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Electrical and Computer Engineering

Electrical and Computer Engineering Publications

2005

Articles 1 - 20 of 20

Full-Text Articles in Engineering

Study Of System Parameters And Control Design For A Flexible Manipulator Using Piezoelectric Transducers, Mehrdad Kermani Ph.D., P.Eng., Mehrdad Moallem, Rajni Patel Jul 2005

Study Of System Parameters And Control Design For A Flexible Manipulator Using Piezoelectric Transducers, Mehrdad Kermani Ph.D., P.Eng., Mehrdad Moallem, Rajni Patel

Electrical and Computer Engineering Publications

No abstract provided.

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Gan Resistive Hydrogen Gas Sensors, Feng Yun, Serguei A. Chevtchenko, Yong-Tae Moon, Hadis Morkoç, Timothy J. Fawcett, John T. Wolan Jan 2005

Gan Resistive Hydrogen Gas Sensors, Feng Yun, Serguei A. Chevtchenko, Yong-Tae Moon, Hadis Morkoç, Timothy J. Fawcett, John T. Wolan

Electrical and Computer Engineering Publications

GaN epilayers grown by organometallic vapor phase epitaxy have been used to fabricate resistivegas sensors with a pair of planar ohmic contacts. Detectible sensitivity to H2 gas for a wide range of gas mixtures in an Ar ambient has been realized; the lowest concentration tested is ∼0.1% H2 (in Ar), well below the lower combustion limit in air. No saturation of the signal is observed up to 100% H2 flow. Real-time response to H2 shows a clear and sharp response with no memory effects during the ramping cycles of H2 concentration. The change in current at a fixed voltage to …

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Enhancement Of Phase Separation In The Ingan Layer For Self-Assembled In-Rich Quantum Dots, Il-Kyu Park, Min-Ki Kwon, Sung-Ho Baek, Young-Woo Ok, Tae-Yeon Seong, Seong-Ju Park, Yoon-Seok Kim, Yong-Tae Moon, Dong-Joon Kim Jan 2005

Enhancement Of Phase Separation In The Ingan Layer For Self-Assembled In-Rich Quantum Dots, Il-Kyu Park, Min-Ki Kwon, Sung-Ho Baek, Young-Woo Ok, Tae-Yeon Seong, Seong-Ju Park, Yoon-Seok Kim, Yong-Tae Moon, Dong-Joon Kim

Electrical and Computer Engineering Publications

The enhancement of phase separation in the InGaN layer grown on a GaN layer with a rough surface was investigated for the formation of self-assembled In-rich quantum dots(QDs) in the InGaN layer. Transmission electron microscopy images showed that In-rich QDs with a size of 2–5 nm were formed even in an InGaN layer with a low indium content, and a layer thickness less than the critical thickness. The room-temperature photoluminescence(PL) spectrum of this layer showed emission peaks corresponding to In-rich QDs. The temperature-dependent PL spectra showed dominant peak shifts to the lower energy side, indicating that the self-assembled In-rich QDs …

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Effect Of N+-Gan Subcontact Layer On 4h–Sic High-Power Photoconductive Switch, K. Zhu, S. Doğan, Y.-T. Moon, J. Leach, F. Yun, D. Johnstone, Hadis Morkoç, G. Li, B. Ganguly Jan 2005

Effect Of N+-Gan Subcontact Layer On 4h–Sic High-Power Photoconductive Switch, K. Zhu, S. Doğan, Y.-T. Moon, J. Leach, F. Yun, D. Johnstone, Hadis Morkoç, G. Li, B. Ganguly

Electrical and Computer Engineering Publications

High-power photoconductive semiconductor switching devices were fabricated on 4H–SiC. In order to prevent current crowding, reduce the contact resistance, and avoid contact degradation, a highly n-doped GaN subcontact layer was inserted between the contact metal and the high resistivity SiC bulk. This method led to a two orders of magnitude reduction in the on-state resistance and, similarly, the photocurrent efficiency was increased by two orders of magnitude with the GaN subcontact layer following the initial high current operation. Both dry etching and wet etching were used to remove the GaN subcontact layer in the channel area. Wet etching was found …

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Visible-Ultraviolet Spectroscopic Ellipsometry Of Lead Zirconate Titanate Thin Films, Hosun Lee, Youn Seon Kang, Sang-Jun Cho, Bo Xiao, Hadis Morkoç, Tae Dong Kang Jan 2005

Visible-Ultraviolet Spectroscopic Ellipsometry Of Lead Zirconate Titanate Thin Films, Hosun Lee, Youn Seon Kang, Sang-Jun Cho, Bo Xiao, Hadis Morkoç, Tae Dong Kang

Electrical and Computer Engineering Publications

We measured pseudodielectric functions in the visible-ultraviolet spectral range of Pb(ZrxTi1−x)O3 (x=0.2, 0.56, 0.82) (PZT)grown on platinized silicon substrate using the sol-gel method and also on (0001) sapphire using radio frequency sputtering method. Using a parametric optical constant model, we estimated the dielectric functions of the PZTthin films. Taking the second derivative of the fitted layer dielectric functions and using the standard critical point model, we determined the parameters of the critical points. In the second derivative spectra, the lowest bandgap energy peak near 4eV is fitted as a double peak for annealedPZTs associated with the perovskite phase. As-grown PZTs …

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Surface Charging And Current Collapse In An Algan∕Gan Heterostructure Field Effect Transistor, S. Sabuktagin, S. Doğan, A. A. Baski, Hadis Morkoç Jan 2005

Surface Charging And Current Collapse In An Algan∕Gan Heterostructure Field Effect Transistor, S. Sabuktagin, S. Doğan, A. A. Baski, Hadis Morkoç

Electrical and Computer Engineering Publications

This work investigates the correlation between surfacecharging and current collapse in an AlGaN∕GaNheterostructurefield effect transistor.Surfacecharging due to applied biases was sensed by mapping the surface potential between the gate and drain using scanning Kelvin probe microscopy. Due to the bias, the surface band bending near the gate edge was observed to increase by as much as 1 eV. This increase of band bending is caused by an accumulation of excess charge near the surface during the applied bias. By varying the duration of the applied bias, we find that this accumulation of excess charge near the gate takes about 20 …

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Are Spin Junction Transistors Suitable For Signal Processing?, S. Bandyopadhyay, M. Cahay Jan 2005

Are Spin Junction Transistors Suitable For Signal Processing?, S. Bandyopadhyay, M. Cahay

Electrical and Computer Engineering Publications

A number of spintronic analogs of bipolar junction transistors have been proposed for signal processing applications. Here, we show that some of these transistors unfortunately may not have sufficient voltage and current gains for signal processing. They may also have poor isolation between input and output terminals which hinders unidirectional propagation of logic signal from the driver stage to the output. Therefore, these devices may not improve state-of-the-art signal processing capability, although they may provide some additional functionality by offering nonvolatile storage. They may also have niche applications in nonlinear circuits.

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Photoresponse Of N-Zno∕P-Sic Heterojunction Diodes Grown By Plasma-Assisted Molecular-Beam Epitaxy, Ya. I. Alivov, Ü. Özgür, S. Doğan, D. Johnstone, Vitaliy Avrutin, N. Onojima, C. Liu, J. Xie, Q. Fan, Hadis Morkoç Jan 2005

Photoresponse Of N-Zno∕P-Sic Heterojunction Diodes Grown By Plasma-Assisted Molecular-Beam Epitaxy, Ya. I. Alivov, Ü. Özgür, S. Doğan, D. Johnstone, Vitaliy Avrutin, N. Onojima, C. Liu, J. Xie, Q. Fan, Hadis Morkoç

Electrical and Computer Engineering Publications

High quality n-ZnOfilms on commercial p-type 6H–SiC substrates have been grown by plasma-assisted molecular-beam epitaxy, and n-ZnO∕p-SiCheterojunction mesa structures have been fabricated. Current-voltage characteristics of the structures had a very good rectifying diode-like behavior with a leakage current less than 2×10−4A/cm2 at −10V, a breakdown voltage greater than 20V, a forward turn on voltage of ∼5V, and a forward current of ∼2A/cm2 at 8V. Photosensitivity of the diodes was studied at room temperature and a photoresponsivity of as high as 0.045A∕W at −7.5V reverse bias was observed for photonenergies higher than 3.0eV.

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Effectiveness Of Tin Porous Templates On The Reduction Of Threading Dislocations In Gan Overgrowth By Organometallic Vapor-Phase Epitaxy, Y. Fu, Y.-T. Moon, F. Yun, Ü. Özgür, J. Xie, S. Doğan, Hadis Morkoç, C. K. Inoki, T. S. Kuan, Lin Zhou, David J. Smith Jan 2005

Effectiveness Of Tin Porous Templates On The Reduction Of Threading Dislocations In Gan Overgrowth By Organometallic Vapor-Phase Epitaxy, Y. Fu, Y.-T. Moon, F. Yun, Ü. Özgür, J. Xie, S. Doğan, Hadis Morkoç, C. K. Inoki, T. S. Kuan, Lin Zhou, David J. Smith

Electrical and Computer Engineering Publications

We report on the reduction of threading dislocations in GaN overlayers grown by organometallic vapor phase epitaxy on micro-porous TiN networks. These networks were obtained by in situannealing of thin Ti layers deposited in a metalization chamber, on the (0001) face of GaN templates. Observations by transmission electron microscopy indicate dislocation reduction by factors of up to 10 in GaN layers grown on TiN networks compared with the control GaN.X-ray diffraction shows that GaNgrown on the TiN network has a smaller (102) plane peak width (4.6 arcmin) than the control GaN (7.8 arcmin). In low temperature photoluminescence spectra, a …

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Near-Field Optical Spectroscopy And Microscopy Of Self-Assembled Gan∕Aln Nanostructures, A. Neogi, B. P. Gorman, Hadis Morkoç, T. Kawazoe, M. Ohtsu Jan 2005

Near-Field Optical Spectroscopy And Microscopy Of Self-Assembled Gan∕Aln Nanostructures, A. Neogi, B. P. Gorman, Hadis Morkoç, T. Kawazoe, M. Ohtsu

Electrical and Computer Engineering Publications

The spatial distribution and emission properties of small clusters of GaNquantum dots in an AlN matrix are studied using high-resolution electron and optical microscopy. High-resolution transmission electron microscopy reveals near vertical correlation among the GaNdots due to a sufficiently thin AlN spacer layer thickness, which allows strain induced stacking. Scanning electron and atomic force microscopy show lateral coupling due to a surface roughness of ∼50–60nm. Near-field photoluminescence in the illumination mode (both spatially and spectrally resolved) at 10K revealed emission from individual dots, which exhibits size distribution of GaNdots from localized sites in the stacked nanostructure. Strong spatial localization of …

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Long Carrier Lifetimes In Gan Epitaxial Layers Grown Using Tin Porous Network Templates, Ü. Özgür, Y. Fu, Y.-T. Moon, F. Yun, Hadis Morkoç, H. O. Everitt, S. S. Park, K. Y. Lee Jan 2005

Long Carrier Lifetimes In Gan Epitaxial Layers Grown Using Tin Porous Network Templates, Ü. Özgür, Y. Fu, Y.-T. Moon, F. Yun, Hadis Morkoç, H. O. Everitt, S. S. Park, K. Y. Lee

Electrical and Computer Engineering Publications

Improved structural quality and radiative efficiency were observed in GaNthin filmsgrown by metalorganic chemical vapor deposition on TiN porous network templates formed by in situthermal annealing of Ti in ammonia. The room-temperature decay times obtained from biexponential fits to time-resolved photoluminescence data are longer than ever reported for GaN. The carrier lifetime of 1.86 ns measured for a TiN network sample is slightly longer than that for a 200 μm thick high-quality freestanding GaN. The linewidth of the asymmetric x-ray diffraction(XRD)(101¯2) peak decreases considerably with the use of TiN layer and with increasing in situannealing time, indicating the …

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Dielectric Functions And Electronic Band Structure Of Lead Zirconate Titanate Thin Films, Hosun Lee, Youn Seon Kang, Sang-Jun Cho, Bo Xiao, Hadis Morkoç, Tae Dong Kang, Ghil Soo Lee, Jingbo Li, Su-Huai Wei, P. G. Snyder, J. T. Evans Jan 2005

Dielectric Functions And Electronic Band Structure Of Lead Zirconate Titanate Thin Films, Hosun Lee, Youn Seon Kang, Sang-Jun Cho, Bo Xiao, Hadis Morkoç, Tae Dong Kang, Ghil Soo Lee, Jingbo Li, Su-Huai Wei, P. G. Snyder, J. T. Evans

Electrical and Computer Engineering Publications

We measure pseudodielectric functions in the visible-deep ultraviolet spectral range of Pb(ZrxTi1−x)O3 (x=0.2,0.56,0.82) (PZT), Pb0.98Nb0.04 (Zr0.2Ti0.8)0.96O3, Pb0.91La0.09 (Zr0.65Ti0.35)0.98O3, and Pb0.85La0.15Ti0.96O3 films grown on platinized silicon substrates using a sol-gel method and on (0001) sapphire using a radio-frequency sputtering method. Using a parametric optical constant model, we estimate the dielectric functions(ϵ) of the perovskite oxide thin films. Taking the second derivative of the fitted layer dielectric functions and using the standard critical-point model, we determine the parameters of the critical points. In the second derivative spectra, the lowest band-gapenergy peak near 4 eVis fitted as a double peak for annealed PZTs …

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Proposed Model For Bistability In Nanowire Nonvolatile Memory, V. Pokalyakin, S. Tereshin, A. Varfolomeev, D. Zaretsky, A. Baranov, A. Banerjee, Y. Wang, S. Ramanathan, S. Bandyopadhyay Jan 2005

Proposed Model For Bistability In Nanowire Nonvolatile Memory, V. Pokalyakin, S. Tereshin, A. Varfolomeev, D. Zaretsky, A. Baranov, A. Banerjee, Y. Wang, S. Ramanathan, S. Bandyopadhyay

Electrical and Computer Engineering Publications

Cadmium sulfide nanowires of 10‐nm diameter, electrodeposited in porous anodic alumina films, exhibit an electronic bistability that can be harnessed for nonvolatile memory. The current–voltage characteristics of the wires show two stable conductance states that are well separated (conductances differ by more than four orders of magnitude) and long lived (longevity>1 yr at room temperature). These two states can encode binary bits 0 and 1. It is possible to switch between them by varying the voltage across the wires, thus “writing” data. Transport behavior of this system has been investigated at different temperatures in an effort to understand the …

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Growth And Characterization Of Sic Epitaxial Layers On Si- And C-Face 4h Sic Substrates By Chemical-Vapor Deposition, Kodigala Subba Ramaiah, I. Bhat, T. P. Chow, J. K. Kim, E. F. Schubert, D. Johnstone, S. Akarca-Biyikli Jan 2005

Growth And Characterization Of Sic Epitaxial Layers On Si- And C-Face 4h Sic Substrates By Chemical-Vapor Deposition, Kodigala Subba Ramaiah, I. Bhat, T. P. Chow, J. K. Kim, E. F. Schubert, D. Johnstone, S. Akarca-Biyikli

Electrical and Computer Engineering Publications

High-quality Schottky junctions have been fabricated on n-type 4H SiC epitaxial layers grown by chemical-vapor deposition on C- and Si-face substrates in order to understand the effect of growth direction on the growth mechanism and formation of defects. Atomic force microscopy analysis showed dramatic differences between the surfaces of SiC epilayers grown on C and Si faces. There was a significant step bunching in the SiC grown on Si-face substrates. Current-voltage, capacitance-voltage, and deep-level transient spectroscopy (DLTS) measurements were carried out on the Schottky junctions to analyze the junction characteristics. The Schottky junctions on C-face SiC showed larger barrier heights …

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Efficacy Of Single And Double Sinx Interlayers On Defect Reduction In Gan Overlayers Grown By Organometallic Vapor-Phase Epitaxy, F. Yun, Y.-T. Moon, Y. Fu, K. Zhu, U. Ozgur, H. Morkoç, C. K. Inoki, T.S. Kuan, Ashutosh Sagar, R. M. Feenstra Jan 2005

Efficacy Of Single And Double Sinx Interlayers On Defect Reduction In Gan Overlayers Grown By Organometallic Vapor-Phase Epitaxy, F. Yun, Y.-T. Moon, Y. Fu, K. Zhu, U. Ozgur, H. Morkoç, C. K. Inoki, T.S. Kuan, Ashutosh Sagar, R. M. Feenstra

Electrical and Computer Engineering Publications

We report on the growth of and evolution of defects in GaN epilayers having single- and double-layer SiNx nanoporous insertion layers. The SiNx was formed in situ in the growth chamber of an organometallic vapor-phase epitaxy system by simultaneous flow of diluted silane and ammonia. The GaN epilayers and SiNx interlayers were grown on 6H-SiC substrates using three different nucleation layers, namely, low-temperature GaN, high-temperature GaN, and high-temperature AlN nucleation layers. X-ray-diffraction rocking curves and cross-sectional and plan-view transmission electron microscope analyses indicated that a nanoporous SiNx layer can reduce the dislocations density in the GaN overgrown layer to ∼3×108cm−2 …

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Structural Analysis Of Ferromagnetic Mn-Doped Zno Thin Films Deposited By Radio Frequency Magnetron Sputtering, C. Liu, F. Yun, B. Xiao, S.-J. Cho, Y. T. Moon, H. Morkoç, Morad Abouzaid, R. Ruterana, K. M. Yu, W. Walukiewicz Jan 2005

Structural Analysis Of Ferromagnetic Mn-Doped Zno Thin Films Deposited By Radio Frequency Magnetron Sputtering, C. Liu, F. Yun, B. Xiao, S.-J. Cho, Y. T. Moon, H. Morkoç, Morad Abouzaid, R. Ruterana, K. M. Yu, W. Walukiewicz

Electrical and Computer Engineering Publications

We report on the structural analysis of ferromagnetic Mn-doped ZnO thin films deposited by radio frequency magnetron sputtering, using transmission electron microscopy (TEM), high-resolution x-ray diffraction, and Rutherford backscattering spectroscopy (RBS) measurements. The ferromagnetic Mn-doped ZnO film showed magnetization hysteresis at 5 and 300 K. A TEM analysis revealed that the Mn-doped ZnO included a high density of round-shaped cubic and elongated hexagonal MnZn oxide precipitates. The incorporation of Mn caused a large amount of structural disorder in the crystalline columnar ZnO lattice, although the wurtzite crystal structure was maintained. The observed ferromagnetism is discussed based on the structural characteristics …

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Luminescence Properties Of Defects In Gan, Michael A. Reshchikov, Hadis Morkoç Jan 2005

Luminescence Properties Of Defects In Gan, Michael A. Reshchikov, Hadis Morkoç

Electrical and Computer Engineering Publications

Gallium nitride (GaN) and its allied binaries InN and AIN as well as their ternary compounds have gained an unprecedented attention due to their wide-ranging applications encompassing green, blue, violet, and ultraviolet (UV) emitters and detectors (in photon ranges inaccessible by other semiconductors) and high-power amplifiers. However, even the best of the three binaries, GaN, contains many structural and point defects caused to a large extent by lattice and stacking mismatch with substrates. These defects notably affect the electrical and optical properties of the host material and can seriously degrade the performance and reliability of devices made based on these …

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A Comprehensive Review Of Zno Materials And Devices, Ü. Özgür, Ya. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, S. Doğan, Vitaliy Avrutin, S.-J. Cho, H. Morkoç Jan 2005

A Comprehensive Review Of Zno Materials And Devices, Ü. Özgür, Ya. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, S. Doğan, Vitaliy Avrutin, S.-J. Cho, H. Morkoç

Electrical and Computer Engineering Publications

The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60 meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with …

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Increased Carrier Lifetimes In Gan Epitaxial Films Grown Using Sin And Tin Porous Network Layers, Ü. Özgür, Y. Fu, Y. T. Moon, F. Yun, H. Morkoç, H. O. Everitt Jan 2005

Increased Carrier Lifetimes In Gan Epitaxial Films Grown Using Sin And Tin Porous Network Layers, Ü. Özgür, Y. Fu, Y. T. Moon, F. Yun, H. Morkoç, H. O. Everitt

Electrical and Computer Engineering Publications

Improved structural quality and radiative efficiency were observed in GaN thin films grown by metalorganic chemical vapor deposition on SiN and TiN porous network templates. The room-temperature decay times obtained from biexponential fits to time-resolved photoluminescence data are increased with the inclusion of SiN and TiN layers. The carrier lifetime of 1.86 ns measured for a TiN network sample is slightly longer than that for a 200μm-thick high-quality freestanding GaN. The linewidth of the asymmetric x-ray diffraction (XRD) (101¯2) peak decreases considerably with the use of SiN and TiN layers, indicating the reduction in threading dislocation density. However, no direct …

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Applying Unbalanced Rsa To Authentication And Key Distribution In 802.11, Zhong Zheng, Kemal Tepe, Huapeng Wu Jan 2005

Applying Unbalanced Rsa To Authentication And Key Distribution In 802.11, Zhong Zheng, Kemal Tepe, Huapeng Wu

Electrical and Computer Engineering Publications

It is well known that the data confidentiality algorithm, called Wired Equivalent Privacy (WEP), offerred by the original IEEE 802.11 is not secure mainly due to its improper implementation of RC4 algorithm [3], [4]. The IEEE 802.11 Task Group ’I’ (TGi) has designed two options to address this problem. One is called Temporal Key Integrity Protocol (TKIP), intended to be used as a short-term patch for currently deployed equipment. The other one uses Advanced Encryption Standard (AES), a powerful block cipher recommended by NIST to replace DES in 2000, as a long-term solution

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