ORCID Profile
0000-0002-9863-8330
Current Organisation
University of Sydney
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Publisher: Research Square Platform LLC
Date: 19-01-2022
DOI: 10.21203/RS.3.RS-1267475/V1
Abstract: Interaction of light with collective charge oscillations termed as plasmon-polariton and with polar lattice vibrations termed phonon-polariton is a new frontier in nano-photonics. Traditionally doped-semiconductors and conducting metal oxides (CMO) are used to achieve plasmon-polaritons in the near-to-mid infrared (IR), while polar dielectrics are utilized for realizing phonon-polaritons in the long-wavelength IR (LWIR) spectral regions. However, demonstrating plasmon- and phonon-polariton in one host material with low-loss is challenging due to the mutually conflicting physical property requirements. In this article, we demonstrate high-quality tunable short-wavelength IR (SWIR) plasmon-polariton and LWIR phonon-polariton in complementary metal-oxide-semiconductor (CMOS) compatible group III-V polar semiconducting scandium nitride (ScN) thin films. We achieve both resonances by utilizing n -type (oxygen) and p -type (magnesium) doping in ScN that allows modulation of carrier concentration from 5 × 10 18 to 1.6 × 10 21 cm -3 . Our work enables infrared nano-photonics with an epitaxial group-III semiconducting nitride, opening the possibility for practical applications.
Publisher: AIP Publishing
Date: 23-11-2020
DOI: 10.1063/5.0027091
Abstract: Scandium nitride (ScN) is an emerging rock salt indirect bandgap semiconductor and has attracted significant interest in recent years for thermoelectric energy conversion, as a substrate for defect-free GaN growth, as a semiconducting component in single-crystalline metal/semiconductor superlattices for thermionic energy conversion, as well as for Al1−xScxN-based bulk and surface acoustic devices for 5G technologies. Most ScN film growth traditionally utilizes physical vapor deposition techniques such as magnetron sputtering and molecular beam epitaxy, which results in stoichiometric films but with varying crystal quality, orientations, microstructures, and physical properties. As epitaxial single-crystalline ScN films with smooth surfaces are essential for device applications, it is important to understand the ScN growth modes and parameters that impact and control their microstructure. In this Letter, we demonstrate that large adatom mobility is essential to overcome the Ehrlich–Schwoebel (E–S) and grain boundary migration barriers and achieve defect (voids, dislocations, stacking faults, etc.)-free single-crystalline ScN films. Using the substrate temperature to tune adatom mobility, we show that nominally single-crystalline ScN films are achieved when the homologous temperature is higher than ∼0.3. For homologous temperatures ranging from 0.23 to 0.30, ScN films are found to exhibit significant structural voids in between pyramidal growth regions with multiple in-plane orientations resulting from additional lateral growth off the facets of the pyramids and broken epitaxy after ∼80 nm of growth. The in-depth discussion of the growth modes of ScN presented here explains its varying electrical and optical properties and will help achieve high-quality ScN for device applications.
Publisher: American Chemical Society (ACS)
Date: 17-06-2022
DOI: 10.1021/ACS.NANOLETT.2C00912
Abstract: The interaction of light with collective charge oscillations, called plasmon-polariton, and with polar lattice vibrations, called phonon-polariton, are essential for confining light at deep subwavelength dimensions and achieving strong resonances. Traditionally, doped-semiconductors and conducting metal oxides (CMO) are used to achieve plasmon-polaritons in the near-to-mid infrared (IR), while polar dielectrics are utilized for realizing phonon-polaritons in the long-wavelength IR (LWIR) spectral regions. However, demonstrating low-loss plasmon- and phonon-polaritons in one host material will make it attractive for practical applications. Here, we demonstrate high-quality tunable short-wavelength IR (SWIR) plasmon-polariton and LWIR phonon-polariton in complementary metal-oxide-semiconductor compatible group III-V polar semiconducting scandium nitride (ScN) thin films. We achieve both resonances by utilizing
Publisher: Elsevier BV
Date: 04-2022
Publisher: AIP Publishing
Date: 02-2021
DOI: 10.1063/5.0038459
Abstract: Point defects create exotic properties in materials such as defect-induced luminescence in wide-bandgap semiconductors, magnetism in nonmagnetic materials, single-photon emission from semiconductors, etc. In this article, oxygen defect formation in metallic TiN and semiconducting rock salt-(Al,Sc)N is investigated with a combination of first-principles density functional theory, synchrotron-based x-ray absorption spectroscopy (XAS) analysis, and scanning transmission electron microscopy–energy-dispersive x-ray spectroscopy mapping. Modeling results show that oxygen in TiN and rock salt-(Al,Sc)N prefers to be in the defect complex of substitutional and interstitial oxygen (nON + Oi) types. While in TiN, the preferential interstitial sites of oxygen in ON + Oi are at the tetrahedral site, in rock salt-(Al,Sc)N, a split interstitial site along the [111] direction was found to be energetically preferable. Simulations performed as a function of the oxygen partial pressure show that under experimental growth conditions, four oxygen atoms at the substitutional sites of nitrogen (4ON), along with four Ti atoms, decorate around an interstitial oxygen atom at the tetrahedral site (Oi) in the energetically favored configuration. However, in rock salt-(Al,Sc)N, n in nON + Oi was found to vary from two to four depending on the oxygen partial pressure. Theoretical predictions agree well with the experimentally obtained XAS results. These results are not only important for a fundamental understanding of oxygen impurity defect behavior in rock salt nitride materials but will also help in the development of epitaxial metal/semiconductor superlattices with efficient thermionic properties.
Publisher: Elsevier BV
Date: 11-2021
Publisher: Wiley
Date: 23-12-2022
Abstract: Traditional computation based on von Neumann architecture is limited by time and energy consumption due to data transfer between the storage and the processing units. The von Neumann architecture is also inefficient in solving unstructured, probabilistic, and real‐time problems. To address these challenges, a new brain‐inspired neuromorphic computational architecture is required. Due to the absence of resistance–capacitance delay, high bandwidth, and low power consumption, optoelectronic artificial synaptic devices are highly attractive. Yet, stable, scalable, and complementary metal–oxide–semiconductor (CMOS)‐compatible materials exhibiting both inhibitory and excitatory optoelectronic synaptic functionalities have not been demonstrated. Here, epitaxial CMOS‐compatible scandium nitride (ScN) optoelectronic artificial synaptic devices that emulate both inhibitory and excitatory biological synaptic activities are presented. The negative and positive persistent photoconductivity of undoped and magnesium‐doped ScN is equated to the inhibitory and excitatory synaptic plasticity, respectively, which leads to functionalities like learning–forgetting, frequency‐selective optical filtering, frequency‐dependent potentiation and depression, Hebbian learning, and logic‐gate operations. Temperature‐dependent photoresponse and photo‐Hall measurements reveal that scattering of photogenerated carriers from charged defect centers results in negative photoconductivity in undoped degenerate ScN. This work opens up the possibility of utilizing a group‐III epitaxial semiconducting nitride material with inhibitory and excitatory optoelectronic synaptic functionalities for practical neuromorphic applications.
Publisher: AIP Publishing
Date: 29-05-2023
DOI: 10.1063/5.0150185
Abstract: Ferrell and Berreman modes are absorption resonances in thin metal films and polar-dielectric media that arise from radiative bulk plasmon-polariton and phonon-polariton excitations. Compared to surface polaritons, Ferrell and Berreman modes occur due to volume charge oscillations across the medium and provide a unique pathway for light–matter interactions. Though the resonances are studied in idually, stringent polarization and material requirements have prevented their observation in one host medium. Here, we show simultaneous excitation of Ferrell and Berreman absorption resonances in refractory epitaxial TiN/Al0.72Sc0.28N plasmonic metal olar-dielectric hyperbolic metamaterials in the visible and far-infrared spectral ranges. The nanoscale periodicity of the superlattices enables the coupling of bulk plasmons (and longitudinal optical phonons) across different TiN (and Al0.72Sc0.28N) layers and allows polarization matching with free-space light that results in Ferrell (and Berreman) mode excitations. Ferrell and Berreman absorption resonances can be used for strong light confinement in radiative cooling, thermophotovoltaics, and other dual-band applications.
Publisher: American Physical Society (APS)
Date: 22-09-2023
Publisher: AIP Publishing
Date: 17-05-2021
DOI: 10.1063/5.0052877
Abstract: Aluminum scandium nitride (AlxSc1-xN) is an emerging III-nitride semiconductor that has attracted significant interest in recent years in surface and bulk acoustic resonators for its high piezoelectric coefficient and applications in high-power electronic devices. AlxSc1-xN stabilizes in the rock salt phase for x & 0.52 when deposited directly on (001) MgO substrates and has been utilized as a semiconductor in single-crystalline TiN/AlxSc1-xN metal/semiconductor superlattices for thermionic energy conversion, optical hyperbolic metamaterials, and the fundamental studies on heat and current transport in materials. However, due to the presence of oxygen impurities and native defects, such as nitrogen vacancies, sputter-deposited rock salt-AlxSc1-xN exhibits a high carrier concentration in the (2–4) × 1020 cm−3 range that leads to its Ohmic tunneling contact with metals and prevents observation of thermionic emission. In this Letter, we demonstrate that magnesium (Mg) acts as an efficient hole-dopant in r-AlxSc1-xN, increases its resistivity, and reduces its carrier concentration as a function of Mg concentration to as low as 1.4 × 1018 cm−3. A combination of spectroscopy, microscopy, and first-principles modeling demonstrate (a) epitaxial 001 oriented AlxSc1-xN:Mg growth for the first 35–75 nm and subsequent pyramidal growth with multiple in-plane orientations, (b) MgxNy to form a uniform and homogeneous solid solution with r-AlxSc1-xN without any precipitation, phase separation, or secondary phase formation, and (c) Mg-defect states are located deep inside the valence and conduction bands that leave behind a pristine r-AlxSc1-xN bandgap and band edges. The demonstration of Mg-hole doping in r-AlxSc1-xN marks significant progress in r-AlxSc1-xN thin film and superlattice-based devices.
Publisher: Elsevier BV
Date: 10-2022
Publisher: American Chemical Society (ACS)
Date: 20-05-2022
Publisher: AIP Publishing
Date: 29-03-2021
DOI: 10.1063/5.0041879
Abstract: Erbium nitride (ErN) is an emerging semiconducting rare-earth pnictide with unique electronic and magnetic properties. ErN has attracted significant interest for spin superlattices and spintronic devices and as a second-stage regenerator for Gifford–McMahon cryo-coolers. Solid-solution alloys of ErN with III-nitride semiconductors such as GaN have been studied extensively for use in solid-state lasers, lifiers, and light-emitting devices operating in the retina-safe and fiber-optic communication wavelength window of 1.54 μm. However, due to the high affinity of Er toward oxygen, ErN is prone to oxidation in ambient conditions. To date, no reports on the deposition of the high-quality ErN thin film and its thermoelectric properties have been published. In this Letter, semiconducting ErN thin films are deposited inside an ultrahigh-vacuum chamber and capped with thin (3 nm) AlN layers to stabilize it in ambient conditions. Structural, optical, and electronic characterization reveals that ErN thin films (a) grow with (111) and (002) orientations on (0001) Al2O3 and (001) MgO substrates with sharp and abrupt ErN–substrate interfaces, (b) demonstrate a direct bandgap of 1.9 eV, and (c) exhibit a high carrier concentration in the range of 4.3 × 1020 to 1.4 × 1021 cm−3. Thermoelectric measurements show a moderately high Seebeck coefficient of –72.6 μV/K at 640 K and a maximum power factor of 0.44 × 10−3 W/m K2 at 486 K. Demonstration of an ambient-stable semiconducting ErN thin film and its high thermoelectric power factor marks significant progress in rare-earth pnictide research and will help develop ErN-based spintronic and thermoelectric devices.
Publisher: American Physical Society (APS)
Date: 22-11-2021
No related grants have been discovered for ASHALATHA INDIRADEVI KAMALASANAN PILLAI.