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Articles 211 - 240 of 364

Full-Text Articles in Electrical and Computer Engineering

Nanoelectrospray Aerosols From Microporous Polymer Wick Sources, Gary C. Tepper, Royal Kessick Jan 2009

Nanoelectrospray Aerosols From Microporous Polymer Wick Sources, Gary C. Tepper, Royal Kessick

Electrical and Computer Engineering Publications

Nanoelectrospray aerosols were formed from microporous polymer wick sources. Current-voltage characteristics were measured as a function of solution electrical conductivity and surface tension and two distinct electrospray modes were observed. In the first mode, when the maximum capillary flow rate through the wick exceeds the electrospray flow rate, a single electrospray forms from a droplet at the end of the wick. In the second mode, when the maximum capillary flow rate is less than the electrospray flow rate, a multitude of microscopic nanoelectrospray sources are formed from within the surface of the wick tip.

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Retraction: “Observation Of Numerous E2 Mode Phonon Replicas In The Room Temperature Photoluminescence Spectra Of Zno Nanowires: Evidence Of Strong Deformation Potential Electron-Phonon Coupling” [Appl. Phys. Lett.89, 143121 (2006)], S. Ramanathan, Supriyo Bandyopadhyay, L. K. Hussey, M. Muñoz Jan 2009

Retraction: “Observation Of Numerous E2 Mode Phonon Replicas In The Room Temperature Photoluminescence Spectra Of Zno Nanowires: Evidence Of Strong Deformation Potential Electron-Phonon Coupling” [Appl. Phys. Lett.89, 143121 (2006)], S. Ramanathan, Supriyo Bandyopadhyay, L. K. Hussey, M. Muñoz

Electrical and Computer Engineering Publications

No abstract provided.

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Effect Of Large Strain On Dielectric And Ferroelectric Properties Of Ba0.5sr0.5tio3 Thin Films, Bo Xiao, Vitaliy Avrutin, Hongrui Liu, Emmanuel Rowe, Jacob H. Leach, Xing Gu, Ü. Özgür, Hadis Morkoç, W. Chang, L. M.B. Alldredge, S. W. Kirchoefer, J. M. Pond Jan 2009

Effect Of Large Strain On Dielectric And Ferroelectric Properties Of Ba0.5sr0.5tio3 Thin Films, Bo Xiao, Vitaliy Avrutin, Hongrui Liu, Emmanuel Rowe, Jacob H. Leach, Xing Gu, Ü. Özgür, Hadis Morkoç, W. Chang, L. M.B. Alldredge, S. W. Kirchoefer, J. M. Pond

Electrical and Computer Engineering Publications

BaxSr1−xTiO3 is ideally suited as a tunable medium for radio frequency passive component. In this context we have studied the effect of biaxial strain on the dielectric and ferroelectricproperties of Ba0.5Sr0.5TiO3thin filmsgrown epitaxially on SrTiO3 (001) substrates. The lattice parameters of the films determined by high-resolution x-ray diffraction with the thickness varying from 160 to 1000 nm indicated large biaxial compressive strain which decreased from 2.54% to 1.14% with increasing film thickness. Temperature-dependent measurements of the dielectric constant in our strained Ba0.5Sr0.5TiO3thin films revealed a significant increase in the Curie temperature as the film thickness is below 500 nm. Enhanced …

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Energy Relaxation Probed By Weak Antilocalization Measurements In Gan Heterostructures, H. Cheng, N. Biyikli, J. Xie, Ç. Kurdak, H. Morkoç Jan 2009

Energy Relaxation Probed By Weak Antilocalization Measurements In Gan Heterostructures, H. Cheng, N. Biyikli, J. Xie, Ç. Kurdak, H. Morkoç

Electrical and Computer Engineering Publications

Energy relaxation and electron-phonon (e-p) interaction are investigated in wurtzite Al0.15Ga0.85N/AlN/GaN and Al0.83In0.17N/AlN/GaN heterostructures with polarization induced two-dimensional electron gases in the Bloch–Grüneisen regime. Weak antilocalization (WAL) and Shubnikov–de Haas measurements were performed on gated Hall bar structures at temperatures down to 0.3 K. We used WAL as a thermometer to measure the electron temperature Te as a function of the dc bias current. We found that the power dissipated per electron, Pe, was proportional to T4e due to piezoelectric acoustic phonon emission by hot electrons. We calculated Pe as a function of Te without any adjustable parameters for both …

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Correlated Growth Of Organic Material Tris (8-Hydroxyquinoline) Aluminum (Alq3) And Its Relation To Optical Properties, Bhargava R. Kanchibotla, K. Garre, Deeder Aurongzeb Jan 2009

Correlated Growth Of Organic Material Tris (8-Hydroxyquinoline) Aluminum (Alq3) And Its Relation To Optical Properties, Bhargava R. Kanchibotla, K. Garre, Deeder Aurongzeb

Electrical and Computer Engineering Publications

We report slow correlated growth mode in energetic cluster vapor deposited organic light emissive material tris(8-hydroxyquinoline) aluminum from 5 to 100 nm. Phase modulated atomic force microscopy shows very slow grain growth with thickness, with very small phase differences within the film.Fractal dimension calculated from correlation function shows growth process above 10 nm consistent with diffusion-limited aggregation. For low thickness (5 nm), photoluminescence measurement shows the emission peak is shifted by ∼0.4 eV toward lower wavelength.

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Electron Drift Velocity In Lattice-Matched Alinn/Aln/Gan Channel At High Electric Fields, L. Ardaravičius, M. Ramonas, J. Liberis, O. Kiprijanovič, A. Matulionis, J. Xie, M. Wu, J. H. Leach, H. Morkoç Jan 2009

Electron Drift Velocity In Lattice-Matched Alinn/Aln/Gan Channel At High Electric Fields, L. Ardaravičius, M. Ramonas, J. Liberis, O. Kiprijanovič, A. Matulionis, J. Xie, M. Wu, J. H. Leach, H. Morkoç

Electrical and Computer Engineering Publications

Hot-electron transport was probed by nanosecond-pulsed measurements for a nominally undoped two-dimensional channel confined in a nearly lattice-matched Al0.82In0.18N/AlN/GaN structure at room temperature. The electric field was applied parallel to the interface, the pulsed technique enabled minimization of Joule heating. No current saturation was reached at fields up to 180 kV/cm. The effect of the channel length on the current is considered. The electron drift velocity is deduced under the assumption of uniform electric field and field-independent electron density. The highest estimated drift velocity reaches ∼3.2×107 cm/s when the AlN spacer thickness is 1 nm. At high fields, a weak …

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Internal Quantum Efficiency Of C-Plane Ingan And M-Plane Ingan On Si And Gan, X. Ni, J. Lee, M. Wu, X. Li, Ryoko Shimada, Ü. Özgür, A. A. Baski, Hadis Morkoç, T. Paskova, G. Mulholland, K. R. Evans Jan 2009

Internal Quantum Efficiency Of C-Plane Ingan And M-Plane Ingan On Si And Gan, X. Ni, J. Lee, M. Wu, X. Li, Ryoko Shimada, Ü. Özgür, A. A. Baski, Hadis Morkoç, T. Paskova, G. Mulholland, K. R. Evans

Electrical and Computer Engineering Publications

We investigated internal quantum efficiency (IQE) of polar (0001) InGaN on c-sapphire, and (11¯00) nonpolar m-plane InGaN on both m-plane GaN and specially patterned Si. The IQE values were extracted from the resonant photoluminescence intensity versus the excitation power. Data indicate that at comparable generatedcarrier concentrations the efficiency of the m-plane InGaN on patterned Si is approximately a factor of 2 higher than that of the highly optimized c-plane layer. At the highest laser excitation employed (∼1.2×1018 cm−3), the IQE of m-plane InGaN double heterostructure on Si is approximately 65%. We believe that the m-plane would remain inherently advantageous, particularly …

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Spin Transport Studies In Nanoscale Spin Valves And Magnetic Tunnel Junctions, Sridhar Patibandla Oct 2008

Spin Transport Studies In Nanoscale Spin Valves And Magnetic Tunnel Junctions, Sridhar Patibandla

Theses and Dissertations

Spintronics or electronics that utilizes the spin degree of freedom of a single charge carrier (or an ensemble of charge carriers) to store, process, sense or communicate data and information is a rapidly burgeoning field in electronics. In spintronic devices, information is encoded in the spin polarization of a single carrier (or multiple carriers) and the spin(s) of these carrier(s) are manipulated for device operation. This strategy could lead to devices with low power consumption. This dissertation investigates spin transport in one dimensional and two dimensional semiconductors, with a view to applications in spintronic devices.

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Fiber Bragg Grating (Fbg) Based Chemical Sensor, Gopakumar Sethuraman Aug 2008

Fiber Bragg Grating (Fbg) Based Chemical Sensor, Gopakumar Sethuraman

Theses and Dissertations

In this work, reagentless fiber optic-based chemical sensors for water quality testing were fabricated by coating fiber Bragg gratings with the glassy polymer cellulose acetate. With this polymeric matrix capable of localizing or concentrating chemical constituents within its structure, immersion of the coated grating in various chemical solutions causes the rigid polymer to expand and mechanically strain the glass fiber. The corresponding changes in the periodicity of the grating subsequently result in altered Bragg-reflected responses. A high-resolution tunable fiber ring laser interrogator is used to obtain room temperature reflectance spectrograms from two fiber gratings at 1550 nm and 1540 nm …

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Field Emission From Self-Assembled Arrays Of Lanthanum Monosulfide Nanoprotrusions, V. Semet, Vu Thien Binh, M. Cahay, K. Garre, S. Fairchild, L. Grazulis, J. W. Fraser, D. J. Lockwood, S. Pramanik, B. Kanchibotla, Supriyo Bandyopadhyay Jan 2008

Field Emission From Self-Assembled Arrays Of Lanthanum Monosulfide Nanoprotrusions, V. Semet, Vu Thien Binh, M. Cahay, K. Garre, S. Fairchild, L. Grazulis, J. W. Fraser, D. J. Lockwood, S. Pramanik, B. Kanchibotla, Supriyo Bandyopadhyay

Electrical and Computer Engineering Publications

The field emission properties of LaS nanoprotrusions called nanodomes, formed by pulsed laser deposition on porous anodic alumina films, have been analyzed with scanning anode field emission microscopy. The voltage necessary to produce a given field emission current is 3.5 times less for nanodomes than for thin films. Assuming the same work function for LaS thin films and nanoprotrusions, that is, 1 eV, a field enhancement factor of 5.8 is extracted for the nanodome emitters from Fowler-Nordheim plots of the field emission data. This correlates well with the aspect ratio of the tallest nanodomes observed in atomic force micrograph measurements.

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Reduction Of Efficiency Droop In Ingan Light Emitting Diodes By Coupled Quantum Wells, Xianfeng Ni, Qian Fan, Ryoko Shimada, Ü. Özgür, Hadis Morkoç Jan 2008

Reduction Of Efficiency Droop In Ingan Light Emitting Diodes By Coupled Quantum Wells, Xianfeng Ni, Qian Fan, Ryoko Shimada, Ü. Özgür, Hadis Morkoç

Electrical and Computer Engineering Publications

Light emitting diodes(LEDs) based on InGaN suffer from efficiency droop at current injection levels as low as 50 A cm−2. We investigated multiple quantum wellInGaNLEDs with varying InGaN barrier thicknesses (3–12 nm) emitting at ∼400–410 nm to investigate the effect of hole mass and also to find out possible solutions to prevent the efficiency droop. In LEDs with electron blocking layers, when we reduced the InGaN barriers from 12 to 3 nm, the current density for the peak or saturation of external quantum efficiency increased from 200 to 1100 A cm−2 under pulsed injection conditions, which eliminates the heating effects …

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Large Pyroelectric Effect In Undoped Epitaxial Pb(Zr,Ti)O3 Thin Films On Srtio3 Substrates, Bo Xiao, Vitaliy Avrutin, Huiyong Liu, Ü. Özgür, Hadis Morkoç, Changzhi Lu Jan 2008

Large Pyroelectric Effect In Undoped Epitaxial Pb(Zr,Ti)O3 Thin Films On Srtio3 Substrates, Bo Xiao, Vitaliy Avrutin, Huiyong Liu, Ü. Özgür, Hadis Morkoç, Changzhi Lu

Electrical and Computer Engineering Publications

We have studied pyroelectric and ferroelectric properties of Pb(Zr,Ti)O3thin filmsgrown epitaxially on SrTiO3(001) substrates by rf magnetron sputtering. The pyroelectric coefficient was measured in the temperature range from 280 to 370 K using the Byer–Roundy method. Values as high as 48 nC/cm2 K have been obtained at 300 K. The PZTthin films exhibited a remanent polarization of 45–58 μC/cm2. The improved pyroelectric coefficient was attributed to a high crystalline quality of the films, as revealed by x-ray diffraction that showed only (001)-oriented perovskitePZT phase and a ω-rocking curve full width at half maximum value as low as 4.2 arc min …

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On The Efficiency Droop In Ingan Multiple Quantum Well Blue Light Emitting Diodes And Its Reduction With P-Doped Quantum Well Barriers, Jinqiao Xie, Xianfeng Ni, Qian Fan, Ryoko Shimada, Ü. Özgür, Hadis Morkoç Jan 2008

On The Efficiency Droop In Ingan Multiple Quantum Well Blue Light Emitting Diodes And Its Reduction With P-Doped Quantum Well Barriers, Jinqiao Xie, Xianfeng Ni, Qian Fan, Ryoko Shimada, Ü. Özgür, Hadis Morkoç

Electrical and Computer Engineering Publications

Multiple quantum well(MQW) InGaN light emitting diodes with and without electron blocking layers, with relatively small and large barriers, with and without p-type doping in the MQW region emitting at ∼420nm were used to determine the genesis of efficiency droop observed at injection levels of approximately ⩾50A/cm2. Pulsed electroluminescence measurements, to avoid heating effects, revealed that the efficiency peak occurs at ∼900A/cm2current density for the Mg-doped barrier, near 550A/cm2 for the lightly dopedn-GaN injection layer, meant to bring the electron injection level closer to that of holes, and below 220A/cm2 for the undoped InGaN barrier cases. For samples with GaN …

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Cavity Polaritons In Zno-Based Hybrid Microcavities, R. Shimada, J. Xie, Vitaliy Avrutin, Ü. Özgür, Hadis Morkoç Jan 2008

Cavity Polaritons In Zno-Based Hybrid Microcavities, R. Shimada, J. Xie, Vitaliy Avrutin, Ü. Özgür, Hadis Morkoç

Electrical and Computer Engineering Publications

Among wide-bandgap semiconductors, ZnO is a very attractive candidate for blue-ultraviolet lasers operating at room temperature owing to its large exciton binding energy and oscillator strength. Especially, ZnO-based microcavity structures are most conducive for polariton lasing at room temperature. We report the observation of cavitypolaritons in bulk ZnO-based hybrid microcavities at room temperature. The bulk ZnO-based hybrid microcavities are composed of 29 pairs of Al0.5Ga0.5N∕GaNdistributed Bragg reflector (DBR) at the bottom of the λ-thick cavity layer and eight pairs of SiO2∕Si3N4 DBR as the top mirror, which provided cavityQvalues of ∼100. Anticrossing behavior between the lower and upper polariton branches …

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Self-Assembled Deoxyguanosine Based Molecular Electronic Device On Gan Substrates, H. Liddar, J. Li, A. Neogi, P. B. Neogi, A. Sarkar, S. Cho, Hadis Morkoç Jan 2008

Self-Assembled Deoxyguanosine Based Molecular Electronic Device On Gan Substrates, H. Liddar, J. Li, A. Neogi, P. B. Neogi, A. Sarkar, S. Cho, Hadis Morkoç

Electrical and Computer Engineering Publications

Nanoscale hybrid molecular organic photodetectors based on self-assembled guanosine molecules conjugated to wide-bandgap GaNsemiconductors has been realized in the ultraviolet wavelength regime. Metal-semiconductor-metal based photodetector is fabricated using ordering of modified guanosine based semiconductor nanowires which exhibit I-Vcharacteristics with high current response and higher rectification ratio compared to Si based hybrid photodetectors. Photocurrent response of a two-terminal device shows the typical characteristics of a semiconductorphotodiode with a cutoff wavelength at ∼325nm. The I-Vcharacteristics have been elucidated using the induced polarization properties of self-assembled guanosine semiconductor.

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Transverse Spin Relaxation Time In Organic Molecules, B. Kanchibotla, S. Pramanik, S. Bandyopadhyay, M. Cahay Jan 2008

Transverse Spin Relaxation Time In Organic Molecules, B. Kanchibotla, S. Pramanik, S. Bandyopadhyay, M. Cahay

Electrical and Computer Engineering Publications

We report a measurement of the ensemble-averaged transverse spin relaxation time (T∗2) in bulk and few molecules of the organic semiconductor tris-(8-hydroxyquinolinolato aluminum) or Alq3. This system exhibits two characteristic T∗2 times: the longer of which is temperature independent and the shorter is temperature dependent, indicating that the latter is most likely limited by spin-phonon interaction. Based on the measured data, we infer that the single-particle T2 time is probably long enough to meet Knill’s criterion for fault-tolerant quantum computing even at room temperature. Alq3 is also an optically active organic, and we propose a simple …

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Magnetic Field Effects On Spin Texturing In A Quantum Wire With Rashba Spin-Orbit Interaction, P. Upadhyaya, S. Pramanik, S. Bandyopadhyay, M. Cahay Jan 2008

Magnetic Field Effects On Spin Texturing In A Quantum Wire With Rashba Spin-Orbit Interaction, P. Upadhyaya, S. Pramanik, S. Bandyopadhyay, M. Cahay

Electrical and Computer Engineering Publications

A quantum wire with strong Rashba spin-orbit interaction is known to exhibit spatial modulation of spin density along its width owing to coupling between subbands caused by the Rashba interaction. This is known as spin texturing. Here, we show that a transverse external magnetic field introduces additional complex features in spin texturing, some of which reflect the intricate details of the underlying energy dispersion relations of the spin-split subbands. One particularly intriguing feature is a 90° phase shift between the spatial modulations of two orthogonal components of the spin density, which is observed at moderate field strengths and when only …

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Optical Transitions In A Quantum Wire With Spin-Orbit Interaction And Its Applications In Terahertz Electronics: Beyond Zeroth-Order Theory, P. Upadhyaya, S. Pramanik, S. Bandyopadhyay Jan 2008

Optical Transitions In A Quantum Wire With Spin-Orbit Interaction And Its Applications In Terahertz Electronics: Beyond Zeroth-Order Theory, P. Upadhyaya, S. Pramanik, S. Bandyopadhyay

Electrical and Computer Engineering Publications

We calculate the terahertz absorption spectra associated with intersubband transitions in a semiconductor quantum wire in the presence of spin-orbit interaction and a transverse magnetic field. The frequencies and intensities of the absorption peaks are found to depend strongly on the spin-orbit coupling strength, which can be varied with an external electric field. This feature can be exploited to realize reconfigurable multispectral terahertz detectors and amplitude and/or frequency modulators. We also show that electric dipole transitions between spin-split levels in the same subband (which are normally deemed forbidden) become allowed because of spin texturing effects. The absorption associated with these …

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The Inequality Of Charge And Spin Diffusion Coefficients, Sandipan Pramanik, Supriyo Bandyopadhyay, Marc Cahay Jan 2008

The Inequality Of Charge And Spin Diffusion Coefficients, Sandipan Pramanik, Supriyo Bandyopadhyay, Marc Cahay

Electrical and Computer Engineering Publications

Since spin and charge are both carried by electrons (or holes) in a solid, it is natural to assume that charge and spin diffusion coefficients will be the same. Drift-diffusion models of spin transport typically assume so. Here, we show analytically that the two diffusion coefficients can be vastly different in quantum wires. Although we do not consider quantum wells or bulk systems, it is likely that the two coefficients will be different in those systems as well. Thus, it is important to distinguish between them in transportmodels, particularly those applied to quantum wire based devices.

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Current Versus Voltage Characteristics Of Gan/Algan/Gan Double Heterostructures With Varying Algan Thickness And Composition Under Hydrostatic Pressure, I. P. Steinke, P. P. Ruden, X. Ni, H. Morkoç, K.-A. Son Jan 2008

Current Versus Voltage Characteristics Of Gan/Algan/Gan Double Heterostructures With Varying Algan Thickness And Composition Under Hydrostatic Pressure, I. P. Steinke, P. P. Ruden, X. Ni, H. Morkoç, K.-A. Son

Electrical and Computer Engineering Publications

We have studied current versus voltage characteristics of n-GaN∕u-AlGaN∕n-GaN double heterostructure devices under hydrostatic pressure up to 500MPa. Devices were grown on c-plane sapphire substrates by organometallic vapor phase epitaxy using epitaxial layer overgrowth. The effect of AlGaN layer thickness and composition on the pressure sensitivity was investigated. For a fixed applied bias, we found that the current decreases approximately linearly in magnitude with increasing hydrostatic pressure over the range of voltages and pressures applied. The decrease in current magnitude can be attributed to piezoelectric effects and is consistent with model calculations. The polarizationcharge densities at the GaN∕AlGaN interfaces change …

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Single Spin Toffoli-Fredkin Logic Gate, Amit Ranjan Trivedi, S. Bandyopadhyay Jan 2008

Single Spin Toffoli-Fredkin Logic Gate, Amit Ranjan Trivedi, S. Bandyopadhyay

Electrical and Computer Engineering Publications

The Toffoli–Fredkin (TF) gate is a universal reversible logic gate capable of performing logic operations without dissipating energy. Here, we show that a linear array of three quantum dots, each hosting a single electron, can realize the TF gate, if we encode logic bits in the spin polarization of the electrons and allow nearest neighbor exchange coupling. The dynamics of the TF gate is realized by selectively driving spin resonances in the coupled spin system with an acmagnetic field. The conditions for gate operation are established, and an estimate of the switching speed and gate error are provided.

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Prediction Of Breathing Patterns Using Neural Networks, Pavani Davuluri Jan 2008

Prediction Of Breathing Patterns Using Neural Networks, Pavani Davuluri

Theses and Dissertations

During the radio therapy treatment, it has been difficult to synchronize the radiation beam with the tumor position. Many compensation techniques have been used before. But all these techniques have some system latency, up to a few hundred milliseconds. Hence it is necessary to predict tumor position to compensate for the control system latency. In recent years, many attempts have been made to predict the position of a moving tumor during respiration. Analyzing external breathing signals presents a methodology in predicting the tumor position. Breathing patterns vary from very regular to irregular patterns. The irregular breathing patterns make prediction difficult. …

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High Quality Molecular Beam Epitaxy Growth And Characterization Of Lead Titanate Zirconate Based Complex-Oxides, Xing Gu Dec 2007

High Quality Molecular Beam Epitaxy Growth And Characterization Of Lead Titanate Zirconate Based Complex-Oxides, Xing Gu

Theses and Dissertations

Research interest in complex oxides has resurged owing to progress in modern epitaxial techniques. Among such oxides, lead-titanate-based thin films such as PbTiO3 (PTO) and Pb(ZrxTi1−x)O3 (PZT) offer attractive advantages for a wide variety of applications. Moreover, integration between functional oxides with compound semiconductors has the potential to realize multi-functional devices which enjoy the properties from both groups of materials. Ferroelectric materials with a perovskite structure (ABO3) and semiconductors such as GaN with a hexagonal structure, require a careful choice of a bridge layer and suitable epitaxial technique. Molecular beam epitaxy (MBE) …

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Electron Mobility In Ingan Channel Heterostructure Field Effect Transistor Structures With Different Barriers, J. Xie, J. H. Leach, X. Ni, M. Wu, R. Shimada, Ü. Özgür, Hadis Morkoç Jan 2007

Electron Mobility In Ingan Channel Heterostructure Field Effect Transistor Structures With Different Barriers, J. Xie, J. H. Leach, X. Ni, M. Wu, R. Shimada, Ü. Özgür, Hadis Morkoç

Electrical and Computer Engineering Publications

InGaN possesses higher electron mobility and velocity than GaN, and therefore is expected to lead to relatively better performances for heterostructure field effect transistors (HFETs). However, the reported mobilities for AlGaN∕InGaNHFETs are lower than GaN channel HFETs. To address this issue, we studied the effect of different barriers on the Hall mobility for InGaN channel HFETs grown by metal organic chemical vapor deposition. Unlike the conventional AlGaN barrier, the AlInN barrier can be grown at the same temperature as the InGaN channel layer, alleviating some of the technological roadblocks. Specifically, this avoids possible degradation of the thin InGaN channel during …

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Structural And Electrical Properties Of Pb(Zr,Ti)O3 Films Grown By Molecular Beam Epitaxy, N. Izyumskaya, Vitaliy Avrutin, X. Gu, B. Xiao, Serguei A. Chevtchenko, J-G Yoon, Hadis Morkoç, Lin Zhou, David J. Smith Jan 2007

Structural And Electrical Properties Of Pb(Zr,Ti)O3 Films Grown By Molecular Beam Epitaxy, N. Izyumskaya, Vitaliy Avrutin, X. Gu, B. Xiao, Serguei A. Chevtchenko, J-G Yoon, Hadis Morkoç, Lin Zhou, David J. Smith

Electrical and Computer Engineering Publications

Single-crystal, single-phase Pb(ZrxTi1−x)O3 films (x=0–0.4) were grown on (001)SrTiO3 and SrTiO3:Nb substrates by molecular beam epitaxy. Layer-by-layer growth of thePb(Zr,Ti)O3 films was achieved by using PbTiO3 buffer layers between the SrTiO3substrates and the Pb(Zr,Ti)O3 films. The layers with low Zr content showed high crystallinity with full width at half maximum of ω -rocking curves as low as 4arcmin , whereas increase in Zr concentration led to pronounced angular broadening. The PbZr0.07Ti0.93O3 filmsexhibited remanent polarization as high as 83μC/cm2 , but local areas suffered from nonuniform leakage current.

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Epitaxial Growth Of Zro2 On Gan Templates By Oxide Molecular Beam Epitaxy, Xing Gu, Natalia Izyumskaya, Vitaliy Avrutin, Bo Xiao, Hadis Morkoç Jan 2007

Epitaxial Growth Of Zro2 On Gan Templates By Oxide Molecular Beam Epitaxy, Xing Gu, Natalia Izyumskaya, Vitaliy Avrutin, Bo Xiao, Hadis Morkoç

Electrical and Computer Engineering Publications

Molecular beam epitaxial growth of ZrO2 has been achieved on GaN(0001)∕c-Al2O3substrates employing a reactive H2O2 oxygen source. A low temperature buffer followed by in situ annealing and high temperature growth has been employed to attain monoclinic, (100)-oriented ZrO2thin films. The typical full width at half maximum of a 30-nm-thick ZrO2 (100) film rocking curves is 0.4arcdeg and the root-mean-square surface roughness is ∼4Å. ω−2θand pole figure x-ray diffraction patterns confirm the monoclinic structure of ZrO2. Data support an in-plane epitaxial relationship of ZrO2 [010]∥∥GaN[112¯] and ZrO2 [001]∥∥GaN[11¯00]. X-ray diffraction and reflection high-energy electron diffraction analyses reveal in-plane compressive strain, which …

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Structural And Electrical Properties Of Pb(Zr,Ti)O3 Grown On (0001) Gan Using A Double Pbtio3∕Pbo Bridge Layer, Bo Xiao, Xing Gu, Natalia Izyumskaya, Vitaliy Avrutin, Jinqiao Xie, Huiyong Liu, Hadis Morkoç Jan 2007

Structural And Electrical Properties Of Pb(Zr,Ti)O3 Grown On (0001) Gan Using A Double Pbtio3∕Pbo Bridge Layer, Bo Xiao, Xing Gu, Natalia Izyumskaya, Vitaliy Avrutin, Jinqiao Xie, Huiyong Liu, Hadis Morkoç

Electrical and Computer Engineering Publications

Pb(Zr0.52Ti0.48)O3 films were deposited by rf magnetron sputtering on silicon-doped GaN(0001)∕c-sapphire with a PbTiO3∕PbO oxide bridge layer grown by molecular beam epitaxy. X-ray diffraction data showed the highly (111)-oriented perovskite phase in lead zirconate titanate(PZT) films with PbTiO3∕PbO bridge layers, compared to the pyrochlore phase grown directly on GaN. The in-plane epitaxial relationships were found from x-ray pole figures to be PZT[112¯]∥∥GaN[11¯00] and PZT[11¯0]∥∥GaN[112¯0]. The polarization-electric field measurements revealed the ferroelectric behavior with remanent polarization of 30–40μC/cm2 and asymmetric hysteresis loops due to the depletion layer formed in GaN under reverse bias which resulted in a high negative coercive electric …

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Dielectric Functions And Critical Points Of Pbtio3, Pbzro3, And Pbzr0.57ti0.43o3 Grown On Srtio3 Substrate, T. D. Kang, Hosun Lee, G. Xing, N. Izyumskaya, Vitaliy Avrutin, Bo Xiao, Hadis Morkoç Jan 2007

Dielectric Functions And Critical Points Of Pbtio3, Pbzro3, And Pbzr0.57ti0.43o3 Grown On Srtio3 Substrate, T. D. Kang, Hosun Lee, G. Xing, N. Izyumskaya, Vitaliy Avrutin, Bo Xiao, Hadis Morkoç

Electrical and Computer Engineering Publications

Single crystalline PbTiO3, PbZrO3, and PbZr0.57Ti0.43O3 thin films on SrTiO3 (001) substrates were grown by a combination of molecular beam epitaxy and rf sputtering methods. The authors measured the dielectric functions of the thin films using spectroscopic ellipsometry and determined the interband critical point energies using standard critical point model. They compared the critical point energies to the band structure calculations in the literature. The data suggest that anticrossing behavior occurs between Ea and Eb near Zr=0.17. This phenomenon is attributed to a coupling between X1c and X3c bands caused by intrinsic alloy disorder.

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Defect Reduction In Gan Epilayers Grown By Metal-Organic Chemical Vapor Deposition With In Situ Sinx Nanonetwork, Jinqiao Xie, Serguei A. Chevtchenko, Ü. Özgür, Hadis Morkoç Jan 2007

Defect Reduction In Gan Epilayers Grown By Metal-Organic Chemical Vapor Deposition With In Situ Sinx Nanonetwork, Jinqiao Xie, Serguei A. Chevtchenko, Ü. Özgür, Hadis Morkoç

Electrical and Computer Engineering Publications

Line and point defect reductions in thin GaN epilayers with single and double in situ SiNxnanonetworks on sapphire substrates grown by metal-organic chemical vapor deposition were studied by deep-level transient spectroscopy(DLTS), augmented by x-ray diffraction(XRD), and low temperature photoluminescence(PL). All samples measured by DLTS in the temperature range from 80to400K exhibited trap A (peak at ∼325K) with an activation energy of 0.55–0.58eV, and trap B (peak at ∼155K) with an activation energy of 0.21–0.28eV. The concentrations of both traps were much lower for layers with SiNx nanonetwork compared to the reference sample. The lowest concentration was achieved for the sample …

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High Electron Mobility In Nearly Lattice-Matched Alinn∕Aln∕Gan Heterostructure Field Effect Transistors, Jinqiao Xie, Xianfeng Ni, Mo Wu, Jacob H. Leach, Ü. Özgür, Hadis Morkoç Jan 2007

High Electron Mobility In Nearly Lattice-Matched Alinn∕Aln∕Gan Heterostructure Field Effect Transistors, Jinqiao Xie, Xianfeng Ni, Mo Wu, Jacob H. Leach, Ü. Özgür, Hadis Morkoç

Electrical and Computer Engineering Publications

High electron mobility was achieved in Al1−xInxN∕AlN∕GaN (x=0.20–0.12)heterostructurefield effect transistors(HFETs) grown by metal-organic chemical vapor deposition. Reduction of In composition from 20% to 12% increased the room temperature equivalent two-dimensional-electron-gas density from 0.90×1013to1.64×1013cm−2 with corresponding electron mobilities of 1600 and 1410cm2/Vs, respectively. The 10Kmobility reached 17600cm2/Vs for the nearly lattice-matched Al0.82In0.18N∕AlN∕GaNheterostructure with a sheet carrier density of 9.6×1012cm−2. For comparison, the AlInN∕GaNheterostructure without the AlN spacer exhibited a high sheet carrier density(2.42×1013cm−2) with low mobility(120cm2/Vs) at room temperature. The high mobility in our samples is in part attributed to ∼1nm AlN spacer which significantly reduces the alloy scattering as well …

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