study of intermixing in a GaAs/AlGaAs quantum-well structure using doped spin-on silica layers
Publisher: AIP Publishing
Date: 18-02-2002
DOI: 10.1063/1.1449522
Abstract: The effect of two different dopants, P and Ga, in spin-on glass (SOG) films on impurity-free vacancy disordering (IFVD) in GaAs/AlGaAs quantum-well structures has been investigated. It is observed that by varying the annealing and baking temperatures, P-doped SOG films created a similar amount of intermixing as the undoped SOG films. This is different from the results of other studies of P-doped SiO2 and is ascribed to the low doping concentration of P, indicating that the doping concentration of P in the SiO2 layer is one of the key parameters that may control intermixing. On the other hand, for all the s les encapsulated with Ga-doped SOG layers, significant suppression of the intermixing was observed, making them very promising candidates with which to achieve the selective-area defect engineering that is required for any successful application of IFVD.
GaAs based anti-resonant Fabry–Perot saturable absorber fabricated by metal organic vapor phase epitaxy and ion implantation
Publisher: AIP Publishing
Date: 23-06-1997
DOI: 10.1063/1.119192
Abstract: We have fabricated an antiresonant Fabry–Perot saturable absorber (A-FPSA), for potential use in laser passive mode locking, using metalorganic vapor phase epitaxy followed by ion implantation and thermal annealing. We show that the implantation/annealing cycle shortens the free-carrier dwell time without degrading the other optical properties of the A-FPSA.
Merged beam laser design for reduction of gain-saturation and two-photon absorption in high power single mode semiconductor lasers
Publisher: The Optical Society
Date: 28-03-2013
DOI: 10.1364/OE.21.008276
Growth and properties of III–V compound semiconductor heterostructure nanowires
Publisher: IOP Publishing
Date: 27-03-2012
In-plane coupling of light from InP-based photonic crystal band-edge lasers into single-mode waveguides
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-2007
Integration of quantum dot optoelectronic devices using selective-area MOCVD
Publisher: IEEE
Date: 10-2006
Spatial selectivity of impurity free vacancy disordering using different dielectric layers for photonic/optoelectronic integrated circuits
Publisher: IEEE
Date: 2003
A prospective cohort for the investigation of alteration in temporal transcriptional and microbiome trajectories preceding preterm birth: a study protocol
Publisher: BMJ
Date: 2019
DOI: 10.1136/BMJOPEN-2018-023417
Abstract: Preterm birth (PTB) results from heterogeneous influences and is a major contributor to neonatal mortality and morbidity that continues to have adverse effects on infants beyond the neonatal period. This protocol describes the procedures to determine molecular signatures predictive of PTB through high-frequency s ling during pregnancy, at delivery and the postpartum period. Four hundred first trimester pregnant women from either Myanmar or Thailand of either Karen or Burman ethnicity, with a viable, singleton pregnancy will be enrolled in this non-interventional, prospective pregnancy birth cohort study and will be followed through to the postpartum period. Fortnightly finger prick capillary blood s ling will allow the monitoring of genome-wide transcript abundance in whole blood. Collection of stool s les and vaginal swabs each trimester, at delivery and postpartum will allow monitoring of intestinal and vaginal microbial composition. In a nested case–control analysis, perturbations of transcript abundance in capillary blood as well as longitudinal changes of the gut, vaginal and oral microbiome will be compared between mothers giving birth to preterm and matched cases giving birth to term neonates. Placenta tissue of preterm and term neonates will be used to determine bacterial colonisation as well as for the establishment of coding and non-coding RNA profiles. In addition, RNA profiles of circulating, non-coding RNA in cord blood serum will be compared with those of maternal peripheral blood serum at time of delivery. This research protocol that aims to detect perturbations in molecular trajectories preceding adverse pregnancy outcomes was approved by the ethics committee of the Faculty of Tropical Medicine, Mahidol University in Bangkok, Thailand (Ethics Reference: TMEC 15–062), the Oxford Tropical Research Ethics Committee (Ethics Reference: OxTREC: 33–15) and the local Tak Province Community Ethics Advisory Board. The results of this cooperative project will be disseminated in multiple publications staggered over time in international peer-reviewed scientific journals. NCT02797327 Pre-results.
Implantation-induced electrical isolation of GaAsN epilayers grown by metalorganic chemical vapor deposition
Publisher: AIP Publishing
Date: 15-10-2003
DOI: 10.1063/1.1621089
Abstract: The electrical isolation of p-type GaAs1−xNx epilayers (x=0.6%, 1.4%, and 2.3%) produced by H, Li, C, or O ion implantation and its thermal stability in nominally undoped GaAs0.986N0.014 epilayers were investigated. Results show that the sheet resistance of p-type GaAsN layers can be increased by about five or six orders of magnitude by ion implantation and the threshold fluence (Fth) to convert a conductive layer to a highly resistive one depends on the original free carrier concentration and the number of implantation-generated atomic displacements, and does not depend on the nitrogen content. The thermal stability of electrical isolation in GaAsN depends on the ratio of the final fluence to the threshold fluence. The electrical isolation can be preserved up to 550 °C when the accumulated fluence is above 3.3 Fth.
Modeling and characterization of InAs∕GaAs quantum dot lasers grown using metal organic chemical vapor deposition
Publisher: AIP Publishing
Date: 2007
DOI: 10.1063/1.2409612
Abstract: We report on the lasing characteristics of three- and five-stack InAs∕GaAs quantum dot (QD) lasers grown by metal organic chemical vapor deposition. By increasing the number of stacked dot layers to 5, lasing was achieved from the ground state at 1135nm for device lengths as short as 1.5mm (no reflectivity coatings). The un lified spontaneous emission and Z ratio as a function of injection current were also investigated. While the five-stack QD lasers behaved as expected with Z ratios of ≈2 prior to lasing, the three-stack QD lasers, which lased from the excited state, exhibited Z-ratio values as high as 4. A simple model was developed and indicated that high Z ratios can be generated by three nonradiative recombination pathways: (i) high monomolecular recombination within the wetting layer, (ii) Auger recombination involving carriers within the QDs (“unmixed” Auger), and (iii) Auger recombination involving both the QD and wetting layer states (“mixed” Auger), which dominate once the excited and wetting layer states become populated.
Prevalences of inherited red blood cell disorders in pregnant women of different ethnicities living along the Thailand-Myanmar border
Publisher: F1000 Research Ltd
Date: 02-11-2017
DOI: 10.12688/WELLCOMEOPENRES.12338.2
Abstract: Background : Inherited red blood cell disorders are prevalent in populations living in malaria endemic areas G6PD deficiency is associated with oxidant-induced haemolysis and abnormal haemoglobin variants may cause chronic anaemia. In pregnant women, microcytic anaemia caused by haemoglobinopathies mimics iron deficiency, complicating diagnosis and treatment. Anaemia during pregnancy is associated with morbidity and mortality. The aim of this study was to characterise the prevalence of G6PD deficiency and haemoglobinopathies among the pregnant population living along the Thailand-Myanmar border. Pregnant women attending antenatal clinics in this area belong to several distinct ethnic groups. Methods : Data were available for 13,520 women attending antenatal care between July 2012 and September 2016. Screening for G6PD deficiency was done by fluorescent spot test routinely. G6PD genotyping and quantitative phenotyping by spectrophotometry were analysed in a subs le of women. Haemoglobin variants were diagnosed by HPLC or capillary electrophoresis and molecular methods. The prevalence and distribution of inherited red blood cell disorders was analysed with respect to ethnicity. Results : G6PD deficiency was common, especially in the Sgaw Karen ethnic group, in whom the G6PD Mahidol variant allele frequency was 20.7%. Quantitative G6PD phenotyping showed that 60.5% of heterozygous women had an intermediate enzymatic activity between 30% and 70% of the population median. HbE, beta-thalassaemia trait and Hb Constant Spring were found overall in 15.6% of women. Only 45.2% of women with low percentage of HbA 2 were carriers of mutations on the alpha globin genes. Conclusions : Distribution of G6PD and haemoglobin variants varied among the different ethnic groups, but the prevalence was generally high throughout the cohort. These findings encourage the implementation of an extended program of information and genetic counselling to women of reproductive age and will help inform future studies and current clinical management of anaemia in the pregnant population in this region.
Three-dimensional electronic spectroscopy of excitons in asymmetric double quantum wells
Publisher: AIP Publishing
Date: 28-07-2011
DOI: 10.1063/1.3613679
Abstract: We demonstrate three-dimensional (3D) electronic spectroscopy of excitons in a double quantum well system using a three-dimensional phase retrieval algorithm to obtain the phase information that is lost in the measurement of intensities. By extending the analysis of two-dimensional spectroscopy to three dimensions, contributions from different quantum mechanical pathways can be further separated allowing greater insight into the mechanisms responsible for the observed peaks. By examining different slices of the complete three-dimensional spectrum, not only can the relative litudes be determined, but the peak shapes can also be analysed to reveal further details of the interactions with the environment and inhomogeneous broadening. We apply this technique to study the coupling between two coupled quantum wells, 5.7 nm and 8 nm wide, separated by a 4 nm barrier. Coupling between the heavy-hole excitons of each well results in a circular cross-peak indicating no correlation of the inhomogeneous broadening. An additional cross-peak is isolated in the 3D spectrum which is elongated in the diagonal direction indicating correlated inhomogeneous broadening. This is attributed to coupling of the excitons involving the two delocalised light-hole states and the electron state localised on the wide well. The attribution of this peak and the analysis of the peak shapes is supported by numerical simulations of the electron and hole wavefunctions and the three-dimensional spectrum based on a density matrix approach. An additional benefit of extending the phase retrieval algorithm from two to three dimensions is that it becomes substantially more reliable and less susceptible to noise as a result of the more extensive use of a priori information.
Wavelength Tuning of GaAs/AlGaAs Quantum-Well Infrared Photodetectors by Thermal Interdiffusion
Publisher: IOP Publishing
Date: 09-1999
DOI: 10.1143/JJAP.38.5044
Abstract: Thermal interdiffusion is used to shift peak response wavelength of quantum well infrared photodetectors. A maximum 0.7 µm red-shift for 900°C annealed devices compared with as-grown one has been obtained. Error function potential profile is used to calculate the intermixing process. The large red-shift is attributed to Si-dopant enhanced intermixing. Dark current is decreased about 5 times for 900°C annealed s le than as-grown one, which is attributed to Si-dopant out-diffusion. The experimentally observed reduction in the responsivity is attributed to out-diffusion of Si-dopant and degradation of interfaces.
Wavelength shifting of adjacent quantum wells in V-groove quantum wire structure by selective implantation and annealing
Publisher: AIP Publishing
Date: 02-2000
DOI: 10.1063/1.372051
Abstract: Intermixing induced by selective implantation was used to modify the two-dimensional (2D) quantum wells in the V-grooved quantum wire structure. Photoluminescence measurement of the implanted s les shows the obvious blueshift of the interband transition energy while quantum wire is not influenced by implantation. So the selective implantation method has been demonstrated in this article as a useful technique to isolate the energy levels of quantum wire structure from its neighbor 2D structures, which is preferred for the optoelectronic device application of quantum wire.
Why is WHO failing women with falciparum malaria in the first trimester of pregnancy?
Publisher: Elsevier BV
Date: 03-2020
Titanium Nano-Antenna for High-Power Pulsed Operation
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2013
Interdiffused quantum-well infrared photodetectors for color sensitive arrays
Publisher: AIP Publishing
Date: 16-08-1999
DOI: 10.1063/1.124555
Abstract: Proton implantation and rapid thermal annealing were used to tune the infrared spectral response of quantum-well infrared photodetectors (QWIP) by up to 1.4 μm. Multiple proton implants at energies between 200 and 420 keV were used to create homogeneous quantum-well intermixing throughout the device’s multiple-quantum-well structure. Photoluminescence and spectral response measurements were used to study the effect of proton implantation on QWIPs for a series of doses up to 3.5×1015 protons cm−2. By using a mask during implantation, a method of constructing a color sensitive array is proposed.
Nature of heterointerfaces in GaAs/InAs and InAs/GaAs axial nanowire heterostructures
Publisher: AIP Publishing
Date: 08-09-2008
DOI: 10.1063/1.2978959
Abstract: The structural and compositional characteristics of heterointerfaces of Au-catalyzed GaAs/InAs and InAs/GaAs axial nanowire heterostructures were comprehensively investigated by transmission electron microscopy. It has been found that the GaAs/InAs interface is not sharp and contains an InGaAs transition segment, and in contrast, the InAs/GaAs interface is atomically sharp. This difference in the nature of heterointerfaces can be attributed to the difference in the affinity of the group III elements with the catalyst material.
Effects of Zn Doping on Intermixing in InGaAs/AlGaAs Laser Diode Structures
Publisher: The Electrochemical Society
Date: 2003
DOI: 10.1149/1.1588304
Analysis of optically pumped compact laterally coupled distributed feedback lasers with three symmetric defect regions
Publisher: AIP Publishing
Date: 15-10-2007
DOI: 10.1063/1.2800285
Abstract: This article analyzes compact laterally coupled distributed feedback (DFB) lasers with three defect regions. These devices are more flexible and smaller than conventional DFB lasers, having typical lengths between 20 and 50μm and a width less than 1μm (lateral gratings are inserted in a single-mode waveguide). We optimize the defect regions to achieve an improved performance. In other words, an adequate choice of phase shifts may lead to single-mode operation, lower threshold optical power, higher quantum differential efficiency, and more uniform field distribution. This device is designed to operate under optical pumping.
Precursor flow rate manipulation for the controlled fabrication of twin-free GaAs nanowires on silicon substrates
Publisher: IOP Publishing
Date: 27-09-2012
DOI: 10.1088/0957-4484/23/41/415702
Abstract: Vertically oriented GaAs nanowires (NWs) are grown on Si(111) substrates using metal-organic chemical vapor deposition. Controlled epitaxial growth along the direction is demonstrated following the deposition of thin GaAs buffer layers and the elimination of structural defects, such as twin defects and stacking faults, is found for high growth rates. By systematically manipulating the AsH(3) (group-V) and TMGa (group-III) precursor flow rates, it is found that the TMGa flow rate has the most significant effect on the nanowire quality. After capping the minimal tapering and twin-free GaAs NWs with an AlGaAs shell, long exciton lifetimes (over 700 ps) are obtained for high TMGa flow rate s les. It is observed that the Ga adatom concentration significantly affects the growth of GaAs NWs, with a high concentration and rapid growth leading to desirable characteristics for optoelectronic nanowire device applications including improved morphology, crystal structure and optical performance.
Validation of the Refugee Health Screener-15 for the assessment of perinatal depression among Karen and Burmese women on the Thai-Myanmar border
Publisher: Public Library of Science (PLoS)
Date: 21-05-2018
In(Ga)As/GaAs quantum dots for optoelectronic devices
Publisher: SPIE
Date: 27-12-2006
DOI: 10.1117/12.706526
Wavelength Tuning of GaAs/AlGaAs Quantum-Well Infrared Photo-detectors by Proton Implantation Induced Intermixing
Publisher: IOP Publishing
Date: 04-2000
DOI: 10.1143/JJAP.39.1687
Abstract: Proton implantation induced intermixing was used to tune the quantum well infrared photo-detector (QWIP) response wavelength, which may provide a method of fabricating two-color QWIP devices. Obvious red shift of response wavelength as large as 0.6 µm was observed relative to the reference s le that was annealed without implantation, from 7.7 µm to 8.3 µm. Two response wavelengths for the highest-dose implanted s le were observed in the photo-current spectra. In the highest dose case (5×10 15 H/cm 2 ), the dark current increased by an order of magnitude and peak responsivity decreased by a factor of 3 for the implanted and annealed s le. This has been attributed to the raising of the ground state energy level in the intermixed quantum well and residual damage in the implanted and annealed QWIPs.
Influence of Electrical Design on Core–Shell GaAs Nanowire Array Solar Cells
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2015
Understanding the true shape of Au-catalyzed GaAs nanowires
Publisher: American Chemical Society (ACS)
Date: 22-09-2014
DOI: 10.1021/NL5027937
Abstract: With increasing interest in nanowire-based devices, a thorough understanding of the nanowire shape is required to gain tight control of the quality of nanowire heterostructures and improve the performance of related devices. We present a systematic study of the sidewalls of Au-catalyzed GaAs nanowires by investigating the faceting process from the beginning with vapor-liquid-solid (VLS) nucleation, followed by the simultaneous radial growth on the sidewalls, and to the end with sidewall transformation during annealing. The VLS nucleation interface of our GaAs nanowires is revealed by examining cross sections of the nanowire, where the nanowire exhibits a Reuleaux triangular shape with three curved surfaces along {112}A. These curved surfaces are not thermodynamically stable and adopt {112}A facets during radial growth. We observe clear differences in radial growth rate between the ⟨112⟩A and ⟨112⟩B directions with {112}B facets forming due to the slower radial growth rate along ⟨112⟩B directions. These sidewalls transform to {110} facets after high temperature (>500 °C) annealing. A nucleation model is proposed to explain the origin of the Reuleaux triangular shape of the nanowires, and the sidewall evolution is explained by surface kinetic and thermodynamic limitations.
Using graded barriers to control the optical properties of ZnO/Zn0.7Mg0.3O quantum wells with an intrinsic internal electric field
Publisher: AIP Publishing
Date: 10-05-2010
DOI: 10.1063/1.3428430
Abstract: Quantum wells with graded barriers are demonstrated as a means to control both the transition energy and electron-hole wave function overlap for quantum wells with an intrinsic internal electric field. In the case of c-axis grown ZnO/ZnMgO quantum wells, the graded barriers are produced by stepping the magnesium composition during the growth process. Four quantum wells with different structures are examined, where each well has similar transition energy, yet a wide range of wave function overlaps are observed. Photoluminescence and time resolved photoluminescence show good agreement with calculations.
Tunable, high beam quality and narrow linewidth semiconductor disk laser
Publisher: SPIE-Intl Soc Optical Eng
Date: 10-2010
DOI: 10.1117/1.3490418
Emission wavelength extension of mid-infrared InAsSb/InP nanostructures using InGaAsSb sandwich layers
Publisher: IOP Publishing
Date: 13-07-2010
DOI: 10.1088/0022-3727/43/30/302001
Abstract: This paper presents a study on the emission wavelength extension of InAsSb nanostructures using InGaAsSb sandwich layers. Due to the reduced lattice mismatch between InAsSb nanostructure layer and buffer/capping layer, the introduction of InGaAsSb sandwich layers leads to larger island size, reduced compressive strain and lower confinement barrier for InAsSb nanostructures, thus resulting in a longer emission wavelength. For InGaAsSb sandwich layers with nominal Sb concentration higher than 10%, type II band alignment is observed for the InAsSb/InGaAsSb heterostructure, which also contributes to the extension of emission wavelength. The InGaAsSb sandwich layers provide an effective approach to extend the emission wavelength of InAsSb nanostructures well beyond 2 µm, which is very useful for device applications in the mid-infrared region.
Design of InAs nanosheet arrays with ultrawide polarization-independent high absorption for infrared photodetection
Publisher: AIP Publishing
Date: 14-02-2022
DOI: 10.1063/5.0066507
Abstract: InAs nanowires have been considered as good candidates for infrared photodetection. However, one-dimensional geometry of a nanowire makes it unsuitable for broadband light absorption. In this work, we propose and design InAs nanosheet arrays to achieve polarization-independent, angle-insensitive, and ultrawide infrared absorption. Simulations demonstrate that two-dimensional InAs nanosheets can support multiple resonance modes, thus leading to a strong and broadband absorption from visible light to mid-wave infrared. Moreover, we can tune polarization-dependent property in InAs nanosheets to be polarization-insensitive by forming a nanosheet based clover-like and snowflake-like nanostructures. We further optimized the design of InAs nanosheet arrays based on such structures and achieved high absorption (up to 99.6%) covering a broad wavelength range from 500 to 3200 nm. These absorption properties are much superior to their nanowire and planar film counterparts, making it attractive for infrared photodetection applications. The architecture of such nanostructures can provide a promising route for the development of high-performance room-temperature broadband infrared photodetectors.
Resonant harmonic generation in AlGaAs nanoantennas probed by cylindrical vector beams
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8NR08034H
Abstract: Cylindrical vector beams with radial and azimuthal polarizations are used to study harmonic generation from in idual AlGaAs nanoantennas.
Directional optically pumped laterally coupled DFB lasers with circular mirrors
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2009
Effects of growth rate on InP nanowires morphology and crystal structure
Publisher: Elsevier BV
Date: 11-2013
Quantum well intermixing and wavelength-shifting in GaAs lasers by proton irradiation
Publisher: IEEE
Date: 1996
Evolution of Epitaxial InAs Nanowires on GaAs (111)B
Publisher: Wiley
Date: 06-02-2009
Electrical characterization of impurity-free disordering-induced defects in n-GaAs using native oxide layers
Publisher: Springer Science and Business Media LLC
Date: 04-2003
Possibility of improved frequency response from intermixed quantum-well devices
Publisher: Elsevier BV
Date: 02-2001
Mapping 123 million neonatal, infant and child deaths between 2000 and 2017
Publisher: Springer Science and Business Media LLC
Date: 16-10-2019
DOI: 10.1038/S41586-019-1545-0
Abstract: Since 2000, many countries have achieved considerable success in improving child survival, but localized progress remains unclear. To inform efforts towards United Nations Sustainable Development Goal 3.2—to end preventable child deaths by 2030—we need consistently estimated data at the subnational level regarding child mortality rates and trends. Here we quantified, for the period 2000–2017, the subnational variation in mortality rates and number of deaths of neonates, infants and children under 5 years of age within 99 low- and middle-income countries using a geostatistical survival model. We estimated that 32% of children under 5 in these countries lived in districts that had attained rates of 25 or fewer child deaths per 1,000 live births by 2017, and that 58% of child deaths between 2000 and 2017 in these countries could have been averted in the absence of geographical inequality. This study enables the identification of high-mortality clusters, patterns of progress and geographical inequalities to inform appropriate investments and implementations that will help to improve the health of all populations.
Polarity-driven 3-fold symmetry of GaAs/AlGaAs core multishell nanowires
Publisher: American Chemical Society (ACS)
Date: 02-07-2013
DOI: 10.1021/NL401680K
Abstract: AlGaAs/GaAs quantum well heterostructures based on core-multishell nanowires exhibit excellent optical properties which are acutely sensitive to structure and morphology. We characterize these heterostructures and observe them to have 3-fold symmetry about the nanowire axis. Using aberration-corrected annular dark field scanning transmission electron microscopy (ADF-STEM), we measure directly the polarity of the crystal structure and correlate this with the shape and facet orientation of the GaAs core, quantum wells and cap, and the width of radial Al-rich bands. We discuss how the underlying polarity of the crystal structure drives the growth of these heterostructures with a 3-fold symmetry resulting in a nonuniform GaAs quantum well tube and AlGaAs shell. These observations suggest that the AlGaAs growth rate is faster along the [112] B compared to the [112] A directions and/or that there is a polarity driven surface reconstruction generating AlGaAs growth fronts inclined to the {110} planes. In contrast, the observations suggest that the opposite is true for the GaAs growth, with the preferred surface reconstruction plane being parallel to {110} and an apparent faster growth rate along the [112] A. This two-dimensional layer growth of the nanowire multishells strongly depends on the surface energies and surface reconstruction of the facets which are related to the crystal polarity and lead to the 3-fold symmetry observed here.
Combined optical trapping and microphotoluminescence of single InP nanowires
Publisher: AIP Publishing
Date: 07-09-2009
DOI: 10.1063/1.3225148
Abstract: In this letter, we demonstrate that microphotoluminescence may be combined with optical trapping for effective optical characterization of single target InP semiconductor nanowires in suspension. Using this technique, we may investigate structural properties of optically trapped nanowires, such as crystalline polytypes and stacking faults. This arrangement may also be used to resolve structural variations along the axis of the trapped nanowire. These results show that photoluminescence measurements may be coupled with optical tweezers without degrading the performance of the optical trap and provide a powerful interrogation tool for preselection of components for nanowire photonic devices.
Controlling the morphology and optical properties of self-assembled InAsSb/InGaAs/InP nanostructures via Sb exposure
Publisher: AIP Publishing
Date: 07-11-2011
DOI: 10.1063/1.3659695
Abstract: Engineering the surface energy, interface energy, and elastic strain energy in the system via Sb exposure is used to realize the control on the morphology and optical properties of self-assembled InP-based InAsSb/InGaAs nanostructures. By flowing trimethylantimony precursor over the surface of InGaAs buffer layer before the growth of InAsSb nanostructures, the surface/interface energy in the system is reduced, while the strain energy in the system is enhanced, which lead to a shape transition from dot to dash, and to wire for the InAsSb nanostructures. As a result of their morphology changes, the InAsSb nanostructures show different polarization characteristics in their photoluminescence emission.
Effects of annealing and substrate orientation on epitaxial growth of GaAs on Si
Publisher: AIP Publishing
Date: 15-10-2009
DOI: 10.1063/1.3248372
Abstract: GaAs thin films grown on Si (100) and (111) substrates by metal-organic chemical vapor deposition were investigated by electron microscopy. It was found that the growth rate of the GaAs epitaxial layers on Si (100) was faster than that on Si (111) due to a lower Si (111) surface energy. The morphologies and internal crystal structure quality of GaAs films grown on Si (111) were better than those grown on Si (100). It was also found that postannealing at high temperature can improve the morphology of the epitaxial layer surface and reduce lattice defects in the thin films.
In situ mechanical resonance behaviour of pristine and defective zinc blende GaAs nanowires
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C7NR07449B
Abstract: Mechanical resonance of GaAs nanowires allows for measurement of the effect of stacking faults on Young's modulus and quality factor.
Integration of an InGaAs quantum-dot laser with a low-loss passive waveguide using selective-area epitaxy
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2006
High quantum efficiency (Al) GaAs nanowires for optoelectronic devices
Publisher: IEEE
Date: 07-2014
DOI: 10.1109/SUM.2014.14
Resonant Excitation and Imaging of Nonequilibrium Exciton Spins in Single Core−Shell GaAs−AlGaAs Nanowires
Publisher: American Chemical Society (ACS)
Date: 15-02-2007
DOI: 10.1021/NL062383Q
Abstract: Nonequilibrium spin distributions in single GaAs/AlGaAs core-shell nanowires are excited using resonant polarized excitation at 10 K. At all excitation energies, we observe strong photoluminescence polarization due to suppressed radiative recombination of excitons with dipoles aligned perpendicular to the nanowire. Excitation resonances are observed at 1- or 2-LO phonon energies above the exciton ground states. Using rate equation modeling, we show that, at the lowest energies, strongly nonequilibrium spin distributions are present and we estimate their spin relaxation rate.
Analysis of Multi-wavelength Photonic Crystal Single-defect Laser Arrays
Publisher: IEEE
Date: 11-2010
Strong Carrier Lifetime Enhancement in GaAs Nanowires Coated with Semiconducting Polymer
Publisher: American Chemical Society (ACS)
Date: 29-11-2012
DOI: 10.1021/NL3034027
Abstract: The ultrafast charge carrier dynamics in GaAs/conjugated polymer type II heterojunctions are investigated using time-resolved photoluminescence spectroscopy at 10 K. By probing the photoluminescence at the band edge of GaAs, we observe strong carrier lifetime enhancement for nanowires blended with semiconducting polymers. The enhancement is found to depend crucially on the ionization potential of the polymers with respect to the Fermi energy level at the surface of the GaAs nanowires. We attribute these effects to electron doping by the polymer which reduces the unsaturated surface-state density in GaAs. We find that when the surface of nanowires is terminated by native oxide, the electron injection across the interface is greatly reduced and such surface doping is absent. Our results suggest that surface engineering via π-conjugated polymers can substantially improve the carrier lifetime in nanowire hybrid heterojunctions with applications in photovoltaics and nanoscale photodetectors.
Determination of Young's Modulus of Ultrathin Nanomaterials
Publisher: American Chemical Society (ACS)
Date: 22-07-2015
DOI: 10.1021/ACS.NANOLETT.5B01603
Abstract: Determination of the elastic modulus of nanostructures with sizes at several nm range is a challenge. In this study, we designed an experiment to measure the elastic modulus of amorphous Al2O3 films with thicknesses varying between 2 and 25 nm. The amorphous Al2O3 was in the form of a shell, wrapped around GaAs nanowires, thereby forming an effective core/shell structure. The GaAs core comprised a single crystal structure with a diameter of 100 nm. Combined in situ compression transmission electron microscopy and finite element analysis were used to evaluate the elastic modulus of the overall core/shell nanowires. A core/shell model was applied to deconvolute the elastic modulus of the Al2O3 shell from the core. The results indicate that the elastic modulus of amorphous Al2O3 increases significantly when the thickness of the layer is smaller than 5 nm. This novel nanoscale material can be attributed to the reconstruction of the bonding at the surface of the material, coupled with the increase of the surface-to-volume ratio with nanoscale dimensions. Moreover, the experimental technique and analysis methods presented in this study may be extended to measure the elastic modulus of other materials with dimensions of just several nanometers.
Epitaxially grown GaAsN random laser
Publisher: AIP Publishing
Date: 09-05-2003
DOI: 10.1063/1.1568533
Abstract: We have studied the photoluminescence properties of as-grown GaAs1−xNx epitaxial layers grown on GaAs containing 0.6%, 1.77%, and 2.8% nitrogen. We found laser emission from thick (d& nm) GaAs0.972N0.028 layers exhibiting the characteristic lasing properties of random lasers. This is unusual because random lasers have so far only been associated with highly disordered or random media. We believe that high gain in combination with structural inhomogeneities that are evident in these GaAs0.972N0.028 layers, can explain the random lasing in such epitaxial layers.
Improvement of the kink-free operation in ridge-waveguide laser diodes due to coupling of the optical field to the metal layers outside the ridge
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2003
Compound semiconductor optoelectronics research at the Australian National University
Publisher: IEEE
Date: 2005
Polarization tunable, multicolor emission from core-shell photonic III-V semiconductor nanowires
Publisher: American Chemical Society (ACS)
Date: 09-11-2012
DOI: 10.1021/NL303787A
Abstract: We demonstrate luminescence from both the core and the shell of III-V semiconductor photonic nanowires by coupling them to plasmonic silver nanoparticles. This demonstration paves the way for increasing the quantum efficiency of large surface area nanowire light emitters. The relative emission intensity from the core and the shell is tuned by varying the polarization of the excitation source since their polarization response can be independently controlled. Independent control on emission wavelength and polarization dependence of emission from core-shell nanowire heterostructures opens up opportunities that have not yet been imagined for nanoscale polarization sensitive, wavelength-selective, or multicolor photonic devices based on single nanowires or nanowire arrays.
Optically pumped room-temperature GaAs nanowire lasers
Publisher: Springer Science and Business Media LLC
Date: 17-11-2013
Enhancing the electrical performance of InAs nanowire field-effect transistors by improving the surface and interface properties by coating with thermally oxidized Y2O3
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2NR02736D
Abstract: High-performance InAs nanowire transistors are realized by improving the surface and interfaces by coating with thermally oxidized Y 2 O 3.
Taper-free and kinked germanium nanowires grown on silicon via purging and the two-temperature process
Publisher: IOP Publishing
Date: 28-02-2012
DOI: 10.1088/0957-4484/23/11/115603
Abstract: We investigate the growth procedures for achieving taper-free and kinked germanium nanowires epitaxially grown on silicon substrates by chemical vapor deposition. Singly and multiply kinked germanium nanowires consisting of segments were formed by employing a reactant gas purging process. Unlike non-epitaxial kinked nanowires, a two-temperature process is necessary to maintain the taper-free nature of segments in our kinked germanium nanowires on silicon. As an application, nanobridges formed between (111) side walls of V-grooved (100) silicon substrates have been demonstrated.
Defect-Free GaAs/AlGaAs Core–Shell Nanowires on Si Substrates
Publisher: American Chemical Society (ACS)
Date: 27-05-2011
DOI: 10.1021/CG2003657
III-V compound semiconductor nanowires
Publisher: IEEE
Date: 06-2009
Deep-level transient spectroscopy study of electron traps in rapid thermally annealed SiO2-capped n-type GaAs layers grown by metalorganic chemical vapour deposition
Publisher: Elsevier BV
Date: 12-2001
Near-field studies of arrays of chirped subwavelength apertures
Publisher: Wiley
Date: 21-07-2010
Mode Profiling of Semiconductor Nanowire Lasers
Publisher: American Chemical Society (ACS)
Date: 22-07-2015
DOI: 10.1021/ACS.NANOLETT.5B01713
Abstract: We experimentally determine the lasing mode(s) in optically pumped semiconductor nanowire lasers. The spatially resolved and angle-resolved far-field emission profiles of single InP nanowire lasers lying horizontally on a SiO2 substrate are characterized in a microphotoluminescence (μ-PL) setup. The experimentally obtained polarization dependent far-field profiles match very well with numerical simulations and enable unambiguous identification of the lasing mode(s). This technique can be applied to characterize lasing modes in other type of nanolasers that are integrated on a substrate in either vertical or horizontal configurations.
Selective area epitaxy of III–V nanostructure arrays and networks: Growth, applications, and future directions
Publisher: AIP Publishing
Date: 02-04-2021
DOI: 10.1063/5.0044706
Abstract: Selective area epitaxy (SAE) can be used to grow highly uniform III–V nanostructure arrays in a fully controllable way and is thus of great interest in both basic science and device applications. Here, an overview of this promising technique is presented, focusing on the growth fundamentals, formation of III–V nanowire arrays, monolithic integration of III–V nanowire arrays on silicon, the growth of nanowire heterostructures, and networks of various shapes. The applications of these III–V nanostructure arrays in photonics, electronics, optoelectronics, and quantum science are also reviewed. Finally, the current challenges and opportunities provided by SAE are discussed.
Design Considerations for Semiconductor Nanowire-Plasmonic Nanoparticle Coupled Systems for High Quantum Efficiency Nanowires
Publisher: Wiley
Date: 12-06-2013
Abstract: The optimal geometries for reducing the radiative recombination lifetime and thus enhancing the quantum efficiency of III-V semiconductor nanowires by coupling them to plasmonic nanoparticles are established. The quantum efficiency enhancement factor due to coupling to plasmonic nanoparticles reduces as the initial quality of the nanowire increases. Significant quantum efficiency enhancement is observed for semiconductors only within about 15 nm from the nanoparticle. It is also identified that the modes responsible for resonant enhancement in the quantum efficiency of an emitter in the nanowire are geometric resonances of surface plasmon polariton modes supported at the nanowire/nanoparticle interface.
Effect of Eggshell Thinning on Water Vapor Conductance of Malleefowl Eggs
Publisher: Oxford University Press (OUP)
Date: 08-1987
DOI: 10.2307/1368635
Evolution of Wurtzite Structured GaAs Shells Around InAs Nanowire Cores
Publisher: Springer Science and Business Media LLC
Date: 06-05-2009
DOI: 10.1007/S11671-009-9326-6
Abstract: GaAs was radially deposited on InAs nanowires by metal–organic chemical vapor deposition and resultant nanowire heterostructures were characterized by detailed electron microscopy investigations. The GaAs shells have been grown in wurtzite structure, epitaxially on the wurtzite structured InAs nanowire cores. The fundamental reason of structural evolution in terms of material nucleation and interfacial structure is given.
Quantum Dots and Nanowires Grown by Metal–Organic Chemical Vapor Deposition for Optoelectronic Device Applications
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 11-2006
Global age-sex-specific fertility, mortality, healthy life expectancy (HALE), and population estimates in 204 countries and territories, 1950-2019: a comprehensive demographic analysis for the Global Burden of Disease Study 2019
Publisher: Elsevier BV
Date: 10-2020
On the nature of radiative recombination in GaAsN
Publisher: AIP Publishing
Date: 25-11-2002
DOI: 10.1063/1.1526913
Abstract: Radiative recombination at low temperatures in GaAsN is often associated with localized excitons. In this short note, we report results from high-resolution time-resolved photoluminescence spectroscopy that indicate that excitons, localized or otherwise, cannot be involved in the recombination process of this alloy system. The risetime of the photoluminescence signal is more than two orders of magnitude shorter than that expected, and found from excitonic recombination in other III–V materials, such as GaAs. We suggest that the radiative recombination in GaAsN takes place between localized electrons and delocalized holes.
Photonic crystal phase detector
Publisher: Optica Publishing Group
Date: 21-08-2008
Carrier capture into InGaAs/GaAs quantum wells via impurity mediated resonant tunneling
Publisher: AIP Publishing
Date: 20-04-1998
DOI: 10.1063/1.121248
Abstract: We have investigated the photoexcited carrier dynamics in In1−xGaxAs/GaAs quantum wells using the photoluminescence up-conversion technique. We found a unique capture process which was exceptional both in terms of the capture time and its temperature dependence. In the case of a specific quantum well with wide barriers, the photoluminescence rise time, a parameter which includes the overall capture time and the exciton formation time, was less than 600 fs instead of the expected few hundred picoseconds. We show in this work that this unusually rapid process is the result of the capture of the photoexcited carriers (or excitons) by impurities in the GaAs barriers, from where they resonantly tunnel into the quantum well.
Growth and Characterization of Self-Assembled InAs/InP Quantum Dot Structures
Publisher: American Scientific Publishers
Date: 03-2010
Abstract: InAs quantum dots (QDs) are grown on InP or lattice matched GaInAsP buffers using horizontal flow metal-organic chemical vapor deposition (MOCVD) at a pressure of 180 mbar. A range of techniques, such as photoluminescence (PL), atomic force microscopy, and plan-view transmission electron microscopy is used to characterize the QD and other semiconductor layers. The effects of different growth parameters, such as V/III ratio and growth time, and the effects of buffer layers, interlayers, and cap layers are investigated and the optimized growth conditions are discussed. In the case of the QDs grown on InP buffers, the As/P exchange reaction is found to be prominent. A very thin (0.6 nm) GaAs interlayer grown between the buffer and the QD layers consumes segregated indium and minimizes the As/P exchange reaction. As a result, the QD PL emission energy increases, the PL intensity improves, and the PL linewidth decreases. The experimental results show that by changing the thickness of a GaAs interlayer (0.3-0.6 nm), the emission wavelength/energy of the QDs grown on a lattice matched GaInAsP buffer can be tuned over a wide range covering 1550 nm. However, further increase in the thickness of the GaAs interlayer results in the agglomeration of the QDs and the deterioration of the QD optical properties. Detailed microscopy studies show that capped QDs have higher density and are smaller in size on average compared to uncapped QDs, which undergo coalescence during cooling of the s le after growth. Overall, the QDs grown for shorter time with a smaller V/III ratio (approximately 8) show improved PL intensity and narrower PL linewidth.
Quality of silica capping layer and its influence on quantum-well intermixing
Publisher: AIP Publishing
Date: 14-02-2000
DOI: 10.1063/1.125601
Abstract: The quality of spin-on silica films prebaked at different temperatures has been studied using Fourier transform infrared spectroscopy, spectroscopic ellipsometry, and P-etch [HF(40%):HNO3(70%):H2O=3:2:60] measurements. Low-temperature photoluminescence (PL) was performed on GaAs/AlGaAs quantum-well (QW) structures encapsulated by the same films. For all the prebaked films, not only the Si–O–Si peaks, but also OH-related peaks were detected in the IR spectra. After annealing at 950 °C for 60 s, almost all OH-related peaks disappeared. Spectroscopic ellipsometry modeling and P-etch measurements showed that the porosity of high-temperature (& °C) baked s les was similar, and was significantly higher than the low-temperature (210 °C) baked s le. The same trend was observed in the PL energy shifts from the GaAs/AlGaAs QWs, indicating a direct correlation between the film quality and quantum-well intermixing.
The effect of Sn addition on GaAs nanowire grown by vapor–liquid–solid growth mechanism
Publisher: IOP Publishing
Date: 19-09-2018
Abstract: Impurity addition is a crucial aspect for III-V nanowire growth. In this study, we demonstrated the effect of the Sn addition on GaAs nanowire growth by metal-organic chemical vapor deposition. With increasing the tetraethyltin flow rate, the nanowire axial growth was suppressed while the nanowire lateral growth was promoted, as well as planar defects were increased. Systematic electron microscopy characterizations suggested that the Sn addition tuned the catalyst composition, changed the vapor-solid-liquid surfaces energies and hindered the Ga atoms diffusion on nanowire sidewalls, which is responsible for the observed changes in morphology and structural quality of grown GaAs nanowires. This study contributes to understanding the role of impurity dopants on III-V nanowires growth, which will be of benefit for the design and fabrication of future nanowire-based devices.
Effect of active region position in Fabry-Perot single transverse mode broad-waveguide InGaAsP/InP lasers
Publisher: The Optical Society
Date: 04-2014
DOI: 10.1364/OE.22.008156
Ion irradiation-induced disordering of semiconductors: defect structures and applications
Publisher: Informa UK Limited
Date: 02-2005
Feeding practices and risk factors for chronic infant undernutrition among refugees and migrants along the Thailand-Myanmar border: a mixed-methods study
Publisher: Springer Science and Business Media LLC
Date: 28-11-2019
DOI: 10.1186/S12889-019-7825-7
Abstract: This study aims to provide a comprehensive understanding of maternal risk factors, infant risk factors and maternal infant feeding practices among refugees and migrants along the Thailand-Myanmar border. This study employed a mixed-methods approach with two components: (1) cross-sectional survey ( n = 390) and (2) focus group discussions ( n = 63). Participants were chosen from one of three clinics providing antenatal and delivery services for Karen and Burman refugees and migrants along the border. Participants were pregnant women and mother-infant dyads. Refugee and migrant mothers demonstrated high rates of suboptimal breastfeeding and low rates of minimum dietary ersity and acceptable diet. Multivariable regression models showed infant stunting (AOR: 2.08, 95% CI: 1.12, 3.84, p = 0.020) and underweight (AOR: 2.26, 95% CI: 1.17, 4.36, p = 0.015) to have increased odds among migrants, while each 5 cm increase in maternal height had decreased odds of stunting (AOR: 0.50, 95% CI: 0.38, 0.66, p 0.001) and underweight (AOR: 0.64, 95% CI: 0.48, 0.85, p = 0.002). In addition, small-for-gestational-age adjusted for length of gestation, infant age and gender increased odds of infant’s stunting (AOR: 3.42, 95% CI: 1.88, 6.22, p 0.001) and underweight (AOR: 4.44, 95% CI: 2.36, 8.34, p 0.001). Using the Integrated Behavioural Model, focus group discussions explained the cross-sectional findings in characterising attitudes, perceived norms, and personal agency as they relate to maternal nutrition, infant malnutrition, and infant feeding practices. Inadequate infant feeding practices are widespread in refugee and migrant communities along the Thailand-Myanmar border. Risk factors particular to maternal nutrition and infant birth should be considered for future programming to reduce the burden of chronic malnutrition in infants.
Temperature Dependence of Interband Transitions in Wurtzite InP Nanowires
Publisher: American Chemical Society (ACS)
Date: 31-03-2015
Abstract: Semiconductor nanowires (NWs) formed by non-nitride III-V compounds grow preferentially with wurtzite (WZ) lattice. This is contrary to bulk and two-dimensional layers of the same compounds, where only zincblende (ZB) is observed. The absorption spectrum of WZ materials differs largely from their ZB counterparts and shows three transitions, referred to as A, B, and C in order of increasing energy, involving the minimum of the conduction band and different critical points of the valence band. In this work, we determine the temperature dependence (T = 10-310 K) of the energy of transitions A, B, and C in ensembles of WZ InP NWs by photoluminescence (PL) and PL excitation (PLE) spectroscopy. For the whole temperature and energy ranges investigated, the PL and PLE spectra are quantitatively reproduced by a theoretical model taking into account contribution from both exciton and continuum states. WZ InP is found to behave very similarly to wide band gap III-nitrides and II-VI compounds, where the energy of A, B, and C displays the same temperature dependence. This finding unveils a general feature of the thermal properties of WZ materials that holds regardless of the bond polarity and energy gap of the crystal. Furthermore, no differences are observed in the temperature dependence of the fundamental band gap energy in WZ InP NWs and ZB InP (both NWs and bulk). This result points to a negligible role played by the WZ/ZB differences in determining the deformation potentials and the extent of the electron-phonon interaction that is a direct consequence of the similar nearest neighbor arrangement in the two lattices.
Defect Evolution in Annealed p-type GaAsN Epilayers Grown by Metalorganic Chemical Vapour Deposition
Publisher: IOP Publishing
Date: 10-11-2003
DOI: 10.1143/JJAP.42.6827
Determination of carrier-transfer length from side-wall quantum well to quantum wire by micro-photoluminescence scanning
Publisher: Springer Science and Business Media LLC
Date: 08-2003
InP–InxGa1−xAs core-multi-shell nanowire quantum wells with tunable emission in the 1.3–1.55 μm wavelength range
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7NR04598K
Abstract: Wurtzite phase InP–In x Ga 1−x As nanowire radial quantum wells were grown for the first time, with tunable emission in the 1.3–1.55 μm optical communication wavelength range.
Picosecond carrier lifetime in GaAs implanted with high doses of As ions: An alternative material to low-temperature GaAs for optoelectronic applications
Publisher: AIP Publishing
Date: 12-06-1995
DOI: 10.1063/1.113738
Abstract: Nonstoichiometric GaAs obtained by implantation with 2 MeV arsenic ions at 1015 cm−2 dose is studied. As-implanted s les show a & fs lifetime of photocarriers and low resistivity due to hopping, with mobility less than 1 cm2/V s. Annealing of the s les at 600 °C leads to substantial recovery of postimplant damage, as seen from Rutherford backscattering channeling spectra and mobility increase to about 2000 cm2/V s, but photocarrier lifetime is still about 1 ps. These parameters are similar to those of low-temperature GaAs annealed at 600 °C, and make arsenic implanted GaAs an interesting material for optoelectronic applications.
Super Deformability and Young's Modulus of GaAs Nanowires
Publisher: Wiley
Date: 15-02-2011
Carrier transfer between V-grooved quantum wire and vertical quantum well
Publisher: Elsevier BV
Date: 02-2001
Effects of well thickness on the spectral properties of In0.5Ga0.5As∕GaAs∕Al0.2Ga0.8As quantum dots-in-a-well infrared photodetectors
Publisher: AIP Publishing
Date: 12-05-2008
DOI: 10.1063/1.2927487
Abstract: We report on the effects of the quantum well (QW) thickness on the spectral response and other characteristics of In0.5Ga0.5As∕GaAs∕Al0.2Ga0.8As quantum dots-in-a-well infrared photodetectors grown by low-pressure metal-organic chemical vapor deposition. The main device properties are observed to have a strong dependence on the QW parameters.
Application of Selective Implantation in Al<SUB>0.5</SUB>Ga<SUB>0.5</SUB>As/In <SUB>0.25</SUB>Ga<SUB>0.75</SUB>As/GaAs Pseudomorphic Single Quantum Wire
Publisher: American Scientific Publishers
Date: 12-2001
DOI: 10.1166/JNN.2001.064
Abstract: A pseudomorphic Al0.5Ga0.5As/In0.25Ga0.75As/GaAs asymmetric quantum wire (QWR) structure was grown on GaAs V-grooved substrate by low pressure metal organic vapor phase epitaxy. The formation of crescent shaped QWRs at the bottom of the V-grooves was confirmed by both transmission electron microscopy and photoluminescence (PL) spectra. The temperature dependence of PL spectra demonstrated a fast decrease of the sidewall quantum well PL intensity with increasing temperature, which originates from relaxation of carriers from well to wire region. The self-aligned dual implantation technique was successfully used to selectively disable the adjacent quantum structures. Decrease of the PL intensity of QWR at 8 K was observed after selective implantation, which resulted from a decreased number of carriers relaxed from adjacent quantum structures.
Department of Error
Publisher: Elsevier BV
Date: 06-2020
High Purity GaAs Nanowires Free of Planar Defects: Growth and Characterization
Publisher: Wiley
Date: 08-12-2008
Asian G6PD-Mahidol Reticulocytes Sustain Normal Plasmodium Vivax Development
Publisher: Oxford University Press (OUP)
Date: 07-06-2017
P. falciparum infection and maternofetal antibody transfer in malaria-endemic settings of varying transmission.
Publisher: Public Library of Science (PLoS)
Date: 13-10-2017
Characteristics of MOCVD-Grown Thin p-Clad InGaAs Quantum-Dot Lasers
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2004
Enhanced minority carrier lifetimes in GaAs/AlGaAs core-shell nanowires through shell growth optimization
Publisher: American Chemical Society (ACS)
Date: 18-10-2013
DOI: 10.1021/NL4023385
Abstract: The effects of AlGaAs shell thickness and growth time on the minority carrier lifetime in the GaAs core of GaAs/AlGaAs core-shell nanowires grown by metal-organic chemical vapor deposition are investigated. The carrier lifetime increases with increasing AlGaAs shell thickness up to a certain value as a result of reducing tunneling probability of carriers through the AlGaAs shell, beyond which the carrier lifetime reduces due to the diffusion of Ga-Al and/or impurities across the GaAs/AlGaAs heterointerface. Interdiffusion at the heterointerface is observed directly using high-angle annular dark field scanning transmission electron microscopy. We achieve room temperature minority carrier lifetimes of 1.9 ns by optimizing the shell growth with the intention of reducing the effect of interdiffusion.
InxGa1−xAs nanowires with uniform composition, pure wurtzite crystal phase and taper-free morphology
Publisher: IOP Publishing
Date: 30-04-2015
DOI: 10.1088/0957-4484/26/20/205604
Abstract: Obtaining compositional homogeneity without compromising morphological or structural quality is one of the biggest challenges in growing ternary alloy compound semiconductor nanowires. Here we report growth of Au-seeded InxGa1-xAs nanowires via metal-organic vapour phase epitaxy with uniform composition, morphology and pure wurtzite (WZ) crystal phase by carefully optimizing growth temperature and V/III ratio. We find that high growth temperatures allow the InxGa1-xAs composition to be more uniform by suppressing the formation of typically observed spontaneous In-rich shells. A low V/III ratio results in the growth of pure WZ phase InxGa1-xAs nanowires with uniform composition and morphology while a high V/III ratio allows pure zinc-blende (ZB) phase to form. Ga incorporation is found to be dependent on the crystal phase favouring higher Ga concentration in ZB phase compared to the WZ phase. Tapering is also found to be more prominent in defective nanowires hence it is critical to maintain the highest crystal structure purity in order to minimize tapering and inhomogeneity. The InP capped pure WZ In0.65Ga0.35As core-shell nanowire heterostructures show 1.54 μm photoluminescence, close to the technologically important optical fibre telecommunication wavelength, which is promising for application in photodetectors and nanoscale lasers.
Mechanisms of electrical isolation inO + Publisher:
American Physical Society (APS)
Date:
25-07-2008
Publisher: American Physical Society (APS)
Date: 25-07-2008
Formation and shape control of InAsSb/InP (001) nanostructures
Publisher: AIP Publishing
Date: 06-07-2009
DOI: 10.1063/1.3160738
Abstract: This paper presents a study on the formation and shape control of InAsSb/InP nanostructures on InP (001) substrates. For the formation of InAsSb nanostructures, incorporation of Sb atoms into InAs islands results in significant morphology change in the islands due to the surfactant effect of Sb atoms and the large strain in the system. And, shape control of InAsSb/InP nanostructures is achieved by optimizing their growth parameters. Low growth temperature and high growth rate will induce the formation of InAsSb elongated quantum dots, while high growth temperature and low growth rate will promote the formation of InAsSb quantum wires or dashes.
Merging Photonic Wire Lasers and Nanoantennas
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 09-2011
Atomic interdiffusion for integration of quantum dot optoelectronic devices
Publisher: IEEE
Date: 2002
Unexpected benefits of stacking faults on the electronic structure and optical emission in wurtzite GaAs/GaInP core/shell nanowires
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9NR01213C
Abstract: Superior passivation of GaInP shell and the revealed carrier dynamics in WZ polytype GaAs nanowires.
Spatial variation of PM2.5, PM10, PM2.5 absorbance and PMcoarse concentrations between and within 20 European study areas and the relationship with NO2 – Results of the ESCAPE project
Publisher: Elsevier BV
Date: 12-2012
Nonlinear optical absorption and temporal response of arsenic- and oxygen-implanted GaAs
Publisher: AIP Publishing
Date: 05-04-1999
DOI: 10.1063/1.123724
Abstract: We have measured the nonlinear optical absorption of arsenic and oxygen implanted epitaxial GaAs for a range of ion doses and annealing temperatures. The response time, τA, and a parameter, Mmax, which characterizes the performance of the structures as modulators, are both reduced by implantation, and correspondingly the nonbleachable losses are increased. We show that similar combinations of (τA, Mmax) can be achieved using either ion species and various combinations of dose and annealing temperatures. Furthermore, the data were all located on a well-defined curve in the (τA, Mmax) plane, provided amorphization, which occurs at high implant doses, was avoided. We deduce that there exists a limit to the modulation if a specific response time is required.
Non-thermal and thermal effects on mechanical strain in substrate-transferred wafer-scale hBN films
Publisher: AIP Publishing
Date: 13-09-2022
DOI: 10.1063/5.0102617
Abstract: Wafer-scale thin films of hexagonal boron nitride have exceptional thermal and mechanical properties, which harness the potential use of these materials in two-dimensional electronic, device applications. Along with unavoidable defects, grains, and wrinkles, which develop during the growth process, underlying substrates influence the physical and mechanical properties of these films. Understanding the interactions of these large-scale films with different substrates is, thus, important for the implementation of this 2D system in device fabrication. MOVPE-grown 2 and 30 nm hBN/sapphire films of size 2 in. diameter are delaminated chemically and transferred on quartz, SiO2/Si, and sapphire substrates. The structural characteristics of these films are investigated by employing Raman spectroscopy. Our results suggest that not only the roughness but also the height modulation at the surface of the substrates play a pivotal role in determining substrate-mediated mechanical strain inhomogeneity in these films. The statistical analysis of the spectral parameters provides us with the overall characteristics of the films. Furthermore, a Stark difference in the thermal evolution of strain in these films depending on substrate materials is observed. It has been demonstrated that not only the differential thermal expansion coefficient of the substrates and the films, but also slippage of the latter during the thermal treatment determines the net strain in the films. The role of the slippage is significantly higher in 2 nm films than in 30 nm films. We believe that the observations provide crucial information on the structural characteristics of the substrate-coupled wafer-scale hBN films for their future use in technology.
Proton irradiation-induced intermixing in InGaAs/(Al)GaAs quantum wells and quantum-well lasers
Publisher: AIP Publishing
Date: 05-1999
DOI: 10.1063/1.370291
Abstract: Proton irradiation with subsequent rapid thermal annealing was used to investigate intermixing of InGaAs/GaAs and InGaAs/AlGaAs quantum wells. Large photoluminescence (PL) energy shifts were observed in both materials. Comparatively, InGaAs/AlGaAs s les showed larger PL energy shifts than InGaAs/GaAs s les because of the presence of Al in the barriers and also better recovery of PL intensities, which is mainly due to dynamic annealing effects in AlGaAs during irradiation. Based on this, InGaAs/AlGaAs quantum-well lasers were fabricated and up to 49.3-nm-emission wavelength shift was observed in the proton-irradiated laser with no significant degradation in device characteristics.
Investigation of the blueshift in electroluminescence spectra from MOCVD grown InGaAs quantum dots
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 10-2004
Electronic comparison of InAs wurtzite and zincblende phases using nanowire transistors
Publisher: Wiley
Date: 25-07-2013
InGaAs quantum dots grown with GaP strain compensation layers
Publisher: AIP Publishing
Date: 06-05-2004
DOI: 10.1063/1.1707230
Abstract: A major obstacle in the growth of stacked dot structures with a large number of layers is the high degree of strain in the dot layers. Strain buildup can affect the nucleation of the dots, which may cause defects that are detrimental to device performance. In this work, thin GaP layers are inserted below the quantum dot (QD) layer in single and stacked In0.5Ga0.5As/GaAs QD structures. These layers counterbalance the strain caused by the previous layers. Changes in dot nucleation are observed for dots grown directly on GaP layers. The QDs are found to be smaller in width and height. The luminescence from these dots is blueshifted due to interdiffusion between the dots and the GaP buffer layer. In a single layer of dots, no change in dot formation is seen when a thin GaAs barrier layer is deposited between the GaP layer and the QD layer. However, in stacked structures, the addition of a GaP layer below each QD layer is found to increase the density of the dots in the top layer of the stack. The room-temperature photoluminescence intensity is also increased.
Taper-Free and Vertically Oriented Ge Nanowires on Ge/Si Substrates Grown by a Two-Temperature Process
Publisher: American Chemical Society (ACS)
Date: 02-12-2011
DOI: 10.1021/CG2008914
Vertically oriented epitaxial germanium nanowires on silicon substrates using thin germanium buffer layers
Publisher: IOP Publishing
Date: 29-06-2010
DOI: 10.1088/0957-4484/21/29/295602
Abstract: We demonstrate a method to realize vertically oriented Ge nanowires on Si(111) substrates. Ge nanowires were grown by chemical vapor deposition using Au nanoparticles to seed nanowire growth via a vapor-liquid-solid growth mechanism. Rapid oxidation of Si during Au nanoparticle application inhibits the growth of vertically oriented Ge nanowires directly on Si. The present method employs thin Ge buffer layers grown at low temperature less than 600 degrees C to circumvent the oxidation problem. By using a thin Ge buffer layer with root-mean-square roughness of approximately 2 nm, the yield of vertically oriented Ge nanowires is as high as 96.3%. This yield is comparable to that of homoepitaxial Ge nanowires. Furthermore, branched Ge nanowires could be successfully grown on these vertically oriented Ge nanowires by a secondary seeding technique. Since the buffer layers are grown under moderate conditions without any high temperature processing steps, this method has a wide process window highly suitable for Si-based microelectronics.
Growth of Straight InAs-on-GaAs Nanowire Heterostructures
Publisher: American Chemical Society (ACS)
Date: 28-07-2011
DOI: 10.1021/NL202051W
Abstract: One of the main motivations for the great interest in semiconductor nanowires is the possibility of easily growing advanced heterostructures that might be difficult or even impossible to achieve in thin films. For III-V semiconductor nanowires, axial heterostructures with an interchange of the group III element typically grow straight in only one interface direction. In the case of InAs-GaAs heterostructures, straight nanowire growth has been demonstrated for growth of GaAs on top of InAs, but so far never in the other direction. In this article, we demonstrate the growth of straight axial heterostructures of InAs on top of GaAs. The heterostructure interface is sharp and we observe a dependence on growth parameters closely related to crystal structure as well as a diameter dependence on straight nanowire growth. The results are discussed by means of accurate first principles calculations of the interfacial energies. In addition, the role of the gold seed particle, the effect of its composition at different stages during growth, and its size are discussed in relation to the results observed.
Self-sustained output power pulsations in InGaAs quantum dot ridge-waveguide lasers
Publisher: AIP Publishing
Date: 14-01-2008
DOI: 10.1063/1.2830998
Abstract: Self-sustained pulsations in the output power of metal-organic chemical vapor deposition grown ridge-waveguide lasers with InGaAs quantum dot active region are reported. The characteristics of the output power pulsations (range, frequency, and modulation depth) are presented. The origin of the pulsations is explained in terms of the properties of the quantum dot active region.
A Comparison of Low-Energy As Ion Implantation and Impurity-Free Disordering Induced Defects in N-Type GaAs Epitaxial Layers
Publisher: IOP Publishing
Date: 15-03-2003
DOI: 10.1143/JJAP.42.1158
Ultrafast trapping times in ion implanted InP
Publisher: AIP Publishing
Date: 16-08-2002
DOI: 10.1063/1.1493651
Abstract: As + and P+ implantation was performed on semi-insulating (SI) and p-type InP s les for the purpose of creating a material suitable for ultrafast optoelectronic applications. SI InP s les were implanted with a dose of 1×1016 cm−2 and p-type InP was implanted with doses between 1×1012 and 1×1016 cm−2. Subsequently, rapid thermal annealing at temperatures between 400 and 700 °C was performed for 30 sec. Hall-effect measurements, double-crystal x-ray diffraction, and time-resolved femtosecond differential reflectivity showed that, for the highest-annealing temperatures, the implanted SI InP s les exhibited high mobility, low resistivity, short response times, and minimal structural damage. Similar measurements on implanted p-type InP showed that the fast response time, high mobility, and good structural recovery could be retained while increasing the resistivity.
Observation of coherent biexcitons in ZnO∕ZnMgO multiple quantum wells at room temperature
Publisher: AIP Publishing
Date: 30-10-2006
DOI: 10.1063/1.2372747
Abstract: We have studied ZnO∕ZnMgO multiple quantum wells by spectrally resolved transient four-wave mixing with both one- and two-color excitations. The presence of an extended signal at negative interpulse delays in the two-color experiment is attributed to the two-photon coherence resulting from the generation of biexcitons. This technique provides a means to observe a transient four-wave mixing from biexcitons in the absence of any other signal, and thereby provides the first clear evidence that biexcitons are present in narrow ZnO∕ZnMgO quantum wells at room temperature. Dephasing times of the order of 100fs for the biexcitons are measured.
Influence of surface passivation on ultrafast carrier dynamics and terahertz radiation generation in GaAs
Publisher: AIP Publishing
Date: 04-12-2006
DOI: 10.1063/1.2398915
Abstract: The carrier dynamics of photoexcited electrons in the vicinity of the surface of (NH4)2S-passivated GaAs were studied via terahertz emission spectroscopy and optical-pump terahertz-probe spectroscopy. Terahertz emission spectroscopy measurements, coupled with Monte Carlo simulations of terahertz emission, revealed that the surface electric field of GaAs reverses after passivation. The conductivity of photoexcited electrons was determined via optical-pump terahertz-probe spectroscopy and was found to double after passivation. These experiments demonstrate that passivation significantly reduces the surface state density and surface recombination velocity of GaAs. Finally, it was demonstrated that passivation leads to an enhancement in the power radiated by photoconductive switch terahertz emitters, thereby showing the important influence of surface chemistry on the performance of ultrafast terahertz photonic devices.
Effect of matrix material on the morphology and optical properties of InP-based InAsSb nanostructures
Publisher: AIP Publishing
Date: 05-10-2009
DOI: 10.1063/1.3246165
Abstract: This paper presents a study on the effect of matrix material on the morphology and optical properties of self-assembled InP-based InAsSb nanostructures. Due to the differences in surface roughness of the growth front, In0.53Ga0.47As matrix layer induces the formation of short quantum dashes (QDashes) and elongated quantum dots, while InP and In0.52Al0.48As matrix layers promote the formation of long QDashes and quantum wires, respectively. The shape anisotropy of InAsSb nanostructures on In0.53Ga0.47As, InP, and In0.52Al0.48As layers is further investigated with polarized photoluminescence measurements. The InAsSb nanostructures show a luminescence polarization degree of 8.5%, 14.3%, and 29% for In0.53Ga0.47As, InP, and In0.52Al0.48As matrixes, which corresponds well with the shape anisotropy observed with atomic force microscope. Furthermore, InAsSb/In0.53Ga0.47As nanostructures also show the longest, thermally stable emission wavelength, which serves as a promising material system for fabricating midinfrared emitters.
Twin-Free Uniform Epitaxial GaAs Nanowires Grown by a Two-Temperature Process
Publisher: American Chemical Society (ACS)
Date: 03-03-2007
DOI: 10.1021/NL062755V
Abstract: We demonstrate vertically aligned epitaxial GaAs nanowires of excellent crystallographic quality and optimal shape, grown by Au nanoparticle-catalyzed metalorganic chemical vapor deposition. This is achieved by a two-temperature growth procedure, consisting of a brief initial high-temperature growth step followed by prolonged growth at a lower temperature. The initial high-temperature step is essential for obtaining straight, vertically aligned epitaxial nanowires on the (111)B GaAs substrate. The lower temperature employed for subsequent growth imparts superior nanowire morphology and crystallographic quality by minimizing radial growth and eliminating twinning defects. Photoluminescence measurements confirm the excellent optical quality of these two-temperature grown nanowires. Two mechanisms are proposed to explain the success of this two-temperature growth process, one involving Au nanoparticle-GaAs interface conditions and the other involving melting-solidification temperature hysteresis of the Au-Ga nanoparticle alloy.
Impurity free vacancy disordering of InGaAs quantum dots
Publisher: AIP Publishing
Date: 02-12-2004
DOI: 10.1063/1.1803948
Abstract: The effect of thermal interdiffusion on In(Ga)As∕GaAs quantum dot structures is very significant, due to the large strain and high concentration of indium within the dots. The traditional high temperature annealing conditions used in impurity free vacancy disordering of quantum wells cannot be used for quantum dots, as the dots can be destroyed at these temperatures. However, additional shifts due to capping layers can be achieved at low annealing temperatures. Spin-on-glass, plasma enhanced chemical vapor deposited SiO2, Si3N4, and electron-beam evaporated TiO2 layers are used to both enhance and suppress the interdiffusion in single and stacked quantum dot structures. After annealing at only 750°C the different cappings enable a shift in band gap energy of 100meV to be obtained across the s le.
Proton implantation-induced intermixing effects on AlGaAs/GaAs single QW structures
Publisher: Elsevier BV
Date: 12-2000
An ion-implanted InP receiver for polarization resolved terahertz spectroscopy
Publisher: The Optical Society
Date: 2007
DOI: 10.1364/OE.15.007047
Abstract: We report on the construction, optical alignment and performance of a receiver which is capable of recording the full polarization state of coherent terahertz radiation. The photoconductive detector was fabricated on InP which had been implanted with Fe(+) ions. The device operated successfully when it was gated with near infrared femtosecond pulses from either a Ti:sapphire laser oscillator or a 1 kHz regenerative laser lifier. When illuminated with terahertz radiation from a typical photoconductive source, the optimized device had a signal to noise figure of 100:1 with a usable spectral bandwidth of up to 4 THz. The device was shown to be very sensitive to terahertz polarization, being able to resolve changes in polarization of 0.34 degrees. Additionally, we have demonstrated the usefulness of this device for (i) polarization sensitive terahertz spectroscopy, by measuring the birefringence of quartz and (ii) terahertz emission experiments, by measuring the polarization dependence of radiation generated by optical rectification in (110)-ZnTe.
Investigation of deep levels in rapid thermally annealed SiO2-capped n-GaAs grown by metal-organic chemical vapor deposition
Publisher: AIP Publishing
Date: 31-07-2000
DOI: 10.1063/1.127089
Spontaneous formation of core-shell GaAsP nanowires and their enhanced electrical conductivity
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4TC02305F
Abstract: Spontaneous formation of core–shell GaAsP nanowires with P-enriched cores and As-enriched shells, demonstrating enhanced electrical conductivity.
Carrier Lifetime and Mobility Enhancement in Nearly Defect-Free Core−Shell Nanowires Measured Using Time-Resolved Terahertz Spectroscopy
Publisher: American Chemical Society (ACS)
Date: 28-07-2009
DOI: 10.1021/NL9016336
Abstract: We have used transient terahertz photoconductivity measurements to assess the efficacy of two-temperature growth and core-shell encapsulation techniques on the electronic properties of GaAs nanowires. We demonstrate that two-temperature growth of the GaAs core leads to an almost doubling in charge-carrier mobility and a tripling of carrier lifetime. In addition, overcoating the GaAs core with a larger-bandgap material is shown to reduce the density of surface traps by 82%, thereby enhancing the charge conductivity.
Strategies for the prevention of perinatal hepatitis B transmission in a marginalized population on the Thailand-Myanmar border: a cost-effectiveness analysis
Publisher: Springer Science and Business Media LLC
Date: 09-08-2017
Nearly intrinsic exciton lifetimes in single twin-free GaAs∕AlGaAs core-shell nanowire heterostructures
Publisher: AIP Publishing
Date: 04-08-2008
DOI: 10.1063/1.2967877
Abstract: CW and time-resolved photoluminescence measurements are used to investigate exciton recombination dynamics in GaAs∕AlGaAs heterostructure nanowires grown with a recently developed technique which minimizes twinning. A thin capping layer is deposited to eliminate the possibility of oxidation of the AlGaAs shell as a source of oxygen defects in the GaAs core. We observe exciton lifetimes of ∼1ns, comparable to high quality two-dimensional double heterostructures. These GaAs nanowires allow one to observe state filling and many-body effects resulting from the increased carrier densities accessible with pulsed laser excitation.
Temperature effect on device characteristics of InGaAs/GaAs quantum dot solar cell
Publisher: IEEE
Date: 11-2010
Facet-dependent growth of InAsP quantum wells in InP nanowire and nanomembrane arrays
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0NH00410C
Abstract: Selective area epitaxy is a powerful growth technique to produce III–V semiconductor nanoshape arrays and heterostructures for photonic and electronic applications.
Ion damage buildup and amorphization processes in AlxGa1−xAs
Publisher: AIP Publishing
Date: 1995
DOI: 10.1063/1.359358
Abstract: The nature of keV ion damage buildup and amorphization in AlxGa1−xAs at liquid-nitrogen temperature is investigated for various Al compositions using Rutherford backscattering channeling, transmission electron microscopy, and in situ time-resolved-reflectivity techniques. Two distinct damage buildup processes are observed in AlxGa1−xAs depending on Al content. At low Al content, the behavior is similar to GaAs whereby collisional disorder is ‘‘frozen in’’ and amorphization proceeds with increasing dose via the overlap of damage cascades and small amorphous zones created by in idual ion tracks. However, some dynamic annealing occurs during implantation in AlGaAs and this effect is accentuated with increasing Al content. For high Al content, crystallinity is retained at moderate ion damage with disorder building up in the form of stacking faults, planar, and other extended defects. In the latter case, amorphization is nucleation limited and proceeds abruptly when the level of crystalline disorder exceeds a critical level. The amorphization threshold dose increases with increasing Al composition by over two orders of magnitude from GaAs to AlAs. Dynamic annealing and damage creation processes during implantation compete very strongly in AlxGa1−xAs even at liquid-nitrogen temperatures. This behavior is discussed in terms of both the availability of very fast mobile defects and bonding configurational changes related to the Al sublattice in AlxGa1−xAs of high Al content.
Role of implantation-induced defects on the response time of semiconductor saturable absorbers
Publisher: AIP Publishing
Date: 06-09-1999
DOI: 10.1063/1.124718
Abstract: Arsenic ion implantation with thermal annealing was used to shorten the response times of GaAs-based saturable absorber structures. Ultrafast absorption bleaching measurements indicated that the recovery time was decreased with increasing the implantation dose. However, above a certain dose the recovery time increased again. This behavior was correlated with the microstructure of the residual implantation defects.
Mapping routine measles vaccination in low- and middle-income countries
Publisher: Springer Science and Business Media LLC
Date: 16-12-2020
DOI: 10.1038/S41586-020-03043-4
Abstract: The safe, highly effective measles vaccine has been recommended globally since 1974, yet in 2017 there were more than 17 million cases of measles and 83,400 deaths in children under 5 years old, and more than 99% of both occurred in low- and middle-income countries (LMICs) 1–4 . Globally comparable, annual, local estimates of routine first-dose measles-containing vaccine (MCV1) coverage are critical for understanding geographically precise immunity patterns, progress towards the targets of the Global Vaccine Action Plan (GVAP), and high-risk areas amid disruptions to vaccination programmes caused by coronavirus disease 2019 (COVID-19) 5–8 . Here we generated annual estimates of routine childhood MCV1 coverage at 5 × 5-km 2 pixel and second administrative levels from 2000 to 2019 in 101 LMICs, quantified geographical inequality and assessed vaccination status by geographical remoteness. After widespread MCV1 gains from 2000 to 2010, coverage regressed in more than half of the districts between 2010 and 2019, leaving many LMICs far from the GVAP goal of 80% coverage in all districts by 2019. MCV1 coverage was lower in rural than in urban locations, although a larger proportion of unvaccinated children overall lived in urban locations strategies to provide essential vaccination services should address both geographical contexts. These results provide a tool for decision-makers to strengthen routine MCV1 immunization programmes and provide equitable disease protection for all children.
An order of magnitude increase in the quantum efficiency of (Al)GaAs nanowires using hybrid photonic-plasmonic modes
Publisher: American Chemical Society (ACS)
Date: 29-12-2015
DOI: 10.1021/NL503593W
Abstract: We demonstrate 900% relative enhancement in the quantum efficiency (QE) of surface passivated GaAs nanowires by coupling them to resonant nanocavities that support hybrid photonic-plasmonic modes. This nonconventional approach to increase the QE of GaAs nanowires results in QE enhancement over the entire nanowire volume and is not limited to the near-field of the plasmonic structure. Our cavity design enables spatially and spectrally tunable resonant modes and efficient in- and out-coupling of light from the nanowires. Furthermore, this approach is not fabrication intensive it is scalable and can be adapted to enhance the QE of a wide range of low QE semiconductor nanostructures.
Coupling Analysis of GaAs-Based Microdisk Lasers With Different External Claddings
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 11-2009
Nanostructured photovoltaics PREFACE
Publisher: IOP Publishing
Date: 17-12-2013
DOI: 10.1088/0022-3727/46/2/020301
Abstract: Energy and the environment are two of the most important global issues that we currently face. The development of clean and sustainable energy resources is essential to reduce greenhouse gas emission and meet our ever-increasing demand for energy. Over the last decade photovoltaics, as one of the leading technologies to meet these challenges, has seen a continuous increase in research, development and investment. Meanwhile, nanotechnology, which is considered to be the technology of the future, is gradually revolutionizing our everyday life through adaptation and incorporation into many traditional technologies, particularly energy-related technologies, such as photovoltaics. While the record for the highest efficiency is firmly held by multijunction III–V solar cells, there has never been a shortage of new research effort put into improving the efficiencies of all types of solar cells and making them more cost effective. In particular, there have been extensive and exciting developments in employing nanostructures features with different low dimensionalities, such as quantum wells, nanowires, nanotubes, nanoparticles and quantum dots, have been incorporated into existing photovoltaic technologies to enhance their performance and/or reduce their cost. Investigations into light trapping using plasmonic nanostructures to effectively increase light absorption in various solar cells are also being rigorously pursued. In addition, nanotechnology provides researchers with great opportunities to explore the new ideas and physics offered by nanostructures to implement advanced solar cell concepts such as hot carrier, multi-exciton and intermediate band solar cells. This special issue of Journal of Physics D: Applied Physics contains selected papers on nanostructured photovoltaics written by researchers in their respective fields of expertise. These papers capture the current excitement, as well as addressing some open questions in the field, covering topics including the III–V quantum well superlattice and quantum dot solar cells, Si quantum dot tandem cells, nanostructure-enhanced dye-sensitized solar cells and nanopatterned organic solar cells. We thank all the authors and reviewers for their contribution to this special issue. Special thanks are due to the journal's Publisher, Dr Olivia Roche and the editorial and publishing staff for their help and support.
Low-Dimensional Nanostructures for Optoelectronic Applications
Publisher: Hindawi Limited
Date: 2014
DOI: 10.1155/2014/734614
Zn3As2 Nanowires and Nanoplatelets: Highly Efficient Infrared Emission and Photodetection by an Earth Abundant Material
Publisher: American Chemical Society (ACS)
Date: 03-12-2014
DOI: 10.1021/NL5036918
Abstract: The development of earth abundant materials for optoelectronics and photovoltaics promises improvements in sustainability and scalability. Recent studies have further demonstrated enhanced material efficiency through the superior light management of novel nanoscale geometries such as the nanowire. Here we show that an industry standard epitaxy technique can be used to fabricate high quality II-V nanowires (1D) and nanoplatelets (2D) of the earth abundant semiconductor Zn3As2. We go on to establish the optoelectronic potential of this material by demonstrating efficient photoemission and detection at 1.0 eV, an energy which is significant to the fields of both photovoltaics and optical telecommunications. Through dynamical spectroscopy this superior performance is found to arise from a low rate of surface recombination combined with a high rate of radiative recombination. These results introduce nanostructured Zn3As2 as a high quality optoelectronic material ready for device exploration.
Thermal quenching of photoluminescence in ZnO/ZnMgO multiple quantum wells following oxygen implantation and rapid thermal annealing
Publisher: Elsevier BV
Date: 02-2009
Improved carrier collection in intermixed InGaAs/GaAs quantum wells
Publisher: AIP Publishing
Date: 07-12-1998
DOI: 10.1063/1.122780
Abstract: We have used photoluminescence up conversion to study the carrier capture times into intermixed InGaAs/GaAs quantum wells. We have found that the capture into the intermixed wells is markedly faster than capture into the reference (unintermixed) quantum wells. The reasons for the significant reduction in the capture time is related to the shape of the intermixed quantum well. Such a reduction in the capture time is beneficial both in terms of the quantum efficiency and the frequency response of intermixed optoelectronic devices.
Structural characteristics of GaSb∕GaAs nanowire heterostructures grown by metal-organic chemical vapor deposition
Publisher: AIP Publishing
Date: 04-12-2006
DOI: 10.1063/1.2402234
Abstract: Highly lattice mismatched (7.8%) GaAs∕GaSb nanowire heterostructures were grown by metal-organic chemical vapor deposition and their detailed structural characteristics were determined by electron microscopy. The facts that (i) no defects have been found in GaSb and its interfaces with GaAs and (ii) the lattice mismatch between GaSb∕GaAs was fully relaxed suggest that the growth of GaSb nanowires is purely governed by the thermodynamics. The authors believe that the low growth rate of GaSb nanowires leads to the equilibrium growth.
Low loss, thin p-clad 980-nm InGaAs semiconductor laser diodes with an asymmetric structure design
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2003
Effect of ion-implantation enhanced intermixing on luminescence of InAs/InP quantum dots
Publisher: IOP Publishing
Date: 10-2008
Observation of blue shifts in ZnO/ZnMgO multiple quantum well structures by ion-implantation induced intermixing
Publisher: IOP Publishing
Date: 20-01-2006
Multiple wavelength InGaAs quantum dot lasers using ion implantation induced intermixing
Publisher: Springer Science and Business Media LLC
Date: 25-09-2007
Characterization of deep levels and carrier compensation created by proton irradiation in undoped GaAs
Publisher: AIP Publishing
Date: 08-1995
DOI: 10.1063/1.360237
Abstract: Deep levels and carrier compensation created in undoped metal-organic chemical-vapor deposition grown GaAs by low fluence proton irradiation (1×108−1×1010 cm−2) are investigated by the deep level transient spectroscopy technique and capacitance-voltage profiling. At least five main electron traps are observed after room-temperature irradiation in addition to the EL2 present in the as-grown material. Irradiation generates additional EL2, which annihilate at much lower temperatures than one would expect for isolated EL2. However, with further increase in irradiation fluence, the magnitude for this additional increment begin to decrease. The apparent decrease in the EL2 peak is accompanied by an increase of a broad peak in the deep level transient spectroscopic spectrum. This broad peak has a highly nonexponential capacitance transient and it is suggested to result from the interaction of the additional EL2 with EL6. One of the observed traps, with energy level, (Ec−0.40) eV, has not previously been reported in proton irradiated GaAs. The signature of this trap resembles that of EL5 and is quite stable at moderate annealing temperatures annihilating completely only at a temperature of ∼600 °C. This level shows a saturation effect with increasing irradiation dose and we believe it is related to complex defect-impurity formation. The temperature dependence of the carrier profiles reveals some complex behavior of carrier compensation, including acceptor- and donor-like properties of the various traps.
Growth temperature and V/III ratio effects on the morphology and crystal structure of InP nanowires
Publisher: IOP Publishing
Date: 15-10-2010
DOI: 10.1088/0022-3727/43/44/445402
Abstract: The effects of growth temperature and V/III ratio on the morphology and crystallographic phases of InP nanowires that are grown by metal organic chemical vapour deposition have been studied. We show that higher growth temperatures or higher V/III ratios promote the formation of wurtzite nanowires while zinc-blende nanowires are favourable at lower growth temperatures and lower V/III ratios. A schematic map of distribution of zinc-blende and wurtzite structures has been developed in the range of growth temperatures (400–510 °C) and V/III ratios (44 to 700) investigated in this study.
Electrical and structural analysis of high-dose Si implantation in GaN
Publisher: AIP Publishing
Date: 19-05-1997
DOI: 10.1063/1.119254
Abstract: For the development of ion implantation processes for GaN to advanced devices, it is important to understand the dose dependence of impurity activation along with implantation-induced damage generation and removal. We find that Si implantation in GaN can achieve 50% activation at a dose of 1×1016 cm−2, despite significant residual damage after the 1100 °C activation anneal. The possibility that the generated free carriers are due to implantation damage alone and not Si-donor activation is ruled out by comparing the Si results to those for implantation of the neutral species Ar. Ion channeling and cross-sectional transmission electron microscopy are used to characterize the implantation-induced damage both as implanted and after a 1100 °C anneal. Both techniques confirm that significant damage remains after the anneal, which suggests that activation of implanted Si donors in GaN doses not require complete damage removal. However, an improved annealing process may be needed to further optimize the transport properties of implanted regions in GaN.
Illuminating the Second Conduction Band and Spin–Orbit Energy in Single Wurtzite InP Nanowires
Publisher: American Chemical Society (ACS)
Date: 23-10-2013
DOI: 10.1021/NL4028878
Abstract: We use polarized photoluminescence excitation spectroscopy to observe the energy and symmetry of the predicted second conduction band in 130 nm diameter wurtzite InP nanowires. We find direct spectroscopic signatures for optical transitions among the A, B, and C hole bands and both the first and the second conduction bands. We determine that the splitting between the first and second conduction bands is 228 ± 7 meV in excellent agreement with theory. From these energies we show that the spin-orbit energy changes substantially between zinc blende and wurtzite InP. We discuss the two quite different solutions within the quasi-cubic approximation and the implications for these measurements. Finally, the observation of well-defined optical transitions between the B- and C-hole bands and the second conduction band suggests that either the theoretical description of the second conduction band as possessing Γ8 symmetry is incomplete, or other interactions are enabling these forbidden transitions.
Second-order surface-plasmon assisted responsivity enhancement in germanium nano-photodetectors with bull's eye antennas
Publisher: The Optical Society
Date: 20-06-2014
DOI: 10.1364/OE.22.015949
An antiresonant Fabry-Perot saturable absorber for passive mode-locking fabricated by metal-organic vapor phase epitaxy and ion implantation design, characterization, and mode-locking
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 1998
DOI: 10.1109/3.726608
Novel growth and properties of GaAs nanowires on Si substrates
Publisher: IOP Publishing
Date: 07-12-2009
DOI: 10.1088/0957-4484/21/3/035604
Abstract: Straight, vertically aligned GaAs nanowires were grown on Si(111) substrates coated with thin GaAs buffer layers. We find that the V/III precursor ratio and growth temperature are crucial factors influencing the morphology and quality of buffer layers. A double layer structure, consisting of a thin initial layer grown at low V/III ratio and low temperature followed by a layer grown at high V/III ratio and high temperature, is crucial for achieving straight, vertically aligned GaAs nanowires on Si(111) substrates. An in situ annealing step at high temperature after buffer layer growth improves the surface and structural properties of the buffer layer, which further improves the morphology of the GaAs nanowire growth. Through such optimizations we show that vertically aligned GaAs nanowires can be fabricated on Si(111) substrates and achieve the same structural and optical properties as GaAs nanowires grown directly on GaAs(111)B substrates.
Evidence of blocking effect on carrier trapping process by necking region in very narrow AlGaAs/GaAs V-grooved quantum wire structure
Publisher: AIP Publishing
Date: 15-11-2001
DOI: 10.1063/1.1410317
Abstract: Transient band-gap renormalization (BGR) effects are investigated in AlGaAs/GaAs V-grooved quantum structures. The temperature-dependent transient BGR effects in the sidewall quantum well (SQWL) provide direct evidence of the existence of the blocking effect by the necking region barrier on the carrier trapping process. These effects provide a useful method to show the existence of the necking region, particularly for very thin SQWL structures. The temperature-dependent lifetimes of the SQWL and quantum wire (QWR) provide further proof of the carrier trapping process from the SQWL to the QWR.
International estimated fetal weight standards of the INTERGROWTH-21stProject
Publisher: Wiley
Date: 05-03-2017
DOI: 10.1002/UOG.17347
Full tip imaging in atom probe tomography
Publisher: Elsevier BV
Date: 2013
DOI: 10.1016/J.ULTRAMIC.2012.08.014
Abstract: Atom probe tomography (APT) is capable of simultaneously revealing the chemical identities and three dimensional positions of in idual atoms within a needle-shaped specimen, but suffers from a limited field-of-view (FOV), i.e., only the core of the specimen is effectively detected. Therefore, the capacity to analyze the full tip is crucial and much desired in cases that the shell of the specimen is also the region of interest. In this paper, we demonstrate that, in the analysis of III-V nanowires epitaxially grown from a substrate, the presence of the flat substrate positioned only micrometers away from the analyzed tip apex alters the field distribution and ion trajectories, which provides extra image compression that allows for the analysis of the entire specimen. An array of experimental results, including field desorption maps, elemental distributions, and crystallographic features clearly demonstrate the fact that the whole tip has been imaged, which is confirmed by electrostatic simulations.
Tuning the detection wavelength of quantum-well infrared photodetectors by single high-energy implantation
Publisher: AIP Publishing
Date: 2001
DOI: 10.1063/1.1332984
Abstract: Single high-energy (0.9 MeV) proton implantation and rapid thermal annealing was used to tune the spectral response of the quantum-well infrared photodetectors (QWIPs). In addition to the large redshift of the QWIPs’ response wavelength after implantation, either narrowed or broadened spectrum was obtained at different interdiffusion extent. In general, the overall device performance for the low-dose implantation was not significantly degraded. In comparison with the other implantation schemes, this single high-energy implantation is the most effective and simple technique in tuning the wavelength of QWIPs, thus, to achieve the fabrication of multicolor detectors.
CdS/CdSe lateral heterostructure nanobelts by a two-step physical vapor transport method
Publisher: IOP Publishing
Date: 10-03-2010
DOI: 10.1088/0957-4484/21/14/145602
Abstract: The two-dimensional heterostructure nanobelts with a central CdSe region and lateral CdS structures are synthesized by a two-step physical vapor transport method. The large growth rate difference between lateral CdS structures on both +/- (0001) sides of the CdSe region is found. The growth anisotropy is discussed in terms of the polar nature of the side +/- (0001) surfaces of CdSe. High-resolution transmission electron microscopy reveals the CdSe central region covered with non-uniform CdS layer/islands. From micro-photoluminescence measurements, a systematic blueshift of emission energy from the central CdSe region in accordance with the increase of lateral CdS growth temperature is observed. This result indicates that the intermixing rate in the CdSe region with CdS increases with the increase of lateral CdS growth temperature. In conventional CdSSe ternary nanostructures, morphology and emission wavelength were correlated parameters. However, the morphology and emission wavelength are independently controllable in the CdS/CdSe lateral heterostructure nanobelts. This structure is attractive for applications in visible optoelectronic devices.
Preferential nucleation and growth of InAs/GaAs(0 0 1) quantum dots on defected sites by droplet epitaxy
Publisher: Elsevier BV
Date: 10-2013
Study of intermixing in InGaAs∕(Al)GaAs quantum well and quantum dot structures for optoelectronic∕photonic integration
Publisher: Institution of Engineering and Technology (IET)
Date: 2005
Characterization of Semiconductor Nanowires Using Optical Tweezers
Publisher: American Chemical Society (ACS)
Date: 02-05-2011
DOI: 10.1021/NL200720M
Abstract: We report on the optical trapping characteristics of InP nanowires with dimensions of 30 (±6) nm in diameter and 2-15 μm in length. We describe a method for calibrating the absolute position of in idual nanowires relative to the trapping center using synchronous high-speed position sensing and acousto-optic beam switching. Through brownian dynamics we investigate effects of the laser power and polarization on trap stability, as well as length dependence and the effect of simultaneous trapping multiple nanowires.
Antimony Induced {112}A Faceted Triangular GaAs1−xSbx/InP Core/Shell Nanowires and Their Enhanced Optical Quality
Publisher: Wiley
Date: 27-07-2015
Nanowires Grown on InP (100): Growth Directions, Facets, Crystal Structures, and Relative Yield Control
Publisher: American Chemical Society (ACS)
Date: 05-06-2014
DOI: 10.1021/NN5017428
Abstract: Growth of III-V nanowires on the [100]-oriented industry standard substrates is critical for future integrated nanowire device development. Here we present an in-depth analysis of the seemingly complex ensembles of epitaxial nanowires grown on InP (100) substrates. The nanowires are categorized into three types as vertical, nonvertical, and planar, and the growth directions, facets, and crystal structure of each type are investigated. The nonvertical growth directions are mathematically modeled using a three-dimensional multiple-order twinning concept. The nonvertical nanowires can be further classified into two different types, with one type growing in the ⟨111⟩ directions and the other in the ⟨100⟩ directions after initial multiple three-dimensional twinning. We find that 99% of the total nanowires are grown either along ⟨100⟩, ⟨111⟩, or ⟨110⟩ growth directions by {100} or {111} growth facets. We also demonstrate relative control of yield of these different types of nanowires, by tuning pregrowth annealing conditions and growth parameters. Together, the knowledge and controllability of the types of nanowires provide an ideal foundation to explore novel geometries that combine different crystal structures, with potential for both fundamental science research and device applications.
Optical measurement of the distribution of damage in ion-implanted GaAs
Publisher: IOP Publishing
Date: 08-1994
The natural course of a localized BCG vaccine abscess
Publisher: Elsevier BV
Date: 05-2019
Room-temperature optically detected magnetic resonance of single defects in hexagonal boron nitride
Publisher: Springer Science and Business Media LLC
Date: 02-2022
DOI: 10.1038/S41467-022-28169-Z
Abstract: Optically addressable solid-state spins are important platforms for quantum technologies, such as repeaters and sensors. Spins in two-dimensional materials offer an advantage, as the reduced dimensionality enables feasible on-chip integration into devices. Here, we report room-temperature optically detected magnetic resonance (ODMR) from single carbon-related defects in hexagonal boron nitride with up to 100 times stronger contrast than the ensemble average. We identify two distinct bunching timescales in the second-order intensity-correlation measurements for ODMR-active defects, but only one for those without an ODMR response. We also observe either positive or negative ODMR signal for each defect. Based on kinematic models, we relate this bipolarity to highly tuneable internal optical rates. Finally, we resolve an ODMR fine structure in the form of an angle-dependent doublet resonance, indicative of weak but finite zero-field splitting. Our results offer a promising route towards realising a room-temperature spin-photon quantum interface in hexagonal boron nitride.
Vertically standing Ge nanowires on GaAs(110) substrates
Publisher: IOP Publishing
Date: 21-02-2008
DOI: 10.1088/0957-4484/19/12/125602
Abstract: The growth of epitaxial Ge nanowires is investigated on (100), (111) B and (110) GaAs substrates in the growth temperature range from 300 to 380 °C. Unlike epitaxial Ge nanowires on Ge or Si substrates, Ge nanowires on GaAs substrates grow predominantly along the [Formula: see text] direction. Using this unique property, vertical [Formula: see text] Ge nanowires epitaxially grown on GaAs(110) surface are realized. In addition, these Ge nanowires exhibit minimal tapering and uniform diameters, regardless of growth temperatures, which is an advantageous property for device applications. Ge nanowires growing along the [Formula: see text] directions are particularly attractive candidates for forming nanobridge devices on conventional (100) surfaces.
Nanowires for optoelectronic device applications
Publisher: Wiley
Date: 12-2009
The role of intersubband optical transitions on the electrical properties of InGaAs/GaAs quantum dot solar cells
Publisher: Wiley
Date: 14-03-2013
DOI: 10.1002/PIP.2161
Polarity driven simultaneous growth of free-standing and lateral GaAsP epitaxial nanowires on GaAs (001) substrate
Publisher: AIP Publishing
Date: 25-11-2013
DOI: 10.1063/1.4834377
Abstract: Simultaneous growth of ⟨111⟩B free-standing and ±[110] lateral GaAsP epitaxial nanowires on GaAs (001) substrates were observed and investigated by electron microscopy and crystallographic analysis. It was found that the growth of both free-standing and lateral ternary nanowires via Au catalysts was driven by the fact that Au catalysts prefer to maintain low-energy {111}B interfaces with surrounding GaAs(P) materials: in the case of free-standing nanowires, Au catalysts maintain {111}B interfaces with their underlying GaAsP nanowires while in the case of lateral nanowires, each Au catalyst remain their side {111}B interfaces with the surrounding GaAs(P) material during the lateral nanowire growth.
Analysis of semiconductors by ion channelling: Applications and pitfalls
Publisher: Elsevier BV
Date: 03-1998
A comparison of impurity-free and ion-implantation-induced intermixing of InGaAs/InP quantum wells
Publisher: AIP Publishing
Date: 11-2000
DOI: 10.1063/1.1314904
Abstract: We have compared the time integrated photoluminescence (PL) and the time resolved PL of several lattice matched InGaAs/InP quantum wells intermixed either by ion implantation or an impurity-free method. We have found that the carrier capture rates into quantum wells and carrier relaxation from the wells depend on the type of intermixing used. Our results indicate that the carrier lifetimes are significantly longer in s les intermixed by the impurity-free methods, while the carrier collection efficiency of the quantum wells is more efficient in s les intermixed by ion implantation.
Dynamics of Strongly Degenerate Electron−Hole Plasmas and Excitons in Single InP Nanowires
Publisher: American Chemical Society (ACS)
Date: 29-09-2007
DOI: 10.1021/NL071733L
Abstract: Low-temperature time-resolved photoluminescence spectroscopy is used to probe the dynamics of photoexcited carriers in single InP nanowires. At early times after pulsed excitation, the photoluminescence line shape displays a characteristic broadening, consistent with emission from a degenerate, high-density electron-hole plasma. As the electron-hole plasma cools and the carrier density decreases, the emission rapidly converges toward a relatively narrow band consistent with free exciton emission from the InP nanowire. The free excitons in these single InP nanowires exhibit recombination lifetimes closely approaching that measured in a high-quality epilayer, suggesting that in these InP nanowires, electrons and holes are relatively insensitive to surface states. This results in higher quantum efficiencies than other single-nanowire systems as well as significant state-filling and band gap renormalization, which is observed at high electron-hole carrier densities.
Research ethics in context: understanding the vulnerabilities, agency and resourcefulness of research participants living along the Thai–Myanmar border
Publisher: Oxford University Press (OUP)
Date: 11-2020
DOI: 10.1093/INTHEALTH/IHAA052
Abstract: Research ethics guidelines set a high bar for conducting research with vulnerable populations, often resulting in their exclusion from beneficial research. Our study aims to better characterise participants’ vulnerabilities, agency, resourcefulness and sources of support. We undertook qualitative research around two clinical studies involving migrant women living along the Thai–Myanmar border. We conducted 32 in-depth interviews and 10 focus group discussions with research participants, families, researchers and key informants. We found that being ‘undocumented’ is at the core of many structural vulnerabilities, reflecting political, economic, social and health needs. Although migrant women lead challenging lives, they have a support network that includes family, employers, community leaders, non-governmental organisations and research networks. Migrant women choose to participate in research to access quality healthcare, gain knowledge and obtain extra money. However, research has the potential to exacerbate existing vulnerabilities, such as the burdens of cross-border travel, foregoing work and being more visible as migrants. Our study confirms that research is important to provide evidence-based care and was viewed by participants as offering many benefits, but it also has hidden burdens. Migrant women exercised agency and resourcefulness when navigating challenges in their lives and research participation.
Investigations of impurity-free vacancy disordering in (Al)InGaAs(P)/InGaAs quantum wells
Publisher: IOP Publishing
Date: 20-04-2010
Far‐Field Polarization Engineering from Nonlinear Nanoresonators
Publisher: Wiley
Date: 10-10-2022
Abstract: Nanoresonators fabricated from low‐loss dielectrics with second‐order nonlinearity have emerged as a widespread platform for nonlinear frequency conversion at the nanoscale. However, a persisting challenge in this research is the generated complex far‐field polarization state of the upconverted light, which is a limiting factor in many applications. It will be highly desirable to generate uniform far‐field polarization states across all propagation directions, to control the polarization truly along the optical axis and to simultaneously be able to tune the polarization along the entire circumference of the Poincaré sphere by solely modifying the excitation polarization. Here, a nonlinear nanoresonator combining all these properties is theoretically proposed and experimentally demonstrated. At first, an analytical model connecting the induced multipolar content of a nanoresonator with a desired far‐field polarization is derived. Based on this, a nonlinear dielectric nanoresonator is designed to enable sum‐frequency generation (SFG) with highly pure and tuneable far‐field polarization states. In the experiment, the nanoresonators fabricated from the III‐V semiconductor gallium arsenide in (110)‐orientation are excited in an SFG scheme with in idually controllable excitation beams. The generation of highly uniform and tuneable far‐field polarization states is demonstrated by combining back‐focal plane measurements with Stokes polarimetry.
Electronic and isochronal annealing properties of electron traps in rapid thermally annealed SiO2-capped n-type GaAs epitaxial layers
Publisher: AIP Publishing
Date: 11-2000
DOI: 10.1063/1.1314907
Abstract: We have recently shown [P. N. K. Deenapanray et al., Appl. Phys. Lett. 77, 626 (2000)] that four electron traps S1(Ec−0.23 eV), S2(Ec−0.46 eV), S3(Ec−0.72 eV), and S4(Ec−0.74 eV) are introduced in rapid thermally-annealed (RTA) SiO2-capped n-type GaAs epitaxial layers. In the present study, we have used deep level transient spectroscopy to investigate the electronic and annealing properties of these deep levels. The electron emission kinetics of S1 is enhanced by an electric field, and the activation energy of S1 decreases linearly from ∼233 to ∼199 meV when the field is increased from 7.5×104 to 13.4×104 V cm−1. The intensities of S1, S2, and S4 show Arrhenius-like dependencies on the RTA temperature, which relate to the outdiffusion of Ga atoms into the SiO2 layer. The intensity of S2(VGa–SiGa) also increases exponentially with the square of the annealing time for RTA at 800 °C. Isochronal annealing experiments show that S1 and S2 are thermally stable below 500 and 400 °C, respectively. S4, which is a member of the EL2 family, is stable up to 600 °C. Secondary defects are introduced during isochronal annealing above 400 °C, and some of these defects are thermally stable at 600 °C.
Video-based feedback as a method for training rural healthcare workers to manage medical emergencies: A pilot study
Publisher: No publisher found
Date: 2017
Spin-Resolved Purcell Effect in a Quantum Dot Microcavity System
Publisher: American Chemical Society (ACS)
Date: 18-06-2012
DOI: 10.1021/NL3008083
Abstract: We demonstrate the spin selective coupling of the exciton state with cavity mode in a single quantum dot (QD)-micropillar cavity system. By tuning an external magnetic field, each spin polarized exciton state can be selectively coupled with the cavity mode due to the Zeeman effect. A significant enhancement of spontaneous emission rate of each spin state is achieved, giving rise to a tunable circular polarization degree from -90% to 93%. A four-level rate equation model is developed, and it agrees well with our experimental data. In addition, the coupling between photon mode and each exciton spin state is also achieved by varying temperature, demonstrating the full manipulation over the spin states in the QD-cavity system. Our results pave the way for the realization of future quantum light sources and the quantum information processing applications.
Preparation of V2O5 dot-decorated WO3 nanorod arrays for high performance multi-color electrochromic devices
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8TC04247K
Abstract: Inorganic electrochromic nanostructures based on WO 3 nanorod/V 2 O 5 dot arrays exhibiting multi-color and superior stability are obtained.
Tailoring GaAs, InAs, and InGaAs Nanowires for Optoelectronic Device Applications
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2011
Picosecond Time-Resolved Bleaching Dynamics of Self-Assembled Quantum Dots
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 09-2004
A transmission electron microscopy study of defects formed through the capping layer of self-assembled InAs/GaAs quantum dot samples
Publisher: AIP Publishing
Date: 06-2006
DOI: 10.1063/1.2197038
Abstract: Plan-view and cross-sectional transmission electron microscopy have been used for a detailed study of the defects formed in capped InAs∕GaAs quantum dot (QD) s les. Three main types of defects, V-shaped defects, single stacking faults, and stacking fault pyramids, were found to form under growth conditions that led to either very large, indium enriched, or coalesced islands. All three types of defects originate at the buried quantum dot layer and then travel through the GaAs cap to the surface on the {111} planes. The V-shaped defects were the most common and typically consisted of two pairs of closely spaced 60° Shockley partials with a ⟨211⟩ line direction. The two pairs originate together at the buried QD layer and then travel in “opposite” directions on different {111} planes. The second type of defect is the single stacking fault which consists of a single pair of partial dislocations separated by an ≈50nm wide stacking fault. Finally, both complete and incomplete stacking fault pyramids were observed. In the case of the complete stacking fault pyramid the bounding dislocations along the [110], [11¯0], [101¯], and [101] directions were identified as stair rods. A possible mechanism for the stacking fault pyramid formation, which can also account for the creation of incomplete stacking fault pyramids, is presented.
Suppression of thermal atomic interdiffusion in C-doped InGaAs∕AlGaAs quantum well laser structures using TiO2 dielectric layers
Publisher: AIP Publishing
Date: 06-12-2004
DOI: 10.1063/1.1833563
Abstract: The effects of thermal annealing on C-doped InGaAs∕AlGaAs quantum well laser structures capped with titanium dioxide (TiO2) layers were investigated. The atomic interdiffusion was greatly suppressed by the presence of a TiO2 capping layer during annealing, inhibiting even the thermal intermixing observed in the uncapped s le. An increase in the amount of lattice contraction associated with the presence of substitutional carbon CAs after annealing without a capping layer was observed, but not after annealing with a TiO2 capping layer. Capacitance–voltage measurements confirmed the electrical activation of carbon after annealing without a dielectric layer and show a negligible change after annealing using a TiO2 capping layer. The possible mechanisms involving both the atomic intermixing on the group III sublattice and carbon activation on the group V sublattice and the implications for optoelectronic device integration using impurity-free intermixing are discussed.
Tuning the bandgap of InAs quantum dots by selective-area MOCVD
Publisher: IOP Publishing
Date: 14-03-2008
The Role of Socioeconomic Status in the Association of Lung Function and Air Pollution—A Pooled Analysis of Three Adult ESCAPE Cohorts
Publisher: MDPI AG
Date: 29-05-2019
Abstract: Ambient air pollution is a leading environmental risk factor and its broad spectrum of adverse health effects includes a decrease in lung function. Socioeconomic status (SES) is known to be associated with both air pollution exposure and respiratory function. This study assesses the role of SES either as confounder or effect modifier of the association between ambient air pollution and lung function. Cross-sectional data from three European multicenter adult cohorts were pooled to assess factors associated with lung function, including annual means of home outdoor NO2. Pre-bronchodilator lung function was measured according to the ATS-criteria. Multiple mixed linear models with random intercepts for study areas were used. Three different factors (education, occupation and neighborhood unemployment rate) were considered to represent SES. NO2 exposure was negatively associated with lung function. Occupation and neighborhood unemployment rates were not associated with lung function. However, the inclusion of the SES-variable education improved the models and the air pollution-lung function associations got slightly stronger. NO2 associations with lung function were not substantially modified by SES-variables. In this multicenter European study we could show that SES plays a role as a confounder in the association of ambient NO2 exposure with lung function.
High temperature rapid thermal annealing of phosphorous ion implanted InAs∕InP quantum dots
Publisher: AIP Publishing
Date: 26-02-2007
DOI: 10.1063/1.2710006
Abstract: The effect of high temperature annealing of the InAs∕InP quantum dots (QDs) containing a thin GaAs interlayer is investigated. The QDs are rapid thermally annealed at 750, 800, 850, and 900°C for 30s. The QDs with the GaAs interlayer show good thermal stability up to 850°C as well as enhanced integrated photoluminescence (PL) intensity and reduced PL linewidth. The effect of high energy (450keV) phosphorous ion implantation at room temperature with doses of 5×1011–5×1013ions∕cm2 with subsequent high temperature (750–850°C) rapid thermal annealing is also studied. A large implantation-induced energy shift of up to 309meV (400nm) is observed. The implanted s les annealed at 850°C show reduced PL linewidth and enhanced integrated PL intensity compared to the implanted s les annealed at 750°C.
Anodic-oxide-induced interdiffusion in GaAs/AlGaAs quantum wells
Publisher: AIP Publishing
Date: 02-1998
DOI: 10.1063/1.366830
Abstract: Enhancement of interdiffusion in GaAs/AlGaAs quantum wells due to anodic oxides was studied. Photoluminescence, transmission electron microscopy, and quantum well modeling were used to understand the effects of intermixing on the quantum well shape. Residual water in the oxide was found to increase the intermixing, though it was not the prime cause for intermixing. Injection of defects such as group III vacancies or interstitials was considered to be a driving force for the intermixing. Different current densities used in the experimental range to create anodic oxides had little effect on the intermixing.
Proton implantation-induced intermixing of InAs∕InP quantum dots
Publisher: AIP Publishing
Date: 29-05-2006
DOI: 10.1063/1.2208371
Abstract: Proton implantation-induced intermixing of InAs quantum dots (QDs) capped with InP, GaInAsP, and InP and InGaAs layers grown by metal-organic chemical vapor deposition is investigated. The s les are annealed at 750, 800, 850, and 900°C for 30s and thermal stability of the QDs is studied. The optimum annealing temperature is around 800°C which gives maximum implantation-induced energy shift. The QDs capped with InP layers show the highest implantation-induced energy shift due to strong group V interdiffusion whereas the QDs grown on and capped with GaInAsP layers show the least implantation-induced energy shift due to weak group V and group III interdiffusion. The QDs capped with InP and InGaAs layers show intermediate implantation-induced energy shift and are less thermally stable compared to the QDs grown on and capped with GaInAsP layers. The QDs capped with InP layers show enhanced photoluminescence (PL) intensity when implanted with lower proton dose (less than 5×1014ions∕cm2). On the other hand higher proton dose (more than 1×1014ions∕cm2) reduces the PL linewidth in all s les.
<title>Impurity-free vacancy disordering of InGaAs quantum dots</title>
Publisher: SPIE
Date: 29-03-2002
DOI: 10.1117/12.460800
Suppression of interdiffusion in GaAs/AlGaAs quantum-well structure capped with dielectric films by deposition of gallium oxide
Publisher: AIP Publishing
Date: 18-09-2002
DOI: 10.1063/1.1503857
Abstract: In this work, different dielectric caps were deposited on the GaAs/AlGaAs quantum well (QW) structures followed by rapid thermal annealing to generate different degrees of interdiffusion. Deposition of a layer of GaxOy on top of these dielectric caps resulted in significant suppression of interdiffusion. In these s les, it was found that although the deposition of GaxOy and subsequent annealing caused additional injection of Ga into the SiO2 layer, Ga atoms were still able to outdiffuse from the GaAs QW structure during annealing, to generate excess Ga vacancies. The suppression of interdiffusion with the presence of Ga vacancies was explained by the thermal stress effect which suppressed Ga vacancy diffusion during annealing. It suggests that GaxOy may therefore be used as a mask material in conjunction with other dielectric capping layers in order to control and selectively achieve impurity-free vacancy disordering.
The temperature dependence of InGaAs single-wavelength quantum well and multi-wavelength quantum dot square resonator microlasers
Publisher: IOP Publishing
Date: 18-03-2010
Defect-Free <110> Zinc-Blende Structured InAs Nanowires Catalyzed by Palladium
Publisher: American Chemical Society (ACS)
Date: 05-10-2012
DOI: 10.1021/NL303028U
Abstract: We report the epitaxial growth of defect-free zinc-blende structured InAs nanowires on GaAs{111}(B) substrates using palladium catalysts in a metal-organic chemical vapor deposition reactor. Through detailed morphological, structural, and chemical characterizations using electron microscopy, it is found that these defect-free InAs nanowires grew along the directions with four low-energy {111} faceted side walls and {1[combining overline]1[combining overline]3[combining overline]} nanowire/catalyst interfaces. It is anticipated that these defect-free nanowires benefit from the fact that the nanowire/catalyst interfaces does not contain the {111} planes, and the nanowire growth direction is not along the directions. This study provides an effective approach to control the crystal structure and quality of epitaxial III-V nanowires.
Increasing the coupling efficiency of a microdisk laser to waveguides by using well designed spiral structures
Publisher: AIP Publishing
Date: 15-02-2010
DOI: 10.1063/1.3309748
Abstract: In this article, we optimize the coupling efficiency from a GaAs microdisk resonator into a single mode spiral waveguide. A classical microdisk resonator coupling light into a nonevanescent straight waveguide reaches a typical coupling efficiency of 67%. We show that the introduction of a spiral waveguide that works both as a waveguide and circular Bragg reflector can improve such efficiency to almost 90%. The same structure with the addition of a taper can couple up to 80% of the generated power into a slot waveguide.
Five insights from the Global Burden of Disease Study 2019
Publisher: Elsevier BV
Date: 10-2020
On the origin of dislocation generation and annihilation in α -Ga2O3 epilayers on sapphire
Publisher: AIP Publishing
Date: 28-10-2019
DOI: 10.1063/1.5120554
Abstract: Epitaxial film quality is critical to the success of high-performance α-Ga2O3 vertical power devices. In this work, the origins of threading dislocation generation and annihilation in thick α-Ga2O3 films heteroepitaxially grown on sapphire by the mist-CVD technique have been examined by means of high-resolution X-ray diffraction and transmission electron microscopies. By increasing the nominal thickness, screw dislocations exhibit an independent characteristic with a low density of about 1.8 × 106 cm−2, while edge dislocations propagating along the c-axis are dominant, which decrease down to 2.1 × 109 cm−2 in density for an 8 μm-thick α-Ga2O3 layer and exhibit an inverse dependence on the thickness. In the framework of the glide analytical model, parallel edge dislocations are generated at the interface due to the misfit-induced strain relaxation, while the dislocation glide and coalescence result in the annihilation and fusion behaviors. The optimal thick α-Ga2O3 with low dislocation densities may provide a prospective alternative to fully realize α-Ga2O3 power devices.
‘Because the baby asks for it’: a mixed-methods study on local perceptions toward nutrition during pregnancy among marginalised migrant women along the Myanmar–Thailand border
Publisher: Informa UK Limited
Date: 2018
Optimal Duration of Follow-up for Assessing Antimalarial Efficacy in Pregnancy: A Retrospective Analysis of a Cohort Followed Up Until Delivery on the Thailand–Myanmar Border
Publisher: Oxford University Press (OUP)
Date: 31-05-2019
DOI: 10.1093/OFID/OFZ264
Abstract: Follow-up for 28–42 days is recommended by the World Health Organization to assess antimalarial drug efficacy for nonpregnant populations. This study aimed to determine the optimal duration for pregnant women, as no specific guidance currently exists. The distributions of time to recrudescence (treatment failure), confirmed by polymerase chain reaction genotyping for different antimalarial drugs in pregnancy, were analyzed by accelerated failure time models using secondary data on microscopically confirmed recurrent falciparum malaria collected in prospective studies on the Thailand–Myanmar border between 1994 and 2010. Of 946 paired isolates from 703 women, the median duration of follow-up for each genotyped recurrence (interquartile range) was 129 (83–174) days, with 429 polymerase chain reaction–confirmed recrudescent. Five different treatments were evaluated, and 382 Plasmodium falciparum recrudescences were identified as eligible. With log-logistic models adjusted for baseline parasitemia, the predicted cumulative proportions of all the recrudescences that were detected by 28 days were 70% (95% confidence interval [CI], 65%–74%) for quinine monotherapy (n = 295), 66% (95% CI, 53%–76%) for artesunate monotherapy (n = 43), 62% (95% CI, 42%–79%) for artemether–lumefantrine (AL n = 19), 46% (95% CI, 26%–67%) for artesunate with clindamycin (n = 19), and 34% (95% CI, 11%–67%) for dihydroartemisinin–piperaquine (DP n = 6). Corresponding figures by day 42 were 89% (95% CI, 77%–95%) for AL and 71% (95% CI, 38%–91%) for DP. Follow-up for 63 days was predicted to detect ≥95% of all recrudescence, except for DP. In low-transmission settings, antimalarial drug efficacy assessments in pregnancy require longer follow-up than for nonpregnant populations.
Polarity driven formation of InAs/GaAs hierarchical nanowire heterostructures
Publisher: AIP Publishing
Date: 17-11-2008
DOI: 10.1063/1.3033551
Abstract: The structural and morphological characteristics of InAs/GaAs radial nanowire heterostructures were investigated using transmission electron microscopy. It has been found that the radial growth of InAs was preferentially initiated on the {112}A sidewalls of GaAs nanowires. This preferential deposition leads to extraordinarily asymmetric InAs/GaAs radial nanowire heterostructures. Such formation of radial nanowire heterostructures provides an opportunity to engineer hierarchical nanostructures, which further widens the potential applications of semiconductor nanostructures.
III-V nanowires for optoelectronics
Publisher: SPIE
Date: 22-09-2006
DOI: 10.1117/12.692715
Effects of annealing on the spectral response and dark current of quantum dot infrared photodetectors
Publisher: IOP Publishing
Date: 06-10-2008
Strengthening brittle semiconductor nanowires through stacking faults: Insights from in situ mechanical testing
Publisher: American Chemical Society (ACS)
Date: 03-09-2013
DOI: 10.1021/NL402180K
Abstract: Quantitative mechanical testing of single-crystal GaAs nanowires was conducted using in situ deformation transmission electron microscopy. Both zinc-blende and wurtzite structured GaAs nanowires showed essentially elastic deformation until bending failure associated with buckling occurred. These nanowires fail at compressive stresses of ~5.4 GPa and 6.2 GPa, respectively, which are close to those values calculated by molecular dynamics simulations. Interestingly, wurtzite nanowires with a high density of stacking faults fail at a very high compressive stress of ~9.0 GPa, demonstrating that the nanowires can be strengthened through defect engineering. The reasons for the observed phenomenon are discussed.
Photonic device integration using MOCVD grown quantum dots
Publisher: IEEE
Date: 12-2006
Enhanced carrier collection efficiency and reduced quantum state absorption by electron doping in self-assembled quantum dot solar cells
Publisher: AIP Publishing
Date: 02-02-2015
DOI: 10.1063/1.4907348
Abstract: Reduced quantum dot (QD) absorption due to state filling effects and enhanced electron transport in doped QDs are demonstrated to play a key role in solar energy conversion. Reduced QD state absorption with increased n-doping is observed in the self-assembled In0.5Ga0.5As/GaAs QDs from high resolution below-bandgap external quantum efficiency (EQE) measurement, which is a direct consequence of the Pauli exclusion principle. We also show that besides partial filling of the quantum states, electron-doping produces negatively charged QDs that exert a repulsive Coulomb force on the mobile electrons, thus altering the electron trajectory and reducing the probability of electron capture, leading to an improved collection efficiency of photo-generated carriers, as indicated by an absolute above-bandgap EQE measurement. The resulting redistribution of the mobile electron in the planar direction is further validated by the observed photoluminescence intensity dependence on doping.
Optical properties of erbium-implanted porous silicon microcavities
Publisher: AIP Publishing
Date: 18-10-2004
DOI: 10.1063/1.1808235
Abstract: We have used ion implantation for erbium doping of mesoporous silicon microcavities. Optically active erbium-doped microcavities with Q factors in excess of 1500 have been demonstrated. We observed strong modification of the emission properties of the erbium in the microcavity with an accompanying cavity enhancement factor of 25. In addition, power- and temperature-dependent photoluminescence measurements indicate that erbium-implanted porous silicon has excitation mechanism very similar to that of erbium in a crystalline silicon host.
Investigation of ion implantation induced intermixing in InP based quaternary quantum wells
Publisher: IOP Publishing
Date: 08-11-2011
DOI: 10.1088/0022-3727/44/47/475105
Abstract: In this work, proton and arsenic ion implantation induced intermixing in AlInGaAs/InGaAs quantum wells (QWs) has been studied and compared with InGaAsP/InGaAs QWs. The different interdiffusion results obtained from the two QW structures are compared and discussed based on thermal annealing studies, different implantation ion species, dynamic annealing effects of barrier layers, as well as interdiffusion mechanisms.
Multipulse operation of a Ti:sapphire laser mode locked by an ion-implanted semiconductor saturable-absorber mirror
Publisher: The Optical Society
Date: 06-1999
Effects of rapid thermal annealing on device characteristics of InGaAs∕GaAs quantum dot infrared photodetectors
Publisher: AIP Publishing
Date: 06-2006
DOI: 10.1063/1.2202704
Abstract: In this work, rapid thermal annealing was performed on InGaAs∕GaAs quantum dot infrared photodetectors (QDIPs) at different temperatures. The photoluminescence showed a blueshifted spectrum in comparison with the as-grown s le when the annealing temperature was higher than 700°C, as a result of thermal interdiffusion of the quantum dots (QDs). Correspondingly, the spectral response from the annealed QDIP exhibited a redshift. At the higher annealing temperature of 800°C, in addition to the largely redshifted photoresponse peak of 7.4μm (compared with the 6.1μm of the as-grown QDIP), a high energy peak at 5.6μm (220meV) was also observed, leading to a broad spectrum linewidth of 40%. This is due to the large interdiffusion effect which could greatly vary the composition of the QDs and thus increase the relative optical absorption intensity at higher energy. The other important detector characteristics such as dark current, peak responsivity, and detectivity were also measured. It was found that the overall device performance was not affected by low annealing temperature, however, for high annealing temperature, some degradation in device detectivity (but not responsivity) was observed. This is a consequence of increased dark current due to defect formation and increased ground state energy.
Direct imaging of the spatial diffusion of excitons in single semiconductor nanowires
Publisher: AIP Publishing
Date: 26-12-2011
DOI: 10.1063/1.3671367
Abstract: We use spatially and temporally resolved photoluminescence to measure exciton diffusion in single zinc blende GaAs/AlGaAs core/shell and mixed phase InP nanowires. Excitons in the single phase GaAs/AlGaAs nanowires are seen to diffuse rapidly throughout the nanowire with a measured diffusion constant ranging from 45 to 100 cm2/s, while in the mixed phase, InP nanowire electrons and holes are seen to rapidly localize to the quantum confined states in the zinc blende and wurtzite segments, respectively. The diffusion constant in the GaAs/AlGaAs nanowire is similar to the best hole mobilities observed in modulation doped heterostructures.
Intermixing of InGaAs/GaAs quantum wells and quantum dots using sputter-deposited silicon oxynitride capping layers
Publisher: AIP Publishing
Date: 12-2012
DOI: 10.1063/1.4768283
Abstract: Various approaches can be used to selectively control the amount of intermixing in III-V quantum well and quantum dot structures. Impurity-free vacancy disordering is one technique that is favored for its simplicity, however this mechanism is sensitive to many experimental parameters. In this study, a series of silicon oxynitride capping layers have been used in the intermixing of InGaAs/GaAs quantum well and quantum dot structures. These thin films were deposited by sputter deposition in order to minimize the incorporation of hydrogen, which has been reported to influence impurity-free vacancy disordering. The degree of intermixing was probed by photoluminescence spectroscopy and this is discussed with respect to the properties of the SiOxNy films. This work was also designed to monitor any additional intermixing that might be attributed to the sputtering process. In addition, the high-temperature stress is known to affect the group-III vacancy concentration, which is central to the intermixing process. This stress was directly measured and the experimental values are compared with an elastic-deformation model.
High-pressure high-temperature annealing of ion-implanted GaN films monitored by visible and ultraviolet micro-Raman scattering
Publisher: AIP Publishing
Date: 15-03-2000
DOI: 10.1063/1.372248
Abstract: Visible and ultraviolet micro-Raman scattering was employed to monitor the high-pressure high-temperature annealing of Mg/P-implanted GaN films. The results illustrate the use of Raman scattering to monitor processing of GaN where fast feedback is required. Temperatures up to 1500 °C with nitrogen overpressures of 1–1.5 GPa were used during the annealing. The crystalline quality, the strain, and the free carrier concentration in the ion-implanted GaN films was monitored, averaged over the layer thickness and in a 40-nm-thin surface layer of the s le. Annealing temperatures of 1400–1500 °C were found to result in the nearly full recovery of the crystalline quality of ion-implanted GaN. No significant surface degradation occurred during the annealing. High nitrogen overpressures proved very effective in preventing the nitrogen out-diffusion from the GaN surface at high temperatures. Strain was introduced during the annealing. Changes in the free carrier concentration were studied.
Influence of cap layer on implantation induced interdiffusion in InP/InGaAs quantum wells
Publisher: AIP Publishing
Date: 28-03-2003
DOI: 10.1063/1.1555273
Abstract: We have investigated the effect of implantation at room temperature and 200 °C into lattice matched InP/InGaAs quantum well structures capped with InP and InGaAs layers. P− ions of 20 keV were implanted into the cap layer at doses of 1×1012−1×1014 cm−2. The dose dependent evolution of shifts in photoluminescence energy for the InP capped s le was found to be affected by the implant temperature. Rutherford back scattering measurements show that the nature of the damage induced at different implant temperatures is responsible for this behavior. It was found that the InGaAs capped s le was less sensitive to the implant temperature than the InP capped s le.
Emergence of localized states in narrow GaAs/AlGaAs nanowire quantum well tubes
Publisher: American Chemical Society (ACS)
Date: 27-02-2015
DOI: 10.1021/NL5046878
Abstract: We use low-temperature photoluminescence, photoluminescence excitation, and photoluminescence imaging spectroscopy to explore the optical and electronic properties of GaAs/AlGaAs quantum well tube (QWT) heterostructured nanowires (NWs). We find that GaAs QWTs with widths >5 nm have electronic states which are delocalized and continuous along the length of the NW. As the NW QWT width decreases from 5 to 1.5 nm, only a single electron state is bound to the well, and no optical excitations to a confined excited state are present. Simultaneously, narrow emission lines (fwhm < 600 μeV) appear which are localized to single spatial points along the length of the NW. We find that these quantum-dot-like states broaden at higher temperatures and quench at temperatures above 80 K. The lifetimes of these localized states are observed to vary from dot to dot from 160 to 400 ps. The presence of delocalized states and then localized states as the QWTs become more confined suggests both opportunities and challenges for possible incorporation into quantum-confined device structures.
Quantitative dopant distributions in GaAs nanowires using atom probe tomography
Publisher: Elsevier BV
Date: 09-2013
DOI: 10.1016/J.ULTRAMIC.2013.02.012
Abstract: Controllable doping of semiconductor nanowires is critical to realize their proposed applications, however precise and reliable characterization of dopant distributions remains challenging. In this article, we demonstrate an atomic-resolution three-dimensional elemental mapping of pristine semiconductor nanowires on growth substrates by using atom probe tomography to tackle this major challenge. This highly transferrable method is able to analyze the full diameter of a nanowire, with a depth resolution better than 0.17 nm thanks to an advanced reconstruction method exploiting the specimen's crystallography, and an enhanced chemical sensitivity of better than 8-fold increase in the signal-to-noise ratio.
Electrochemical hydrogenated TiO2 nanotube arrays decorated with 3D cotton-like porous MnO2 enables superior supercapacitive performance
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7RA04883A
Abstract: Highly conducting TiO 2 nanotube arrays (EH-TNTAs) decorated with unique 3D cotton-like porous MnO 2 enables superior supercapacitive performance.
Spectral tuning of InGaAs/GaAs quantum dot infrared photodetectors with bandpass guided-mode resonance filters
Publisher: Wiley
Date: 04-11-2014
Ultralow Surface Recombination Velocity in InP Nanowires Probed by Terahertz Spectroscopy
Publisher: American Chemical Society (ACS)
Date: 13-09-2012
DOI: 10.1021/NL3026828
Abstract: Using transient terahertz photoconductivity measurements, we have made noncontact, room temperature measurements of the ultrafast charge carrier dynamics in InP nanowires. InP nanowires exhibited a very long photoconductivity lifetime of over 1 ns, and carrier lifetimes were remarkably insensitive to surface states despite the large nanowire surface area-to-volume ratio. An exceptionally low surface recombination velocity (170 cm/s) was recorded at room temperature. These results suggest that InP nanowires are prime candidates for optoelectronic devices, particularly photovoltaic devices, without the need for surface passivation. We found that the carrier mobility is not limited by nanowire diameter but is strongly limited by the presence of planar crystallographic defects such as stacking faults in these predominantly wurtzite nanowires. These findings show the great potential of very narrow InP nanowires for electronic devices but indicate that improvements in the crystallographic uniformity of InP nanowires will be critical for future nanowire device engineering.
Two-color InGaAs∕GaAs quantum dot infrared photodetectors by selective area interdiffusion
Publisher: AIP Publishing
Date: 07-07-2008
DOI: 10.1063/1.2955517
Abstract: We report the postgrowth fabrication of two-color InGaAs∕GaAs quantum dot infrared photodetectors (QDIPs). By capping half of the as-grown QDIP structure with titanium dioxide (TiO2) and performing rapid thermal annealing under the optimized condition, a blueshifted photoluminescence from the uncapped region was obtained compared with the TiO2 covered region. The corresponding device spectral photoresponse from the two adjacent regions exhibited a shift of 0.8μm around the wavelength of 6μm. This is a result of the simultaneous promotion and suppression of thermal interdiffusion during rapid thermal annealing.
Ultrafast carrier trapping and recombination in highly resistive ion implanted InP
Publisher: AIP Publishing
Date: 26-06-2003
DOI: 10.1063/1.1576516
Abstract: MeV P+ implanted and annealed p-InP, and Fe+ implanted and annealed semi-insulating InP have both been shown to produce the high resistivity, good mobility, and ultrafast optical response desired for ultrafast photodetectors. Hall effect measurements and time resolved photoluminescence were used to analyze the electrical and optical features of such implanted materials. Low temperature annealing was found to yield the fastest response times—130 fs for Fe+ implanted and 400 fs for P+ implanted InP, as well as resistivities of the order ∼106 Ω/square. It was found that the electrical activation of Fe-related centers, useful for achieving high resistivities in Fe+ implanted semi-insulating InP, was not fully realized at the annealing temperatures chosen to produce the fastest optical response. Implanting p-InP in the dose regime where type conversion occurs, and subsequent annealing at 500 °C, produces high resistivities and ultrafast carrier trapping times that are only marginally dose dependent.
Effects of annealing on the properties of In0.5Ga0.5As/GaAs/Al0.2Ga0.8As quantum dots-in-a-well infrared photodetectors
Publisher: IOP Publishing
Date: 07-05-2009
Cross-sectional associations between air pollution and chronic bronchitis: an ESCAPE meta-analysis across five cohorts
Publisher: BMJ
Date: 11-08-2014
DOI: 10.1136/THORAXJNL-2013-204352
Abstract: This study aimed to assess associations of outdoor air pollution on prevalence of chronic bronchitis symptoms in adults in five cohort studies (Asthma-E3N, ECRHS, NSHD, SALIA, SAPALDIA) participating in the European Study of Cohorts for Air Pollution Effects (ESCAPE) project. Annual average particulate matter (PM(10), PM(2.5), PM(absorbance), PM(coarse)), NO(2), nitrogen oxides (NO(x)) and road traffic measures modelled from ESCAPE measurement c aigns 2008-2011 were assigned to home address at most recent assessments (1998-2011). Symptoms examined were chronic bronchitis (cough and phlegm for ≥3 months of the year for ≥2 years), chronic cough (with/without phlegm) and chronic phlegm (with/without cough). Cohort-specific cross-sectional multivariable logistic regression analyses were conducted using common confounder sets (age, sex, smoking, interview season, education), followed by meta-analysis. 15 279 and 10 537 participants respectively were included in the main NO(2) and PM analyses at assessments in 1998-2011. Overall, there were no statistically significant associations with any air pollutant or traffic exposure. Sensitivity analyses including in asthmatics only, females only or using back-extrapolated NO(2) and PM10 for assessments in 1985-2002 (ECRHS, NSHD, SALIA, SAPALDIA) did not alter conclusions. In never-smokers, all associations were positive, but reached statistical significance only for chronic phlegm with PM(coarse) OR 1.31 (1.05 to 1.64) per 5 µg/m(3) increase and PM(10) with similar effect size. Sensitivity analyses of older cohorts showed increased risk of chronic cough with PM(2.5abs) (black carbon) exposures. Results do not show consistent associations between chronic bronchitis symptoms and current traffic-related air pollution in adult European populations.
Formulation and Biological Evaluation of Mesoporous Silica Nanoparticles Loaded with Combinations of Sortase A Inhibitors and Antimicrobial Peptides
Publisher: MDPI AG
Date: 04-05-2022
DOI: 10.3390/PHARMACEUTICS14050986
Abstract: This study aimed to develop synergistic therapies to treat superbug infections through the encapsulation of sortase A inhibitors (SrtAIs trans-chalcone (TC), curcumin (CUR), quercetin (QC), or berberine chloride (BR)) into MCM-41 mesoporous silica nanoparticles (MSNs) or a phosphonate-modified analogue (MCM-41-PO3−) to overcome their poor aqueous solubility. A resazurin-modified minimum inhibitory concentration (MIC) and checkerboard assays, to measure SrtAI synergy in combination with leading antimicrobial peptides (AMPs pexiganan (PEX), indolicidin (INDO), and [I5, R8] mastoparan (MASTO)), were determined against methicillin-sensitive (MSSA) and methicillin-resistant (MRSA) Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. The results demonstrated that the MCM-41 and MCM-41-PO3− formulations significantly improved the aqueous solubility of each SrtAI. The MICs for SrtAI/MCM-41-PO3− formulations were lower compared to the SrtAI/MCM-41 formulations against tested bacterial strains, except for the cases of BR/MCM-41 and QC/MCM-41 against P. aeruginosa. Furthermore, the following combinations demonstrated synergy: PEX with TC/MCM-41 (against all strains) or TC/MCM-41-PO3− (against all strains except P. aeruginosa) PEX with BR/MCM-41 or BR/MCM-41-PO3− (against MSSA and MRSA) INDO with QC/MCM-41 or QC/MCM-41-PO3− (against MRSA) and MASTO with CUR/MCM-41 (against E. coli). These combinations also reduced each components’ toxicity against human embryonic kidney cells. In conclusion, MCM-41 MSNs provide a platform to enhance SrtAI solubility and demonstrated antimicrobial synergy with AMPs and reduced toxicity, providing novel superbug treatment opportunities.
Polarization and temperature dependence of photoluminescence from zincblende and wurtzite InP nanowires
Publisher: AIP Publishing
Date: 24-12-2007
DOI: 10.1063/1.2828034
Abstract: We use polarization-resolved and temperature-dependent photoluminescence of single zincblende (ZB) (cubic) and wurtzite (WZ) (hexagonal) InP nanowires to probe differences in selection rules and bandgaps between these two semiconductor nanostructures. The WZ nanowires exhibit a bandgap 80meV higher in energy than the ZB nanowires. The temperature dependence of the PL is similar but not identical for the WZ and ZB nanowires. We find that ZB nanowires exhibit strong polarization parallel to the nanowire axis, while the WZ nanowires exhibit polarized emission perpendicular to the nanowire axis. This behavior is interpreted in terms of the different selection rules for WZ and ZB crystal structures.
Atomic relocation processes in impurity-free disordered p-GaAs epilayers studied by deep level transient spectroscopy
Publisher: AIP Publishing
Date: 28-10-2002
DOI: 10.1063/1.1519728
Abstract: We have used capacitance–voltage and deep level transient spectroscopy techniques to study the relocation of impurities, such as Zn and Cu, in impurity-free disordered (IFD) p-type GaAs. A four-fold increase in the doping concentration is observed after annealing at 925 °C. Two electrically active defects HA (EV+0.39 eV) and HB2 (EV+0.54 eV), which we have attributed to Cu- and Asi/AsGa-related levels, respectively, are observed in the disordered p-GaAs layers. The injection of gallium vacancies causes segregation of Zn dopant atoms and Cu towards the surface of IFD s les. The atomic relocation process is critically assessed in terms of the application of IFD to the band gap engineering of doped GaAs-based heterostructures.
In0.2Ga0.8As/GaAs quantum well laser with C doped cladding and ohmic contact layers
Publisher: Springer Science and Business Media LLC
Date: 09-1998
Photonic crystal-enhanced quantum dot infrared photodetectors
Publisher: SPIE
Date: 28-08-2008
DOI: 10.1117/12.793558
Effect of GaP strain compensation layers on rapid thermally annealed InGaAs∕GaAs quantum dot infrared photodetectors grown by metal-organic chemical-vapor deposition
Publisher: AIP Publishing
Date: 13-08-2007
DOI: 10.1063/1.2770765
Abstract: The effect of GaP strain compensation layers was investigated on ten-layer InGaAs∕GaAs quantum dot infrared photodetectors (QDIPs) grown by metal-organic chemical-vapor deposition. Compared with the normal QDIP structure, the insertion of GaP has led to a narrowed spectral linewidth and slightly improved detector performance. A more significant influence of GaP was observed after the structure was annealed at various temperatures. While a similar amount of wavelength tuning was obtained, the GaP QDIPs exhibited much less degradation in device characteristics with increasing annealing temperature.
Spatially Resolved Doping Concentration and Nonradiative Lifetime Profiles in Single Si-Doped InP Nanowires Using Photoluminescence Mapping
Publisher: American Chemical Society (ACS)
Date: 03-04-2015
DOI: 10.1021/NL504929N
Abstract: We report an analysis method that combines microphotoluminescence mapping and lifetime mapping data of single semiconductor nanowires to extract the doping concentration, nonradiative lifetime, and internal quantum efficiency along the length of the nanowires. Using this method, the doping concentration of single Si-doped wurtzite InP nanowires are mapped out and confirmed by the electrical measurements of single nanowire devices. Our method has important implication for single nanowire detectors and LEDs and nanowire solar cells applications.
Selective Intermixing of InGaAs/GaAs Quantum Dot Infrared Photodetectors
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2011
First-trimester artemisinin derivatives and quinine treatments and the risk of adverse pregnancy outcomes in Africa and Asia: A meta-analysis of observational studies
Publisher: Public Library of Science (PLoS)
Date: 02-05-2017
Association of ambient air pollution with the prevalence and incidence of COPD
Publisher: European Respiratory Society (ERS)
Date: 31-01-2014
DOI: 10.1183/09031936.00132213
Abstract: The role of air pollution in chronic obstructive pulmonary disease (COPD) remains uncertain. The aim was to assess the impact of chronic exposure to air pollution on COPD in four cohorts using the standardised ESCAPE exposure estimates. Annual average particulate matter (PM), nitrogen oxides (NOx) and road traffic exposure were assigned to home addresses using land-use regression models. COPD was defined by NHANES reference equation (forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) less than the lower limit of normal) and the Global Initiative for Chronic Obstructive Lung Disease criterion (FEV1/FVC <0.70) and categorised by severity in non-asthmatics. We included 6550 subjects with assigned NOx and 3692 with PM measures. COPD was not associated with NO2 or PM10 in any in idual cohort. In meta-analyses only NO2, NOx, PM10 and the traffic indicators were positively, although not significantly, associated with COPD. The only statistically significant associations were seen in females (COPD prevalence using GOLD: OR 1.57, 95% CI 1.11-2.23 and incidence: OR 1.79, 95% CI 1.21-2.68). None of the principal results were statistically significant, the weak positive associations of exposure with COPD and the significant subgroup findings need to be evaluated in further well standardised cohorts followed up for longer time, and with time-matched exposure assignments.
Thermal expansion coefficients and composition of sputter-deposited silicon oxynitride thin films
Publisher: IOP Publishing
Date: 05-08-2010
DOI: 10.1088/0022-3727/43/33/335104
Abstract: Modern technology is heavily reliant on silicon dioxide and silicon nitride thin films. These films have many electronic and optical applications, and in some cases silicon oxynitride films of intermediate composition are desirable. We have systematically deposited several SiO x N y films by magnetron sputter deposition and thoroughly investigated their composition with Rutherford backscattering spectrometry and optical measurements. The as-deposited stress in these thin films was also measured and all were found to be compressive. Temperature-dependent stress measurements up to 450 ° C were then used to extract the biaxial modulus and coefficient of thermal expansion for each SiO x N y . The SiO 2 -like films exhibit negative thermal expansion, which is consistent with a strong but porous structure. Increasing the nitrogen content results in the thermal expansion coefficient increasing towards values reported elsewhere for Si 3 N 4 .
Methodology of assessment and reporting of safety in anti-malarial treatment efficacy studies of uncomplicated falciparum malaria in pregnancy: a systematic literature review
Publisher: Springer Science and Business Media LLC
Date: 12-2017
Threshold reduction and yield improvement of semiconductor nanowire lasers via processing-related end-facet optimization
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9NA00479C
Abstract: For nanowire lasers, end-facets matter a rigorous statistical study demonstrates that short ultrasound or PDMA transfer provides optimized lasing performance.
Electron dynamics in modulation p-doped InGaAs/GaAs quantum dots
Publisher: Springer Science and Business Media LLC
Date: 03-2008
Pharmacokinetics of Oral Tenofovir Disoproxil Fumarate in Pregnancy and Lactation: A Systematic Review
Publisher: SAGE Publications
Date: 10-2018
DOI: 10.3851/IMP3341
Abstract: Tenofovir disoproxil fumarate (TDF), the oral prodrug of tenofovir (TFV), is advocated in pregnancy for prevention of mother-to-child transmission (PMCT) with failure of hepatitis B immunoglobulin and vaccination. The pharmacokinetics of TDF monotherapy for PMCT-HBV is important if deployment is to emulate the success of multiple antiretrovirals (ARVs) for PMCT-HIV in resource-constrained settings. This systematic review followed a protocol and is reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement (PRISMA) guidelines. We included studies that enrolled pregnant women who received oral TDF therapy as mono-therapy or in combination with other ARVs: irrespective of the reason for receiving the drug (for ex le, HIV, HBV or pre-exposure prophylaxis) and reported pharmacokinetics. The area under the concentration–time curve (AUC), maximum plasma concentrations (C max ) and last measurable plasma concentration (C last ) of TFV were decreased in the second and third trimester compared with first trimester or post-partum. In none of the manuscripts was the non-pregnant HBV threshold of C max of 300 ng/ml reached, but the 50% effective concentration (EC 50 ) of TFV is lower for treatment of HBV compared with HIV. The TFV concentration in breastfed infants was 0.03% of the recommended infant dose. Most knowledge of pharmacokinetics of TFV in pregnancy results from studies on HIV involving multiple ARVs. Increased TFV clearance occurred in the second and third trimester when optimal TFV concentrations are required to maximize suppression of HBV in the window before birth. Dose or duration adjustments will be better conceptualized with concurrent analysis of the pharmacokinetics of TFV monotherapy and hepatitis B pharmacodynamics in pregnancy.
Micrometer-Scale Deep-Level Spectral Photoluminescence From Dislocations in Multicrystalline Silicon
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2015
Electron mobilities approaching bulk limits in surface-free GaAs nanowires
Publisher: American Chemical Society (ACS)
Date: 26-09-2014
DOI: 10.1021/NL503043P
Abstract: Achieving bulk-like charge carrier mobilities in semiconductor nanowires is a major challenge facing the development of nanowire-based electronic devices. Here we demonstrate that engineering the GaAs nanowire surface by overcoating with optimized AlGaAs shells is an effective means of obtaining exceptionally high carrier mobilities and lifetimes. We performed measurements of GaAs/AlGaAs core-shell nanowires using optical pump-terahertz probe spectroscopy: a noncontact and accurate probe of carrier transport on ultrafast time scales. The carrier lifetimes and mobilities both improved significantly with increasing AlGaAs shell thickness. Remarkably, optimized GaAs/AlGaAs core-shell nanowires exhibited electron mobilities up to 3000 cm(2) V(-1) s(-1), reaching over 65% of the electron mobility typical of high quality undoped bulk GaAs at equivalent photoexcited carrier densities. This points to the high interface quality and the very low levels of ionized impurities and lattice defects in these nanowires. The improvements in mobility were concomitant with drastic improvements in photoconductivity lifetime, reaching 1.6 ns. Comparison of photoconductivity and photoluminescence dynamics indicates that midgap GaAs surface states, and consequently surface band-bending and depletion, are effectively eliminated in these high quality heterostructures.
Carrier dynamics in p-type InGaAs/GaAs quantum dots
Publisher: Springer Science and Business Media LLC
Date: 07-04-2007
Self-frequency-conversion nanowire lasers
Publisher: Springer Science and Business Media LLC
Date: 29-04-2022
DOI: 10.1038/S41377-022-00807-7
Abstract: Semiconductor nanowires (NWs) could simultaneously provide gain medium and optical cavity for performing nanoscale lasers with easy integration, ultracompact footprint, and low energy consumption. Here, we report III–V semiconductor NW lasers can also be used for self-frequency conversion to extend their output wavelengths, as a result of their non-centrosymmetric crystal structure and strongly localized optical field in the NWs. From a GaAs/In 0.16 Ga 0.84 As core/shell NW lasing at 1016 nm, an extra visible laser output at 508 nm is obtained via the process of second-harmonic generation, as confirmed by the far-field polarization dependence measurements and numerical modeling. From another NW laser with a larger diameter which supports multiple fundamental lasing wavelengths, multiple self-frequency-conversion lasing modes are observed due to second-harmonic generation and sum-frequency generation. The demonstrated self-frequency conversion of NW lasers opens an avenue for extending the working wavelengths of nanoscale lasers, even to the deep ultraviolet and THz range.
Identification and modulation of electronic band structures of single-phase β-(Alx Ga1-x )2 O3 alloys grown by laser molecular beam epitaxy
Publisher: AIP Publishing
Date: 23-07-2018
DOI: 10.1063/1.5027763
Abstract: Understanding the band structure evolution of (AlxGa1−x)2O3 alloys is of fundamental importance for developing Ga2O3-based power electronic devices and vacuum ultraviolet super-radiation hard detectors. Here, we report on the bandgap engineering of β-(AlxGa1−x)2O3 thin films and the identification of compositionally dependent electronic band structures by a combination of absorption spectra analyses and density functional theory calculations. Single-monoclinic β-phase (AlxGa1−x)2O3 (0 ≤ x ≤ 0.54) films with a preferred (−201) orientation were grown by laser molecular beam epitaxy with tunable bandgap ranging from 4.5 to 5.5 eV. The excellent fitting of absorption spectra by the relation of (αhν)1/2 ∝ (hν-E) unambiguously identifies that β-(AlxGa1−x)2O3 alloys are indirect bandgap semiconductors. Theoretical calculations predict that the indirect nature of β-(AlxGa1−x)2O3 becomes more pronounced with increased Al composition due to the increased eigenvalue energy gap between M and Г points in the valence band. The experimentally determined indirect bandgap exhibits almost a linear relationship with Al composition, which is consistent with the theoretical calculation and indicates a small bowing effect and a good miscibility. The identification and modulation of (AlxGa1−x)2O3 band structures allows rational design of ultra-wide bandgap oxide heterostructures for the applications in power electronics and solar-blind or X-ray detection.
Comparison of proton and arsenic implantation-induced intermixing in InGaAsP/InGaAs/InP and InAlGaAs/InGaAs/InP quantum wells
Publisher: IEEE
Date: 02-2008
Postgrowth wavelength tuning of optoelectronic devices by ion implantation induced quantum well intermixing
Publisher: IEEE
Date: 2000
Decoupling the roles of defects/impurities and wrinkles in thermal conductivity of wafer-scale hBN films
Publisher: AIP Publishing
Date: 20-10-2023
DOI: 10.1063/5.0168186
The effect of V/III ratio and catalyst particle size on the crystal structure and optical properties of InP nanowires
Publisher: IOP Publishing
Date: 13-05-2009
DOI: 10.1088/0957-4484/20/22/225606
Abstract: InP nanowires were grown on 111B InP substrates by metal-organic chemical vapour deposition in the presence of colloidal gold particles as catalysts. Transmission electron microscopy and photoluminescence measurements were carried out to investigate the effects of V/III ratio and nanowire diameter on structural and optical properties. Results show that InP nanowires grow preferably in the wurtzite crystal structure than the zinc blende crystal structure with increasing V/III ratio or decreasing diameter. Additionally, time-resolved photoluminescence (TRPL) studies have revealed that wurtzite nanowires show longer recombination lifetimes of approximately 2500 ps with notably higher quantum efficiencies.
Towards a better understanding of the operative mechanisms underlying impurity-free disordering of GaAs: Effect of stress
Publisher: American Vacuum Society
Date: 2003
DOI: 10.1116/1.1535927
Abstract: The effect of stress on defect creation and diffusion during impurity-free disordering of SiOx-capped n-GaAs epitaxial layers has been investigated using deep level transient spectroscopy. The oxygen content in the SiOx layer and the nature of the stress that it imposes on the GaAs layer were varied by changing the nitrous oxide flow rate, N, during plasma-enhanced chemical vapor deposition of the capping layer. The peak intensity of defects S1 and S4 increased with the increasing nitrous oxide flow rate to exhibit a maximum in the range 80 sccm& N& sccm. Any further increase in N resulted in a decrease in peak defect intensity, which reached an almost constant value for N& sccm. On the other hand, the peak intensity of S2* increased linearly with N. We have explained the maximum in the intensity of defects S1 and S4 for 80 sccm& N& sccm to be due to a corresponding maximum in the compressive stress which is experienced by the capped GaAs layer during annealing. Although the creation of S2*, which we have proposed to be a complex involving the gallium vacancy (VGa), is enhanced with the increasing compressive stress, it also becomes efficiently converted into the arsenic-antisite, AsGa. The compound effect of these opposing mechanisms results in a linear dependence of the peak intensity of S2* on N. This study is to the best of our knowledge the first to provide the evidence for the stress-dependent anti-correlation between VGa- and AsGa-related defects in GaAs. We have also narrowed the origin of S1 to complexes involving arsenic interstitials, Asi, and/or AsGa.
The risk of Plasmodium vivax parasitaemia after P. falciparum malaria: An individual patient data meta-analysis from the WorldWide Antimalarial Resistance Network
Publisher: Public Library of Science (PLoS)
Date: 19-11-2020
DOI: 10.1371/JOURNAL.PMED.1003393
Abstract: There is a high risk of Plasmodium vivax parasitaemia following treatment of falciparum malaria. Our study aimed to quantify this risk and the associated determinants using an in idual patient data meta-analysis in order to identify populations in which a policy of universal radical cure, combining artemisinin-based combination therapy (ACT) with a hypnozoitocidal antimalarial drug, would be beneficial. A systematic review of Medline, Embase, Web of Science, and the Cochrane Database of Systematic Reviews identified efficacy studies of uncomplicated falciparum malaria treated with ACT that were undertaken in regions coendemic for P . vivax between 1 January 1960 and 5 January 2018. Data from eligible studies were pooled using standardised methodology. The risk of P . vivax parasitaemia at days 42 and 63 and associated risk factors were investigated by multivariable Cox regression analyses. Study quality was assessed using a tool developed by the Joanna Briggs Institute. The study was registered in the International Prospective Register of Systematic Reviews (PROSPERO: CRD42018097400). In total, 42 studies enrolling 15,341 patients were included in the analysis, including 30 randomised controlled trials and 12 cohort studies. Overall, 14,146 (92.2%) patients had P . falciparum monoinfection and 1,195 (7.8%) mixed infection with P . falciparum and P . vivax . The median age was 17.0 years (interquartile range [IQR] = 9.0–29.0 years range = 0–80 years), with 1,584 (10.3%) patients younger than 5 years. 2,711 (17.7%) patients were treated with artemether-lumefantrine (AL, 13 studies), 651 (4.2%) with artesunate-amodiaquine (AA, 6 studies), 7,340 (47.8%) with artesunate-mefloquine (AM, 25 studies), and 4,639 (30.2%) with dihydroartemisinin-piperaquine (DP, 16 studies). 14,537 patients (94.8%) were enrolled from the Asia-Pacific region, 684 (4.5%) from the Americas, and 120 (0.8%) from Africa. At day 42, the cumulative risk of vivax parasitaemia following treatment of P . falciparum was 31.1% (95% CI 28.9–33.4) after AL, 14.1% (95% CI 10.8–18.3) after AA, 7.4% (95% CI 6.7–8.1) after AM, and 4.5% (95% CI 3.9–5.3) after DP. By day 63, the risks had risen to 39.9% (95% CI 36.6–43.3), 42.4% (95% CI 34.7–51.2), 22.8% (95% CI 21.2–24.4), and 12.8% (95% CI 11.4–14.5), respectively. In multivariable analyses, the highest rate of P . vivax parasitaemia over 42 days of follow-up was in patients residing in areas of short relapse periodicity (adjusted hazard ratio [AHR] = 6.2, 95% CI 2.0–19.5 p = 0.002) patients treated with AL (AHR = 6.2, 95% CI 4.6–8.5 p 0.001), AA (AHR = 2.3, 95% CI 1.4–3.7 p = 0.001), or AM (AHR = 1.4, 95% CI 1.0–1.9 p = 0.028) compared with DP and patients who did not clear their initial parasitaemia within 2 days (AHR = 1.8, 95% CI 1.4–2.3 p 0.001). The analysis was limited by heterogeneity between study populations and lack of data from very low transmission settings. Study quality was high. In this meta-analysis, we found a high risk of P . vivax parasitaemia after treatment of P . falciparum malaria that varied significantly between studies. These P . vivax infections are likely attributable to relapses that could be prevented with radical cure including a hypnozoitocidal agent however, the benefits of such a novel strategy will vary considerably between geographical areas.
Electrical isolation of n- and p-In0.53Ga0.47As epilayers using ion irradiation
Publisher: AIP Publishing
Date: 31-10-2003
DOI: 10.1063/1.1619567
Abstract: A study of the evolution of sheet resistance of p- and n-type In0.53Ga0.47As epilayers during O, C, Li, and H irradiation was conducted. The threshold dose at which the material becomes highly resistive increased upon decreasing the mass of the implanted ion, was higher for n-InGaAs as compared to p-InGaAs and was greater for s les with a higher initial free carrier concentration. Implantation with H+ yielded isolation behavior that was different from that for implantation with the three medium-mass ions. The thermal stability of defects induced by implantation was also investigated by cumulative annealing, and was found to be slightly higher in n-InGaAs as compared to p-InGaAs. Shallow donor production in the InGaAs epilayer during implantation played a crucial role in determining the electrical characteristics of the s les.
Three-dimensional cross-nanowire networks recover full terahertz state
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-2020
Abstract: Terahertz (THz) radiation is an interesting region of the electromagnetic spectrum lying between microwaves and infrared. Non-ionizing and transparent to most fabrics, it is finding application in security screening and imaging but is also being developed for communication and chemical sensing. To date, most THz detectors have focused just on signal intensity, an effort that discards half the signal in terms of the full optical state, including polarization. Peng et al. developed a THz detector based on crossed nanowires (arranged in a hash structure) that is capable of resolving the full state of the THz light. The approach provides a nanophotonic platform for the further development of THz-based technologies. Science , this issue p. 510
The role of arsine in the self-assembled growth of InAs/GaAs quantum dots by metal organic chemical vapor deposition
Publisher: AIP Publishing
Date: 15-02-2006
DOI: 10.1063/1.2173687
Abstract: The influence of various growth parameters such as coverage, the AsH3 flow (V∕III ratio), and growth interrupts on the self-assembled growth of InAs∕GaAs quantum dots (QDs) by metal organic chemical vapor deposition is reported. Of the various growth parameters, the AsH3 flow has a particularly strong influence. Higher AsH3 flows during deposition led to a faster nucleation process and larger islands, while the presence of AsH3 after nucleation led to continued island ripening. We suggest that this is the result of increased indium redistribution from the highly strained wetting layer to the islands, and possibly between the islands, at higher AsH3 flows. A large defect density was observed by plan-view transmission electron microscopy, whenever the growth parameters led to larger islands. Using our optimized growth conditions we are able to avoid such defect generation and still achieve a high QD density (3×1010cm−2).
Department of Error
Publisher: Elsevier BV
Date: 06-2019
Mapping geographical inequalities in oral rehydration therapy coverage in low-income and middle-income countries, 2000–17
Publisher: Elsevier BV
Date: 08-2020
Suppression of the internal electric field effects in ZnO/Zn0.7Mg0.3O quantum wells by ion-implantation induced intermixing
Publisher: IOP Publishing
Date: 14-01-2008
DOI: 10.1088/0957-4484/19/05/055205
Abstract: Strong suppression of the effects caused by the internal electric field in ZnO/ZnMgO quantum wells following ion-implantation and rapid thermal annealing, is revealed by photoluminescence, time-resolved photoluminescence, and band structure calculations. The implantation and annealing induces Zn/Mg intermixing, resulting in graded quantum well interfaces. This reduces the quantum-confined Stark shift and increases electron-hole wavefunction overlap, which significantly reduces the exciton lifetime and increases the oscillator strength.
Migrant perinatal depression study: a prospective cohort study of perinatal depression on the Thai-Myanmar border
Publisher: BMJ
Date: 2018
Optically pumped in-plane photonic crystal microcavity laser arrays coupled to waveguides
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2008
A study of quantum well solar cell structures with bound-to-continuum transitions for reduced carrier recombination
Publisher: AIP Publishing
Date: 27-05-2013
DOI: 10.1063/1.4807506
Abstract: A bound-to-continuum quantum well solar cell structure is proposed, and the band structure and absorption spectra are analyzed by the use of an eight band k·p model. The structure is based on quantum wells that only support bound states for the valence band. The absence of bound conduction band states has a number of potential advantages, including a reduction of electron trapping and, therefore, a reduction of quantum well induced photocarrier recombination due to reduced spatial overlap of the electron and hole wavefunctions.
Evolution of InAs branches in InAs∕GaAs nanowire heterostructures
Publisher: AIP Publishing
Date: 24-09-2007
DOI: 10.1063/1.2790486
Abstract: Branched nanowire heterostructures of InAs∕GaAs were observed during Au-assisted growth of InAs on GaAs nanowires. The evolution of these branches has been determined through detailed electron microscopy characterization with the following sequence: (1) in the initial stage of InAs growth, the Au droplet is observed to slide down the side of the GaAs nanowire, (2) the downward movement of Au nanoparticle later terminates when the nanoparticle encounters InAs growing radially on the GaAs nanowire sidewalls, and (3) with further supply of In and As vapor reactants, the Au nanoparticles assist the formation of InAs branches with a well-defined orientation relationship with GaAs∕InAs core/shell stems. We anticipate that these observations advance the understanding of the kink formation in axial nanowire heterostructures.
Single-crystalline hexagonal ZnO microtube optical resonators
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/C0JM00172D
High resistivity and picosecond carrier lifetime of GaAs implanted with MeV Ga ions at high fluences
Publisher: AIP Publishing
Date: 18-09-1995
DOI: 10.1063/1.115029
Abstract: Rutherford backscattering spectrometry-channeling, double-crystal x-ray diffraction, optical absorption studies, and electrical measurements have been carried out on 2 MeV Ga-implanted GaAs at fluences of 1×1015 and 5×1015 cm−2. Implanted s les exhibited a strain field associated with implantation-induced damage, low resistivity due to hopping conduction and mobilities of about 1 cm2/V s. Annealing of these s les at 600 °C caused substantial recovery of postimplant damage and an increase of resistivity of more than four orders of magnitude, with mobility up to about 2600 cm2/V s. Photocarrier lifetime of annealed s les is in the few picoseconds range. These properties are strikingly similar to those of arsenic implanted GaAs, suggesting that arsenic precipitates are unlikely to be solely responsible for short carrier lifetime in the latter case. Thus Ga-implanted GaAs may be an interesting prospect for fast optoelectronic device applications.
Thermally stimulated luminescence in ion-implanted GaAs
Publisher: Elsevier BV
Date: 03-2002
Carrier Dynamics and Quantum Confinement in type II ZB-WZ InP Nanowire Homostructures
Publisher: American Chemical Society (ACS)
Date: 26-01-2009
DOI: 10.1021/NL802997P
Abstract: We use time-resolved photoluminescence from single InP nanowires containing both wurtzite (WZ) and zincblende (ZB) crystalline phases to measure the carrier dynamics of quantum confined excitons in a type-II homostructure. The observed recombination lifetime increases by nearly 2 orders of magnitude from 170 ps for excitons above the conduction and valence band barriers to more than 8400 ps for electrons and holes that are strongly confined in quantum wells defined by monolayer-scale ZB sections in a predominantly WZ nanowire. A simple computational model, guided by detailed high-resolution transmission electron microscopy measurements from a single nanowire, demonstrates that the dynamics are consistent with the calculated distribution of confined states for the electrons and holes.
Long minority carrier lifetime in Au-catalyzed GaAs/Alx Ga1-x As core-shell nanowires
Publisher: AIP Publishing
Date: 09-07-2012
DOI: 10.1063/1.4735002
Abstract: GaAs/AlxGa1−xAs core-shell nanowires were grown by metal organic chemical vapor deposition with optimized AlxGa1−xAs shell and twin-free Au-catalyzed GaAs cores. Time-resolved photoluminescence measurements were carried out on single nanowires at room temperature, revealing minority carrier lifetimes of 1.02 ± 0.43 ns, comparable to self-assisted nanowires grown by molecular beam epitaxy. The long minority carrier lifetimes are mainly attributed to improvement of the GaAs/AlxGa1−xAs interface quality. The upper limit of surface recombination velocity of the structure is calculated to be 1300 cm/s with the AlxGa1−xAs shell grown at 750 °C, which is comparable with planar double heterostructures.
Effect of Rapid Thermal Annealing on the Atomic Intermixing of Zn- and C-Doped InGaAs∕AlGaAs Quantum Well Laser Structures
Publisher: The Electrochemical Society
Date: 2006
DOI: 10.1149/1.2220066
Erratum: Room-Temperature Preparation of InGaAsN Quantum Dot Lasers Grown by MOCVD [Electrochem. Solid-State Lett. 8 G57 (2005)]
Publisher: The Electrochemical Society
Date: 2005
DOI: 10.1149/1.1872016
Comparison of InAs quantum dots grown on GaInAsP and InP
Publisher: IOP Publishing
Date: 15-03-2006
Controlling the morphology, composition and crystal structure in gold-seeded GaAs1-xSbx nanowires
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4NR06307D
Abstract: GaAs 1−x Sb x nanowires show zinc blende twin free structure at low TMSb flow while high TMSb flow results in inclined faults and nanowire kinking thanks to its surfactant role. Increase of wetting angle is observed, replying the change of surface energy.
Adult lung function and long-term air pollution exposure. ESCAPE: a multicentre cohort study and meta-analysis
Publisher: European Respiratory Society (ERS)
Date: 05-09-2014
DOI: 10.1183/09031936.00130014
Abstract: The chronic impact of ambient air pollutants on lung function in adults is not fully understood. The objective of this study was to investigate the association of long-term exposure to ambient air pollution with lung function in adult participants from five cohorts in the European Study of Cohorts for Air Pollution Effects (ESCAPE). Residential exposure to nitrogen oxides (NO 2 , NO x ) and particulate matter (PM) was modelled and traffic indicators were assessed in a standardised manner. The spirometric parameters forced expiratory volume in 1 s (FEV 1 ) and forced vital capacity (FVC) from 7613 subjects were considered as outcomes. Cohort-specific results were combined using meta-analysis. We did not observe an association of air pollution with longitudinal change in lung function, but we observed that a 10 μg·m −3 increase in NO 2 exposure was associated with lower levels of FEV 1 (−14.0 mL, 95% CI −25.8 to −2.1) and FVC (−14.9 mL, 95% CI −28.7 to −1.1). An increase of 10 μg·m −3 in PM 10 , but not other PM metrics (PM 2.5 , coarse fraction of PM, PM absorbance), was associated with a lower level of FEV 1 (−44.6 mL, 95% CI −85.4 to −3.8) and FVC (−59.0 mL, 95% CI −112.3 to −5.6). The associations were particularly strong in obese persons. This study adds to the evidence for an adverse association of ambient air pollution with lung function in adults at very low levels in Europe.
Global burden of 87 risk factors in 204 countries and territories, 1990–2019: a systematic analysis for the Global Burden of Disease Study 2019
Publisher: Elsevier BV
Date: 10-2020
Ultrafast Dynamics of Exciton Formation in Semiconductor Nanowires
Publisher: Wiley
Date: 22-03-2012
Abstract: The dynamics of free electron-hole pairs and excitons in GaAs-AlGaAs-GaAs core-shell-skin nanowires is investigated using femtosecond transient photoluminescence spectroscopy at 10 K. Following nonresonant excitation, a bimolecular interconversion of the initially generated electron-hole plasma into an exciton population is observed. This conducting-to-insulating transition appears to occur gradually over electron-hole charge pair densities of 2-4 × 10(16) cm(-3) . The smoothness of the Mott transition is attributed to the slow carrier-cooling during the bimolecular interconversion of free charge carriers into excitons and to the presence of chemical-potential fluctuations leading to inhomogeneous spectral characteristics. These results demonstrate that high-quality nanowires are model systems for investigating fundamental scientific effects in 1D heterostructures.
Phase Separation Induced by Au Catalysts in Ternary InGaAs Nanowires
Publisher: American Chemical Society (ACS)
Date: 18-01-2013
DOI: 10.1021/NL304237B
Abstract: We report a novel phase separation phenomenon observed in the growth of ternary In(x)Ga(1-x)As nanowires by metalorganic chemical vapor deposition. A spontaneous formation of core-shell nanowires is investigated by cross-sectional transmission electron microscopy, revealing the compositional complexity within the ternary nanowires. It has been found that for In(x)Ga(1-x)As nanowires high precursor flow rates generate ternary In(x)Ga(1-x)As cores with In-rich shells, while low precursor flow rates produce binary GaAs cores with ternary In(x)Ga(1-x)As shells. First-principle calculations combined with thermodynamic considerations suggest that this phenomenon is due to competitive alloying of different group-III elements with Au catalysts, and variations in elemental concentrations of group-III materials in the catalyst under different precursor flow rates. This study shows that precursor flow rates are critical factors for manipulating Au catalysts to produce nanowires of desired composition.
Unexpected Benefits of Rapid Growth Rate for III−V Nanowires
Publisher: American Chemical Society (ACS)
Date: 30-12-2008
DOI: 10.1021/NL803182C
Abstract: In conventional planar growth of bulk III-V materials, a slow growth rate favors high crystallographic quality, optical quality, and purity of the resulting material. Surprisingly, we observe exactly the opposite effect for Au-assisted GaAs nanowire growth. By employing a rapid growth rate, the resulting nanowires are markedly less tapered, are free of planar crystallographic defects, and have very high purity with minimal intrinsic dopant incorporation. Importantly, carrier lifetimes are not adversely affected. These results reveal intriguing behavior in the growth of nanoscale materials, and represent a significant advance toward the rational growth of nanowires for device applications.
Ion implantation into gallium nitride
Publisher: IEEE
Date: 1996
Vertical integration of dual wavelength index guided lasers
Publisher: Institution of Engineering and Technology (IET)
Date: 1999
DOI: 10.1049/EL:19990554
Tunable and nonlinear fishnet metamaterials based on liquid crystal infiltration
Publisher: SPIE
Date: 24-09-2012
DOI: 10.1117/12.931309
Mediation of the effect of malaria in pregnancy on stillbirth and neonatal death in an area of low transmission: observational data analysis.
Publisher: Springer Science and Business Media LLC
Date: 10-05-2017
Nonlinear Optical Processes in Optically Trapped InP Nanowires
Publisher: American Chemical Society (ACS)
Date: 07-09-2011
DOI: 10.1021/NL2020262
Abstract: We report on the observation of nonlinear optical excitation and related photoluminescence from single InP semiconductor nanowires held in suspension using a gradient force optical tweezers. Photoexcitation of free carriers is achieved through absorption of infrared (1.17 eV) photons from the trapping source via a combination of two- and three-photon processes. This was confirmed by power-dependent photoluminescence measurements. Marked differences in spectral features are noted between nonlinear optical excitation and direct excitation and are related to band-filling effects. Direct observation of second harmonic generation in trapped InP nanowires confirms the presence of nonlinear optical processes.
Investigation of AlGaAs/GaAs V-grooved Quantum Wire Infrared Photodetector Structures
Publisher: IOP Publishing
Date: 09-2000
DOI: 10.1143/JJAP.39.5124
Abstract: An Al 0.5 Ga 0.5 As/GaAs quantum wires infrared photo-detectors (QWRIP) based on V-grooved substrate is fabricated. The inter-band transition in the quantum wires is characterized by spatially resolved micro-photoluminescence (micro-PL) measurement. The theoretical calculation of electronic structures is accomplished based on the Green function. The inter-subband transition is measured by photocurrent at 80 K, and the origin of the infrared response at 9 µm is from the inter-subband transition in quantum wire region, which is confirmed by the theoretical calculation results.
Polarized Light Absorption in Wurtzite InP Nanowire Ensembles
Publisher: American Chemical Society (ACS)
Date: 16-01-2015
DOI: 10.1021/NL5038374
Abstract: We investigate the absorption properties of ensembles of wurtzite (WZ) InP nanowires (NWs) by high-resolution polarization-resolved photoluminescence excitation (PLE) spectroscopy at T = 10 K. The degree of linear polarization of absorbed light, ρ(abs), resulting from the PLE spectra is governed by a competition between the dielectric mismatch effect and the WZ selection rules acting differently on different optical transitions. These two contributions are deconvoluted with the help of finite-difference time-domain simulations, thus providing information about the symmetry of the three highest valence bands (A, B, and C) of WZ InP and the extent of the spin-orbit interaction on these states. Moreover, ρ(abs) shows two characteristic dips corresponding to the two sharp A and B exciton resonances in the PLE spectra. A model developed for the dip in A provides the first experimental evidence of an enhancement in the dielectric mismatch effect originating from the Coulomb interaction between electron and hole.
Large energy shifts in GaAs-AlGaAs quantum wells by proton irradiation-induced intermixing
Publisher: AIP Publishing
Date: 22-04-1996
DOI: 10.1063/1.116147
Abstract: Proton irradiation and subsequent rapid-thermal annealing are used to create intermixing in GaAs-Al0.54Ga0.46As quantum wells of various thicknesses. Very large energy shifts (up to 200 meV) with no apparent saturation have been observed even up to a dose of about 4×1016 cm−2. This effect is explained in terms of the dilute irradiation damage and the evolution of discrete (point) defects during annealing. In comparison to heavy ion irradiation effects, high point defect fraction in the case of light ions leads to efficient intermixing with large energy shifts. Although much of the proton energy loss occurs across the quantum wells, the generated defect density is dilute, and hence good recovery in photoluminescence intensities is achieved after rapid thermal annealing.
Impurity-free disordering of InAs∕InP quantum dots
Publisher: AIP Publishing
Date: 11-06-2007
DOI: 10.1063/1.2748845
Abstract: Impurity-free disordering (IFD) of the InAs quantum dots (QDs) capped with either an InP layer or an InGaAs∕InP bilayer is studied. The s les are coated with a SiO2 or TiO2 dielectric layer followed by rapid thermal annealing at 700, 750, 800, and 850°C for 30s. A large differential energy shift of 157meV is induced by SiO2 in the QDs capped with an InGaAs∕InP bilayer. Contrary to the reported results on the suppression of intermixing of GaAs based QDs by TiO2, the authors find that intermixing of InAs∕InP QDs is promoted by TiO2. X-ray photoelectron spectroscopy depth profiles show that both In and P outdiffuse to a TiO2 layer whereas Ga, In, and P outdiffuse to a SiO2 layer leading to different degrees of intermixing. The results indicate that a group V interstitial diffusion mechanism might be responsible for IFD of InAs∕InP QDs.
Direct Observation of Charge-Carrier Heating at WZ–ZB InP Nanowire Heterojunctions
Publisher: American Chemical Society (ACS)
Date: 12-08-2013
DOI: 10.1021/NL402050Q
Abstract: We have investigated the dynamics of hot charge carriers in InP nanowire ensembles containing a range of densities of zinc-blende inclusions along the otherwise wurtzite nanowires. From time-dependent photoluminescence spectra, we extract the temperature of the charge carriers as a function of time after nonresonant excitation. We find that charge-carrier temperature initially decreases rapidly with time in accordance with efficient heat transfer to lattice vibrations. However, cooling rates are subsequently slowed and are significantly lower for nanowires containing a higher density of stacking faults. We conclude that the transfer of charges across the type II interface is followed by release of additional energy to the lattice, which raises the phonon bath temperature above equilibrium and impedes the carrier cooling occurring through interaction with such phonons. These results demonstrate that type II heterointerfaces in semiconductor nanowires can sustain a hot charge-carrier distribution over an extended time period. In photovoltaic applications, such heterointerfaces may hence both reduce recombination rates and limit energy losses by allowing hot-carrier harvesting.
Attraction of semiconductor nanowires: An in situ observation
Publisher: Elsevier BV
Date: 11-2013
Controlling the properties of InGaAs quantum dots by selective-area epitaxy
Publisher: AIP Publishing
Date: 08-03-2005
DOI: 10.1063/1.1875745
Abstract: Selective growth of InGaAs quantum dots on GaAs is reported. It is demonstrated that selective-area epitaxy can be used for in-plane bandgap energy control of quantum dots. Atomic force microscopy and cathodoluminescence are used for characterization of the selectively grown dots. Our results show that the composition, size, and uniformity of dots are determined by the dimensions of the mask used for patterning the substrate. Properties of dots can be selectively tuned by varying the mask dimensions. A single-step growth of a thin InGaAs quantum well and InGaAs quantum dots on the same wafer is demonstrated. By using a single-step growth, dots luminescing at different wavelengths, in the range 1150–1230nm, in different parts of the same wafer are achieved.
Proton irradiation-induced intermixing in InxGa1−xAs/InP quantum wells—the effect of In composition
Publisher: IOP Publishing
Date: 05-09-2006
Antibody Responses to Plasmodium falciparum and Plasmodium vivax and Prospective Risk of Plasmodium spp. Infection Postpartum.
Publisher: American Society of Tropical Medicine and Hygiene
Date: 03-05-2017
Energy sublevels in an Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As quantum wire
Publisher: Elsevier BV
Date: 11-1999
Selective-Area Epitaxy of Pure Wurtzite InP Nanowires: High Quantum Efficiency and Room-Temperature Lasing
Publisher: American Chemical Society (ACS)
Date: 15-08-2014
DOI: 10.1021/NL5021409
Abstract: We report the growth of stacking-fault-free and taper-free wurtzite InP nanowires with diameters ranging from 80 to 600 nm using selective-area metal-organic vapor-phase epitaxy and experimentally determine a quantum efficiency of ∼50%, which is on par with InP epilayers. We also demonstrate room-temperature, photonic mode lasing from these nanowires. Their excellent structural and optical quality opens up new possibilities for both fundamental quantum optics and optoelectronic devices.
Growth Mechanism of Truncated Triangular III–V Nanowires
Publisher: Wiley
Date: 05-03-2007
The state filling effect in p-doped InGaAs/GaAs quantum dots
Publisher: IOP Publishing
Date: 31-08-2007
Seroprevalence of Toxoplasma gondii Infection in Refugee and Migrant Pregnant Women along the Thailand–Myanmar Border
Publisher: American Society of Tropical Medicine and Hygiene
Date: 12-07-2017
Silane flow rate dependence of SiOx cap layer induced impurity-free intermixing of GaAs/AlGaAs quantum wells
Publisher: The Electrochemical Society
Date: 2000
DOI: 10.1149/1.1393464
The invisible burden of malaria-attributable stillbirths
Publisher: Elsevier BV
Date: 2020
Transient Terahertz Conductivity of GaAs Nanowires
Publisher: American Chemical Society (ACS)
Date: 27-06-2007
DOI: 10.1021/NL071162X
Global, regional, and national progress towards Sustainable Development Goal 3.2 for neonatal and child health: all-cause and cause-specific mortality findings from the Global Burden of Disease Study
Publisher: Elsevier BV
Date: 09-2021
Obstetric ultrasound aids prompt referral of gestational trophoblastic disease in marginalized populations on the Thailand–Myanmar border
Publisher: Informa UK Limited
Date: 2017
Electrically programmable solid-state metasurfaces via flash localised heating
Publisher: Springer Science and Business Media LLC
Date: 22-02-2023
DOI: 10.1038/S41377-023-01078-6
Abstract: In the last decades, metasurfaces have attracted much attention because of their extraordinary light-scattering properties. However, their inherently static geometry is an obstacle to many applications where dynamic tunability in their optical behaviour is required. Currently, there is a quest to enable dynamic tuning of metasurface properties, particularly with fast tuning rate, large modulation by small electrical signals, solid state and programmable across multiple pixels. Here, we demonstrate electrically tunable metasurfaces driven by thermo-optic effect and flash-heating in silicon. We show a 9-fold change in transmission by V biasing voltage and the modulation rise-time of µs. Our device consists of a silicon hole array metasurface encapsulated by transparent conducting oxide as a localised heater. It allows for video frame rate optical switching over multiple pixels that can be electrically programmed. Some of the advantages of the proposed tuning method compared with other methods are the possibility to apply it for modulation in the visible and near-infrared region, large modulation depth, working at transmission regime, exhibiting low optical loss, low input voltage requirement, and operating with higher than video-rate switching speed. The device is furthermore compatible with modern electronic display technologies and could be ideal for personal electronic devices such as flat displays, virtual reality holography and light detection and ranging, where fast, solid-state and transparent optical switches are required.
Effect of dopants in the spin-on glass layer on the bandgap shift in GaAs/AlGaAs and InGaAs/AlGaAs intermixed quantum wells
Publisher: IEEE
Date: 2000
High power, kink-free 970 nm InGaAs/AlGaAs laser diodes with asymmetric structure
Publisher: IEEE
Date: 2000
Erratum: ‘‘Picosecond carrier lifetime in GaAs implanted with high doses of As ions: An alternative to low-temperature GaAs for optoelectronic applications’’ [Appl. Phys. Lett. 66, 3304 (1995)]
Publisher: AIP Publishing
Date: 18-03-1996
DOI: 10.1063/1.116788
Ion-implanted InP for ultrafast photodetector applications
Publisher: IEEE
Date: 2000
Proton implantation and rapid thermal annealing effects on GaAs/AlGaAs quantum well infrared photodetectors
Publisher: Elsevier BV
Date: 11-1999
Nanomechanical behavior of single taper-free GaAs nanowires unravelled by in-situ TEM mechanical testing and molecular dynamics simulation
Publisher: Elsevier BV
Date: 03-2021
Temperature dependence of photoluminescence from single core-shell GaAs–AlGaAs nanowires
Publisher: AIP Publishing
Date: 23-10-2006
DOI: 10.1063/1.2364885
Abstract: Temperature-dependent polarized microphotoluminescence measurements of single GaAs∕AlGaAs core-shell nanowires are used to probe their electronic states. The low-temperature emission from these wires is strongly enhanced compared with that observed in bare GaAs nanowires and is strongly polarized, reflecting the dielectric mismatch between the nanowire and the surrounding air. The temperature-dependent band gap of the nanowires is seen to be somewhat different from that observed in bulk GaAs, and the PL rapidly quenches above 120K, with an activation energy of 17meV reflecting the presence of nonradiative defects.
Early life risk factors of motor, cognitive and language development: a pooled analysis of studies from low/middle-income countries
Publisher: BMJ
Date: 10-2019
DOI: 10.1136/BMJOPEN-2018-026449
Abstract: To determine the magnitude of relationships of early life factors with child development in low/middle-income countries (LMICs). Meta-analyses of standardised mean differences (SMDs) estimated from published and unpublished data. We searched Medline, bibliographies of key articles and reviews, and grey literature to identify studies from LMICs that collected data on early life exposures and child development. The most recent search was done on 4 November 2014. We then invited the first authors of the publications and investigators of unpublished studies to participate in the study. Studies that assessed at least one domain of child development in at least 100 children under 7 years of age and collected at least one early life factor of interest were included in the study. Linear regression models were used to assess SMDs in child development by parental and child factors within each study. We then produced pooled estimates across studies using random effects meta-analyses. We retrieved data from 21 studies including 20 882 children across 13 LMICs, to assess the associations of exposure to 14 major risk factors with child development. Children of mothers with secondary schooling had 0.14 SD (95% CI 0.05 to 0.25) higher cognitive scores compared with children whose mothers had primary education. Preterm birth was associated with 0.14 SD (–0.24 to –0.05) and 0.23 SD (–0.42 to –0.03) reductions in cognitive and motor scores, respectively. Maternal short stature, anaemia in infancy and lack of access to clean water and sanitation had significant negative associations with cognitive and motor development with effects ranging from −0.18 to −0.10 SDs. Differential parental, environmental and nutritional factors contribute to disparities in child development across LMICs. Targeting these factors from prepregnancy through childhood may improve health and development of children.
Origin of stress in radio frequency magnetron sputtered zinc oxide thin films
Publisher: AIP Publishing
Date: 15-03-2011
DOI: 10.1063/1.3552928
Abstract: Highly c-axis oriented ZnO thin films have been deposited on silicon substrates by planar rf magnetron sputtering under varying pressure (10–50 mTorr) and oxygen percentage (50–100%) in the reactive gas (Ar + O2) mixture. The as-grown films were found to be stressed over a wide range from −1 × 1011 to −2 × 108 dyne/cm2 that in turn depends strongly on the processing conditions, and the film becomes stress free at a unique combination of sputtering pressure and reactive gas composition. Raman spectroscopy and photoluminescence (PL) analyses identified the origin of stress as lattice distortion due to defects introduced in the ZnO thin film. FTIR study reveals that Zn-O bond becomes stronger with the increase in oxygen fraction in the reactive gas mixture. The lattice distortion or stress depends on the type of defects introduced during deposition. PL spectra show the formation of a shoulder in band emission with an increase in the processing pressure and are related to the presence of stress. The ratio of band emission to defect emission decreases with the increase in oxygen percentage from 50 to 100%. The studies show a correlation of stress with the structural, vibrational, and photoluminescence properties of the ZnO thin film. The systematic study of the stress will help in the fabrication of efficient devices based on ZnO film.
High vertical yield InP nanowire growth on Si(111) using a thin buffer layer
Publisher: IOP Publishing
Date: 24-10-2013
DOI: 10.1088/0957-4484/24/46/465602
Abstract: We demonstrate the growth of InP nanowires on Si(111) using a thin InP buffer layer. The buffer layer is grown using a two-step procedure. The initial layer formation is ensured by using a very low growth temperature. An extremely high V/III ratio is necessary to prevent In droplet formation at this low temperature. The second layer is grown on the initial layer at a higher temperature and we find that post-growth annealing of the buffer layer does not improve its crystal quality significantly. It is found that the layers inherently have the (111)B polarity. Nanowires grown on this buffer layer have the same morphology and optical properties as nanowires grown on InP (111)B substrates. The vertical yield of the nanowires grown on the buffer layer is over 97% and we also find that crystal defects in the buffer layer do not affect the morphology, vertical yield or optical properties of the nanowires significantly.
Mapping geographical inequalities in access to drinking water and sanitation facilities in low-income and middle-income countries, 2000–17
Publisher: Elsevier BV
Date: 09-2020
Carrier transfer and magneto-transport in single modulation-doped V-grooved quantum wire modified by ion implantation
Publisher: Elsevier BV
Date: 07-2006
Population Pharmacokinetics of the Antimalarial Amodiaquine: a Pooled Analysis To Optimize Dosing
Publisher: American Society for Microbiology
Date: 10-2018
DOI: 10.1128/AAC.02193-17
Abstract: Amodiaquine plus artesunate is the recommended antimalarial treatment in many countries where malaria is endemic. However, pediatric doses are largely based on a linear extrapolation from adult doses.
Development of Land Use Regression Models for PM2.5, PM2.5 Absorbance, PM10 and PMcoarse in 20 European Study Areas; Results of the ESCAPE Project
Publisher: American Chemical Society (ACS)
Date: 10-2012
DOI: 10.1021/ES301948K
Abstract: Land Use Regression (LUR) models have been used increasingly for modeling small-scale spatial variation in air pollution concentrations and estimating in idual exposure for participants of cohort studies. Within the ESCAPE project, concentrations of PM(2.5), PM(2.5) absorbance, PM(10), and PM(coarse) were measured in 20 European study areas at 20 sites per area. GIS-derived predictor variables (e.g., traffic intensity, population, and land-use) were evaluated to model spatial variation of annual average concentrations for each study area. The median model explained variance (R(2)) was 71% for PM(2.5) (range across study areas 35-94%). Model R(2) was higher for PM(2.5) absorbance (median 89%, range 56-97%) and lower for PM(coarse) (median 68%, range 32- 81%). Models included between two and five predictor variables, with various traffic indicators as the most common predictors. Lower R(2) was related to small concentration variability or limited availability of predictor variables, especially traffic intensity. Cross validation R(2) results were on average 8-11% lower than model R(2). Careful selection of monitoring sites, examination of influential observations and skewed variable distributions were essential for developing stable LUR models. The final LUR models are used to estimate air pollution concentrations at the home addresses of participants in the health studies involved in ESCAPE.
Probing valence band structure in wurtzite InP nanowires using excitation spectroscopy
Publisher: AIP Publishing
Date: 12-07-2010
DOI: 10.1063/1.3463036
Abstract: We use time-resolved photoluminescence spectroscopy and photoluminescence excitation spectroscopy to measure the valence band parameters of hexagonal wurtzite InP nanowires. The A exciton emission and excitation energy is observed at 1.504 eV as expected. Excitation spectra show that the B and C hole bands are 30 and 161 meV above the A hole band. From these measurements, we obtain the crystal field and spin-orbit energies of 52 meV and 139 meV, respectively.
Formation of Hierarchical InAs Nanoring / GaAs Nanowire Heterostructures
Publisher: Wiley
Date: 12-01-2009
Controlled growth of porous oxygen-deficient NiCo2O4 nanobelts as high-efficiency electrocatalysts for oxygen evolution reaction
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0CY01669A
Abstract: NiCo 2 O 4 with a controlled oxygen vacancy concentration introduced by an Ar-annealing process greatly improved OER activity.
Damage to epitaxial GaN layers by silicon implantation
Publisher: AIP Publishing
Date: 14-10-1996
DOI: 10.1063/1.117526
Abstract: Ion channeling and cross-sectional transmission electron microscopy were used to study the extent and nature of Si ion implantation damage in epitaxial GaN layers at liquid nitrogen temperature. Results indicate that displacement damage produced by the implantation undergoes substantial dynamic annealing during implantation. As a result, at moderate implantation doses residual implantation damage consists of a dense network of secondary defects, such as clusters and loops, which are a consequence of incomplete annihilation of implantation-produced defects. Amorphous layers can be produced, but the doses required are extremely high (≳1016 cm−2) and amorphization appears to ‘‘nucleate’’ at the surface.
Efficacy of artemisinin-based and quinine-based treatments for uncomplicated falciparum malaria in pregnancy: a protocol for systematic review and individual patient data (IPD) meta-analysis
Publisher: BMJ
Date: 05-2019
DOI: 10.1136/BMJOPEN-2018-027503
Abstract: Pregnant women are more vulnerable to malaria leading to adverse impact on both mothers and fetuses. However, knowledge on the efficacy and safety of antimalarials in pregnancy is limited by the paucity of randomised control trials and the lack of standardised protocols in this special subpopulation. Pooling in idual patient data (IPD) for meta-analysis could address in part these limitations to summarise accurately the currently available evidence on treatment efficacy and risk factors for treatment failure. To assess the treatment efficacy of artemisinin-based and quinine-based treatments for uncomplicated falciparum malaria in pregnancy, seven databases (Medline, Embase, Global Health, Cochrane Library, Scopus, Web of Science and Literatura Latino Americana em Ciências da Saúde) and two clinical trial registries (International Clinical Trials Registry Platform and ClinicalTrial.gov) were searched. Both interventional and observational cohort studies following up for at least 28 days will be included. IPD of the identified eligible published or unpublished studies will be sought by inviting principal investigators. Raw IPD will be shared through the web-based secure platform developed by the WorldWide Antimalarial Resistance Network using the established methodology. The primary objective is to compare the risk of PCR-corrected treatment failure among different treatments and to find the risk factors. One-stage IPD meta-analysis by Cox model with shared frailty will be conducted. A risk of bias assessment will be conducted to address the impact of unshared potential data and of the quality of in idual studies. Potential limitations include difficulty in acquiring the IPD and heterogeneity of the study designs due to the lack of standard. This IPD meta-analysis consists of secondary analyses of existing anonymous data and meets the criteria for waiver of ethics review by the Oxford Tropical Research Ethics Committee. The results of this IPD meta-analysis will be disseminated through open-access publications at peer-reviewed journals. The study results will lead to a better understanding of malaria treatment in pregnancy, which can be used for clinical decision-making and conducting further studies. CRD42018104013.
Integration of bandpass guided-mode resonance filters with mid-wavelength infrared photodetectors
Publisher: IOP Publishing
Date: 05-02-2013
Temperature dependent photoluminescence in oxygen ion implanted and rapid thermally annealed ZnO∕ZnMgO multiple quantum wells
Publisher: AIP Publishing
Date: 28-05-2007
DOI: 10.1063/1.2745264
Abstract: The authors investigate the effect of oxygen implantation and rapid thermal annealing in ZnO∕ZnMgO multiple quantum wells using photoluminescence. A blueshift in the photoluminescence is observed in the implanted s les. For a low implantation dose, a significant increase of activation energy and a slight increase of the photoluminescence efficiency are observed. This is attributed to the suppression of the point defect complexes and transformation between defect structures by implantation and subsequent rapid thermal annealing. A high dose of implantation leads to lattice damage and agglomeration of defects leading to large defect clusters, which result to an increase in nonradiative recombination.
Metalorganic chemical vapor deposition of GaAsN epilayers: microstructures and optical properties
Publisher: Elsevier BV
Date: 03-2004
Mapping local patterns of childhood overweight and wasting in low- and middle-income countries between 2000 and 2017
Publisher: Springer Science and Business Media LLC
Date: 20-04-2020
DOI: 10.1038/S41591-020-0807-6
Abstract: A double burden of malnutrition occurs when in iduals, household members or communities experience both undernutrition and overweight. Here, we show geospatial estimates of overweight and wasting prevalence among children under 5 years of age in 105 low- and middle-income countries (LMICs) from 2000 to 2017 and aggregate these to policy-relevant administrative units. Wasting decreased overall across LMICs between 2000 and 2017, from 8.4% (62.3 (55.1–70.8) million) to 6.4% (58.3 (47.6–70.7) million), but is predicted to remain above the World Health Organization’s Global Nutrition Target of % in over half of LMICs by 2025. Prevalence of overweight increased from 5.2% (30 (22.8–38.5) million) in 2000 to 6.0% (55.5 (44.8–67.9) million) children aged under 5 years in 2017. Areas most affected by double burden of malnutrition were located in Indonesia, Thailand, southeastern China, Botswana, Cameroon and central Nigeria. Our estimates provide a new perspective to researchers, policy makers and public health agencies in their efforts to address this global childhood syndemic.
Periodic dielectric structures for light-trapping in InGaAs/GaAs quantum well solar cells
Publisher: The Optical Society
Date: 02-04-2013
DOI: 10.1364/OE.21.00A324
Thermal annealing recovery of intersubband transitions in proton-irradiated GaAs/AlGaAs multiple quantum wells
Publisher: AIP Publishing
Date: 30-10-2000
DOI: 10.1063/1.1320846
Abstract: Intersubband transitions in 1 MeV proton-irradiated GaAs/AlGaAs multiple quantum wells were studied using an optical absorption technique and isochronal thermal annealing. The intersubband transitions were completely depleted in s les irradiated with doses as low as 4×1014 cm−2. More than 80% recovery of these depleted transitions was achieved after the s les were thermally annealed at temperatures less than 650 °C. The total integrated areas and peak position energies of the intersubband transitions in irradiated and unirradiated s les were monitored as a function of annealing temperature. It was noted that the recovery of the depleted intersubband transitions in irradiated s les depend on the irradiation dose and thermal annealing temperature.
Effects of thermal stress on interdiffusion in InGaAsN/GaAs quantum dots
Publisher: AIP Publishing
Date: 28-05-2004
DOI: 10.1063/1.1760886
Abstract: Thermal-stress controlled interdiffusion in InGaAsN/GaAs quantum dots (QDs) has been studied by deposition of titanium oxide (TiO2) layers combined with rapid thermal annealing. Without TiO2 cap layers, blueshifting of the band gap from 1.033 to 1.180 eV at 77 K has been observed after annealing at 850 °C for 30 s due to the thermal interdiffusion. The thermal interdiffusion has been effectively suppressed by depositing TiO2 layers on the s les without degrading the photoluminescence properties. By a combination of annealing temperature and TiO2 thickness, controlled blueshifting of the band gap has been achieved. We suggest that the mechanism of suppression of thermal interdiffusion is the thermal stress imposed on the QD structure generated by TiO2 layers during annealing.
Can misfit dislocations be located above the interface of InAs/GaAs (001) epitaxial quantum dots?
Publisher: Springer Science and Business Media LLC
Date: 31-08-2012
Abstract: InAs/GaAs(001) quantum dots grown by droplet epitaxy were investigated using electron microscopy. Misfit dislocations in relaxed InAs/GaAs(001) islands were found to be located approximately 2 nm above the crystalline s le surface, which provides an impression that the misfit dislocations did not form at the island/substrate interface. However, detailed microscopy data analysis indicates that the observation is in fact an artefact caused by the surface oxidation of the material that resulted in substrate surface moving down about 2 nm. As such, caution is needed in explaining the observed interfacial structure.
An avalanche-and-surge robust ultrawide-bandgap heterojunction for power electronics
Publisher: Springer Science and Business Media LLC
Date: 25-07-2023
DOI: 10.1038/S41467-023-40194-0
Abstract: Avalanche and surge robustness involve fundamental carrier dynamics under high electric field and current density. They are also prerequisites of any power device to survive common overvoltage and overcurrent stresses in power electronics applications such as electric vehicles, electricity grids, and renewable energy processing. Despite tremendous efforts to develop the next-generation power devices using emerging ultra-wide bandgap semiconductors, the lack of effective bipolar doping has been a daunting obstacle for achieving the necessary robustness in these devices. Here we report avalanche and surge robustness in a heterojunction formed between the ultra-wide bandgap n-type gallium oxide and the wide-bandgap p-type nickel oxide. Under 1500 V reverse bias, impact ionization initiates in gallium oxide, and the staggered band alignment favors efficient hole removal, enabling a high avalanche current over 50 A. Under forward bias, bipolar conductivity modulation enables the junction to survive over 50 A surge current. Moreover, the asymmetric carrier lifetime makes the high-level carrier injection dominant in nickel oxide, enabling a fast reverse recovery within 15 ns. This heterojunction breaks the fundamental trade-off between robustness and switching speed in conventional homojunctions and removes a key hurdle to advance ultra-wide bandgap semiconductor devices for power industrial applications.
Paediatric Research in Emergency Departments International Collaborative (PREDICT): first steps towards the development of an Australian and New Zealand research network.
Publisher: Wiley
Date: 04-2006
DOI: 10.1111/J.1742-6723.2006.00823.X
Abstract: Paediatric emergency research is h ered by a number of barriers that can be overcome by a multicentre approach. In 2004, an Australia and New Zealand-based paediatric emergency research network was formed, the Paediatric Research in Emergency Departments International Collaborative (PREDICT). The founding sites include all major tertiary children's hospital EDs in Australia and New Zealand and a major mixed ED in Australia. PREDICT aims to provide leadership and infrastructure for multicentre research at the highest standard, facilitate collaboration between institutions, health-care providers and researchers and ultimately improve patient outcome. Initial network-wide projects have been determined. The present article describes the development of the network, its structure and future goals.
Electronic properties of GaAs, InAs and InP nanowires studied by terahertz spectroscopy
Publisher: IOP Publishing
Date: 25-04-2013
DOI: 10.1088/0957-4484/24/21/214006
Abstract: We have performed a comparative study of ultrafast charge carrier dynamics in a range of III-V nanowires using optical pump-terahertz probe spectroscopy. This versatile technique allows measurement of important parameters for device applications, including carrier lifetimes, surface recombination velocities, carrier mobilities and donor doping levels. GaAs, InAs and InP nanowires of varying diameters were measured. For all s les, the electronic response was dominated by a pronounced surface plasmon mode. Of the three nanowire materials, InAs nanowires exhibited the highest electron mobilities of 6000 cm² V⁻¹ s⁻¹, which highlights their potential for high mobility applications, such as field effect transistors. InP nanowires exhibited the longest carrier lifetimes and the lowest surface recombination velocity of 170 cm s⁻¹. This very low surface recombination velocity makes InP nanowires suitable for applications where carrier lifetime is crucial, such as in photovoltaics. In contrast, the carrier lifetimes in GaAs nanowires were extremely short, of the order of picoseconds, due to the high surface recombination velocity, which was measured as 5.4 × 10⁵ cm s⁻¹. These findings will assist in the choice of nanowires for different applications, and identify the challenges in producing nanowires suitable for future electronic and optoelectronic devices.
Systematic literature review and meta-analysis of the efficacy of artemisinin-based and quinine-based treatments for uncomplicated falciparum malaria in pregnancy: methodological challenges
Publisher: Springer Science and Business Media LLC
Date: 12-2017
Suppression of interdiffusion in InGaAs/GaAs quantum dots using dielectric layer of titanium dioxide
Publisher: AIP Publishing
Date: 14-04-2003
DOI: 10.1063/1.1569046
Abstract: In this work, titanium dioxide (TiO2) film was deposited onto the In0.5Ga0.5As/GaAs quantum-dot structure by electron-beam evaporation to investigate its effect on interdiffusion. A large redshifted and broadened spectrum from the dot emission was observed compared with that from the uncapped (but annealed) reference s le, indicating the suppression of thermal interdiffusion due to TiO2 deposition. The structure was also capped with a silicon dioxide (SiO2) single layer or SiO2/TiO2 bilayer with the thickness of SiO2 varied from ∼6 to ∼145 nm. In the former case, an increased amount of impurity-free vacancy disordering (IFVD) was introduced with the increase of SiO2 thickness due to the enhanced Ga outdiffusion into the film. With TiO2 deposited on top, IFVD and thermal interdiffusion were suppressed to different extents with the variation of SiO2 thickness. To explain the suppression of interdiffusion, thermal stress introduced by the large thermal expansion coefficient of TiO2 (when compared with GaAs) as well as the metallurgical reactions between the TiO2 and GaAs were proposed as possible mechanisms.
Toward quantum-dot-based photonic integrated circuits
Publisher: SPIE
Date: 25-03-2005
DOI: 10.1117/12.592313
High-density, defect-free, and taper-restrained epitaxial GaAs nanowires induced from annealed Au thin films
Publisher: American Chemical Society (ACS)
Date: 08-03-2012
DOI: 10.1021/CG201725G
Electron-hole recombination properties of In0.5Ga0.5As/GaAs quantum dot solar cells and the influence on the open circuit voltage
Publisher: AIP Publishing
Date: 20-09-2010
DOI: 10.1063/1.3492836
Abstract: We report on a detailed analysis of the temperature dependent electrical properties of In0.5Ga0.5As/GaAs quantum dot solar cells. The effects leading to a reduction in the open circuit voltage are found to be the thermal injection of carriers from the n and p-type layers into the depletion region where they recombine with carriers occupying quantum dot states due to a thermal distribution. The departure of the device studied here from an ideal intermediate band solar cell is discussed.
Mapping geographical inequalities in childhood diarrhoeal morbidity and mortality in low-income and middle-income countries, 2000–17: analysis for the Global Burden of Disease Study 2017
Publisher: Elsevier BV
Date: 06-2020
Raman spectra, photoluminescence and dielectric relaxation in Bi 1.5 ZnNb1.5 O7 pyrochlore
Publisher: Elsevier BV
Date: 05-2011
Si-implantation activation annealing of GaN up to 1400°C
Publisher: Springer Science and Business Media LLC
Date: 04-1998
US Immigration Westernizes the Human Gut Microbiome
Publisher: Elsevier BV
Date: 11-2018
Plasmonic quantum dot solar cells for enhanced infrared response
Publisher: AIP Publishing
Date: 05-03-2012
DOI: 10.1063/1.3691917
Abstract: Enhanced near infrared photoresponse in plasmonic InGaAs/GaAs quantum dot solar cells (QDSC) is demonstrated. Long wavelength light absorption in the wetting-layer and quantum-dot region of the quantum dot solar cell is enhanced through scattering of light by silver nanoparticles deposited on the solar cell surface. Plasmonic light trapping results in simultaneous increase in short-circuit current density by 5.3% and open circuit voltage by 0.9% in the QDSC, leading to an overall efficiency enhancement of 7.6%.
3D Atomic‐Scale Insights into Anisotropic Core–Shell‐Structured InGaAs Nanowires Grown by Metal–Organic Chemical Vapor Deposition
Publisher: Wiley
Date: 19-06-2017
Abstract: III–V ternary InGaAs nanowires have great potential for electronic and optoelectronic device applications however, the 3D structure and chemistry at the atomic‐scale inside the nanowires remain unclear, which hinders tailoring the nanowires for specific applications. Here, atom probe tomography is used in conjunction with a first‐principles simulation to investigate the 3D structure and chemistry of InGaAs nanowires, and reveals i) the nanowires form a spontaneous core–shell structure with a Ga‐enriched core and an In‐enriched shell, due to different growth mechanisms in the axial and lateral directions ii) the shape of the core evolves from hexagon into Reuleaux triangle and grows larger, which results from In outward and Ga inward interdiffusion occurring at the core–shell interface and iii) the irregular hexagonal shell manifests an anisotropic growth rate on {112}A and {112}B facets. Accordingly, a model in terms of the core–shell shape and chemistry evolution is proposed, which provides fresh insights into the growth of these nanowires.
Global, regional, and national mortality among young people aged 10–24 years, 1950–2019: a systematic analysis for the Global Burden of Disease Study 2019
Publisher: Elsevier BV
Date: 10-2021
Single nanowire photoconductive terahertz detectors
Publisher: American Chemical Society (ACS)
Date: 18-12-2015
DOI: 10.1021/NL5033843
Abstract: Spectroscopy and imaging in the terahertz (THz) region of the electromagnetic spectrum has proven to provide important insights in fields as erse as chemical analysis, materials characterization, security screening, and nondestructive testing. However, compact optoelectronics suited to the most powerful terahertz technique, time-domain spectroscopy, are lacking. Here, we implement single GaAs nanowires as microscopic coherent THz sensors and for the first time incorporated them into the pulsed time-domain technique. We also demonstrate the functionality of the single nanowire THz detector as a spectrometer by using it to measure the transmission spectrum of a 290 GHz low pass filter. Thus, nanowires are shown to be well suited for THz device applications and hold particular promise as near-field THz sensors.
Longer exposure to a new refugee food ration is associated with reduced prevalence of small for gestational age: results from 2 cross-sectional surveys on the Thailand-Myanmar border
Publisher: Elsevier BV
Date: 06-2017
Photo-assisted synthesis of coaxial-structured polypyrrole/electrochemically hydrogenated TiO2 nanotube arrays as a high performance supercapacitor electrode
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C7RA13166F
Abstract: An organic–inorganic coaxial-structured hybrid of PPy/EH-TNTAs electrode was developed and applied for high performance supercapacitors.
Measuring universal health coverage based on an index of effective coverage of health services in 204 countries and territories, 1990–2019: a systematic analysis for the Global Burden of Disease Study
Publisher: Elsevier BV
Date: 10-2020
Liquid crystal based nonlinear fishnet metamaterials
Publisher: AIP Publishing
Date: 19-03-2012
DOI: 10.1063/1.3695165
Abstract: We study experimentally the nonlinear properties of fishnet metamaterials infiltrated with nematic liquid crystals and find that moderate laser powers result in significant changes of the optical transmission of the composite structures. We also show that the nonlinear response of our structure can be further tuned with a bias electric field, enabling the realization of electrically tunable nonlinear metamaterials.
Electron-Beam Patterning of Polymer Electrolyte Films To Make Multiple Nanoscale Gates for Nanowire Transistors
Publisher: American Chemical Society (ACS)
Date: 18-12-2014
DOI: 10.1021/NL403299U
Abstract: We report an electron-beam based method for the nanoscale patterning of the poly(ethylene oxide)/LiClO4 polymer electrolyte. We use the patterned polymer electrolyte as a high capacitance gate dielectric in single nanowire transistors and obtain subthreshold swings comparable to conventional metal/oxide wrap-gated nanowire transistors. Patterning eliminates gate/contact overlap, which reduces parasitic effects and enables multiple, independently controllable gates. The method's simplicity broadens the scope for using polymer electrolyte gating in studies of nanowires and other nanoscale devices.
Optimised Two-Temperature Growth of GaAs Nanowires by Metalorganic Chemical Vapour Deposition
Publisher: IEEE
Date: 12-2006
Implant isolation of AlGaAs multilayer DBR
Publisher: Elsevier BV
Date: 06-2004
Quantum confinement of excitons in wurtzite InP nanowires
Publisher: AIP Publishing
Date: 19-05-2015
DOI: 10.1063/1.4921109
Abstract: Exciton resonances are observed in photocurrent spectra of 80 nm wurtzite InP nanowire devices at low temperatures, which correspond to transitions between the A, B, and C valence bands and the lower conduction band. Photocurrent spectra for 30 nm WZ nanowires exhibit shifts of the exciton resonances to higher energy, which are consistent with finite element calculations of wavefunctions of the confined electrons and holes for the various bands.
Quantitative study of GaAs nanowires catalyzed by Au film of different thicknesses
Publisher: Springer Science and Business Media LLC
Date: 24-10-2012
Abstract: In this letter, we quantitatively investigated epitaxial GaAs nanowires catalyzed by thin Au films of different thicknesses on GaAs (111) B substrates in a metal-organic chemical vapor deposition reactor. Prior to nanowire growth, the de-wetting of Au thin films to form Au nanoparticles on GaAs (111) B in AsH 3 ambient at different temperatures is investigated. It is found that with increasing film thickness, the size of the Au nanoparticles increases while the density of the nanoparticles reduces. Furthermore, higher annealing temperature produces larger Au nanoparticles for a fixed film thickness. As expected, the diameters and densities of the as-grown GaAs nanowires catalyzed by these thin Au films reflect these trends.
Thermal stability of ion-implanted ZnO
Publisher: AIP Publishing
Date: 12-2005
DOI: 10.1063/1.2140481
Abstract: Zinc oxide single crystals implanted at room temperature with high-dose (1.4×1017cm−2) 300 keV As+ ions are annealed at 1000–1200 °C. Damage recovery is studied by a combination of Rutherford backscattering/channeling spectrometry (RBS/C), cross-sectional transmission electron microscopy (XTEM), and atomic force microscopy. Results show that such a thermal treatment leads to the decomposition and evaporation of the heavily damaged layer instead of apparent defect recovery and recrystallization that could be inferred from RBS/C and XTEM data alone. This study shows that heavily damaged ZnO has relatively poor thermal stability compared to as-grown ZnO which is a significant result and has implications for understanding results on thermal annealing of ion-implanted ZnO.
Origin of gate hysteresis in p-type Si-doped AlGaAs/GaAs heterostructures
Publisher: American Physical Society (APS)
Date: 08-10-2012
Structural, electrical, and optical studies of GaAs implanted with MeV As or Ga Ions
Publisher: Springer Science and Business Media LLC
Date: 05-1997
Unequal P Distribution in Nanowires and the Planar Layer during GaAsP Growth on GaAs {111}B by Metal–Organic Chemical Vapor Deposition
Publisher: American Chemical Society (ACS)
Date: 04-09-2013
DOI: 10.1021/JP406294T
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Funder: Australian Research Council
View Funded ActivityLinkage Projects - Grant ID: LP180100332
Start Date: 08-2019
End Date: 12-2022
Amount: $430,000.00
Funder: Australian Research Council
View Funded ActivityLinkage Infrastructure, Equipment And Facilities - Grant ID: LE100100104
Start Date: 2010
End Date: 12-2011
Amount: $400,000.00
Funder: Australian Research Council
View Funded ActivityLinkage Infrastructure, Equipment And Facilities - Grant ID: LE190100014
Start Date: 06-2019
End Date: 06-2020
Amount: $376,358.00
Funder: Australian Research Council
View Funded ActivityLinkage Infrastructure, Equipment And Facilities - Grant ID: LE210100125
Start Date: 2021
End Date: 04-2022
Amount: $837,000.00
Funder: Australian Research Council
View Funded ActivityDiscovery Projects - Grant ID: DP110102003
Start Date: 2011
End Date: 12-2014
Amount: $556,000.00
Funder: Australian Research Council
View Funded ActivitySpecial Research Initiatives - Grant ID: SR0354682
Start Date: 12-2003
End Date: 12-2004
Amount: $10,000.00
Funder: Australian Research Council
View Funded ActivityLinkage Infrastructure, Equipment And Facilities - Grant ID: LE0882816
Start Date: 08-2008
End Date: 05-2009
Amount: $500,000.00
Funder: Australian Research Council
View Funded ActivityLinkage Infrastructure, Equipment And Facilities - Grant ID: LE200100174
Start Date: 11-2020
End Date: 12-2022
Amount: $425,000.00
Funder: Australian Research Council
View Funded ActivityDiscovery Projects - Grant ID: DP140103278
Start Date: 04-2014
End Date: 12-2016
Amount: $475,000.00
Funder: Australian Research Council
View Funded ActivityResearch Networks - Grant ID: RN0459611
Start Date: 07-2004
End Date: 12-2010
Amount: $1,900,000.00
Funder: Australian Research Council
View Funded Activity