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Articles 151 - 180 of 364

Full-Text Articles in Electrical and Computer Engineering

The Effect Of Stair Case Electron Injector Design On Electron Overflow In Ingan Light Emitting Diodes, F. Zhang, X. Li, S. Hafiz, S. Okur, Vitaliy Avrutin, U. Ozgur, Hadis Morkoç, A. Matulionis Jan 2013

The Effect Of Stair Case Electron Injector Design On Electron Overflow In Ingan Light Emitting Diodes, F. Zhang, X. Li, S. Hafiz, S. Okur, Vitaliy Avrutin, U. Ozgur, Hadis Morkoç, A. Matulionis

Electrical and Computer Engineering Publications

Effect of two-layer (In0.04Ga0.96N and In0.08Ga0.92N) staircase electron injector (SEI) on quantum efficiency of light-emitting-diodes (LEDs) in the context of active regions composed of single and quad 3 nm double heterostructures (DHs) is reported. The experiments were augmented with the first order model calculations of electron overflow percentile. Increasing the two-layer SEI thickness from 4 + 4 nm up to 20 + 20 nm substantially reduced, if not totally eliminated, the electron overflow in single DH LEDs at low injections without degrading the material quality evidenced by the high optical efficiency observed at 15K and room temperature. The improvement in …

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Ultra-Low-Energy Non-Volatile Straintronic Computing Using Single Multiferroic Composites, Kuntal Roy Jan 2013

Ultra-Low-Energy Non-Volatile Straintronic Computing Using Single Multiferroic Composites, Kuntal Roy

Electrical and Computer Engineering Publications

The primary impediment to continued downscaling of traditional charge-based electronic devices in accordance with Moore's law is the excessive energy dissipation that takes place in the device during switching of bits. One very promising solution is to utilize multiferroicheterostructures, comprised of a single-domain magnetostrictive nanomagnet strain-coupled to a piezoelectric layer, in which the magnetization can be switched between its two stable states while dissipating minuscule amount of energy. However, no efficient and viable means of computing is proposed so far. Here we show that such single multiferroic composites can act as universal logic gates for computing purposes, which we demonstrate …

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Reliability Of Algan/Gan High Electron Mobility Transistors On Low Dislocation Density Bulk Gan Substrate: Implications Of Surface Step Edges, N. Killat, M. Montes Bajo, T. Paskova, K. R. Evans, J. Leach, X. Li, Ü. Özgür, Hadis Morkoç, K. D. Chabak, A. Crespo, J. K. Gillespie, R. Fitch, M. Kossler, D. E. Walker, M. Trejo, G. D. Via, J. D. Blevins, M. Kuball Jan 2013

Reliability Of Algan/Gan High Electron Mobility Transistors On Low Dislocation Density Bulk Gan Substrate: Implications Of Surface Step Edges, N. Killat, M. Montes Bajo, T. Paskova, K. R. Evans, J. Leach, X. Li, Ü. Özgür, Hadis Morkoç, K. D. Chabak, A. Crespo, J. K. Gillespie, R. Fitch, M. Kossler, D. E. Walker, M. Trejo, G. D. Via, J. D. Blevins, M. Kuball

Electrical and Computer Engineering Publications

To enable gaining insight into degradation mechanisms of AlGaN/GaN high electron mobility transistors, devices grown on a low-dislocation-density bulk-GaN substrate were studied. Gateleakage current and electroluminescence (EL) monitoring revealed a progressive appearance of EL spots during off-state stress which signify the generation of gate current leakage paths.Atomic force microscopy evidenced the formation of semiconductor surface pits at the failure location, which corresponds to the interaction region of the gate contact edge and the edges ofsurface steps.

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Acoustically Assisted Spin-Transfer-Torque Switching Of Nanomagnets: An Energy-Efficient Hybrid Writing Scheme For Non-Volatile Memory, Ayan K. Biswas, Supriyo Bandyopadhyay, Jayasimha Atulasimha Jan 2013

Acoustically Assisted Spin-Transfer-Torque Switching Of Nanomagnets: An Energy-Efficient Hybrid Writing Scheme For Non-Volatile Memory, Ayan K. Biswas, Supriyo Bandyopadhyay, Jayasimha Atulasimha

Electrical and Computer Engineering Publications

We show that the energy dissipated to write bits in spin-transfer-torque random access memory can be reduced by an order of magnitude if a surface acoustic wave (SAW) is launched underneath the magneto-tunneling junctions (MTJs) storing the bits. The SAW-generated strain rotates the magnetization of every MTJs' soft magnet from the easy towards the hard axis, whereupon passage of a small spin-polarized current through a target MTJ selectively switches it to the desired state with > 99.99% probability at room temperature, thereby writing the bit. The other MTJs return to their original states at the completion of the SAW cycle.

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Correlation Between Si Doping And Stacking Fault Related Luminescence In Homoepitaxial M-Plane Gan, S. Khromov, B. Monemar, Vitaliy Avrutin, Hadis Morkoç, L. Hultman, G. Pozina Jan 2013

Correlation Between Si Doping And Stacking Fault Related Luminescence In Homoepitaxial M-Plane Gan, S. Khromov, B. Monemar, Vitaliy Avrutin, Hadis Morkoç, L. Hultman, G. Pozina

Electrical and Computer Engineering Publications

Si-doped GaN layers grown by metal organic vapor phase epitaxy on m-plane GaN substrates were investigated by low-temperature cathodoluminescence (CL). We have observed stacking fault (SF) related emission in the range of 3.29–3.42 eV for samples with moderate doping, while for the layers with high concentration of dopants, no CL lines related to SFs have been noted. Perturbation of the SF potential profile by neighboring impurity atoms can explain localization ofexcitons at SFs, while this effect would vanish at high doping levels due to screening.

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Microscopic Distribution Of Extended Defects And Blockage Of Threading Dislocations By Stacking Faults In Semipolar (1101)(1101)()(1101)() Gan Revealed From Spatially Resolved Luminescence, S. Okur, S. Metzner, N. Izyumskaya, F. Zhang, Vitaliy Avrutin, C. Karbaum, F. Bertram, J. Christen, Hadis Morkoç, Ü. Özgür Jan 2013

Microscopic Distribution Of Extended Defects And Blockage Of Threading Dislocations By Stacking Faults In Semipolar (1101)(1101)()(1101)() Gan Revealed From Spatially Resolved Luminescence, S. Okur, S. Metzner, N. Izyumskaya, F. Zhang, Vitaliy Avrutin, C. Karbaum, F. Bertram, J. Christen, Hadis Morkoç, Ü. Özgür

Electrical and Computer Engineering Publications

Spatial distribution of extended defects in semipolar -oriented GaN layers grown on patterned(001) Si substrates with striped grooves of varying width was investigated by optical means only using near-field scanning optical microscopy (NSOM) and cathodoluminescence (CL). A high density of basal and prismatic stacking faults was observed in the c− wings, and the threadingdislocations in c+ wings, which appear as dark patterns in the NSOM and CL images, were found to bend toward the surface during the initial stages of growth. In the case when growingc+ front of GaN made contact with the SiO2 masking layer during growth, stacking …

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Strain Induced Variations In Band Offsets And Built-In Electric Fields In Ingan/Gan Multiple Quantum Wells, L. Dong, J. V. Mantese, Vitaliy Avrutin, Ü. Özgür, H. Morkoç, S. P. Alpay Jan 2013

Strain Induced Variations In Band Offsets And Built-In Electric Fields In Ingan/Gan Multiple Quantum Wells, L. Dong, J. V. Mantese, Vitaliy Avrutin, Ü. Özgür, H. Morkoç, S. P. Alpay

Electrical and Computer Engineering Publications

The band structure, quantum confinement of charge carriers, and their localization affect the optoelectronic properties of compound semiconductor heterostructures and multiple quantum wells (MQWs). We present here the results of a systematic first-principles based density functional theory (DFT) investigation of the dependence of the valence band offsets and band bending in polar and non-polar strain-free and in-plane strained heteroepitaxial In x Ga1- xN(InGaN)/GaN multilayers on the In composition and misfit strain. The results indicate that for non-polar m-plane configurations with [12¯10]InGaN // [12¯10]GaN and [0001]InGaN // [0001]GaN epitaxial alignments, the valence band offset changes linearly from 0 to 0.57 eV …

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Enhanced Microwave Dielectric Tunability Of Ba0.5sr0.5tio3 Thin Films Grown With Reduced Strain On Dysco3 Substrates By Three-Step Technique, Hongrui Liu, Vitaliy Avrutin, Congyong Zhu, Ümit Özgür, Juan Yang, Changzhi Lu, Hadis Morkoç Jan 2013

Enhanced Microwave Dielectric Tunability Of Ba0.5sr0.5tio3 Thin Films Grown With Reduced Strain On Dysco3 Substrates By Three-Step Technique, Hongrui Liu, Vitaliy Avrutin, Congyong Zhu, Ümit Özgür, Juan Yang, Changzhi Lu, Hadis Morkoç

Electrical and Computer Engineering Publications

Tunable dielectric properties of epitaxial ferroelectric Ba0.5Sr0.5TiO3 (BST) thin films deposited on nearly lattice-matched DyScO3 substrates by radio frequency magnetron sputtering have been investigated at microwave frequencies and correlated with residual compressive strain. To reduce the residual strain of the BST films caused by substrate clamping and improve their microwave properties, a three-step deposition method was devised and employed. A high-temperature deposition at 1068 K of the nucleation layer was followed by a relatively low-temperature deposition (varied in the range of 673–873 K) of the BST interlayer and a high-temperature deposition at 1068 K …

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Spectral Distribution Of Excitation-Dependent Recombination Rate In An In0.13ga0.87n Epilayer, K. Jarašiūnas, S. Nargelas, R. Aleksiejūnas, S. Miasojedovas, M. Vengris, S. Okur, H. Morkoç, Ü Özgür, C. Giesen, Ö. Tuna, M. Heuken Jan 2013

Spectral Distribution Of Excitation-Dependent Recombination Rate In An In0.13ga0.87n Epilayer, K. Jarašiūnas, S. Nargelas, R. Aleksiejūnas, S. Miasojedovas, M. Vengris, S. Okur, H. Morkoç, Ü Özgür, C. Giesen, Ö. Tuna, M. Heuken

Electrical and Computer Engineering Publications

Time-resolved optical techniques of photoluminescence (PL), light-induced transient grating(LITG), and differential transmission spectroscopy were used to investigate carrier dynamics in a single 50-nm thick In0.13Ga0.97N epilayer at high photoexcitation levels. Data in wide spectral, temporal, excitation, and temperature ranges revealed novel features in spectral distribution of recombination rates as follows: at low injection levels, an inverse correlation of carrier life time increasing with temperature and diffusivity decreasing with temperature confirmed a mechanism of diffusion-limited nonradiative recombination at extended defects. Carrier dynamics in the spectral region below the absorption edge but ∼70 meV above the PL band …

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Optical Studies Of Strain And Defect Distribution In Semipolar (1(1)Over-Bar01) Gan On Patterned Si Substrates, N. Izyumskaya, F. Zhang, S. Okur, T. Selden, V. Avrutin, Ü. Özgür, S. Metzner, C. Karbaum, F. Bertram, J. Christen, H. Morkoç Jan 2013

Optical Studies Of Strain And Defect Distribution In Semipolar (1(1)Over-Bar01) Gan On Patterned Si Substrates, N. Izyumskaya, F. Zhang, S. Okur, T. Selden, V. Avrutin, Ü. Özgür, S. Metzner, C. Karbaum, F. Bertram, J. Christen, H. Morkoç

Electrical and Computer Engineering Publications

Formation of defects in semipolar ( 11¯01 )-oriented GaN layers grown by metal-organic chemical vapor deposition on patterned Si (001) substrates and their effects on optical properties were investigated by steady-state and time-resolved photoluminescence (PL) and spectrally and spatially resolved cathodoluminescence (CL). Near-band edge emission is found to be dominant in the c +-wings of semipolar ( 11¯01 )GaN, which are mainly free from defect-related emission lines, while the c – wings contain a large number of basal stacking faults. When the advancing c+ and c — fronts meet to coalesce into a continuous film, the existing stacking faults contained …

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Extending Device Performance In Photonic Devices Using Piezoelectric Properties, Gregory Edward Triplett Jan 2013

Extending Device Performance In Photonic Devices Using Piezoelectric Properties, Gregory Edward Triplett

Electrical and Computer Engineering Publications

This study focuses on the influence of epi-layer strain and piezoelectric effects in asymmetric GaInAs/GaAlAs action regions that potentially lead to intra-cavity frequency mixing. The theoretical limits for conduction and valence band offsets in lattice-matched semiconductor structures have resulted in the deployment of non-traditional approaches such as strain compensation to extend wavelength in intersubband devices, where strain limits are related to misfit dislocation generation. Strain and piezoelectric effects have been studied and verified using select photonic device designs. Metrics under this effort also included dipole strength, oscillator strength, and offset of energy transitions, which are strongly correlated with induced piezoelectric …

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Pseudomorphic Growth Of Inas On Misoriented Gaas For Extending Quantum Cascade Laser Wavelength, Gregory Edward Triplett, Charles Meyer, Emily Cheng, Justin Grayer, David Mueller, Denzil Roberts, Samuel Graham Jan 2013

Pseudomorphic Growth Of Inas On Misoriented Gaas For Extending Quantum Cascade Laser Wavelength, Gregory Edward Triplett, Charles Meyer, Emily Cheng, Justin Grayer, David Mueller, Denzil Roberts, Samuel Graham

Electrical and Computer Engineering Publications

The authors have studied the impact of epilayer strain on the deposition of InAs/GaAs on (100) and (111)B with 2 degrees offset toward 2-1-1 surfaces. Consequences of a 7% lattice mismatch between these orientations in the form of three-dimensional growth are less apparent for (111)B with 2 degrees offset toward 2-1-1 surfaces compared to (100). By exploring a range of molecular beam epitaxy process parameters for InAs/GaAs growth and utilizing scanning electron microscopy, atomic force microscopy, and Raman spectroscopy to evaluate the quality of these strained layers, the authors develop empirical models that describe the influence of the process conditions …

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Information Processing With Electron Spins, Supriyo Bandyopadhyay Jan 2012

Information Processing With Electron Spins, Supriyo Bandyopadhyay

Electrical and Computer Engineering Publications

Information processors process information in a variety of ways. The human brain processes information through a highly interconnected system of neurons and synapses, while a digital computer processes information by having a binary switch toggle on and off in response to a stream of binary bits. The “switch” is the most primitive unit of the modern computer. The better it is (faster, more energy efficient, more reliable, etc.), the more advanced is the computer hardware. Energy efficiency, however, is more important than any other attribute, not so much because energy is costly, but because too much energy dissipation prevents increasing …

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Metastable State In A Shape-Anisotropic Single-Domain Nanomagnet Subjected To Spin-Transfer-Torque, Kuntal Roy, Supriyo Bandyopadhyay, Jayasimha Atulasimha Jan 2012

Metastable State In A Shape-Anisotropic Single-Domain Nanomagnet Subjected To Spin-Transfer-Torque, Kuntal Roy, Supriyo Bandyopadhyay, Jayasimha Atulasimha

Electrical and Computer Engineering Publications

We predict the existence of a metastable magnetization state in a single-domain nanomagnet with uniaxial shape anisotropy. It emerges when a spin-polarized current, which delivers a spin-transfer-torque possessing a field-like component, is injected into the nanomagnet. At a metastable state, the internal torque due to nanomagnet's shape anisotropy cancels the externally applied spin-transfer-torque and hence the nettorque acting on the magnetization becomes zero. Therefore, it prevents spin-transfer-torque from switching the magnetization from one stable state along the easy axis to the other, even in the presence of room-temperature thermal fluctuations.

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Degradation And Phase Noise Of Inaln/Aln/Gan Heterojunction Field Effect Transistors: Implications For Hot Electron/Phonon Effects, C. Y. Zhu, M. Wu, C. Kayis, F. Zhang, X. Li, R. A. Ferreyra, A. Matulionis, Vitaliy Avrutin, Umit Ozgur, Hadis Morkoc Jan 2012

Degradation And Phase Noise Of Inaln/Aln/Gan Heterojunction Field Effect Transistors: Implications For Hot Electron/Phonon Effects, C. Y. Zhu, M. Wu, C. Kayis, F. Zhang, X. Li, R. A. Ferreyra, A. Matulionis, Vitaliy Avrutin, Umit Ozgur, Hadis Morkoc

Electrical and Computer Engineering Publications

In15.7%Al84.3%N/AlN/GaN heterojunctionfield effect transistors have been electrically stressed under four different bias conditions: on-state-low-field stress, reverse-gate-bias stress, off-state-high-field stress, and on-state-high-field stress, in an effort to elaborate on hot electron/phonon and thermal effects. DC current and phase noise have been measured before and after the stress. The possible locations of the failures as well as their influence on the electrical properties have been identified. The reverse-gate-bias stress causes trap generation around the gate area near the surface which has indirect influence on the channel. The off-state-high-field stress and the on-state-high-field stress induce deterioration of the channel, …

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Optical And Structural Studies Of Homoepitaxially Grown M-Plane Gan, S. Khromov, B. Monemar, Vitaliy Avrutin, Xing Li, Hadis Morkoç, L. Hultman, G. Pozina Jan 2012

Optical And Structural Studies Of Homoepitaxially Grown M-Plane Gan, S. Khromov, B. Monemar, Vitaliy Avrutin, Xing Li, Hadis Morkoç, L. Hultman, G. Pozina

Electrical and Computer Engineering Publications

Cathodoluminescence(CL) and transmission electron microscopy studies of homoepitaxiallygrownm-plane Mg-doped GaN layers are reported. Layers contain basal plane and prismatic stacking faults (SFs) with ∼106 cm−1 density. Broad emission peaks commonly ascribed to SFs were found to be insignificant in these samples. A set of quite strong, sharp lines were detected in the same spectral region of 3.36–3.42 eV. The observed peaks are tentatively explained as excitons bound to some impurity defects, which can also be related to SFs. Donor-acceptor pair (DAP) recombination involving Si or O and Mg was ruled out by fitting DAP energies and …

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Anisotropy Of Free-Carrier Absorption And Diffusivity In M-Plane Gan, P. Ščajev, K. Jarašiūnas, U. Ozgur, Hadis Morkoç, J. Leach, T. Paskova Jan 2012

Anisotropy Of Free-Carrier Absorption And Diffusivity In M-Plane Gan, P. Ščajev, K. Jarašiūnas, U. Ozgur, Hadis Morkoç, J. Leach, T. Paskova

Electrical and Computer Engineering Publications

Polarization-dependent free-carrier absorption (FCA) in bulk m-plane GaN at 1053 nm revealed approximately 6 times stronger hole-related absorption for E⊥c than for E||c probe polarization both at low and high carrier injection levels. In contrast, FCA at 527 nm was found isotropic at low injection levels due to electron resonant transitions between the upper and lower conduction bands, whereas the anisotropic impact of holes was present only at high injection levels by temporarily blocking electron transitions. Carrier transport was also found to be anisotropic under two-photon excitation, with a ratio of 1.17 for diffusivity perpendicular and parallel to the c-axis.

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Improved Quantum Efficiency In Ingan Light Emitting Diodes With Multi-Double-Heterostructure Active Regions, X. Li, Serdal Okur, F. Zhang, S. A. Hafiz, Vitaliy Avrutin, Umit Ozgur, Hadis Morkoç, K. Jarašiūnas Jan 2012

Improved Quantum Efficiency In Ingan Light Emitting Diodes With Multi-Double-Heterostructure Active Regions, X. Li, Serdal Okur, F. Zhang, S. A. Hafiz, Vitaliy Avrutin, Umit Ozgur, Hadis Morkoç, K. Jarašiūnas

Electrical and Computer Engineering Publications

InGaN light emitting diodes(LEDs) with multiple thin double-heterostrucutre (DH) active regions separated by thin and low energy barriers were investigated to shed light on processes affecting the quantum efficiency and means to improve it. With increasing number of 3 nm-thick DH active layers up to four, the electroluminescence efficiency scaled nearly linearly with the active region thickness owing to reduced carrier overflow with increasing total thickness, showing almost no discernible efficiency degradation at high injection levels up to the measured current density of 500 A/cm2. Comparison of the resonant excitation dependent photoluminescence measurements at 10 K and room …

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Impurity Distribution And Microstructure Of Ga-Doped Zno Films Grown By Molecular Beam Epitaxy, A. V. Kvit, A. B. Yankovich, V. Avrutin, H. Liu, N. Izyumskaya, Ü. H. Özgür, H. Morkoç, P. M. Voyles Jan 2012

Impurity Distribution And Microstructure Of Ga-Doped Zno Films Grown By Molecular Beam Epitaxy, A. V. Kvit, A. B. Yankovich, V. Avrutin, H. Liu, N. Izyumskaya, Ü. H. Özgür, H. Morkoç, P. M. Voyles

Electrical and Computer Engineering Publications

We report microstructural characterization of heavily Ga-doped ZnO (GZO) thin films on GaN and sapphire by aberration-corrected scanning transmission electron microscopy. Growth under oxygen-rich and metal-rich growth conditions leads to changes in the GZO polarity and different extended defects. For GZO layers on sapphire, the primary extended defects are voids, inversion domain boundaries, and low-angle grain boundaries. Ga doping of ZnO grown under metal-rich conditions causes a switch from pure oxygen polarity to mixed oxygen and zinc polarity in small domains. Electron energy loss spectroscopy and energy dispersive spectroscopy spectrum imaging show that Ga is homogeneous, but other residual impurities …

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Donor Behavior Of Sb In Zno, H. Y. Liu, N. Izyumskaya, Vitaliy Avrutin, Ü. Özgür, A. B. Yankovich, A. V. Kvit, P. M. Voyles, H. Morkoç Jan 2012

Donor Behavior Of Sb In Zno, H. Y. Liu, N. Izyumskaya, Vitaliy Avrutin, Ü. Özgür, A. B. Yankovich, A. V. Kvit, P. M. Voyles, H. Morkoç

Electrical and Computer Engineering Publications

Electrical behavior of Sb in ZnO:Sb layers doped in a wide concentration range was studied using temperature dependent Hall effect measurements. The layers were grown by plasma-enhanced molecular beam epitaxy, and the Sb concentration was changed by varying the Sb flux, resulting in electron concentrations in the range of 1016 to nearly 1020 cm−3. Upon annealing, the electron concentration increased slightly and more notable was that the electron mobility significantly improved, reaching a room-temperature value of 110 cm2/V s and a low-temperature value of 145 cm2/V s, close to the maximum of …

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Energy Dissipation And Switching Delay In Stress-Induced Switching Of Multiferroic Nanomagnets In The Presence Of Thermal Fluctuations, Kuntal Roy, Supriyo Bandyopadhyay, Jayasimha Atulasimha Jan 2012

Energy Dissipation And Switching Delay In Stress-Induced Switching Of Multiferroic Nanomagnets In The Presence Of Thermal Fluctuations, Kuntal Roy, Supriyo Bandyopadhyay, Jayasimha Atulasimha

Electrical and Computer Engineering Publications

Switching the magnetization of a shape-anisotropic 2-phase multiferroic nanomagnet with voltage-generated stress is known to dissipate very little energy (<1 aJ for a switching time of ∼0.5 ns) at 0 K temperature. Here, we show by solving the stochastic Landau-Lifshitz-Gilbert equation that switching can be carried out with ∼100% probability in less than 1 ns while dissipating less than 1.5 aJ at room temperature. This makes nanomagnetic logic and memory systems, predicated on stress-induced magnetic reversal, one of the most energy-efficient computing hardware extant. We also study the dependence of energy dissipation, switching delay, and the critical stress needed to switch, on the rate at which stress on the nanomagnet is ramped up or down.

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Impact Of Active Layer Design On Ingan Radiative Recombination Coefficient And Led Performance, X. Li, S. Okur, F. Zhang, V. Avrutin, Ü. Özgür, H. Morkoç, S. M. Hong, S. H. Yen, T. C. Hsu, A. Matulionis Jan 2012

Impact Of Active Layer Design On Ingan Radiative Recombination Coefficient And Led Performance, X. Li, S. Okur, F. Zhang, V. Avrutin, Ü. Özgür, H. Morkoç, S. M. Hong, S. H. Yen, T. C. Hsu, A. Matulionis

Electrical and Computer Engineering Publications

The relative roles of radiative and nonradiative processes and the polarization field on the light emission from blue (∼425 nm) InGaN light emitting diodes (LEDs) have been studied. Single and multiple double heterostructure (DH) designs have been investigated with multiple DH structures showing improved efficiencies. Experimental results supported by numerical simulations of injection dependent electron and hole wavefunction overlap and the corresponding radiative recombination coefficients suggest that increasing the effective active region thickness by employing multiple InGaN DH structures separated by thin and low barriers is promising for LEDs with high efficiency retention at high injection. The use of thin …

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Hexagonal-Based Pyramid Void Defects In Gan And Ingan, A. B. Yankovich, A. V. Kvit, X. Li, F. Zhang, V. Avrutin, H. Y. Liu, N. Izyumskaya, Ü. Özgür, H. Morkoç, P. M. Voyles Jan 2012

Hexagonal-Based Pyramid Void Defects In Gan And Ingan, A. B. Yankovich, A. V. Kvit, X. Li, F. Zhang, V. Avrutin, H. Y. Liu, N. Izyumskaya, Ü. Özgür, H. Morkoç, P. M. Voyles

Electrical and Computer Engineering Publications

We report a void defect in gallium nitride (GaN) and InGaN, revealed by aberration-corrected scanning transmission electron microscopy (STEM). The voids are pyramids with symmetric hexagonal {0001} base facets and {101¯1} side facets. Each pyramid void has a dislocation at the peak of the pyramid, which continues up along the [0001] growth direction to the surface. Some of the dislocations are hexagonal open core screw dislocations with {101¯0} side facets, varying lateral widths, and varying degrees of hexagonal symmetry. STEM electron energy loss spectroscopy spectrum imaging showed a large C concentration inside the void and on the void surfaces. There …

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Carrier Dynamics In Bulk Gan, Patrick Ščajev, Kęstutis Jarašiūnas, Serdal Okur, Ümit Özgür, Hadis Morkoç Jan 2012

Carrier Dynamics In Bulk Gan, Patrick Ščajev, Kęstutis Jarašiūnas, Serdal Okur, Ümit Özgür, Hadis Morkoç

Electrical and Computer Engineering Publications

Carrier dynamics in hydride vapor phase epitaxy grown bulk GaN with very low density of dislocations, 5–8 × 105 cm−2, have been investigated by time-resolved photoluminescence (PL), free carrier absorption, and light-induced transient grating techniques in the carrier density range of 1015 to ∼1019 cm−3 under single and two photon excitation. For two-photon carrier injection to the bulk (527 nm excitation), diffusivity dependence on the excess carrier density revealed a transfer from minority to ambipolar carrier transport with the ambipolar diffusion coefficient D a saturating at 1.6 cm2/s at room temperature. An …

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Electron Scattering Mechanisms In Gzo Films Grown On A-Sapphire Substrates By Plasma-Enhanced Molecular Beam Epitaxy, H. Y. Liu, V. Avrutin, N. Izyumskaya, Ü. Özgür, A. B. Yankovich, A. V. Kvit, P. M. Voyles, H. Morkoç Jan 2012

Electron Scattering Mechanisms In Gzo Films Grown On A-Sapphire Substrates By Plasma-Enhanced Molecular Beam Epitaxy, H. Y. Liu, V. Avrutin, N. Izyumskaya, Ü. Özgür, A. B. Yankovich, A. V. Kvit, P. M. Voyles, H. Morkoç

Electrical and Computer Engineering Publications

We report on the mechanisms governing electron transport using a comprehensive set of ZnO layers heavily doped with Ga (GZO) grown by plasma-enhanced molecular-beam epitaxy on a-plane sapphire substrates with varying oxygen-to-metal ratios and Ga fluxes. The analyses were conducted by temperature dependent Hall measurements which were supported by microstructural investigations as well. Highly degenerate GZO layers with n > 5 × 1020 cm−3 grown under metal-rich conditions (reactive oxygen-to-metal ratio c-direction. For highly conductive GZO layers, ionized-impurity scattering with almost no compensation is the dominant mechanism limiting the mobility in the temperature range from 15 to 330 K …

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Structural And Optical Quality Of Gan Grown On Sc2o3/Y2o3/Si(111), L. Tarnawska, P. Zaumseil, M. A. Schubert, S. Okur, U. Ozgur, H. Morkoç, R. Paszkiewicz, P. Storck, T. Schroeder Jan 2012

Structural And Optical Quality Of Gan Grown On Sc2o3/Y2o3/Si(111), L. Tarnawska, P. Zaumseil, M. A. Schubert, S. Okur, U. Ozgur, H. Morkoç, R. Paszkiewicz, P. Storck, T. Schroeder

Electrical and Computer Engineering Publications

Thick (∼900 nm) GaN layers were grown by molecular beam epitaxy on cost-effective Sc2O3/Y2O3/Si(111) substrates and characterized by x-ray diffraction and photoluminescence. Samples grown in Ga-rich condition show superior structural and optical quality with reduced density of cubic GaN inclusions within the hexagonal matrix and a relatively strong photoluminescence emission at 3.45 eV at 10 K. Cubic inclusions are formed in the initial growth stage and their concentration is reduced with increasing film thickness and after rapid thermal annealing.

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Degradation In Inaln/Aln/Gan Heterostructure Field-Effect Transistors As Monitored By Low-Frequency Noise Measurements: Hot Phonon Effects, C. Kayis, Romualdo A. Ferreyra, M. Wu, X. Li, Ü. Özgür, A. Matulionis, Hadis Morkoç Jan 2011

Degradation In Inaln/Aln/Gan Heterostructure Field-Effect Transistors As Monitored By Low-Frequency Noise Measurements: Hot Phonon Effects, C. Kayis, Romualdo A. Ferreyra, M. Wu, X. Li, Ü. Özgür, A. Matulionis, Hadis Morkoç

Electrical and Computer Engineering Publications

Low-frequency noise technique was applied to analyze performance of nearly lattice-matched InAlN/AlN/GaN heterostructure field-effect transistors and their degradation caused by electrical stress. Nearly identical devices from the same wafer have undergone a 7 h DC electrical stress at a fixed DC drain bias of VDS = 20 V and different gate biases. We noted up to 32 dB/Hz higher low-frequency noise for stressed devices over the entire frequency range of 1 Hz-100 kHz. The measurements showed the minimum degradation at a gate-controlled two-dimensional electron gas density of 9.4 × 1012 cm−2. This result is in good …

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Camelback Channel For Fast Decay Of Lo Phonons In Gan Heterostructure Field-Effect Transistor At High Electron Density, E. Šermukšnis, J. Liberis, M. Ramonas, Jacob H. Leach, M. Wu, Vitaliy Avrutin, Hadis Morkoç Jan 2011

Camelback Channel For Fast Decay Of Lo Phonons In Gan Heterostructure Field-Effect Transistor At High Electron Density, E. Šermukšnis, J. Liberis, M. Ramonas, Jacob H. Leach, M. Wu, Vitaliy Avrutin, Hadis Morkoç

Electrical and Computer Engineering Publications

Fluctuation technique is used to measure hot-phonon lifetime in dual channel GaN-based configuration proposed to support high-power operation at high frequencies. The channel is formed of a composite Al0.1Ga0.9N/GaN structure situated in an Al0.82In0.18N/AlN/Al0.1Ga0.9N/GaN heterostructure. According to capacitance–voltage measurements and simultaneous treatment of Schrödinger–Poisson equations, the mobile electrons in this dual channel configuration form a camelback density profile at elevated hot-electron temperatures. The hot-phonon lifetime was found to depend on the shape of the electron profile rather than solely on its sheet density. The camelback channel with an …

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Hybrid Spintronics And Straintronics: A Magnetic Technology For Ultra Low Energy Computing And Signal Processing, Kuntal Roy, Supriyo Bandyopadhyay, Jayasimha Atulasimha Jan 2011

Hybrid Spintronics And Straintronics: A Magnetic Technology For Ultra Low Energy Computing And Signal Processing, Kuntal Roy, Supriyo Bandyopadhyay, Jayasimha Atulasimha

Electrical and Computer Engineering Publications

The authors show that the magnetization of a 2-phase magnetostrictive/piezoelectric multiferroic single-domain shape-anisotropic nanomagnet can be switched with very small voltages that generate strain in the magnetostrictive layer. This can be the basis of ultralow power computing and signal processing. With appropriate material choice, the energy dissipated per switching event can be reduced to ∼45 kT at room temperature for a switching delay of ∼100 ns and ∼70 kT for a switching delay of ∼10 ns, if the energy barrier separating the two stable magnetization directions is ∼32 kT. Such devices can be powered by harvesting energy exclusively from the …

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Motional Modes In Bulk Powder And Few-Molecule Clusters Of Tris(8-Hydroxyquinoline Aluminum) And Their Relation To Spin Dephasing, Lopamurda Das, Jennette Mateo, Saumil Bandyopadhyay, Supriyo Bandyopadhyay, Jarrod D. Edwards, John Anderson Jan 2011

Motional Modes In Bulk Powder And Few-Molecule Clusters Of Tris(8-Hydroxyquinoline Aluminum) And Their Relation To Spin Dephasing, Lopamurda Das, Jennette Mateo, Saumil Bandyopadhyay, Supriyo Bandyopadhyay, Jarrod D. Edwards, John Anderson

Electrical and Computer Engineering Publications

The ensemble averaged spin dephasing rate of localized electrons in the organic molecule tris(8-hydroxyquinoline aluminum) or Alq3 has been found to be significantly larger in bulk powder than in single- or few-molecule clusters confined within 1–2 nm sized nanocavities [B. Kanchibotla et al., Phys. Rev. B78, 193306 (2008)]. To understand this observation, we have compared the midinfrared absorption spectra of bulk powder and single- or few-molecule clusters. It appears that molecules have additional vibrational modes in bulk powder possibly due to multimerization. Their coupling with spin may be responsible for the increased spin dephasing rate in bulk powder.

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