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Articles 1 - 30 of 46
Full-Text Articles in Engineering
Hybrid Solar Cells From Water-Soluble Polymers, James T. Mcleskey Jr., Qiquan Qiao
Hybrid Solar Cells From Water-Soluble Polymers, James T. Mcleskey Jr., Qiquan Qiao
Mechanical and Nuclear Engineering Publications
We report on the use of a water-soluble, light-absorbing polythiophene polymer to fabricate novel photovoltaic devices. The polymer is a water-soluble thiophene known as sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate] or PTEBS. The intention is to take advantage of the properties of conjugated polymers (flexible, tunable, and easy to process) and incorporate the additional benefits of water solubility (easily controlled evaporation rates and environmentally friendly). The PTEBS polythiophene has shown significant photovoltaic response and has been found to be effective for making solar cells. To date, solar cells in three different configurations have been produced: titanium dioxide (TiO2) bilayer cells, TiO2 bulk heterojunction solar …
Normal And Inverse Spin-Valve Effect In Organic Semiconductor Nanowires And The Background Monotonic Magnetoresistance, Sandipan Pramanik, Supriyo Bandyopadhyay, Kalyan Garre, Marc Cahay
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 …
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
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 …
Design And Validation Of A Full Contact Gait Simulator For The Cadaveric Lower Extremity, Joseph Michael Iaquinto
Design And Validation Of A Full Contact Gait Simulator For The Cadaveric Lower Extremity, Joseph Michael Iaquinto
Theses and Dissertations
The projects goal was to create a device to simulate full contact gait in the cadaveric lower extremity. The Contact Gait Simulation System loads specific muscles to recreate anatomical dorsi and plantar flexion of the ankle under axial loading. A system of pneumatic load generation was connected a LabVIEW virtual instrument (VI), which controlled the application of these loads. The loads were roughly based off literature cited EMG data, and further modified from feedback. In addition to controlling the load system, the VI also coordinates external sensor timing. Along with this simulator, software was developed specifically for analyzing pressure data …
Development Of A Software Application To Extract The Features Of Normal Respiratory Sounds From The Lungs And The Trachea, Ranjani Sabarinathan
Development Of A Software Application To Extract The Features Of Normal Respiratory Sounds From The Lungs And The Trachea, Ranjani Sabarinathan
Theses and Dissertations
Auscultation has been widely regarded as one of the most important noninvasive diagnostic tools for clinical diagnosis of the respiratory tract. The purpose of this thesis was to develop a software application capable of extracting the key features of respiratory sound signals from the lungs and trachea of healthy persons. The efficacy of the program was evaluated by the verification of the important features of the sound signals from the left and right lungs and the trachea such as 1) right and left lung symmetry and 2) dissimilarity between the trachea and both lungs. The program was developed in LabView …
The Effect Of Stationary Uv Excitation On The Optical Behavior Of Electrochemically Self-Assembled Semiconductor Nanowires, Rajesh A. Katkar
The Effect Of Stationary Uv Excitation On The Optical Behavior Of Electrochemically Self-Assembled Semiconductor Nanowires, Rajesh A. Katkar
Theses and Dissertations
In this work, we investigate the optical response of the semiconductor quantum wire array when excited by stationary UV light. The array is synthesized by selectively electro-depositing the semiconductor material in electrochemically self-assembled porous alumina templates. Our studies are based on the optical behavioral changes in CdS, ZnO, ZnSe and CdSe quantum wires of 50-, 25- and 10-nm diameters. We use a set of generalized Bloch equations to solve the interband polarization function of the semiconductors derived within the Hartree-Fock approximation, and theoretically model the UV excitation effect on the quantum wires. The solutions which consider the effects of screening, …
A Wireless Surface Electromyography (Wsemg) System, Aleeta E. Bell
A Wireless Surface Electromyography (Wsemg) System, Aleeta E. Bell
Theses and Dissertations
Surface Electromyography (SEMG) systems are utilized throughout the medical industry to study abnormal electrical activity of the human muscle. Historically, SEMG systems employ surface (skin) mounted sensors that transmit electrical muscle data to a computer base via an umbilical cord. A typical SEMG analysis may exercise multiple sensors, each representing a unique data channel, positioned about the patient's body. Data transmission cables are linked between the surface mounted sensor nodes and a backpack worn by the patient. As the number of sensors increases, the patient's freedom of mobility decreases due to the lengthy data cables linked between the surface sensors …
Detection, Identification And Classification Of Suck, Swallow And Breathing Activity In Premature Infants During Bottle-Feeding, Fedra Adnani
Theses and Dissertations
Prematurity, especially if extreme, is one of the leading causes of problems and/or death after delivery. Among all the problems encountered by premature infants, feeding difficulties are very common. Many premature infants are fed intravenously at first, and they progress to milk feedings provided by a tube passed into the stomach. At around 34 weeks of gestation, premature infants should be able to breastfeed or take a bottle. At the same time such premature infants are usually faced with difficulty making the transition from tube-feeding to full oral feeding. In this study three physiological measurements of premature infants including sucking, …
Evaluation Of Prototype Cell Delivery Catheters Using Agarose Gel And Cell Culture Experiments, Sagar Panse
Evaluation Of Prototype Cell Delivery Catheters Using Agarose Gel And Cell Culture Experiments, Sagar Panse
Theses and Dissertations
Neurodegenerative diseases and brain tumors affect millions of patients worldwide and are associated with significant morbidity and mortality. The blood brain barrier constitutes a major obstacle to delivery of therapeutic agents administered systemically for treating these disorders. Intracranial drug delivery provides a novel way of bypassing the blood brain barrier and achieving high concentration of therapeutic agents in the brain while avoiding systemic side effects. However damage to tissues during insertion of catheters, release of air in the brain and consequent backtracking of dye are some disadvantages with this mode of treatment. We evaluated prototype cell delivery catheters (each with …
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
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 …
Band Offset Measurements Of Zno∕6h-Sic Heterostructure System, Ya. I. Alivov, Bo Xiao, Q. Fan, Hadis Morkoç, D. Johnstone
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.
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
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 …
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
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 …
I-V Characteristics Of Au∕Ni Schottky Diodes On Gan With Sinx Nanonetwork, J. Xie, Yi Fu, Xianfeng Ni, S. A. Chevtchenko, Hadis Morkoç
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 …
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
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.
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
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.
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
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 …
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
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.
Infrared Absorption In A Quantum Wire: A Technique To Measure Different Types Of Spin-Orbit Interaction Strengths, S. Bandyopadhyay, S. Sarkar
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 …
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
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, …
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
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 …
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
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 …
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
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.
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
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 …
Admittance Of Cds Nanowires Embedded In Porous Alumina Template, A. Varfolomeev, D. Zaretsky, V. Pokalyakin, S. Tereshin, S. Pramanik, S. Bandyopadhyay
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.
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
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 …
Spin Relaxation Of “Upstream” Electrons In Quantum Wires: Failure Of The Drift Diffusion Model, Sandipan Pramanik, Supriyo Bandyopadhyay, Marc Cahay
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) …
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
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.
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
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 …
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
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 …