bluuebunny/crossref_metadata_2025 huggingface dataset:
Defects and leakage currents in BF2-implanted preamorphized silicon
Authors: Brotherton S. D. , Gowers J. P. , Young N. D. , Clegg J. B. , Ayres J. R.
Published: July 2002

High-dose silicon implants have been used to preamorphize the surface of single-crystal silicon prior to the implantation of low-energy BF2. The preamorphization results in shallow junction formation with minimal channeling of the boron, but high concentrations of electrically active defects are formed, leading to excessive reverse bias leakage currents. Measurements of leakage current and deep-level defects indicated that two distinct types of electrically active defects were important: those associated with what are probably complexes or clusters of point defects located near the far end of the range of the implanted silicon, and those associated with extended defects (loops) at the edge of the regrown amorphous region. The former defects were deep-level donors present in high concentrations (>1017 cm−3) after regrowth of the amorphous layer at 600 or 700 °C and resulted in leakage currents >10−4 A/cm2. These centers could be annealed out at 800 °C reducing the leakage current to values between 5×10−8 and 2×10−5 A/cm2 depending upon the relative locations of the extended defects and the metallurgical junction. Measurements and modeling have shown that the location of the band of extended defects is critical in controlling the leakage current and that it will need to be a few hundred angstroms shallower than the junction itself for the associated generation current to be fully suppressed.
Optical properties of plasma-enhanced chemical vapor deposited silicon-oxynitride films
Authors: Cros Y. , Rostaing J. C. , Peisner J. , Leveque G. , Ance C.
Published: July 2002

By transmission and reflection spectroscopy between 1.5 and 9.5 eV, at 300 and 100 K, we have obtained the absorption coefficient α of silicon oxynitride films grown by plasma-enhanced chemical vapor desposition from gas mixtures of SiH4 and N2O at 430 °C. IR, electron spin resonance (ESR), and transport measurements have been performed previously on this sample of SiOxNyHz known composition by elastic recoil detection analysis (ERDA). The optical gap EG, the slope B of Tauc’s plot (αhν)1/2=B(hν−EG), and the reciprocal slope Eo of the Urbach tail present strong correlation in SiOxNyHz and SiNyHz films. Below a percolation limit for oxygen, nitrogen, and hydrogen incorporation in the a-Si amorphous network, the relevant physical parameter for the composition is x in SiOx, (y+z) in SiNyHz, and (x+y+z) in SiOxNyHz . Thus, we find single curves for the variation with the composition of E04 (the energy at which α=104 cm−1), E0, and 1/B. Above the percolation composition the optical absorption below the principal absorption edge is dominated by defect states in the gap. According to ESR and ERDA measurements, the absorption shoulder between 7 and 8 eV may be explained by the presence of OH− or O+3 diamagnetic centers in the insulator.
Molecular-beam-epitaxial growth of GaAs(331)
Authors: Uppal P. N. , Ahearn J. S. , Musser D. P.
Published: July 2002

The molecular-beam epitaxial growth of (331)-oriented GaAs and (100)-oriented GaAs were compared. Silicon-doping behavior was studied as a function of As/Ga flux ratio and substrate temperature at constant Si cell temperature. GaAs layers grown on (100) and (331)B were always n type. For growths on the (100) substrates, the carrier concentration increased by about a factor of 5 as the As/Ga ratio was increased from about 1 to 50. On (331)B GaAs, the carrier concentration started out 3 times higher than on GaAs(100) and remained relatively level up to a flux ratio of 20; it then began to rise, becoming about 30% higher at a V/III ratio near 50. (331)A layers were invariably p type at low As/Ga ratios. As the flux increased, the acceptor concentration dropped rapidly. At high flux ratios, the (331)A GaAs became n type, with a donor concentration approaching that on (100). Photoluminescence (PL) measurements taken on crystals grown side by side showed pronounced defect exciton peaks for GaAs(100), less pronounced peaks for (331)A crystals, and no peaks for (331)B crystals. The carbon acceptor peaks for (331)A crystals were at least an order of magnitude more intense than the exciton peaks. PL measurements were also taken on multiquantum wells grown on the (100) and (331)A orientations. PL data also indicated that carbon was incorporated more readily in the (100) and (331)A layers than in the (331)B layers. The results of these experiments can be explained on the basis of the crystal structure of the surface, the As/Ga flux ratios, and the amphoteric nature of silicon. At the surface of the (331)GaAs, both cation and anion dangling bonds extend into the vacuum: two Ga dangling bonds for every As dangling bond on (331)A, and the reverse for (331)B. In contrast, there is only one site offered in the (100) orientation: either a gallium or arsenic double dangling bond. Thus, the number of sites available for As bonding should be a determinant of carbon incorporation. Since the (331)B has the fewest such sites, it should incorporate the least carbon, as, indeed, was confirmed by our PL and capacitance-voltage data.
Influence of the substrate orientation on Si incorporation in molecular-beam epitaxial GaAs
Authors: Bose S. S. , Lee B. , Kim M. H. , Stillman G. E. , Wang W. I.
Published: July 2002

The incorporation of Si in high-purity lightly Si-doped GaAs grown simultaneously on (100), (311)A, and (311)B GaAs substrates by molecular-beam epitaxy has been studied. Photothermal ionization spectroscopy shows that Si is incorporated predominantly as a donor for growth on (100) and (311)B substrates, whereas low-temperature photoluminescence shows that Si is incorporated predominantly as an acceptor for growth on a (311)A substrate. Spectroscopic and Hall-effect measurements show that the dominance of Si donors in the samples grown on the (100) and (311)B substrates renders these samples n-type while the dominance of Si acceptors in the sample grown on the (311)A substrate renders that sample p-type.
Substrate-polarity dependence of metal-organic vapor-phase epitaxy-grown GaN on SiC
Authors: Sasaki T. , Matsuoka T.
Published: July 2002

Single-crystal gallium nitride was grown on each of the two polar {0001} planes of 6H-silicon carbide substrates utilizing metal-organic vapor-phase epitaxy. The substrate polarity is clearly shown to strongly influence the surface morphology and the photoluminescence property of the layer. The examination of the layer surfaces using x-ray photoelectron spectroscopy revealed that {0001} GaN grown on the basal planes of SiC changes its polarity in accordance with the substrate polarity.
Temperature dependence of electron trapping in metal-oxide-semiconductor devices as a function of the injection mode
Authors: Gildenblat G. Sh. , Huang C.-L. , Grot S. A.
Published: July 2002

Temperature dependence of electron trapping in metal-oxide-semiconductor (MOS) devices is controlled by the injection mode. In particular, for avalanche, photoinjection, or hot-carrier injection the electron trapping and device degradation are accelerated at 77 K. However, for the tunneling injection the electron trapping decreases as the temperature is reduced. In this injection mode the temperature dependence of the electron trapping is similar to that of the SiO2 breakdown, which indicates that the two phenomena may be related. The temperature dependence of MOS breakdown is investigated experimentally in the 77–400-K temperature range. It is shown that the corresponding activation energy changes drastically between 200 and 300 K.
Quenching rates of Ar metastables in radio-frequency glow discharges
Authors: Scheller Geoffrey R. , Gottscho Richard A. , Graves D. B. , Intrator T.
Published: July 2002

Although rate coefficients are essential ingredients in modeling chemical processes such as chemical vapor deposition and plasma etching, the values measured as a function of temperature under well-defined equilibrium conditions may be inappropriate for use in models of nonequilibrium systems. For this reason, it is important to have measurements of in situ rates that can be used as input parameters or can provide stringent tests for reactor simulations. Using time-resolved plasma-induced emission and laser-induced fluorescence spectroscopy, we measured quenching rates for Ar metastable states in radio-frequency discharges through mixtures of Ar and the molecular gases SF6, Cl2, BCl3, and N2. After verifying the validity of modulation spectroscopy to measure in situ rates, the effects of discharge power, pressure, and flowrate are investigated. The most important effect occurs when the discharge power is increased; the decline in quenching rates with increased power is attributed to increased molecular dissociation that produces products with lower collision cross sections.
Experimental evidence for the existence of an overlap length in spin glasses
Authors: Sandlund L. , Svedlindh P. , Granberg P. , Nordblad P. , Lundgren L.
Published: July 2002

Zero-field-cooled magnetization measurements on a Cu(10 at.% Mn) spin glass are reported. The relaxation of the magnetization is recorded after specific temperature variations of the sample in the spin-glass phase. The data are discussed within the framework of new domain theories of the spin-glass phase. A qualitative agreement between the theoretical predictions and the experimental results is found. Specifically, empirical support for the theoretical concept overlap length is given.
Structural characterization of boron nitride films
Authors: Duncan T. M. , Levy R. A. , Gallagher P. K. , Walsh M. W.
Published: July 2002

The microstructure of amorphous hydrogenated boron nitride films, with nominal composition B3N:H, is characterized with respect to hydrogen bonding and distribution by combined application of nuclear-magnetic-resonance (NMR) spectroscopy, electron-spin-resonance spectroscopy, and evolved gas analysis. Previous infrared studies on annealed films suggest that hydrogen is present in multiple configurations; qualitatively, low-temperature anneals (∼600 °C) deplete N-H moieties whereas B-H configurations are depleted at higher temperatures (∼1050 °C). Gas analysis corroborates these results, showing H2 peaks at ∼570 and ∼950 °C. From an analysis of nuclear dipolar couplings extracted from the 1H NMR spectra, it is concluded that the hydrogen is essentially randomly distributed as monohydrides; other configurations, such as dihydrides and monohydride clusters, are estimated to be less than 20% total. Furthermore, the 1H NMR spectra show no evidence of molecular H2 trapped in the films. In a film exposed to a high x-ray dose (∼30 kJ cm−3), it was determined that the damage was equivalent to 1 unpaired electron spin per 175 B3N:H units. The 1H NMR linewidth did not change after irradiation, which suggests that the hydrogen spatial distribution was unaffected.
Band structure and charge control studies of n- and p-type pseudomorphic modulation-doped field-effect transistors
Authors: Jaffe Mark , Singh Jasprit
Published: July 2002

We present results of a numerical formalism developed to address the band structure and the charge control problem in pseudomorphic n- and p-type modulation-doped field-effect transistors (MODFETs), which are created by adding excess indium in the active channel region. For n-type structures, the tight-bonding formalism is used to study the effect of strain on the crystal electronic properties. A finite-difference technique to solve the Schrödinger equation simultaneously with the Poisson equation is used to model the MODFET. The enhanced performance in n-type pseudomorphic devices has been shown to be primarily due to better charge confinement. Results are also presented as a function of channel strain. For p-type structures, the Kohn–Luttinger formulation is used together with deformation potential theory to describe the hole states. Significant reductions in the mass of the hole gas due to biaxial compressive strain are demonstrated, suggesting dramatic potential improvement in the operation characteristics of p-type pseudomorphic devices. As an application of the formalism, a comparison of pulse and uniform doping in the barrier region is carried out. The improvement in carrier transfer efficiency and the potential reduction of gate leakage current are discussed.
AlGaAs epitaxial growth on (111)B substrates by metalorganic vapor-phase epitaxy
Authors: Kato Kazutoshi , Hasumi Yuji , Kozen Atsuo , Temmyo Jiro
Published: July 2002

AlGaAs epitaxial layers were grown on (111)B-oriented GaAs substrates by metalorganic vapor-phase epitaxy (MOVPE). Mirrorlike surfaces can be obtained with a growth temperature of 875–900 °C and a V/III ratio of 10–20, while a high density of hillocks appears with lower temperatures and/or larger V/III ratios. Hillock density is reduced by introducing misorientation on (111)B substrates. In this case, however, macrosteps appear on the surface when the misorientation angle is larger than 0.2°. Low-temperature photoluminescence indicates that single quantum wells can be formed on (111)B substrates by using MOVPE.
Investigation of the charge pumping current in metal-oxide-semiconductor structures
Authors: Ghibaudo Gerard , Saks Nelson S.
Published: July 2002

A study of the charge pumping phenomena occurring in a metal-oxide-semiconductor structure is presented. This study, which is based on numerical simulations of charge pumping in the time domain, enables a good overall description of the charge pumping characteristics to be obtained. In particular, the influence of various charge pumping configurations is analyzed relative to gate voltage signal characteristics such as rise/fall times, low/high gate biases, pulse duration, and signal waveform, and to device parameters such as interface-state density, flat-band voltage, and threshold voltage. The numerical simulations are also compared to typical experimental charge pumping characteristics. The adequacy of analytical or simplified models generally used to exploit the charge pumping data is also discussed.
Spatial light modulation by nonlinear absorbers
Authors: Speiser Shammai , Dantsker David , Orenstein Meir
Published: July 2002

A novel spatial light modulator (SLM) based on nonlinear absorption of light by excited molecules is suggested. A kinetic analysis is applied to calculate the relative populations of molecular levels in singlet and triplet manifolds. It is shown that for many actual cases a probe light can be modulated by propagating through a medium excited by another light source. The dependence of the molecular SLM on the photophysical parameters of the SLM medium is discussed.
Impact damage model for ceramic materials
Authors: Rajendran A. M. , Kroupa J. L.
Published: July 2002

The fracture process in ceramic materials upon impact loading is complex in nature. Most often, the brittle ceramic deforms inelastically due to microcracking under shock (compression) loading. At high-velocity impact, the shock generated microcracks rapidly open and extend under subsequent tension (due to the release waves from the stress-free boundaries) leading to complete pulverization of the ceramic materials. The main objective of this paper is to model the damage process in ceramics due to impact loading. A computationally oriented continuum damage-based constitutive model is considered. Several modifications incorporating strain rate and damage effects on the compressive strength have been introduced into the model. Results are presented in terms of numerical simulations of a plate-impact test configuration. Effects of the model parameters on the compressive strength and spall strength are described. The proposed damage model has been used successfully to match the measured stress history from a plate-impact experiment on AD-85 (85% aluminum oxide) ceramic target material.
Analysis of a self-aligned AlGaAs/GaAs heterostructure bipolar transistor: Steady-state and transient simulations
Authors: Meyyappan M. , Andrews G. , Grubin H. L. , Kreskovsky J. P.
Published: July 2002

Traditionally, circuit simulators using one-dimensional device models have been used to estimate the switching time of semiconductor devices. These one-dimensional models do not adequately describe the switching behavior of heterostructure bipolar transistors. This paper describes the results of a two-dimensional steady-state and transient simulation to examine the switching behavior of a self-aligned AlGaAs/GaAs heterostructure bipolar transistor. Both on-transient and off-transient behavior are examined. It is shown that the distributed resistance and capacitance, and the ensuing two-dimensional transport in the base region determine the switching time.
Determination of minority-carrier lifetime and surface recombination velocity by optical-beam-induced-current measurements at different light wavelengths
Authors: Flohr Th. , Helbig R.
Published: July 2002

An analysis of the optically generated excess current through a plane p-n junction perpendicular to the surface is given both for the steady state and for periodic generation. The finite dimensions of the sample are taken into account. The sample is assumed to be bounded by a plane parallel to the junction. An exponential light generation function according to Beer’s law is considered. By variation of the wavelength and thus the penetration depth of the light, the influence of surface recombination on the measured signal can be controlled. Therefore, the determination of bulk diffusion length and surface recombination velocity is unambiguously possible from a set of steady-state optical-beam-induced-current curves at different light wavelengths. From additional high-frequency measurements, the diffusion constant and thus the bulk lifetime of the excess carriers may be obtained. The results are demonstrated by measurements on various p+nn+diodes.
Analysis of the capacitive coupling of Josephson transmission lines
Authors: Cirillo M. , Bishop A. R. , Lomdahl P. S. , Pace S.
Published: July 2002

We study the capacitive coupling of two long Josephson junctions by imposing appropriate boundary conditions at the ends of the junctions. Numerical simulations show good agreement with analytical estimates of the parameter range for which reflections of fluxons at the coupled end of the junction occur. We discuss our results in terms of recent experiments concerning phase-locking phenomena in Josephson junctions fluxon oscillators devices.
Interface and bulk trap generation in metal-oxide-semiconductor capacitors
Authors: Buchanan D. A. , DiMaria D. J.
Published: July 2002

The effects of electron-hole pair recombination near the silicon/silicon dioxide interface of aluminum-gate metal-oxide-semiconductor capacitors have been studied. For the first time, electron-heating-induced trap generation and interface state creation is separated from those defects created through electron-hole pair recombination. The midgap interface state density is observed to increase linearly with the number of recombination events and approaches saturation in the mid 1011 eV−1 cm−2 range for trapped hole densities greater than about 1012 cm−2. However, the total integrated interface state density, although showing a similar net increase to that of the midgap interface state density, does not saturate for the largest trapped hole densities introduced in this work. For hot-electron-induced defects, a dramatic increase in the interface state generation rate is observed for average electric fields above a threshold of 1.5×106 V cm−1. An increase in the electron trapping rate above the heating threshold is also detected at both the cathode and anode interfaces. The rate is found to be approximately 10−5 traps or interface states generated per injected electron for average electric fields below the heating threshold, while above the threshold this rate increases by an order of magnitude. These rates were measured for injected electron fluences as low as 10−3 C cm−2. These high trapping and interface state generation rates are believed to be due to the high concentration of hydrogen (or hydrogen-related species) in these films.
Measurement of the Faraday effect of a few optical glasses using a direct polarimetric method
Authors: Kim S. Y. , Won Y. H. , Kim H. N.
Published: July 2002

A new method of measuring the longitudinal magneto-optic effect has been introduced. This method does not require a modulator; instead, the analyzer is rotated and the intensity of light is collected as a function of the analyzer angle. The Fourier analysis of the intensity date versus the analyzer angle yields the information about the rotation angle and the ellipticity of the transmitted light. This method is simple in design as well as fast and accurate in data acquisition by virtue of computer-assisted data collection. It was applied to the real samples of the optical glasses of Schott—SF2, F2, SF6, and SF10. The rotation angle was linearly proportional to the magnetic intensity and the Verdet constants showed a normal dispersion versus photon energy. The results were in a good agreement with other published values. Some possible applications of the present technique to the measurement of a very small birefringence have been discussed.
Strain effects on GaxIn1−xAs/InP single quantum wells grown by organometallic vapor-phase epitaxy with 0≤x≤1
Authors: Wang T. Y. , Stringfellow G. B.
Published: July 2002

Single-quantum-well structures were grown by atmospheric pressure organometallic vapor-phase epitaxy, with GaxIn1−xAs layers (0≤x≤1) coherently strained to match the lattice parameter of the InP barrier layers in the (100) growth plane. The strain effects on the band lineups were analyzed using the ‘‘model solid’’ theory of Van de Walle and Martin. The hydrostatic strain component for alloys with x≊1 is shown to be sufficient to marginally convert the type-II lineups for the unstrained case to type I. The band lineups remain type I for x≊0. Considering the effect of strain, the ‖ (3)/(2) , (1)/(2) 〉 valence subband becomes a slowly varying function of x. Band offsets are predicted over the entire alloy composition and compared with the reported data. The photoluminescence (10 K) peak energies for the 100-Å GaxIn1−xAs/InP single quantum wells compare quite favorably with the calculated strained band gap versus x. For nominal monolayer quantum wells, the peak energies are slightly above 1.1 eV over the entire alloy range. It is shown that for x>0.47, the LH1 and HH1 subbands cross at a smaller well width as x increases. The ground-state exciton is light hole-like for larger values of x and Lz, and heavy hole-like for smaller x and Lz.
On the origin of misfit dislocations in InGaAs/GaAs strained layers
Authors: Dixon R. H. , Goodhew P. J.
Published: July 2002

InxGa1−xAs/GaAs (x≤0.25) strained layers grown by molecular-beam epitaxy have been examined by plan-view transmission electron microscopy. Evidence is presented for the existence of two critical thicknesses, corresponding to the turnover of threading disloca- tions and the nucleation of new dislocations. From a quantitative analysis of dislocation intersections it is deduced that not all interfacial dislocations act to relieve the misfit strain.
Effect of heat treatment on InGaAs/GaAs quantum wells
Authors: Elman B. , Koteles Emil S. , Melman P. , Jagannath C. , Armiento C. A. , Rothman M.
Published: July 2002

We report on the effect of furnace annealing on 60-Å-wide InxGa1−xAs/GaAs single quantum wells (SQWs) in the range of indium composition 0.1≤x≤0.5. Excitonic energy shifts of up to 120 meV were observed after annealing of the samples at 825 °C for 30 min. The fact that these energy shifts were strongly dependent of the indium composition in the well material was consistent with enhancement on the indium diffusion out of the wells associated with the presence of dislocations. The most dramatic changes, as a result of annealing, manifested by strain recovery were observed from the SQW with x=0.3 which as-grown had a low dislocation density (quantum well thickness slightly exceeding the critical layer thickness for formation of dislocations).
Model dielectric function of hexagonal CdSe
Authors: Adachi Sadao
Published: July 2002

We present a calculation of the complex dielectric function, ε(ω)=ε1(ω)+iε2(ω), at energies below and above the fundamental absorption edge of the hexagonal, wurtzite-type semiconductor CdSe. This model includes the E0, E1, and Eidg (indirect) gaps as the main dispersion mechanisms. The model is made to properly account for the excitonic effects at these critical points. Results are in satisfactory agreement with recent ellipsometric measurements over the entire range of photon energies (E=0–5.0 eV). Detailed discussions are presented on the results, with emphasis on the information about the electronic energy-band structures and their group-symmetrical selection rules of this material.
Formation of multiply faulted defects in oxygen implanted silicon-on-insulator material
Authors: Visitserngtrakul Supapan , Krause Stephen J. , Cordts Bernhard F.
Published: July 2002

A multiply faulted defect (MFD), has been observed at a density of 108 cm−2 in oxygen implanted silicon-on-insulator material at implantation temperatures of ≥600 °C over a dose range from 0.3 to 1.8×1018 cm−2. The MFDs are 40–140 nm long and are created at the upper edge of the high-dose implantation region. They consist of combinations of several discontinuous stacking faults within 2–8 atomic layers which generate an irregularity along the defect. The atomic arrangement of the MFDs indicates that they form by shearing of the lattice due to the volume change associated with oxide precipitation. The defects have a randomly faulted arrangement from cross slip and from the presence of several inhomogeneous nucleation sites along the edge of the same defect.
An enhanced and linear Stark shift in n-i-n AlGaAs/GaAs symmetric and asymmetric coupled quantum wells
Authors: Kuhn Kelin J. , Juang Cheng , Darling Robert B.
Published: July 2002

Stark shift in AlGaAs/GaAs symmetric and asymmetric coupled quantum wells is compared experimentally and theoretically. Symmetric coupled quantum wells possess a linear and enhanced Stark shift which is relatively insensitive to small perturbations in quantum well width and mismatch ratio. Asymmetric coupled quantum wells also possess a linear and enhanced Stark shift. However, in contrast to symmetric wells, the Stark shift is quite sensitive to well width and mismatch ratio. The linear and enhanced Stark shift in AlGaAs/GaAs asymmetric and symmetric coupled quantum wells is experimentally confirmed using photoluminescence on an n-i-n device structure.
On the normal acceleration sensitivity of contoured quartz resonators with the mode shape displaced with respect to rectangular supports
Authors: Zhou Y. S. , Tiersten H. F.
Published: July 2002

It is shown that the normal acceleration sensitivity of contoured quartz resonators with rectangular supports vanishes when the centers of the mode shape and support rectangle coincide. This result is a consequence of symmetry and applies to many other shapes. Since it is essentially impossible to realize this situation in practice, an analysis of the influence of an offset of the centers on the normal acceleration sensitivity is performed. The biasing deformation is determined by means of a variational approximation procedure using the variational principle with all natural conditions for anisotropic static flexure. The very important accompanying strains varying quadratically across the thickness are determined recursively, as in earlier work. The resulting flexural biasing states are employed in an existing perturbation equation along with the equivalent trapped-energy-mode shapes of the contoured resonators to calculate the normal acceleration sensitivities. It is shown that for small offsets the acceleration sensitivity increases linearly with offset, and orientations for which this effect is minimized are found.
Study on further reducing the epitaxial silicon temperature down to 250 °C in low-energy bias sputtering
Authors: Ohmi Tadahiro , Hashimoto Keiichi , Morita Makoto , Shibata Tadashi
Published: July 2002

The epitaxial silicon growth temperature has been reduced to as low as 250 °C by optimizing the ion bombardment condition in low-energy bias sputtering process. Independent and precise control of ion bombardment energy and ion flux density incident on a growing film surface is most essential to realize very low temperature epitaxy. It has been experimentally shown that the deficit in energy for epitaxial growth by reducing the substrate temperature is able to be compensated for by increasing the total energy dose on a film surface by low-energy ion bombardment. Increase in the impact energy of individual ions, however, results in the formation of high-density defects in the film. Therefore, the right direction to enhance the total energy deposition by ion bombardment is to increase the ion flux density while keeping the ion impact energy at an optimum value. As a result of such optimization, epitaxial growth of silicon has become possible at a temperature as low as 250 °C. The etch pit density in this low-temperature growth film is less than 3×103 cm−2, the detection limit of our experiments. The carbon and oxygen concentrations in a grown film as measured by secondary ion mass spectroscopy increase with the background pressure, and these impurity concentrations are correlated to the crystallinity of the film. From these observations, the profound effect of contamination on the reduction of silicon epitaxial temperature is demonstrated.
Microstructural evolution during the heteroepitaxy of Ge on vicinal Si(100)
Authors: Krishnamurthy Mohan , Drucker J. S. , Venables J. A.
Published: July 2002

Microstructural evolution during the initial stages of islanding of Ge on vicinal Si(100) has been studied in situ with nanometer resolution in an ultrahigh-vacuum scanning transmission electron microscope. Ge is deposited using molecular-beam-epitaxy (MBE) techniques on vicinal Si(100) misoriented 1° and 5° toward 〈110〉. For MBE-type experiments, there is evidence for metastable growth of the Ge intermediate layer to much greater than the equilibrium critical thickness. The layer may grow up to seven monolayers thick before islanding in the Stranski–Krastanov growth mode. The presence of strong adatom sinks significantly alters the growth and size distribution of the islands when the spacing of these sinks is less than an adatom diffusion distance. Studies of the initial stages of islanding in solid-phase MBE indicate that there is no long-range adatom diffusion. There is an initial fast transformation from a disordered layer growth, followed by a sluggish growth of islands. We have studied the coarsening of these islands at the earliest stages with sensitivity to islands as small as 2 nm in radius. It appears that there is a novel coarsening mechanism influenced by an unstable intermediate layer and dislocation-free islands. In all cases, the dislocation-free islands grow more slowly than those which have relaxed by the introduction of misfit dislocations.
Oxide field and thickness dependence of trap generation in 9–30 nm dry and dry/wet/dry oxides
Authors: Nishida Toshikazu , Thompson Scott E.
Published: July 2002

The oxide electric field and thickness dependencies of the oxide electron trap generation rate measured on 86–315 Å thick 900 °C dry oxide and 850 °C dry/wet/dry oxide stressed by substrate electron injection at average dc oxide fields of 1–9 MV/cm are reported. A minimum in the steady-state gate voltage shift versus oxide electric field is discovered which suggests a balance of the field-dependent electron trap charging and discharging rates with the generation rate of oxide traps by oxide field-accelerated hot electrons. The thickness and field dependencies of trap charging, discharging, and generation are compared for two industrial oxidation processes, 900 °C dry and 850 °C dry/wet/dry oxides, and are shown to have similar trap generation rates. A new two-trap generation-charging-discharging model is proposed and shown to give excellent agreement with the experimental data.
Observation of negative differential resistance in GaAs field-effect transistors
Authors: Muzumdar P. , Mirchandani K. , Mil’shtein S.
Published: July 2002

Negative differential resistance (NDR) is observed in GaAs metal-semiconductor field-effect transistors. The device under test is a GaAs dual-gate device. The observation of NDR is attributed to intervalley transfer in GaAs. The characteristic is field controlled and is n type in shape. NDR can be controlled by independent control of the two gates. It is also seen for a fixed ratio of gate voltages.
Mechanism of dc conduction in lightly doped polypyrrole films
Authors: Singh Ramadhar , Tandon R. P. , Chandra Subhas
Published: July 2002

The dc conductivity of lightly doped polypyrrole films has been measured in the temperature range 77–300 K and the conductivity data has been successfully explained in terms of Mott’s variable-range hopping conduction model.
Discrete conductance fluctuations in silicon emitter junctions due to defect clustering and evidence for structural changes by high-energy electron irradiation and annealing
Authors: Andersson Gert I. , Andersson Mats O. , Engström Olof
Published: July 2002

Observations of discrete conductance fluctuations are reported at voltages well below the breakdown voltage in selected reverse-biased p+-n++ base-emitter junctions originating from gate turn-off thyristors. The occurrence of the phenomenon is attributed to the presence of defect clusters at the p-n junctions. The defect clusters introduce field confinements which activate tunneling processes that would not otherwise be present in these nonabrupt p-n junctions. The fluctuating reverse current was only observed in voltage and temperature regions where the total reverse current was influenced by tunneling-related conduction mechanisms. The experimental observations concerning the voltage and temperature dependences of the fluctuation amplitude and rate deviate from earlier reports on decisive points. Both the amplitude and the switching rate of the observed fluctuations were unstable in time and influenced by the measurement procedure itself. This instability is attributed to small structural changes of the defect clusters. Furthermore, the unstable behavior of the defect clusters also influences the static reverse current-voltage characteristic. Distinct changes were found in the static reverse current-voltage characteristics of selected samples due to high-energy electron irradiation and annealing at 200 °C. A clearly increased uniformity of the reverse current-voltage characteristics between the gate-cathode junctions of gate-turn off thyristors was also found as a result of electron irradiation. The changes observed are interpreted as evidence of structural changes of the defect clusters.
Magnetic decoupling in sputtered Fe/Si superlattices and multilayers
Authors: Fullerton Eric E. , Mattson J. E. , Lee S. R. , Sowers C. H. , Huang Y. Y. , Felcher G. , Bader S. D. , Parker F. T.
Published: July 2002

Sputtered Fe/Si superlattices were grown to study the magnetic coupling between ferromagnetic Fe layers (30 Å thick) for Si spacer-layer thicknesses (tSi) between 10 and 40 Å. The material is ferromagnetical for tSi≤13 Å and antiferromagnetically coupled for 13 Å≤tSi≤17 Å. For tSi≥17 Å the Fe layers are uncoupled. X-ray analysis indicates that the system is well layered, but that the crystal structure remains coherent only for tSi≤17 Å. These results, along with our Mössbauer investigation, strongly suggest that the Si layer is crystalline for tSi≤17 Å, and is silicide in nature. For thicker spacers, Si becomes amorphous. We propose a model of the layering that is consistent with the known properties of Fe silicide.
Epitaxial τ (Mn,Ni)Al/(Al,Ga)As heterostructures: Magnetic and magneto-optic properties
Authors: Cheeks T. L. , Brasil M. J. S. P. , De Boeck Jo , Harbison J. P. , Sands T. , Tanaka M. , Scherer A. , Keramidas V. G.
Published: July 2002

Ferromagnetic perpendicularly magnetized epitaxial thin films of τ (Mn,Ni)Al have been successfully grown on AlAs/GaAs heterostructures by molecular beam epitaxy. We have investigated the polar Kerr rotation and magnetization of τ MnAl and (Mn,Ni)Al as a function of Mn and Ni concentration. The largest polar Kerr rotation and remnant magnetization were obtained for Mn0.5Al0.5 thin films with values of 0.16° and 224 emu/cm3, respectively. We observed that the Kerr rotation and magnetization remained constant with Ni additions up to about 12 at. % and subsequently decreased with further Ni additions. We discuss these results and one possible method of enhancing the Kerr rotation.
Optimizing the radiation resistance of InP solar cells: Effect of dopant density and cell thickness
Authors: Keavney C. J. , Walters R.J. , Drevinsky P. J.
Published: July 2002

The effect of 1 MeV electron and 10 MeV proton irradiations on the electrical properties of high-efficiency InP solar cells grown by metalorganic chemical-vapor deposition has been measured and analyzed. The base dopant levels ranged from 3×1015 to 2×1017 cm−3, and the effect of the dopant concentration on the radiation response is presented and analyzed. The radiation-induced degradation of the solar cells was measured through both dark and 1 sun air mass zero current-voltage measurements and through spectral response measurements. The radiation-induced defects in the solar-cell junction were monitored by deep-level transient spectroscopy. Thermal and photoinjection annealing experiments were performed on the irradiated cells. The highest postirradiation efficiencies measured after a fluence of 1016, 1 MeV electrons cm−2 were 11.6% which is higher than has been reported for any other solar-cell material. Although all of the cells showed high radiation resistance, the cells with a lightly doped base (essentially an n-i-p structure after irradiation) degraded more in the open-circuit voltage and less in the short-circuit current than the more heavily doped cells. Modeling indicates that the thickness of the junction and base layers is very important in determining the end of life efficiency of the cell. Using the measured data, efficiencies up to 14.1% are predicted with a thin base and a back surface reflector, following irradiation with 1016 1 MeV electrons cm−2.
Generation of Si–SiO2 interface states by high electric field stress from low (100 K) to high (450 K) temperatures
Authors: Vuillaume Dominique , Mir Abdellah , Bouchakour Rachid , Jourdain Marc , El-Hdiy Abdelillah , Salace Guy
Published: July 2002

The temperature dependence (in the range 100–450 K) of the generation of fast interface states at the Si–SiO2 interface by high electric field stress in metal–oxide-semiconductor capacitors when electrons are injected by Fowler–Nordheim tunneling from the Si substrate (n type Si, with a positively biased gate) and from the gate (p type Si, with a negatively biased gate) was analyzed. In both cases, two different temperature regimes can be distinguished, which correspond to two mechanisms responsible for the creation of fast interface states. At stress temperature Ts larger than 180 K, a temperature-activated regime is shown to be consistent with a diffusion of hydrogen-related species, while for Ts<180 K, a nonactivated regime seems consistent with the trapped-hole model. The diffusion coefficients of these hydrogen-related species in the intermediate Ts range 180 K<Ts<300 K were determined. It is DH≊10−14–10−11 cm2/s, in good agreement with the extrapolated values from the known data for the hydrogen diffusion in SiO2 determined at higher temperatures.
Polar phonon-intersubband plasmon coupling in Si delta-doped GaAs
Authors: Mlayah A. , Carles R. , Bedel E. , Muñoz-Yagüe A.
Published: July 2002

The present work is devoted to Raman scattering by coupled phonon-intersubband plasmon excitations in Si δ-doped GaAs. The signature of the coupled modes is pointed out by means of difference Raman scattering, and their symmetry determined according to the selection rules. A good agreement is found between the experimental spectra and those calculated in the frame of the dielectric response theory. Raman depth profiling measurements have been performed for two locations of the Si-doped sheet with respect to the sample surface. These results give evidence for electron localization in the vicinity of the doped sheet and allow the spatial extent of the electron gas to be estimated. The change undergone by the Raman signal of the coupled phonon-plasmon system is studied as a function of doping level, and the ion spreading effects are discussed. The measurements performed in a wide range of temperature are also presented and analyzed.
Single-mode optically activated phase modulator on GaAs/GaAlAs compound semiconductor rib waveguides
Authors: Chen R. T. , Shih R. , Robinson D. , Jannson T.
Published: July 2002

We report on an optically activated phase modulator (OAM) and modulator array on GaAs-GaAlAs compound semiconductor rib waveguides. A rib waveguide device with an optical activation window of 5 μm in diameter was fabricated. Optical activation was produced by using a HeNe 632.8 nm wavelength as the free-carrier generator and a 1.3 μm laser as the signal carrier. A 33% modulation depth was observed and 10−2 index modulation was experimentally confirmed on an OAM working in the phase modulation regime. OAMs working in both phase- and cutoff-modulation regimes were further determined by considering the variation of the waveguide confinement factor. An 8.2 dB modulation depth was observed on an OAM working at the cutoff regime. Furthermore, the activation source for the free-carrier generation is in the mW power region, which significantly reduces the size and cost of all optical switching devices.
Study of strain and disorder of InxGa1−xP/(GaAs, graded GaP) (0.25≤x≤0.8) using spectroscopic ellipsometry and Raman spectroscopy
Authors: Lee H. , Biswas D. , Klein M. V. , Morkoç H. , Aspnes D. E. , Choe B. D. , Kim J. , Griffiths C. O.
Published: July 2002

The optical properties of InxGa1−xP/GaAs and InxGa1−xP/graded InGaP/GaP (0.25≤x≤0.8) epitaxial layers have been studied using spectroscopic ellipsometry and Raman spectroscopy. The (E1,E1+Δ1) critical points and the first-order phonon frequencies were determined as a function of In composition. The general behavior of the peak shifts and broadenings of both the E1 gaps and the optical phonons of InxGa1−xP/GaAs can be explained in terms of biaxial strain and strain relaxation caused by lattice-mismatch. The near-cancellation of E1 gap change due to the compensation effect between alloy composition and misfit strain is observed. As misfit strain increases, the E1 gap broadens whereas the phonon line shape does not change. In strain relaxed samples of InxGa1−xP/(GaAs, graded GaP) (0.3≤x≤0.8), the E1 gap linewidth shows upward bowing as a function of In composition.
Low-frequency, high-temperature conductance and capacitance measurements on metal-oxide-silicon carbide capacitors
Authors: Ouisse T. , Bécourt N. , Jaussaud C. , Templier F.
Published: July 2002

Low-frequency capacitance and conductance measurements have been extensively performed from 1 Hz to 100 kHz and in the 293–673 K temperature range, on metal-oxide-semiconductor (MOS) capacitors made on silicon carbide material. The energy distribution of the trap time constants, capture cross sections, and interface-state density are presented. It is shown that only low-frequency and high-temperature measurements may provide the ability to scan the midgap region of the forbidden band gap. The experimental results fully confirm the feasibility of MOS devices on silicon carbide material. Furthermore, conductance measurements at high temperature indicate the presence of deep bulk levels.
Wet thermal oxidation of AlxGa1−xAs compounds
Authors: Burton R. S. , Schlesinger T. E.
Published: July 2002

Results are presented on the wet thermal oxidation of AlxGa1−xAs. The growth of wet thermal oxides of AlxGa1−xAs is shown to be linear with time. An O2 carrier gas was found to form a self-terminating oxide for compositions investigated (x≳0.4), but required elevated temperatures for substantial growth. The use of a medium oxygen concentration (∼20%) in a N2 carrier formed nonuniform oxides for all compositions investigated. A low O2 concentration (0.1%) in the N2 carrier was found to reduce the activation energy of the oxidation process for Al0.6Ga0.4As from 1.9 to 1.0 eV while increasing the activation energy of Al0.8Ga0.2As from 1.6 to 1.75 eV. For these wet thermal oxides it is observed that lateral oxidation at heterojunction interfaces is enhanced. This enhanced lateral oxidation can be attributed to local stress due to the smaller volume of the growing oxide compared to the volume of the consumed semiconductor.
Measurement of local porosities and dielectric dispersion for a water-saturated porous medium
Authors: Haslund Espen , Hansen Bent Dahle , Hilfer Rudolf , No/st Bjarne
Published: July 2002

The frequency-dependent conductivity and dielectric constant of a salt-water-saturated porous glass specimen have been measured. The measurements cover the full frequency range of the Maxwell–Wagner dispersion. The experimental results have been compared with the recently introduced local porosity theory and with previous theories. For the purpose of comparing with the local porosity theory experimental measurements of local porosity distributions from digitized pore space images are presented. These experimental porosity distributions are then used for a first experimental test of local porosity theory. The comparison with previous theoretical expressions for the frequency-dependent effective dielectric function shows that local porosity theory constitutes a significant improvement in the quantitative agreement.
Two-dimensional model of the ignition phase of high-pressure glow discharges
Authors: Simon G. , Bötticher W.
Published: July 2002

A self-consistent two-dimensional (2D) model of large volume inhomogeneously preionized transient high-pressure glows as used in XeCl lasers is described. The basic concept is to use a curvilinear orthogonal coordinate system generated by conformal mapping of a cartesian system. The model uses the local field approximation and is based on a cartesian 2D model of J.-P. Boeuf and L. C. Pitchford [IEEE Trans. Plasma Sci. 19, 286 (1991)]. As only direct ionization is taken into account, applications are limited to the ignition phase. Application to a discharge between cylindrical rods predicts a high degree of E-field homogenization due to space charges and demonstrates the limits of parallel resistor models. Inside the cathode sheath an explosive formation of a very thin highly ionized layer is predicted. This sheath ignition is also seen in experiments.
ac surface discharge on dielectric materials observed by advanced Pockels effect technique
Authors: Kawasaki Toshiyuki , Terashima Tokihiro , Suzuki Saburo , Takada Tatsuo
Published: July 2002

Techniques for visualization and quantification of the latent electric charge image on dielectric materials have been developed using Pockels effect of a BSO (Bi12SiO20) single crystal, a charge coupled device camera recording system, and a computer image processing technique. The Pockels device of the BSO single crystal was used as a transducer to transfer the surface charge density to retard the transmitted light beam. The basic principle of advanced electro-optical surface charge measurement is described and typical surface charge distributions of positive and negative discharge streamers produced by an ac (50 Hz) high voltage are demonstrated. The measured surface charge images are shown on a computer monitor as three-dimensional figures.
Recent progress in the theory of interlayer exchange coupling (invited)
Authors: Bruno P.
Published: July 2002

Recent progress in the theory of interlayer exchange coupling is presented. The interlayer coupling is described in terms of quantum interferences in the spacer layer, due to reflections of Bloch waves on the spacer boundaries. This approach is used to discuss (i) the coupling variation with respect to ferromagnetic layers thickness, and (ii) the coupling across a nonmetallic spacer layer.