bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical absorption below the absorption edge in Hg1−xCdxTe
Authors: Mroczkowski J. A. , Nelson D. A.
Published: February 2003

The optical absorption below the absorption edge in x=0.2 and x=0.3 Hg1−xCdxTe alloys has been investigated. In p-type alloys of both compositions and at wavelengths equivalent to approximately 0.75 Eg to 20 μm, the measured optical absorption cross sections at 90 K were close to the intervalence cross sections calculated using first-order Kane k⋅p theory with a bandstructure parameter P of 8.4×10−8 eV cm and a heavy hole mass of 0.5 m. For Hg0.8Cd0.2Te the absorption cross sections were close to 1.8×10−15 cm2 for wavelengths between 15 and 20 μm. For Hg0.7Cd0.3Te , the absorption cross sections increased from approximately 1×10−15 cm2 at 5 μm to about 3×10−15 cm2 at 20 μm. At higher temperatures the intervalence absorption cross sections decreased; in addition, an intraband contribution to the total hole absorption cross section was observed.
Behavior of Cs+-UF−6 ion-pair plasmas in radiofrequency quadrupole-dipole fields. I. Experiment
Authors: Wexler S. , Parks E. K. , Young C. E. , Bennett R. A.
Published: February 2003

The behavior of a flowing Cs+-UF−6 ion-pair plasma in the radiofrequency (rf) quadrupole-dipole fields of a mass filter has been studied experimentally. The flowing plasma was formed by collision of a beam of accelerated UF6 molecules with an intense beam of thermal Cs atoms. The maximum current (positive- or negative-ion flux) entering the mass filter was 0.5×10−3 A, corresponding to a positive- or negative-ion density in the injection region of ∼1.1×1010 ions/cm3. Four aspects of the interaction of the plasma with the radiofrequency fields were investigated: (1) the injection of the ion-pair plasma into the quadrupole-dipole field, (2) confinement by and transmission of the flowing plasma through a quadrupole field, (3) mass-sensitive ejection of ions from the plasma by superimposed quadrupole and dipole fields, and (4) effects of the extraction and exit fringe fields on the flowing plasma. In particular, the effects of increasing plasma density in relation to the above topics was experimentally determined. The results of the experimental observations in conjunction with the theoretical calculations discussed in the following paper suggest that the limiting-ion flux that can be confined within a quadrupole mass filter is determined by the requirement that the plasma frequency νp must be lower than or at most equal to the applied rf quadrupole frequency ν1. If νp >ν1, the rf field causes rapid destruction of the plasma. The mass-resolving power of the mass filter was found to deteriorate significantly with increasing plasma throughput, a result of the increasing space-charge forces within the plasma and their interaction with the applied dipole field.
Limitation to the accuracy of interferometrically measured electron density profiles of laser-produced plasmas
Authors: Burgess M. D. J. , Gillman G. B. , Luther-Davies B.
Published: February 2003

Using a double pulse ultraviolet holographic interferometer we have investigated the effects of interferometer focusing accuracy on the measured density profiles in an experimental study of plasmas generated by 20-ps duration Neodymium laser pulses on carbon fiber targets. We have found that in accordance with predictions made previously using computer models the critical density region can only be measured accurately in very small spherical plasmas when the interferometer focusing error is less than about 5 μm.
Effect of ion-beam damage on x-ray diffraction and Raman spectra of amorphous GeSe2
Authors: Marcus M. , Dynes R. C. , Griffiths J. E. , McWhan D.
Published: February 2003

Raman and x-ray measurements were done on amorphous GeSe2 films before and after damage with 1017α+cm2. The first diffraction peak got smaller and shifted to higher wave vectors. The Raman spectrum did not change. The order seen as the first sharp diffraction peak may not be that manifested by the ‘‘companion’’ Raman line.
Effect of Al electrodes on dc and ac current-voltage characteristics of chalcogenide glass films
Authors: Takeda Toshio , Nogami Gyoichi
Published: February 2003

dc current-voltage (I-V) characteristics and ac switching phenomena have been investigated in amorphous semiconductor films of Si12Te48As30Ge10 (STAG) sandwiched between evaporated electrodes of Al and Au on an insulating glass substrate. The results show that Al and Au do not form rectifying contacts to STAG. When oxidized Al is used as an electrode an anomaly is observed in both dc and ac charateristics.
Enhancement of permeability in ferrite toroids subjected to rotating magnetic fields
Authors: Zini G. , Ronconi F. , Masoli F. , Buttino G.
Published: February 2003

This paper reports the effects of test field parameters on the measurements of complex permeability in flat ferrite toroids, carried out by the ac bridge method during the rotation of a dc magnetic field, applied in the toroid plane. Under such conditions the permeability is generally higher than when measured with the dc field in a fixed direction and it can be controlled by a proper choice of the test and rotating magnetic fields. The enhancement has been interpreted as due mostly to a direct influence of the test field upon the irreversible wall displacements produced by the rotating field.
Rutherford backscattering evidence for solid phase laser annealing of Corning 7059 glass and ZnO thin films
Authors: Dutta Subhadra , Jackson Howard E. , Boyd J. T. , White C. W.
Published: February 2003

Rutherford backscattering measurements have been made on ZnO and Corning 7059 glass optical waveguides before and after laser annealing to investigate whether melting is associated with the dramatic improvement in scattering loss which occurs after laser annealing. These measurements indicate that no redistribution of impurities takes place during annealing. We conclude that no melting occurs and that the annealing occurs in the solid phase.
Comment on ‘‘X-ray photoelectron spectroscopic studies of oxygen chemisorption on thick films of photoconducting cadmium sulfide’’
Authors: Lichtensteiger M. , Webb C.
Published: February 2003

A recent paper by Amalnerkar, et al. on x-ray photoelectron spectroscopic studies of oxygen chemisorption on thick films of photoconducting cadmium sulfide, is compared and contrasted with literature data and earlier studies by ourselves. We find that the interpretation of the XP S(2p) features by Amalnerkar et al. cannot be correct. The source of confusion is identified as originating from indeterminate stray AlKα radiation.
Thickness of GaP liquid phase epitaxial layers grown by step-cooling, equilibrium-cooling, and ramp-cooling methods
Authors: Kao Y. C. , Eknoyan O.
Published: February 2003

Using three different cooling processes, a series of liquid phase epitaxial growth experiments for GaP are performed to determine layer thickness, d, as a function of growth time, t, and amount of supercooling temperature, Δ. Comparison is made with layer thickness predictions that are derived from a diffusion-controlled model. Good agreement is obtained for growth times, t, less than the diffusion time, τ, of solute in the melt. The results indicate that, in addition to GaAs and InP, the diffusion-controlled model generally provides good predictions for liquid phase epitaxial grown GaP layers thickness as well.
Quantitative analysis of fiber texture in cubic films
Authors: Rao Satish , Houska C. R.
Published: February 2003

The method of Roe and Krigbaum for determining fiber texture has been extended to thin film applications. It is often desirable to make in situ pole density measurements of a film on a thick substrate. This does not permit complete data to be collected by x-ray transmission techniques. If the data are restricted to the range 0≤χ≤75°, obtained by reflection, incomplete pole density plots are obtained, and it is necessary to devise a self-consistent extrapolation technique that extends the pole density data to 90°. This requires least-squares fitting over the range from χ=0 to 75° and an iterative procedure for extrapolating with functions consistent with a single orientation function. The example of a 1.14-μ Mo film on a (111) Si substrate requires an expansion of the symmetry relations to order 46. The procedure established herein is readily extended to include the effect of static displacements resulting from embedded gas atoms that are associated with sputtered films.
Determination of band-gap parameters of Hg1−xCdxTe based on high-temperature carrier concentration
Authors: Finkman E.
Published: February 2003

The temperature dependence of the carrier concentration of Hg1−xCdx Te at elevated temperatures is used to determine its band parameters near the bandedge. The electron concentration is calculated by using the Kane model (k⋅p method), and is fit to observed values derived from measurements of the Hall coefficient in the near-intrinsic region. This procedure results in expressions for the following parameters: the band-gap Eg and its dependence on temperature and composition; Kane’s interband-coupling matrix element and the heavy-hole effective mass ratio. Modified values of the intrinsic carrier concentration are calculated using these parameters.
Theory of silicon superlattices: Electronic structure and enhanced mobility
Authors: Moriarty John A. , Krishnamurthy Srinivasan
Published: February 2003

A realistic tight-binding band-structure model of silicon superlattices is formulated and used to study systems of potential applied interest, including periodic layered Si-Si1−xGex heterostructures. The results suggest a possible new mechanism for achieving enhanced transverse carrier mobility in such structures: reduced transverse conductivity effective masses associated with the superlattice band structure. For electrons in [100]-oriented superlattices, a reduced conductivity mass arises intrinsically from the lower symmetry of the superlattice and its unique effect on the indirect bulk silicon band gap. An order of magnitude estimate of the range of mobility enhancement expected from ths mechanism appears to be consistent with preliminary experimental results on Si-Si1−xGex superlattices.
A model of conduction in inhomogeneous degenerate semiconductors: Application to silicon-on-sapphire films
Authors: Robert J. L. , Dusseau J. M. , Girard P. , Sicart J.
Published: February 2003

The electrical properties of silicon-on-sapphire films were investigated between 4.2 and 300 K. The experimental results can be explained by considering the conduction process exclusively in the transition layer of the Si-Al2O3 interface. The properties of silicon-on-sapphire are interpreted in this study by means of a model in which long range fluctuations in potential occur, caused by the existence of inhomogeneities or local defects in the films.
Electron trapping in thin films of thermal SiO2 at temperatures between 30 and 300 K
Authors: Itsumi Manabu
Published: February 2003

Temperature dependence of electron trapping in thermally grown SiO2 has been studied using metal–silicon dioxide–silicon (MOS) structures. The MOS samples are charged using avalanche injection from the Si substrate at temperatures between 30 and 300 K. It is found that the rate of electron trapping increases monotonically as temperature decreases from 300 to 30 K for both oxides subjected to H2/N2 annealing and oxides subjected to no H2/N2 annealing. The majority of electrons trapped at 77 K is thermally reemitted, as the samples are warmed to room temperature. Analyses of the experimental results indicate that neutral trap centers responsible for electron trapping are characterized by the two discrete energies of 23 and 4 meV below the conduction band edge of SiO2.
A flux analysis of the current–voltage characteristics of thin film frontwall illuminated and backwall illuminated liquid junction and metal junction solar cells
Authors: Hinckley S. , McCann J. F. , Haneman D.
Published: February 2003

The flux method was used to derive analytical expressions for the photocurrent–voltage characteristics of thin film frontwall and backwall illuminated liquid junction solar cells as functions of film thickness. Expressions for these types of cells were derived without assuming the depletion layer was a minority carrier sink but with inclusion of the effects of depletion and bulk recombination, reflection, and restricted transmission at the semiconductor junction and reflection at the back contact. The effects of film thickness, donor concentration, and of partial reflection and imperfect transmission at the depletion layer/bulk layer boundary are examined. The results from this flux method are qualitatively similar to those obtained previously from different starting equations in the cases where both treatments are applicable, lending support to both approaches. In particular, the short circuit current is shown to be significantly reduced by depletion layer recombination, and by slow charge transfer when depletion layer recombination is not negligible.
Deposition and properties of zinc phosphide films
Authors: Chu T. L. , Chu Shirley S. , Murthy K. , Stokes E. D. , Russell P. E.
Published: February 2003

Thin films of zinc phosphide have been deposited on tungsten-coated steel substrates at 400–600 °C by the reaction of zinc and phosphine in a hydrogen atmosphere; tungsten was used as a barrier against the diffusion of iron from the substrate into zinc phosphide. By using a proper PH3/Zn molar ratio, the deposited films have been identified by electron microprobe and x-ray diffraction techniques to be Zn3P2. The electrical resistivity and photovoltage of unintentionally doped zinc phosphide films were measured as a function of the composition of the reaction mixture. The effective intragrain minority carrier diffusion length in nearly stoichiometric films was measured by the scanned beam method using a Schottky barrier structure. The incorporation of dopants into zinc phosphide films was also explored.
Electron density of the two-dimensional electron gas in modulation doped layers
Authors: Lee Kwyro , Shur Michael , Drummond Timothy J. , Morkoç Hadis
Published: February 2003

The electron density of the two-dimensional electron gas in modulation doped structures is calculated as a function of the doping density in (Al,Ga)As, the thickness of the undoped (Al,Ga)As layer, the lattice temperature, and other device parameters. The results of the calculation show that the depletion approximation is not accurate enough and that the Fermi–Dirac statistics (rather than the Boltzmann statistics) should be used in the calculation. A simple analytical model which takes these factors into account is shown to be in good agreement with our computer calculations and experimental data. The obtained results may be used to evaluate the maximum intrinsic transconductance and the maximum gate voltage swing for the modulation doped field effect transistors.
X-ray diffraction data from the high pressure phase of AlSb
Authors: Baublitz M. , Ruoff A. L.
Published: February 2003

Powder diffraction data from a high pressure phase of AlSb have been obtained using the energy dispersive diffraction technique with synchrotron radiation from the Cornell High Energy Synchrotron Source. The diffraction pattern of the high pressure phase of AlSb has been indexed with an orthorhombic unit cell.
Modification of the transient capacitance analysis of GaAs MIS structures for minority carrier lifetime determination
Authors: Bhattacharyya A. B. , Lakshmi E.
Published: February 2003

The insulators of GaAs MIS structures, because of their low temperature deposition, have relatively low resistivities compared to SiO2. This is responsible for finite leakage through the insulator when a voltage is applied across the MIS structure. The present work reports on the implications of leakage on the transient capacitance plot which is widely used for the determination of minority carrier lifetime in semiconductors.
Computer simulation of the self-sputtering of uranium
Authors: Robinson Mark T.
Published: February 2003

The sputtering of polycrystalline α-uranium by uranium ions of energies below 10 keV has been studied in the binary collision approximation using the computer simulation program marlowe. Satisfactory agreement of the computed sputtering yields with the small amount of available experimental data was achieved using the Molière interatomic potential, a semilocal inelastic loss function, and a planar surface binding barrier, all with conventional parameters. The model is used to discuss low energy sputtering processes and the energy and angular distributions of the reflected primaries and the sputtered target particles.
Determination of the oscillator strengths of the 6D→61P1 atomic energy mercury transitions
Authors: van de Weijer P. , Cremers R. M. M.
Published: February 2003

The magnitude of the oscillator strengths ( f  values) of the 6D→61P1 transitions of atomic mercury is of interest, e.g., for the determination of the 61P1 mercury density in gas discharges by optical methods. However, contradictory results for these f values have been reported in the literature. Using the accurately known radiative lifetime of the 73S1 level as a starting point, we performed combined emission and hook measurements. As a result we found f=0.28±0.04 and f=0.25±0.05 for the 577.0 nm (63D2→61P1) and 579.1 nm (61D2→61P1) line, respectively.
Specific heats of Lu6Mn23, Gd6Mn23, Dy6Mn23, and Er6Mn23 from 1.7–18 K
Authors: Graves Tompson R. J. , White H. W. , Hardman K. , James W. J.
Published: February 2003

Specific heat results are reported for the intermetallic rare earth compounds Lu6Mn23, Gd6Mn23, Dy6Mn23, and Er6Mn23 in the temperature range 1.7–18 K. No evidence was found which indicated changes in magnetic spin structure for Gd6Mn23 and Dy6Mn23. The origin of a broad bump in the region from 2–8 K for Er6Mn23 is not understood. The specific heat of the diamagnetic compound Lu6Mn23 was well described by the expression, C=γT+αT3+δT5, where γ=0.277±0.005 and δ=0.00285±0.00005 when C is in units of J/mol K. From the value of α, θD was calculated to be 270±2 K.
Comments on ‘‘Carrier recombination through shallow donor/acceptor levels in heavily doped silicon’’
Authors: Tyagi M. S.
Published: February 2003

Carrier recombination through shallow donor/acceptor levels in heavily doped silicon is analyzed. It is found that the Shockley, Read, and Hall theory of recombination is unable to explain the sharp decrease in lifetime with increasing dopant concentrations. However, trap assisted Auger recombination through these levels satisfactorily explains the observed lifetimes as well as their temperature dependences.
Incomplete space-charge layers in semiconductors
Authors: Redfield David
Published: February 2003

Analysis of the potential and field profiles in space-charge layers near semiconductor interfaces is extended to consider cases in which the thickness of the semiconductor layer is less than the conventional ‘‘width’’ of the space-charge region that would exist if the semiconductor were very thick. It is shown that both electrostatic effects and possible Fermi-level changes are important in these cases. The apparent deficiency of charge that such thin layers present is found to be illusory; adequate charge is always available. However, the process which provides this charge may alter the work function of the semiconductor and therefore change the potential distribution.
The magnetic anisotropy of an aligned MnAlC magnet
Authors: Ram U. S. , Gaunt P.
Published: February 2003

The magnetic anisotropy constants K1 and K2 have been measured for an aligned MnAlC magnet. The information is extracted from magnetization curves with the magnetic field parallel and perpendicular to the alignment axis. The anisotropy field HA =2(K1+2K2)/IS (IS is the saturation magnetization) was determined from a break point in a plot of the perpendicular magnetization against the inverse square of the field. K1 and K2 were then found from modified Sucksmith–Thomson plots. The data is used to calculate the 180° wall energies and widths and an estimate of the temperature coefficient of coercive field variation is made and compared with experiment.
High resolution imaging of the interfacial region in metal-insulator-semiconductor and Schottky diodes
Authors: Green Martin A. , Blakers Andrew W. , Krivanek Ondrej L.
Published: February 2003

Interfacial oxides can greatly influence the properties of metal-semiconductor heterojunctions as demonstrated by recent work on metal-insulator-semiconductor solar cells. The physical structure of such interfacial regions is examined using High Resolution Electron Microscopy. Simultaneous imaging of the lattice structure on both sides of the interfacial region is reported for the first time.
Spectrum studies on a GaAs-AlGaAs multi-quantum-well laser diode grown by molecular beam epitaxy
Authors: Iwamura Hidetoshi , Saku Tadashi , Kobayashi Hideki , Horikoshi Yoshiji
Published: February 2003

Spontaneous and stimulated emission spectrum and the different characteristics between TE and TM polarizations were investigated on a GaAs–AlGaAs multi-quantum-well (MQW) laser diode grown by molecular beam epitaxy. The MQW laser lases at 38 meV below the photoluminescence peak energy corresponding to the lowest confined electron to heavy hole recombination energy E1h, calculated using the Kronig–Penney model. However, this energy separation cannot be interpreted in terms of the LO-phonon assisted recombination which is usually accepted. The LO-phonon assisted recombination model can be ruled out by comparing the spontaneous emission and the stimulated emission for various injection current levels. The emission energy of the TE polarization was lower than that of the TM polarization. The intensity of the TE is much larger than the TM polarization. These differences can be interpreted in terms of the selection rule for the dipole recombination between confined electron to heavy hole and electron to light hole bands.
Spin coated amorphous chalcogenide films: Structural characterization
Authors: Chern G. C. , Lauks I.
Published: February 2003

Thin films that are substantially amorphous arsenic sulfide have been prepared by spin deposition from solutions of n-propylamine or n-butylamine. These materials have been investigated by nuclear magnetic resonance, infrared absorption, and elemental analysis. A structural model is suggested based on As2S3 clusters surrounded by amine as an amine salt.
Oxidation kinetics of laser formed MoSi2 on polycrystalline silicon
Authors: Wakita A. S. , Sigmon T. W. , Gibbons J. F.
Published: February 2003

Thin films of laser formed MoSi2 on polycrystalline silicon were oxidized in either dry or wet O2. These films were oxidized in dry O2 at temperatures of 808–1104 °C for times that ranged from 0.5–42 h, and in wet O2 at 800° to 1000 °C for 0.5–2 h. For both oxidation conditions, the growth of SiO2 on the silicide surface is parabolic with time. Activation energies for the dry and wet processes have been measured to be 1.6 and 1.3 eV, respectively. As the oxidation proceeds and the underlying silicon decreases in thickness, the phase remains as MoSi2. However, upon complete consumption of the underlying silicon, the MoSi2 phase transforms to Mo3Si.
Thermal oxidation of niobium silicide thin films
Authors: Chow T. P. , Hamzeh K. , Steckl A. J.
Published: February 2003

Thermal oxidation of niobium silicide thin films on oxidized silicon substrates has been investigated. The silicide films were rf sputtered from a hot-pressed alloy target of stoichiometric composition (Si/Nb∼2) onto heated (350 °C) substrates. Oxidation was carried out in dry and wet oxygen between 550 and 850 °C. From Rutherford Backscattering Spectroscopy (RBS) measurements, it was determined that the oxide films exhibited the same Si/Nb ratio as the initial silicide layer. While only Nb2O5 has been cleary identified, density considerations and experimental values of oxide thickness suggest that niobium and silicon oxides coexist. The composition of the remaining silicide layer did not change significantly during oxidation. The oxide growth was found to follow a (tox)nα (time) relationship, with n∼1.1 for dry oxygen and 1.4 for wet oxygen. Activation energies of 1.9 and 1.6 eV were determined for the dry and wet oxidation processes.
The limits of solar photochemical conversion and its dependence on climate
Authors: Amato U. , Cuomo V. , Macchiato M.
Published: February 2003

The limits of the yield of photochemical conversion have always been analyzed in standard atmospheric conditions. In this paper we discuss their dependence on climate. We analyze conversion efficiency both in clear and in cloudy sky conditions and we take into account the seasonal trend of absorbing and scattering gases in the atmosphere at various latitudes. We discuss how the maximum value of conversion efficiency and the correspondent threshold wavelength depend on climate. We introduce a general method which allows one to calculate long-term efficiency of photochemical devices in a simple way.
Microstructure, electrical properties, and failure prediction in low clamping voltage zinc oxide varistors
Authors: Bowen Leslie J. , Avella Frank J.
Published: February 2003

Preparation and properties are described for ZnO varistors which clamp at sufficiently low voltages (≊10 V) for overvoltage protection of integrated circuits. The desired electrical characteristics have been obtained by microstructure control using alumina as a ZnO grain growth enhancer. Pulse degradation studies on these low voltage varistor compositions suggest that degradation occurs by premature failure of weak depletion layers and excessive current concentration at microstructural flaws. Capacitance–voltage measurements can be employed to detect these artifacts and predict the possibility of varistor failure during high current surges. A nondestructive scheme for varistor evaluation is outlined which utilizes the rate of change of capacitance and dissipation factor with dc bias voltage both above and below the varistor breakdown voltage.
Analysis of nonexponential transient capacitance in silicon diodes heavily doped with platinum
Authors: Phillips Willie E. , Lowney Jeremiah R.
Published: February 2003

An analysis having improved rigor has been made of the capacitance transient due to thermal emission from charged defect centers in a semiconductor depletion region. This analysis extends the range of applicability of capacitance–transient defect characterization techniques to nonexponential transient conditions which occur in diodes with trap densities of the same order as the net shallow dopant density or in diodes with somewhat smaller trap densities when defect centers are charged initially in only a part of the depletion region. An example of the improvement is shown for three silicon diodes heavily doped with platinum.
Theory of heterostructure inversion-mode metal-insulator-semiconductor field-effect transistors
Authors: Kobayashi Takeshi
Published: February 2003

The heterostructure inversion-mode metal-insulator-semiconductor field effect transistor (HI-MISFET) is proposed and the basic characteristics are analyzed for a Al2O3-InP-In0.53Ga0.47As HI-MISFET. The new device is characterized in its structure by introducing a thin wide band-gap layer between the gate insulator and the narrow gap layer. This provides a buried inversion channel in the narrow gap layer. Under a certain condition, the buried channel is accompanied with a simultaneous channel formation inside the wide gap outer layer. The field effect mobility μfe, a measure of the device performance, in excess of 9000 cm2/Vs is obtained. Even when the U-shaped surface state distribution commonly observed at Al2O3-InP interface is taken into account, the HI-MISFET exhibits μfe as high as 8000 cm2/Vs. In the capacitance-voltage curve, the turn-on voltage is found to shift toward a lower value with a decrease in the outer layer thickness (InP). Also discussed is the nonequilibrium HI-MISFET, where the Imref along the channel reveals a different distribution from channel to channel. The higher pinch-off voltage of the inner channel results in very high drain conductance in the saturation region. These results indicate that the electrical characteristics of the proposed HI-MISFET is much superior to the conventional MISFETS.
Efficiency of GaAlAs heterostructure red light-emitting diodes
Authors: Nishizawa J. , Koike M. , Jin C. C.
Published: February 2003

Electroluminescence efficiency of GaAlAs heterostructure light-emitting diodes (LED’s) fabricated by the temperature difference method is discussed by measuring electroluminescence, carrier lifetime, and absorption coefficient of the active layer. Deep levels, distribution of carriers in the indirect valley and the reabsorption of the emitted light in the active layer contribute to the reduction of the efficiency of the red LED’s. The measured absorption coefficient of Ga0.65Al0.35As active layer is about 103 cm−1 at 6500 Å; therefore the active layer thickness should be designed to be less than about 10 μm, to minimize the reabsorption region of the emitted light. The maximum luminescence efficiency is calculated for GaAlAs double heterostructure LED’s, taking the active layer thickness and the potential barrier height into consideration.
A transition-metal–rare-earth alloy for perpendicular magnetic recording
Authors: Jeanniot D. , Desserre J.
Published: February 2003

Several Co-based media have been recognized to be convenient for perpendicular magnetic recording. These alloys present a good perpendicular magnetic anisotropy and high saturation magnetization, but high demagnetizing fields and a poor perpendicular hysteresis loop squareness σ⊥. This paper describes the conditions of deposition, magnetic properties, and recording tests results obtained with radio-frequence diode-sputtered FeTbGd thin films. Near to the compensation composition, the saturation magnetization and demagnetizing fields are low and σ⊥ is nearly 1. A SiO2 protective layer covered medium has been tested for magnetic recording with a conventional Winchester ferrite head. In these recording conditions, a density as high as 162 kiloflux changes per inch has been obtained. Such results show that transition-metal–rare-earth (TM-RE) alloys are suitable for perpendicular magnetic recording.
Calibration of commercial manganin stress gauges under static uniaxial strain conditions
Authors: Rosenberg Z. , Partom Y. , Keren B.
Published: February 2003

We have calibrated commercial manganin stress gauges, statically, in the 0–1.0 GPa range, under uniaxial strain conditions. This was achieved in an arrangement, called the butt joint configuration, in which a very thin adhesive layer was compressed axially between two rigid cylinders. We have shown that if the ratio of thickness to diameter for this layer is less than 0.5% one can consider the layer as though it were undergoing purely uniaxial strain. This state of strain condition also exists in shocked specimens undergoing planer shock loading. Consequently a direct comparison to the dynamic calibration of these gauges could be made. We found that the static and dynamic calibration curves agreed, to within 2%, which was a significant improvement over the existing difference of 20% between hydrostatic and dynamic calibrations.
Two-frequency multiphoton absorption in UF6
Authors: Koren G.
Published: February 2003

The multiphoton absorption of 9.3-μm CO2 laser radiation induced by multiphoton absorption of 16-μm CF4 laser radiation in UF6 is reported. An average vibrational energy deposition in the range of 1 to 2.8 eV per molecule is found, which is sufficient to cause the observed dissociation either by collision-assisted or unimolecular decomposition processes.
Surface states at semiconductor-liquid junction
Authors: Kobayashi Kenkichiro , Aikawa Yoshihiro , Sukigara Mitsunori
Published: February 2003

Surface states at a junction of n-TiO2 and aqueous solution were studied by means of the capacitance measurement. It appeared that, from the relation between surface-state capacitance and electrode potential, surface states with state density of 8×1012 cm−2 were located at 0.5 eV below the bottom of the conduction band. The electron capture cross section of 2.0×10−19 cm2 was obtained from the frequency dependence of surface-state capacitance. The effect of the UV irradiation of TiO2 on the surface-state capacitance suggested that this surface state originated from adsorbates.
Tunnel barriers on Pb–In–Au alloy films
Authors: Baker John M. , Magerlein J. H.
Published: February 2003

Tunnel barrier oxides consisting primarily of In2O3 formed on Pb–In–Au alloys by various thermal and rf-plasma oxidation techniques were characterized in situ using ellipsometry and Auger Electron Spectroscopy (AES). The results were compared to measurements of the Josephson critical current density j1 and the specific capacitance of tunnel junctions fabricated on the same wafers. It was found for junctions with oxides consisting entirely of In2O3 that j1 exceeded 3 KA/cm2 and did not depend strongly on oxide thickness from about 3 nm (for thermally-grown oxides) to 4.5–7 nm (for rf-grown oxides). The addition of a thin layer of PbOx at the top of the barrier, either by backscattering during rf oxidation or by deposition onto a thermal oxide, caused by a substantial decrease in j1, while the presence of PbO in the bulk of the oxide had little effect. The specific capacitance of the lower current density junctions was essentially the same for either 3- or 4.5–6-nm thick oxides and was consistent with a barrier thickness of order 2 nm. These results are interpreted as evidence that tunneling occurs through a Schottky barrier in the indium oxide at the interface with the counterelectrode. Such a barrier, which is consistent with the known behavior of In2O3 as a degenerately-doped semiconductor, would account for effective tunneling and capacitive thicknesses less than the physical oxide thickness.
Dispersion and luminescence measurements of optical waveguides
Authors: Faik A. , Allen L. , Eicher C. , Gagola A. , Townsend P. D. , Pitt C. W.
Published: February 2003

Measurements are reported for the dispersion curves in the visible wavelength range of a variety of optical waveguides. Waveguides were formed in LiNbO3 and LiTaO3 by the implantation of helium ions. The radiation damage reduces the refractive index in both materials by about 12% throughout the visible region. This is thought to result from amorphization of the lattice. Waveguides formed by impurity enhancement of the refractive index were measured in soda lime glass doped by ion exchange of Li, K, Rb, Cs, or Ag. In each case the percentage increase in index was wavelength dependent. In particular, the Ag ion exchange waveguides have features attributed to colloidal silver metal. The metal colloids give both dispersion anomalies and a red luminescence. The luminescence was used to measure the losses in the waveguide.
Birefringence and structural defects in Cu2O crystals
Authors: Haydar A. , Labusch R. , Coret A.
Published: February 2003

We have investigated the birefringence in Cu2O crystals which is induced by internal stress. The observed birefringence near precipitations, called ‘‘teratoides,’’ in as-grown crystals is shown to be related to pile-ups formed in (100) planes. This interpretation is supported by the direct observation of etch pits in the birefringent regions near teratoides and by the observation of the same birefringence in other pile-ups that are not related to teratoides. The analysis of the birefringence using a quarter-wave plate shows that the slow principal axis in the crystal is parallel to Burgers vector of dislocations in pile-ups. Comparison of the birefringence observed in plastically deformed crystals with that near pile-ups in as-grown crystals, indicates the formation of pile-ups by plastic deformation. The pile-ups in this case are perpendicular to the branches of cross shaped birefringent regions. This result is in agreement with the prediction of the excitonic photoconductivity measurements.
Energy dependence of the sputtering yield of silicon bombarded with neon, argon, krypton, and xenon ions
Authors: Zalm P. C.
Published: February 2003

Sputtering yields of Si were determined for bombardment with Ne, Ar, Kr, and Xe ions at normal incidence in the energy range 0.2–20 keV under ultrahigh vacuum conditions (<10−7 Pa). Mass selection was employed and the energy spread was limited to a few electron volts. High fluences in excess of 1018 cm−2 were used to obtain stationary state yields. A special method was adopted for the yield determination, involving accurate current integration and eroded crater volume measurement with a micromechanical stylus. As a spinoff of the adopted technique, relative sputtering yields for Mo could also be determined. Our data agree with the sparse other recent experimental results. Discrepancies with older data sets are sizeable but can be attributed to our improved beam definition and better surface conditions. The measured yields are, even quantitatively, in surprisingly good agreement with predictions from Sigmund’s linear cascade theory in the low and intermediate energy range. At higher energy the yields fall off more rapidly than the theory predicts, the deviations increasing with decreasing projectile mass. This behavior cannot be explained entirely in terms of the parameters and assumptions entering the Sigmund model. Various proposed empirical modifications and alternatives for Sigmund’s theory are critically examined and a new quite useful simplification of the latter is derived.
Si implantation in GaAs
Authors: Bhattacharya R. S. , Rai A. K. , Yeo Y. K. , Pronko P. P. , Ling S. C. , Wilson S. R. , Park Y. S.
Published: February 2003

High-resolution Rutherford backscattering, transmission electron microscopy, and proton-induced x-ray emission with channeling have been used to investigate the damage and lattice site location of Si-implanted GaAs. Semi-insulating Cr-doped GaAs(100) crystals were implanted at room temperature with Si+ ions of single (120 keV) and multiple energies (50–400 keV). The total dose of implanted ions varies from 3×1015 cm−2 to 5×1015 cm−2. The residual damage and the lattice location of the implant are determined after 15 min annealing of the samples at 850 °C and 950 °C. It is shown that about 60%–70% of the Si atoms occupy substitutional lattice sites. The amount of precipitation has been evaluated and found to be very low (≤2%). For the dose of 5×1015 cm−2, microtwins lying on the (111) planes are found to be present after annealing at 850 °C in addition to the usual dislocation loops. However, after annealing at 950 °C, the primary residual damage consists of dislocation loops in addition to some small precipitates. Electrical activation efficiency has been measured in the case of 3×1015 cm−2 implant and found to be very low (≤2%). SiGa–SiAs neutral pair association is suggested to be the most probable reason for low electrical activity.
Internal friction due to hysteretic dislocation motion in solid solution crystals
Authors: Boser O.
Published: February 2003

In analogy to Rayleigh’s law in magnetism a Rayleigh law of plastic deformation is defined to explain the amplitude dependent internal friction and the modulus defect in materials with high solute concentrations. The forces opposing dislocation motion in a solid solution crystal with high solute concentrations are described with the help of random functions. Using this statistical treatment it is possible to calculate the parameters of Rayleigh’s law of plastic deformation and explain quantitatively the amplitude and concentration dependence of the internal friction and modulus defect in alpha brass.
Fragmentation behavior of Armco iron and HF-1 steel explosive-filled cylinders
Authors: Mock Willis , Holt William H.
Published: February 2003

The fragmentation response of explosive-filled cylinders of Armco iron and HF-1 steel with two heat treatments has been determined. The cylinders were filled with cast-in-place composition B explosive and detonated. At least 99% of the metal mass was recovered in all the experiments. The recovered fragments had both brittle and shear fracture surfaces. The average fragment mass for the Armco iron and HF-1 steel experiments was 6.3 and 0.9 g, respectively. Average engineering radial strain values for the fragments were 0.35 and 0.12 for Armco iron and HF-1 steel, respectively. A scheme was devised for characterizing the recovered fragments according to their cylindrical and fracture surfaces. Fragment mass distributions are presented for the characterized fragments.
Dynamical behavior of interstitials in elemental semiconductors
Authors: Talwar D. N.
Published: February 2003

The dynamical behavior of isolated interstitials in elemental semiconductors has been described using the well-known Greens function theory. Assuming the defect to be at the tetrahedral site, we have exploited the symmetry properties of the point group {Td} so as to make the problem amenable to calculations. The conditions for the occurrence of impurity modes and IR absorption have been derived in terms of the mass of the interstitial and the impurity-host interactions. All the involved lattice Greens functions are calculated by incorporating the phonons obtained from a simplified second-neighbor force model fitted to neutron scattering experiments on silicon. Numerical calculations are made for the localized vibrational modes and the impurity-induced IR absorption for different interstitials in Si. The calculated results are compared with existing theoretical and experimental data.
Influence of thermoelastic bending on photoacoustic experiments related to measurements of thermal diffusivity of metals
Authors: Rousset G. , Lepoutre F. , Bertrand L.
Published: February 2003

In some photoacoustic experiments, thermoelastic bendings of solid samples produce strong signals which cannot be analyzed by usual photoacoustic calculations. We propose a model that, using the thermoelastic equations, analytically explains the effect of this bending. It is found that the model agrees well with data obtained from an experiment sensitive to thermoelastic deformations only. Furthermore, the model is also consistent with previous piezoelectric-photoacoustic calculations. This experiment also leads to measurements of thermal diffusivities.
The role of solitons and the kinetics of precipitate growth in boron doped silicon–germanium alloys
Authors: Savvides N.
Published: February 2003

The time dependence of the thermoelectric transport properties of boron doped Si70Ge30 alloys has been investigated for times between 1 and 8700 h at an isothermal heat treatment temperature of 1100 K. Changes in the Seebeck coefficient, electrical resistivity, and carrier concentration which result from the precipitation of boron are reported. Three distinct stages are observed in the precipitation process: (a) an initial stage of precipitate zone growth lasting for about 1000 h characterized by a parabolic rate law, (b) a final stage commencing after about 4000 h and obeying the conventional Lifshitz–Slyozov post nucleation rate law, and (c) a lengthy intermediate stage lasting for about 3000 h in which the transition from initial to final stage takes place. A recently proposed soliton model for the kinetics of precipitate growth in binary phase systems is found to correctly reproduce the experimental observations. It is also reported that the precipitation process is reversible and the precipitated boron can be put back into solid solution by high temperature annealing.
Anodic bonding of imperfect surfaces
Authors: Anthony Thomas R.
Published: February 2003

The intimate surface contact necessary for anodic bonding of a metal to a glass is examined in terms of the electrostatic forces which promote this contact and surface imperfections which prevent this contact. Surface imperfections that are considered include foreign particles, isolated hillocks, and periodic curved and angular surfaces. With curved and angular surfaces, a critical voltage exists that causes spontaneous mating of the surfaces by elastic or plastic deformation. Below this voltage, intimate surface contact is achieved by viscous flow. For isolated hillocks and foreign particles, surface conformation generally occurs by viscous flow because of large stress concentrations at these imperfections. The resulting time required for intimate surface contact is a very sensitive function of the imperfection size.
Ti–W alloy interaction with silicon in the presence of PtSi
Authors: Nava F. , Nobili C. , Ferla G. , Iannuzzi G. , Queirolo G. , Celotti G.
Published: February 2003

Ti–W alloy film was deposited by conventional dc sputtering in a PtSi film grown on a 〈100〉 silicon substrate. Two sets of samples were prepared with different oxygen content in the Ti–W film. MeV 4He+ backscattering analysis shows, after vacuum annealing, the formation of a ternary mixture (TixW1−x)Si2(x=0.24) . The Ti:W ratio in the mixture is the same as in the as-deposited film. The growth in the 625–775 °C temperature range, is directly proportional to the time and the process is thermally activated with an activation energy of 3.3±0.1 eV. During the thermal annealing the platinum silicide is always located between the ternary mixture and the Si substrate. X-ray diffraction indicates the formation of a pseudobinary solid solution with an hexagonal structure with a=4.61±0.01 Å and c=6.47±0.02 Å. The presence of the oxygen slows down the reaction but does not change the mechanism of the compound formation. The content and distribution of impurities was measured using Auger technique combined with Ar sputtering. In the two sets of samples the average oxygen concentration is 1% and about 5%, respectively. The oxygen is mainly located at the Ti–W/PtSi interface. During the compound formation the oxygen distribution is not modified.
Electron power loss in the (100) n channel of a Si metal-oxide-semiconductor field-effect transistor. I. Intrasubband phonon scattering
Authors: Krowne Clifford M.
Published: February 2003

The electron energy relaxation is studied as a function of the ‘‘electron temperature’’ Te in the n channel of a (100) surface silicon MOSFET (metal-oxide-semiconductor field-effect transistor) device by inspecting the phenomenological energy relaxation time τε(Te) at 4.2 °K, 77 °K, and 300 °K lattice temperatures. τε is theoretically calculated in order to determine the relative contributions of shear horizontal (SH), pressure-shear vertical (P-SV), shear vertical-pressure (SV-P), total reflection shear vertical pressure (TR), and Rayleigh (R) surface acoustic phonon modes to the electron energy relaxation at the interface. Two-dimensional electron transport is assumed and the effects of subbanding near the interface are included. Only electron scatter events within subbands are studied (intrasubband). This exhaustive study finds that surface modes do not dominate the electron energy relaxation at the Si–SiO2 interface at TL =4.2 °K. Some other mechanism(s) must predominate at TL =4.2 °K.
Electron and hole carrier mobilities for liquid phase epitaxially grown GaP in the temperature range 200–550 K
Authors: Kao Y. C. , Eknoyan O.
Published: February 2003

Mobility data for GaP in the temperature range 200–550 K as a function of impurity concentration are presented. The data were determined from sheet Hall coefficient and resistivity measurements obtained using the van der Pauw method. The results are given for a wide range of concentrations ranging from unintentionally doped to degenerately doped conditions. The maximum values of the electron and hole mobilities at room temperature were found to be 160 and 135 cm2/Vs, respectively. The observed average temperature dependence of the mobility is T−1.7 for electrons and T−2.3 for holes.