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Articles 331 - 347 of 347
Full-Text Articles in Engineering
Transient Photoluminescence Of Defect Transitions In Freestanding Gan, Michael A. Reshchikov, Hadis Morkoç, S. S. Park, K. Y. Lee
Transient Photoluminescence Of Defect Transitions In Freestanding Gan, Michael A. Reshchikov, Hadis Morkoç, S. S. Park, K. Y. Lee
Electrical and Computer Engineering Publications
Deep level defects responsible for the 2.4 eV photoluminescence (PL) band in a freestanding GaN template were studied by transient photoluminescence. A nonexponential decay of PL intensity observed at low temperature is attributed to a donor–acceptor pair recombination involving a shallow donor and a deep acceptor. At room temperature, a single-exponential PL decay with a lifetime of 30 μs was observed at the high-energy side of the band, whereas the second component with a lifetime of about 750 μs was detected at the low-energy side of the band. The PL decay and transformation of the PL spectrum at room temperature …
Characterization Of Free-Standing Hydride Vapor Phase Epitaxy Gan, J. Jasinski, W. Sider, Z. Lilental-Weber, P. Visconti, K. M. Jones, Michael A. Reshchikov, F. Yun, Hadis Morkoç, S. S. Park, K. Y. Lee
Characterization Of Free-Standing Hydride Vapor Phase Epitaxy Gan, J. Jasinski, W. Sider, Z. Lilental-Weber, P. Visconti, K. M. Jones, Michael A. Reshchikov, F. Yun, Hadis Morkoç, S. S. Park, K. Y. Lee
Electrical and Computer Engineering Publications
A free-standing GaN template grown by hydride vapor phase epitaxy has been characterized by transmission electron microscopy(TEM). The TEM investigation was augmented by x-ray diffraction, defect delineation etching process followed by imaging with atomic force microscopy and variable temperature photoluminescence. The density of dislocations near the N face was determined to be, in order, 3±1×107, 4±1×107, and about 1×107 cm−2 by cross-sectional TEM, plan-view TEM, and a defect revealing etch, respectively. The same methods on the Ga face revealed the defect concentration to be, in order, less than 1×107 cm−2 by plan-view TEM, less than 5×106 cm−2 by cross-sectional TEM, …
Deep Centers In A Free-Standing Gan Layer, Z.-Q. Fang, D. C. Look, P. Visconti, D.-F. Wang, C.-Z. Lu, F. Yun, Hadis Morkoç, S. S. Park, K. Y. Lee
Deep Centers In A Free-Standing Gan Layer, Z.-Q. Fang, D. C. Look, P. Visconti, D.-F. Wang, C.-Z. Lu, F. Yun, Hadis Morkoç, S. S. Park, K. Y. Lee
Electrical and Computer Engineering Publications
Schottky barrierdiodes, on both Ga and N faces of a ∼300-μm-thick free-standing GaN layer, grown by hydride vapor phase epitaxy(HVPE) on Al2O3 followed by laser separation, were studied by capacitance–voltage and deep level transient spectroscopy(DLTS) measurements. From a 1/C2 vs V analysis, the barrier heights of Ni/Au Schottky contacts were determined to be different for the two polar faces: 1.27 eV for the Ga face, and 0.75 eV for the N face. In addition to the four common DLTS traps observed previously in other epitaxial GaN including HVPE-grown GaN a new trap B′ with activation energyET=0.53 eV was found in …
Blue Photoluminescence Activated By Surface States In Gan Grown By Molecular Beam Epitaxy, Michael A. Reshchikov, P. Visconti, Hadis Morkoç
Blue Photoluminescence Activated By Surface States In Gan Grown By Molecular Beam Epitaxy, Michael A. Reshchikov, P. Visconti, Hadis Morkoç
Electrical and Computer Engineering Publications
We have studied the broad blue band, which emerges in the photoluminescence(PL)spectrum of c-plane GaN layers after etching in hot H3PO4 and subsequent exposure to air. This band exhibited a 100 meV blueshift with increasing excitation intensity and a thermal quenching with activation energies of 12 and 100 meV. These observations led us to suggest that surface states may be formed on etchedsurfaces and cause bandbending, which leads to a shift in transition energy with excitation. The blue PL is related to transitions from the shallow donors filled with nonequilibrium electrons to the surface states, which capture the photogenerated …
Giant Photoresistivity And Optically Controlled Switching In Self-Assembled Nanowires, N. Kouklin, L. Menon, A. Z. Wong, D. W. Thompson, J. A. Woollam, P. F. Williams, Supriyo Bandyopadhyay
Giant Photoresistivity And Optically Controlled Switching In Self-Assembled Nanowires, N. Kouklin, L. Menon, A. Z. Wong, D. W. Thompson, J. A. Woollam, P. F. Williams, Supriyo Bandyopadhyay
Electrical and Computer Engineering Publications
We report the observation of giant photoresistivity in electrochemically self-assembledCdS and ZnSenanowireselectrodeposited in a porous alumina film. The resistance of these nanowires increases by one to two orders of magnitude when exposed to infrared radiation, possibly because of real-space transfer of electrons from the nanowires into the surrounding alumina by photon absorption. This phenomenon has potential applications in “normally on” infrared photodetectors and optically controlled switches.
Characteristics Of Free-Standing Hydride-Vapor-Phase-Epitaxy-Grown Gan With Very Low Defect Concentration, P. Visconti, K. M. Jones, Michael A. Reshchikov, F. Yun, R. Cingolani, Hadis Morkoç, S. S. Park, K. Y. Lee
Characteristics Of Free-Standing Hydride-Vapor-Phase-Epitaxy-Grown Gan With Very Low Defect Concentration, P. Visconti, K. M. Jones, Michael A. Reshchikov, F. Yun, R. Cingolani, Hadis Morkoç, S. S. Park, K. Y. Lee
Electrical and Computer Engineering Publications
A free-standing 300-μm-thick GaN template grown by hydride vapor phase epitaxy has been characterized for its structural and optical properties using x-ray diffraction, defect delineation etch followed by imaging with atomic force microscopy, and variable temperature photoluminescence. The Ga face and the N face of the c-plane GaN exhibited a wide variation in terms of the defect density. The defect concentrations on Ga and N faces were about 5×105 cm−2 for the former and about 1×107 cm−2 for the latter. The full width at half maximum of the symmetric (0002) x-ray diffraction peak was 69 and 160 arc sec …
Bias-Assisted Photoelectrochemical Etching Of P-Gan At 300 K, J. E. Borton, C. Cai, M. I. Nathan, P. Chow, J. M. Van Hove, A. Wowchak, Hadis Morkoç
Bias-Assisted Photoelectrochemical Etching Of P-Gan At 300 K, J. E. Borton, C. Cai, M. I. Nathan, P. Chow, J. M. Van Hove, A. Wowchak, Hadis Morkoç
Electrical and Computer Engineering Publications
Photoelectrochemical (PEC)etching of p-type GaN has been realized in room temperature, 0.1 M KOH solutions. PECetching of GaN was achieved by applying a positive bias to the surface of the p-GaN layer through a deposited titanium mask. The applied bias reduces the field at the semiconductor surface, which induced the dissolution of the GaN. The effect of bias on etch rate and morphology was examined. It was found that insulating the Ti mask from the KOH solution with Si3N4 significantly increases the etch rate. The rms roughness of the etched region decreased as the bias voltage increased. Etch rates …
Dislocation Density In Gan Determined By Photoelectrochemical And Hot-Wet Etching, P. Visconti, K. M. Jones, Michael A. Reshchikov, R. Cingolani, Hadis Morkoç, R. J. Molnar
Dislocation Density In Gan Determined By Photoelectrochemical And Hot-Wet Etching, P. Visconti, K. M. Jones, Michael A. Reshchikov, R. Cingolani, Hadis Morkoç, R. J. Molnar
Electrical and Computer Engineering Publications
Defects in GaN layers grown by hydride vapor-phase epitaxy have been investigated by photoelectrochemical (PEC)etching, and by wet etching in hot H3PO4acid and molten potassium hydroxide (KOH). Threading vertical wires (i.e., whiskers) and hexagonal-shaped etch pits are formed on the etched sample surfaces by PEC and wet etching, respectively. Using atomic-force microscopy, we find the density of “whisker-like” features to be 2×109 cm−2, the same value found for the etch-pit density on samples etched with both H3PO4 and molten KOH. This value is comparable to the dislocation density obtained in similar samples with tunnelingelectron microscopy, and is also consistent with …
Observation Of Electronic Raman Scattering From Mg-Doped Wurtzite Gan, K. T. Tsen, C. Koch, Y. Chen, Hadis Morkoç, J. Li, J. Y. Lin, H. X. Jiang
Observation Of Electronic Raman Scattering From Mg-Doped Wurtzite Gan, K. T. Tsen, C. Koch, Y. Chen, Hadis Morkoç, J. Li, J. Y. Lin, H. X. Jiang
Electrical and Computer Engineering Publications
Electronic Raman scattering experiments have been carried out on both molecular beam epitaxy and metal-organic chemical vapor deposition-grown Mg-doped wurtzite GaN samples. Aside from the expected Raman lines, a broad structure (full width at half maximum≅15 cm−1)observed at around 841 cm−1 is attributed to the electronic Raman scattering from neutral Mg impurities in Mg-doped GaN. Our experimental results demonstrate that the energy between the ground and first excited states of Mg impurities in wurtzite GaN is about one-half of its binding energy.
Well-Width Dependence Of The Ground Level Emission Of Gan/Algan Quantum Wells, A. Bonfiglio, M. Lomascolo, G. Traetta, R. Cingolani, A. Di Carlo, F. Della Sala, P. Lugli, A. Botchkarev, H. Morkoç
Well-Width Dependence Of The Ground Level Emission Of Gan/Algan Quantum Wells, A. Bonfiglio, M. Lomascolo, G. Traetta, R. Cingolani, A. Di Carlo, F. Della Sala, P. Lugli, A. Botchkarev, H. Morkoç
Electrical and Computer Engineering Publications
We have performed a systematic investigation of GaN/AlGaN quantum wells grown on different buffer layers (either GaN or AlGaN) in order to clarify the role of strain, structural parameters, and built-in field in determining the well-width dependence of the ground level emission energy. We find that identical quantum wells grown on different buffer layers exhibit strong variation of the ground level energy but similar well-width dependence. The data are quantitatively explained by an analytic model based on the envelope function formalism which accounts for screening and built-in field, and by a full self-consistent tight binding model.
Photoreflectance Investigations Of The Bowing Parameter In Algan Alloys Lattice-Matched To Gan, Tomasz J. Ochalski, Bernard Gil, Pierre Lefebvre, Nicolas Grandjean, Mathieu Leroux, Jean Massies, Shuji Nakamura, Hadis Morkoç
Photoreflectance Investigations Of The Bowing Parameter In Algan Alloys Lattice-Matched To Gan, Tomasz J. Ochalski, Bernard Gil, Pierre Lefebvre, Nicolas Grandjean, Mathieu Leroux, Jean Massies, Shuji Nakamura, Hadis Morkoç
Electrical and Computer Engineering Publications
Room temperature photoreflectance investigations have been performed on a series of AlGaN layers grown both by metalorganic vapor phase epitaxy and molecular beam epitaxy on c-plane sapphire substrates. The aluminum composition was ranging between 0% and 20%, and was determined independently in the different growth laboratories, by various methods. It is found that within the experimental uncertainty, there is no detectable bowing parameter in these alloys. This contradicts some previous experimental investigations and confirms other ones.
Piezoelectric Effects On The Optical Properties Of Gan/Alxga1−Xn Multiple Quantum Wells, H. S. Kim, J. Y. Lin, H. X. Jiang, W. W. Chow, A. Botchkarev, Hadis Morkoç
Piezoelectric Effects On The Optical Properties Of Gan/Alxga1−Xn Multiple Quantum Wells, H. S. Kim, J. Y. Lin, H. X. Jiang, W. W. Chow, A. Botchkarev, Hadis Morkoç
Electrical and Computer Engineering Publications
Piezoelectric effects on the optical properties of GaN/AlGaN multiple quantum wells(MQWs) have been investigated by picosecond time-resolvedphotoluminescence(PL)measurements. For MQWs with well thicknesses 30 and 40 Å, the excitonic transition peak positions at 10 K in continuous wave (cw) spectra are redshifted with respect to the GaN epilayer by 13 and 45 meV, respectively. The time-resolvedPL spectra of the 30 and 40 Å well MQWs reveal that the excitonic transition is in fact blueshifted at early delay times due to quantum confinement of carriers. The spectral peak position shifts toward lower energies as the delay time increases and becomes redshifted at …
Deep Centers In N-Gan Grown By Reactive Molecular Beam Epitaxy, Z.-Q. Fang, D. C. Look, W. Kim, Z. Fan, A. Botchkarev, Hadis Morkoç
Deep Centers In N-Gan Grown By Reactive Molecular Beam Epitaxy, Z.-Q. Fang, D. C. Look, W. Kim, Z. Fan, A. Botchkarev, Hadis Morkoç
Electrical and Computer Engineering Publications
Deep centers in Si-doped n-GaN layers grown by reactive molecular beam epitaxy have been studied by deep-level transient spectroscopy as a function of growth conditions. Si-doped GaN samples grown on a Si-doped n+-GaN contact layer at 800 °C show a dominant trap C1 with activation energyET=0.44 eV and capture cross-section σT=1.3×10−15 cm−2, while samples grown at 750 °C on an undoped semi-insulating GaN buffer show prominent traps D1and E1, with ET=0.20 eV and σT=8.4×10−17 cm2, and ET=0.21 eV and σT=1.6×10−14 cm2, respectively. Trap E1 is believed to be related to a N-vacancy defect, since the Arrhenius signature for E1 is …
Plasma Heating In Highly Excited Gan/Algan Multiple Quantum Wells, K. C. Zeng, R. Mair, J. Y. Lin, H. X. Jiang, W. W. Chow, A. Botchkarev, Hadis Morkoç
Plasma Heating In Highly Excited Gan/Algan Multiple Quantum Wells, K. C. Zeng, R. Mair, J. Y. Lin, H. X. Jiang, W. W. Chow, A. Botchkarev, Hadis Morkoç
Electrical and Computer Engineering Publications
Time-resolvedphotoluminescence(PL)spectroscopy was used to investigate carrier distributions in a GaN/AlGaN multiple quantum well(MQW) sample under high excitation intensities necessary to achieve lasing threshold. Room temperaturePL spectra showed optical transitions involving both confined and unconfined states in the quantum well structure. Analysis of the experimental results using a microscopic theory, indicates that at high excitation the carrier distributions are characterized by plasma temperatures which are significantly higher than the lattice temperature. The implications of our findings on GaN MQW laser design are also discussed.
Deep Level Defects In N-Type Gan Grown By Molecular Beam Epitaxy, C. D. Wang, L. S. Yu, S. S. Lau, E. T. Yu, W. Kim, A. E. Botchkarev, Hadis Morkoç
Deep Level Defects In N-Type Gan Grown By Molecular Beam Epitaxy, C. D. Wang, L. S. Yu, S. S. Lau, E. T. Yu, W. Kim, A. E. Botchkarev, Hadis Morkoç
Electrical and Computer Engineering Publications
Deep-level transient spectroscopy has been used to characterize electronic defects in n-type GaN grown by reactive molecular-beam epitaxy. Five deep-level electronic defects were observed, with activation energiesE1=0.234±0.006, E2=0.578±0.006, E3=0.657±0.031, E4=0.961±0.026, and E5=0.240±0.012 eV. Among these, the levels labeled E1, E2, and E3are interpreted as corresponding to deep levels previously reported in n-GaN grown by both hydride vapor-phase epitaxy and metal organic chemical vapor deposition. Levels E4 and E5do not correspond to any previously reported defect levels, and are characterized for the first time in our studies.
Optical Modes Within Iii-Nitride Multiple Quantum Well Microdisk Cavities, R. A. Mair, K. C. Zeng, J. Y. Lin, H. X. Jiang, B. Zhang, L. Dai, A. Botchkarev, W. Kim, Hadis Morkoç, M. A. Khan
Optical Modes Within Iii-Nitride Multiple Quantum Well Microdisk Cavities, R. A. Mair, K. C. Zeng, J. Y. Lin, H. X. Jiang, B. Zhang, L. Dai, A. Botchkarev, W. Kim, Hadis Morkoç, M. A. Khan
Electrical and Computer Engineering Publications
Optical resonance modes have been observed in optically pumped microdisk cavitiesfabricated from 50 Å/50 Å GaN/AlxGa1−xN(x∼0.07) and 45 Å/45 Å InxGa1−xN/GaN(x∼0.15)multiple quantum well structures. Microdisks, approximately 9 μm in diameter and regularly spaced every 50 μm, were formed by an ion beametch process. Individual disks were pumped at 300 and 10 K with 290 nm laser pulses focused to a spot size much smaller than the disk diameter. Optical modes corresponding to (i) the radial mode type with a spacing of 49–51 meV (both TE and TM) and (ii) the Whispering Gallery mode with a spacing of 15–16 meV were …
Effect Of Ammonia Flow Rate On Impurity Incorporation And Material Properties Of Si-Doped Gan Epitaxial Films Grown By Reactive Molecular Beam Epitaxy, Wook Kim, A. E. Botchkarev, H. Morkoç, Z.-Q. Fang, D. C. Look, David J. Smith
Effect Of Ammonia Flow Rate On Impurity Incorporation And Material Properties Of Si-Doped Gan Epitaxial Films Grown By Reactive Molecular Beam Epitaxy, Wook Kim, A. E. Botchkarev, H. Morkoç, Z.-Q. Fang, D. C. Look, David J. Smith
Electrical and Computer Engineering Publications
Effect of ammonia flow rate on the impurity incorporation and material properties of Si-doped GaN films grown by reactive molecular beam epitaxy (RMBE) process is discussed. It appears that the ammonia flow rate has a marginal effect on the incorporation of impurities into the Si-doped GaN films except there was a little decrease in O and Si with increasing ammonia flow rate when the Si concentration in the film is higher than 1018 cm−3. Electron Hall mobility of Si-doped GaN films grown by RMBE varies with ammonia flow rate used during film growth. From deep level transient spectroscopy(DLTS) measurements for …