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Kevin F Brennan - One of the best experts on this subject based on the ideXlab platform.
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Dielectric functions of wurtzite and Zincblende structure GaN
MRS Proceedings, 2011Co-Authors: R Wang, Ismail H Oguzman, J Kolnik, P P Ruden, Kevin F BrennanAbstract:The authors present calculated longitudinal frequency and wavevector dependent dielectric functions of Zincblende and wurtzite structure GaN using band energies and wavefunctions generated in the framework of the empirical pseudopotential method. They discuss the anisotropy of the static dielectric function and find that the results are in satisfactory agreement with experimental data for {vert_bar}{rvec q}{vert_bar} {yields} 0.
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full band monte carlo simulation of Zincblende gan mesfet s including realistic impact ionization rates
IEEE Transactions on Electron Devices, 1999Co-Authors: M Farahmand, Kevin F BrennanAbstract:In this paper, we present the first theoretical study of the breakdown properties of Zincblende phase GaN MESFET devices. The calculations are made using a full band, ensemble Monte Carlo simulation that includes a numerical formulation of the impact ionization transition rates. The breakdown voltage, transconductance and cutoff frequency are calculated for the GaN MESFET under two different conditions, with and without semiconductor-oxide interface states. Uniform surface depletion regions model the effect of the interface states. It is found that the breakdown voltage of the Zincblende GaN MESFET is less dependent upon the surface depletion conditions than a corresponding GaAs MESFET. It is also found that the drain current increases more gradually with increasing drain-source voltage at the onset of breakdown and that the breakdown voltage of the Zincblende GaN MESFET is predicted to be several times larger than that of a comparable GaAs MESFET. The maximum current gain cutoff frequency of a 0.1 /spl mu/m gate length GaN MESFET is calculated to be 230 and 220 GHz, for the non-surface-depleted and the surface depleted devices respectively.
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theory of hole initiated impact ionization in bulk Zincblende and wurtzite gan
Journal of Applied Physics, 1997Co-Authors: Ismail H Oguzman, Enrico Bellotti, Kevin F Brennan, J Kolnik, R Wang, P P RudenAbstract:In this article, the first calculations of hole initiated interband impact ionization in bulk Zincblende and wurtzite phase GaN are presented. The calculations are made using an ensemble Monte Carlo simulation including the full details of all of the relevant valence bands, derived from an empirical pseudopotential approach, for each crystal type. The model also includes numerically generated hole initiated impact ionization transition rates, calculated based on the pseudopotential band structure. The calculations predict that both the average hole energies and ionization coefficients are substantially higher in the Zincblende phase than in the wurtzite phase. This difference is attributed to the higher valence band effective masses and equivalently higher effective density of states found in the wurtzite polytype. Furthermore, the hole ionization coefficient is found to be comparable to the previously calculated electron ionization coefficient in Zincblende GaN at an applied electric field strength of 3 MV/cm. In the wurtzite phase, the electron and hole impact ionization coefficients are predicted to be similar at high electric fields, but at lower fields, the hole ionization rate appears to be greater.
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dielectric properties of wurtzite and Zincblende structure gallium nitride
Journal of Physics and Chemistry of Solids, 1997Co-Authors: R Wang, Ismail H Oguzman, J Kolnik, P P Ruden, Kevin F BrennanAbstract:Abstract We present calculated results for the wavevector and frequency dependent dielectric functions of Zincblende and wurtzite GaN based on empirical pseudopotential band structures. The q → -dependent static dielectric functions, ϵ∞( q → ), are found to be similar for the two crystal modifications. The optical dielectric functions, ϵ∞(ω), however, are different in the range 6 eV
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electronic transport studies of bulk Zincblende and wurtzite phases of gan based on an ensemble monte carlo calculation including a full zone band structure
Journal of Applied Physics, 1995Co-Authors: J Kolnik, Ismail H Oguzman, Kevin F Brennan, R Wang, P P Ruden, Yang WangAbstract:The ensemble Monte Carlo technique including the details of the first four conduction bands within the full Brillouin zone is used to calculate the basic electronic transport properties for both Zincblende and wurtzite crystal phases of bulk gallium nitride. The band structure throughout the Brillouin zone is determined using the empirical pseudopotential method. Calculations of the electron steady‐state drift velocity, average energy, valley occupancy and band occupancy in the range of electric fields up to 500 kV/cm are presented. It is found that the threshold electric field for intervalley transfer is greater and that the second conduction band is more readily occupied in wurtzite than in Zincblende GaN over the range of electric fields examined here.
David Wallis - One of the best experts on this subject based on the ideXlab platform.
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alloy segregation at stacking faults in Zincblende gan heterostructures
Journal of Applied Physics, 2020Co-Authors: B Ding, Menno J. Kappers, Martin Frentrup, David Wallis, Simon M Fairclough, M Jain, A Kovacs, Rachel A OliverAbstract:Current cubic Zincblende III-Nitride epilayers grown on 3C-SiC/Si(001) substrates by metal-organic vapor-phase epitaxy contain a high density of stacking faults lying on the {111} planes. A combination of high-resolution scanning transmission electron microscopy and energy dispersive x-ray spectrometry is used to investigate the effects of alloy segregation around stacking faults in a Zincblende III-nitride light-emitting structure, incorporating InGaN quantum wells and an AlGaN electron blocking layer. It is found that in the vicinity of the stacking faults, the indium and aluminum contents were a factor of 2.3 ± 1.3 and 1.9 ± 0.5 higher, respectively, than that in the surrounding material. Indium and aluminum are also observed to segregate differently in relation to stacking faults with indium segregating adjacent to the stacking fault while aluminum segregates directly on the stacking fault.
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investigation of movpe grown Zincblende gan nucleation layers on 3c sic si substrates
Journal of Crystal Growth, 2019Co-Authors: Lok Yi Lee, Menno J. Kappers, Fabien Massabuau, Martin Frentrup, David Wallis, Petr Vacek, Rachel A OliverAbstract:Cubic Zincblende (zb-)GaN nucleation layers (NLs) grown by MOVPE on 3C-SiC/Si substrates were studied to determine their optimal thickness for subsequent zb-GaN epilayer growth. The layers were characterised by atomic force microscopy, X-ray diffraction and scanning transmission electron microscopy. The as-grown NLs, with nominal thicknesses varying from 3 nm to 44 nm, consist of small grains which are elongated in the [1 −1 0] direction, and cover the underlying SiC surface almost entirely. Thermal annealing of the NLs by heating in a H2/NH3 atmosphere to the elevated epilayer growth temperature reduces the substrate coverage of the films that are less than 22 nm thick, due to both material desorption and the ripening of islands. The compressive biaxial in-plane strain of the NLs reduces with increasing NL thickness to the value of relaxed GaN for a thickness of 44 nm. Both the as-grown and annealed NLs are crystalline and have high Zincblende phase purity, but contain defects including misfit dislocations and stacking faults. The zb-GaN epilayers grown on the thinnest NLs show an enhanced fraction of the wurtzite phase, most likely formed by nucleation on the exposed substrate surface at elevated temperature, thus dictating the minimum NL thickness for phase-pure zb-GaN epilayer growth.
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investigation of stacking faults in movpe grown Zincblende gan by xrd and tem
Journal of Applied Physics, 2019Co-Authors: Lok Yi Lee, Menno J. Kappers, Martin Frentrup, David Wallis, Petr Vacek, Rachel A OliverAbstract:X-ray diffraction and bright-field transmission electron microscopy are used to investigate the distribution and density of {111}-type stacking faults (SFs) present in a heteroepitaxial Zincblende ...
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effect of growth temperature and v iii ratio on the surface morphology of movpe grown cubic Zincblende gan
Journal of Applied Physics, 2018Co-Authors: Lok Yi Lee, Menno J. Kappers, Martin Frentrup, Rachel A Oliver, C J Humphreys, David WallisAbstract:The influence of growth temperature and V/III-ratio on the surface morphology of (001) cubic Zincblende GaN epilayers during metal organic vapour phase epitaxy growth has been investigated using atomic force microscopy and transmission electron microscopy. The Zincblende phase purity as determined by X-ray diffraction was found to be above 98% for most GaN epilayers studied. As the growth temperature was increased from 850 °C to 910 °C and as the V/III-ratio was separately increased from 38 to 300, surface features were found to be elongated in the [1-10] direction, and the ratio of the length to width of such surface features was found to increase. Faceting was observed at V/III-ratios below 38 and above 300, which in the latter case was accompanied by a reduction of the Zincblende phase purity. An explanation for these morphological trends is proposed based on effects such as the reduced symmetry of the top monolayer of the (001)-oriented Zincblende GaN lattice, diffusion of Ga and N adatoms on such a surface, and the relative energies of the crystal facets.
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effect of stacking faults on the photoluminescence spectrum of Zincblende gan
Journal of Applied Physics, 2018Co-Authors: Stephen Church, Simon Hammersley, P. W. Mitchell, Menno J. Kappers, Lok Yi Lee, Fabien Massabuau, S.-l. Sahonta, Martin Frentrup, L. J. Shaw, David WallisAbstract:The photoluminescence spectra of a Zincblende GaN epilayer grown via metal-organic chemical vapour deposition upon 3C-SiC/Si (001) substrates were investigated. Of particular interest was a broad emission band centered at 3.4 eV, with a FWHM of 200 meV, which extends above the bandgap of both Zincblende and wurtzite GaN. Photoluminescence excitation measurements show that this band is associated with an absorption edge centered at 3.6 eV. Photoluminescence time decays for the band are monoexponential, with lifetimes that reduce from 0.67 ns to 0.15 ns as the recombination energy increases. TEM measurements show no evidence of wurtzite GaN inclusions which are typically used to explain emission in this energy range. However, dense stacking fault bunches are present in the epilayers. A model for the band alignment at the stacking faults was developed to explain this emission band, showing how both electrons and holes can be confined adjacent to stacking faults. Different stacking fault separations can change the carrier confinement energies sufficiently to explain the width of the emission band, and change the carrier wavefunction overlap to account for the variation in decay time.
H Ohno - One of the best experts on this subject based on the ideXlab platform.
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Molecular Beam Epitaxy and Properties of Cr-Doped GaSb
Journal of Superconductivity, 2004Co-Authors: E Abe, J H Zhao, F Matsukura, Y Ohno, K. Sato, H OhnoAbstract:Molecular beam epitaxy of GaSb films, with several percents of Cr, and their characterization are reported. Their electric and magnetic properties depend on their growth temperature and Cr composition. Although magnetization measurements reveal that all the films are ferromagnetic even at room temperature, this is most probably due to the precipitation of ferromagnetic Zincblende CrSb. The magnetotransport measurements show that Cr spins may couple antiferromagnetically in GaSb host matrix.
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Zincblende crsb gaas multilayer structures with room temperature ferromagnetism
Materials Science in Semiconductor Processing, 2003Co-Authors: J H Zhao, F Matsukura, K Takamura, Daichi Chiba, Y Ohno, K Ohtani, H OhnoAbstract:Abstract CrSb (1 ML)/GaAs (5 nm) multilayers with period up to 4 have been grown on GaAs substrates by solid-source molecular-beam epitaxy at 250°C. Reflection high-energy electron diffraction reveals Zincblende characteristics throughout the growth of multilayer structures. High-resolution cross-sectional transmission electron microscopy also indicates that the crystal structure of the multilayers is Zincblende and with no dislocations at the interfaces. The presence of room-temperature ferromagnetism is confirmed by magnetization measurements.
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room temperature ferromagnetism in Zincblende crsb grown by molecular beam epitaxy
Applied Physics Letters, 2001Co-Authors: J H Zhao, F Matsukura, K Takamura, Daichi Chiba, E Abe, H OhnoAbstract:Thin films of CrSb grown by solid-source molecular-beam epitaxy on GaAs, (Al, Ga)Sb, and GaSb are found to exhibit ferromagnetism. Reflection high-energy electron diffraction and high-resolution cross sectional transmission electron microscopy both indicate that the structure is Zincblende. Temperature dependence of remanent magnetization shows that the ferromagnetic transition temperature is beyond 400 K.
J Kolnik - One of the best experts on this subject based on the ideXlab platform.
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Dielectric functions of wurtzite and Zincblende structure GaN
MRS Proceedings, 2011Co-Authors: R Wang, Ismail H Oguzman, J Kolnik, P P Ruden, Kevin F BrennanAbstract:The authors present calculated longitudinal frequency and wavevector dependent dielectric functions of Zincblende and wurtzite structure GaN using band energies and wavefunctions generated in the framework of the empirical pseudopotential method. They discuss the anisotropy of the static dielectric function and find that the results are in satisfactory agreement with experimental data for {vert_bar}{rvec q}{vert_bar} {yields} 0.
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theory of hole initiated impact ionization in bulk Zincblende and wurtzite gan
Journal of Applied Physics, 1997Co-Authors: Ismail H Oguzman, Enrico Bellotti, Kevin F Brennan, J Kolnik, R Wang, P P RudenAbstract:In this article, the first calculations of hole initiated interband impact ionization in bulk Zincblende and wurtzite phase GaN are presented. The calculations are made using an ensemble Monte Carlo simulation including the full details of all of the relevant valence bands, derived from an empirical pseudopotential approach, for each crystal type. The model also includes numerically generated hole initiated impact ionization transition rates, calculated based on the pseudopotential band structure. The calculations predict that both the average hole energies and ionization coefficients are substantially higher in the Zincblende phase than in the wurtzite phase. This difference is attributed to the higher valence band effective masses and equivalently higher effective density of states found in the wurtzite polytype. Furthermore, the hole ionization coefficient is found to be comparable to the previously calculated electron ionization coefficient in Zincblende GaN at an applied electric field strength of 3 MV/cm. In the wurtzite phase, the electron and hole impact ionization coefficients are predicted to be similar at high electric fields, but at lower fields, the hole ionization rate appears to be greater.
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dielectric properties of wurtzite and Zincblende structure gallium nitride
Journal of Physics and Chemistry of Solids, 1997Co-Authors: R Wang, Ismail H Oguzman, J Kolnik, P P Ruden, Kevin F BrennanAbstract:Abstract We present calculated results for the wavevector and frequency dependent dielectric functions of Zincblende and wurtzite GaN based on empirical pseudopotential band structures. The q → -dependent static dielectric functions, ϵ∞( q → ), are found to be similar for the two crystal modifications. The optical dielectric functions, ϵ∞(ω), however, are different in the range 6 eV
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electronic transport studies of bulk Zincblende and wurtzite phases of gan based on an ensemble monte carlo calculation including a full zone band structure
Journal of Applied Physics, 1995Co-Authors: J Kolnik, Ismail H Oguzman, Kevin F Brennan, R Wang, P P Ruden, Yang WangAbstract:The ensemble Monte Carlo technique including the details of the first four conduction bands within the full Brillouin zone is used to calculate the basic electronic transport properties for both Zincblende and wurtzite crystal phases of bulk gallium nitride. The band structure throughout the Brillouin zone is determined using the empirical pseudopotential method. Calculations of the electron steady‐state drift velocity, average energy, valley occupancy and band occupancy in the range of electric fields up to 500 kV/cm are presented. It is found that the threshold electric field for intervalley transfer is greater and that the second conduction band is more readily occupied in wurtzite than in Zincblende GaN over the range of electric fields examined here.
B. Grandidier - One of the best experts on this subject based on the ideXlab platform.
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Iuliacumite: A Novel Chemical Short-Range Order in a Two-Dimensional Wurtzite Single Monolayer InAs 1– x Sb x Shell on InAs Nanowires
Nano Letters, 2019Co-Authors: M. Schnedler, I. Lefebvre, J.-p. Nys, S Plissard, M. Berthe, H. Eisele, R. Dunin-borkowski, Ph. Ebert, B. GrandidierAbstract:A chemical short range order is found in single monolayer InAs 1-x Sb x shells, which inherit a wurtzite structure from the underlying InAs nanowire, instead of crystallizing in the energetically preferred Zincblende structure. The chemical order is characterized by an anti-correlation ordering vector in 1120 direction and arises from strong Sb-Sb repulsive interactions along the atomic chains in 1120 direction.
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Iuliacumite: a novel two-dimensional chemical short range order in a wurtzite single monolayer InAs 1-x Sb x shell on InAs nanowires
2019Co-Authors: M. Schnedler, I. Lefebvre, J.-p. Nys, S Plissard, M. Berthe, H. Eisele, R. Dunin-borkowski, Ph. Ebert, P. Caroff, B. GrandidierAbstract:A chemical short range order is found in single monolayer InAs1-xSbx shells, which inherit a wurtzite structure from the underlying InAs nanowire, instead of crystallizing in the energetically preferred Zincblende structure. The chemical order is characterized by an ordering vector in [0001] and an anti-ordering vector in 1120 direction and arises from strong Sb-Sb repulsive interactions along the atomic chains in 1120 direction.
