bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the third-order piezoelectric constants of quartz using the extentional mode of rods
Authors: Hruska Carl K.
Published: July 2002

The dc field-induced change in the frequency of the extentional mode of rods is used to determine the fundamental nonlinear third-order piezoelectric constants of quartz. Five combinations of the total number of eight third-order piezoelectric constants are determined by least-squares fit to data obtained from 50 different rods. The results are notable for their small standard errors of less than 2% on average. They also agree very well with the values obtained independently by the transit-time method.
Si (111) surface cleaning using atomic hydrogen and SiH2 studied using reflection high-energy electron diffraction
Authors: Hirayama Hiroyuki , Tatsumi Toru
Published: July 2002

The Si(111) wafer covered by a thin protective oxide layer was cleaned in disilane gas source Si molecular-beam epitaxy chamber. The effect of the electron cyclotron resonance (ECR) cracked/uncracked disilane or hydrogen irradiation on the initial surface cleaning was studied by observing the reflection high-energy electron diffraction pattern change. The ECR-cracked disilane irradiation was the most effective for lowering the cleaning temperature and the surface cleaning was achieved at 680 °C. The uncracked disilane and the ECR-cracked hydrogen irradiation were also effective for lowering the cleaning temperature. The uncracked hydrogen irradiation has no effect for lowering the cleaning temperature. The SiH2 and H were main species of the ECR-cracked disilane and these played important roles in the cleaning process.
Light emission excited by hot electrons in MgF2 thin-film devices
Authors: Shu Q. Q. , Zu Z. R. , Lu J. W.
Published: July 2002

We report an observation of light emission from a new dc-operated device consisting of a 100–200-Å-thick MgF2 film sandwiched between two metal films. The device can be biased to above 10 V, and the observed emission spectrum ranges from 3600 to 9000 Å. The analysis of the emission spectrum suggests that the light emission can be ascribed to processes wherein the hot electrons produced by the high electric field excite the surface plasmons and the interband transitions.
Lubricating performance enhancement of amorphous silicon carbide film by annealing effects and microbeam analyses of the tribological interface
Authors: Sugimoto Iwao , Miyake Shojiro
Published: July 2002

The lubricating performance of amorphous silicon carbide films deposited by electron cyclotron resonance plasma is greatly improved by annealing at 800 °C. The annealed film has a significantly long lubricating life with a low friction coefficient. Detailed information about the molecular structures at the tribological interface is obtained using microbeam surface analytical methods (micro-Fourier-transform-infrared spectroscopy, laser Raman spectroscopy, micro-x-ray-photoelectron spectroscopy, and scanning Auger microprobe). These analyses show that the lubrication performance is improved as a result of a wear-resistant molecular network composed of the covalent bonds between poorly hydrogenated silicon and carbon. The low hydrogen content in these moieties is achieved from the high-temperature annealing effect.
A comparative study of electron transport phenomenon in the keV range
Authors: Pandey L. N. , Rustgi M. L.
Published: July 2002

On incorporating two different electron inelastic scattering cross sections by Möller [Z. Phys. 70, 786 (1931)] and Gryzinski [Phys. Rev. 138, 336 (1965)], Monte Carlo calculations have been performed to calculate the energy, angular distribution, and coefficients of transmitted and backscattered electrons in Al films of different thicknesses for 15- and 20-keV incident electron energies. The calculations from both the models are found to yield similar results and both of them give good agreement with the available experimental data.
Photoemission study of oxygen adsorption on (001) silicon carbide surfaces
Authors: Bermudez V. M.
Published: July 2002

X-ray photoemission (ZrMζ, hν=151.4 eV, and MgKα, hν=1253.6 eV) and electron energy loss spectroscopies, low-energy electron diffraction and work-function measurement have been used to study the initial adsorption of oxygen on cubic β-SiC(001) at room temperature. Three different SiC surfaces have been considered—Si-rich [two-domain (3×1) low-energy electron diffraction pattern], stoichiometric [two-domain (2×1)], and Si-deficient [c(2×2)]. Similar data have also been obtained for a Si(001)-(2×1) surface. For SiC the initial rates of O uptake are in the order (2×1)>(3×1)>c(2×2), and the rates for all three are much less than that for Si (2×1). A model for the initial adsorption of O on SiC is proposed in which the rates for the different SiC surfaces reflect the relative ease of formation of Si-O-Si bridges between surface Si atoms while the greater rate for Si versus SiC results from the difficulty in inserting O into SiC backbonds.
Surface stoichiometry and valence electronic structure of YBa2Cu3O7−x
Authors: Parmigiani F. , Samoggia G. , Calandra C. , Manghi F.
Published: July 2002

We report x-ray photoemission data from YBa2Cu3O7−x showing that the measured composition and the electronic structure changes significantly upon the photoelectron escape depth. For large take-off angles the valence band spectrum near the Fermi edge is well structured and shows a number of features arising from Cu-O hybrid states. Their intensities are drastically reduced in the energy distribution curves measured at grazing angles. These results are interpreted assuming that the surface is mainly composed by Ba-O planes. This interpretation is shown to be consistent with electronic structure calculations for the bulk and for a YBa2Cu3O7−x surface terminated with a Ba plane and produced by cutting the Cu2  O4 bond normal to the c axis. The local density of states calculated on this basis and taking into account electron correlation effects is shown to be consistent with many significant behaviors experimentally observed in the YBa2Cu3O7−x valence band.
A new composite-cavity laser with two different waveguide cores for stable longitudinal mode operation
Authors: Naito H. , Nagai H. , Yuri M. , Tateoka K. , Kume M. , Hamada K. , Shimizu H.
Published: July 2002

We have developed a new composite-cavity laser with two different waveguide cores connected near the front mirror in the same cladding. This composite cavity has a built-in structure that is capable of giving high mode selectivity because of strongly modulated reflectivity of the front mirror. The laser shows very stable single longitudinal mode operation in a temperature range as wide as about 50 °C for output powers from 3 to 100 mW without mode hopping.
Defect generation in silicon-implanted gate insulators of insulated gate field-effect transistors
Authors: Sune C. T. , Reisman A. , Williams C. K.
Published: July 2002

In this paper, the effects on insulated gate field-effect transistor device characteristics due to implantation of silicon into the gate insulator have been studied. Contrary to what one might have expected in an oxygen-deficient insulator, the primary defects generated, as detected by optically assisted injection of electrons into the gate insulators of damaged devices, are large quantities, as much as 1.3×1012 cm−2, of neutral electron traps (NET). Secondary types of defects found appear to be fixed negative charge, approximately 2.3×1011 cm−2 in the worse case, and a smaller amount of fixed positive charge (FPC), approximately 1.7×1011 cm−2 in the worse case. It was found that none of these defects could be removed by employing conventional postmetal annealing conditions in forming gas (10% H2, 90% N2) at 400 °C for up to 60 min. The defects created by ion implantation appear to be quite different from those created by x-ray or electron irradiation, where large quantities of FPC and NET are generated which can be annealed in a similar postmetal annealing cycles.
Defect-accelerated donor diffusion and layer intermixing of GaAs/AlAs superlattices on laser-patterned substrates
Authors: Kish F. A. , Plano W. E. , Hsieh K. C. , Sugg A. R. , Holonyak N. , Baker J. E.
Published: July 2002

Data are presented showing that donor diffusion and Alx Ga1−x As-GaAs layer intermixing are greatly enhanced in the presence of defects created by crystal overgrowth on locally laser-melted substrates. Accelerated defect and impurity-induced layer disordering, and donor diffusion from a solid source (SiO2 ), a vapor source (Ge), and from a grown-in source (Se) are observed in regions of high defect density. The enhanced donor diffusion and crystal self-diffusion are attributed to an increased density of column-III defects and dislocations in the crystal.
Transient solution of the diffusion equation for a composite system heated with a laser beam
Authors: Young J. F. , Kelly P. , Abtahi A. , Braunlich P. F. , Jones S. C.
Published: July 2002

The general solution of the thermal diffusion equation for the case of a semi-infinite two-layer system that is heated with a localized cw laser beam of circularly uniform intensity profile is extended to times after the pulse is switched off. An application of that solution in the field of solid-state dosimetry is illustrated by simulating the experimental thermoluminescence response curves obtained from LiF:(Mg,Ti)-phosphor-coated borasilicate glass, for the special case of heating with a CO2-laser beam that has a uniform and square intensity profile: In effect, we solve the diffusion equation experimentally.
Raman spectra of SinGem superlattices: Theory and experiment
Authors: Alonso M. I. , Cerdeira F. , Niles D. , Cardona M. , Kasper E. , Kibbel H.
Published: July 2002

We discuss the Raman spectra of SinGem short-period superlattices both theoretically and experimentally. A lattice dynamical model is used to generate spectra which are compared to experimental results. This comparison is useful for determining superlattice periods and detecting interface roughness.
Field-dependent conductivity of lightly doped p-Si at 77 K
Authors: Reggiani L. , Varani L. , Vaissiere J. C. , Nougier J. P. , Mitin V.
Published: July 2002

A theoretical investigation and new experiments on the conductivity of lightly doped p-Si (boron) at 77 K are presented. The conductivity is studied as a function of the electric field in the range 10<E<104 V/cm. The experimental results are interpreted within an original Monto Carlo simulation which includes the mechanism of generation and recombination from impurity centers, thus allowing a simultaneous calculation of the mobility and the fraction of ionized impurities. The good agreement between the theory and the experiments supports the reliability of the physical model suggested.
Hall effect in gratinglike potential modulated inversion layers
Authors: Vettese F. , Sicart J. , Robert J. L. , Vincent G.
Published: July 2002

We present a quantitative approach to the potential fluctuation model we have previously developed in disordered semiconductors. MOSFET (metal-oxide-semiconductor field-effect transistors) were irradiated along lines parallel (L structures) or perpendicular (T structures) to the drain-source direction, using a 20-keV scanned e-beam. Thus, in the inversion regime, the surface potential ψs was periodically modulated, thereby strongly modifying the conduction processes. Hall measurements were performed as a function of temperature and gate voltage at various irradiation doses and for different periods. Conduction in L structures was influenced by lateral potential barrier scattering, whereas it was barrier controlled in T structures. The experimental results are interpreted by a simple model of energetic distribution of both carrier density n(E) and mobility μ(E), based on the existence of a conduction threshold. When barriers were wide in T structures, Hall measurements showed that part of the carriers did not participate in conductivity in the weak inversion regime, while mixed conduction processes occurred when barriers were narrow. In contrast, all the carriers conducted in the strong inversion regime, and only the mobility was perturbed. Thus the field effect in irradiated MOSFET was used to correlate the Hall carrier density with the conduction threshold energy.
MeV ion channeling studies of (111) CdTe films on (111) GaAs substrates
Authors: Wilkens B. J. , Farrell H. H. , Pollard K. , Erbil A.
Published: July 2002

Group II-VI compound semiconductors such as CdTe can be grown epitaxially on III-V materials such as GaAs. These films possess better physical properties than their bulk-grown counterparts. This work explores the (111) CdTe/(111) GaAs system by means of MeV ion channeling. Good epitaxy is found (backscatter minimum yields of 15%) for a thickness greater than 1000 Å, which is remarkable considering the 14% lattice mismatch between film and substrate. A narrowing of the Cd angular scan suggests Cd atom displacement. A model based on Te vacancies is presented to describe our data.
Proton stitching of layers of SiO2 particles to fused silica
Authors: Musket R. G. , Thomas I. M.
Published: July 2002

Irradiation with 100-keV protons to doses of 2.3×1015–7.6×1016 H/cm2 enhanced the adhesion and abrasion resistance of 220-nm-thick antireflective, optical coatings on fused silica substrates without adversely affecting the optical transmission and laser-damage threshold for 1064-nm photons. The as-deposited, sol-gel coatings consisted of porous layers of uniform, spherical silica particles having diameters of either 8 or 20 nm. The proton doses required for significant improvements in adhesion and abrasion resistance increased with particle diameter and decreased slightly for coatings precleaned by exposure to ultraviolet radiation in the presence of reactive gases.
Buried-heterostructure semiconductor Raman laser with threshold pump power less than 1 W
Authors: Suto Ken , Ogasawara Shigemasa , Kimura Tomoyuki , Nishizawa Jun-ichi
Published: July 2002

The low-power operation of a semiconductor buried-heterostructure Raman laser is reported. We are developing these devices for very wide-band optical communication in the terahertz frequency region. It has a structure with a GaP active layer and AlxGa1−xP cladding layers, which are grown by the temperature-difference method under controlled vapor pressure. By making the stripe width 30–40 μm, we have obtained a threshold pump power of 500 mW. A low-threshold semiconductor Raman laser can be pumped by semiconductor injection lasers. We have measured the optical loss of the waveguide and detected the contribution from scattering and leakage at heterointerfaces.
Laser direct writing of channel waveguides using spin-on polymers
Authors: Krchnavek Robert R. , Lalk Gail R. , Hartman Davis H.
Published: July 2002

A focused argon-ion laser beam (λ=350 nm) is used to fabricate optical channel waveguides on oxidized silicon wafers using a commerically available spin-on polymer. The polymerization process is photon induced, thus allowing the reaction to occur in a room-temperature ambient. This allows the fabrication of waveguides on a variety of substrates including those with low melting points. The losses in these waveguides are typically less then 1 dB/cm, making them applicable to a variety of optical interconnect problems. In particular, we demonstrate their use in the fabrication of an optical power tap.
On the deconvolution of heat-pulse-like signals
Authors: Leal Ferreira G. F.
Published: July 2002

Approximate solutions devised by Biot [Variational Principles in Heat Transfer (Clarendon, Oxford, 1970)] of the heat-flow pattern inside a slab, caused by excitation at one of its faces, exist that are characterized by a running front. We show that this allows us to deconvolute the current and voltage signals in some instances by performing repeated differentiations of products of the signal and the position of the front. Three cases are studied: the usual heat-pulse method, constant illumination, and the thermal step at one of the sample’s faces.
Tunable photoluminescence from amorphous silicon doping modulated multilayers
Authors: Zhang D. H. , Haneman D. , Shi Z. R.
Published: July 2002

The low-temperature photoluminescence has been measured from nipi ... doping modulated multilayers of amorphous hydrogenated silicon with a range of i layer thickness di. It shows a monotonic decrease from 1.40 to 1.14 eV in peak energy photoluminescence EPL as di reduces, unlike the behavior of optical band gap and persistent photoconductivity which show a peak. The results are interpreted to show that P and B diffusion occur during layer growth to form compensated regions with the degree of compensation controlling the value of EPL. A value of the P diffusion coefficient at 220 °C is deduced of 4×10−17 cm2 s−1.
Effect of anisotropy on atomic fluorescence: Influence on the detection of a hyperfine transition in a cesium beam
Authors: Théobald G. , Dimarcq N. , Giordano V. , Hamel A. , Cérez P.
Published: July 2002

The problem of the fluorescence anisotropy resulting from alignment in the excited state is investigated in the case of a cesium beam illuminated by a broadband laser diode tuned to the cesium D2 line. Its effect on the collection efficiency is derived when photon fluorescence collection is performed inside a small solid angle about the quantization axis. Excitation schemes leading to a noticeable increase of the fluorescence yield are pointed out and experimental results agree quite well with the predictions.
Low-noise Nd:LaMgAl11O19 laser for use in magnetometry
Authors: Bohler Christopher L.
Published: July 2002

A stable, low-noise, tunable, solid-state laser has been constructed for use in magnetometry. The system is designed specifically for applications in which a rugged, magnetically clean source is required. A La1−xNdxMgAl11O19 (LNA or LMA) laser crystal provides the 1083-nm radiation necessary for optical pumping of gaseous helium, the process on which our magnetometer design is based. Laser characteristics of the 0.5-W SDL 2432 laser-diode-pumped device consist of 112-mW free-running laser output near 1082 nm, a threshold of 35 mW, and an output power of up to 26 mW within a single longitudinal mode at the helium metastable resonance wavelengths, obtained by insertion of an intracavity solid étalon. The structure of the ‘‘hand-held’’ laser unit is presented with particular emphasis on the laser parameters required for low-noise operation of this source at the wavelengths of interest.
Self-focusing of Langmuir waves in a plasma including the effect of Landau damping
Authors: Pandey H. D. , Sharma A. K.
Published: July 2002

Langmuir waves have a tendency to self-focus around the intensity maxima at moderate power densities. A paraxial ray theory of self-focusing, through ponderomotive nonlinearity, reveals that the self-focusing length Rn≂avth/vosc where a is the radial width of the Langmuir wave, and vth and vosc are the electron thermal and oscillatory velocities. The damping tends to inhibit the self-focusing effect.
Parallel stress and perpendicular strain depth distributions in [001] silicon amorphized by ion implantation
Authors: Fabbri R. , Servidori M. , Zani A.
Published: July 2002

Measurements performed by x-ray diffraction techniques on silicon wafers implanted with silicon ions show that surface amorphous film and underlying interstitial defects are able to induce wafer convexity. The simulation of the rocking curves obtained by double-crystal diffraction before and after annealing, the measurement of the total vertical expansion of the implanted layer, the determination of the curvature radius, and the use of a theoretical model, directly compatible with the output of rocking curve simulation, recently developed for multilayered crystalline structures, allow us to determine the tangential stress depth distribution of the implanted wafer and the average relaxed volume expansion of the amorphous layer. The results obtained show that both stress and volume expansion increase with dose for a given ion-beam energy. A comparison is made with similar data reported recently in the literature for high-dose arsenic-implanted silicon.
The applicability of approximate nonisothermal methods for the studies of processes with critical temperature
Authors: Holender J. M. , Sol/tys J.
Published: July 2002

The applicability of peak methods of nonisothermal kinetic data analysis is considered in this paper with focus on the influence of critical temperature; cooling experiments are also discussed. The method of analysis used in the paper is based on the Johnson–Mehl–Avrami [W. A. Johnson and K. F. Mehl, Trans. AIME 135, 315 (1941) and M. Avrami, J. Chem. Phys. 7, 1103 (1939)] rate equation, combined with the modified temperature dependence of reaction rate (including critical temperature). Using this method model, temperatures corresponding to the maximum reaction rate for different cooling/heating rates were found, and the applicability of different peak methods was tested. It is concluded that only the Kissinger [J. Res. Natl. Bur. Stand. 57, 217 (1965)] method gives correct values of activation energy, and that even this method can only be applied when analyzing reactions without (or with very low) critical temperature during heating experiments.
Comparison of mechanically and optically measured mode-I fracture toughnesses in transparent brittle materials
Authors: Tossell D. A.
Published: July 2002

The optical phenomenon of frustrated total internal reflection (FTIR) has been used to measure mode-I opening displacements at the crack tip of an air-filled crack in a glass block. Knowledge of the optical and mechanical properties of the block allow the mode-I stress intensity factor KI to be derived. Fracture tests on glass specimens have been carried out at a variety of crack velocities using the double cantilever beam (DCB) and double torsion (DT) test configurations. Simultaneously measured optical (FTIR) and mechanical (standard fracture mechanics analysis) values for KI agree well for the DCB test geometry but not so well for the DT configuration. The lack of agreement in the latter case is attributed to the curved crack front that is generated by the geometry of the DT specimen.
Superstrained superlattices: A processing approach
Authors: Dunstan D. J. , Homewood K. P.
Published: July 2002

Strained layer semiconductor heterostructures produced by molecular-beam epitaxy or metalorganic chemical vapor deposition growth are limited in thickness by relaxation producing dislocations, if a critical thickness tc is exceeded. We propose that, for a given thickness, strain values up to twice as large may be induced by post-growth processing with selective diffusion of the elemental constituents of the heterostructure.
Phase-shift measurement in photorefractive holographic recording
Authors: Garcia Paulo Magno , Cescato Lucila , Frejlich Jaime
Published: July 2002

A simple direct method for measuring the interference pattern of a light-to-recorded hologram phase shift in photorefractive crystals is reported. The method is used for studying the recording in Bi12SiO20 under an externally applied electric field. The results are then compared with theory and used for computing the density of photoelectron traps.
Diffraction and bremsstrahlung radiation from a loop charge in a cylindrical pipe with a step change in wall radius
Authors: Schill Robert A. , Seshadri S. R.
Published: July 2002

A theory is developed to model diffraction and bremsstrahlung radiation in the transverse magnetic mode from a loop of charge in a cylindrical pipe with a discontinuous change in wall radius. The beam kinetics is assumed a priori. A consistent definition of the longitudinal coupling resistance is developed. Scattering effects peak at the cutoff frequencies of the modes of the larger pipe. When kinetic losses are sufficiently large, a change in loop charge radius may alter the propagation of the dominant mode when the charge moves from a larger to smaller diameter pipe. This effect is not present if the charge motion is in the reverse direction.
Defect generation in silicon dioxide from synchrotron radiation below 41 eV
Authors: Williams C. K. , Reisman A. , Bhattacharya P.
Published: July 2002

Generation of fixed positive charge, neutral electron traps, and fixed negative charge in SiO2 due to exposure to x radiation in the photon energy range below 41 eV from a synchrotron source is reported. For constant incident x-radiation exposure levels of 120 mJ/cm2 with both monochromatic and broadband radiation, the number of defects generated in the monitoring devices was at or below the detection limit of the equipment. This is in sharp contrast with the results obtained at photon energies above 300 eV reported earlier [C. K. Williams, A. Reisman, P. K. Bhattacharya, and W. Ng, J. Appl. Phys. 64, 1145 (1988)] in which a large number of each of the three defects mentioned above were generated. The lack of damage indicates that the problems associated with x-ray-induced insulator damage due to x-ray lithography may be solved by tailoring the photon energy, provided suitable mask and photoresist materials can be developed.
The impact of various annealing methods on silicon implant activation properties for GaAs crystals
Authors: Gray M. L. , Parsey J. M.
Published: July 2002

Wafers obtained from undoped, semi-insulating GaAs crystals grown by liquid-encapsulated Czochralski and vertical gradient freeze techniques were implanted with 29Si at a dose of 3×1012 ions/cm2 and an energy of 60 keV. Activation of the implanted region was carried out by furnace or rapid thermal annealing methods, with and without the use of an SiO2 encapsulant. Profiles of the electron concentration and distribution were obtained by the capacitance-voltage method. Significant variations in the donor distributions were found to be dependent upon the annealing technique employed. The dissimilarities in implant activation properties for GaAs wafers grown by the two techniques, and subjected to identical annealing cycles, have been attributed to variations in melt stoichiometry and native point defects.
Fractal models for the autocatalytic growth of amorphous thin films
Authors: Pan Xiao-dan , Szasz Andras , Fabian Derek J.
Published: July 2002

Fractal models are proposed for the autocatalytic growth of amorphous thin films. The models give good agreement with the growth kinetics measured for electroless deposited films of amorphous nickel-phosphorus. A universal result obtained from the models is discussed, and only self-similarity is found to be important; randomness is effectively eliminated in the model.
Mobile ion effects in low-temperature silicon oxides
Authors: Young N. D. , Gill A. , Clarence I. R.
Published: July 2002

Mobile ions in oxides formed on silicon by low-temperature processes have been studied using a combination of bias-temperature stress and triangular voltage sweep experiments. It is found that these oxides contain intrinsically low concentrations of mobile ions (<1010 cm−2) and that the ionic instabilities which are seen are due to alkali metal ions rather than other contaminants or the inherent water and hydrogen. Mobile sodium behaves slightly differently in low-temperature oxides compared with conventional thermal oxides, and can be gettered and passivated using a low-temperature process. It is shown that sodium ions are trapped by polycrystalline silicon during plasma hydrogenation, and that atomic hydrogen is involved in this process. The trapped ions are released back into the oxide during subsequent bias-temperature stressing.
Selective area solution growth of Ge and GaAs on Si
Authors: Zolper John C. , Barnett Allen M.
Published: July 2002

Ge and GaAs have been grown on Si substrates by selective area solution growth from saturated metal solutions. Prior to this work, the growth of GaAs on Si has been almost exclusively done by molecular-beam epitaxy or metalorganic chemical vapor deposition. A primary advantage of the solution growth process is the prospect for selective area growth where growth is limited solely to openings in a SiO2 mask. The selectively grown Ge and GaAs crystal compositions were determined by energy dispersive analysis by x ray with the GaAs material demonstrating stoichiometry without detectable Si or Ge incorporation. The GaAs crystals on Si were also fabricated into simple light-emitting diode structures that emitted infrared light at 0.7–0.8 V forward bias.
Influence of the return current effects on the diocotron instability of a relativistic hollow electron beam
Authors: Choi Eun H. , Uhm Han S. , Song Sun K. , Choi Duk I.
Published: July 2002

Influence of the return current effects on the diocotron instability of a relativistic hollow electron beam propagating through a background plasma is investigated within the framework of a cold fluid model. The return current density induced in the background plasma is taken to be steadily proportional to the axial electron beam current density. By making use of the linearized fluid-Maxwell equations, a dispersion relation for the eigenfrequencies of the system is derived and used to examine instabilities. It is found that as the fraction of current neutralization increases, lower mode instabilities become dominant while higher mode perturbations are stabilized except in the case of very thin beams. It is also observed that for all values of the fraction of current neutralization, increasing the plasma density gradient or decreasing the beam thickness causes a destabilizing influence.
High-optical-quality GaInP and GaInP/AlInP double heterostructure lasers grown on GaAs substrates by gas-source molecular-beam epitaxy
Authors: Kikuchi Akihiko , Kishino Katsumi , Kaneko Yawara
Published: July 2002

By gas-source molecular-beam epitaxy, we obtained a device-quality GaInP epitaxial layer lattice matched to (100)-GaAs substrates, with a photoluminescence efficiency comparable to that of a crystal grown by liquid-phase epitaxy. A GaInP/AlInP double heterostructure laser with a GaInP active layer was fabricated, and pulsed lasing operation was achieved at room temperature for, we believe, the first time.
A novel field-effect mobility measurement on a gateless InGaAs/InAlAs heterojunction in a parallel magnetic field
Authors: Nealon M. , Pepper M. , Scott E. G. , Davies G. J.
Published: July 2002

A technique for measuring the field-effect mobility of a gateless In0.53Ga047As/In0.52Al0.48As heterojunction has been developed by using the nonpersistent photoconductive effect. Subband depopulation in a parallel magnetic field is consistent with the ‘‘universal’’ depopulation observed in InAs, InSb, and HgCdTe metal-oxide-semiconductor field-effect transistors.
Laser-induced electron source in a vacuum diode
Authors: Ghera U. , Boxman R. L. , Kleinman H. , Ruschin S.
Published: July 2002

Experiments were conducted in which a high-power CO2 TEA laser interacted with metallic cathode in a high-vacuum (10−8 Torr) diode. For power densities lower than 5×107 W/cm2, no current was detected. For power densities in the range of 5×107–5×108 W/cm2, the Cu cathode emitted a maximum current of 40 mA. At a higher power density level, a circuit-limited current of 8 A was detected. The jump of a few orders of magnitude in the current is attributed to breakdown of the diode gap. The experimental results are similar to those of a triggered vacuum gap, and a thorough comparison is presented in this paper. The influence of the pressure in the vacuum chamber on the current magnitude shows the active role that adsorbed gas molecules have in the initial breakdown. When the cathode material was changed from metal to metal oxide, much lower laser power densities were required to reach the breakdown current region.
Deep trapping controlled switching characteristics in amorphous silicon thin-film transistors
Authors: van Berkel C. , Hughes J. R. , Powell M. J.
Published: July 2002

We report transient effects in amorphous silicon thin-film transistors occurring upon switch-on and switch-off, which are controlled by trapping and emission from the deep states in the amorphous silicon. We develop a unifying theoretical description which is applicable to both switch-on and switch-off. The model is based on carrier thermalization to the deep states and includes the spatial dependence of the thermalization process in the band-bending region. The model is able to explain the experimentally observed switch-on and switch-off behavior. In the case of switch-on, electrons are progressively trapped into the deep states in the bulk a-Si:H throughout the entire thickness of the layer. The range of trapping times is large and this leads to a dynamic threshold votage shift and a time dependence of the source-drain current extending between 1 μs and 1 s. In the case of switch-off, two processes occur sequentially. First, there is emission of electrons from the bulk a-Si:H deep states, which leads to a uniform space charge throughout the thickness of the layer. After that, a redistribution of the space charge occurs, leading to the eventual thermal equilibrium space-charge distribution. These processes give rise to two different time constants in the measured decay of the total charge stored in the transistor. Full thermal equilibrium can take several hours to reach.
Read/write characteristics of a single-pole head using Fe-C/Ni-Fe multilayered film
Authors: Takano Hisashi , Kobayashi Toshio , Shiiki Kazui , Nakamura Yoshihisa
Published: July 2002

The advantage of a film with high saturation magnetic flux density for perpendicular magnetic recording is investigated through computer simulations and read/write measurements. A single-pole head using Fe-C/Ni-Fe multilayered film with a saturation magnetic flux density of 2.0 T is fabricated. Read/write tests are performed with the Co-Cr double-layer media. It is shown that the recording ability of this head is very high and does not change with increasing Co-Cr layer coercivity. Computer simulations show that the recording ability also increases when using film with high saturation magnetic flux density for the back layer of a double-layer medium. The upper limit of saturation magnetization of the recording layer can be extended by increasing coercivity. Thus, the higher saturation magnetization medium, which offers higher output voltage and resolution, can be used by applying film with high saturation magnetic flux density for the main pole and the back layer.
Evaluation of residual stress and viscosity in SiO2-core/F-SiO2 clad single-mode optical fibers from Brillouin gain spectra
Authors: Hibino Yoshinori , Edahiro Takao , Horiguchi Tsuneo , Azuma Yuji , Shibata Nori
Published: July 2002

A new method is presented for evaluating residual stress and viscosity in SiO2-core/F-SiO2 clad single-mode optical fibers from Brillouin gain spectra. The residual stress, which strongly influences refractive index and density in the core, is found theoretically and experimentally to be closely related to Brillouin frequency shift. The residual stress and viscosity calculated from the Brillouin frequency shift agree well with those measured with the photoelastic method. As a result, the average residual stress of long-length optical fibers can be obtained by this evaluation method.
Intense beam fundamental mode large-orbit gyrotron studies
Authors: Destler W. W. , Irwin K. , Lawson W. , Rodgers J. , Segalov Z. , Scannell E. P. , Spang S. T.
Published: July 2002

Experimental and theoretical studies of a fundamental mode large-orbit gyrotron designed to produce high-power rf radiation in the TE11 mode at about 1 GHz are reported. Theoretical calculations performed as part of the experimental design process are presented. Results of initial experiments are reported in which 500–1000 MW of rf radiation was observed at frequencies 700 and 1200 MHz, consistent with theoretical expectations. The estimated eletronic efficiency of the device is about 10%. Gas cell breakdown patterns produced by the rf pulse are consistent with operation in the desired TE11 mode.
Generation of highly uniform electrostatic fields by a slotted conducting spherical shell
Authors: Boridy Elie
Published: July 2002

The generation of quasi-static uniform electric fields by a slotted conducting spherical shell is fully analyzed for an arbitrary number of slots pairs, and optimum surface potential and slots position are determined. Numerical results for spherical shells with up to 14 slots are discussed.
Chemical modifications at Teflon interfaces induced by MeV ion beams
Authors: Ingemarsson P. Anders , Keane Michael P. , Gelius Ulrik
Published: July 2002

The effect of MeV ion beams incident on Teflon surfaces was studied by x-ray photoelectron spectroscopy (XPS). Irradiation with 20-MeV 35Cl4+ was carried out at doses ranging from 1012 to 1014 ions/cm2. Residual gas analysis was performed during irradiation to identify molecular fragments released from the Teflon surface. XPS spectra were recorded before and after ion irradiation. On some substrates, gold thin films were evaporated before and after ion bombardment, respectively, to detect possible modifications in thin-film adhesion. Changes in the XPS spectra were interpreted in terms of chemical and structural shifts, and related to the observed adhesion modifications.
Aggregate structure in CuBSe2/Mo films (B=In,Ga): Its relation to their electrical activity
Authors: Margulis Lev , Hodes Gary , Jakubowicz Abram , Cahen David
Published: July 2002

CuBSe2/Mo films of about 3 μm in thickness prepared on different substrates (Si single crystal, glass, alumina) by three-source evaporation have been investigated by electron and optical microscopic techniques: Scanning electron microscopy [including (EBIC) electron-beam-induced current mode], conventional transmission electron microscopy (TEM), and optical Nomarski microscopy. They show, on top of their well-known dense polycrystalline structure (≊1 μm average grain size), a more coarse ‘‘aggregate’’ structure with aggregate dimensions of 20–100 μm, depending on the substrate used. The aggregate boundaries are characterized by very poor EBIC collection efficiency. For samples on glass substrates, this structure, as detected in EBIC, correlates with deformation patterns of the Mo layer seen by Nomarski contrast when viewed through the glass side of the samples. Local electrical measurements made on small Schottky contacts reveal a correlation between the aggregate structure and the I-V characteristics. TEM studies show the presence of both cubic (sphalerite) and tetragonal (chalcopyrite) phases with very clear intergranular phase separation. In many of the grains, twinning was observed. Separate studies of the aggregate boundaries show them to be made up of very tiny crystallites (≊50 Å), apparently mixed with amorphous material. Some of these crystallites in the CuInSe2 films are identified as CuSe and In2Se3 particles.
Excimer laser photolysis study of NH3 and SO2 mixtures at 193 nm
Authors: Ikeda Tetsuya , Danno Minoru , Makihara Hiroshi
Published: July 2002

Photolysis in the NH3-SO2 system was studied by using an ArF excimer laser. The concentration of SO2 decreases during an irradiation of a mixture of NH3 and SO2. It was found from a quadrupole-mass spectroscopic analysis of the photolyzed gases and x-ray diffraction analysis of the solid products that the conversion of SO2 and NH3 yields S (solid) and (NH4)2SO4.
Quantum-well-wire growth by molecular-beam epitaxy: A computer simulation study
Authors: Hugill K. J. , Clarke S. , Vvedensky D. D. , Joyce B. A.
Published: July 2002

A computer simulation developed for modeling the growth of low-dimensional III-V alloy structures by molecular-beam epitaxy (MBE) is used to assess the potential of MBE as a method for growing high-quality quantum-well wires. The existence of a temperature window for optimum growth quality is demonstrated, with the position and width of the window showing a sensitivity to the beam flux.
A cyclotron resonance mechanism for very-low-frequency whistler-mode sideband wave radiation. III. Effect of the inhomogeneity on sideband resonances
Authors: Sá L. A. D.
Published: July 2002

This part of the paper addresses the effects of the inhomogeneity of the magnetic field of the earth on the resonances studied previously. We find that the inhomogeneity introduces phase shifts on the equilibrium positions of both types of resonance we have treated. Those phase shifts are time dependent if either the main carrier in the case of internal resonances, or the interacting carriers in the case of external resonances have time-dependent amplitudes. The time-dependent phase shifts will translate themselves into sideband wave frequency shifts. If the carriers have constant amplitudes, the phase shifts are locally constant. However, frequency shifts observable at the end of the interaction region can still be produced if the amplitude of the radiated sidebands are locally time dependent. Since the phase shifts are dependent in v⊥, the sideband waves should undergo an increase in width as they shift away from their nominal positions. A strong enough inhomogeneity will destroy a resonance completely. It is found that trapped resonances are much more resilient to the effects of the inhomogeneity than external resonances, this being one of the main reasons why we can experimentally observe the creation of sizable sidebands by extremely weak carriers.
Growth and orientation of crystallites in Y-Ba-Cu-O superconductors
Authors: Leventouri Th. , Calamiotou M. , Perdicatsis V. , Faulkner J. S.
Published: July 2002

We have studied the orientation of crystallites in samples of the ceramic superconductor YBa2Cu3Ox using x-ray diffraction and optical microscopy. Although none of the special techniques for developing texture in this material were employed in the synthesis of our samples, it appears from our data that there is considerable orientation of the crystallites and that the pattern of orientation extends throughout the sample. The degree of orientation increases in a predictable way with the amount of processing. We describe a mechanism for explaining these observations.
The thermoelectric power in 3D quantum-well structures of Kane-type semiconductors under large magnetic field
Authors: Ghatak K. P. , Mondal M.
Published: July 2002

An attempt is made to study the thermoelectric power of the electrons in three-dimensional quantum-well structures of Kane-type semiconductors under strong magnetic field on the basis of a generalized electron-dispersion law within the framework of k⋅p formalism and taking n-CdGeAs2 as an example. It is found that the same power decreases with increasing electron concentration, decreasing magnetic field, and decreasing film thickness, respectively, in an oscillatory manner. The corresponding results for the three-band Kane model, two-band Kane model, and that of parabolic energy bands have also been derived as special cases of our generalized formulation.
The positive corona in air: A simplified analytic approach
Authors: Stearns Richard G.
Published: July 2002

The stable positive corona in air is analyzed; the coaxial cylindrical geometry is considered in detail. The analysis separates the corona into two physical regions, corresponding to the absence or presence of significant electron impact ionization. Continuity of electric field and carrier flux across the boundary between these regions gives rise to the criterion for the stable discharge. Electron attachment and detachment are included in the analysis, in an approximate manner. Three secondary-electron-generation processes are considered: secondary emission at the cathode wall due to positive ion impact, photoemission of electrons from the cathode wall, and photoionization in the volume of the air. Comparison of the analysis with experimental data suggests that secondary processes associated with the cathode wall play a minor role in the atmospheric positive corona discharge in cylindrical geometry. Evidence is shown that photoionization of the air is a viable candidate to be the leading secondary-electron-generation process in the discharge.
Low-temperature formation of polycrystalline silicon films on silicon oxide by pyrolyzing silane in a tungsten heater
Authors: Yokota Katsuhiro , Takeshita Kouji , Yamaura Kazuaki , Tamura Susumu
Published: July 2002

Polycrystalline silicon (polysilicon) films are deposited on thermally oxidized silicon above 250 °C by pyrolyzing silane by a tungsten heater. The deposition rate and the structure of the polysilicon films are a function of substrate temperature, heater current, and total pressure. Polysilicon films deposited at 340 and 450 °C have 〈110〉 and 〈100〉 preferred orientations. Films deposited at other temperatures have no preferred orientations. The resistivity varies in a range of 4×107–5×10−4 Ω cm as the heater current increases from 19 to 24 A. Lower resistivities are caused by the fact that tungsten evaporating from the heater during deposition is doped into the polysilicon.
Excitonic behavior in pseudomorphic InGaAs/(Al,Ga)As quantum wells grown by molecular-beam epitaxy
Authors: Ackley D. E. , Lee H. , Colvard C. , Nouri N.
Published: July 2002

Photoluminescence and photoluminescence excitation spectroscopy have been used to study excitons in undoped InGaAs pseudomorphic quantum wells with GaAs and AlGaAs barrier layers. Luminescence features from samples incorporating a top AlGaAs barrier layer were strikingly different from those with bottom AlGaAs barriers. The 2-K luminescence from the latter structures showed free and bound exciton contributions with a linewidth ≤1.5 meV. In contrast, the luminescence from samples with top AlGaAs barriers was much broader, presumably the result of statistical variations in well width due to island formation at the top interface. Fits to the temperature dependence of the PL linewidth show that while the homogeneous broadening is similar in all the structures, the inhomogeneous broadening introduced by the interfaces is fundamentally different. The results could have important implications for the optimization of heterostructure devices in this pseudomorphic system.
Wavelength multiple soliton amplification and transmission with an Er3+-doped optical fiber
Authors: Nakazawa Masataka , Kimura Yasuo , Suzuki Kazunori , Kubota Hirokazu
Published: July 2002

Gain characteristics of an Er3+ -doped fiber for high-power picosecond input pulses are studied with an InGaAsP laser diode pump source at 1.46–1.48 μm. The output energy and peak power of the amplified pulses reach as high as 7.9 pJ and 792 mW for a repetition rate of 100 MHz and a pulse width of 10 ps. The gain saturation is so slow that the gain in high-speed pulse transmission systems is determined by a steady-state saturated gain. With the Er3+ -doped fiber amplifier, it is shown that solitons can be amplified and transmitted over a long dispersion-shifted fiber by using the dynamic range of an N=1 soliton. Furthermore, optical solitons at wavelengths of 1.535 and 1.552 μm have been amplified and transmitted simultaneously over 30 km with an Er3+ -doped fiber repeater for the first time. The collision experiments between these different wavelength solitons is described. It is shown that there is a saturation-induced cross talk between multichannel solitons, and the cross talk (the gain decrease) is determined by the average input power in high bit-rate transmission systems.
InGaAs/InAlAs(Si) modulation-doped heterostructures intentionally lattice mismatched to InP substrates
Authors: Harmand J. C. , Matsuno T. , Inoue K.
Published: July 2002

Modulation-doped InyAl1−yAs/InxGa1−xAs heterostructures were grown on InP substrates by molecular beam epitaxy. With the aim of increasing the InAs mole fraction of the InGaAs layer, the epilayers were intentionally lattice mismatched with respect to the substrate. The samples were characterized by optical microscopy, x-ray analysis, and the van der Pauw method. In a structure with x=0.68, y=0.67, and a 0.5-μm-thick InyAl1−yAs buffer layer, Hall mobilities as high as 13 140 cm2/V s and 78 000 cm2/V s were measured at 300 and 77 K despite an estimated dislocation density of 2×105 cm−1 in a 〈110〉 direction at the substrate-epilayer interface.