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Electrical and Computer Engineering

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Virginia Commonwealth University

2002

Articles 1 - 8 of 8

Full-Text Articles in Engineering

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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