bluuebunny/crossref_metadata_2025 huggingface dataset:
Strain relaxation behavior of InxGa1−xAs quantum wells on vicinal GaAs (111)B substrates
Authors: Gutiérrez M. , González D. , Aragón G. , Garcı́a R. , Hopkinson M. , Sánchez J. J. , Izpura I.
Published: July 2002

A number of reports have suggested that InGaAs/GaAs (111)B strained layer epitaxy has the prospect of reaching a higher critical layer thickness than that which can be achieved for (001) substrates. This has motivated a study of the relaxation mechanism of InGaAs/GaAs (111)B quantum wells with high In content (0.12<x<0.35). Transmission electron microscopy has revealed the existence of a different misfit dislocation (MD) configuration for high In contents (x>0.25), which, we believe, has not been reported until now. For such compositions, plastic relaxation takes place through a polygonal network of MDs, which have Burgers vectors in the interface plane. The origin of this network is an unusual dislocation source that occurs through the formation of a three-pointed star-shaped configuration. The characteristics of this misfit dislocation network, which has a higher misfit relieving component and a glide plane coincident with the interface plane, imply a reduction of the previous critical layer thickness estimates for high In content InGaAs/GaAs (111)B heterostructures. However, we observe that none of the (111)B samples shows evidence of a transition to a three-dimensional growth mode, which represents a significant advantage compared to the behavior of high In content quantum wells on (001) substrates.
Deep-level defect characteristics in pentacene organic thin films
Authors: Yang Yong Suk , Kim Seong Hyun , Lee Jeong-Ik , Chu Hye Yong , Do Lee-Mi , Lee Hyoyoung , Oh Jiyoung , Zyung Taehyoung , Ryu Min Ki , Jang Min Su
Published: July 2002

Organic thin-film transistors using the pentacene as an active electronic material have shown the mobility of 0.8 cm2/V s and the grains larger than 1 μm. To study the characteristics of electronic charge concentrations and the interface traps of the pentacene thin films, the capacitance properties were measured in the metal/insulator/organic semiconductor structure device by employing the capacitance–voltage and deep-level transient spectroscopy (DLTS) measurements. Based on the DLTS measurements, the concentrations and the energy levels of hole and electron traps in the obtained pentacene films were formed to be approximately 4.2×1015 cm−3 at Ev+0.24 eV, 9.6×1014 cm−3 at Ev+1.08 eV, 6.5×1015  cm−3 at Ev+0.31 eV and 2.6×1014 cm−3 at Ec−0.69 eV.
Numerical simulation of the 3ω method for measuring the thermal conductivity
Authors: Jacquot A. , Lenoir B. , Dauscher A. , Stölzer M. , Meusel J.
Published: July 2002

A four-pad 3ω method was developed for determining the thermal conductivity of bulk and thin film materials. The heat conduction in the sample geometry was investigated by numerical simulation employing the finite volume technique. As a result, the conditions (i.e., sample geometry, frequency range) can be predicted when conventional analytical formulas are suited to determine the thermal conductivity of bulk and thin film material from the data measured. Experiments were performed that confirm the validity and accuracy of the numerical calculations.
Cylindrical mirror multipass Lissajous system for laser photoacoustic spectroscopy
Authors: Hao Lu-yuan , Qiang Shi , Wu Guo-rong , Qi Li , Feng Dang , Zhu Qing-shi , Hong Zhang
Published: July 2002

A simple optical multiple reflection system is developed with two cylindrical concave mirrors at an appropriate spacing. The two cylindrical mirrors have different focal lengths and their principal sections are orthogonal. The alternate focusing of the two cylindrical mirrors at different direction keep the reflecting spots small. The reflecting spots fall on Lissajous patterns on the cylindrical mirrors. The mathematics for this optical system is described and the calculated coordinates of beam spots are very close matches of the experimental observations. The cylindrical mirror optical system is easy to construct and align, with a suitable method for obtaining long optical paths and a large number of passes in small volumes. In a photoacoustic spectrometer the beam family enhance the effective power in the photoacoustic cell and thus the signal-to-noise ratio of photoacoustic signal. An experimental result for photoacoustic spectrum of HDSe gas is given.
The effect of strain on the resistivity of indium tin oxide films prepared by pulsed laser deposition
Authors: Fang Hui , Miller Timothy M. , Magruder Robert H. , Weller Robert A.
Published: July 2002

The piezoresistivity of thin films of indium tin oxide prepared by pulsed laser deposition has been measured as a function of processing parameters. The thickness of the films ranged from 200 to 1200 nm. Resistivity and strain sensitivity measurements as a function of laser deposition parameters are reported. Gauge factors, defined as the ratio of the fractional resistance change to the applied strain, were observed to vary from approximately 0.2 for deposition in vacuum to as large as −14.7 for deposition with a residual atmosphere of 50 mTorr of oxygen. The response of gauges to strains up to the measurement limit of approximately 220 με was both linear and free of hysteresis. This fabrication strategy makes possible the direct deposition of sub-mm strain gauges onto surfaces and components, including those of micro electromechanical systems.
Epitaxial Y-stabilized ZrO2 films on silicon: Dynamic growth process and interface structure
Authors: Wang S. J. , Ong C. K.
Published: July 2002

We have studied the initial stage of the growth of yttria-stabilized zirconia (YSZ) films on natively oxidized (100) Si wafer by pulsed-laser deposition. X-ray photoelectron spectroscopy and high-resolution electron microscopy show that, for the first few monolayers of crystalline YSZ deposited on (100) Si, the dynamic processes appear to be the decomposition of SiO2 to SiO, the formation of ZrO2, and the desorption of SiO. The native amorphous SiO2 layer is removed completely with the continued deposition of YSZ. The atomically sharp and commensurate YSZ/Si interface is suggested to have a sequence of Si–Si–O–Zr–O–.
Large remanent polarization of (Bi,Nd)4Ti3O12 epitaxial thin films grown by metalorganic chemical vapor deposition
Authors: Kojima Takashi , Sakai Tomohiro , Watanabe Takayuki , Funakubo Hiroshi , Saito Keisuke , Osada Minoru
Published: July 2002

(104)-oriented Bi4Ti3O12, La-substituted Bi4Ti3O12[(Bi3.44La0.56)Ti3O12] and Nd-substituted Bi4Ti3O12[(Bi3.54Nd0.46)Ti3O12] films were epitaxially grown on (111)SrRuO3//(111)SrTiO3 substrates at 700 °C by metalorganic chemical vapor deposition. All deposited films showed strong (104) orientations. The values of the remanent polarization (Pr) and coercive field (Ec) of the (104)-oriented epitaxial (Bi3.54Nd0.46)Ti3O12 thin film were 25 μC/cm2 and 135 kV/cm, respectively. This Pr value was larger than that of the (104)-oriented (Bi3.44La0.56)Ti3O12 film: Pr and Ec values of the (Bi3.44La0.56)Ti3O12 were 17 μC/cm2 and 145 kV/cm, respectively. These good ferroelectric properties of (Bi3.54Nd0.46)Ti3O12 films can be explained by a large tilting of TiO6 octahedra induced by the substitution of Nd3+, the ionic radius of which is smaller than that of La3+. Moreover, this Pr value is almost equal to that of commercially used lead zirconate titanate (PZT) films for nonvolatile ferroelectric random access memory (FeRAM) applications. These (104)-oriented epitaxial (Bi3.54Nd0.46)Ti3O12 thin films also showed a fatigue-free character. As a result, lead-free Nd-substituted Bi4Ti3O12 films with good ferroelectric properties comparable with those of PZT films are useful candidates for FeRAM applications.
Luminescent properties and electronic structure of conjugated polymer-dielectric nanocrystal composites
Authors: Musikhin S. , Bakueva L. , Sargent E. H. , Shik A.
Published: July 2002

We report results of experimental investigations of the luminescent properties of two different conjugated polymers in which we embedded nanocrystals of Al2O3, Y2O3, ZnO, and SnSbO. The dielectric nanocrystals result in a blueshifting and broadening of luminescence spectra of poly(p-phenylene vinylene) with a simultaneous disappearance of its vibronic structure. The same nanocrystals in a poly[2-(6-cyano-6′-methylheptyloxy)-1,4-phenylene] matrix cause redshifting and spectral broadening. These observations are explained by referring to a model that accounts for the change in the polarization component of the carrier and exciton energy in the vicinity of inclusions.
Effect of hydrogen doping on ultraviolet emission spectra of various types of ZnO
Authors: Ohashi Naoki , Ishigaki Takamasa , Okada Nobuhiro , Sekiguchi Takashi , Sakaguchi Isao , Haneda Hajime
Published: July 2002

A pulse-modulated plasma irradiation technique was applied to hydrogenation of ZnO. Three kinds of ZnO samples were employed to investigate the electronic state of hydrogen in ZnO. Secondary-ion-mass-spectroscopy analysis using isotope tracer revealed that the surface layer to 100 nm was doped with hydrogen after the irradiation and its concentration was in the order of 1016 cm−3. The efficiency of band edge emission was increased by the hydrogenation. However, the the degree of the improvements depended on impurity and defect concentration in the original samples. It was concluded that hydrogen in ZnO passivates deep donor and acceptor states by electron transfer from hydrogen to the defects.
Spin-coherent transport in ferromagnetically contacted carbon nanotubes
Authors: Zhao B. , Mönch I. , Vinzelberg H. , Mühl T. , Schneider C. M.
Published: July 2002

The spin-coherent quantum transport through multiwall carbon nanotubes contacted by ferromagnetic Co pads is investigated experimentally. At 4.2 K, the devices show a remarkable increase of the magnetoresistance (MR) ratio with decreasing junction bias, reaching a maximum MR ratio of 30% at a junction bias current of 1 nA. The experimental results suggest the transport to be dominated by spin-dependent tunneling processes at the Co/nanotube interfaces and governed by the local magnetization. We also observe an asymmetry of the magnetoresistance peak position and width which is attributed to a local exchange biasing in the electrode material.
The vibrational energies of ozone up to the dissociation threshold: Dynamics calculations on an accurate potential energy surface
Authors: Siebert Rüdiger , Fleurat-Lessard Paul , Schinke Reinhard , Bittererová Martina , Farantos S. C.
Published: July 2002

We present an ab initio potential energy surface for the ground electronic state of ozone. It is global, i.e., it covers the three identical C2v (open) minima, the D3h (ring) minimum, as well as the O(3P)+O2(3Σg−) dissociation threshold. The electronic structure calculations are performed at the multireference configuration interaction level with complete active space self-consistent-field reference functions and correlation consistent polarized quadruple zeta atomic basis functions. Two of the O–O bond distances, R1 and R2, and the O–O–O bending angle are varied on a regular grid (ca. 5000 points with R1⩾R2). An analytical representation is obtained by a three-dimensional cubic spline. The calculated potential energy surface has a tiny dissociation barrier and a shallow van der Waals minimum in the exit channel. The ring minimum is separated from the three open minima by a high potential barrier and therefore presumably does not influence the low-temperature kinetics. The dissociation energy is reproduced up to 90% of the experimental value. All bound states of nonrotating ozone up to more than 99% of the dissociation energy are calculated using the filter diagonalization technique and employing Jacobi coordinates. The three lowest transition energies for O316 are 1101.9 cm−1 (1103.14 cm−1), 698.5 cm−1 (700.93 cm−1), and 1043.9 cm−1 (1042.14 cm−1) for the symmetric stretch, the bending, and the antisymmetric stretch modes, respectively; the numbers in parentheses are the experimental values. The root-mean-square error for all measured transition energies for O316 is only 5 cm−1. The comparison is equally favorable for all other isotopomers, for which experimental frequencies are available. The assignment is made in terms of normal modes, despite the observation that with increasing energy an increasing number of states acquires local-mode character. At energies close to the threshold a large fraction of states is still unambiguously assignable, particularly those of the overtone progressions. This is in accord with the existence of stable classical periodic orbits up to very high energies.
Effects of wet-oxidation treatment on Al0.45Ga0.55As/GaAs graded-like superlattice-emitter bipolar transistor with low turn-on voltage
Authors: Lour Wen-Shiung , Wu Yen-Wei , Tan Shih-Wei , Tsai Ming-Kwen , Yang Ying-Jay
Published: July 2002

We report an AlxGa1−xAs/GaAs heterojunction bipolar transistor (HBT) with a high Al mole fraction of x=0.45. A digital graded superlattice emitter, forming a step-wise graded composition, is used to smooth out the potential spike resulting from a large conduction-band offset. HBT’s with such a digital graded emitter as a passivation layer exhibit a small offset voltage of 55 mV, a low turn-on voltage of 0.87 V and a current gain as high as 400. Effects of wet-oxidation treatment on fabricated HBT’s are also investigated. Experimental results reveal that the studied HBT’s exhibit reduced collector currents at a fixed base current in the early stage of the wet-oxidation treatment. However, better surface passivation and higher current gain are available after an appropriate wet-oxidation treatment is used to reduce base current. We qualitatively modeled these behaviors by introducing a concept of built-in field along the graded emitter.
Estimation of the impact of electrostatic discharge on density of states in hydrogenated amorphous silicon thin-film transistors
Authors: Golo Natasa Tosic , van der Wal Siebrigje , Kuper Fred G. , Mouthaan Ton
Published: July 2002

The objective of this letter is to give an estimation of the impact of an electrostatic discharge (ESD) stress on the density of states (DOS) within the energy gap of hydrogenated amorphous silicon (a-Si:H) thin-film transistors. ESD stresses were applied by means of a transmission line model tester. The DOS in the a-Si:H was determined by Suzuki’s algorithm using field-effect conductance measurements. A comparison of stressed and unstressed devices shows that there is a threshold ESD stress voltage, below which there is no damage. Above the threshold stress level, first an increase of the deep gap states is found and when stress is increased further, also in the tail states.
Higher-order harmonics of a magnetically soft sensor: Application to remote query temperature measurement
Authors: Ong Keat G. , Grimes Dale M. , Grimes Craig A.
Published: July 2002

This letter describes the application of magnetically soft ribbons for remote query temperature monitoring based upon amplitude changes in the higher-order harmonics emitted by the sensor in response to a magnetic interrogation signal. The harmonic-based temperature sensor is placed, or rigidly embedded since there are no moving parts, within the region of interest where it is remotely monitored using a single interrogation and detection coil. Taking the amplitude ratio between two or more different-order harmonics eliminates the effect of relative orientation between the sensor and monitoring coil, enabling wide-area monitoring. Remote query monitoring of temperature from within a concrete block is demonstrated. The wireless and passive nature of the described sensor platform makes it ideally suited for long-term monitoring applications, such as measuring the temperature inside a concrete roadway or building structure.
Surface quasigeostrophic turbulence: The study of an active scalar
Authors: Sukhatme Jai , Pierrehumbert Raymond T.
Published: July 2002

We study the statistical and geometrical properties of the potential temperature (PT) field in the surface quasigeostrophic (SQG) system of equations. In addition to extracting information in a global sense via tools such as the power spectrum, the g-beta spectrum, and the structure functions we explore the local nature of the PT field by means of the wavelet transform method. The primary indication is that an initially smooth PT field becomes rough (within specified scales), though in a qualitatively sparse fashion. Similarly, initially one-dimensional iso-PT contours (i.e., PT level sets) are seen to acquire a fractal nature. Moreover, the dimensions of the iso-PT contours satisfy existing analytical bounds. The expectation that the roughness will manifest itself in the singular nature of the gradient fields is confirmed via the multifractal nature of the dissipation field. Following earlier work on the subject, the singular and oscillatory nature of the gradient field is investigated by examining the scaling of a probability measure and a sign singular measure, respectively. A physically motivated derivation of the relations between the variety of scaling exponents is presented, the aim being to bring out some of the underlying assumptions which seem to have gone unnoticed in previous presentations. Apart from concentrating on specific properties of the SQG system, a broader theme of the paper is a comparison of the diagnostic inertial range properties of the SQG system with both the two- and three-dimensional Euler equations.
High-power (λ∼9 μm) quantum cascade lasers
Authors: Slivken S. , Huang Z. , Evans A. , Razeghi M.
Published: July 2002

High-power quantum cascade lasers emitting at λ>9 μm are demonstrated. Accurate control of layer thickness and interfaces is evidenced by x-ray diffraction. Excellent peak power for uncoated lasers, up to 3.5 W per facet for a 25 μm emitter width, is obtained at 300 K for 75 period structures. The threshold current density at 300 K is only 1.4 kA/cm2. From 300 to 425 K, the laser exhibits a characteristic temperature, T0, of 167 K. Over 150 mW of average power is measured per facet for a duty cycle of 6%. Simulation of the average power output reveals a thermal resistance of 12 K/W for epilayer-up mounted ridges.
Electroreflectance of the AlGaN/GaN heterostructure and two-dimensional electron gas
Authors: Kurtz S. R. , Allerman A. A. , Koleske D. D. , Peake G. M.
Published: July 2002

A contacted electroreflectance technique was used to characterize the electronic properties of AlGaN/GaN heterostructures and field-effect transistors. By studying variations in the electroreflectance with applied electric field, spectral features associated with the AlGaN barrier, the two-dimensional electron gas at the interface, and bulk GaN were observed. The AlGaN barrier displayed Franz–Keldysh oscillations which provided estimates of barrier-layer composition and electric field. The electron gas Fermi energy was determined from analysis of the broad two-dimensional electron gas feature.
Probability phenomena due to separatrix crossing
Authors: Neishtadt A. I.
Published: July 2002

The effect of a small or slow perturbation on a Hamiltonian system with one degree of freedom is considered. It is assumed that the phase portrait (‘‘phase plane’’) of the unperturbed system is divided by separatrices into several regions and that under the action of the perturbations phase points can cross these separatrices. The probabilistic phenomena are described that arise due to these separatrix crossings, including the scattering of trajectories, random jumps in the values of adiabatic invariants, and adiabatic chaos. These phenomena occur both in idealized problems in classical mechanics and in real physical systems in planetary science and plasma physics contexts.
Order and chaos in semiconductor microstructures
Authors: Lin W. A. , Delos J. B. , Jensen R. V.
Published: July 2002

The semiclassical theory of ballistic electron transport in semiconductor microstructures provides a description of the quantum conductance fluctuations in terms of the classical distributions for the lengths and directed areas of the scattering trajectories. Because the classical dynamics differs for integrable (circular) and chaotic (stadium) scattering domains, experimental measurements of the conductance of these microstructures provide a unique probe of the quantum properties of classically regular and chaotic systems. To advance these theoretical and experimental studies we compare geometrical formulas for the classical distributions of lengths and areas with numerical simulations for microstructures examined in recent experiments, we assess the effects of lead size and placement, and we provide a critical analysis of the role of scattering ‘‘noise’’ on the classical and semiclassical predictions. Finally, we present a detailed comparison of the semiclassical theory with recent experimental measurements of the conductance fluctuations in circular- and stadium-shaped microstructures.
Probabilistic and thermodynamic aspects of dynamical systems
Authors: Nicolis G. , Daems D.
Published: July 2002

The probabilistic approach to dynamical systems giving rise to irreversible behavior at the macroscopic, mesoscopic, and microscopic levels of description is outlined. Signatures of the complexity of the underlying dynamics on the spectral properties of the Liouville, Frobenius–Perron, and Fokker–Planck operators are identified. Entropy and entropy production-like quantities are introduced and the connection between their properties in nonequilibrium steady states and the characteristics of the dynamics in phase space are explored.
Velocity statistics in excited granular media
Authors: Losert W. , Cooper D. G. W. , Delour J. , Kudrolli A. , Gollub J. P.
Published: July 2002

We present an experimental study of velocity statistics for a partial layer of inelastic colliding beads driven by a vertically oscillating boundary. Over a wide range of parameters (accelerations 3–8 times the gravitational acceleration), the probability distribution P(v) deviates measurably from a Gaussian for the two horizontal velocity components. It can be described by P(v)∼exp(−|v/vc|1.5), in agreement with a recent theory. The characteristic velocity vc is proportional to the peak velocity of the boundary. The granular temperature, defined as the mean square particle velocity, varies with particle density and exhibits a maximum at intermediate densities. On the other hand, for free cooling in the absence of excitation, we find an exponential velocity distribution. Finally, we examine the sharing of energy between particles of different mass. The more massive particles are found to have greater kinetic energy.
Algorithms and software for ordinary differential equations and differential- algebraic equations, Part II: Higher-order methods and software packages
Authors: Hindmarsh Alan C. , Petzold Linda R.
Published: July 2002

Department Editor: William J. Thompson
High-field electron capture and emission in nitrided oxides
Authors: Terry F. L. , Wyatt P. W. , Naiman M. L. , Mathur B. P. , Kirk C. T. , Senturia S. D.
Published: July 2002

High-field, constant current injection has been used to study electron trapping and reemission processes in ammonia-annealed (nitrided) silicon dioxide. The gate voltage during injection versus injected charge exhibits two rates. The first provides the capture cross section and trap density information. The second provides information on reemission of trapped charge by tunneling. From the tunneling data, the electron trap depth can be estimated to be 3.5–4 eV below the insulator conduction band. Nitrogen annealing reduces the density of these traps.
Be redistribution during growth of GaAs and AlGaAs by molecular beam epitaxy
Authors: Miller D. L. , Asbeck P. M.
Published: July 2002

The redistribution of the p-type dopant Be during the growth of GaAs and AlGaAs by molecular beam epitaxy has been studied using secondary ion mass spectrometry and capacitance–voltage carrier profiling. An asymmetric redistribution of Be toward the epitaxial layer surface has been observed in GaAs, along with a more symmetric diffusion in AlGaAs. The effects of Be concentration, growth conditions, and Fermi level on Be redistribution have been investigated. The long-range asymmetric redistribution may be due to Be carried forward with the growth surface, while the more symmetric redistribution observed in AlGaAs is consistent with an interstitial–substitutional model for Be diffusion.
Enhanced elastic modulus in composition modulated copper-nickel-iron foils
Authors: Jankowski A. , Tsakalakos T.
Published: July 2002

Young’s modulus was measured by tensile testing on Cu/NiFe thin foils containing short-wavelength composition modulation of 1.4–10.0 nm. The foils, of 53% Cu/40% Ni-7% Fe composition, were produced by vapor deposition using a three-source evaporator. As compared with homogeneous foils of the same average composition, the modulated foils exhibited an appreciable increase (up to 300%) in modulus for two distinct ranges of composition wavelength: 2.1–2.7 and 3.6–4.1 nm. The increase was proportional to the square of the composition amplitude. The stress-strain curves of the modulated foils displayed a Hookean behavior below 0.2% strain.
Quantum yield of electron impact ionization in silicon
Authors: Chang Chi , Hu Chenming , Brodersen Robert W.
Published: July 2002

p-channel Si-gate metal-oxide-semiconductor transistors of very thin oxides are used for the study of quantum yield of electron impact ionization in silicon. Electrons are injected into silicon from the polysilicon gate by tunneling to give an approximate δ-function energy distribution. This energy distribution is preserved when electrons pass through the oxide by direct tunneling. Using the carrier-separation properties of the induced junction, we are able to experimentally measure the number of generated electron-hole pairs as a function of the incident electron energy, up to 5 eV. Our results are found to be in excellent agreement with recent theoretical calculations of quantum yield. Beyond 5 eV, the interpretations on the experimental data are difficult due to the broadening of the incident electron energy distribution. This broadening effect is caused by strong scattering in the oxide when electrons tunnel by the Fowler–Nordheim (F–N) process. It is observed that the average energy of those electrons tunneled by the Fowler–Nordheim process becomes a function of oxide field, relatively independent of the oxide thickness.
Improvement of a proposed model for heat conduction in an electrode submitted to an electric discharge: Application to the indirect determination of the anodic and cathodic voltage drops
Authors: Benzerga L. , Lhiaubet C. , Meyer R. M.
Published: July 2002

We present an improved version of a heat-conduction model which leads to better-computed values of the anodic voltage drops for electric discharges in a liquid dielectric, with a short interelectrode gap (about 50 μm) and short duration (10–1000 μs). The results obtained show monotonic variations according to the duration of the discharge and peak current, and correspond to the measured value of the total interelectrode voltage drop.
Computer modeling study of the effects of inhomogeneous doping and/or composition in GaAs solar-cell devices
Authors: Hamaker H. C.
Published: July 2002

The effects of inhomogeneous doping and/or composition profiles in the active regions of AlGaAs/GaAs heteroface solar cells have been studied using a realistic computer model. It is found that for n-p devices with moderate surface recombination velocities S, only modest improvements in the cell efficiency are obtained by including linear or exponential profiles. Such gradients become more valuable, however, whenever (1) S increases, (2) the solar illumination is increased through concentration, or (3) a p-n device is desired.
Theory of response of radiation sensing field effect transistors
Authors: Hughes R. C.
Published: July 2002

Radiation sensing field effect transistors display a variety of nonlinear and saturating responses to ionizing radiation. A model involving the numerical solutions to the photoconductivity equations is presented which describes the response under a wide range of radiation doses and applied fields. The large, unexpected, response for zero bias demonstrates the importance of diffusion of the photocarriers. The simulations are consistent with the known transport parameters for SiO2, with the main unknowns being the concentration of electron and hole traps. A variety of data at different applied voltages and doses can be fit with the same transport parameters.
Silicon damage caused by CCl4 reactive ion etching: Its characterization and removal by rapid thermal annealing
Authors: Fonash S. J. , Singh Ranbir , Rohatgi A. , Rai-Choudhury P. , Caplan P. J. , Poindexter E. H.
Published: July 2002

It is demonstrated that CCl4 reactive ion etching produces lattice damage, chlorine contamination, and modified electrical properties at etched silicon surfaces. The structural and electrical property changes caused by the chemical-physical etching of CCl4 reactive ion etching are found to be similar to the structural and electrical property changes caused by the physical etching of inert gas ion beam etching. Rapid thermal anneals of 1100 °C for 10 sec are shown to give both structural recovery and electrical property recovery to CCl4-etched silicon surfaces. The chlorine contamination is also shown to be driven off by this rapid thermal anneal. Although it has been reported that rapid thermal annealing does not restore reactive ion-etched silicon surfaces in the case of certain other etching gases, it is effective here in a case where no substantial residue layer is present after etching and impurities present after etching evolve out during the rapid heat pulse.
High mobility two-dimensional hole gas in an Al0.26Ga0.74As/GaAs heterojunction
Authors: Wang W. I. , Mendez E. E. , Iye Y. , Lee B. , Kim M. H. , Stillman G. E.
Published: July 2002

We have obtained two-dimensional hole gas with low temperature mobility as high as 3.8×105 cm2 V−1 s−1 at a density of 1×1011 cm−2. The sample was grown on (311)A orientation. We give arguments to show that (100) orientation is not the optimum orientation for the growth of high purity materials.
Bulk electron traps in zinc oxide varistors
Authors: Cordaro J. F. , Shim Y. , May J. E.
Published: July 2002

Three types of commercial zinc oxide varistor materials were examined using admittance spectroscopy between 30 and 350 K. Maxima in the ac conductance at frequencies from 1 to 100 kHz are observed. The maxima are interpreted as arising from electron traps located within the depletion regions of double Schottky barriers at ZnO-ZnO grain boundaries. Two traps are observed in each material and are likely to be from common origin. The trap energies are found to be 0.17 and 0.33 eV below the conduction-band edge. The traps are likely to be associated with native defects in ZnO and may influence device characteristics such as voltage overshoot.
Electrical properties of polycrystalline silicon layers under solar illumination
Authors: Dimitriadis C. A. , Alexandrou A. , Economou N. A.
Published: July 2002

A model of recombination of carriers at the grain boundaries in polycrystalline silicon layers, taking into account the dynamics of capture and emission of carriers at the grain boundaries trapping states, is presented. Based on this model we investigate the electrical properties of polycrystalline silicon as a function of grain size under solar illumination. Comparison of our theoretical results with experimental results indicates that there is satisfactory agreement.
A kinetic model for the thermal nitridation of SiO2/Si
Authors: Vasquez R. P. , Madhukar A.
Published: July 2002

A kinetic model has been developed in order to understand the underlying reasons for observed nitrogen distributions in SiO2 films on Si which have been thermally nitrided in NH3. The calculations simulate the nitridation process, considering first-order chemical kinetics and Arrhenius dependence of the diffusion and reaction rates on temperature. The calculations show that as the substrate reacts with diffusing species, which initially consist primarily of nitrogen, a nitrogen-rich oxynitride forms at the interface. For nitridation temperature of 1000 °C and above, an oxygen-rich oxynitride subsequently forms at the interface due to reaction of the substrate with an increasing concentration of diffusion oxygen which has been displaced by the slower nitridation of the SiO2. This sequence of events results in a nitrogen distribution in which the peak in the interfacial nitrogen concentration occurs away from the the interface. The results of the calculations are compared with observed nitrogen distributions. The calculations correctly predict that, (i) for a nitridation temperature of 800 °C, the peak of the interfacial nitrogen concentration remains at the interface, while for nitridation temperatures≥1000 °C it moves away from the interface, and (ii) for a nitridation temperature of 1150 °C, the peak interfacial nitrogen concentration is lower than that which occurs at 1000 °C, even though the position of the peak is essentially the same. The effect of interfacial strain is included in the simulations, and is found to be necessary to account for the observed width of the interfacial nitrogen distribution.
Determination of carrier capture cross sections of traps by deep level transient spectroscopy of semiconductors
Authors: Zhao Jian H. , Schlesinger T. E. , Milnes A. G.
Published: July 2002

The conventional method of determining trap capture cross sections by deep level transient spectroscopy (DLTS) of semiconductors involves observing the DLTS peak amplitude as a function of filling pulse duration. Pulses that are inconveniently short and time-consuming experimental measurements may be required. A method is proposed that involves observing the DLTS peak amplitude change as the observation rate window (t2−t1) is varied for a fixed-duration filling pulse. This gives consistent results for the capture cross section and its dependence on temperature. Analysis of the technique is given and a comparison between theory and experiment is presented for two electron traps in bulk n-GaAs. For the trap at EC- 0.215 eV, σ∞ is 2.3×10−15 cm2 and the activation energy from σ(T)=σ∞  exp(−Eσ /kT) is 0.116±0.003 eV. For the trap at EC -0.35 eV, the cross section σ∞ is 1.0×10−13 cm2 and the activation energy is 0.200±0.025 eV. Large variations of cross section with temperature such as these have been reported in other studies, and are a consequence of lattice relaxation effects.
Properties of high-purity AlxGa1−xAs grown by the metalorganic vapor-phase-epitaxy technique using methyl precursors
Authors: Kuech T. F. , Wolford D. J. , Veuhoff E. , Deline V. , Mooney P. M. , Potemski R. , Bradley J.
Published: July 2002

The metalorganic vapor-phase epitaxy (MOVPE) of AlxGa1−xAs most commonly employs the methyl precursors Al(CH3)3 and Ga(CH3)3. These precursors were used in the growth of AlxGa1−xAs over the entire range of alloy composition in a low-pressure horizontal MOVPE reactor. A complete chemical, electrical, and optical characterization of high-purity MOVPE AlxGa1−xAs grown over the entire range of growth temperatures (600–800 °C) was carried out in order to determine the relationship of the materials properties to the growth conditions. Carbon, the primary impurity in the layers, dominates the electrical properties of the epitaxial layers. A superlinear dependence of carbon incorporation on AlAs mole fraction is observed, along with a two-slope dependence on growth temperature. Photoluminescence spectra (2 K) were obtained from materials with AlAs mole fraction over the range 0≤x≤0.80. The photoluminescence intensity of the layers also exhibits a systematic dependence on alloy composition and growth temperature. The in situ gettering of oxygen by the growth reactants is necessary to achieve high luminescence intensity and low electrical compensation. The influence of the reactor design on this gettering process is modeled.
Noise spectroscopy of deep level (D
X) centers in GaAs-AlxGa1−xAs heterostructures
Authors: Kirtley J. R. , Theis T. N. , Mooney P. M. , Wright S. L.
Published: July 2002

We have measured the generation-recombination noise from the donor-related DX centers in current biased GaAs/AlxGa1−xAs heterostructures from 1 Hz to 25 kHz and from 77 to 330 K. A significant noise contribution from these traps is observed even at Al mole fractions below 0.2, where the trap level is resonant with the conduction band. The activated behavior of the noise spectrum from this resonant level is very similar to that observed at higher Al mole fractions, when the level lies deep in the fundamental gap. This result can be predicted, based on the recently elucidated relationship of the trap level to the band structure of AlxGa1−xAs. In accordance with other experimental results, the noise spectra demonstrate that the emission and capture kinetics of the level are unperturbed by its resonance with the conduction band. We briefly discuss some implications of these results for heterostructure transistor design.
Free-carrier density determination in p-type GaAs using Raman scattering from coupled plasmon-phonon modes
Authors: Wan Kam , Young Jeff F. , Devine R. L. S. , Moore W. T. , SpringThorpe A. J. , Miner C. J. , Mandeville P.
Published: July 2002

A nondestructive optical means of determining the activated hole concentration in p-type polar semiconductors is described. The Raman spectra from coupled plasmon-longitudinal-optical-phonon modes in five samples of Be-doped GaAs are measured and fitted using a theory which takes into account the degenerate light- and heavy-hole valence bands. The results indicate that coupled plasmon-longitudinal-optical-phonon modes in p-type material differ both quantitatively and qualitatively from those in n-type semiconductors.
Spin-resolved photoemission from Fe3Pt(001) Invar and γ-Fe films (invited)
Authors: Carbone C. , Sohal G. S. , Kisker E. , Wassermann E. F.
Published: July 2002

We have investigated the electronic structure of ordered Fe3Pt(001) by using spin- and angle-dependent photoemission with synchrotron radiation. The features in the spin-resolved energy distribution curves (SREDC’s) can be understood in terms of the recent band-structure calculations for Fe3Pt. We have observed temperature-dependent changes in the EDC’s which reveal some analogy to the 2γ-state model of Weiss. In our spin- and angle-resolved photoemission study of epitaxially grown ultrathin films of fcc Fe we observe major differences in its magnetic properties, depending on whether these films are grown on Cu(001) or on Cu3Au(001), i.e., substrates with small or large lattice constants.
Frequency dependence of coercivity and initial permeability in ferromagnetic metallic glasses
Authors: Jen S. U. , Weng C. J.
Published: July 2002

Coercivity Hc( f ) and initial permeability χi( f ) of two kinds of ferromagnetic glasses, 2605S2 and VAC6030, have been measured as a function of frequency from 4 Hz to 2 kHz. Field annealing and stretching of samples have been used to define an easy axis along the longitudinal direction. Some samples were thinned to see the thickness effect. We have analyzed the f dependence of coercivity and initial permeability based on the wall pinning model.
Effects of controlled As pressure annealing on deep levels of liquid-encapsulated Czochralski GaAs single crystals
Authors: Chichibu Shigefusa , Ohkubo Norio , Matsumoto Satoru
Published: July 2002

Effects of controlled arsenic vapor pressure thermal treatments on deep levels of liquid-encapsulated Czochralski (LEC) GaAs, especially on the midgap donor EL2, are investigated. Undoped LEC n-type conductive and semi-insulating GaAs crystals are annealed in vacuum or under As vapor pressure. From depth profiles of EL2 concentration, it is confirmed that the thermal conversion on semi-insulating GaAs is caused by the reduction of EL2 concentration and the introduction of native acceptor (VAs). A three-step model for EL2 out-diffusion is proposed. The formation of EL2 occurs during the cooling process at a relatively low temperature of around 650 °C.
Interactions of thin Ti films with Si, SiO2, Si3N4, and SiOxNy under rapid thermal annealing
Authors: Morgan A. E. , Broadbent E. K. , Ritz K. N. , Sadana D. K. , Burrow B. J.
Published: July 2002

Thin Ti films sputter deposited onto single-crystal Si, thermal SiO2, and low-pressure chemical vapor deposited Si3N4 and SiOxNy (x≊y≊1) substrates have been rapid thermal annealed in N2 or Ar, with and without an amorphous Si overlayer, and the reactions followed using Auger elecron spectroscopy, transmission electron microscopy, electron diffraction, and sheet resistance measurements. A multilayer film is created in practically every case with each layer containing essentially a single reaction product, viz.,TiSix, TiOx, δ-TiN, or TiNxO1−x. The results are discussed in light of published Ti-Si-O and Ti-Si-N phase diagrams.
Thermal conductivity of binary, ternary, and quaternary III-V compounds
Authors: Nakwaski Wl/odzimierz
Published: July 2002

The room-temperature thermal conductivity of III-V compounds is analyzed. The phenomenological approach of Abeles is applied to take into account disordered structure of ternary and quaternary alloys. The procedure is used for the In1−xGaxAsyP1−y quaternary alloy. The approximate analytical expression for this case is derived. A more exact method of the calculations is also proposed. It enables presenting the thermal conductivity and the thermal diffusivity for both the InP lattice-matched and GaAs lattice-matched In1−xGaxAsyP1−y alloys as a function of their composition.
Model for molecular-beam-epitaxy growth over nonplanar surfaces
Authors: Ohtsuka Mitsuru , Miyazawa Seiichi
Published: July 2002

A model for molecular-beam-epitaxy growth is proposed to describe the morphology formed on a nonplanar, profiled surface that may consist of multifaceted crystal structures. Anisotropy of growth rate is introduced as a main factor for explaining the observed growth morphology. We show that on the nonplanar surface, the migration of adatoms modifies the growth rate at each point of the growing surface and thus affects the formation of the morphology within the range of migration length. The model can successfully describe the growth behavior including the development of sharp facet edges, since it is formulated in terms of a difference (rather than differential) equation which does not require the continuity of surface slope. The morphology simulated on the basis of this model agrees to experimental results of GaAs growth.
Studies of lattice distortion and crystal curvature in arsenic-implanted silicon
Authors: Kuo C. L. , Kao Y. H. , Arnold Emil , Bilello J. C.
Published: July 2002

The lattice distortion and crystal curvature in arsenic-implanted silicon wafers are investigated using a technique of double-crystal topography. In this study, a method for quantitative determination of the curvature of asymmetric crystal reflection planes as well as the concavity of specimens is demonstrated. Measurements of samples with different arsenic-implantation fluences indicate that all the crystal surfaces are convex and the radius of curvature decreases with increasing arsenic fluence. Effects of thermal annealing are shown to result in a reduction of the crystal curvature and local lattice distortion.
Magnetoresistance and anisotropy of the resistivity in Ni/Nb and Ni/Si multilayers
Authors: Pérez-Frías M. T. , Flores J. , Vicent J. L.
Published: July 2002

Multilayers of Nb/Ni and Ni/Si have been fabricated by dc triode sputtering. Standard x-ray diffraction in the reflection geometry shows good layering for both systems with several orders in small-angle scans which correspond to the modulation of the films. High-angle scans show that Nb/Ni films growth with (111) texture for Ni layers and (110) for Nb layers. Ni/Si multilayers do not show any texture. Transverse magnetoresistance (TMR), longitudinal magnetoresistance (LMR), and the spontaneous anisotropy of the resistivity (SAR) have been measured with an applied field up to 70 kOe and between 10 and 110 K and bilayer thicknesses between 60 and 200 Å. Both systems show LMR and TMR to be very small in comparison with pure Ni films. The SAR effect is temperature independent and increases with bilayer thickness. Also, it is higher for Nb/Ni than Ni/Si multilayers with ρ∥ >ρ⊥ for Ni/Si but ρ∥ <ρ⊥ for Nb/Ni samples.
Thermal relaxation of pseudomorphic Si-Ge superlattices by enhanced diffusion and dislocation multiplication
Authors: Iyer S. S. , LeGoues F. K.
Published: July 2002

Pseudomorphic Si/Si-Ge strained layer superlattices are metastable and will relax to lower-energy, less strained, states on thermal annealing. Such relaxation may occur by the generation of misfit dislocation or by compositional homogenization of the superlattice. The particular mechanism adopted is shown to depend on the initial dislocation density of the structures. In cases where a significant portion of the strain is accommodated by an array of misfit dislocations in the as-grown state there is a propensity to relax by generating additional misfit dislocations. In the case of structures where only a very small fraction of the misfit is relieved by dislocations in the as-grown state, additional relaxation does not involve the multiplication of dislocations but proceeds by the interdiffusion of Si and Ge towards the homogenizing of the superlattice structure. This strain-enhanced diffusion has previously been observed in metals and we confirm its existence in semiconductor systems as well. The implication of the above observations on device structures and the growth of such layers is discussed.
InAs monomolecular plane in GaAs grown by flow-rate modulation epitaxy
Authors: Sato Michio , Horikoshi Yoshiji
Published: July 2002

InAs monomolecular planes are grown in GaAs by flow-rate modulation epitaxy. This structure exhibits low-temperature (2 K) photoluminescence with high intensity and a small linewidth. Two InAs planes separated by N monolayers of GaAs also exhibit intense, narrow photoluminescence. The peak photon energies drastically increase with the distance between the planes. Assuming that an InAs plane in GaAs forms a 1-monolayer-thick InAs/GaAs quantum well, the photoluminescence peak photon energies and the drastic increase are explained using a finite square well model.
Observation of large peak-to-valley current ratios and large peak current densities in AlSb/InAs/AlSb double-barrier tunnel structures
Authors: Söderström J. R. , Chow D. H. , McGill T. C.
Published: July 2002

We report improved peak-to-valley current ratios and peak current densities in InAs/AlSb double-barrier, negative differential resistance tunnel structures. Our peak-to-valley current ratios are 2.9 at room temperature and 10 at liquid-nitrogen temperatures. Furthermore, we have observed peak current densities of 1.7×105 A/cm2. These figures of merit are substantially better than previously reported values. The improvements are obtained by adding spacer layers near the barriers, thinner well regions, and thinner barriers.
Third-order optical susceptibility in short-period GaAs doping superlattices
Authors: Choquette Kent D. , McCaughan Leon , Misemer D. K.
Published: July 2002

We propose that short-period doping superlattices are suitable for the enhancement of a third-order susceptibility arising from free carriers in nonparabolic energy subbands. The inherent advantage lies in the ability to simply engineer the superlattice potential profile, yielding control of miniband energy dispersion. We consider short-period GaAs doping superlattices composed of uniformly doped donor and acceptor layers, and planar-doped n- and p-type monolayers separated by intrinsic regions. Calculations of the electronic structure of compensated and n-type noncompensated n-i-p-i superlattices incorporating miniband dispersion at nonzero temperature are reported. We show that small modulations of the superlattice potential lead to large subband nonparabolicities and we calculate a twentyfold improvement in the third-order susceptibility over bulk GaAs at room temperature, comparable to that predicted for GaAs/AlGaAs compositional superlattices.