ORCID Profile
0000-0002-5050-4202
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)
Condensed Matter Physics | Nanotechnology | Nanotechnology | Materials Engineering | Materials Engineering Not Elsewhere Classified | Surfaces and Structural Properties of Condensed Matter | Condensed Matter Physics—Structural Properties | Condensed Matter Characterisation Technique Development | Nanoscale Characterisation | Other Electronic Engineering | Compound Semiconductors | Elemental Semiconductors | Optics And Opto-Electronic Physics | Nanofabrication, Growth and Self Assembly | Mathematical Physics | Photodetectors, Optical Sensors and Solar Cells | Optical And Photonic Systems | Condensed Matter Physics not elsewhere classified | Nanomaterials | Communications Technologies | Interdisciplinary Engineering Not Elsewhere Classified | Photonics, Optoelectronics and Optical Communications | Electronic and Magnetic Properties of Condensed Matter; Superconductivity | Condensed Matter Physics—Electronic And Magnetic Properties; | Condensed Matter Imaging | Condensed Matter Physics—Other
ANZSRC Socio-Economic Objective (SEO)
Integrated circuits and devices | Physical sciences | Expanding Knowledge in the Physical Sciences | Communication equipment not elsewhere classified | Other | Solar-Photovoltaic Energy | Expanding Knowledge in Engineering | Telecommunications | Ceramics | Preparation and Production of Energy Sources not elsewhere classified | Manufacturing not elsewhere classified | Earth sciences | Expanding Knowledge in Technology | Expanding Knowledge in the Chemical Sciences |
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Publications
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.
Understanding the role of facets and twin defects in the optical performance of GaAs nanowires for laser applications
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1NH00079A
Abstract: GaAs nanowires are regarded as promising building blocks of future optoelectronic devices.
Total area of spontaneous portosystemic shunts independently predicts hepatic encephalopathy and mortality in liver cirrhosis
Publisher: Elsevier BV
Date: 06-2020
DOI: 10.1016/J.JHEP.2019.12.021
Abstract: Spontaneous portosystemic shunts (SPSS) frequently develop in liver cirrhosis. Recent data suggested that the presence of a single large SPSS is associated with complications, especially overt hepatic encephalopathy (oHE). However, the presence of >1 SPSS is common. This study evaluates the impact of total cross-sectional SPSS area (TSA) on outcomes in patients with liver cirrhosis. In this retrospective international multicentric study, CT scans of 908 cirrhotic patients with SPSS were evaluated for TSA. Clinical and laboratory data were recorded. Each detected SPSS radius was measured and TSA calculated. One-year survival was the primary endpoint and acute decompensation (oHE, variceal bleeding, ascites) was the secondary endpoint. A total of 301 patients (169 male) were included in the training cohort. Thirty percent of all patients presented with >1 SPSS. A TSA cut-off of 83 mm This study suggests that TSA >83 mm The prevalence of spontaneous portosystemic shunts (SPSS) is higher in patients with more advanced chronic liver disease. The presence of more than 1 SPSS is common in advanced chronic liver disease and is associated with the development of hepatic encephalopathy. This study shows that total cross-sectional SPSS area (rather than diameter of the single largest SPSS) predicts survival in patients with advanced chronic liver disease. Our results support the clinical use of total cross-sectional SPSS area for risk stratification and decision-making in the management of SPSS.
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.
Simultaneous Selective-Area and Vapor-Liquid-Solid Growth of InP Nanowire Arrays
Publisher: American Chemical Society (ACS)
Date: 06-06-2016
DOI: 10.1021/ACS.NANOLETT.6B01461
Abstract: Selective-area epitaxy is highly successful in producing application-ready size-homogeneous arrays of III-V nanowires without the need to use metal catalysts. Previous works have demonstrated excellent control of nanowire properties but the growth mechanisms remain rather unclear. Herein, we report a detailed growth study revealing that fundamental growth mechanisms of pure wurtzite InP ⟨111⟩A nanowires can indeed differ significantly from the simple picture of a facet-limited selective-area growth process. A dual growth regime with and without metallic droplet is found to coexist under the same growth conditions for different diameter nanowires. Incubation times and highly nonmonotonous growth rate behaviors are revealed and explained within a dedicated kinetic model.
Voids and Nanocavities in Silicon
Publisher: Springer Berlin Heidelberg
Date: 2009
Selective Intermixing of InGaAs/GaAs Quantum Dot Infrared Photodetectors
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2011
Nanoindentation-induced deformation of Ge
Publisher: AIP Publishing
Date: 10-04-2002
DOI: 10.1063/1.1469660
Abstract: The deformation mechanisms of crystalline (100) Ge were studied using nanoindentation, cross sectional transmission electron microscopy (XTEM) and Raman microspectroscopy. For a wide range of indentation conditions using both spherical and pointed indenters, multiple discontinuities were found in the force–displacement curves on loading, but no discontinuities were found on unloading. Raman microspectroscopy, measured from s les which had plastically deformed on loading, showed a spectrum shift from that in pristine Ge, suggesting only residual strain. No evidence (such as extra Raman bands) was found to suggest that any pressure-induced phase transformations had occurred, despite the fact that the material had undergone severe plastic deformation. Selected area diffraction pattern studies of the mechanically damaged regions also confirmed the absence of additional phases. Moreover, XTEM showed that, at low loads, plastic deformation occurs by twinning and dislocation motion. This indicates that the hardness of Ge measured by indentation is not primarily dominated by phase transformation, rather by the nucleation and propagation of twin bands and/or dislocations.
Effects of high temperature annealing on defects and luminescence properties in H implanted ZnO
Publisher: IOP Publishing
Date: 29-07-2014
Electronic comparison of InAs wurtzite and zincblende phases using nanowire transistors
Publisher: Wiley
Date: 25-07-2013
Study of defects in ion-implanted silicon using photoluminescence and positron annihilation
Publisher: Elsevier BV
Date: 12-2003
Anderson-like localization in ultrathin nanocomposite alloy films on polymeric substrates
Publisher: Elsevier BV
Date: 11-2012
Ion implantation effects in silicon with high carbon content characterised by photoluminescence
Publisher: Elsevier BV
Date: 12-2003
InAs quantum dots grown on InGaAs buffer layers by metal-organic chemical vapor deposition
Publisher: Elsevier BV
Date: 08-2005
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.
Identification by photoluminescence and positron annihilation of vacancy and interstitial intrinsic defects in ion-implanted silicon
Publisher: AIP Publishing
Date: 10-2006
DOI: 10.1063/1.2354332
Abstract: Defect centers generated in crystalline silicon by MeV Si implants have been investigated by a combination of photoluminescence, variable-energy positron annihilation measurements, depth profiling by etching, annealing studies, and the dependence on impurities. The broad 935meV photoluminescence band occurs at intrinsic interstitial complexes, the 835meV band at small vacancy clusters, and the 1062meV line at a low concentration of vacancy clusters which are possibly formed by aggregation of the 835meV centers.
Ion mass effect on vacancy-related deep levels in Si induced by ion implantation
Publisher: American Physical Society (APS)
Date: 28-05-2002
Measuring the electrical properties of semiconductor nanowires using terahertz conductivity spectroscopy
Publisher: SPIE
Date: 07-12-2013
DOI: 10.1117/12.2049016
Critical Temperature for the Conversion from Wurtzite to Zincblende of the Optical Emission of InAs Nanowires
Publisher: American Chemical Society (ACS)
Date: 21-07-2017
Photoluminescence Excitation Spectroscopy of Diffused Layers on Crystalline Silicon Wafers
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2016
Electric field assisted annealing and formation of prominent deep-level defect in ion-implanted n-type 4H-SiC
Publisher: AIP Publishing
Date: 07-04-2008
DOI: 10.1063/1.2907693
Abstract: High-purity and low-doped n-type epitaxial layers of 4H-SiC have been implanted with N and C ions by using energies in the MeV range and doses from 2×108to1×109cm−2. Postimplant annealing was performed at 1100°C prior to s le analysis by deep-level transient spectroscopy (DLTS). A drastic and irreversible instability of the prominent EH7 deep-level defect occurs during the first DLTS temperature scan because of the electric field applied during the measurements. Depending on the implanted species, EH7 can decrease (N implants) as well as increase (C implants) in strength and the effect is attributed to charge-state controlled annealing and formation processes of EH7. The origin of EH7 is discussed and the experimental data support a model invoking interstitial C atoms.
Flow modulation epitaxy of hexagonal boron nitride
Publisher: IOP Publishing
Date: 14-08-2018
Tailoring GaAs, InAs, and InGaAs Nanowires for Optoelectronic Device Applications
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2011
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.
Probing the critical electronic properties of III-V nanowires using optical pump-terahertz probe spectroscopy
Publisher: IEEE
Date: 09-2013
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.
Tuning the bandgap of InAs quantum dots by selective-area MOCVD
Publisher: IOP Publishing
Date: 14-03-2008
Ion-implantation-induced extended defect formation in (0001) and (11(2)over-bar0) 4H-SiC
Publisher: American Physical Society (APS)
Date: 26-04-2005
Perovskite Photovoltaic Integrated CdS/TiO2 Photoanode for Unbiased Photoelectrochemical Hydrogen Generation
Publisher: American Chemical Society (ACS)
Date: 25-06-2018
Abstract: Photoelectrolysis of water using solar energy into storable and environment-friendly chemical fuel in the form of hydrogen provides a potential solution to address the environmental concerns and fulfill future energy requirements in a sustainable manner. Achieving efficient and spontaneous hydrogen evolution in water using solar light as the only energy input is a highly desirable but a difficult target. In this work, we report perovskite solar cell integrated CdS-based photoanode for unbiased photoelectrochemical hydrogen evolution. An integrated tandem device consisting of mesoporous CdS/TiO
Insights into Twinning Formation in Cubic and Tetragonal Multi-cation Mixed-Halide Perovskite
Publisher: American Chemical Society (ACS)
Date: 11-03-2020
Fluence, flux, and implantation temperature dependence of ion-implantation-induced defect production in 4H–SiC
Publisher: AIP Publishing
Date: 06-01-2005
DOI: 10.1063/1.1844618
Abstract: Vacancy-type defect production in Al- and Si-implanted 4H–SiC has been studied as a function of ion fluence, ion flux, and implantation temperature in the projected ion range region by positron annihilation spectroscopy and Rutherford backscattering techniques. Ion channeling measurements show that the concentration of displaced silicon atoms increases rapidly with increasing ion fluence. In the ion fluence interval of 1013–1014cm−2 the positron annihilation parameters are roughly constant at a defect level tentatively associated with the acancy VCVSi. Above the ion fluence of 1014cm−2 larger vacancy clusters are formed. For implantations as a function of ion flux (cm−2s−1), ion channeling and positron annihilation measurements behave similarly, i.e., indicating increasing damage in the projected range region with increasing ion flux. However, for s les implanted at different temperatures the positron annihilation parameter S shows a clear minimum at approximately 100°C, whereas the normalized backscattering yield decrease continuously with increasing implantation temperature. This is explained by the formation of larger vacancy clusters when the implantation temperature is increased.
Capture cross sections of the acceptor level of iron-boron pairs in p-type silicon by injection-level dependent lifetime measurements
Publisher: AIP Publishing
Date: 15-06-2001
DOI: 10.1063/1.1372156
Abstract: Injection-level dependent recombination lifetime measurements of iron-diffused, boron-doped silicon wafers of different resistivities are used to determine the electron and hole capture cross sections of the acceptor level of iron–boron pairs in silicon. The relative populations of iron–boron pairs and interstitial iron were varied by exposing the s les to different levels of illumination prior to lifetime measurements. The components of the effective lifetime due to interstitial iron and iron–boron pairs were then modeled with Shockley–Read–Hall statistics. By forcing the sum of the modeled iron–boron and interstitial iron concentrations to equal the implanted iron dose, in conjunction with the strong dependence of the shape of the lifetime curves on dopant density, the electron and hole capture cross sections of the acceptor level of iron–boron pairs have been determined as (3±2)×10−14 cm−2 and (2±1)×10−15 cm−2.
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.
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.
Understanding the Chemical and Structural Properties of Multiple-Cation Mixed Halide Perovskite
Publisher: American Chemical Society (ACS)
Date: 08-10-2019
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).
Electron-pinned defect-dipoles for high-performance colossal permittivity materials
Publisher: Springer Science and Business Media LLC
Date: 30-06-2013
DOI: 10.1038/NMAT3691
Abstract: The immense potential of colossal permittivity (CP) materials for use in modern microelectronics as well as for high-energy-density storage applications has propelled much recent research and development. Despite the discovery of several new classes of CP materials, the development of such materials with the required high performance is still a highly challenging task. Here, we propose a new electron-pinned, defect-dipole route to ideal CP behaviour, where hopping electrons are localized by designated lattice defect states to generate giant defect-dipoles and result in high-performance CP materials. We present a concrete ex le, (Nb+In) co-doped TiO₂ rutile, that exhibits a largely temperature- and frequency-independent colossal permittivity (> 10(4)) as well as a low dielectric loss (mostly < 0.05) over a very broad temperature range from 80 to 450 K. A systematic defect analysis coupled with density functional theory modelling suggests that 'triangular' In₂(3+)Vo(••)Ti(3+) and 'diamond' shaped Nb₂(5+)Ti(3+)A(Ti) (A = Ti(3+)/In(3+)/Ti(4+)) defect complexes are strongly correlated, giving rise to large defect-dipole clusters containing highly localized electrons that are together responsible for the excellent CP properties observed in co-doped TiO₂. This combined experimental and theoretical work opens up a promising feasible route to the systematic development of new high-performance CP materials via defect engineering.
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.
Vacancy and interstitial depth profiles in ion-implanted silicon
Publisher: AIP Publishing
Date: 27-12-2003
DOI: 10.1063/1.1528304
Abstract: An experimental method of studying shifts between concentration-versus-depth profiles of vacancy- and interstitial-type defects in ion-implanted silicon is demonstrated. The concept is based on deep level transient spectroscopy measurements utilizing the filling pulse variation technique. The vacancy profile, represented by the vacancy–oxygen center, and the interstitial profile, represented by the interstitial carbon–substitutional carbon pair, are obtained at the same s le temperature by varying the duration of the filling pulse. The effect of the capture in the Debye tail has been extensively studied and taken into account. Thus, the two profiles can be recorded with a high relative depth resolution. Using low doses, point defects have been introduced in lightly doped float zone n-type silicon by implantation with 6.8 MeV boron ions and 680 keV and 1.3 MeV protons at room temperature. The effect of the angle of ion incidence has also been investigated. For all implantation conditions the peak of the interstitial profile is displaced towards larger depths compared to that of the vacancy profile. The litude of this displacement increases as the width of the initial point defect distribution increases. This behavior is explained by a simple model where the preferential forward momentum of recoiling silicon atoms and the highly efficient direct recombination of primary point defects are taken into account.
Association Between Portosystemic Shunts and Increased Complications and Mortality in Patients With Cirrhosis
Publisher: Elsevier BV
Date: 05-2018
DOI: 10.1053/J.GASTRO.2018.01.028
Abstract: Spontaneous portosystemic shunts (SPSS) have been associated with hepatic encephalopathy (HE). Little is known about their prevalence among patients with cirrhosis or clinical effects. We investigated the prevalence and characteristics of SPSS in patients with cirrhosis and their outcomes. We performed a retrospective study of 1729 patients with cirrhosis who underwent abdominal computed tomography or magnetic resonance imaging analysis from 2010 through 2015 at 14 centers in Canada and Europe. We collected data on demographic features, etiology of liver disease, comorbidities, complications, treatments, laboratory and clinical parameters, Model for End-Stage Liver Disease (MELD) score, and endoscopy findings. Abdominal images were reviewed by a radiologist (or a hepatologist trained by a radiologist) and searched for the presence of SPSS, defined as spontaneous communications between the portal venous system or splanchnic veins and the systemic venous system, excluding gastroesophageal varices. Patients were assigned to groups with large SPSS (L-SPSS, ≥8 mm), small SPSS (S-SPSS, <8 mm), or without SPSS (W-SPSS). The main outcomes were the incidence of complications of cirrhosis and mortality according to the presence of SPSS. Secondary measurements were the prevalence of SPSS in patients with cirrhosis and their radiologic features. L-SPSS were identified in 488 (28%) patients, S-SPSS in 548 (32%) patients, and no shunt (W-SPSS) in 693 (40%) patients. The most common L-SPSS was splenorenal (46% of L-SPSS). The presence and size of SPSS increased with liver dysfunction: among patients with MELD scores of 6-9, 14% had L-SPSS and 28% had S-SPSS among patients with MELD scores of 10-13, 30% had L-SPSS and 34% had S-SPSS among patients with MELD scores of 14 or higher, 40% had L-SPSS and 32% had S-SPSS (P < .001 for multiple comparison among MELD groups). HE was reported in 48% of patients with L-SPSS, 34% of patients with S-SPSS, and 20% of patients W-SPSS (P < .001 for multiple comparison among SPSS groups). Recurrent or persistent HE was reported in 52% of patients with L-SPSS, 44% of patients with S-SPSS, and 37% of patients W-SPSS (P = .007 for multiple comparison among SPSS groups). Patients with SPSS also had a larger number of portal hypertension-related complications (bleeding or ascites) than those W-SPSS. Quality of life and transplantation-free survival were lower in patients with SPSS vs without. SPSS were an independent factor associated with death or liver transplantation (hazard ratio, 1.26 95% confidence interval, 1.06-1.49) (P = .008) in multivariate analysis. When patients were stratified by MELD score, SPSS were associated with HE independently of liver function: among patients with MELD scores of 6-9, HE was reported in 23% with L-SPSS, 12% with S-SPSS, and 5% with W-SPSS (P < .001 for multiple comparison among SPSS groups) among those with MELD scores of 10-13, HE was reported in 48% with L-SPSS, 33% with S-SPSS, and 23% with W-SPSS (P < .001 for multiple comparison among SPSS groups) among patients with MELD scores of 14 or more, HE was reported in 59% with L-SPSS, 57% with S-SPSS, and 48% with W-SPSS (P = .043 for multiple comparison among SPSS groups). Patients with SPSS and MELD scores of 6-9 were at higher risk for ascites (40.5% vs 23% P < .001) and bleeding (15% vs 9% P = .038) than patients W-SPSS and had lower odds of transplant-free survival (hazard ratio 1.71 95% confidence interval, 1.16-2.51) (P = .006). In a retrospective analysis of almost 2000 patients, we found 60% to have SPSS prevalence increases with deterioration of liver function. SPSS increase risk for HE and with a chronic course. In patients with preserved liver function, SPSS increase risk for complications and death. ClinicalTrials.gov ID NCT02692430.
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.
Effect of crystal orientation on the implant profile of 60 keV Al into 4H-SiC crystals
Publisher: AIP Publishing
Date: 19-05-2003
DOI: 10.1063/1.1569972
Abstract: 4H-SiC wafers of orientations (0001) and (112̄0) were implanted with 60 keV Al− in different major axial, planar, and low symmetry (“random”) directions to ascertain the degree of channeling and to determine the optimum tilt conditions for ion implantation. Significant channeling was observed for all axial directions with the [112̄0] channel exhibiting the deepest channeling with a maximum penetration depth 45 times greater than the projected range of the random implants. Significant channeling was observed for the {112̄0} and especially the {0001} planar channels while the implants in the {101̄0} planar channels did not differ from the corresponding random implants. To minimize channeling in (0001) crystals, our results show that beam alignment normal to the surface is advisable for off-axis (0001) wafers with the miscut toward 〈112̄0〉, while tilting of the wafer is necessary when the miscut is toward 〈101̄0〉. For the (112̄0) material, channeling can be minimized by a tilt of ≳10° toward the [0001] direction.
Forecast-skill-based simulation of streamflow forecasts
Publisher: Elsevier BV
Date: 09-2014
Erratum: Effects of high temperature annealing on defects and luminescence properties in H implanted ZnO (2014 J. Phys. D: Appl. Phys. 47 342001)
Publisher: IOP Publishing
Date: 10-09-2014
Engineering III–V Semiconductor Nanowires for Device Applications
Publisher: Wiley
Date: 17-10-2019
Abstract: III-V semiconductor nanowires offer potential new device applications because of the unique properties associated with their 1D geometry and the ability to create quantum wells and other heterostructures with a radial and an axial geometry. Here, an overview of challenges in the bottom-up approaches for nanowire synthesis using catalyst and catalyst-free methods and the growth of axial and radial heterostructures is given. The work on nanowire devices such as lasers, light emitting nanowires, and solar cells and an overview of the top-down approaches for water splitting technologies is reviewed. The authors conclude with an analysis of the research field and the future research directions.
Engineering the Photoresponse of InAs Nanowires
Publisher: American Chemical Society (ACS)
Date: 11-12-2017
Abstract: We report on in idual-InAs nanowire optoelectronic devices which can be tailored to exhibit either negative or positive photoconductivity (NPC or PPC). The NPC photoresponse time and magnitude is found to be highly tunable by varying the nanowire diameter under controlled growth conditions. Using hysteresis characterization, we decouple the observed photoexcitation-induced hot electron trapping from conventional electric field-induced trapping to gain a fundamental insight into the interface trap states responsible for NPC. Furthermore, we demonstrate surface passivation without chemical etching which both enhances the field-effect mobility of the nanowires by approximately an order of magnitude and effectively eliminates the hot carrier trapping found to be responsible for NPC, thus restoring an "intrinsic" positive photoresponse. This opens pathways toward engineering semiconductor nanowires for novel optical-memory and photodetector applications.
Tunable Polarity in a III-V Nanowire by Droplet Wetting and Surface Energy Engineering
Publisher: Wiley
Date: 17-09-2015
Abstract: Controllable axial switching of polarity in GaAs nanowires with minimal tapering and perfect twin-free ZB structure based on the fundamental understanding of nanowire growth and kinking mechanism is presented. The polarity of the bottom segment is confirmed to be (111)A by atomically resolved scanning transmission electron microscopy.
InGaAsP as a Promising Narrow Band Gap Semiconductor for Photoelectrochemical Water Splitting
Publisher: American Chemical Society (ACS)
Date: 24-06-2019
Abstract: While photoelectrochemical (PEC) water splitting is a very promising route toward zero-carbon energy, conversion efficiency remains limited. Semiconductors with narrower band gaps can absorb a much greater portion of the solar spectrum, thereby increasing efficiency. However, narrow band gap (∼1 eV) III-V semiconductor photoelectrodes have not yet been thoroughly investigated. In this study, the narrow band gap quaternary III-V alloy InGaAsP is demonstrated for the first time to have great potential for PEC water splitting, with the long-term goal of developing high-efficiency tandem PEC devices. TiO
A comparison of extended defect formation induced by ion implantation in (0001) and (11(2)over-bar-0) 4H-SiC
Publisher: Elsevier BV
Date: 12-2003
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.
Zn precipitation and Li depletion in Zn implanted ZnO
Publisher: AIP Publishing
Date: 11-07-2016
DOI: 10.1063/1.4958693
Abstract: Ion implantation of Zn substituting elements in ZnO has been shown to result in a dramatic Li depletion of several microns in hydrothermally grown ZnO. This has been ascribed to a burst of mobile Zn interstials. In this study, we seek to understand the reason behind this interstitial mediated transient enhanced diffusion in Li-containing ZnO s les after Zn implantation. ZnO wafers were implanted with Zn to two doses, 5 × 1015 cm−2 and 1 × 1017 cm−2. Secondary ion mass spectrometry was carried out to profile the Li depletion depth for different annealing temperatures between 600 and 800 °C. The 800 °C annealing had the most significant Li depletion of close to 60 μm. Transmission electron microscopy (TEM) was carried out in selected s les to identify the reason behind the Li depletion. In particular, TEM investigations of s les annealed at 750 °C show significant Zn precipitation just below the depth of the projected range of the implanted ions. We propose that the Zn precipitation is indicative of Zn supersaturation. Both the Li depletion and Zn precipitation are competing synchronous processes aimed at reducing the excess Zn interstitials.
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.
Suppression of ion-implantation induced porosity in germanium by a silicon dioxide capping layer
Publisher: AIP Publishing
Date: 22-08-2016
DOI: 10.1063/1.4961620
Abstract: Ion implantation with high ion fluences is indispensable for successful use of germanium (Ge) in the next generation of electronic and photonic devices. However, Ge readily becomes porous after a moderate fluence implant (∼1×1015 ion cm−2) at room temperature, and for heavy ion species such as tin (Sn), holding the target at liquid nitrogen (LN2) temperature suppresses porosity formation only up to a fluence of 2×1016 ion cm−2. We show, using stylus profilometry and electron microscopy, that a nanometer scale capping layer of silicon dioxide significantly suppresses the development of the porous structure in Ge during a Sn− implant at a fluence of 4.5×1016 ion cm−2 at LN2 temperature. The significant loss of the implanted species through sputtering is also suppressed. The effectiveness of the capping layer in preventing porosity, as well as suppressing sputter removal of Ge, permits the attainment of an implanted Sn concentration in Ge of ∼15 at.%, which is about 2.5 times the maximum value previously attained. The crystallinity of the Ge-Sn layer following pulsed-laser-melting induced solidification is also greatly improved compared with that of uncapped material, thus opening up potential applications of the Ge-Sn alloy as a direct bandgap material fabricated by an ion beam synthesis technique.
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.
Ion irradiation-induced disordering of semiconductors: defect structures and applications
Publisher: Informa UK Limited
Date: 02-2005
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.
Photoluminescence response of ion-implanted silicon
Publisher: AIP Publishing
Date: 30-10-2006
DOI: 10.1063/1.2378402
Abstract: The photoluminescence intensity from ion-implanted silicon can be quenched by the radiation damage implicit in the implantation. Annealing is then required before the intensity of the luminescence from a defect center is approximately proportional to the concentration of that center. Data from positron annihilation and photoluminescence experiments establish that severe quenching of the luminescence occurs when the mean separation of the small vacancy clusters is less than ∼30 atomic spacings, and the authors map out where, in the annealing and implantation phase space, the luminescence intensity is expected to be approximately proportional to the concentration of the optical centers.
Effect of boron on formation of interstitial-related luminescence centres in ion implanted silicon
Publisher: Wiley
Date: 09-12-2011
Ion implantation in 4H-SiC
Publisher: Elsevier BV
Date: 04-2008
Direct correlation of R-line luminescence with rod-like defect evolution in ion-implanted and annealed silicon
Publisher: Springer Science and Business Media LLC
Date: 09-2012
DOI: 10.1557/MRC.2012.17
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.
Characterisation of the Subthreshold Damage in MeV Ion Implanted p Si
Publisher: Springer Science and Business Media LLC
Date: 1998
DOI: 10.1557/PROC-510-411
Abstract: Subthreshold damage in p-type Si implanted and annealed at elevated temperature is characterized using deep level transient spectroscopy (DLTS) and transmission electron microscopy (TEM). P-type Si is implanted with Si, Ge and Sn with energies in the range of 4 to 8.5 MeV, doses from 7 × 10 12 to 1×10 14 cm −2 and all annealed at 800°C for 15 min. For each implanted specie, DLTS spectra show a transition dose called threshold dose above which point defects transform in to extended defects. DLTS measurements have shown for the doses below threshold, a sharp peak, corresponding to the signature of point defects and for doses above threshold a broad peak indicating the presence of extended defects. This is found to be consistent with TEM analyses where no defects are seen for the doses below threshold and the presence of extended defects for the doses above threshold. This suggests a defect transformation regime where point defects present below threshold are acting like nucleating sites for the extended defects. Also the mass dependence on the damage evolution has been observed, where rod-like defects are observed in the case of Si and (rod-like defects and loops) for Ge and Sn despite the fact that peak concentration of vacancies for Ge and Sn are normalized to the peak number of vacancies for Si.
Self-assembled Au nanoparticles in SiO2 by ion implantation and wet oxidation
Publisher: AIP Publishing
Date: 15-11-2009
DOI: 10.1063/1.3262621
Abstract: Implantation, annealing, and oxidation processes have been used to form Au nanoparticles with a narrow size and depth distribution in a SiO2 layer. Different approaches have been attempted: in particular, the gettering of Au to fill preformed nanocavities (obtained by H-implantation and annealing) and thus overcome the broad particle size distribution that is normally associated with nanoparticles formed by implantation and annealing. The results suggest that nanocavities cannot be directly formed in SiO2 by H-implantation and a subsequent annealing due partly to the high mobility of H atoms in SiO2. However, cavities formed in Si are useful in obtaining a narrow size and depth distribution of Au precipitates: the Si substrate can then be oxidized to form Au nanoparticles in SiO2. Sequential wet oxidations of Si s les containing Au nanoparticles have revealed several interesting phenomena, namely, segregation of Au particles at a growing oxide interface, Au-enhanced oxidation, dissolution and reprecipitation of Au precipitates during oxidation, and preferential wetting of Au on the oxide layer. In particular, the Au dissolution and reprecipitation processes are Si interstitial mediated. By completely oxidizing the top Si layer, an array of Au precipitates can be confined at a precise depth within a SiO2 layer corresponding to the front interface of a buried oxide layer. The size distribution of the resulting Au precipitates in SiO2 is smallest when Au is first gettered to cavities and vacancies are subsequently introduced into the Si layer prior to oxidation.
Improving the Morphology and Crystal Quality of AlN Grown on Two-Dimensional hBN
Publisher: American Chemical Society (ACS)
Date: 04-02-2020
Mn Implantation for New Applications of 4H-SiC
Publisher: Trans Tech Publications, Ltd.
Date: 05-2012
DOI: 10.4028/WWW.SCIENTIFIC.NET/MSF.717-720.221
Abstract: Structural disorder and lattice recovery of high dose, manganese implanted, semi-insulating, 4H-SiC have been studied by secondary ion mass spectrometry, Rutherford backscattering in channeling directions, visible-to-near infrared optical spectroscopy as well as with transmission electron microscopy. After heat treatment at 1400 and 1600 °C, a substantial rearrangement of manganese is observed in the implanted region. However, the crystal has not been fully recovered. More disorder remains in the [11 3] compared to the [0001] channel direction. Stacking faults, voids and 3C inclusions are observed in the implanted region. A Mn containing phase has most likely formed.
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
Impact of Halide Anions in CsX (X = I, Br, Cl) on the Microstructure and Photovoltaic Performance of FAPbI3-Based Perovskite Solar Cells
Publisher: Wiley
Date: 09-06-2022
Abstract: The key role of Cs cation and X halide anions (X = I, Br, Cl) on the microstructure, crystal structure, structural defects, optoelectronic properties, and photovoltaic parameters of FAPbI 3 ‐based perovskite solar cells is investigated. The CsCl–FAPbI 3 perovskite film shows the highest photoluminescence (PL) intensity, longest PL lifetime, and highest power conversion efficiency compared with the CsI–FAPbI 3 and CsBr–FAPbI 3 perovskite films. The morphology and crystallography of c nanotwins and stacking faults of perovskite films are studied using transmission electron microscopy and selected‐area electron diffraction. The microstructure, crystallography, and atomic structure model of intersecting twin boundaries are presented. Finally, the degradation pathways and the mechanism behind the formation of FAPbI 3 ‐based perovskites under ambient conditions are systematically studied. The grain boundaries of the perovskite films are nonuniformly damaged, resulting in many black nanoparticles after 4 weeks. Electron diffraction analyses of the black nanoparticles confirm the hexagonal PbI 2 phase formation in all CsX–FAPbI 3 perovskite s les after 4 weeks of aging.
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.
Dopant effects on the photoluminescence of interstitial-related centers in ion implanted silicon
Publisher: AIP Publishing
Date: 05-2012
DOI: 10.1063/1.4710991
Abstract: The dopant dependence of photoluminescence (PL) from interstitial-related centers formed by ion implantation and a subsequent anneal in the range 175–525 °C is presented. The evolution of these centers is strongly effected by interstitial-dopant clustering even in the low temperature regime. There is a significant decrease in the W line (1018.2 meV) PL intensity with increasing B concentration. However, an enhancement is also observed in a narrow fabrication window in s les implanted with either P or Ga. The anneal temperature at which the W line intensity is optimized is sensitive to the dopant concentration and type. Furthermore, dopants which are implanted but not activated prior to low temperature thermal processing are found to have a more detrimental effect on the resulting PL. Splitting of the X line (1039.8 meV) arising from implantation damage induced strain is also observed.
Multiwavelength Single Nanowire InGaAs/InP Quantum Well Light-Emitting Diodes
Publisher: American Chemical Society (ACS)
Date: 29-05-2019
DOI: 10.1021/ACS.NANOLETT.9B00959
Abstract: We report multiwavelength single InGaAs/InP quantum well nanowire light-emitting diodes grown by metal organic chemical vapor deposition using selective area epitaxy technique and reveal the complex origins of their electroluminescence properties. We observe that the single InGaAs/InP quantum well embedded in the nanowire consists of three components with different chemical compositions, axial quantum well, ring quantum well, and radial quantum well, leading to the electroluminescence emission with multiple wavelengths. The electroluminescence measurements show a strong dependence on current injection levels as well as temperatures and these are explained by interpreting the equivalent circuits in a minimized area of the device. It is also found that the electroluminescence properties are closely related to the distinctive triangular morphology with an inclined facet of the quantum well nanowire. Our study provides important new insights for further design, growth, and fabrication of high-performance quantum well-based nanowire light sources for a wide range of future optoelectronic and photonic applications.
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.
Comparison of the structural properties of Zn-face and O-face single crystal homoepitaxial ZnO epilayers grown by RF-magnetron sputtering
Publisher: AIP Publishing
Date: 04-01-2017
DOI: 10.1063/1.4973342
Abstract: Homoepitaxial ZnO growth is demonstrated from conventional RF-sputtering at 400 °C on both Zn and O polar faces of hydrothermally grown ZnO substrates. A minimum yield for the Rutherford backscattering and channeling spectrum, χmin, equal to ∼3% and ∼12% and a full width at half maximum of the 00.2 diffraction peak rocking curve of (70 ± 10) arc sec and (1400 ± 100) arc sec have been found for s les grown on the Zn and O face, respectively. The structural characteristics of the film deposited on the Zn face are comparable with those of epilayers grown by more complex techniques like molecular beam epitaxy. In contrast, the film simultaneously deposited on the O-face exhibits an inferior crystalline structure ∼0.7% strained in the c-direction and a higher atomic number contrast compared with the substrate, as revealed by high angle annular dark field imaging measurements. These differences between the Zn- and O-face films are discussed in detail and associated with the different growth mechanisms prevailing on the two surfaces.
Newborn Screening for Presymptomatic Diagnosis of Complement and Phagocyte Deficiencies
Publisher: Frontiers Media SA
Date: 17-03-2020
Identification of hydrogen related defects in proton implanted float-zone silicon
Publisher: EDP Sciences
Date: 29-11-2003
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.
Ion implantation induced defects in ZnO
Publisher: Elsevier BV
Date: 05-2012
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.
Achieving a narrow size distribution of Au particles at a precise depth in SiO2by segregation of Au precipitates
Publisher: IOP Publishing
Date: 15-04-2009
DOI: 10.1088/0957-4484/20/18/185603
Abstract: We propose a new method of confining Au nanoparticles of a narrow size distribution at a precise depth in an SiO2 matrix. The process involves the formation of nanocavities in silicon by hydrogen implantation and annealing (at 850 degrees C), followed by Au gettering to and precipitation in such cavities and a wet oxidation at 900 degrees C. Starting with a silicon-on-insulator wafer, Au precipitates can be segregated behind a growing Si/SiO2 interface during wet oxidation and ultimately trapped in SiO2 at the front interface of a buried oxide layer. The shape of the precipitates has been examined by transmission electron microscopy and found to be spherical. The average diameters of these precipitates before and after oxidation have been determined as around 15 nm and 30 nm, respectively.
Sidewall evolution in VLS grown GaAs nanowires
Publisher: IEEE
Date: 12-2014
Acceptor-like deep level defects in ion-implanted ZnO
Publisher: AIP Publishing
Date: 21-05-2012
DOI: 10.1063/1.4720514
Abstract: N-type ZnO s les have been implanted with MeV Zn+ ions at room temperature to doses between 1×108 and 2×1010cm-2, and the defect evolution has been studied by capacitance-voltage and deep level transient spectroscopy measurements. The results show a dose dependent compensation by acceptor-like defects along the implantation depth profile, and at least four ion-induced deep-level defects arise, where two levels with energy positions of 1.06 and 1.2 eV below the conduction band increase linearly with ion dose and are attributed to intrinsic defects. Moreover, a re-distribution of defects as a function of depth is observed already at temperatures below 400 K.
Point defect engineered Si sub-bandgap light-emitting diodes
Publisher: SPIE
Date: 21-12-2007
DOI: 10.1117/12.758543
Equilibrium shape of nano-cavities in H implanted ZnO
Publisher: AIP Publishing
Date: 25-05-2015
DOI: 10.1063/1.4921788
Abstract: Thermally equilibrated nano-cavities are formed in ZnO by H implantation and subsequent high temperature annealing to determine the relative surface formation energies and step energies of ZnO from reverse Wulff construction and related analysis. H adsorption, vicinal surfaces, and surface polarity are found to play an important role in determining the final thermal equilibrium shape of the nano-cavities. Under H coverage, the O-terminated surface shows a significantly lower surface formation energy than the Zn-terminated surface.
InAs nanowire arrays for room-temperature ultra-broadband infrared photodetection
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3NR00340J
Abstract: Wurtzite dominant InAs nanowire arrays with a low density of stacking faults were grown by using selective area metal–organic vapour-phase epitaxy, for the demonstration of high-performance short- and mid-wave infrared photodetector applications.
Influence of rapid thermal annealing on a 30 stack InAs/GaAs quantum dot infrared photodetector
Publisher: AIP Publishing
Date: 30-09-2003
DOI: 10.1063/1.1609634
Abstract: In this article the effect of rapid thermal annealing (RTA) on a 30 stacked InAs/GaAs, molecular beam epitaxially grown quantum dot infrared photodetector (QDIP) device is studied. Temperatures in the range of 600–800 °C for 60 s, typical of atomic interdiffusion methods are used. After rapid thermal annealing the devices exhibited large dark currents and no photoresponse could be measured. Double crystal x-ray diffraction and cross sectional transmission electron microscopy studies indicate that this could be the result of strain relaxation. V-shaped dislocations which extended across many quantum dot (QD) layers formed in the RTA s les. Smaller defect centers were observed throughout the as-grown s le and are also likely a strain relaxation mechanism. This supports the idea that strained structures containing dislocations are more likely to relax via the formation of dislocations and/or the propagation of existing dislocations, instead of creating atomic interdiffusion during RTA. Photoluminescence (PL) studies also found that Si related complexes developed in the Si doped GaAs contact layers with RTA. The PL from these Si related complexes overlaps and dominates the PL from our QD ground state.
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.
Influence of Interface Morphology on Hysteresis in Vapor‐Deposited Perovskite Solar Cells
Publisher: Wiley
Date: 30-12-2016
Radial Growth Evolution of InGaAs/InP Multi-Quantum-Well Nanowires Grown by Selective-Area Metal Organic Vapor-Phase Epitaxy
Publisher: American Chemical Society (ACS)
Date: 03-10-2018
Abstract: III-V semiconductor multi-quantum-well nanowires (MQW NWs) via selective-area epitaxy (SAE) is of great importance for the development of nanoscale light-emitting devices for applications such as optical communication, silicon photonics, and quantum computing. To achieve highly efficient light-emitting devices, not only the high-quality materials but also a deep understanding of their growth mechanisms and material properties (structural, optical, and electrical) are extremely critical. In particular, the three-dimensional growth mechanism of MQWs embedded in a NW structure by SAE is expected to be different from that of those grown in a planar structure or with a catalyst and has not yet been thoroughly investigated. In this work, we reveal a distinctive radial growth evolution of InGaAs/InP MQW NWs grown by the SAE metal organic vapor-phase epitaxy (MOVPE) technique. We observe the formation of zinc blende (ZB) QW discs induced by the axial InGaAs QW growth on the wurtzite (WZ) base-InP NW and propose it as the key factor driving the overall structure of radial growth. The role of the ZB-to-WZ change in the driving of the overall growth evolution is supported by a growth formalism, taking into account the formation-energy difference between different facets. Despite a polytypic crystal structure with mixed ZB and WZ phases across the MQW region, the NWs exhibit high uniformity and desirable QW spatial layout with bright room-temperature photoluminescence at an optical communication wavelength of ∼1.3 μm, which is promising for the future development of high-efficiency light-emitting devices.
Effect of boron on interstitial-related luminescence centers in silicon
Publisher: AIP Publishing
Date: 02-2010
DOI: 10.1063/1.3300836
Abstract: Photoluminescence measurements have been used to investigate the optically active defect centers formed by silicon implantation and a subsequent anneal at 275, 400, or 525 °C. The presence of boron in p-type silicon is found to produce deleterious effects on the luminescence of the interstitial-related W- and X-centers as well as a lower energy broad luminescence band. This effect has not been previously reported but it is consistent with the suppression of interstitial-related {311} extended defect formation in the presence of high boron concentrations at higher annealing temperatures. The results presented in this letter provide insight into the role of boron in the initial stages of interstitial cluster formation.
Response to Comment on 'Separation of vacancy and interstitial depth profiles in ion-implanted silicon: Experimental observation'
Publisher: AIP Publishing
Date: 25-02-2002
DOI: 10.1063/1.1455141
The formation, migration, agglomeration and annealing of vacancy-type defects in self-implanted Si
Publisher: Springer Science and Business Media LLC
Date: 12-12-2007
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.
Dynamic annealing in ion implanted SiC: Flux versus temperature dependence
Publisher: AIP Publishing
Date: 10-11-2003
DOI: 10.1063/1.1622797
Abstract: A strong influence of ion implantation flux on the accumulation of radiation damage, the so-called dose rate effect, is observed and systematically studied in SiC. 100 keV Si+ ions were implanted into bulk 4H-SiC wafers using different ion fluxes (1.9×1010–4.9×1013 ions/cm2 s) and keeping the implantation dose constant at 5×1014 Si+/cm2. The implants were performed both at room and elevated temperatures, up to 220 °C. Rutherford backscattering spectrometry in the channelling mode using 2 MeV He+ ions was employed to measure ion implantation damage profiles in the s les. For the flux interval used the most, pronounced dynamic annealing effect was detected at 80–160 °C, having an activation energy of 1.3 eV. For ex le, at 100 °C the amount of disordered Si atoms at the projected ion range is reduced by a factor of 4 by decreasing the ion flux from 4.9×1013 to 1.9×1010 ions/cm2 s. The results are discussed in terms of migration and annihilation of intrinsic type defects for both the Si- and C-sublattices. In addition, two regions for the damage accumulation – at the surface and at the damage peak for 100 keV Si+ ions – are observed.
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University Of Bristol
Location: United Kingdom of Great Britain and Northern Ireland
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