bluuebunny/crossref_metadata_2025 huggingface dataset:
Super-energy tensor for space–times with vanishing scalar curvature
Authors: Bonilla Miguel Á. G. , Sopuerta Carlos F.
Published: July 2002

A four-index tensor is constructed with terms both quadratic in the Riemann tensor and linear in its second derivatives, which has zero divergence for space–times with vanishing scalar curvature. This tensor reduces in vacuum to the Bel–Robinson tensor. Furthermore, the completely timelike component referred to any observer is positive, and zero if and only if the space–time is flat (excluding some unphysical space–times). We also show that this tensor is the unique one that can be constructed with these properties. Such a tensor does not exist for general gravitational fields. Finally, we study this tensor in several examples: the Friedmann–Lemaı̂tre–Robertson–Walker space–times filled with radiation, the plane–fronted gravitational waves, and the Vaidya radiating metric.
Center and universal R-matrix for quantized Borcherds superalgebras
Authors: Hong Jin
Published: July 2002

We construct a nondegenerate symmetric bilinear form on quantized enveloping algebras associated to Borcherds superalgebras. With this, we study its center and its universal R matrix.
Symmetry reductions of the BKP hierarchy
Authors: Loris Ignace , Willox Ralph
Published: July 2002

A general symmetry of the bilinear BKP hierarchy is studied in terms of tau functions. We use this symmetry to define reductions of the BKP hierarchy, among which new integrable systems can be found. The reductions are connected to constraints on the Lax operator as well as on the bilinear formulation. A class of solutions for the reduced equations is derived.
Construction of Kac–Moody superalgebras as minimal graded Lie superalgebras and weight multiplicities for Kac–Moody superalgebras
Authors: Kim Jeong-Ah , Shin Dong-Uy
Published: July 2002

We construct a Kac–Moody superalgebra ℒ as the minimal graded Lie superalgebra with local part V*⊕ge⊕V, where 𝔤 is a “smaller” Lie superalgebra inside ℒ, V is an irreducible highest weight 𝔤-module, and V* is the contragredient of V. We show that the weight multiplicities of irreducible highest weight modules over Kac–Moody superalgebras of finite type and affine type [more precisely, Kac–Moody superalgebras of type B(0,r), B(1)(0,r), A(4)(2r,0), A(2)(2r−1,0), and C(2)(r+1)] are given by polynomials in the rank r. The degree of these weight multiplicity polynomials are less than or equal to the depth of weights.
Current sheet stability and accelerated reconnection of magnetic field lines
Authors: Kleva Robert G.
Published: July 2002

The stability of a narrow current sheet embedded in a sheared magnetic field to short wavelength microtearing modes is examined and a mechanism for the accelerated reconnection of magnetic field lines during the fast crash of sawteeth in tokamaks is presented. The stability of the sheet is shown to depend crucially on the sign of Il/ k′∥, where Il is the line current in the sheet and k∥ ≡dk∥(x)/dx is the rate of change of the parallel wave number in the direction of the inhomogeneity, as well as on three important characteristic lengths: Δr, the distance between the center of the current sheet and the resonant surface of the mode; the width σs of the sheet; and the resonant layer width wr of the mode. When Il/k′∥ is positive, the current sheet can be unstable only if Δr < 1/2  max(σs,wr); otherwise, the sheet is stable. Conversely, when Il/k∥ is negative the sheet can be unstable only if Δr > 1/2  max(σs,wr); otherwise, the sheet is stable. Expressions for the unstable spectrum and the growth rate of the unstable modes as a function of the relative magnitude of Δr, σs, and wr are presented. For narrow current sheets with σs<wr, the growth rate of the tearing mode actually increases as the plasma resistivity decreases.

The stability analysis is applied to the current sheet generated around the X point of a q=1 mode during the fast crash of the central temperature during sawteeth in tokamaks. The sheet is unstable if σs is less than a critical width σsc/a ≡‖Is/I0‖ ×(4/qa), where Is/I0 is the ratio of the current Is in the sheet to the total current I0, a is the minor radius, and qa is the safety factor at the edge of the plasma. For typical TFTR tokamak [Plasma Physics and Controlled Nuclear Fusion Research, Kyoto, 1986 (IAEA, Vienna, 1986), Vol. 1, p. 421] parameters, σsc is a few ion gyroradii. The sheet generated by the q=1 mode in a hot tokamak like TFTR or JET is much narrower than σsc. As a consequence, the sheet is unstable to a broad spectrum of short wavelength perturbations with m, n>100, where m and n are the poloidal and toroidal mode numbers, respectively. These modes grow rapidly with a growth time of the order of 1 μsec, much less than the sawtooth crash time of 50–100 μsec. This short wavelength turbulence will likely broaden the current sheet to the marginally stable width σsc and thereby increase the rate of reconnection of magnetic field lines by the q=1 mode, resulting in a fast crash of the central temperature.
Fluctuation-induced transport and poloidal rotation in the interchangeable module stellarator
Authors: Matthews P. G. , Anderson D. T. , Anderson F. S. B. , Shohet J. L. , Talmadge J. N.
Published: July 2002

Probe measurements over the two-dimensional plasma cross section of the average and fluctuating density, electron temperature, and potential, as well as the Reynolds stress, have been made in the Interchangeable Module Stellarator (IMS) [D. T. Anderson, J. A. Derr, and J. L. Shohet, IEEE Trans. Plasma Sci. PS-9, 212 (1981)]. These measurements were performed at two magnetic field strengths, and also when a positively biased electrode induces a poloidal plasma flow. The data shows the fluctuation-induced transport to be poloidally asymmetric and dependent upon the location of the electron cyclotron resonance position, and upon the electrode biasing. The induced poloidal plasma flow changes the nominally outward fluctuation-induced particle transport to be inward (negative radial transport) by changing the phase relationship of the density and potential oscillations. The amplitude of the density and potential fluctuations are, in general, not reduced by the sheared poloidal flow. Calculations are presented comparing the computed Reynolds stress induced poloidal plasma flows with the flow calculated from momentum balance.
Destabilization of magnetohydrodynamic modes with finite Larmor radius effects in tandem mirrors
Authors: Kotschenreuther M. , Berk H. L.
Published: July 2002

Difficulties in the stabilization of ideal magnetohydrodynamic (MHD) ballooning modes by finite Larmor radius (FLR) effects are considered, in tandem mirror geometry for azimuthal mode numbers l>1. A kinetic formalism is used to obtain corrections to the long, thin approximation, when keeping terms of quadratic order in the curvature. If ηi =∂ ln Ti /∂ ln ni ≥0, with Ti, ni, the ion temperature and density, ion resonance effects eliminate absolute FLR stability, though the residual growth rates are substantially reduced from the MHD values. However, the residual modes are still important, and mixing length estimates of the confinement degradation from modes with l>l indicate they can still severely limit the achievement of reactor-grade operation near and above the threshold beta values predicted from the ideal MHD theory. This is most severe if the ion temperature decreases radially (ni>0), whereupon significant instabilities can even arise below the ideal threshold. However, if −2/3<η<0, the lowest order FLR theory suffices to produce stability.
Wake and wake-induced shear-layer excitation in an annular jet
Authors: Lam K. M. , Ko N. W. M. , Lau K. K.
Published: July 2002

The wake and wake-induced structures in the initial region of an annular jet (with a center body truncated at the jet exit plane) are studied from the measurements of velocity correlation and conditional sampling. Both sets of structures are found to play an important role in momentum transports and Reynolds stress production. They are also found to be oriented in a quasi-two-dimensional orderly pattern. In the initial outer shear layer, a large-scale instability is induced by the shedding of the vortex-street-like wake structures from the center body. This wake-induced instability is associated with the formation of the induced coherent structures and the subsequent zigzag staggered pattern occupied by them and the inner wake structures on the quasi-two-dimensional orderly plane.
Integrability and structural stability of solutions to the Ginzburg–Landau equation
Authors: Keefe Laurence R.
Published: July 2002

The integrability of the Ginzburg–Landau equation is studied to investigate if the existence of chaotic solutions found numerically could have been predicted a priori. The equation is shown not to possess the Painlevé property, except for a special case of the coefficients that corresponds to the integrable, nonlinear Schrödinger (NLS) equation. Regarding the Ginzburg–Landau equation as a dissipative perturbation of the NLS, numerical experiments show all but one of a family of two-tori solutions, possessed by the NLS under particular conditions, to disappear under real perturbations to the NLS coefficients of O(10−6).
Reynolds number scaling of turbulent diffusivity in wall flows
Authors: Yakhot Victor
Published: July 2002

The quantitative interpretation of the recent experiments on turbulent diffusivity in high-Reynolds-number Couette–Taylor flow by Tam and Swinney [Phys. Rev. A 36, 1374 (1987)], is presented.
Investigation of closure models for nonpremixed turbulent reacting flows
Authors: Mell W. E. , Nilsen V. , Kosály G. , Riley J. J.
Published: July 2002

The stationary laminar flamelet model and the conditional moment closure are two salient approaches to the decoupling of the chemistry problem from the turbulence problem. These two models are investigated using direct numerical simulations. The results and their analyses show that a full understanding of the validity of the stationary laminar flamelet model cannot be reached based upon the reaction zone thickness in Z space. A new condition regarding the quasisteadiness of the chemical reaction is derived and applied to the interpretation of the data. The conditional moment closure leads to excellent data predictions provided the average scalar dissipation rate conditioned on the mixture fraction is properly modeled.
Nonlinear modeling of jet atomization in the wind-induced regime
Authors: Spangler Christopher A. , Hilbing James H. , Heister Stephen D.
Published: July 2002

A boundary element method (BEM) has been developed to solve for the nonlinear evolution of a liquid jet acting under the influence of both surface tension and the aerodynamic interactions with the surrounding atmosphere. For longer waves, aerodynamic effects are shown to cause a ‘‘swelling’’ of the liquid surface in the trough region. The model predicts the presence of satellite drops in the first wind-induced regime, and predicts the evolution of a ‘‘spiked’’ surface at the periphery of the jet for conditions consistent with the second wind-induced regime. The effects of the disturbance wave number, the liquid Weber number, and the density ratio between the liquid jet and the surrounding gas on the breakup of the jet have been examined. Transition points between various flow regimes have also been identified.
Pressure spectra for vortex models of fine-scale homogeneous turbulence
Authors: Pullin D. I.
Published: July 2002

Pressure spectra at large wave numbers are calculated for Lundgren–Townsend vortex models of the fine scales of homogeneous turbulence. Specific results are given for the Burgers vortex and also for the Lundgren-strained spiral vortex. For the latter case, it is found that the contribution to the shell-summed spectrum produced by the interaction between the axisymmetric and nonaxisymmetric components of the velocity field is proportional to k−7/3 (k=‖k‖ is the modulus of the wave number) in agreement with Kolmogorov-type dimensional arguments. Numerical estimates of the dimensionless prefactors for this component are obtained in Kolmogorov scaling variables and comparisons are made with results from the Batchelor–Kolmogorov theory, and with experimental measurement.
Recovery of equilibrium turbulent boundary layers downstream of obstacles
Authors: Nigim Hani H.
Published: July 2002

In this paper the behavior of a turbulent boundary layer perturbed from its equilibrium state, due to the presence of an obstacle on an otherwise smooth surface, was investigated. The data of the equilibrium turbulent boundary layers are presented in terms of dimensionless integral parameters, where the flow features can be simply estimated. It was found that the rate of recovery to equilibrium, at highly adverse pressure gradients, is almost instantaneous in the inner part of the new boundary layer initiated by the reattachment process. The flow recovery downstream of an obstacle is correlated in term of Clauser’s profile parameter ratio, G/G′.
The morphological evolution and internal convection of E×B-drifting plasma clouds: Theory, dielectric-in-cell simulations, and N-body dielectric simulations
Authors: Borovsky Joseph E. , Hansen Paul J.
Published: July 2002

The evolution of E×B-drifting plasma clouds is investigated with the aid of a computational technique denoted here as “dielectric-in-cell.” Many of the familiar phenomena associated with clouds of collisionless plasma are seen and explained and less-well-known phenomena associated with convection patterns, with the stripping of cloud material, and with the evolution of plasma clouds composed of differing ion species are investigated. The effects of spatially uniform diffusion are studied with the dielectric-in-cell technique and with another computational technique denoted as “N-body dielectric;” the suppression of convection, the suppression of structure growth, the increase in material stripping, and the evolution of cloud anisotropy are examined.
Effect of a snow plow in bursty magnetic reconnection
Authors: Semenov Vladimir S. , Volkonskaya Natalia N. , Biernat Helfried K.
Published: July 2002

This paper concentrates on aspects of magnetic field reconnection for a time-varying reconnection rate. There are a number of aspects of time-dependent reconnection that have no analogous behavior with the steady-state case. The localization of such time-varying features is of particular interest due to the fact that modeling is generally based on the steady-state case. In order to get optimal physical and mathematical insight, the most simple model is used: identical plasma and magnetic field behavior (except for the field orientation) on either side of the reconnection layer; furthermore the plasma is assumed to be incompressible. The primary interest is the distribution of different energy modes as a result of reconnection. Following a pulse of reconnection, propagating field reversal regions (FRRs) form. Inside these FRRs, the magnetic field energy is decreased, leading to accelerated plasma jets. As a result of the fast motion of the FRRs, there is an accumulation of magnetic energy external to their leading fronts (analogous to the snow accumulation in front of a moving snow plow), and a corresponding energy rarefaction in their wake regions.
Chalcogenide hollow fibers for infrared energy transmission
Authors: Bornstein A. , Croitoru N. , Seidman Materials & Electromagnetic Radiation A.
Published: July 2002

Chalcogenide glass hollow fibers were fabricated. The fibers are small, light, and flexible and can transmit CO2 laser light as well as visible light. Their attenuation remains constant even when bent to small radii of 2 cm. The fibers can transmit high power density (0.5 kW/cm2) in a small spot size (100 μm) of light.
Noble-metal-based transparent infrared reflectors: Improved performance caused by nonhomogeneous film structure
Authors: Niklasson G. A. , Granqvist C. G.
Published: July 2002

The radiative properties of nonhomogeneous Au films with a continuous metal network were investigated by computations based on effective medium theories. The inhomogeneities were found to be conducive to high transmittance of solar energy, particularly in the near infrared, while the thermal emittance was not significantly increased. The favorable film structure leads to a conspicuous onset of transmittance at a wavelength which depends on the characteristic shapes of the structural units.
Degenerate four-wave mixing in planar CS2 covered waveguides
Authors: Karaguleff C. , Stegeman G. I. , Fortenberry R. , Zanoni R. , Seaton C. T.
Published: July 2002

Degenerate four-wave mixing in a thin-film waveguide is demonstrated for the first time. A reflectivity of 10−9 at a power density of 5 MW/cm2 was obtained for liquid CS2 placed on top of a glass waveguide.
Seed selection through ion channeling to modify crystallographic orientations of polycrystalline Si films on SiO2: Implant angle dependence
Authors: Kung K. T-Y. , Iverson R. B. , Reif R.
Published: July 2002

Polycrystalline silicon films 4800 Å thick deposited by low pressure chemical vapor deposition at 620 °C on oxidized silicon wafers have been amorphized by implantation with 210-keV Si28 ions to a dose of 1015 cm−2 at 0°, 1°, 3°, 5°, or 7° from normal incidence and subsequently recrystallized at 700 °C. The as-deposited film was {110} textured with the 〈110〉 directions within ±20° of the surface normal. After the 0°, 1°, or 3° implant and subsequent recrystallization, most of the 〈110〉 directions were confined to within ±4° of the corresponding implant direction. For the 5° and 7° implants, the 〈110〉 directions in the recrystallized layers became randomly oriented; that is, the films lost their {110} texture. These results can be explained by the process of seed selection through ion channeling (SSIC): the grains that survived the 0°, 1°, or 3° implant due to ion channeling acted as seeds during recrystallization. The fact that the direction of the 〈110〉 axes in the recrystallized films was coincident with the implant angle strongly supports the existence of the SSIC process.
Silicon near-surface disorder and etch residues caused by CCIF3/H2 reactive ion etching
Authors: Oehrlein G. S. , Ransom C. M. , Chakravarti S. N. , Lee Y. H.
Published: July 2002

The effects of SiO2 reactive ion etching (RIE) in CClF3/H2 on the surface properties of the underlying Si substrate have been studied by photoemission and He ion scattering/channeling techniques. We find that RIE introduces a F, C, and Cl containing layer on the Si surface. Furthermore, displacement damage is introduced in the Si near-surface region during RIE processing. The efficacy of O2 plasma or rapid thermal annealing RIE post-treatments for removal of contamination and/or displacement damage has been investigated.
Structural damage at the Si/SiO2 interface resulting from electron injection in metal-oxide-semiconductor devices
Authors: Mikawa R. E. , Lenahan P. M.
Published: July 2002

With electron spin resonance, we have observed structural changes in metal-oxide-semiconductor structures resulting from the photoemisson of electrons from the silicon into the oxide. A trivalent silicon defect at the Si/SiO2 interface, termed Pb, is shown to be responsible for the interface states induced by electron injection. We find that these Pb centers are amphoteric interface state defects.
Silicon molecular beam epitaxy on gallium arsenide
Authors: Zalm P. C. , Marée P. M. J. , Olthof R. I. J.
Published: July 2002

Si overlayers have been grown under ultrahigh vacuum conditions on GaAs (100) single crystals by means of molecular beam epitaxy. For growth temperatures above 400 °C (2×1) low-energy electron diffraction patterns of the Si overlayers were observed at all film thicknesses produced (1–5000 Å). By means of Auger electron spectroscopy it was found that the surface of the grown Si was enriched with As and Ga. Two different mechanisms contribute to the enrichment and lead to a high (∼1018/cm3) background doping level. With Rutherford backscattering using ion channeling it was found that there is considerable lattice disorder at the Si-GaAs interface, although the crystal quality of the Si improves markedly towards the Si surface for thicker layers where the minimum channeling yield drops to 9%. With medium energy ion scattering it was established that no island formation occurs during initial stages of the growth.
InP single crystal film fabrication on a glass substrate
Authors: Iida Shosan
Published: July 2002

A new method for fabricating an InP single crystal film on a glass substrate is given. It uses a molecular beam deposition technique in combination with other techniques such as recrystallization and liquid phase epitaxy techniques. By this method an InP layer covered with an In layer is fabricated on a glass substrate and treated in situ. After the treatment, it is confirmed that an InP single crystal film has been fabricated on the glass substrate through crystallographical examinations by means of an electron probe x-ray microanalyzer, x-ray Laue photography, and x-ray diffractometer using the Bond technique for single crystals.
Transient capacitance analysis of III-V semiconductors with organic-on-inorganic semiconductor contact barrier diodes
Authors: Stavola Michael , Parsey John M. , Forrest Stephen R. , Kaplan Martin L. , Schmidt Paul H. , Young Morris S. S.
Published: July 2002

We have investigated the suitability of organic-on-inorganic (OI) semiconductor contact barrier diodes for use in deep level transient spectroscopy (DLTS) of III-V semiconductors. The diodes are formed by vacuum deposition of a thin film of an organic molecular solid onto semiconductor samples as has been previously reported. DLTS measurements performed on n-type GaAs using conventional Au Schottky barriers have been compared with those using OI diodes DLTS measurements have also been made on as-grown p-type GaAs and n-type InP (upon which high quality conventional Schottky barriers cannot readily be fabricated) using OI diodes. OI devices can be made upon many semiconductors for which conventional Schottky barriers cannot be fabricated, require no sample heating, and can be easily removed without detrimental effects to the inorganic semiconductor material.
Photoinduced diffusion of Ag in GexSe1−x glass
Authors: Leung W. , Cheung N. , Neureuther A. R.
Published: July 2002

Diffusion of Ag in GexSe1−x (x∼0.1) under UV light irradiation is studied using Rutherford backscattering spectrometry and microlithography techniques. The diffusion coefficient at 21 °C and 2 mW/cm2 is determined to be 2.7 nm2/s. The temperature dependence of the diffusivity follows an Arrhenius-type equation with an activation energy of 5.32 kcal/mole (0.23 eV) and a pre-exponent factor of 2.5×104 nm2/s. The reciprocity of irradiation intensity and exposure time with respect to the diffusion distance is confirmed. Specifically, the diffusivity is found to be directly proportional to the irradiation intensity.
Oxygen distribution in a horizontal Bridgman-grown, semi-insulating GaAs ingot
Authors: Shikano Koji , Kobayashi Kenji , Miyazawa Shintaro
Published: July 2002

Oxygen concentration in a horizontal Bridgman-grown, chromium and oxygen-doped, semi-insulating GaAs ingot was analyzed using charged particle activation analysis. The oxygen concentration ranged from 2.0×1015 at seed end to 7.2×1015 cm−3 at tail end. The change of oxygen concentration measured along the length of ingot was in accordance with the normal-freeze equation. The effective distribution coefficient of oxygen was estimated to be 0.39.
Measurement of diffusion length gradients in hydrogen passivated silicon ribbon
Authors: Micheels R. H. , Vayman Z. , Hanoka J. I.
Published: July 2002

Hydrogen passivation of p-type Si ribbon was studied by means of diffusion length measurements using the surface photovoltage (SPV) method. The effect of gradients in diffusion length on the SPV measurements and the median depth sampled by this method were investigated by numerical solution of the appropriate diffusion equations. The SPV technique was found to give an average of the diffusion length depth distribution with a median sampling depth of 70 μm. Up to threefold increases in diffusion length were observed due to passivation. Diffusion length profiling measurements made by etching away the surface showed significant passivation occurring at a depth of 200 μm.
GaAs lateral epitaxial growth over a tungsten grating by molecular beam epitaxy
Authors: Kondo Naoto , Kawashima Minoru , Ando Seigo , Oe Kunishige
Published: July 2002

GaAs lateral epitaxial growth over a tungsten grating is achieved by molecular beam epitaxy. Lateral overgrowth is seeded by epitaxial deposits formed on the GaAs (001) surface openings onto a line and space tungsten grating. The condition of obtaining continuous growth surface is investigated. While a rather slow growth rate (0.5 μm/h) results in faceted growth, a growth rate of 1 μm/h at a growth temperature of 730 °C on a 2.5-μm period tungsten grating of 〈110〉 direction permits one to obtain a smooth continuous overgrown layer. The x-ray diffraction pattern on this layer exhibits a single crystalline GaAs (400) pattern and an interface between the buried tungsten and the overgrown layer shows a preferable Schottky characteristic.
Second order gradiometer and dc SQUID integrated on a planar substrate
Authors: van Nieuwenhuyzen G. J. , de Waal V. J.
Published: July 2002

An integrated system of a thin-film niobium dc superconducting quantum interference device (SQUID) and a second order gradiometer on a planar substrate is described. The system consists of a dc SQUID with eight loops in parallel, each sensitive to the second derivative ∂2Bz/∂x2 of the magnetic field. The calculated SQUID inductance is 1.3 nH. With an overall size of 16×16.5 mm2 a sensitivity of 1.5×10−9 Tm−2 Hz−1/2 is obtained. The measured transfer function for uniform fields perpendicular to the plane of the gradiometer is 2.1×10−7 T Φ−10.
Electric variation of the resistance of superconducting tunnel junctions
Authors: Gundlach K. H. , Konishi H.
Published: July 2002

We report on the change of normal resistance in tunnel junctions brought about by the application of a sufficiently large voltage at temperatures of 4.2 K and lower. This effect can be of use in various branches of electron and Cooper-pair tunneling, including the optimization of quasiparticle mixers. The voltage-induced change of the normal resistance can be reversed by warming up the sample to room temperature.
2-Gb/s sensitivity of a Ga0.47In0.53As photoconductive detector/GaAs field-effect transistor hybrid photoreceiver
Authors: Chen C. Y. , Kasper B. L. , Cox H. M. , Plourde J. K.
Published: July 2002

We have measured the 2-Gb/s sensitivity of a photoreceiver consisting of a Ga0.47In0.53As photoconductive detector and a GaAs low-noise field-effect transistor. For a bit error rate of 10−9, the photoconductive receiver shows a sensitivity of −28.8 dBm at 2 Gb/s and 1.51 μm. In view of its high receiver sensitivity and simplicity, the Ga0.47In0.53As photoconductive detector may be attractive for applications in high data rate lightwave communication systems, particularly local area networks.
Extended appearance-potential fine structure of GaAs(001) surface
Authors: Terauchi H. , Sekimoto S. , Sano N. , Kato H. , Nakayama M.
Published: July 2002

An extended appearance-potential fine-structure measurement of the As-stable GaAs (001) surface has been carried out. The Ga-As, As-As distances of the surface were quantitatively determined for the first time. The surface structure is consistent with that proposed from results of the electron diffraction and photoemission measurements.
Crosstalk measurements of monolithic GaAs photoconductive detector arrays in the GHz region
Authors: Lam D. K. W. , MacDonald R. I.
Published: July 2002

The crosstalk levels among detectors in a monolithic GaAs photoconductive detector array were measured in the frequency range 250 MHz–1.3 GHz. When the array was mounted on a properly designed microstripline circuit, crosstalk levels below −44 dB were achieved at a detector spacing of 100 μm across the entire 1.3-GHz bandwidth. The provision of a ground plane fabricated monolithically with the array was found to be important. The observed −44 dB crosstalk level in the GHz frequency region confirms the feasibility of a completely integrated broadband optoelectronic switching matrix.
Photoluminescence from In0.53Ga0.47As/InP quantum wells grown by molecular beam epitaxy
Authors: Marsh J. H. , Roberts J. S. , Claxton P. A.
Published: July 2002

Room-temperature and low-temperature photoluminescence from quantum well In0.53Ga0.47As/InP structures grown by molecular beam epitaxy is reported for the first time. A range of well thicknesses from 240 down to 10 Å was studied. Emission as short as 1.16 μm (1.07 eV) at 3.8 K and 1.22 μm (1.02 eV) at 300 K was observed from a well ∼10 Å, and the overall luminescence efficiency of the structure was ∼50 times greater than that of a quaternary sample of similar carrier concentration grown by liquid phase epitaxy. The full width half-maximum of the photoluminescence peak from a 20-Å well was 11.6 meV at 3.8 K. These results indicate the cladding InP as well as the interfaces are of very high quality.
Ion and radical contributions to hydrogenated amorphous silicon film formation in a dc toroidal discharge
Authors: Sugai H. , Toyoda H. , Yoshida A. , Okuda T.
Published: July 2002

Hydrogenated amorphous silicon films are formed in a low-pressure dc toroidal discharge. The good plasma confinement by a toroidal magnetic field ensures considerable growth rate of the films even at a low pressure (0.1–10 mTorr). The contributions of ions and radicals to a-Si:H film growth are clearly separated by the control of substrate bias and gas pressure. The films formed mainly by ion flux indicate large values of optical band gap and hydrogen content, in contrast with films formed by neutral radicals only. In addition, the spectrum of dominant IR absorption is observed to vary with the ratio of ion to radical contributions.
Electron diffraction observation of epitaxial silicon grown on a CaF2/Si(100) structure
Authors: Sasaki Masayoshi , Hirashita Norio , Onoda Hiroshi , Hagiwara Shirou
Published: July 2002

Growth and crystalline quality of epitaxial Si on a CaF2/Si(100) structure have been investigated by in situ reflection high-energy electron diffraction observation. Epitaxial Si/CaF2/Si structures have been formed by vacuum evaporation using the technique of amorphous Si predeposition. It has been shown that the predeposited amorphous Si layer crystallizes epitaxially during subsequent heating, but contains twins in the film. The twins remain in the subsequently grown Si layer as thick as 100 nm. However, the twins no longer remain more than 100 nm thick in the epitaxial Si layer. Three types of superstructures have been found at the surface of Si/CaF2/Si(100) structures for different Si epitaxial temperatures, and they have been related to the amount of Ca segregated at the surface.
Photoluminescence study of InGaAs grown on InP by vapor phase epitaxy—Effects of O2 injection and substrate orientation
Authors: Makita Kikuo , Gomyo Akiko , Taguchi Kenkoh , Suzuki Tohru
Published: July 2002

Photoluminescence measurement at 4.2 K was carried out to investigate factors (O2 injection and substrate orientation) influencing incorporation of impurities in the InGaAs growth during hydride vapor phase epitaxy. Purification with reduction of both donor and acceptor impurities in the O2 injected growth was confirmed spectroscopically for the first time. InGaAs growth on (100) InP substrates slightly misoriented to the (110) direction was found to show a significant increase in incorporation efficiency for impurities.
Carrier lifetime model for the optical degradation of amorphous silicon solar cells
Authors: Smith Z E. , Wagner S. , Faughnan B. W.
Published: July 2002

The light-induced performance degradation of amorphous silicon solar cells is described well by a model in which the carrier lifetimes are determined by the dangling bond density. Degradation will be slower in solar cells operating at lower excess carrier concentrations. This is documented with a comparison of degradation data for cells at open circuit versus load, and for single versus cascade cells. At sufficiently long times, the efficiency will decrease at approximately the same rate for all cases, with an offset in time between the individual cases which can be calculated.
Elimination of oval defects in epilayers by using chemical beam epitaxy
Authors: Tsang W. T.
Published: July 2002

One ubiquitous problem that continues to haunt over molecular beam epitaxy (MBE) persistently throughout all these year and still without a good controllable solution is the presence of oval defects in gallium-containing compound semiconductor epilayers. While these defects have not presented major problems for discrete devices, they are likely to be a serious obstacle for integrated circuit applications. We showed that oval defects were present in GaAs and In0.53Ga0.47As epilayers grown by conventional MBE process using elemental Ga and In as group III sources, and either solid As4 or thermally cracked As4 from gas mixtures of trimethylarsine and hydrogen. On the other hand, the use of the chemical beam epitaxy in which the Ga and In were derived by thermal pyrolysis of their metal alkyls at the heated substrate surface resulted reproducibly in epilayers free of oval defects over the entire substrate surface of ∼8 cm diameter (limited by the substrate holder size). On the basis of the present results it is evident that the oval defects were related to the use of elemental Ga melt as the evaporant in conventional MBE.
Dependence of junction formation on substrate in implanted HgCdTe
Authors: Bubulac L. O.
Published: July 2002

Ion implantation in HgCdTe grown by liquid phase epitaxy on CdTe/Al2O3 and on Bridgman CdTe substrates revealed a dependence of junction formation on the defect and impurity properties of the base substrate evidently transmitted through the epitaxial layer. Techniques such as cathodoluminescence, etch pit count, differential Hall, electron beam induced current, and secondary ion mass spectroscopy led to the following findings concerning junction formation: the carrier concentration distribution in the n region may vary from abrupt to graded, depending on substrate properties; the junction depth and junction carrier profile depend on defect structure in the layer, background impurities, and implant/anneal conditions; in annealed HgCdTe, differences exist in diffusion mechanisms of radiation-induced donors between bulk CdTe substrates and CdTe/Al2O3.
Carrier transport properties of p-type Hg1−xCdxTe liquid phase epitaxial layers in the mixed conduction range
Authors: Eger D. , Zemel A. , Mordowicz D. , Sher Ariel
Published: July 2002

Galvanomagnetic measurements were made on p-type Hg1−xCdxTe liquid phase epitaxial layers as a function of magnetic field and temperature. The dependence of the Hall coefficient on magnetic field was analyzed assuming mixed conduction of electrons and holes. The fitting of the theory to the experimental data permits determination of the concentration of holes and electrons and their mobilities over a range of temperatures. This leads to values of the intrinsic carrier concentration, which are in good agreement with those generated from theoretical calculations.
626.2-nm pulsed operation (300 K) of an AlGaInP double heterostructure laser grown by metalorganic chemical vapor deposition
Authors: Kobayashi Kenichi , Hino Isao , Suzuki Tohru
Published: July 2002

Room-temperature pulsed laser operation of (Al0.55Ga0.45)0.5In0.5P /(Al0.17Ga0.83)0.5In0.5P / (Al0.55Ga0.45)0.5In0.5P double heterostructure laser diodes grown by metalorganic chemical vapor deposition has been achieved. The lasing wavelength is 626.2 nm, which is the shortest ever reported for an AlGaInP double heterostructure laser. Threshold current density is 50 kA/cm2 for a diode with a 20-μm-wide and 200-μm-long stripe.
Spatial distribution of radiation-induced interface traps under the gate of an Al/SiO2/Si capacitor
Authors: Zekeriya Viktor , Wong Amy , Ma T-P.
Published: July 2002

The radiation-induced interface trap density in an Al/SiO2/Si capacitor has been found to exhibit a systematic lateral variation under the gate area as one probes from the edge toward the center of the device. This spatial variation correlates well with the lateral distribution of the gate Al induced interfacial stresses, and the results provide further support to one earlier conclusion that the metal-oxide-Si device radiation sensitivity depends strongly on its interfacial stress distribution.
High-speed electroplating of copper using the laser-jet technique
Authors: von Gutfeld R. J. , Vigliotti D. R.
Published: July 2002

The laser-jet electroplating technique has been applied to the high-speed deposition of copper at rates up to 50 μm/s. The high plating efficiency of the Cu/Cu++ system makes the deposition rate independent of laser power (unlike that of gold). On the other hand, the morphology of the copper is greatly improved with increasing laser power. Four-point probe measurements for laser-jet copper depositions indicate a resistivity close to that of the published bulk value.
Diode structures formed by rapid thermal annealing of boron implanted silicon
Authors: Lunnon M. E. , Chen J. T. , Baker J. E.
Published: July 2002

Rapid annealing of boron implanted (100) silicon has been used to fabricate p+-n diodes. After an implant dose of 3×1015 ion cm−2 and a 1-s anneal at 1100 °C, a sheet resistance of 40 Ω/⧠ is obtained. The junction depth is 0.34 μm, measured by spreading resistance profiling. The leakage current at −5 V is 40 nA cm−2. Secondary ion mass spectrometry shows that the boron dopant diffuses rapidly (≂50 nm) during the first second of an anneal at 1100 °C. The residual implantation damage does not appear to have a deleterious effect on diode characteristics.
Effect of oxygen in atmosphere on 〈100〉 texture of laser-recrystallized silicon on fused quartz
Authors: Kimura Masakazu , Egami Koji , Kanamori Masura
Published: July 2002

Effect of oxygen in an atmosphere on 〈100〉 texture formed by laser melting has been quantitatively examined using x-ray diffraction method. It has been found that oxygen content over several percentage is necessary to be included in an atmosphere during recrystallization for preventing the agglomeration of silicon and achieving strong 〈100〉 texture, but that capping with an SiO2 layer does not induce such strong 〈100〉 texture as that produced with air and no capping. An oxide layer seems not to be necessarily important for strong 〈100〉 texture formation.
One-picosecond optical n
o
r gate at room temperature with a GaAs-AlGaAs multiple-quantum-well nonlinear Fabry–Perot étalon
Authors: Migus A. , Antonetti A. , Hulin D. , Mysyrowicz A. , Gibbs H. M. , Peyghambarian N. , Jewell J. L.
Published: July 2002

The speed of a GaAs-AlGaAs optical logic gate is time resolved using a 100-fs laser system. It shows that the gating operation can be performed in ≂1 ps, the fastest reported for such a low-energy optical device. The lowest incident switching for such a device is ≲3 pJ.
High-performance photovoltaic infrared devices in Hg1−xCdxTe on GaAs
Authors: Gertner E. R. , Shin S. H. , Edwall D. D. , Bubulac L. O. , Lo D. S. , Tennant W. E.
Published: July 2002

A combination of organometallic and isothermal vapor phase epitaxy was used sequentially to grow CdTe and Hg1−xCdxTe on GaAs substrates. Photodiodes in the Hg1−xCdxTe show properties comparable to the best Hg1−xCdxTe grown by liquid phase epitaxy. Resistance-area products were ≥107 Ω cm2 and >104 Ω cm2 at 77 K for Hg1−xCdxTe with cut-off wavelength of 3.73 and 5.54 μm at 77 K, respectively. The backside-illuminated spectral response was broadband with peak external quantum efficiencies typically >50% (without antireflection coating).
Asymmetric quantum well electron barrier diode
Authors: Kirchoefer S. W. , Newman H. S. , Comas J.
Published: July 2002

A new rectifying diode is proposed whose asymmetric current versus voltage characteristic originates from the ground state energies in an asymmetric sequence of quantum wells. Data are presented on devices fabricated from samples of this proposed structure grown by molecular beam epitaxy. These diodes exhibit current versus voltage temperature dependence and reverse bias capacitance which are different from other types of electron barrier devices.
Silicon-on-insulator by oxygen implantation with a stationary beam
Authors: Mogro-Campero A. , Love R. P. , Lewis N. , Hall E. L.
Published: July 2002

A single crystal silicon layer on top of a buried oxide has been achieved by implanting oxygen ions of 180 keV into a silicon substrate. A stationary beam and wafer scanning were used, with a dose of 2.4×1018 cm−2. Similar structures produced by ion beam scanning have been reported previously where scanning rates are sufficiently high to maintain a constant temperature profile during the implantation process. In high current implanters, a stationary beam is often used, and the wafer is scanned instead. The slower scanning rates in the latter process can result in severe temperature cycling during implantation. This was the case in the present investigation. Nevertheless, as determined by transmission electron microscopy, the as-implanted material in this work is similar to that reported when ion beam scanning is used.
Growth of single crystal NiSi2 layers on Si (110)
Authors: Tung R. T. , Nakahara S. , Boone T.
Published: July 2002

Growth of single crystal nickel silicide layers on Si (110) under ultrahigh vacuum conditions is demonstrated. Formation of thin templates followed by deposition of nickel at ∼650 °C produced NiSi2 layers with χmin=3%. Low-energy electron diffraction revealed unreconstructed silicide surfaces. Transmission electron microscopy showed the entire silicide-silicon interface to consist of {111} type inclined facets. Long and straight dislocations were observed at facet boundaries with Burgers’ vectors of 1/4 〈111〉 type. The usual 1/2 〈11̄0〉 type misfit dislocations were also found on inclined facets.
Annealing behavior of implanted nitrogen in AISI 316 stainless steel
Authors: Hirvonen J. , Anttila A.
Published: July 2002

The behavior of implanted nitrogen during post-implantation annealing has been studied at 400, 450, and 500 °C by depth profiling of 15N-implanted samples using the nuclear resonance broadening method. During the initial states of the annealing the nitrogen depth profiles behaved as if all the nitrogen would be able to diffuse, i.e., to be in solution, whereas for the longer annealing times the concentration of migrated nitrogen in the unimplanted region reached equilibrium with the implanted layer. The diffusion coefficients were determined as well as the equilibrium concentrations at the temperatures involved. The published values of the diffusion coefficients were extended to temperatures more than 500° C lower than before.
Second derivative internal photoemission spectroscopy for the study of interdiffusion and compound formation phenomena
Authors: Krawczyk S. K. , Mrabeut T.
Published: July 2002

In this letter a simple spectroscopic method for the study of interdiffusion and compound formation phenomena occurring between two metal layers deposited on the top of oxidized silicon wafer is developed. Using this method, the simultaneous presence of different metallic compounds at the interface with the insulator can be identified and their composition may be evaluated. Experimental results presented here have been obtained with the Al (150 Å)-Au (150 Å)-SiO2-Si and Au (150 Å)-Al (150 Å)-SiO2-Si systems.
Laser produced Ti/Ti-oxide thin-film structures
Authors: Thuillard M. , von Allmen M.
Published: July 2002

Pulsed laser irradiation of thin, vacuum-deposited layers of Ti on suitable substrates in air produces structures consisting of metallic islands connected by oxide filaments. The topology as well as the dimensions of the structures can be controlled by selection of the laser fluence and the film parameters. The electrical characteristics of the structure can be varied continuously from metallic to insulating, covering a range of resistances spanning 10 orders of magnitude.
Effects of heat treatments of GaAs on the near-surface distribution of EL2 defects
Authors: Wada K. , Inoue N.
Published: July 2002

A cluster model is proposed for the midgap state EL2 in GaAs based on a defect reaction similar to that of the thermal donor formation in silicon. Anomalous depth profiles of the EL2 defects in bulk GaAs created by heat treatment have been quantitatively explained, assuming that the EL2 defect is a four point defect cluster. Possible candidates of the point defects are discussed.
Evidence for induced far-infrared emission from p-Ge in crossed electric and magnetic fields
Authors: Komiyama S. , Iizuka N. , Akasaka Y.
Published: July 2002

Experimental evidence is presented for stimulated far-infrared emission from population-inverted hot-carrier system in p Ge. The spectroscopic study by use of an n-InSb cyclotron-resonance detector reveals that the spectrum of the emission consists of a fairly sharp band located at the photon energy ∼5 or ∼10 meV depending on the applied fields.
Bias dependence of doping efficiency in hydrogenated amorphous silicon
Authors: Alvarez F.
Published: July 2002

This letter is concerned with the doping efficiency of phosphorus and boron doped samples of hydrogenated amorphous silicon grown under different substrate bias conditions. Although in a capacitively coupled glow discharge system generally the powered electrode is negatively self-polarized, some control of the dc bias is obtained by changing the electrode areas and/or using an external bias. It has been found that the activation energy of doped samples depends on the polarity and magnitude of an external dc bias applied to the substrate support. This result was used to enhance the incorporation of residual boron in the intrinsic layer of p-i-n structures fabricated onto a indium-tin-oxide coated glass.
Optical properties of ZnSe/(Zn,Mn)Se multiquantum wells
Authors: Hefetz Y. , Nakahara J. , Nurmikko A. V. , Kolodziejski L. A. , Gunshor R. L. , Datta S.
Published: July 2002

Luminescence, excitation, and reflectance spectroscopy have been employed to study the exciton ground state in ZnSe/(Zn,MnSe) multiquantum wells. We find that the ground state shows splittings which are attributed to the superlattice layer strain. The measured large magneto-optical shifts and splittings indicate that the valence-band discontinuity is likely to be quite small in these structures.
Spectral and temporal characteristics of AlGaAs/GaAs superlattice p-i-n photodetectors
Authors: Larsson A. , Yariv A. , Tell R. , Maserjian J. , Eng S. T.
Published: July 2002

We report on measurements of the spectral and the temporal response of AlGaAs/GaAs p-i-n photodetectors with superlattice intrinsic regions grown by molecular beam epitaxy. The feasibility for high-speed applications is demonstrated by a time constant limited impulse response of 200 ps (full width at half-maximum) when excited near the band edge with 100 ps optical pulses. We observed the theory-predicted and recently verified voltage tunability of the band edge with clearly resolved excitonic resonances. The responsivity was measured to be 0.2 A/W.
Inhomogeneities in arrays of Josephson junctions: Their imaging by low-temperature scanning electron microscopy
Authors: Bosch J. , Gross R. , Huebener R. P. , Niemeyer J.
Published: July 2002

The first application of low-temperature scanning electron microscopy for investigating the homogeneity of an array of Josephson tunnel junctions is reported. The experiments were performed on a series configuration of 166 junctions. The junction fabrication process was identical to that developed recently for the fabrication of a frequency-based Josephson voltage standard. The shorted junctions of the array could be easily detected. The quasiparticle imaging method, used previously for investigating spatial structures within individual tunnel junctions, can be extended in a straightforward way also to junction arrays.