bluuebunny/crossref_metadata_2025 huggingface dataset:
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u detection of BH2 and atomic boron by intracavity laser spectroscopy in the plasma dissociation of gaseous B2H6
Authors: Miller D. C. , O’Brien J. J. , Atkinson G. H.
Published: July 2002

Absorption spectra of the BH2 radical and atomic B are detected by intracavity laser spectroscopy (ILS) in situ during the plasma dissociation of gaseous diborane (B2H6). Rovibronic absorption transitions of BH2 are observed near 15 469 cm−1 [(0,11,0)2B′1 –(0,0,0)2A″1] and 13 605 cm−1 [(0,9,0)2B′1 –(0,0,0)2A″1]. Absorption corresponding to the 3p (2P0)-5s (2S) transitions of atomic B are observed at 11 534.6 and 11 532.8 cm−1. Although atomic B has been detected previously under experimental conditions used in the plasma-assisted preparation of boron-containing films from B2H6, the ILS data presented here establish, for the first time, the presence of BH2 under chemical vapor deposition conditions.
ac-dc conversion effect in Y-Ba-Cu-O ceramics
Authors: Ikegawa Sumio , Honda Toshihisa , Ikeda Hiroshi , Maeda Atsutaka , Uchida Shin-ichi , Uchinokura Kunimitsu , Tanaka Shoji
Published: July 2002

In Y-Ba-Cu-O ceramics, the dc voltage (Vdc ) induced by an rf current of 2–20 MHz, which had been previously reported as ‘‘reverse ac Josephson effect,’’ was observed at 77–300 K. The observed Vdc is not found to be due to reverse ac Josephson effect but due to nonlinear current-voltage characteristics, as in the case of BaPb1−xBixO3. However, behavior of the Vdc is different from that in BaPb1−xBixO3, which was related to bulk superconducting transition. The Vdc is observed only in the sample with particular electrical contacts and only when the rf current can flow through the potential electrical contacts. The origin of the rf-to-dc conversion effect in Y-Ba-Cu-O is ascribed to local nonlinear resistance near potential contacts.
Preparation of superconducting Bi-Sr-Ca-Cu-oxide thin films by thermal evaporation
Authors: Habermeier H.-U. , Sommer W. , Mertens G.
Published: July 2002

Superconducting Bi-Sr-Ca-Cu-oxide thin films were prepared by sequential evaporation of two layers of Ca/Cu and Bi/Sr on single-crystal SrTiO3 substrates followed by a two-step oxidation process. The film properties were found to be sensitive to the annealing conditions. The best films showed a narrow transition to superconductivity (5 K) and the completion of the transition above 83 K. X-ray analysis of the films showed a strong correlation of the midpoint of the transition with the dimensions of the unit cell.
Recombination velocity at molecular-beam-epitaxial GaAs regrown interfaces
Authors: Biswas D. , Berger P. R. , Bhattacharya P.
Published: July 2002

We have estimated the recombination velocity and minority-carrier diffusion length at and near molecular-beam-epitaxial GaAs regrowth interfaces. The diffusion length in the regrown layers is ∼1–3 μm and is lowered to 0.3 μm at the interface. The interface recombination velocity is ∼105 cm/s. These parameters are better for a sample which was ion milled and lamp annealed before regrowth, compared to a sample which was wet-chemical etched and annealed in the growth chamber under arsenic flux before regrowth.
Hole mobility in p-type silicon accumulation layers
Authors: Manzini S. , Modelli A.
Published: July 2002

The hole mobility in the accumulated p-type silicon surface has been determined by combined drain conductance and capacitance versus voltage measurements on metal-oxide-silicon field-effect transistors over a wide range of temperatures (78≤T≤425 K), substrate doping concentrations (1016≤NA ≤1.2×1018 cm−3), and surface electric fields (2×105≤FS ≤2×106 V/cm). The surface charge density of holes induced in the accumulation layer has been determined by comparing experimental and theoretical capacitance-voltage characteristics that have been calculated allowing for complete degeneracy of the hole gas and incomplete ionization of acceptors (boron). As a secondary result, the ionization energy of boron in silicon and the hole mobility in the bulk of the semiconductor have been determined as a function of temperature and boron concentration.
Assessment of n-type GaAs by the Hall effect
Authors: Leitch A. W. R.
Published: July 2002

Variable temperature (4–300 K) Hall measurements were used to determine the donor and acceptor concentrations in high-purity epitaxial GaAs grown by metalorganic chemical vapor deposition, molecular-beam epitaxy, and vapor-phase epitaxy. It is found that in many cases the onset of impurity conduction at low temperatures limits the successful determination of the impurity concentrations in the material. Furthermore, attention is drawn to the fact that experimentally determined compensation ratios may differ appreciably from those obtained by the much used method of comparing a single 77 K measurement with theoretically calculated tables.
Interstitial Li doping of a-Si:H
Authors: Winer K. , Street R. A.
Published: July 2002

We study the process of interstitial doping of hydrogenated amorphous silicon (a-Si:H) by Li in-diffusion and thermal annealing after Li+ implantation using secondary ion mass spectrometry, dc dark conductivity [σ(T)], electron-spin resonance, and photothermal deflection spectroscopy measurements. All Li-doped a-Si:H samples were characterized by an inhomogeneous distribution of Li atoms. Doping by Li in-diffusion at 230 °C resulted in a Li-rich (up to 1021 cm−3) region at both sample interfaces, a large increase in σ(300 K), and the creation of deep paramagnetic (g=2.0061±0.0002, ΔHp.p.=5.4±0.4 G) defects with defect densities (up to 2×1018 cm−3) proportional to the interfacial Li concentration. Li+ implantation of a-Si:H at 373 K resulted in the creation of deep paramagnetic (g=2.0056±0.001, ΔHp.p.=6.0±0.5 G) defects with defect densities (up to 2×1018 cm−3) proportional to the implanted Li+ dose. Isochronal vacuum annealing of Li+-implanted a-Si:H up to 545 K resulted in an exponential increase of σ(300 K) and an activated (Ea=+0.32 eV) decrease of the spin density with increasing anneal temperatures. Both Li in-diffused and annealed Li+-implanted a-Si:H films displayed thermal equilibration behavior similar to that characteristic of P-doped a-Si:H, which suggests that the defect compensation model of substitutional doping of a-Si:H is also applicable to the case of interstitial doping. However, the defect structure of a-Si:H doped by Li in-diffusion is significantly different than that of both undoped and P-doped a-Si:H due to the precipitation of Li at the interfaces of heavily Li-doped a-Si:H. We discuss the origin of this behavior.
X-ray microanalysis of InGaAs/InP multilayer structures grown by metalorganic chemical vapor deposition
Authors: McGibbon A. J. , Chapman J. N. , Cullis A. G. , Chew N. G. , Bass S. J. , Taylor L. L.
Published: July 2002

X-ray microanalysis in a scanning transmission electron microscope can be employed to determine concentration profiles with a spatial resolution of ≲2 nm across layer interfaces in III-V compound semiconductor multilayer structures. Here we describe its application to the InGaAs/InP multilayer system grown by metalorganic chemical vapor deposition at atmospheric pressure. The results show that even when the material is structurally perfect, there can be a significant As and Ga content beyond the boundaries of the InGaAs layers. Furthermore, the composition profiles can show a marked asymmetry relating to the growth direction. The results are consistent with previous imaging observations but provide quantitative information with high spatial resolution on individual element distributions. This combination of analytical attributes is not available using any other assessment technique.
Magnetic shielding and relaxation characteristics of superconducting YBa2Cu3O7 tubes
Authors: Symko O. G. , Yeh W. J. , Zheng D. J. , Kulkarni S.
Published: July 2002

High-Tc superconducting tubes have been developed for magnetic shielding of SQUIDs at 77 K. The characteristics of such tubes show that adequate shielding exists for magnetic fields up to a critical field determined by the current density of the tube. Relaxation phenomena with two different time dependencies are observed when the external magnetic field enters the tubes.
Single-crystal YBa2Cu3O7 particle formation by aerosol decomposition
Authors: Kodas Toivo , Datye Abhaya , Lee Victor , Engler Edward
Published: July 2002

Single-crystal YBa2Cu3O7 particles have been formed in a carbon-free gaseous flow system by thermally decomposing droplets containing the nitrate salts of Y, Ba, and Cu in water followed by calcining and annealing in the gas phase. The electron diffraction pattern for particles ranging in size from 0.1 to 1.5 μm corresponded to single crystals of orthorhombic YBa2Cu3O7 while the powder x-ray diffraction pattern confirmed the presence of single-phase material. Energy dispersive spectroscopy showed a similar composition for all particles examined. Iodometric titration showed that the particles were fully oxygenated. Two types of single-crystal particles were observed, equiaxed and elongated. Formation of solid single-crystal particles is favored by operation near the melting point of the material and by long reactor-residence times.
Structural distortions of sputtered niobium nitride films
Authors: Cukauskas E. J. , Qadri S. B. , Carter W. L.
Published: July 2002

The structural properties of NbN thin films have been investigated as a function of vacuum and rapid thermal annealing at temperatures to 1200 °C. X-ray diffraction data were analyzed using a least-squares fit to the cubic and monoclinic structures. Vacuum annealing resulted in a multiphase material with a reduced transition temperature for annealing temperatures above 900 °C. The rapid-thermal-annealed films showed improved electrical characteristics and reduced compressive stress inferred from the monoclinic distortion for all annealing temperatures. NbN thin films sputtered with a methane/nitrogen reactive gas ratio of approximately 0.3 exhibited a slightly distorted cubic lattice and low compressive stress compared to other films sputtered in different reactive gas mixtures. The higher-temperature rapid-thermal-annealed films have structural and electrical characteristics desirable for device fabrication.
Chemically homogeneous fine-grained Mn-Zn ferrites by spray drying
Authors: Kumar K. , Petrovich A. , Williams C. , VanderSande J. B.
Published: July 2002

Chemically and structurally uniform Mn-Zn ferrites have been produced using powders synthesized by the spray decomposition of mixed, aqueous Mn, Fe, and Zn nitrate solutions. The particle size of the as-formed powder depended strongly on the metal ion concentration in solution; higher concentrations produced larger sizes. The as-formed particles are spherical, internally hollow, and consisted mostly of Fe2O3. A 900 °C, 6-h argon treatment removed the internal void space and converted the particles mostly to the ferrite spinel phase. Sintering of compacts from heat-treated powders produced microstructures superior to those from as-formed powders. Uniform, fine-grained materials, with a densification level comparable to that of commercial sintered ferrite, have been produced at the very low sintering temperature of 1100 °C. Preliminary work indicates that a higher initial permeability is obtained when a higher sintering temperature was used and the level of its disaccommodation depended on the oxygen partial pressure present during sintering. Both ‘‘accommodation’’ and disaccommodation were observed in the permeability; their magnitudes depended on the peak value of the applied excitation field.
Transient reflection from a lossy magnetized Lorentz medium (longitudinal propagation)
Authors: Stanić Boz̆idar V. , Milanović Djurdje R.
Published: July 2002

The transient response of a lossy magnetized Lorentz medium illuminated by an impulsive electromagnetic plane wave is obtained. The propagation vector of incident pulse and the vector of external magnetic field were colinear and both perpendicular to the sharp boundary between free space and the Lorentz medium. The transient response is expressed as a convergent infinite series of modified Bessel functions of the first kind with the complex argument. The transient responses are computed for different values of the electron cyclotron and Lorentz medium resonant frequencies ωc and ω0. The obtained results might have a possible use as a diagnostic tool for the evaluation of characteristic parameters of magnetized Lorentz medium and in special cases, (ω0=0) for diagnosing the magnetized plasma.
A new technique for whole-wafer etch-pit density mapping in GaAs
Authors: Look D. C. , Walters D. C. , Sewell J. S. , Dudley S. C. , Mier M. G. , Sizelove J. S.
Published: July 2002

The pits formed on an etched GaAs surface, due to the anisotropic etching around dislocations, are efficient light scatterers, and thus reduce transmission. We have derived a quantitative relationship between the fractional transmission and the etch-pit density (EPD) and have shown that the same absorption apparatus which is commonly used to obtain a whole-wafer [EL2] map can also be used to generate an EPD map. The technique is verified by comparing the fractional transmission with the actual EPD count at 166 points on a three-inch, low-pressure, liquid-encapsulated Czochralski wafer. Also, [EL2] and EPD maps, with more than 3500 points each, are compared.
Turbulent energy at an ablating surface
Authors: Mikaelian Karnig O.
Published: July 2002

We calculate the turbulent energy generated at a surface which is accelerating by ablation. The ablation velocity Va reduces the growth rate n(k) from its classical value for the Rayleigh–Taylor instability. This reduction is reflected in our general expression for Eturbulent, valid for arbitrary Va, which we derive on the basis of the Canuto–Goldman model for turbulence [Phys. Rev. Lett. 54, 430 (1985)]. Out results are analytic and they reduce to particularly simple forms in the classical (Va→0) and strongly inhibited (Va→∞) limits, where we find Eturbulent=(2/3)(56/9π)2Ag/k0 and Eturbulent=(8Ag/3πk0Va)2, respectively.
Experimental and numerical study of thermal transport in 24-beam ultraviolet irradiation of spherical targets
Authors: Barnouin O. , Yaakobi B. , Delettrez J. , Epstein R. , Jaanimagi P. , Goldman L. M.
Published: July 2002

A series of thermal transport experiments using spectral-line signature and ion expansion measurements has been performed in spherical geometry using the 24 UV-converted beams of the Omega laser system at the Laboratory for Laser Energetics of the University of Rochester. Comparison with previous experiments employing only six beams shows a much better agreement in the mass ablation rate, when using 24 beams, between experimental results obtained from charge collectors and code simulations using a flux limiter of 0.1. The influence of nonuniformities in the irradiation, x-ray line reabsorption, and ionization time lag (non-LTE effects) were studied with the help of a collisional-radiative model. These processes were found to alter the falloff rates (determined mainly by the radical profile of the temperature) of the relative x-ray line intensity with overcoat thickness. With these effects included, agreement between calculated and measured burnthrough curves is greatly improved.
Nonequilibrium hydrodynamic theory of scattering of radiation from plasma
Authors: Khan T. P.
Published: July 2002

The spectrum of radiation scattered by plasma has been derived by the use of nonequilibrium hydrodynamic theory of fluctuations. The principal features of ion-acoustic resonances, the Alder–Wainwright velocity autocorrelation function, and initial dispersion in scattering have all been studied in the present analysis.
Temperature dependence of intra-4f-shell photo- and electroluminescence spectra for erbium-doped GaAs
Authors: Takahei Kenichiro , Whitney Peter S. , Nakagome Hiroshi , Uwai Kunihiko
Published: July 2002

Temperature dependencies of linewidth and peak wavelength are studied for the intra-4f-shell photoluminescence and electroluminescence spectra of erbium ions incorporated in GaAs by metalorganic chemical vapor deposition. For both the photo- and electroluminescence spectra, the magnitudes of the linewidth broadening rate (3×10−2 cm−1 /deg) and the peak wavelength shift rate (5×10−3 cm−1 /deg) are comparable to those of rare-earth ions in insulators, such as Nd-doped yttrium aluminum garnet. They are about two orders of magnitude smaller than those for the luminescence line due to band-to-band transition of a typical semiconductor (InGaAs) at the same wavelength region.
Surface barrier junctions: Conversion efficiency and surface recombination
Authors: El Guibaly Fayez
Published: July 2002

Expressions are obtained for the majority- and minority-carrier currents flowing in an illuminated Schottky barrier device in the presence of surface recombination. The analysis assumes arbitrary shapes of the electron and hole quasi-Fermi levels in the space-charge region. The effect of bias, illumination, and surface recombination on the device are discussed. The important parameters affecting the device performance are charge transfer kinetics at the interface, the semiconductor physical parameters, and the distribution and concentration of the interface traps.
Pb2CrO5 thin-film photodetector array for contact-type line-image sensors
Authors: Toda Kohji , Yoshida Shinzo
Published: July 2002

A photodetector array using a Pb2CrO5 thin film evaporated on a glass substrate by an electron-beam evaporation technique is described. The photovoltaic effect in a Pb2CrO5/Au Schottky contact is one of the main operating mechanisms of the photodetector array. The active gold pattern of eight elements (eight elements per mm), each separated from the other by 8 μm, and the lead pattern are directly formed on a highly resistive Pb2CrO5 thin-film surface by Au vacuum evaporation deposition in a single-step process. No special technique for isolating the individual photodetector elements is required. The device responds to a chopped light at a modulation frequency of 80 kHz for wavelengths between 300 and 570 nm. The dark current of the device is very small; the photocurrent-dark current ratio is greater than 1000.
Electrical and optical properties of Cu- and Ga-doped Hg1−xCdxTe layers grown by liquid-phase epitaxy
Authors: Sarusi G. , Zemel A. , Eger D. , Shapira Yoram
Published: July 2002

The influence of Cu (acceptor) and Ga (donor) on the electrical and optical properties of Hg1−xCdxTe (x=0.2) layers was investigated. The layers were grown by liquid-phase epitaxy from Te-rich solutions and the dopants were intentionally introduced during the growth process. Doping efficiencies between 0.025 at a hole concentration of p=6×1018 cm−3 and 0.15 at p=6×1017 cm−3 were found for Cu. The electron concentration in the as-grown Ga-doped layers saturated at n=2×1017 cm−3, but increased significantly to n=8×1018 cm−3 as a result of an annealing process. The doping efficiency was 0.02. The doping and electrical properties of the layers are explained by assuming incorporation of both electrically active and electrically inactive impurity atoms. The high free electron concentrations in the Ga-doped layers resulted in a strong Burstein–Moss shift [T. S. Moss, G. J. Burrell, and B. Ellis, in Semiconductor Optoelectronics (Butterworths, London, 1973), p. 42] of the absorption edge, and effects of plasma frequency. These effects are analyzed and discussed.
A simultaneous electron paramagnetic resonance and optical absorption study of ultraviolet-induced defect centers in Ge-doped silica fibers
Authors: Schwartz Robert N. , Blair G. Richard
Published: July 2002

Simultaneous electron paramagnetic resonance (EPR) and optical absorption studies were carried out at room temperature in a Ge-doped silica fiber-optic waveguide following in situ ultraviolet (UV) irradiation with 254-nm (4.88-eV) photons. We have observed that the UV-induced EPR is directly correlated with the UV-induced optical loss in the energy range 1.77–3.0 eV. No UV-induced loss was observed in the near-infrared spectral region (0.7–1.38 eV). The problem of correlating the UV-induced loss with the optical bands of the various possible defect centers in Ge-doped silica is discussed.
A model for evaluating the efficiency of an interdigital transducer for bulk wave excitation into liquid
Authors: Urabe Heijiro , Toda Kohji
Published: July 2002

An equivalent circuit model analysis of a liquid-loaded interdigital transducer is described. The electric loss related to the complex relative dielectric constant and the electroacoustic conversion efficiency are represented in the form of a function of the specific acoustic impedance (ρv) of the loaded liquid. The conversion efficiency for ultrasound into the liquid is estimated from only the acoustic impedance and the relaxation time of the substrate material, which are obtained relatively easily from the water measurement. The estimated theoretical efficiency is in good agreement with the experimental results for various liquids. These results also coincide with the results from the wave equation for the leaky surface acoustic wave propagation at the solid–liquid boundary.
Dual implant into GaAs with Si+ and Sn+ ions
Authors: Shim Tae Earn , Itoh Tadatsugu
Published: July 2002

Undoped GaAs (100) wafers were implanted with 150-keV Sn+ and/or 50-keV Si+ ions to doses of 5×1013–1×1014/cm2 at room temperature, and annealed at 850 °C for 15 min. The backscattering spectra showed a sufficient crystalline recovery at this annealing condition. The transmission electron microscopy results indicated a significant difference between the samples of Sn+, Si+, and (Sn++Si+) implants in shape, size, and density of dislocations. The dislocations in the dual implant case were smaller than those of single implant in density and size. The electrical activation efficiencies of Sn+, Si+, and (Sn++Si+) implanted GaAs with a dose of 1×1014/cm3 for each ion specimen were 12%, 13%, and 6%, respectively. In the dual-implant case, the carrier concentration was not simple addition of two doses and exhibited a saturation effect near 1×1018/cm3.
Deuterium magnetic resonance study of orientation and poling in poly(vinylidene fluoride) and poly(vinylidene fluoride-co-tetrafluoroethylene)
Authors: Doverspike Montee A. , Conradi Mark S. , DeReggi Aime S. , Cais R. E.
Published: July 2002

Deuteron nuclear magnetic resonance line shapes are reported for oriented samples of poly(vinylidene fluoride) and an (80–20) copolymer of vinylidene fluoride and tetrafluoroethylene. For stretched samples the orientation of the chain axes with respect to the stretch direction is given by a Gaussian distribution of width ≊20°. The width of the distribution was slightly smaller in the more highly stretched copolymer. Surprisingly, as the magnetic field is rotated in the plane perpendicular to the stretch direction, the deuterium spectra of the poled copolymer sample do not change. The occurrence of electrical polarization in the absence of orientation dependence of the deuterium line shape indicates molecular reorientation through 180° in the copolymer.
A diffusion model for the internal photoresponse of PtSi/p-Si Schottky barrier diodes
Authors: Mercer Douglas E. , Helms C. Robert
Published: July 2002

A one-dimensional diffusion model describing the variation of the internal photoyield per absorbed photon of thin-film platinum silicide/p-type silicon Schottky barrier diodes with silicide layer thickness and incident photon energy is developed. In addition to providing a simple result, the diffusion formulation of the problem shows very clearly the relative importance of scattering processes and the barrier transmission probability in the determination of the device photoresponse. The model is demonstrated to accurately describe the available experimental data if the inelastic scattering length in the thin PtSi film is assumed to be ∼4000 Å. The application of this model in conjunction with optical absorption calculations to determine the total quantum yield per incident photon and the optimum silicide thickness as a function of wavelength are also described. This procedure predicts optimum film thicknesses on the order of tens of angstroms, coinciding with experimental observations.
Computer simulation and analytical models for the time-of-flight experiment in amorphous silicon thin films
Authors: Misiakos K. , Lindholm F. A.
Published: July 2002

Computer simulation of the time-of-flight experiment in amorphous silicon p-i-n diodes is used to predict and interpret the terminal response following a transient strongly absorbed optical excitation. Numerical solutions and the associated physical interpretation illuminate the transport physics and the accuracy of the methods used to extract transport parameters. The interaction between free carriers and gap states is discussed on the basis of numerical results on the internal variable profiles. The influence on the transient photocurrent of band mobilities, transient trapping, and transient emission is investigated. Based on the interpretation of the computer solutions, certain analytical approximations are derived that allow extraction of parameters such as band mobilities, transition rates, and density of tail states.
Vibrating reed magnetometry: An application for ceramic superconductors
Authors: Esquinazi P. , Durán C. , Brandt E. H.
Published: July 2002

A vibrating reed of a high-Tc superconductor with electrostatic excitation and sensoring may be used as a sensitive magnetometer. Its sensitivity can be increased (in our preliminary experiment, by a factor of 2.5) by placing the free tip of the reed between two flat superconductors, which may also serve as capacitance electrodes. This arrangement can be used to obtain the irreversible magnetization curve of the electrode material from the resonance frequency of the reed.
Metastable defects in Be-doped AlxGa1−xAs
Authors: Magno R. , Shelby R. , Kennedy T. A. , Spencer M. G.
Published: July 2002

Deep-level transient spectroscopy has been used to study metastable defects in Be-doped Alx Ga1−x As grown by molecular-beam epitaxy. The metastability manifests itself by the appearance of different spectra depending upon whether the sample is cooled from a high temperature with zero bias or a reverse bias applied to it. The defects are found in concentrations of 1015 cm−3 in a sample doped with 1018 Be cm−3 and in much lower concentrations in a 1017 Be cm−3 sample. Isochronal annealing experiments indicate that the defect is multistable and that it is best modeled as a mobile interstitial which can reside at several sites near an acceptor. The activation energies for these defects are between 0.2 and 0.5 eV above the valence band.
Beam focusing in semiconductor directional couplers with saturated gain
Authors: Hwu R. J.
Published: July 2002

The beam focusing behavior in a semiconductor directional coupler with saturated gain is studied as a function of the antiguidance factor, injection current density, input power, and initial beam radius. When the antiguidance factor b=2, and the injection current density J=5×10−5 A/μm2, the upper and lower limits of input power for the beam focusing effect of an injected Gaussian beam in the directional coupler structure considered in this paper to occur are 3.5 and 20 mW, respectively. Over this range of input power levels, the optically induced focusing beam radius shows a strong dependence on the antiguidance factor, injection current density, and initial beam radius. However, the input power is found to have a negligible effect on the focusing beam radius.
Measurement of barium loss from a fluorescent lamp electrode by laser-induced fluorescence
Authors: Bhattacharya A. K.
Published: July 2002

A laser-induced fluorescence method for measuring the loss rate of barium from Ba-Sr-Ca oxide coated electrodes of low-pressure discharge lamps is presented. The oxide coating from the electrode surface is depleted during lamp operation. Using this technique, the Ba loss rate from an electrode, when it is acting both as a cathode and an anode during ac operation, was measured. A significantly larger amount of neutral barium is detected in the vicinity of the electrode when it acts as an anode over when it acts as a cathode. The consumption rate of Ba and hence the life of an oxide coating depends upon the phase of the lamp current, the shape, and the magnitude of the current supplied by the lamp ballast. The consumption rate for the coating increases linearly with the discharge current. A simplified theoretical analysis of the technique for a three-level atomic system irradiated by a pulse laser beam is discussed.
Electron distribution function and axial variation of an electron-beam-generated plasma
Authors: Pointu A. M. , Maynard G.
Published: July 2002

We compute analytically the tail of the electron distribution function, including the radial and axial diffusion, in a plasma generated by an electron beam of a few keV. With this we can determine the ionization efficiency of the tail electrons in creating bulk electrons. The asymptotic behavior that results, for large axial distances, is compared with experimental data for molecular oxygen plasma.
Studies on the preparation and semiconductor properties of clad silicon fibers
Authors: Verma Mallika
Published: July 2002

This paper is a report of some novel and unconventional approaches to device fabrication without necessarily going through the planar fabrication techniques. The paper basically concerns the feasibility of drawing silicon in the form of fine fibers with an outside insulator layer. SiO2 (cladding). The codrawing of silicon and silicon dioxide to form fine single-crystalline SiO2-clad Si fibers presents the material directly for the fabrication of metal oxide semiconductor (MOS) devices. X-ray measurements show that internal core (silicon) is single crystalline in nature and the same orientation is maintained throughout the length of the fiber. Results on the experimental measurements made on fabricated MOS devices offer high transconductance, a large current-carrying capability, and substantial amplifications which can be imporved further. Good capacitance-voltage curves are observed with no built-in oxide charges.
Laser ablation deposition of superconducting Bi-Sr-Ca-Cu-O thin films on zirconia-buffered crystalline quartz
Authors: Bohandy J. , Agostinelli E. , Kim B. F. , Green W. J. , Phillips T. E. , Adrian F. J. , Moorjani K.
Published: July 2002

Thin films of Bi-Sr-Ca-Cu-O have been deposited on crystalline quartz substrates by laser ablation. Without a buffer layer, superconducting regions exist in the films as detected by magnetically modulated microwave absorption. However, with a 1000-Å zirconia buffer layer, also deposited by laser ablation, continuous, superconducting thin films were obtained. It is shown that both annealing temperature and annealing time greatly affect the film quality.
Subnanometer multilayers for x-ray mirrors: Amorphous crystals
Authors: Jankowski A. F. , Makowiecki D. M. , Wall M. A. , McKernan M. A.
Published: July 2002

The use of ‘‘natural’’ crystals as Bragg diffractors has been supplemented by the advent of artificial composition-modulated structures, that is, multilayers. The extension of optical systems using soft x rays to hard x rays is now supplemented by the synthesis of subnanometer repeat period multilayers. These structures consist of layering amorphous planes, each an atomic spacing thick, and may therefore be thought of as ‘‘amorphous crystals.’’
Schottky barrier height variation due to a Mo interfacial layer in W/GaAs systems
Authors: Ohfuji Shin-ichi , Kuriyama Youichi
Published: July 2002

The effect of the interfacial Mo-GaAs alloy layer on the Schottky barrier characteristics of W/GaAs contacts is investigated. Variation in Schottky barrier heights is measured by fabricating W(300 nm thick)/Mo(0–10 nm)/GaAs diodes, where a Ga2 O3 layer 0.9 nm thick is previously formed on the GaAs surface. The oxide layer is intended to detect the initial stage of the interfacial reaction which could remove the oxide layer and influence electrical characteristics. The maximum barrier height and the minimum ideality factor are obtained at a Mo layer thickness of 1 nm after annealing at 450 °C. The Mo layer reduces the Ga2 O3 layer on GaAs surfaces and forms the compounds GaMo3 and Mo5 As4 with the GaAs substrates by a solid-phase reaction. The intimate contact of these compounds to the substrates is thought to be formed some distance below the original Mo/GaAs interface. The formation and control of buried Schottky barrier contacts using refractory metals are experimentally verified. This allows more reliable gate barriers for GaAs metal-semiconductor field-effect transistors.
Time characteristics in laser diffusion of gaseous mixtures through capillaries
Authors: Ursu I. , Alexandrescu Rodica , Grigoriu C. , Mihailescu I. N. , Morjan I. , Prokhorov A. M. , Lagutchev A. S. , Orlov A. N. , Petrov Yu. N.
Published: July 2002

New experimental results are reported pointing to the temporal characteristics of gas mixture flows of resonant and nonresonant molecules through metallic capillary tubes under the action of low-power cw CO2 laser radiation. While a selective laser action was always observed upon resonant molecules, a special category of nonresonant molecules is introduced whose transit through the capillary is influenced besides a pure thermal action by the vibrational energy transfer from the resonant molecules.
a-Si:H solar cell with low-resistance series connection by metal diffusion
Authors: Ishihara Shin-ichiro , Kitagawa Masatoshi
Published: July 2002

Evaporated Al and Cu films were studied as metal diffusion sources for series connection between hydrogenated amorphous silicon p-i-n photodiodes. The Al or Cu film was deposited onto selected areas of the front electrodes of the glass substrate. The Al and the Cu diffused through the amorphous silicon films, during their depositions, at substrate temperatures as low as 150 °C. In this way, we produced a new type of a-Si:H solar cell, series-connected by the Al or Cu diffusion, having 10% efficiency under 100 mW/cm2 AM1 radiation. The electrical power losses of this series connection has remained negligible over a 5-year period.
A novel three-step mesa etching process for semiconductor lasers and the use of Monte Carlo simulations for active-width control
Authors: Chakrabarti U. K. , Agrawal G. P.
Published: July 2002

This paper describes a new three-step mesa etching process for semiconductor lasers that allows fabrication of narrow active widths through the use of selective etching of individual layers of a double-heterostructure base material. The active width can be described by a simple analytic relation involving base material, etching, and lithographic parameters. Using this analytic relation, Monte Carlo simulations were used to obtain the distribution of the active width. Such simulations predict that the three-step etching process is expected to have a relatively high yield. The experimental distribution of the active width is in good agreement with the theoretical prediction.
Voltage/current characteristics at the metal shield surrounding high-current vacuum arcs
Authors: Toya H. , Hayashi T. , Sasao H.
Published: July 2002

Electron and ion currents collected at the metal shield and floating shield potential are measured to study the behavior of high-current (up to 40 kA) vacuum arcs. An arc with a half cycle of 60 Hz is burned between 20-mm-diam electrodes spaced 4 mm apart bounded by a 200-mm-i.d. metal shield in a demountable vacuum chamber. The electron current is measured by connecting the metal shield to the anode and the ion current is collected by connecting the metal shield to the cathode. The floating shield potential is differentially measured relative to the cathode by two resistive potential dividers. It was found that the electron current increases, while the ion current peaks and the shield potential decreases with an increasing arc current. The direction of the ion-current flow is reversed during the discharge of an arc current at a level of more than 20 kA. Correspondingly, the shield potential becomes negative relative to the cathode. This newly found phenomena is attributed to the radial electric field generated from the flow of negatively charged carriers to the shield that originates from the interaction between the anodic jets of vapor and plasma and the cathodic plasma. A correlation between this finding and the anode-spot activity causing severe erosion of the anode is also shown.
Laser heating and melting of thin films with time-dependent absorptance. II. An exact solution for time intervals greater than the transit time
Authors: El-Adawi M. K. , Shalaby S. A. , Elshehawey E. F. , El-Dessouki T.
Published: July 2002

Laser heating and melting are studied considering the laser-induced reflectivity variations R(τ). The study is made for time intervals greater than the transit time τs using the Fourier series expansion technique together with the differential and integral forms of the heat diffusion equation. The obtained results reveal that the equations for the thickness Z(τ) of the molten layer and the rate of melting Z′(τ) are no longer quadratic. A fourth-degree algebraic equation for Z(τ) is obtained similar to that derived for the previous stage τ≤τs, but with different coefficients. Moreover, it is shown that the obtained rate of melting for the considered stage is no longer a constant one. Computations on a thin silver film as an illustrative example for the considered stage are carried out.
Spectroscopic diagnostic of an x-ray laser plasma by use of L-shell spectra
Authors: Peyrusse O. , Combis P. , Louis-Jacquet M. , Naccache D. , Keane C. J. , McGowan B. J. , Matthews D. L.
Published: July 2002

The x-ray spectrum in the range of Ne-like selenium resonance lines coming from a soft x-ray laser plasma has been used to make a spectroscopic diagnostic of the plasma. We performed a modelization of the emission. Computing intensity ratios of Ne-like resonance lines and Na-like satellite lines, plasma parameters (density and temperature) have been obtained. The temperature deduced from the model is found to be lower than expected in hydrodynamical calculations from other authors.
Wentzel–Kramers–Brillouin approximation for a quantum well with internal and external fields
Authors: Wallace A. B. , Deering W. D.
Published: July 2002

The energy shifts corresponding to internal and external electric fields of a particle in a quantum well are discussed in the Wentzel–Kramers–Brillouin approximation. Theoretical calculations reveal that the particle energy increases as the internal field increases and decreases as the external field increases. Excellent agreement between theory and experiment is found for excitons confined to GaAs-GaAlAs quantum wells.
Integrated quantum-well manifold laser
Authors: Waters R. G. , Emanuel M. A. , Dalby R. J.
Published: July 2002

An integrated manifold of quantum-well lasers with up to three quantum wells has been fabricated by metalorganic chemical vapor deposition. cw threshold current densities per well and differential quantum efficiencies are comparable to those for individual devices, and transverse far-field patterns are single lobed. Catastrophic optical damage levels increase with increasing quantum-well count and are substantially higher than those achieved with a single quantum-well laser. Thermal effects in cw operation have been mitigated by using an efficient design with a high characteristic temperature in a low thermal resistance configuration.
MeV implantation masking using an aluminum gallium arsenide metal liftoff layer
Authors: Ghadiri M. M. , Bryan R. P. , Miller L. M. , Tang T. , Givens M. E. , DeTemple T. A. , Coleman J. J.
Published: July 2002

An alternative masking method for high-voltage ion implantation masking of compound semiconductors which incorporates an additional AlGaAs layer between a Pb/Cr/Au metal mask and the sample to be implanted is described. Following patterning by conventional techniques and implantation, the AlGaAs layer is selectively etched to remove the metal mask without damaging the underlying epitaxial structure.
The use of cathodoluminescence imaging of cleaved wafers to investigate the propagation of defects within epitaxial layers grown on GaAs liquid-encapsulated Czochralski substrates
Authors: Noad Julian P.
Published: July 2002

The propagation of crystalline defects and dislocations within epitaxial layers grown by molecular-beam epitaxy and metalorganic chemical vapor deposition on commercial-grade GaAs liquid-encapsulated Czochralski (LEC) substrates has been examined using both conventional (100) cathodoluminescence (CL) and CL imaging of cleaved wafers. High-resolution CL imaging indicates that while dislocations within the substrate propagate readily into epitaxial layers, the epitaxial material surrounding these defects is very uniform and it does not suffer from the decoration or gettering effects that are observed around dislocations within the LEC substrate itself.
Far-infrared absorption spectra of Cd1−xMnxTe from 10 to 300 K
Authors: Clayman B. P. , Orlowski T. A. , Becla P.
Published: July 2002

Absorptivity spectra are presented in the far-infrared (15–700 cm−1) from 10 K to room temperature for Cd1−xMnxTe alloys (x=0–0.64); this covers almost the entire composition range in which the cubic structure is stable. The results are interpreted in terms of the known phonon spectra of these materials, as determined from far-infrared reflectivity, neutron scattering, and Raman scattering measurements, and in terms of anharmonic effects due primarily to an impurity-induced disorder.
The characterization of high electron mobility transistors using Shubnikov–de Haas oscillations and geometrical magnetoresistance measurements
Authors: Chang Chian-Sern , Fetterman Harold R. , Viswanathan Chand R.
Published: July 2002

Shubnikov–de Haas oscillations and geometrical magnetoresistance measurements are used to determine the two most important parameters, channel concentration and mobility, respectively, for high electron mobility transistors. To deduce useful data from measurements, the theory of the Shubnikov–de Haas oscillation for the two-dimensional electrons is derived and discussed in detail. The experimental data for the channel concentration as a function of gate voltage is used to check the accuracy of the charge-control law. We also derive a simple formula of the geometrical magnetoresistance to calculate the mobility for any aspect ratio. The concentration and mobility deduced from the Shubnikov–de Haas and geometrical magnetoresistance measurements give us insight on the nature and properties of the devices. The experimental data shows that the impurity scattering is the dominant mechanism for the low channel concentration. The maximum transconductance occurs at a compromise between the charge-control ability of the gate voltage and the channel mobility. Near the cutoff region the decrease of the conductivity is due to the decrease of both the channel concentration and the mobility.
Structural anomalies in undoped gallium arsenide observed in high-resolution diffraction imaging with monochromatic synchrotron radiation
Authors: Steiner B. , Kuriyama M. , Dobbyn R. C. , Laor U. , Larson D. , Brown M.
Published: July 2002

Novel, streaklike disruption features restricted to the plane of diffraction have recently been observed in images obtained by synchrotron radiation diffraction from undoped, semi-insulating gallium arsenide crystals. These features were identified as ensembles of very thin platelets or interfaces lying in {110} planes, and a structural model consisting of antiphase domain boundaries was proposed. We report here the other principal features observed in high resolution monochromatic synchrotron radiation diffraction images: (quasi)cellular structure; linear, very low-angle subgrain boundaries in 〈110〉 directions, and surface stripes in a 〈110〉 direction. In addition, we report systematic differences in the acceptance angle for images involving various diffraction vectors. When these observations are considered together, a unifying picture emerges. The postulate of thin {110} antiphase boundaries leads to an understanding not only of the streak-like diffraction features but of the other principal features as well. For the formation of such regions we propose two mechanisms, operating in parallel, that appear to be consistent with the mesoscopic structure observed by a variety of techniques.
Surface-modified RuO2-based thick film resistors using Nd:YAG laser
Authors: Gofuku E. , Ogama T. , Takasago H.
Published: July 2002

An RuO2-based thick film resistor (TFR) is a cermet-type resistor which consists of RuO2 particles and glass. Paste containing organic vehicles is printed onto an insulating substrate, and subsequent firing at about 900 °C makes the cermet-type resistors. TFRs are widely utilized as electrical resistive materials in electric devices such as hybrid ICs (integrated circuits) [see, for example, R. W. Vest, Ceram. Bull. 65, 631 (1986)]. The features of an advanced laser application process to control the electrical resistivity of the TFRs were proposed. This new process is an application of surface-modification using laser beams. In this paper, a mechanism of the surface-modification of the TFR is considered using results of morphology observation, x-ray diffraction (XRD), and x-ray photoemission spectroscopy (XPS). The following points should be noticed. (1) In the surface-modifying process using normal mode pulse Nd:YAG laser beams, glass in the TFR is modified and supersaturated with ruthenium impurities because of rapid heating and rapid cooling rates in the irradiation process; the specific resistivity of the modified glass is extremely decreased, estimated at 10−3 Ω cm at most. (2) No new crystalline phase in the ruthenium-oxygen system is detected after the surface modification by results of x-ray diffraction (XRD) analysis. (3) The valence state of the ruthenium ions in the modified glass is more positively charged than that in crystalline RuO2 , while the valence states of lead and oxygen ions in the modified glass are more negatively charged than in as-fired glass before surface modification according to the results obtained by x-ray photoemission spectroscopy (XPS) analysis. It is suggested that if ruthenium ions introduce electrons into the modified glass and if these electrons behave as itinerant electron carriers in the modified glass, a decrease in the resistivity of TFR after the surface modification is quite reasonable for the results of XPS.