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Articles 331 - 360 of 364

Full-Text Articles in Electrical and Computer Engineering

Conductance Modulation Of Spin Interferometers, Marc Cahay, Supriyo Bandyopadhyay Jan 2003

Conductance Modulation Of Spin Interferometers, Marc Cahay, Supriyo Bandyopadhyay

Electrical and Computer Engineering Publications

We study the conductance modulation of gate controlled electron spin interferometers (also known as spin field effect transistors) based on the Rashba spin–orbit coupling effect. It is found that the modulation is dominated by Ramsauer (or Fabry-Perot) type transmission resonances rather than the Rashba effect in typical structures. These transmission resonances are due to reflections at the interferometer’s contacts caused by large interface potential barriers and effective mass mismatch between the contact material and the semiconductor. They are particularly strong in quasi-one-dimensional structures which, in fact, are preferred for spin interferometers because of the energy independence of the spin precession …

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Generation–Recombination Noise In Gallium Nitride-Based Quantum Well Structures, Rolando S. Duran, Grover L. Larkins Jr., Carolyn M. Van Vliet, Hadis Morkoç Jan 2003

Generation–Recombination Noise In Gallium Nitride-Based Quantum Well Structures, Rolando S. Duran, Grover L. Larkins Jr., Carolyn M. Van Vliet, Hadis Morkoç

Electrical and Computer Engineering Publications

Electronic noise has been investigated in AlxGa1−xN/GaN modulation-doped field-effect transistors of submicron dimensions, grown by molecular beam epitaxy techniques. Some 20 devices were grown on a sapphire substrate. Conduction takes place in the quasi-two-dimensional (2D) layer of the junction (xy plane) which is perpendicular to the triangular quantum well (z direction). A nondoped intrinsic buffer layer separates the Si-doped donors in the AlxGa1−xN layer from the 2D transistor plane. Since all contacts must reach through the AlxGa1−xN layer to connect internally to the 2D plane, parallel conduction through this layer is a feature of all modulation-doped devices. The …

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Infrared Optical Absorbance Of Intersubband Transitions In Gan/Algan Multiple Quantum Well Structures, Qiaoying Zhou, Jiayu Chen, B. Pattada, M. O. Manasreh, Faxian Xiu, Steve Putigan, K. S. Ramaiah, Hadis Morkoç Jan 2003

Infrared Optical Absorbance Of Intersubband Transitions In Gan/Algan Multiple Quantum Well Structures, Qiaoying Zhou, Jiayu Chen, B. Pattada, M. O. Manasreh, Faxian Xiu, Steve Putigan, K. S. Ramaiah, Hadis Morkoç

Electrical and Computer Engineering Publications

Intersubband transitions in Si-doped molecular beam epitaxygrown GaN/AlGaN multiple quantum wells on c-plane sapphire were investigated using the Fourier-transform infrared optical absorption technique. Several GaN quantum well samples were grown with either AlGaN bulk or GaN/AlGaN short period superlattice barriers. The measurements were made in a waveguide configuration utilizing a facet polished at 45° to the c plane. The integrated area of the intersubband transitions in several waveguides cut from different location of the wafer was measured, from which we estimated the two-dimensional electron gas density (σ). The measured values of σ are about two orders of magnitude larger …

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Unusual Luminescence Lines In Gan, M. A. Reshchikov, D. Huang, F. Yun, P. Visconti, L. He, H. Morkoç, J. Jasinski, Z. Liliental-Weber, R. J. Molnar, S. S. Park, K. Y. Lee Jan 2003

Unusual Luminescence Lines In Gan, M. A. Reshchikov, D. Huang, F. Yun, P. Visconti, L. He, H. Morkoç, J. Jasinski, Z. Liliental-Weber, R. J. Molnar, S. S. Park, K. Y. Lee

Electrical and Computer Engineering Publications

A series of sharp intense peaks was observed in the low-temperature photoluminescence spectrum of unintentionally doped GaN in the photon energy range between 3.0 and 3.46 eV. We attributed the majority of these peaks to excitons bound to unidentified structural and surface defects. Most of the structural- and surface-related peaks (at 3.21, 3.32, 3.34, 3.35, 3.38, and 3.42 eV) were observed in Ga polar films. In N polar GaN, we often observed the 3.45 eV peak attributed to excitons bound to the inversion domain interfaces.

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Contactless Electroreflectance, In The Range Of 20 K < T < 300 K, Of Freestanding Wurtzite Gan Prepared By Hydride-Vapor-Phase Epitaxy, Y. S. Huang, Fred H. Pollak, S. S. Park, K. Y. Lee, H. Morkoç Jan 2003

Contactless Electroreflectance, In The Range Of 20 K < T < 300 K, Of Freestanding Wurtzite Gan Prepared By Hydride-Vapor-Phase Epitaxy, Y. S. Huang, Fred H. Pollak, S. S. Park, K. Y. Lee, H. Morkoç

Electrical and Computer Engineering Publications

We have performed a detailed contactless electroreflectance study of the interband excitonic transitions on both the Ga and N faces of a 200-μm-thick freestanding hydride-vapor-phase-epitaxy grown wurtzite GaN sample with low defect concentration in the temperature range between 20 and 300 K. The transition energies of the A, B, and C excitons and broadening parameters of the A and B excitons have been determined by least-square fits to the first derivative of a Lorentzian line shape. The energy positions and separations of the excitonic transitions in the sample reveal the existence of residual strain. At 20 K the broadening parameter …

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Two Charge States Of Dominant Acceptor In Unintentionally Doped Gan: Evidence From Photoluminescence Study, Michael A. Reshchikov, Hadis Morkoç, S. S. Park, K. Y. Lee Jan 2002

Two Charge States Of Dominant Acceptor In Unintentionally Doped Gan: Evidence From Photoluminescence Study, Michael A. Reshchikov, Hadis Morkoç, S. S. Park, K. Y. Lee

Electrical and Computer Engineering Publications

Photoluminescence of the dominant deep-level acceptor in high-purity freestanding GaN is studied over a wide range of excitation intensities. A yellow luminescence (YL) band at about 2.2 eV saturates with increasing excitation intensity, whereas a green luminescence (GL) band at about 2.5 eV increases as a square of the excitation intensity. The YL and GL bands are attributed to two charge states of the same defect, presumably a gallium vacancy-oxygen complex.

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Backilluminated Gan/Algan Heterojunction Ultraviolet Photodetector With High Internal Gain, S. K. Zhang, W. B. Wang, I. Shtau, F. Yun, L. He, Hadis Morkoç, X. Zhou, M. Tamargo, R. R. Alfano Jan 2002

Backilluminated Gan/Algan Heterojunction Ultraviolet Photodetector With High Internal Gain, S. K. Zhang, W. B. Wang, I. Shtau, F. Yun, L. He, Hadis Morkoç, X. Zhou, M. Tamargo, R. R. Alfano

Electrical and Computer Engineering Publications

We report on a backilluminated GaN/Al0.18Ga0.82Nheterojunction ultraviolet (UV)photodetector with high internal gain based on metal-semiconductor-metal structures. A narrow band pass spectral response between 365 and 343 nm was achieved. When operating in dc mode, the responsivity reaches up to the order of 102 A/W under weak UVillumination, which is due to enormous internal gain up to 103. The linear dependence of photocurrent on bias and its square root dependence on optical power are found and explained by a trapping and recombination model. The high photocurrent gain is attributed to trapping and recombination centers with an acceptor character induced by dislocations …

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Backilluminated Ultraviolet Photodetector Based On Gan/Algan Multiple Quantum Wells, S. K. Zhang, W. B. Wang, F. Yun, L. He, Hadis Morkoç, X. Zhou, M. Tamargo, R. R. Alfano Jan 2002

Backilluminated Ultraviolet Photodetector Based On Gan/Algan Multiple Quantum Wells, S. K. Zhang, W. B. Wang, F. Yun, L. He, Hadis Morkoç, X. Zhou, M. Tamargo, R. R. Alfano

Electrical and Computer Engineering Publications

The operation of backilluminated ultraviolet (UV)photodetector based on GaN/Al0.27Ga0.73Nmultiple quantum wells(MQWs) is reported. The MQW structure was deposited on a 1-μm-thick Al0.35Ga0.65Nbuffer layer which was epitaxied on a sapphire substrate. Coplanar Ohmic contacts were made on the top side of the MQW structure. By illuminating the Ohmic contact positions from the backside of the detector, a flat and narrow band spectral response is achieved in the UV wavelength range from 297 nm to 352 nm. The electron-heavy hole absorption in the MQW region produces the sharp long-wavelength cutoff at 352 nm and the band-to-band absorption of the Al0.35Ga0.65Nbuffer layer introduces …

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Growth Of Gan Films On Porous Sic Substrate By Molecular-Beam Epitaxy, F. Yun, Michael A. Reshchikov, L. He, Hadis Morkoç, C. K. Inoki, T. S. Kuan Jan 2002

Growth Of Gan Films On Porous Sic Substrate By Molecular-Beam Epitaxy, F. Yun, Michael A. Reshchikov, L. He, Hadis Morkoç, C. K. Inoki, T. S. Kuan

Electrical and Computer Engineering Publications

Porous SiC (PSiC) substrates were used for the growth of GaN by reactive molecular-beam epitaxy with ammonia as the nitrogen source. Improved quality of GaNfilms has been demonstrated for growth on PSiC substrates, as compared to that on standard 6H–SiC substrates. Cross-sectional transmission electron microscopy and electron diffraction showed a reduction in dislocation density and a higher degree of lattice and thermal relaxation in the GaNfilmsgrown on porous substrates. The submicron GaNfilms exhibit a rocking curve linewidth of 3.3 arcmin for (0002) diffraction and 13.7 arcmin for (101̄2) diffraction. Low-temperature photoluminescence showed an excitonic transition with a full width at …

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Defect Reduction With Quantum Dots In Gan Grown On Sapphire Substrates By Molecular Beam Epitaxy, D. Huang, Michael A. Reshchikov, F. Yun, T. King, A. A. Baski, Hadis Morkoç Jan 2002

Defect Reduction With Quantum Dots In Gan Grown On Sapphire Substrates By Molecular Beam Epitaxy, D. Huang, Michael A. Reshchikov, F. Yun, T. King, A. A. Baski, Hadis Morkoç

Electrical and Computer Engineering Publications

The GaN films grown on buffer layers containing quantum dots by molecular beam epitaxy on sapphire substrates were investigated. The density of the dislocations in the films was determined by wet chemical etching and atomic force microscopy. It was found that the insertion of a set of multiple GaN quantum-dot layers in the buffer layer effectively reduces the density of the dislocations in the epitaxial layers. As compared to the dislocation density of ∼1010 cm−2in the typical GaN films grown on AlNbuffer layer, a density of ∼3×107 cm−2 was demonstrated in the GaN films grown with quantum dot layers.

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Properties Of Alxga1−Xn Layers Grown By Plasma-Assisted Molecular-Beam Epitaxy Under Ga-Rich Conditions, L. He, Michael A. Reshchikov, F. Yun, D. Huang, T. King, Hadis Morkoç Jan 2002

Properties Of Alxga1−Xn Layers Grown By Plasma-Assisted Molecular-Beam Epitaxy Under Ga-Rich Conditions, L. He, Michael A. Reshchikov, F. Yun, D. Huang, T. King, Hadis Morkoç

Electrical and Computer Engineering Publications

AlxGa1−xN films were grown by plasma-assisted molecular-beam epitaxy on (0001)sapphire substrates under Ga-rich conditions. To control the AlxGa1−xN composition over the entire range, the Al and Ga arrival rates were fixed while the nitrogen arrival rate was varied. We have found that the Al fraction increased with decreasing N flow due to preferentially favorable bonding of Al and N over Ga and N. Consequently, the growth rate decreased as the Al mole fraction increased. A photoluminescence quantum efficiency at 15 K was markedly higher for the AlxGa1−xN layers grown under Ga-rich conditions (3%–48%) compared to the layers grown under N-rich …

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Room-Temperature Single-Electron Charging In Electrochemically Synthesized Semiconductor Quantum Dot And Wire Array, N. Kouklin, L. Menon, Supriyo Bandyopadhyay Jan 2002

Room-Temperature Single-Electron Charging In Electrochemically Synthesized Semiconductor Quantum Dot And Wire Array, N. Kouklin, L. Menon, Supriyo Bandyopadhyay

Electrical and Computer Engineering Publications

Cylindrical quantum dots of diameter ∼8 nm and height 3–10 nm, and wires of diameter 50 nm and height 500–1000 nm, were self-assembled by electrodepositing semiconductors in the nanometer-sized pores of anodic alumina films. Current–voltage characteristics of both wires and dots show Coulomb blockade at room temperature, while the wires also show a Coulomb staircase when exposed to infrared radiation. These results establish that electrochemicalself-assembly is a viable technique for producing nanostructures that have potential uses in room-temperature single electronics.

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Energy Band Bowing Parameter In Alxga1-Xn Alloys, Feng Yun, Michael A. Reshchikov, Lei He, Thomas King, Hadis Morkoç, Steve W. Novak, Luncun Wei Jan 2002

Energy Band Bowing Parameter In Alxga1-Xn Alloys, Feng Yun, Michael A. Reshchikov, Lei He, Thomas King, Hadis Morkoç, Steve W. Novak, Luncun Wei

Electrical and Computer Engineering Publications

Molecular-beam epitaxy grown AlxGa1−xN alloys covering the entire range of alloy compositions, 0⩽x⩽1, have been used to determine the alloy band gap dependence on its composition. The Alchemical composition was deduced from secondary ion mass spectroscopy and Rutherford backscattering. The composition was also inferred from x-ray diffraction. The band gap of the alloy was extracted from low temperature optical reflectance measurements which are relatively more accurate than photoluminescence. Fitting of the band gap data resulted in a bowing parameter of b=1.0 eV over the entire composition range. The improved accuracy of the composition and band gap determination …

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Systematic Measurement Of Alxga1−Xn Refractive Indices, Ü. Özgür, Grady Webb-Wood, Henry O. Everitt, Feng Yun, Hadis Morkoç Jan 2001

Systematic Measurement Of Alxga1−Xn Refractive Indices, Ü. Özgür, Grady Webb-Wood, Henry O. Everitt, Feng Yun, Hadis Morkoç

Electrical and Computer Engineering Publications

Dispersion of the ordinary and extraordinary indices of refraction have been measured systematically for wurtzitic AlxGa1−xNepitaxial layers with 0.0⩽x⩽1.0 throughout the visible wavelength region. The dispersion, measured by a prism coupling waveguide technique, is found to be well described by a Sellmeier relation. Discrepancies among previous measurements of refractive indexdispersion, as a consequence of different growth conditions and corresponding band gap bowing parameter, are reconciled when the Sellmeier relation is parameterized not by x but by band gapenergy.

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Photoluminescence Of Gan Grown By Molecular-Beam Epitaxy On A Freestanding Gan Template, Michael A. Reshchikov, D. Huang, F. Yun, L. He, Hadis Morkoç, D. C. Reynolds, S. S. Park, K. Y. Lee Jan 2001

Photoluminescence Of Gan Grown By Molecular-Beam Epitaxy On A Freestanding Gan Template, Michael A. Reshchikov, D. Huang, F. Yun, L. He, Hadis Morkoç, D. C. Reynolds, S. S. Park, K. Y. Lee

Electrical and Computer Engineering Publications

Photoluminescence(PL) studies were performed on a 1.5-μm-thick GaN layer grown by molecular-beam epitaxy on a freestanding GaN template that in turn was grown by hydride vapor-phase epitaxy.PL spectra from both the epilayer and the substrate contain a plethora of sharp peaks related to excitonic transitions. We identified the main peaks in the PL spectrum. Taking advantage of the observation of donor bound exciton peaks and their associated two-electron satellites, we have determined the binding energies of two distinct shallow donors (28.8 and 32.6 meV), which are attributed to Si and O, respectively.

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Dependence Of Gan Polarity On The Parameters Of The Buffer Layer Grown By Molecular Beam Epitaxy, D. Huang, P. Visconti, K. M. Jones, Michael A. Reshchikov, F. Yun, A. A. Baski, T. King, Hadis Morkoç Jan 2001

Dependence Of Gan Polarity On The Parameters Of The Buffer Layer Grown By Molecular Beam Epitaxy, D. Huang, P. Visconti, K. M. Jones, Michael A. Reshchikov, F. Yun, A. A. Baski, T. King, Hadis Morkoç

Electrical and Computer Engineering Publications

The polarity of GaNfilmsgrown using GaN and AlNbuffer layers on sapphire substrates by molecular beam epitaxy were investigated by atomic force microscopy, hot wet chemical etching, and reflection high-energy electron diffraction. We found that the GaNfilmsgrown on high temperature AlN (>890 °C) and GaN (770–900 °C) buffer layers invariably show Ga and N polarity, respectively. However, the filmsgrown using low temperature (∼500 °C) buffer layers, either GaN or AlN, could have either Ga or N polarity, depending on the growth rate of the buffer layer.

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Yellow And Green Luminescence In A Freestanding Gan Template, Michael A. Reshchikov, Hadis Morkoç, S. S. Park, K. Y. Lee Jan 2001

Yellow And Green Luminescence In A Freestanding Gan Template, Michael A. Reshchikov, Hadis Morkoç, S. S. Park, K. Y. Lee

Electrical and Computer Engineering Publications

We have studied a broad photoluminescence band in high-mobility freestanding 200-μm-thick GaN template prepared by hydride vapor-phase epitaxy. Variable-excitation intensity and energy experiments showed two defect-related bands: a yellow luminescence (YL) band at about 2.15 eV and a green luminescence (GL) band at about 2.43 eV. In contrast to epitaxial GaN samples prepared by both vapor-phase and molecular-beam epitaxy, the YL in the sample studied is weak and can be easily saturated. However, the GL is dominant. We attribute the GL to isolated defects involving galliumvacancies and the YL to the same defect, but bound to dislocations, or possibly to …

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Transient Photoluminescence Of Defect Transitions In Freestanding Gan, Michael A. Reshchikov, Hadis Morkoç, S. S. Park, K. Y. Lee Jan 2001

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 …

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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 Jan 2001

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, …

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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 Jan 2001

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 …

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Blue Photoluminescence Activated By Surface States In Gan Grown By Molecular Beam Epitaxy, Michael A. Reshchikov, P. Visconti, Hadis Morkoç Jan 2001

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 …

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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 Jan 2001

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.

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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 Jan 2000

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 …

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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 Jan 2000

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 …

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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 Jan 2000

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 …

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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 Jan 2000

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.

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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 Jan 2000

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.

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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 Jan 1999

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.

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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 Jan 1998

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 …

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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 Jan 1998

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 …

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