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Articles 1 - 11 of 11
Full-Text Articles in Electrical and Computer Engineering
Two-Subband Conduction In A Gated High Density Inaln/Aln/Gan Heterostructure, H. Cheng, C. Kurdak, J. H. Leach, M. Wu, Hadis Morkoç
Two-Subband Conduction In A Gated High Density Inaln/Aln/Gan Heterostructure, H. Cheng, C. Kurdak, J. H. Leach, M. Wu, Hadis Morkoç
Electrical and Computer Engineering Publications
Magnetotransport measurements on an In0.16Al0.84N/AlN/GaN gated Hall bar sample have been performed at 0.28 K. By the application of a gate voltage we were able to vary the total two-dimensional electron gas density from 1.83×1013 to 2.32×1013 cm−2. Two frequency Shubnikov–de Haas oscillations indicate occupation of two subbands by electrons. The density of electrons in the first and second sublevels are found to increase linearly with gate voltage with a slope of 2.01×1012 cm−2/V and 0.47×1012 cm−2/V, respectively. And the quantum lifetimes for the first and second subbands ranged from 0.55 to 0.95×10−13 s and from 1.2 to 2.1×10−13 s.
Surface Plasmon Enhanced Uv Emission In Algan/Gan Quantum Well, J. Lin, A. Mohammadizia, A. Neogi, Hadis Morkoç, M. Ohtsu
Surface Plasmon Enhanced Uv Emission In Algan/Gan Quantum Well, J. Lin, A. Mohammadizia, A. Neogi, Hadis Morkoç, M. Ohtsu
Electrical and Computer Engineering Publications
The surface plasmon (SP) energy for resonant enhancement of light has shown to be modified by the epitaxial substrate and the overlying metalthin film. The modification of SP energy in AlGaN/GaN epitaxial layers is studied using spectroscopic ellipsometry for enhanced UV-light emission. Silver induced SP can be extended to the UV wavelength range by increasing the aluminum concentration in AlxGa1−xN epilayer. A threefold increase in the UV-light emission is observed from AlGaN/GaN quantum well due to silver induced SP. Photoluminescence lifetime measurements confirm the resonant plasmon induced increase in Purcell factor as observed from the PL intensity measurements.
Ingan Staircase Electron Injector For Reduction Of Electron Overflow In Ingan Light Emitting Diodes, X. Ni, X. Li, J. Lee, S. Liu, Vitaliy Avrutin, Ü. Özgür, Hadis Morkoç, A. Matulionis, T. Paskova, G. Mulholland, K. R. Evans
Ingan Staircase Electron Injector For Reduction Of Electron Overflow In Ingan Light Emitting Diodes, X. Ni, X. Li, J. Lee, S. Liu, Vitaliy Avrutin, Ü. Özgür, Hadis Morkoç, A. Matulionis, T. Paskova, G. Mulholland, K. R. Evans
Electrical and Computer Engineering Publications
Ballistic and quasiballistic electron transport across the active InGaN layer are shown to be responsible for electron overflow and electroluminescence efficiency droop at high current levels in InGaN light emitting diodes both experimentally and by first-order calculations. An InGaN staircase electron injector with step-like increased In composition, an “electron cooler,” is proposed for an enhanced thermalization of the injected hot electrons to reduce the overflow and mitigate the efficiency droop. The experimental data show that the staircase electron injector results in essentially the same electroluminescence performance for the diodes with and without an electron blocking layer, confirming substantial …
Effect Of Hot Phonon Lifetime On Electron Velocity In Inaln/Aln/Gan Heterostructure Field Effect Transistors On Bulk Gan Substrates, J. H. Leach, C. Y. Zhu, M. Wu, X. Ni, X. Li, J. Xie, Ü. Özgür, Hadis Morkoç, J. Liberis, E. Šermukšnis, A. Matulionis, T. Paskova, E. Preble, K. R. Evans
Effect Of Hot Phonon Lifetime On Electron Velocity In Inaln/Aln/Gan Heterostructure Field Effect Transistors On Bulk Gan Substrates, J. H. Leach, C. Y. Zhu, M. Wu, X. Ni, X. Li, J. Xie, Ü. Özgür, Hadis Morkoç, J. Liberis, E. Šermukšnis, A. Matulionis, T. Paskova, E. Preble, K. R. Evans
Electrical and Computer Engineering Publications
We report on electron velocities deduced from current gain cutoff frequency measurements on GaN heterostructurefield effect transistors(HFETs) with InAlN barriers on Fe-doped semi-insulating bulk GaN substrates. The intrinsic transit time is a strong function of the applied gate bias, and a minimum intrinsic transit time occurs for gate biases corresponding to two-dimensional electron gas densities near 9.3×1012 cm−2. This value correlates with the independently observed density giving the minimum longitudinal optical phonon lifetime. We expect the velocity, which is inversely proportional to the intrinsic transit time, to be limited by scattering with non equilibrium (hot) phonons at the high fields …
Carrier Velocity In Inaln/Aln/Gan Heterostructure Field Effect Transistors On Fe-Doped Bulk Gan Substrates, J. H. Leach, M. Wu., X. Ni, X. Li, J. Xie, Ü. Özgür, Hadis Morkoç, T. Paskova, E. Preble, K. R. Evans, Chang-Zhi Lu
Carrier Velocity In Inaln/Aln/Gan Heterostructure Field Effect Transistors On Fe-Doped Bulk Gan Substrates, J. H. Leach, M. Wu., X. Ni, X. Li, J. Xie, Ü. Özgür, Hadis Morkoç, T. Paskova, E. Preble, K. R. Evans, Chang-Zhi Lu
Electrical and Computer Engineering Publications
We report microwave characteristics of field effect transistors employing InAlN/AlN/GaN heterostructures grown on low-defect-density bulk Fe-doped GaN substrates. We achieved unity current gain cutoff frequencies of 14.3 and 23.7 GHz for devices with gate lengths of 1 and 0.65 μm, respectively. Measurements as a function of applied bias allow us to estimate the average carrier velocity in the channel to be ∼1.0×107 cm/sec for a 1 μm device. Additionally, we found nearly no gate lag in the devices, which is considered a precondition for good performance under large signal operation.
Dominant Spin Relaxation Mechanism In Compound Organic Semiconductors, Supriyo Bandyopadhyay
Dominant Spin Relaxation Mechanism In Compound Organic Semiconductors, Supriyo Bandyopadhyay
Electrical and Computer Engineering Publications
Despite the recent interest in “organic spintronics,” the dominant spin relaxation mechanism of electrons or holes in an organic compound semiconductor has not been conclusively identified. There have been sporadic suggestions that it might be hyperfine interaction caused by background nuclear spins, but no confirmatory evidence to support this has ever been presented. Here, we report the electric-field dependence of the spin-diffusion length in an organic spin-valve structure consisting of an Alq3 spacer layer, and argue that these data, as well as the available data on the temperature dependence of this length, contradict the notion that hyperfine interactions relax spin. …
Electrically And Magnetically Tunable Phase Shifters Based On A Barium Strontium Titanate-Yttrium Iron Garnet Layered Structure, J. H. Leach, H. Liu, V. Avrutin, E. Rowe, Ü. Özgür, H. Morkoç, Y.-Y. Song, M. Wu
Electrically And Magnetically Tunable Phase Shifters Based On A Barium Strontium Titanate-Yttrium Iron Garnet Layered Structure, J. H. Leach, H. Liu, V. Avrutin, E. Rowe, Ü. Özgür, H. Morkoç, Y.-Y. Song, M. Wu
Electrical and Computer Engineering Publications
We report on the tuning of permittivity and permeability of a ferroelectric/ferromagnetic bilayer structure which can be used as a microwavephase shifter with two degrees of tuning freedom. The structure was prepared by the growth of a yttrium iron garnet (YIG) layer on a gadolinium gallium garnet substrate by liquid phase epitaxy, the growth of a barium strontium titanate (BST) layer on the YIG layer through pulsed laser deposition, and then the fabrication of a coplanar waveguide on the top of BST through e-beam evaporation and trilayer liftoff techniques. The phase shifters exhibit a differential phase shift of 38°/cm at …
Large Dielectric Tuning And Microwave Phase Shift At Low Electric Field In Epitaxial Ba0.5sr0.5tio3 On Srtio3, J. H. Leach, H. Liu, V. Avrutin, B. Xiao, Ü. Özgür, H. Morkoç, J. Das, Y. Y. Song, C. E. Patton
Large Dielectric Tuning And Microwave Phase Shift At Low Electric Field In Epitaxial Ba0.5sr0.5tio3 On Srtio3, J. H. Leach, H. Liu, V. Avrutin, B. Xiao, Ü. Özgür, H. Morkoç, J. Das, Y. Y. Song, C. E. Patton
Electrical and Computer Engineering Publications
Dielectric properties of annealed and as-grown ferroelectricBa0.5Sr0.5TiO3 (BST) grown by pulsed laser deposition on sputtered BST seed layers on strontium titanate (STO) substrates were investigated at microwave frequencies in the realm of tunability of its dielectric constant as well as phase shifters based on this material. The as-grown layers were nearly fully relaxed with measured lattice parameters nearly identical to those of bulk BST. The tuning of the relative dielectric constant (∼1750 at zero bias at 10 GHz) of the annealed BST was found to be as high as 59% and 56% at 10 and 19 GHz, respectively. The analysis …
Bias Dependent Two-Channel Conduction In Inaln/Aln/Gan Structures, J. H. Leach, X. Ni, X. Li, M. Wu, Ü. Özgür, H. Morkoç, L. Zhou, D. A. Cullen, D. J. Smith, H. Cheng, Ç. Kurdak, J. R. Meyer, I. Vurgaftman
Bias Dependent Two-Channel Conduction In Inaln/Aln/Gan Structures, J. H. Leach, X. Ni, X. Li, M. Wu, Ü. Özgür, H. Morkoç, L. Zhou, D. A. Cullen, D. J. Smith, H. Cheng, Ç. Kurdak, J. R. Meyer, I. Vurgaftman
Electrical and Computer Engineering Publications
Due to growth temperature differences during deposition of GaN heterostructures utilizing InAlN barriers, an inadvertent parasitic GaN layer can form in the InAlN barrier layer. In structures utilizing AlN spacer layers, this parasitic layer acts as a second conduction channel with a carrier density dependent upon polarization charges and lattice strain as well as the surface potential. The effect of an additional GaN spacer layer in InAlN/AlN/GaN structures is assessed using simulations, electron-microscopy observations, magnetoconductivity measurements with gated Hall bar samples, and with quantitative mobility spectrum analysis. We propose a possible formation mechanism for the parasitic layer, and note that …
Ti/Al/Ni/Au Ohmic Contacts For Alinn/Aln/Gan-Based Heterojunction Field-Effect Transistors, Lin Zhou, Jacob H. Leach, Xianfeng Ni, Hadis Morkoç, David J. Smith
Ti/Al/Ni/Au Ohmic Contacts For Alinn/Aln/Gan-Based Heterojunction Field-Effect Transistors, Lin Zhou, Jacob H. Leach, Xianfeng Ni, Hadis Morkoç, David J. Smith
Electrical and Computer Engineering Publications
The microstructure of AuNiAlTi/Al0.84In0.16N/AlN/GaNOhmic contacts annealed from 700 to 900 °C has been determined using transmission electron microscopy and associated analytical techniques. Intermixing and phase separation of the metal contact layers was observed to degrade the surface roughness. An optimal contact performance was obtained for contacts annealed at 800 °C and was attributed to the formation of TiN contact inclusions that had penetrated through the AlInN layers into the GaN layers underneath. These TiN contact inclusions had an inverted mushroom shape with a density of ∼108 cm−2, and they were invariably located at the positions of mixed-type threading dislocations. These …
Hot Electron Effects On Efficiency Degradation In Ingan Light Emitting Diodes And Designs To Mitigate Them, X. Ni, X. Li, J. Lee, S. Liu, V. Avrutin, Ü. Özgür, H. Morkoç, A. Matulionis
Hot Electron Effects On Efficiency Degradation In Ingan Light Emitting Diodes And Designs To Mitigate Them, X. Ni, X. Li, J. Lee, S. Liu, V. Avrutin, Ü. Özgür, H. Morkoç, A. Matulionis
Electrical and Computer Engineering Publications
Hot electrons and the associated ballistic and quasiballistic transport, heretofore neglected endemically, across the active regions of InGaN light emitting diodes (LEDs) have been incorporated into a first order simple model which explains the experimental observations of electron spillover and the efficiency degradation at high injection levels. The model is in good agreement with experiments wherein an adjustable barrier hot electron stopper, commonly called the electron blocking layer (EBL), is incorporated. The model is also in agreement with experiments wherein the electrons are cooled, eliminating hot electrons, inside a staircase electron injector (SEI) prior to their injection into the active …