bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of lateral carrier diffusion on the modulation response of a semiconductor laser
Authors: Wilt D. , Lau K. Y. , Yariv A.
Published: February 2003

The effect of lateral carrier diffusion upon the modulation characteristics of the semiconductor laser is investigated. A self-consistent analysis of the spatially dependent rate equations is performed using a finite element model. The transverse junction stripe laser is treated as an example and a comparison is made between lateral carrier diffusion and spontaneous emission as damping mechanisms for the resonance peak. Experimental results bear out the conclusion that the relaxation resonance in this device is damped mainly by lateral carrier diffusion. In addition, a simple analytic result is presented which illustrates qualitatively the effect of lateral carrier diffusion upon such devices. The conclusion from this result is that lateral carrier diffusion serves to damp the relaxation resonance in the semiconductor laser quite well, but probably will not serve to improve the upper limit on modulation frequency as might have been suspected.
The diffusive wiggler—a spatially periodic magnetic pump for free-electron lasers
Authors: Jacobs K. D. , Bekefi G. , Freeman J. R.
Published: February 2003

Magnetic diffusion through a spatially periodic assembly of metal conductors yields a large-amplitude, quasi-static pump for use in free-electron lasers. The experimental observations are compared with predictions of a 2-D triangular mesh, finite-difference magnetic-diffusion code (TRIDIF).
Second-harmonic generation in a graded-density plasma containing a colloidal net
Authors: Patel Lalit A.
Published: February 2003

An experimental scheme is proposed to enhance the second-harmonic generation. It consists of a cylindrical waveguide filled with a graded-density plasma and containing a colloidal net whose atoms form a two-level system. An intense laser pulse incident on the waveguide propagates inside and ’’halts’’ in the colloidal net where it excites the atoms by the two-photon absorption mechanism. The subsequent stimulated emission yields a radiation at double the initial frequency.
Decay instability of a whistler in a plasma
Authors: Tewari D. P. , Sharma R. R.
Published: February 2003

The parametric instabilities of a high power whistler in a high-density plasma possess large growth rates when the scattered sideband is an electrostatic lower hybrid mode. The efficient channels of decay include oscillating two stream instability, nonlinear Landau damping, and resonant decay involving ion acoustic and ion cyclotron modes. The processes of nonlinear scattering i.e., the ones possessing whistler sidebands are relatively less significant.
Interaction of CO2 laser pulses with solid targets in magnetic fields
Authors: Loter N. G. , Halverson W. , Lax B.
Published: February 2003

High-temperature plasmas were generated by focussing 225-J gain-switched CO2 laser pulses onto planar solid targets within the bore of a Bitter solenoid magnet. DC magnetic fields up to 100 kG were applied parallel to the laser propagation vector, partially confining a long plasma column streaming away from the target. Target materials included teflon (CF2), graphite, and Al. Soft x-ray diagnostics, including a dual-channel, time-resolving TAP crystal spectrometer, a pinhole camera, and differentially-filtered p-i-n diodes, were used to determine electron density, electron temperature, and axial and radial expansion characteristics of the plasma. From these measurements, it was deduced that effects of refraction became increasingly important as B was increased; furthermore, these effects were strongly dependent on target material. For all targets, refraction occurred late in the pulse when the radially confined plasmas left the focal volume. For teflon and aluminum targets, but not for the lower Z graphite targets, it was inferred that significant side scattering also occurred early in the pulse with sufficiently strong magnetic fields.
Heteroepitaxial silicon growth on polycrystalline MoSi2
Authors: Campisi G. J. , Bevolo A. J. , Shanks H. R. , Schmidt F. A.
Published: February 2003

Heteroepitaxial silicon was grown on polycrystalline MoSi2 by electron beam evaporation at 800 °C in an ultrahigh vacuum. The silicon films with a thickness between 2 and 12 μm grew with either an (111) or (233) orientation. The growth and morphology of the silicon deposit was studied as a function of temperature and the partial pressure of oxygen. Depositions at substrate temperatures of 950 and 1100 °C exceeded the epitaxial temperatures producing films that had faceted grains measuring 2–8 μm in cross section along with larger grains measuring nearly 200 μm across. The introduction of 10−10 Torr partial pressure of oxygen during deposition at 1100 °C changed the morphology and eliminated the large grains. The presence of oxygen at 800 °C prevented epitaxial growth.
Stoichiometric disturbances in ion implanted compound semiconductors
Authors: Christel L. A. , Gibbons J. F.
Published: February 2003

Disturbances in the stoichiometry of compound semiconductors which result from ion implantation are calculated using a Boltzmann transport equation approach. Results for 50-keV boron, 150-keV silicon, and 400-keV selenium implanted into silicon carbide, indium phosphide, and gallium arsenide are presented. Possible complications in the annealing of such implants are discussed.
Stopping power measurements in the 20–150-keV region using thick target backscattering: 1H and 4He on carbon, silicon, and gold
Authors: Pearce J. D. , Hart R. R.
Published: February 2003

Stopping powers for 20–150-keV hydrogen and helium ions in carbon (graphite), silicon, and gold were determined using thick target backscattering. Present results (which have an estimated probable error of less than 5%) are in good agreement with other measurements performed on ’’bulk’’ type targets, indicating that the technique is a viable method for performing absolute stopping power measurements in the intermediate and low-energy regions. However, present results are consistently higher than those reported from thin-film measurements, suggesting that possible allotropic and/or density phenomena are present in evaporated films which effect stopping power measurements at intermediate and low ion energies.
Finite compressibility in shaped charge jet and long rod penetration—the effect of shocks
Authors: Haugstad B. S. , Dullum O. S.
Published: February 2003

The classical theory of high speed jet and long rod penetration assumes incompressibility of both projectile and target. We extend here previous analyses of the implications of finite compressibility by including the effect of stationary shocks. For uniform projectile velocities V≲6×103 ms−1, depending on the type of target material, the total effect of compressibility is in the order of 10% or less, and is well approximated by the volume compressison work considered in the previous analyses [A. Coombs, private communication, Royal Air Force Research and Development Establishment, 1978; B. S. Haugstad, J. Appl. Phys. 52, 1243 (1981)]. At higher velocities shocks play an increasingly dominant role, contributing at least equally to the total compressibility effect at V≲104 ms−1. At these velocities there is a reduction in penetration depth of 10–20% in targets of aluminium or lead, while for plexiglass a full 35% reduction is predicted. Targets of lead or plexiglass experience local melting or even sublimation during penetration. In targets of aluminium, steel, platinum, and probably also in most other metallic targets, melting or sublimation first occurs well above typical projectile velocities.
Photothermal measurements using a localized excitation source
Authors: Aamodt L. C. , Murphy J. C.
Published: February 2003

Optical-beam deflection (OBD) photothermal imaging uses spatially localized excitation to observe spatial variations in the sample surface temperature. This paper analyzes OBD signals produced by localized excitation in terms of three-dimensional thermal diffusion in the sample and in the fluid region in contact with the sample. The dependence of the signals on the local optical absorption coefficient, on gas/sample thermal properties, on modulation frequency, and on the probe/excitation beam radii are discussed with special attention being given to determining the spatial resolution possible for OBD imaging. A criterion for photothermal ’’saturation’’ appropriate to localized optical absorption is developed. Finally, a new variant of the OBD technique is introduced, which is especially adapted to studying optical and thermal boundaries in the plane of the sample. Some comparisons between theory and experiment are provided which illustrate transverse thermal diffusion.
Correlation function studies for snow and ice
Authors: Vallese F. , Kong J. A.
Published: February 2003

In the interpretation of active and passive microwave remote sensing data, the random medium model has been used to characterize snow and ice fields. A correlation function is used to describe the random permittivity fluctuations with its associated mean and variance, and correlation lengths. Several snow and ice samples are studied in this paper, and the correlation functions are shown to be exponential in character with correlation lengths corresponding to the actual size of the ice particles in snow or air bubbles in ice.
Accelerating particles with transverse cavity modes
Authors: Hunter R. O. , Pereira N. R.
Published: February 2003

In optical cavity modes the fields in pulsed operation are limited by skin current heating to large values on order of 0.1–1 GV/m. Moreover, efficient transfer of energy from such modes to relativistic particles seems possible. A single cavity electron accelerator based on such modes would show an appreciable energy gain.
Interpretation of shock-wave data for beryllium and uranium with an elastic-viscoplastic constitutive model
Authors: Steinberg Daniel J. , Sharp Richard W.
Published: February 2003

We have developed a new elastic-viscoplastic constitutive model for metals which can easily be incorporated into a one-dimensional Lagrangian hydrodynamic computer code. Rather than the usual constant relaxation time, we have used one which is a function of temperature (i.e., thermal energy) and strain rate. This allows us to successfully calculate shock-wave profiles, including the effect of spall, in beryllium and uranium over a wide range of stress, temperature, strain, and strain rate.
Electrical measurements on fused quartz under shock compression
Authors: Kondo Ken-ichi , Sawaoka Akira , Ahrens Thomas J.
Published: February 2003

The resistivities of specimens of SiO2 (fused quartz) singly and doubly shocked in the 10–45 and 27–90 GPa ranges, respectively, demonstrate a marked decrease from values of ∼10–0.1 Ω⋅m at a single-shock pressure of ∼40 and a double-shock pressure of ∼74 GPa. These states correspond to calculated shock temperatures of ∼3300 and ∼3600 K, respectively. At shock pressures below 36 GPa the measured resistivity versus calculated shock temperature agrees closely with ambient-pressure and high-temperature resistivity data. This suggests that the ionic conduction mechanisms inferred to control electrical properties at ambient pressure also act under shock-induced high temperatures in quartz and the presumed high-pressure phase, stishovite into which fused quartz appears to transform above 20 GPa. At 36–40 GPa the rapid decrease in resistivity by a factor of 102 suggests a further transformation to an unknown phase which may correspond to the onset of melting. The existing pressure-density Hugoniot data do not demonstrate any anomalous density change associated with this phase change.
Effect of forming gas anneal on Al–SiO2 internal photoemission characteristics
Authors: Solomon P. M. , DiMaria D. J.
Published: February 2003

Internal photoemission characteristics from the Al–SiO2 interface are markedly affected by a 400 °C 20 min forming gas (90% N2 and 10% H2) anneal. The barrier height is raised by about 0.25 eV and the electric field dependence of the photocurrent is increased.
The elastic stiffness coefficients of nickel-iron single-crystal alloys at room temperature
Authors: Kanrar A. , Ghosh U. S.
Published: February 2003

The adiabatic elastic stiffness coefficients of four Ni-Fe single-crystal alloys in the composition range from 90 to 50 wt. % of Ni have been determined by the ultrasonic coherent pulse/ continuous wave (cw) technique at room temperature at a frequency of 8 MHZ. The alloying composition influences the three independent elastic constants C11, C12, and C44 of the Cubic crystal. The striking feature is the highly linear dependence of the shear constants C′[ = (C11−C12)] and C44 on the relative concentration of the constituents.
Luminescence from HgCdTe alloys
Authors: Hunter A. T. , McGill T. C.
Published: February 2003

We report the observation in Hg1−xCdxTe of band-to-band, band-to-acceptor, and donor-acceptor luminescence for material of x = 0.32 and 0.48, and bound exciton recombination luminescence, for material of 0.48. The band-to-band line shape and variation in intensity with pump power is appropriate to an electron-hole plasma with recombination proceeding without wave vector conservation. From line shape separations, we estimate acceptor binding energies of 14.0±1.0 and 15.5±2.0 meV in x = 0.32 and 0.48 material, respectively, and donor binding energies of 1.0±1.0 and 4.5±2.0 meV, respectively. Shifts in luminescence energy across the sample imply a change in composition across the sample of 0.03 cm−1.
Molecular beam epitaxial ZnSe:Mn dc electroluminescent cell with very low threshold voltage
Authors: Mishima Tomoyoshi , Quan-kun Wang , Takahashi Kiyoshi
Published: February 2003

A Au/ZnSe:Mn/n-GaAS dc-operated electroluminescent cell was prepared by molecular beam epitaxy. The lowest threshold voltage achieved was 3.8 V, and the highest power conversion efficiency and brightness were 7.6×10−5W/W(18 V, 0.0027 A/cm2) and 270 fL(16.8 V, 0.25 A/cm2), respectively. These values are superior to any previously reported in ZnSe:Mn EL cells.
Accuracy of theoretical predictions concerning the location of the cross-over points on the secondary-electron emission yield curve
Authors: Flinn E. A. , Salehi M.
Published: February 2003

A series of accurate measurements of the secondary-electron emission properties of a range of amorphous materials, carried out under stringent experimental conditions, have allowed an empirical test of the accuracy of the theoretical expressions derived by Dionne for the locations of the cross-over points on the yield curve. These expressions are found to be in good agreement with observation.
Electron-beam-initiated destruction of low concentrations of vinyl chloride in carrier gases
Authors: Slater R. C. , Douglas-Hamilton D. H.
Published: February 2003

The destruction of ppm levels of vinyl chloride by high-energy electron-beam irradiation has been investigated in various host gases. Measurements of vinyl chloride destruction have been determined over the electron-beam dose range ∼0.01–6 Mrad. The low dose results indicate G values in the range 9–13 are obtained, depending upon the host gas. The high dose results indicate that a factor of 20 reduction in vinyl chloride concentration can be realized for an initial 10 ppm molar vinyl chloride stream in air. A discussion of the kinetic processes responsible for vinyl chloride destruction is presented.
Analysis of the photo voltage decay (PVD) method for measuring minority carrier lifetimes in P-N junction solar cells
Authors: von Roos Oldwig
Published: February 2003

When the diffusion length of minority carriers becomes comparable or even larger than the thickness of a P-N junction solar cell, the characteristic decay of the photogenerated voltage becomes a mixture of contributions with different time constants. The minority carrier recombination lifetime τ and the time constant l2/D, where l is essentially the thickness of the cell and D the minority carrier diffusion length, determine the signal as a function of time. It is shown that for ordinary solar cells (N+-P junctions), particularly when the diffusion length L of the minority carriers is larger than the cell thickness l, the excess carrier density decays according to exp(−t/τ−π2Dt/4l2), τ being the lifetime. Therefore, τ can be readily determined by the photo voltage decay (PVD) method once D and l are known. For ideal back-surface-field (BSF) cells (N+-P-P+ junctions) under the same circumstances the excess number density of carriers decays purely exponentially as exp(−t/τ). However most BSF solar cells are not ideal, possessing an effective surface recombination velocity seff of 100 to 1000 cm/sec at the high-low junction. Therefore, PVD measurements for BSF cells must be treated with caution and must be supplemented with other nonstationary methods recently developed. These facts are important for a determination of diffusion lengths since steady-state methods are notoriously unreliable when the cell thickness is smaller than the diffusion length. Finally a connection will be made with older work on the same subject.
Reassessment of space-charge and central-cell scattering contributions to GaAs electron mobility
Authors: Walukiewicz W. , Lagowski J. , Gatos H. C.
Published: February 2003

Theoretical values of electron mobilities as a function of temperature, calculated on the basis of a rigorous variational method, were found to be in agreement with values obtained experimentally on n-type GaAs. Scattering contributions considered in these calculations were from ionized impurities, optical and acoustic phonons, and piezoelectric scattering. The need in the past to invoke additional significant scattering contributions from short-range potential (e.g., space charge and central cells) was shown to be associated with the inaccurate nature of Mathiessen’s rule, which was used to obtain theoretical mobility values.
Space-charge-limited current effects in n-type CuInSe2/Au Schottky diodes
Authors: Yalcin N. , Al-Saffar I. S. , Tomlinson R. D.
Published: February 2003

Schottky diodes, fabricated by evaporating thin films of Au onto n-type single crystals of CuInSe2 have been shown to exhibit space-charge-limited current effects under foward bias. The observed characteristics are associated with the presence of a high-resistivity layer close to the metal contact.
Electromagnetic properties of thin-film transformer-coupled superconducting tunnel junctions
Authors: Finnegan T. F. , Lacquaniti V. , Vaglio R.
Published: February 2003

Multisection superconducting microstrip transformers with designed output impedances below 0.1 Ω have been fabricated via precise photolithographic techniques to investigate the electromagnetic properties of Nb-Nb oxide-Pb tunnel junctions. The low-impedance transformer sections incorporate a rf sputtered thin-film Ta-oxide dielectric, and the reproducible external coupling achievable with this type of geometry makes possible the systematic investigation of electromagnetic device parameters as a function of tunneling oxide thickness.
Evidence for dislocation damping coefficient increases during gamma ray irradiation of sodium chloride and potassium chloride single crystals
Authors: Bielig G. A.
Published: February 2003

Room-temperature radiation experiments have been carried out on deformed single crystals of ’’ultrapure’’ and nominally pure NaCl and KCl where it has been observed that the decrement may initially increase to some maximum value and then decreases with radiation time. In contrast, the compliance defect was always found to decrease as soon as the crystal was irradiated. If the radiation was stopped during an experiment the decrement kept on decreasing whereas the compliance defect remained essentially constant. Simpson and Sosin have observed a similar decrement maximum with copper foils vibrated at 500 Hz and exposed to 1.0-MeV electrons. Their defect-dragging model is examined in relation to the present work and it is concluded that the model cannot explain the results. The results are also compared with those of Anderson and Pollard who have carried out fast neutron irradiation experiments on NaCl and KCl crystals. It was found that the behavior of B/B0, the fractional change in the damping coefficient, is similar for both neutron and gamma ray experiments at least in the early stage of irradiation.
Compensation in Ge-doped p-type Ga1−xAlx As grown by liquid phase epitaxy
Authors: Swaminathan V. , Anthony P. J. , Zilko J. L. , Sturge M. D. , Schumaker N. E.
Published: February 2003

The effect of compensation on the pair spectra from Ge-doped p-type Ga0.60 Al0.40 As grown by liquid-phase epitaxy under high-purity He ambient is investigated. It is found that when the amount of compensation is high, pair transitions occur mainly via the deep GeAs acceptors at low excitation levels. The addition of oxygen (0.3–0.9 ppm) or H2 (11%) to the He ambient during growth reduces the compensation, with hydrogen found to be more effective than O2. For reduced compensation, pair transitions via the shallow acceptors due to residual C and Si are favored. The compensation is due to the presence of residual donors such as S whose concentration varies from wafer to wafer causing fluctuations in the relative intensities of pair transitions. Since strong pair transitions involving shallow acceptors reflect low concentration of compensating donors and thus improved conductivity in the p layers, the use of H2 in the He ambient gas during the growth of (GaAl)As double-heterolaser structures should be advantageous.
Intrinsic stress in thin films deposited on anisotropic substrates and its influence on the natural frequencies of piezoelectric resonators
Authors: Tiersten H. F. , Sinha B. K. , Meeker T. R.
Published: February 2003

A description of intrinsic stress in thin films deposited on anisotropic (piezoelectric) substrates is obtained from the rotationally invariant equations of nonlinear elasticity (and electroelasticity). The accompanying residual stress state in the substrate is, of course, included in the description, as is the residual stress state in the thin film. The equations for small dynamic fields superposed on the static (intrinsic plus residual) bias are obtained, and the equation for the perturbation in eigenfrequency of a piezoelectric resonator due to the intrinsic and residual stress state is presented. The static biasing equations for both extension and flexure of the plated crystal plate, which are required for the determination of the residual stress state from the intrinsic stress state, are obtained. The important case of a thin film deposited on one side of a plate substrate is treated in detail, and the relation of the flexural curvatures of the plated plate to the components of the intrinsic stress is found. The values of the intrinsic stress components in thin titanium–gold films deposited on one side of AT-cut quartz substrates are obtained from measurements of the curvatures in three independent directions.
Effect of donor impurities on the density of states near the band edge in silicon
Authors: Bennett Herbert S. , Lowney Jeremiah R.
Published: February 2003

Using the effective mass approximation and assuming that the scatteirng events for the electrons and holes by the assembly of donors are independent, we have calculated the effects of heavy doping on the conduction and valence states in silicon. When no bound-electron states asocated with donors exist, the results show that: (1) the electron-donor interaction lowers the energy of the conduction and valence states, (2) band distortions occur, and (3) approeciable band-gap narrowing occurs. Our numerical results tend to support the band-gap estimates interpreted from optical measurements.
Intervalley scattering in Ga1−xAlxAs alloys
Authors: Saxena Ashok K.
Published: February 2003

Hall mobility at 300 K in high-purity epitaxial layers of n-type Ga1−xAlxAs with electron concentrations in the range (5–10)×1015 cm−3 has been measured as a function of alloy compositions in the range 0⩽x⩽0.78 and as a function of hydrostatic pressure for various values of alloy compositions. The data show that nonequivalent intervalley scattering between the direct and various indirect minima play an important role in limiting the electron mobility in this alloy.
Dragging of domains by an electric current in ferromagnetic bulk cobalt at 4 K
Authors: Ramanan V. R. V. , Berger L.
Published: February 2003

The electrical resistivity of cobalt single crystals of high purity has been measured for current densities j up to 400 A/mm2, at 4.2 K. Large deviations from Ohm’s law are observed when j exceeds ≃12 A/mm2, in agreement with theoretical predictions. The electron gas in translation exerts hydromagnetic forces on the domain walls. The deviations from Ohm’s law happen when these forces are large enough to overcome the pinning forces and to set the walls in motion, in a direction parallel to the drift speed of the charge carriers. The dragging forces also tend to reorient the walls in a direction parallel to the current. Magnetic fields parallel to the current are used to minimize this reorientation.
Thermally stimulated currentmeasurements on the trapping levels in a Cu-phthalocyanine binder photoreceptor
Authors: Hoshino Yasushi
Published: February 2003

Thermally-stimulated current (TSC) is measured in a Cu-phthalocyanine binder photoreceptor. The Cu-phthalocyanine powder used has an ε-type crystal form. The binder is polyurethane. It is found that the measured TSC curves have peaks due to thermal liberation from the hole trapping levels and that the peak TSC temperature has an electric field dependence. The following results are obtained from an analysis of these TSC curves: (1) The origin of the trapping levels is the interface between Cu-phthalocyanine particles and the insulating binder. (2) The activation energy Ea of the hole trapping levels has an electric field dependence, Ea = 0.45−0.59×10−3E1/2 eV, where the unit of E is V/cm. This dependence is explained by the Poole-Frenkel theory.
The effects of water on oxide and interface trapped charge generation in thermal SiO2 films
Authors: Feigl F. J. , Young D. R. , DiMaria D. J. , Lai S. , Calise J.
Published: February 2003

Water was diffused into very dry thermal SiO2 films under conditions such that the penetration of water related electron trapping centers was of the order of the oxide thickness. In both dry oxides and water diffused oxides, production of negative bulk oxide charge Qot and positive interface charge Qit by an avalanche-injected electron flux was observed. The efficiencies of both processes were enhanced by water indiffusion. Analysis of the kinetics of charge generation indicated that production of trapped electron centers (Qot ) was required for subsequent production of interface states and charge (Qit ). Models for both processes are discussed. We suggest that inelastic collisions of conduction electrons with the trapped electron centers releases mobile hydrogen atoms or excitons. The mobile species migrate to the Si–SiO2 interface and form states and fixed charge.
Electron beam induced dissociation and conductivity of SnO2 films
Authors: Shapira Yoram
Published: February 2003

The effect of electron bombardment on rf-sputtered SnO2 films was studied using mass spectrometry, Auger electron spectroscopy, and conductivity measurements. The studies show that the electron beam causes surface dissociation and subsequent desorption of atomic oxygen. The dissociation is accompanied by corresponding increase of film conductivity, which persists in ultrahigh vacuum conditions and can eliminated by O2 introduction. A model of the correlated processes is suggested.
Correlation between Schottky barrier heights on compound semiconductors and metal and semiconductor electronegativities
Authors: Morgan D. V. , Frey Jeffrey
Published: February 2003

Examination of experimental results reveals a correlation between the free-surface band-bending and the value of the metal-semiconductor barrier extrapolated to zero electronegativity. Further, in materials with relatively high surface-state densities, the free-surface Fermi level Esf shows only a small variation for a range of semiconductors. It is proposed that this pinning is associated with the electronegativity of the anion. Formulas are presented for the prediction of barrier heights on a wide range of compound semiconductor alloys.
Hydrogen sensitive Schottky barriers in metal-copper phthalocyanine junctions and their photovoltaic effect
Authors: Yamamoto N. , Tonomura S. , Tsubomura H.
Published: February 2003

The photovoltaic and rectification properties of junctions of copper phthalocyanine (CuPc) with metals—Pd, Pt, Au, Cu, In, Al, and Mg—are investigated. Current-voltage characteristics are explained by the p-type nature of copper phthalocyanine that gives rise to a Schottky barrier, which changes with the metal work function. The action spectrum of the photovoltaic effect suggests that the light absorbed only in the space charge layer of CuPc near the interface effectively contributes to the carrier generation. It is concluded that the reversible influence of hydrogen on the current-voltage curve and the photovoltaic effect found for the Pd-CuPc junctions are due to changes in barrier height between Pd and CuPc resulting from changes in the work function of Pd.
Persistent photoconductivity in thin epitaxial GaAs
Authors: Farmer J. W. , Locker D. R.
Published: February 2003

We have studied persistent photoconductivity in thin epitaxial GaAs. The dependence of the persistent photoconductivity on photon dose was studied. At high fluences, a decay component was also observed. The temperature dependence of the persistence was determined. All the data are qualitatively well understood in terms of a macroscopic barrier model of persistent photoconductivity. At low photon fluences, excellent quantitative agreement between theory and data is obtained. At high fluences, the persistent photoconductivity is observed to approach a saturation value. The saturation is attributed to the barrier height reduction by the forward biasing effect of the separated charge. Eventually, the barrier height is reduced to the point that electrons spill over the barrier and prevent any further separation.
Electrical characteristics of TiN contacts to N silicon
Authors: Wittmer M. , Studer B. , Melchior H.
Published: February 2003

We have performed a detailed investigation of TiN contacts on n-type silicon. The barrier height was found to be 0.49±0.01 V and the contact resistivity on 0.001-Ω cm substrates below 10−4 Ω cm2. The TiN layers were produced by reactive sputtering. The resistivity of the layers depends on the partial pressure of N2 in the N2+Ar sputtering gas mixture. A minimum of 55 μΩ cm was obtained, which is below the resistivity of pure Ti films. Finally, we have developed two etching solutions which allow patterning of TiN layers using conventional photolithography techniques.
Refractive index decrease phenomena in SiO2–Ta2O5 waveguide films by CO2 laser irradiation
Authors: Terui Hiroshi , Kobayashi Morio
Published: February 2003

SiO2-Ta2O5 waveguide film exhibits a refractive index decrease up to 2% and a simultaneous film thickness increase proportional to the index decrease by CO2 laser irradiation. A partial restoration to the pre-irradiated state is observed by annealing in air at temperatures between 700 and 780 °C. The origin of the index decrease may be due to the density change with Ta2O5 crystallization. For application to the optical circuit design, the effective refractive indices of the index-decreased area are estimated, and a TE0-TE1 mode separation experiment by a 20°angle is done successfully, in order to examine the usefulness of the effective index.
Single mode laser with a V-shaped active layer grown by metalorganic chemical vapor deposition: A v-shaped double heterostructure laser
Authors: Mori Yoshifumi , Matsuda Osamu , Watanabe Naozo
Published: February 2003

A single-mode AlxGa1−xAs/GaAs laser of excellent performance was made by metalorganic chemical vapor deposition. The laser has a double heterostructure with a small V-shaped active region of a self-aligned junction stripe geometrically grown on a groove-etched substrate. The self-aligning process was based on a newly found anomalous zinc diffusion phenomenon. The minimum threshold current and the maximum differential quantum efficiency in continuous operation were 15 mA and 65% for a 250-μm-long device. The output power up to 40 mW was attained with an Si3N4 coated device. The beam shape from the laser was nearly circular with an aspect ratio less than 1.5.
Repetitive Q-switched operation of x-axis Nd:La2Be2O5
Authors: Tucker Armin W. , Birnbaum Milton , Fincher Curtis L.
Published: February 2003

The performance of an x-axis neodymium-doped lanthanum beryllate laser (Nd:BeL) was compared to that of Nd:YAG operating as repetitively Q-switched lasers. At 1 Hz, the Q-switched outputs of Nd:BeL were twice that of Nd:YAG in rough agreement with their respective stimulated emission cross sections; however, at 10 Hz, the output with Nd:YAG was essentially constant while that of Nd:BeL fell appreciably. Analysis showed that this could be attributed to thermal lensing in Nd:BeL.
A consistency condition for microwave absorption in an air plasma
Authors: Hastings D. E.
Published: February 2003

A consistency condition for microwave maintenance of an air-plasma breakdown wave is derived and discussed for a specific case of f = 92 GHz.
Least-squares autoregressive (maximum entropy) spectral estimation for Fourier spectroscopy and its application to the electron cyclotron emission from plasma
Authors: Iwama N. , Inoue A. , Tsukishima T. , Sato M. , Kawahata K. , Sakai K.
Published: February 2003

A new procedure for the maximum entropy spectral estimation is studied for the purpose of data processing in Fourier transform spectroscopy. The fitting of the autoregressive model to the interferogram is examined under a least-squares criterion based on the Yule-Walker equations. A practical criterion is suggested for selecting the model order. The principal advantage of the new procedure lies in the enhanced frequency resolution, particularly for small values of the maximum optical path difference of the interferogram. The usefulness of the procedure is ascertained by some numerical simulations and further by experiments with respect to a highly coherent submillimeter wave and the electron cyclotron emission from a stellarator plasma.
Voltage-current relationship for pulsed arc discharges
Authors: Walsh Peter J. , Lama William , Hammond Thomas J.
Published: February 2003

A theoretical treatment of the electrical behavior of pulsed discharges in gas-filled flashlamps is presented. The theory is based on a simple model of the plasma and a balance of electrical power input and radiation output. It is assumed that the plasma radiates as a greybody with an emissivity that depends on the electron density. The principal result is an analytic expression for the arc voltage as a function of current, with initial voltage, arc length and diameter, and atom density as parameters. The expression describes the entire voltage pulse, including the initial fall, the following minimum and the peak when the current peaks. The predicted voltages substantially agree with measurements, including dependences on lamp length and diameter and initial voltage. The theory is an improvement on the empirical V-I relation commonly used in flashlamp circuit analyses.
Transmission electron microscopy investigation of silicide formation on slightly oxidized silicon substrates
Authors: Föll H. , Ho P. S.
Published: February 2003

The formation of PtSi and Pd2Si on chemically cleaned and on slightly oxidized Si substrates had been investigated by TEM with cross-sectional specimens. The oxide has been found to influence the silicide-Si interface roughness, the silicide surface roughness,and the corrosion behavior of the silicide layer. The formation of PtSi is more sensitive to the presence of oxide than Pd2Si and may even be suppressed. Remnants of the oxide are identified within the silicide using Auger sputter profiling technique. They can be interpreted as diffusing markers and provide information about the diffusing atomic species. Results of such marker experiments for formation of Pd2Si and PtSi are disussed.
A comparison of melting point relations for metals, tetrahedral semiconductors, and metal carbides and nitrides with the rocksalt structure
Authors: Van Uitert L. G.
Published: February 2003

Melting point and bond length are employed to compare cohesive energy relations for metals, tetrahedral semiconductors, and carbides and nitrides that have the rocksalt structure. Cohesion largely is due to electron transfer in each case. However, the values for each of the three series deviate from a simple exchange relation in a different way. The deviation can be associated with semicovalent bonding in metals, electron spin-pair bond delocalization in the semiconductors, and isolated C or N atoms in octahedral sites effecting an increase in the energy between first and second subset metal d states in the carbides and nitrides.
The effect of thermal annealing on the grain size and electrical characteristics of arsenic ion-implanted and laser-irradiated polycrystalline silicon films
Authors: Shibata Kenji , Onga Shinji
Published: February 2003

Q-switched Nd: YAG laser irradiation and subsequent thermal annealing are carried out for arsenic ion-implanted polycrystalline silicon films. Crystallographical and electrical characteristics of polycrystalline silicon are studied by using transmission electron microscopy and Hall measurements. Almost all implanted arsenic ions are electrically activated on laser irradiation, but grain growth and crystalline recovery are not found. The crystalline recovery begins to occur and carrier mobility increases during subsequent thermal annealing at temperatures of 500 °C and higher. The carrier concentration decreases due to the inactivation of the arsenic atoms with subsequent thermal annealing in the temperature range between 500 and 750 °C. At temperatures above 750 °C, grain growth and defect annihilation take place, and the carrier concentration per cm2 increases due to the diffusion and reactivation of arsenic atoms.
Magnetostriction of bulk Fe-C alloys deposited by high-rate sputter
Authors: Kazama N. S. , Fujimori H.
Published: February 2003

Bulk Fe100−xCx alloys (10?x?20, 1 mm thick and 30 mm diameter) were prepared by dc-sputter deposition. Neutron diffraction analyses were carried out on these samples. The alloy with x = 20 was found to be amorphous while other samples showed a certain degree of crystallization which increased with decreasing carbon content. However the crystallization temperatures of these alloys were almost the same as that of the amorphous Fe80C20 alloy (Tx∼573 K). Magnetostriction measurements have also been made, and the amorphous alloy exhibited large magnetostriction (λs = +30×10−6 at room temperature) which increased with decreasing temperature, as reported for melt quenched and sputter deposited amorphous alloys of Fe with other group IV elements. The observed large positive magnetostriction decreased rapidly with decreasing carbon content and appeared to be going to the value of polycrystalline α-Fe with small negative magnetostriction through the zero magnetostriction.
Ferromagnetic surface layer in amorphous YFe thin films
Authors: Bhagat S. M. , Lloyd J. N.
Published: February 2003

Previous FMR measurements demonstrating the presence of a thin ferromagnetic layer on a-Y1−xFex samples have been extended to a series of evaporated films with x between 50% and 85%. In most cases the thicknesses (t) were varied by a factor of 10 or more during a single evaporation. In all of these films we observe an FMR line, with 4πM increasing with x. Furthermore, as expected from a surface layer, for fixed x the line intensity is essentially independent of t. The temperature dependences of the line width (Γ) and 4πM were studied from about 1K to 300K. Both Γ(T) and 4πM(T) exhibit maximum at about 50 to 70 K. Above 100K, M(T) reduces as T3/2 and yields a spin wave stiffness of about 100 meV Å2 varying only slightly with x. We suggest that the maxima be ascribed to coupling between the ’’stiffness’’ spins and those in the bulk of the film.
Magnetic studies on metallic glass type films
Authors: Rivoire M. , Krishnan R. , Rougier P. , Sztern J. , Sella C.
Published: February 2003

Thin films were sputter deposited from a Metglass 2826 MB ribbon target. Magnetization was in the range 5400–6300 G, lower than that of the target. FMR spectra samples were complex but could be understood in terms of the ion probe profile analysis. For instance, one sample showed a spin wavee (SW) spectrum yielding D = 117 meV A2 a value close to that of the target. Acid etching of another enabled us to correlate the two regions in the FMR spectrum; one with multiple modes and the other with SW modes. The latter arises from the region of the film closer to the substrate and taking the above D value yielded its thickness as 2200 Å. This closely agreed with the ion probe analysis. The films had a strong in plane anisotropy of ∼105 erg⋅cm−3, induced by stresses. Finally, the resonance line widths were as low as 60 Oe and Hc∼5 Oe.
Effect of hydrogen on the magnetoelastic behavior of amorphous transitional metal-metalloid alloys
Authors: Berry B. S. , Pritchet W. C.
Published: February 2003

Internal friction and ΔE-effect measurements have been made on Metglass 2826 and other ferromagnetic metallic glasses, electrolytically charged with hydrogen. Initially, the ΔE-effect and magnetoelastic damping are strongly suppressed. The internal friction is dominated by a peak attributed to the stress-induced reorientation of interstitial hydrogen atoms, with a mean activation energy of 0.5 eV. Various aging effects occur after charging. Recovery of charge-induced bending is followed by a slower decline of the reorientation peak, a recovery of the ΔE-effect, and an accompanying transient appearance of a magnetoelastic internal friction peak. The observed behavior indicates a strong interaction of hydrogen with domain walls, and leads to the prediction, confirmed experimentally, that hydrogen degrades the soft magnetic behavior of these alloys.
Annealing effects on the magnetism of FexPd82−xSi18 metallic glasses
Authors: Dublon Giora
Published: February 2003

Fe9Pd73Si18 and Fe10Pd72Si18 metallic glasses were annealed isothermally below their crystallization temperature and magnetization measurements were made as a function of annealing time. The results suggest changes in the topological short-range order due to structural relaxation such that both the Fe-Fe coordination number in magnetic clusters and long-range magnetization fluctuations increase. In Fe9Pd73Si18 the cluster size decreases while in Fe10Pd72Si18 it seems to increase. It appears that without reaching equilibrium in a glassy state, structural relaxation is eventually accompanied by gradual crystallization. Its onset, as revealed by magnetization measurements, preceeds its detection by large-angle x-ray diffraction.
Studies of chemical homogeneity and magnetic domain walls in Fe-based metallic glasses using small-angle neutron scattering
Authors: Fish G. E. , Child H. R.
Published: February 2003

Metallic glasses Fe77B23, Fe82B18, and Fe81B13.5Si5.5 have been studied as a function of applied field and annealing condition using small-angle neutron scattering (SANS). The data were taken at 300 K for momentum transfer q = 4πsinϑ/λ in the range 0.05–0.3 nm−1. In zero field, all the samples produced similar patterns with intense isotropic SANS for q<0.1 nm−1 which could be fitted with Guinier radii RG∼40 nm. This SANS decreased rapidly in intensity with applied field. The change in SANS on annealing correlated directly with changes in bulk coercivity Hc and domain wall density seen in electron microscopy: For stress-relieved Fe82B18 and Fe81B13.5Si5.5, SANS and Hc decreased slightly, but they increased substantially in Fe77B23 after annealing. This scattering arises primarily from domain walls in accord with dynamical theory. The weak SANS for 0.1<q<0.3 nm−1 suggest that the phase separation and chemical inhomogeneity in these glasses, both as-cast and annealed, are limited.
Electrical resistance and crystallization characteristics of Fe80B20
Authors: Baibich M. N. , Muir W. B. , Van Wyck D. R.
Published: February 2003

The electrical resistance of amorphous Fe80B20 has been measured as a function of time at various temperatures during an isothermal crystallization process. The results fit a universal curve when ΔR/ΔRI is plotted against t/tI. The value of tI as a function of annealing temperature fits the Johnson-Mehl-Avrami equation with n = 3 changing to 1.4 for t/tI≳1.4.  The resistance of a series of partially crystallized samples was measured between 4.2 and 300 K. dR/dT at 300 K and dR/dlogT below the resistance minimum were both found to be linear funtions of ΔR/ΔRI. That is, both the above quantities were found to be strictly proportional to the amount of crystalline phase present. This may pose some difficulty for the structural tunneling model of the low temperature resistance minimum in metallic glasses.
The crystallization kinetics of amorphous Co78−xFexSi8B14 ribbons
Authors: Kuo Y. C. , Zhang L. S. , Zhang W. K.
Published: February 2003

We have studied the crystallization kinetics of amorphous Co78−xFexSi8B14 ribbons (x = 5, 10, 20, 30, 40, at.%) by using the resistivity monitoring method in the higher temperature region and also by using the method of differential thermal analysis (DTA). From 300 K to 1000 K, the φ-T curves of the amorphous alloys with different x are all of the same shape with dφ/dT≳0 before the crystallization starts and an abrupt drop, Δφ, during the crystallization process. The crystallization temperature Tcr lies between 750 K and 830 K and Δφ lies between 29 and 34 μΩ-cm. Experiments also show that after crystallization, the coercive force of these alloys increases conspicuously, some as high as 100–200 Oe. The DTA curves have two prominent exothermic peaks between 720–830 K. During the crystallization process, the curves display two distinct stages, showing that there are two crystallographic phases precipitated. In the vicinity of the temperature of crystallization, we also measured the isothermal variation of resistivity with time of the ribbon Co58Fe20Si8B14. From the annealing curves and Arrhenius relation, the activation energy was estimated to be 80 kcal/mole.
Origin of losses in 2.54 cm wide Metglas Alloy 2605 SC (invited)
Authors: Washko S. D. , Osborn M. L. , Veeraraghaven W. G.
Published: February 2003

The origin of losses during A.C. excitation of Allied Chemicals’ Metglas Alloy R 2605 SC was investigated. Core loss measurements were made at 0.5, 1.0, and 1.5T in the frequency range 0–400Hz. D.C. hysteresis losses were also measured at the same inductions. Magnetic domain structures were observed over the same frequency and induction ranges using the longitudinal Kerr effect technique. Domain spacings were found to be dependent on frequency and induction and approached an equilibrium value for a given frequency when the strip was demagnetized from saturation. Calculated losses, using the equilibrium domain spacing and measured D.C. hysteresis losses, account for 70–90% of the total core loss. The D.C. hysteresis losses alone account for 50–80% of the total losses. The origin of the remaining losses is discussed.