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2006

Electrical and Computer Engineering Publications

Articles 1 - 29 of 29

Full-Text Articles in Engineering

A Multicultural Comparison Of Engineering Students, Zaki Shakir Seddigi, Luiz Fernando Capretz Apr 2006

A Multicultural Comparison Of Engineering Students, Zaki Shakir Seddigi, Luiz Fernando Capretz

Electrical and Computer Engineering Publications

A multicultural personality profile of engineering students is presented in this work. The Myers-Briggs Type Indicator (MBTI) was used as an instrument to sort personality types of engineering students at both King Fahd University of Petroleum and Minerals in Saudi Arabia and University of Western Ontario in Canada. The paper discusses the differences and similarities in the personality profile of Saudi and Canadian engineering students and its implications for engineering education in the light of the MBTI scales.

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Normal And Inverse Spin-Valve Effect In Organic Semiconductor Nanowires And The Background Monotonic Magnetoresistance, Sandipan Pramanik, Supriyo Bandyopadhyay, Kalyan Garre, Marc Cahay Jan 2006

Normal And Inverse Spin-Valve Effect In Organic Semiconductor Nanowires And The Background Monotonic Magnetoresistance, Sandipan Pramanik, Supriyo Bandyopadhyay, Kalyan Garre, Marc Cahay

Electrical and Computer Engineering Publications

We have observed both peaks and troughs in the magnetoresistance of organic nanowires consisting of three layers—cobalt, 8-hydroxy-quinolinolato aluminum (Alq3), and nickel. They always occur between the coercive fields of the ferromagnetic layers, and we attribute them to the normal and inverse spin-valve effect. The latter is caused by resonant tunneling through localized impurity states in the organic material. Peaks are always found to be accompanied by a positive monotonic background magnetoresistance, while troughs are accompanied by a negative monotonic background magnetoresistance. This curious correlation suggests that the background magnetoresistance, whose origin has hitherto remained unexplained, is probably caused by …

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Surface Band Bending Of A-Plane Gan Studied By Scanning Kelvin Probe Microscopy, S. A. Chevtchenko, X. Ni, Q. Fan, A. A. Baski, Hadis Morkoç Jan 2006

Surface Band Bending Of A-Plane Gan Studied By Scanning Kelvin Probe Microscopy, S. A. Chevtchenko, X. Ni, Q. Fan, A. A. Baski, Hadis Morkoç

Electrical and Computer Engineering Publications

We report the value of surface band bending for undoped, a-plane GaN layers grown on r-plane sapphire by metalorganic vapor phase epitaxy. The surface potential was measured directly by ambient scanning Kelvin probe microscopy. The upward surface band bending of GaN films grown in the [112¯0] direction was found to be 1.1±0.1V. Because polarization effects are not present on a-plane GaN, we attribute such band bending to the presence of charged surface states. We have modeled the surface band bending assuming a localized level of surface states in the band gap on the surface. It should be noted that the …

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Defect Reduction In (112¯0) A-Plane Gan By Two-Stage Epitaxial Lateral Overgrowth, X. Ni, Ü. Özgür, Y. Fu, N. Biyikli, J. Xie, A. A. Baski, Hadis Morkoç, Z. Liliental-Weber Jan 2006

Defect Reduction In (112¯0) A-Plane Gan By Two-Stage Epitaxial Lateral Overgrowth, X. Ni, Ü. Özgür, Y. Fu, N. Biyikli, J. Xie, A. A. Baski, Hadis Morkoç, Z. Liliental-Weber

Electrical and Computer Engineering Publications

The authors report a two-stage epitaxial lateral overgrowth (ELO) method to get uniformly coalesced (112¯0) a-plane GaN using metal organic chemical vapor deposition by employing a relatively lower growth temperature in the first stage followed by conditions leading to enhanced lateral growth in the second. Using a two-stage ELO method the average Ga-polar to N-polar wing growth rate ratio has been reduced from 4–6 to 1.5–2, which consequently reduced the height difference between the two approaching wings at the coalescence front that resulted from the wing tilt (0.44° for Ga and 0.37° for N wings, measured by x-ray diffraction), thereby …

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Band Offset Measurements Of Zno∕6h-Sic Heterostructure System, Ya. I. Alivov, Bo Xiao, Q. Fan, Hadis Morkoç, D. Johnstone Jan 2006

Band Offset Measurements Of Zno∕6h-Sic Heterostructure System, Ya. I. Alivov, Bo Xiao, Q. Fan, Hadis Morkoç, D. Johnstone

Electrical and Computer Engineering Publications

The conduction band offset of n-ZnO∕n-6H-SiCheterostructures fabricated by rf-sputtered ZnO on commercial n-type 6H-SiC substrates has been measured by a variety of methods. Temperature dependent current-voltage characteristic, photocapacitance, and deep level transient spectroscopy measurements showed the conduction band offsets to be 1.25, 1.1, and 1.22eV, respectively.

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Near-Field Scanning Optical Microscopy And Time-Resolved Optical Characterization Of Epitaxial Lateral Overgrown C-Plane And A-Plane Gan, Ü. Özgür, X. Ni, Y. Fu, Hadis Morkoç, H. O. Everitt Jan 2006

Near-Field Scanning Optical Microscopy And Time-Resolved Optical Characterization Of Epitaxial Lateral Overgrown C-Plane And A-Plane Gan, Ü. Özgür, X. Ni, Y. Fu, Hadis Morkoç, H. O. Everitt

Electrical and Computer Engineering Publications

Epitaxial lateral overgrowth (ELO) was employed for both c-plane and a-plane GaN layers on sapphire, and a more pronounced optical improvement was observed for the a-plane GaN as evidenced by the significantly increased band edge photoluminescence(PL). Room temperature near-field scanning optical microscopy studies explicitly showed enhanced optical quality in the wing regions of the overgrown GaN due to reduced density of dislocations, and for the a-plane ELOGaN sample the wings and the windows were clearly discernible from PL mapping. Time-resolved PLmeasurements revealed biexponential decays with time constants that were significantly enhanced for the a-plane ELOGaN (τ1=0.08ns, τ2=0.25ns) when compared to …

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Comparative Study Of The (0001) And (0001) Surfaces Of Zno, S. A. Chevtchenko, J. C. Moore, Ü. Özgür, Xing Gu, A. A. Baski, Hadis Morkoç, B. Nemeth, J. E. Nause Jan 2006

Comparative Study Of The (0001) And (0001) Surfaces Of Zno, S. A. Chevtchenko, J. C. Moore, Ü. Özgür, Xing Gu, A. A. Baski, Hadis Morkoç, B. Nemeth, J. E. Nause

Electrical and Computer Engineering Publications

The authors compare the surface and optical properties of the Zn-polar (0001) and O-polar (0001¯)surfaces of bulk ZnO samples. For optical characterization, steady-state photoluminescence using a He–Cd laser was measured at 15 and 300K. At room temperature, the (0001¯)surface demonstrates nearly double the near-band-edge emission intensity seen for the (0001) surface. Using scanning Kelvin probe microscopy, the authors have measured surface contact potentials of 0.39±0.05 and 0.50±0.05V for the (0001) and (0001¯)surfaces, respectively. The resulting small difference in band bending for these two surfaces indicates that charge transfer between the surfaces is not a dominant stabilizing mechanism. Conductive atomic force …

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I-V Characteristics Of Au∕Ni Schottky Diodes On Gan With Sinx Nanonetwork, J. Xie, Yi Fu, Xianfeng Ni, S. A. Chevtchenko, Hadis Morkoç Jan 2006

I-V Characteristics Of Au∕Ni Schottky Diodes On Gan With Sinx Nanonetwork, J. Xie, Yi Fu, Xianfeng Ni, S. A. Chevtchenko, Hadis Morkoç

Electrical and Computer Engineering Publications

Room temperature and temperature dependent current-voltage characteristics of Ni∕AuSchottky diodes fabricated on undoped GaN prepared with and without in situ SiNxnanonetwork by metal organic chemical vapor deposition have been studied. The features of the Schottky diodes depend strongly on the SiNx deposition conditions, namely, its thickness. Reduction in the point and line defect densities caused the Schottky barrier height to increase to1.13eV for 5min SiNx deposition time as compared to 0.78eV without SiNx nanonetwork. Similarly, the breakdown voltage also improved from 76V for the reference to 250V when SiNx nanonetwork was used. With optimized SiNx nanonetwork, full width at half …

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Near-Infrared Wavelength Intersubband Transitions In Gan∕Aln Short Period Superlattices, E. D. Decuir Jr., Emil Fred, B. S. Passmore, A. Muddasani, M. O. Manasreh, Jinqiao Xie, Hadis Morkoç, M. E. Ware, G. J. Salamo Jan 2006

Near-Infrared Wavelength Intersubband Transitions In Gan∕Aln Short Period Superlattices, E. D. Decuir Jr., Emil Fred, B. S. Passmore, A. Muddasani, M. O. Manasreh, Jinqiao Xie, Hadis Morkoç, M. E. Ware, G. J. Salamo

Electrical and Computer Engineering Publications

Intersubband transitions in GaN∕AlN short period superlattices prepared by molecular beam epitaxy were investigated using the optical absorption technique. The peak position wavelengths of these transitions are found to span the spectral range of 1.35–2.90μm for samples cut into 45° waveguides with GaNquantum well thicknesses ranging between 1.70 and2.41nm. The Fermi energy levels are estimated from the carrier concentrations, which were measured using an electrochemical capacitance-voltage profiler. The well widths were inferred from comparing the measured peak position energy of the intersubband transitions and the bound state energy levels calculated using the transfer matrix method.

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Observation Of Numerous E2 Mode Phonon Replicas In The Room Temperature Photoluminescence Spectra Of Zno Nanowires: Evidence Of Strong Deformation Potential Electron-Phonon Coupling, S. Ramanathan, S. Bandyopadhyay, L. K. Hussey, M. Muñoz Jan 2006

Observation Of Numerous E2 Mode Phonon Replicas In The Room Temperature Photoluminescence Spectra Of Zno Nanowires: Evidence Of Strong Deformation Potential Electron-Phonon Coupling, S. Ramanathan, S. Bandyopadhyay, L. K. Hussey, M. Muñoz

Electrical and Computer Engineering Publications

The authors report the observation of numerous (>20)phonon replica peaks in the room temperature photoluminescence spectrum of ZnOnanowires embedded in 50nm diameter pores of an anodic alumina film. The peaks are spaced in energy by ∼54meV, which is the energy of a nonpolar phonon with symmetry E2 in ZnO. These peaks are possibly caused by resonant phonon-assisted decay of photoexcited electrons to an impurity band, followed by radiative recombination. These results suggest that even though ZnO is strongly polar, deformation potential coupling to a nonpolar phonon mode may be stronger than Fröhlich coupling to polar phonon modes.

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High Quality Epitaxial Growth Of Pbtio3 By Molecular Beam Epitaxy Using H2o2 As The Oxygen Source, Xing Gu, Natalia Izyumskaya, Vitaliy Avrutin, Hadis Morkoç, Tae Dong Kang, Hosun Lee Jan 2006

High Quality Epitaxial Growth Of Pbtio3 By Molecular Beam Epitaxy Using H2o2 As The Oxygen Source, Xing Gu, Natalia Izyumskaya, Vitaliy Avrutin, Hadis Morkoç, Tae Dong Kang, Hosun Lee

Electrical and Computer Engineering Publications

Single crystalline PbTiO3films have been epitaxially grown on SrTiO3 (001) substrates by molecular beam epitaxy using H2O2 as the source of active oxygen. The optimum growth conditions have been determined by analyzing a range of growth parameters affecting growth and used to attain single phase and stoichiometric PbTiO3thin films.In situ reflection high-energy electron diffraction pattern indicated the PbTiO3films to be grown under a two-dimensional growth mode. The full width at half maximum of the rocking curve of a relatively thin65nm (001) PbTiO3film is 6.2arcmin which is indicative of high crystal quality. The band gap of PbTiO3, as determined by …

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Subpicosecond Time-Resolved Raman Studies Of Lo Phonons In Gan: Dependence On Photoexcited Carrier Density, K. T. Tsen, Juliann G. Kiang, D. K. Ferry, Hadis Morkoç Jan 2006

Subpicosecond Time-Resolved Raman Studies Of Lo Phonons In Gan: Dependence On Photoexcited Carrier Density, K. T. Tsen, Juliann G. Kiang, D. K. Ferry, Hadis Morkoç

Electrical and Computer Engineering Publications

Subpicosecond time-resolved Raman spectroscopy has been used to measure the lifetime of the LO phonon mode in GaN for photoexcited electron-hole pair density ranging from1016to2×1019cm−3 . The lifetime has been found to decrease from 2.5ps , at low density, to0.35ps , at the highest density. The experimental findings should help resolve the recent controversy over the lifetime of LO phonon mode in GaN.

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Infrared Absorption In A Quantum Wire: A Technique To Measure Different Types Of Spin-Orbit Interaction Strengths, S. Bandyopadhyay, S. Sarkar Jan 2006

Infrared Absorption In A Quantum Wire: A Technique To Measure Different Types Of Spin-Orbit Interaction Strengths, S. Bandyopadhyay, S. Sarkar

Electrical and Computer Engineering Publications

We show that the dominant absorption peak due to intersubband transition in a gated quantum wire will split into a main peak and two satellite peaks if both Rashba and Dresselhaus spin-orbit interactions are present. One satellite peak will be redshifted, and the other blueshifted. From the relative intensity of either satellite peak, and the magnitude of the red- or blueshift, we can determine both Rashba and Dresselhaus interaction strengths separately, if we also carry out a Hall measurement to determine the carrier concentration and a quantized conductance step measurement to determine the energy separation between subbands. This method …

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Quantitative Mobility Spectrum Analysis Of Algan∕Gan Heterostructures Using Variable-Field Hall Measurements, N. Biyikli, J. Xie, Y.-T. Moon, F. Yun, C.-G. Stefanita, S. Bandyopadhyay, Hadis Morkoç, I. Vurgaftman Jan 2006

Quantitative Mobility Spectrum Analysis Of Algan∕Gan Heterostructures Using Variable-Field Hall Measurements, N. Biyikli, J. Xie, Y.-T. Moon, F. Yun, C.-G. Stefanita, S. Bandyopadhyay, Hadis Morkoç, I. Vurgaftman

Electrical and Computer Engineering Publications

Carrier transport properties of AlGaN∕GaNheterostructures have been analyzed with the quantitative mobility spectrum analysis (QMSA) technique. The nominally undoped Al0.08Ga0.92N∕GaN sample was grown by plasma-assisted molecular beam epitaxy on a GaN/sapphire template prepared with hydride vapor phase epitaxy. Variable-magnetic-field Hall measurements were carried out in the temperature range of 5–300K and magnetic field range of 0.01–7T. QMSA was applied to the experimental variable-field data to extract the concentrations and mobilities associated with the high-mobility two-dimensional electron gas and the relatively low-mobility bulk electrons for the temperature range investigated. The mobilities at T=80K are found to be 7100 and 880cm2/Vs, respectively, …

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In Situ Pendeoepitaxy Of Gan Using Heteroepitaxial Algan∕Gan Cracks, Y. T. Moon, C. Liu, J. Xie, X. Ni, Y. Fu, Hadis Morkoç, Lin Zhou, David J. Smith Jan 2006

In Situ Pendeoepitaxy Of Gan Using Heteroepitaxial Algan∕Gan Cracks, Y. T. Moon, C. Liu, J. Xie, X. Ni, Y. Fu, Hadis Morkoç, Lin Zhou, David J. Smith

Electrical and Computer Engineering Publications

Pendeoepitaxy on patterned templates has been proven to be efficient for reducing threading dislocation densities in GaN thin films. In this letter, we report on in situ crack-assisted pendeoepitaxy of GaN using spontaneously formed cracks in AlGaN∕GaNheterostructures. Our approach involves the growth of an AlGaN∕GaNtemplate followed by in situ thermal etching and deposition of an amorphous silicon nitride mask in a low pressure metal organic chemical vapor deposition system. Microwirelike GaN seeds are then formed along the crack lines during the initial stage of GaN overgrowth, which act as nucleation stripes for epitaxial lateral overgrowth. Transmission electron microscopy revealed that …

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Fabrication And Current-Voltage Characterization Of A Ferroelectric Lead Zirconate Titanate/Algan∕Gan Field Effect Transistor, Youn-Seon Kang, Qian Fan, Bo Xiao, Ya. I. Alivov, Jinqiao Xie, Norio Onojima, Sang-Jun Cho, Yong-Tae Moon, Hosun Lee, D. Johnstone, Hadis Morkoç, Young-Soo Park Jan 2006

Fabrication And Current-Voltage Characterization Of A Ferroelectric Lead Zirconate Titanate/Algan∕Gan Field Effect Transistor, Youn-Seon Kang, Qian Fan, Bo Xiao, Ya. I. Alivov, Jinqiao Xie, Norio Onojima, Sang-Jun Cho, Yong-Tae Moon, Hosun Lee, D. Johnstone, Hadis Morkoç, Young-Soo Park

Electrical and Computer Engineering Publications

We demonstrated ferroelectricfield effect transistors (FFETs) with hysteretic I-V characteristics in a modulation-doped field effect transistors(MODFET)AlGaN∕GaN platform with ferroelectricPb(Zr,Ti)O3 between a GaN channel and a gate metal. The pinch-off voltage was about 6–7V comparable to that of conventional Schottky gate MODFET. Counterclockwise hysteresis appeared in the transfer characteristics with a drain current shift of ∼5mA for zero gate-to-source voltage. This direction is opposite and much more pronounced than the defect induced clockwise hysteresis in conventional devices, which suggests that the key factor contributing to the counterclockwise hysteresis of the FFET is the ferroelectric switching effect of the lead zirconate titanate …

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Effect Of Hydrostatic Pressure On The Dc Characteristics Of Algan∕Gan Heterojunction Field Effect Transistors, Y. Liu, P. P. Ruden, J. Xie, Hadis Morkoç, K.-A. Son Jan 2006

Effect Of Hydrostatic Pressure On The Dc Characteristics Of Algan∕Gan Heterojunction Field Effect Transistors, Y. Liu, P. P. Ruden, J. Xie, Hadis Morkoç, K.-A. Son

Electrical and Computer Engineering Publications

We report the effect of compressive hydrostatic pressure on the current-voltage characteristics ofAlGaN∕GaNheterojunction field effect transistors (HFETs) on a sapphire substrate. The drain current increases with hydrostatic pressure and the maximum relative increase occurs when the gate bias is near threshold and drain bias is slightly larger than saturation bias. The increase of the drain current is associated with a pressure induced shift of the threshold voltage by −8.0mV∕kbar that is attributed to an increase of the polarizationcharge density at the AlGaN∕GaN interface due to the piezoelectric effect. The results demonstrate the considerable potential of AlGaN∕GaNHFETs for strain sensor applications.

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Effect Of C∕Si Ratio On Deep Levels In Epitaxial 4h–Sic, C. W. Litton, D. Johnstone, S. Akarca-Biyikli, K. S. Ramaiah, I. Bhat, T. P. Chow, J. K. Kim, E. F. Schubert Jan 2006

Effect Of C∕Si Ratio On Deep Levels In Epitaxial 4h–Sic, C. W. Litton, D. Johnstone, S. Akarca-Biyikli, K. S. Ramaiah, I. Bhat, T. P. Chow, J. K. Kim, E. F. Schubert

Electrical and Computer Engineering Publications

Changing the ratio of carbon to silicon during the epitaxial 4H–SiC growth is expected to alter the dominant deep level trap, which has been attributed to a native defect. The C∕Si ratio was changed from one to six during epitaxialgrowth of SiC. Diodes fabricated on the epitaxial layer were then characterized using current-voltage and deep level transient spectroscopy. The single peak at 340K (Z1/Z2 peak), was deconvolved into two traps, closely spaced in energy. The concentration of one of the Z1/Z2 traps decreased with increasing C∕Si ratio. This result opposes theoretical predictions of carboninterstitial components, and supports assignment to a …

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Admittance Of Cds Nanowires Embedded In Porous Alumina Template, A. Varfolomeev, D. Zaretsky, V. Pokalyakin, S. Tereshin, S. Pramanik, S. Bandyopadhyay Jan 2006

Admittance Of Cds Nanowires Embedded In Porous Alumina Template, A. Varfolomeev, D. Zaretsky, V. Pokalyakin, S. Tereshin, S. Pramanik, S. Bandyopadhyay

Electrical and Computer Engineering Publications

CdSnanowires of 10nm diameter, electrodeposited in porous alumina films, had shown a conductance bistability in the past [Appl. Phys. Lett.76, 460 (2000)]. The conductance has a high (ON) and a low (OFF) state. In the ON state, different sets of nanowires display qualitatively different relation between the conductance and capacitance. We propose a model to explain this anomalous behavior. Based on this model, we predict that the inelastic mean free path of electrons in the nanowires is 3–3.5nm at room temperature. This short mean free path may be a consequence of acoustic phonon confinement.

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Gallium Desorption Kinetics On (0001) Gan Surface During The Growth Of Gan By Molecular-Beam Epitaxy, L. He, Y.-T. Moon, J. Xie, M. Muñoz, D. Johnstone, Hadis Morkoç Jan 2006

Gallium Desorption Kinetics On (0001) Gan Surface During The Growth Of Gan By Molecular-Beam Epitaxy, L. He, Y.-T. Moon, J. Xie, M. Muñoz, D. Johnstone, Hadis Morkoç

Electrical and Computer Engineering Publications

Gallium (Ga) surfacedesorption behavior was investigated using reflection high-energy electron diffraction during the GaNgrowth. It was found that the desorption of Ga atoms from the (0001) GaNsurfaces under different III-V ratio dependents on the coverage of adsorbed atoms. Doing so led to desorption energies of 2.76 eV for Ga droplets, 1.24–1.89 eV for Ga under Ga-rich growth conditions, and 0.82 eV – 0.94 eV for Ga under stoichiometric growth conditions. Moreover, the variation of the GaNsurface morphology under different III-V ratios on porous templates supports the conclusion that Ga desorption energy depends on the coverage, and the III/V ratio dominates …

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Spin Relaxation Of “Upstream” Electrons In Quantum Wires: Failure Of The Drift Diffusion Model, Sandipan Pramanik, Supriyo Bandyopadhyay, Marc Cahay Jan 2006

Spin Relaxation Of “Upstream” Electrons In Quantum Wires: Failure Of The Drift Diffusion Model, Sandipan Pramanik, Supriyo Bandyopadhyay, Marc Cahay

Electrical and Computer Engineering Publications

The classical drift diffusion (DD) model of spin transport treats spin relaxation via an empirical parameter known as the “spin diffusion length.” According to this model, the ensemble averaged spin of electrons drifting and diffusing in a solid decays exponentially with distance due to spin dephasing interactions. The characteristic length scale associated with this decay is the spin diffusion length. The DD model also predicts that this length is different for “upstream” electrons traveling in a decelerating electric field than for “downstream” electrons traveling in an accelerating field. However, this picture ignores energy quantization in confined systems (e.g., quantum wires) …

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Weak Antilocalization And Zero-Field Electron Spin Splitting In Alxga1−Xn∕Aln∕Gan Heterostructures With A Polarization-Induced Two-Dimensional Electron Gas, Ç Kurdak, N. Biyikli, Ü. Özgür, Hadis Morkoç, V. I. Litvinov Jan 2006

Weak Antilocalization And Zero-Field Electron Spin Splitting In Alxga1−Xn∕Aln∕Gan Heterostructures With A Polarization-Induced Two-Dimensional Electron Gas, Ç Kurdak, N. Biyikli, Ü. Özgür, Hadis Morkoç, V. I. Litvinov

Electrical and Computer Engineering Publications

Spin-orbit coupling is studied using the quantum interference corrections to conductance in AlxGa1−xN∕AlN∕GaN two-dimensional electron systems where the carrier density is controlled by the persistent photoconductivity effect. All the samples studied exhibit a weak antilocalization feature with a spin-orbit field of around 1.8mT. The zero-field electron spin splitting energies extracted from the weak antilocalization measurements are found to scale linearly with the Fermi wave vector (ESS=2αkf) with an effective linear spin-orbit coupling parameter α=5.5×10−13eVm. The spin-orbit times extracted from our measurements varied from 0.74 to 8.24pswithin the carrier density range of this experiment.

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Dislocation Reduction In Gan Grown On Porous Tin Networks By Metal-Organic Vapor-Phase Epitaxy, Y. Fu, F. Yun, Y. T. Moon, Ü. Özgür, J. Q. Xie, X. F. Ni, N. Biyikli, H. Morkoç, Lin Zhou, David J. Smith, C. K. Inoki, T. S. Kuan Jan 2006

Dislocation Reduction In Gan Grown On Porous Tin Networks By Metal-Organic Vapor-Phase Epitaxy, Y. Fu, F. Yun, Y. T. Moon, Ü. Özgür, J. Q. Xie, X. F. Ni, N. Biyikli, H. Morkoç, Lin Zhou, David J. Smith, C. K. Inoki, T. S. Kuan

Electrical and Computer Engineering Publications

We report on the effectiveness of porous TiN nanonetworks on the reduction of threading dislocations (TDs) in GaN grown by metal-organic vapor-phase epitaxy (MOVPE). The porous TiN networks were formed by in situ annealing of thin-deposited Ti films deposited ex situ on GaN templates within the MOVPE growth chamber. Different annealing parameters in relation to surface porosity of TiN networks were investigated. Transmission electron micrographs indicated dislocation reduction by factors of up to 10 in GaN layers grown on the TiN nanonetwork, compared with a control sample. TiN prevented many dislocations present in the GaN templates from penetrating into the …

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Effect Of Hydrostatic Pressure On The Current-Voltage Characteristics Of Gan∕Algan∕Gan Heterostructure Devices, Y. Liu, M. Z. Kauser, D. D. Schroepfer, P. P. Ruden, J. Xie, Y. T. Moon, N. Onojima, H. Morkoç, K.-A. Son, M. I. Nathan Jan 2006

Effect Of Hydrostatic Pressure On The Current-Voltage Characteristics Of Gan∕Algan∕Gan Heterostructure Devices, Y. Liu, M. Z. Kauser, D. D. Schroepfer, P. P. Ruden, J. Xie, Y. T. Moon, N. Onojima, H. Morkoç, K.-A. Son, M. I. Nathan

Electrical and Computer Engineering Publications

The current-voltage characteristics of n-GaN∕u-AlGaN∕n-GaN heterostructure devices are investigated for potential pressure sensor applications. Model calculations suggest that the current decreases with pressure as a result of the piezoelectric effect, and this effect becomes more significant with thicker AlGaN layers and increasing AlN composition. The change in current with pressure is shown to be highly sensitive to the change in interfacial polarization charge densities. The concept is verified by measuring the current versus voltage characteristics of an n-GaN∕u-Al0.2Ga0.8N∕n-GaN device under hydrostatic pressure over the range of 0–5 kbars. The measured current is found to decrease approximately linearly with applied pressure …

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Growth Optimization And Structural Analysis For Ferromagnetic Mn-Doped Zno Layers Deposited By Radio Frequency Magnetron Sputtering, M. Abouzaid, P. Ruterana, C. Liu, H. Morkoç Jan 2006

Growth Optimization And Structural Analysis For Ferromagnetic Mn-Doped Zno Layers Deposited By Radio Frequency Magnetron Sputtering, M. Abouzaid, P. Ruterana, C. Liu, H. Morkoç

Electrical and Computer Engineering Publications

The effect of the deposition temperature on the crystalline quality of (Zn,Mn)O is investigated in thin films prepared by radio frequency magnetronsputtering on c-plane sapphire and GaN substrates. The layers are made of a 0.5μm Mn-doped layer towards the surface on top of a 150nm pure ZnO buffer. Depending on the deposition temperature, the layers can exhibit a columnar structure; the adjacent domains are rotated from one another by 90°, putting [101¯0]and [11¯20] directions face to face. At high Mn concentration the columnar structure is blurred by the formation of Mn rich precipitates. Only one variety of domains is observed …

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Spin Relaxation In A Germanium Nanowire, S. Patibandla, S. Pramanik, S. Bandyopadhyay, G. C. Tepper Jan 2006

Spin Relaxation In A Germanium Nanowire, S. Patibandla, S. Pramanik, S. Bandyopadhyay, G. C. Tepper

Electrical and Computer Engineering Publications

We report experimental study of spin transport in nanowirespin valve structures consisting of three layers—cobalt, germanium, and nickel. The spin diffusion length in the Ge is estimated to be about 400nm at 1.9K and the corresponding spin relaxation time is about 4ns. At 100K, the spin diffusion length drops to 180nm and the relaxation time is about 0.81ns. These short relaxation times, which depend weakly on temperature, are caused by strong surface roughness scattering that causes rapid spin relaxation via the Elliott-Yafet mode [Elliott, Phys. Rev.96, 266 (1954)].

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Spectroscopic Ellipsometry And Absorption Study Of Zn1-Xmnxo/Al2o3 (0 <= X <= 0.08) Thin Films, Ghil Soo Lee, Ho Suk Lee, Tae Dong Kang, Hosun Lee, C. Liu, B. Xiao, Ü. Özgür, H. Morkoç Jan 2006

Spectroscopic Ellipsometry And Absorption Study Of Zn1-Xmnxo/Al2o3 (0 <= X <= 0.08) Thin Films, Ghil Soo Lee, Ho Suk Lee, Tae Dong Kang, Hosun Lee, C. Liu, B. Xiao, Ü. Özgür, H. Morkoç

Electrical and Computer Engineering Publications

We grow Zn1−xMnxO∕Al2O3 (0⩽x⩽0.08)thin films on sapphire (0001) using radio-frequency sputtering deposition method with Ar and various N2 flow rates. We examine the effect of N2 codoping on the band gap and Mn-related midgap absorption of (Zn,Mn)O. Using spectroscopic ellipsometry, we measure pseudodielectric functions in the spectral range between 1 and 4.5eV. Using the model of Holden et al. [T. Holden et al., Phys. Rev. B56, 4037 (1997)], we determine the uniaxial (Zn,Mn)O dielectric function and the E0 band-gapenergy. The fitted band gap does not change appreciably with increasing Mn composition up to 2%. We find a very large …

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Illumination And Annealing Characteristics Of Two-Dimensional Electron Gas Systems In Metal-Organic Vapor-Phase Epitaxy Grown Alxga1-Xn/Aln/Gan Heterostructures, N. Biyikli, Ü. Özgür, X. Ni, Y. Fu, H. Morkoç, Ç. Kurdak Jan 2006

Illumination And Annealing Characteristics Of Two-Dimensional Electron Gas Systems In Metal-Organic Vapor-Phase Epitaxy Grown Alxga1-Xn/Aln/Gan Heterostructures, N. Biyikli, Ü. Özgür, X. Ni, Y. Fu, H. Morkoç, Ç. Kurdak

Electrical and Computer Engineering Publications

We studied the persistent photoconductivity (PPC) effect in AlxGa1−xN∕AlN∕GaN heterostructures with two different Al compositions (x=0.15and x=0.25). The two-dimensional electron gas formed at the AlN∕GaN heterointerface was characterized by Shubnikov-de Haas and Hall measurements. Using optical illumination, we were able to increase the carrier density of the Al0.15Ga0.85N∕AlN∕GaN sample from 1.6×1012 to 5.9×1012cm−2, while the electron mobility was enhanced from 9540 to 21400cm2/Vs at T=1.6K. The persistent photocurrent in both samples exhibited a strong dependence on illumination wavelength, being highest close to the band gap and decreasing at longer wavelengths. The PPC effect became fairly weak for illumination wavelengths longer …

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Spin Relaxation In A Germanium Nanowire, S. Patibandla, S. Pramanik, S. Bandyopadhyay, G. C. Tepper Jan 2006

Spin Relaxation In A Germanium Nanowire, S. Patibandla, S. Pramanik, S. Bandyopadhyay, G. C. Tepper

Electrical and Computer Engineering Publications

We report experimental study of spin transport in nanowirespin valve structures consisting of three layers—cobalt, germanium, and nickel. The spin diffusion length in the Ge is estimated to be about 400nm at 1.9K and the corresponding spin relaxation time is about 4ns. At 100K, the spin diffusion length drops to 180nm and the relaxation time is about 0.81ns. These short relaxation times, which depend weakly on temperature, are caused by strong surface roughness scattering that causes rapid spin relaxation via the Elliott-Yafet mode [Elliott, Phys. Rev.96, 266 (1954)].

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