bluuebunny/crossref_metadata_2025 huggingface dataset:
Detailed light-current-voltage analysis of GaP electroluminescent diodes
Authors: Ralston J. M.
Published: February 2004

The light-current-voltage (LIV) characteristics of both red- and green-emitting GaP p-n junctions have been analyzed in detail at room temperature. Device current has been quantitively and accurately decomposed into components corresponding to the Sah-Noyce-Shockley space-charge recombination and to diffusion current. Data analysis is performed rapidly using an automatic iterative procedure developed for this purpose. In the course of calculation, diode resistance in series with the junction is measured and corrected for, thus considerably extending the upper limit of bias current which may be usefully studied. This study has also determined the current dependence of injection efficiency, electroluminescent quantum efficiency, and the effective luminescent recombination efficiency of the bulk semiconductor region adjacent to the junction. Although this method is applicable to broad classes of junction devices, its use involves certain limitations and ambiguities, which are explicitly discussed. This analysis has been applied to the LIV characteristics of representative examples of both red- and green-light-emitting GaP p-n junctions, grown by double liquid-phase epitaxy. For both these cases, it is demonstrated that the simple current models employed (SNS space charge and diffusion) are in excellent agreement with the observed I-V characteristics over more than nine decades of device current. It seems apparent that these techniques will prove relevant to studies of the physics of light-emitting diodes.
Residual acceptors in natural GaSb and Gaxln1−xSb; their contribution to transport between 4.7 and 300 °K
Authors: Campos M. D'Olne , Gouskov A. , Gouskov L. , Pons J. C.
Published: February 2004

A comparative study is made concerning the role played by residual acceptors in transport, for three samples of natural GaSb (one of them is obtained by crystal growing from a nonstoichiometric melt) and three samples of Gaxln1−xSb with x=0.96, 0.90, and 0.775. In GaSb, in the high-temperature range, experimental results of Hall effect and resistivity vs temperature are analyzed in a two valence-band and one acceptor-level model. Activation energy EA and density NA of acceptors are deduced as well as density of compensating donors ND. It is shown that NA is decreased by growing crystal from a nonstoichiometric gallium-rich melt. In the alloy NA and EA decrease with decreasing x. The low-temperature-range conduction is discussed for the samples investigated.
Electron radiation damage and annealing of Hg1−xCdxTe at low temperatures
Authors: Melngailis John , Ryan Jean L. , Harman Theodore C.
Published: February 2004

Samples of Hg1−xCdxTe with x=0.22 and x=0.31 have been irradiated with dosages of up to 4.7×1015 electrons/cm2 of 2.5-MeV electrons. During the irradiation the sample temperature was below 25 °K. The samples were initally p type, i.e., at 77 °K the hole carrier concentrations were in the range (2.5–4.3)×1016cm−3. After irradiation all samples were found to be n type. A dose of 4.7×1015 electrons/cm2 yielded an electron carrier concentration of 1.5×1017 cm−3 at 8 °K and an electrical conductivity σ four orders of magnitude larger than the unirradiated σ at 8 °K. The electron Hall mobility for low dosages and small measured electron concentrations is very low (500–2500 cm2/V sec). As the dosage is increased, the mobility rises rapidly and then saturates. Postirradiation annealing results in almost complete restoration of the transport properties. Much of the annealing occurs between 50 and 75 °K. The luminescence and photovoltaic response (at 8 °K) of the x=0.31 samples were measured before irradiation, after irradiation, and at several stages of the annealing. The irradiation shifts the luminescence and the photovoltaic response cutoffs to lower energies. Most of this change in optical properties anneals out between 100 and 250 °K.
Generation-recombination noise and the microwave emission from InSb
Authors: van Welzenis R. G. , Lodder J. J.
Published: February 2004

A classification of the microwave emission phenomena from InSb is given. An explanation for the high-field microwave emission is proposed. Experimental evidence supporting this theory is discussed. New experimental results obtained by using pulsed high electric fields in a constant-voltage configuration are presented. One result is the observation of microwave emission in the absence of magnetic field. Another result is a confirmation of the burst emission observed earlier, which we associate with the temporary appearance of Gunn-effect domains. An estimate of the domain width and the maximum domain field is given, which results in very wide domains and low domain fields.
Xerographic discharge characteristics of photoreceptors with bulk generation. II. Time-varying exposure
Authors: Chen Inan , Kao Cheng C.
Published: February 2004

The theoretical studies of xerographic discharge with bulk generation have been extended to the case where the exposure time is not short compared to the carrier transit time. The theory has been developed to treat any time-varying exposure. However, only the numerical results for finite and continuous step-function exposures are presented. The results are discussed in terms of the residual potential, exposure to generate one CV0, time to discharge a given fraction of the initial potential V0, and the contrast potential. The effects of the field dependences of carrier mobility and carrier generation efficiency, the asymmetry of the hole and the electron mobilities, the light flux level, the exposure time, and the optical density of the photoreceptor on the above quantities are investigated.
Determination of line-shape parameters of high-gain laser transitions based on line-narrowing measurements
Authors: Gamo Hideya , Ostrem John S. , Chuang Shih-Shung
Published: February 2004

A new method for determining the Lorentzian linewidth, the Doppler linewidth, and the population inversion in high-gain laser media, for which the signal-to-noise ratio is better than that of previous methods owing to superradiant amplification, has been developed. These parameters can be determined based upon the experimental measurement of spectral line narrowing, spontaneous emission linewidth, and small-signal gain with the use of numerical tabulations of the spectral line-narrowing coefficient and the ratio of spontaneous to Doppler linewidths. In case either the spontaneous linewidth or the small-signal gain is not available, the same parameters can be determined by doing a curve fit to the spectral line-narrowing data. The superradiant radiation output of the xenon 3.5-μm line is analyzed by the latter method.
High-energy pulsed CO2-laser-target interactions in air
Authors: Lowder J. E. , Lencioni D. E. , Hilton T. W. , Hull R. J.
Published: February 2004

Observations of the interaction of high-energy CO2 laser radiation with different target materials in air are reported. The plasma initiated on carbon and aluminum targets was observed with high-speed streak and framing cameras and electrostatic probes. The threshold for maintenance of radiation-driven absorption waves was found to be about 4×107 W/cm2 for a focal spot radius of 0.2–0.3 cm. The total impulse delivered to targets of various sizes and materials was measured along with simultaneous measurement of total energy and the power of the laser pulse. The impulse data were correlated with a simple cylindrical shock-wave model, which predicts that the impulse scales as the target area and as the square root of the focal spot area.
Influence of electron trapping on domain dynamics in epitaxial Gunn diodes
Authors: Teszner J. L. , Boccon-Gibod D.
Published: February 2004

Electron trapping has been observed in thin epitaxial Gunn diodes. This effect is significant as soon as the threshold field for domain build-up is crossed. The field-enhanced trapping appears to be strongly correlated with the thickness of the sample. Modification of domain dynamics, due to bidimensional and trapping effects, has been studied theoretically and experimentally, with low- and high-impedance capacitive probes. Previous results on bistable switching have therefore been explained. The nature of traps has been investigated by means of photoluminescence experiments. Trapping appears to be linked with the presence of shallow acceptor levels (which are presumed to be silicon atoms on arsenic sites). The recent hypothesis of the existence of a localized silicon-oxygen complex, behaving as a deep acceptor level in the crystal, fits closely with the present experiments.
Efficient and damage-resistant tunable cw dye laser
Authors: Jacobs R. R. , Lempicki A. , Samelson H.
Published: February 2004

An analysis of the optical problems encountered in cw dye lasers and various design criteria are presented. On this basis a design which proved to be stable, efficient, and damage resistant is described in detail and some performance data are presented.
Thermal and optical generation current in reverse-biased gold-doped silicon p+n junctions without the depletion approximation
Authors: Braun S. , Grimmeiss H. G.
Published: February 2004

Optical and thermal generation currents in reverse-biased p-n junctions have been calculated for an exponential tail of free-charge carriers extending from the neutral regions into the transition region. Net generation of electron-hole pairs can then be neglected at the ends of the transition region because of recombination processes. The width W0 of these regions has been calculated for step junctions and asymmetrical linearly graded junctions. For a symmetrical step junction, W0 is independent of bias at constant illumination intensity. For a linearly graded junction, however, the widths of these regions become monotonically smaller with increasing reverse bias. In all cases, the regions with negligible net generation decrease logarithmically with intensity. The calculations are in good agreement with experimental results for gold-doped silicon diodes. Furthermore, it is shown that, for moderate average electric fields, neither the optical nor the thermal hole emission rate for the gold acceptor in silicon is field dependent.
Electrodynamics of a magnetic levitation coil
Authors: Langerholc J.
Published: February 2004

The electrodynamics of a magnetic leviation coil is studied without the use of Maxwell's thin-plate approximation. Formulas are derived for the forces on and current fluctuation in a vertically perturbed coil and the transient response of a stationary coil in the vicinity of a permeable conducting track. All results are obtained from exact solutions of the Maxwell equations in which the displacement current is neglected. The forces are then linearized and a close coupling approximation for the reflected impedence of the coil is derived.
Field, angular, and defect dependence of the critical current of Nb3Sn for t≤4.2°K
Authors: Cullen G. W. , Cody G. D.
Published: February 2004

Measurements are reported for the critical current of chemically transported Nb3Sn as a function of applied field from 0 to 104 kG. The angular variation of the critical current at constant field is examined in detail. Data are given for the temperature dependence of the transverse and longitudinal critical current as well as the effect of neutron damage on homogeneous low-α specimens of Nb3Sn.
Structure and electrical conductivity of cosputtered gold-chromium alloy films
Authors: Slusark W. , Lalevic B. , Fuschillo N.
Published: February 2004

Cosputtering of Au and Cr produces polycrystalline thin films in the entire compositional range up to solubility limits of 49 at.% Cr in Au corresponding to the phase diagram of bulk material. Compositions of the Au–Cr system were checked by electron-probe microanalysis. The change in lattice constant with addition of Cr in Au shows exactly the same deviation from Vegard's law as bulk. The resistivity changes with increasing Cr content are presented and the temperature coefficient is found to be constant in the range -150–160°C.
A new geometry double-heterostructure injection laser for room-temperature continuous operation: junction-stripe-geometry DH lasers
Authors: Susaki W. , Namizaki H. , Kan H. , Ito A.
Published: February 2004

This paper reports a new junction-stripe-geometry double-heterostructure laser, in which the active region is defined into narrow stripe by means of diffusion technique. These lasers have good thermal characteristics, and the lowest threshold current density is 3500 A/cm2 at continuous operation.
High-power output in Pb1−xSnxTe diode lasers with improved mirror quality
Authors: Walpole J. N. , Calawa A. R. , Ralston R. W. , Harman T. C.
Published: February 2004

Pb1−xSnxTe diode lasers with cw output power over 10 mW, single-longitudinal-mode power up to 6 mW, and incremental external quantum efficiencies up to 0.16 have been obtained using polished rather than cleaved end mirrors. The results indicate that one of the major factors limiting the output power and external efficiency of these lasers is the optical quality of the mirrors.
Strengthening effects in press forged KCl
Authors: Becher P. F. , Rice R. W.
Published: February 2004

Recrystallization of KCl crystals deformed in a <100> direction was utilized to develop polycrystalline microstructures, increasing yield stresses, thus making them more attractive as laser window candidates. Using press forging techniques (i.e., slow compressive deformation in the absence of lateral constraints), large plastic strains (≤ 70%) were achieved at temperatures as low as 150 °C, which resulted in recrystallized grain sizes as fine as 5 μm. Although a residual < 100 > texture was present, there was sufficient grain misorientation to result in general polycrystalline behavior. The yield stresses of the press forged materials increased with decreasing grain size, reaching about 35 MN m−2 (∼5000 psi) at the finest (5 μm) grain size.
Effect of dielectric constant on surface discharge of polymer insulators in vacuum
Authors: Akahane Masao , Kanda Kazuhide , Yahagi Kichinosuke
Published: February 2004

The effect of dielectric constant on surface discharge of polymer insulators (polyethylene, polycarbonate, polytetrafluoroethylene, and polyamide) with right cylindrical shape was investigated. The experimental results showed that dc flashover voltage was decreased with increase of dielectric constant in polymers.
Stimulated emission cross section at 1.061 μm in Nd:YAG
Authors: Birnbaum Milton , Klein Christopher F.
Published: February 2004

The stimulated emission cross section of the 1.061-μm transition (R1—Y1) in Nd: YAG has been measured and is (5.1 ± 0.5) × 10−19 cm2 on the same scale that assigns the value 8.8 × 10−19 cm2 to the 1.064-μm line. The thresholds of the 1.061- and 1.064-μm lines have been determined over the temperature range of 100–300 °K and are equal at 229 °K.
Channeling and dechanneling of ion-implanted phosphorus in silicon
Authors: Reddi V. G. K. , Sansbury J. D.
Published: February 2004

Profiles of channeled and dechanneled 31P ions in the energy range 30–900 keV have been measured in 〈100〉, 〈111〉, 〈112〉, and 〈110〉 Si. The maximum range, Rmax, of the channeled ions has been determined and used to calculate values of electronic stopping power. The variation of these values with substrate orientation agrees qualitatively with that predicted by the Firsov theory, although the actual values are 2–3 times the Firsov prediction. Dechanneled profiles (450 keV) were measured in 0.3° steps up to 1.2° for all four orientations and in 2° steps up to 10° for the 〈100〉 and 〈111〉 orientations. The effect of tilt direction on the dechanneling was studied. Dechanneling from the 〈111〉, 〈112〉, and 〈110〉 orientations exhibited a marked sensitivity to the direction of tilt. By tilting in an appropriate maximum-dechanneling direction, dechanneling from the 〈100〉 and 〈111〉 orientations was found to be continuous, starting with the 0.3° tilt and saturating for tilts above 4.2°. The projected range, Rp, determined from the fully dechanneled or random distributions, was found to vary almost linearly with energy and has a slope of ∼1.1 μm/MeV.
Probing of surface acoustic wave devices with large-diameter laser beam
Authors: Zuliani M. J. J. , Ristic V. M. , Vella P. J. , Stegeman G. I. A.
Published: February 2004

The theory of dark field imaging technique as applied to acousto-optic interactions has been developed and then used in studies of linear and nonlinear surface acoustic waves and volume acoustic waves. The theory is consistently expressed in terms of phase transmittance function. Experimental results show how the technique can be applied in the case of multimode propagation to unfold the complex frequency spectra of spurious modes in surface wave devices, and how to discriminate between different harmonics in the case of nonlinear acoustic propagation.
Phase velocity and damping of torsional waves in viscous-fluid-filled stretched viscoelastic tubes
Authors: Klip Willem , Klip Dorothea A. , van Loon Pieter
Published: February 2004

Using the theory of elasticity for large deformations and a strain energy function of the form W=½Φ(I1 −3)+½Ψ(I2 −3), where Φ and Ψ are constants, formulas for the phase velocity and damping of torsional waves of small amplitude in stretched viscoelastic isotropic vessels of arbitrary wall thickness and filled with a viscous fluid under pressure have been derived and experimentally tested (frequency range 0.3–33 Hz; viscosity of the fluids between 0.01 and 13 P; pressure between 0 and 4×105 dyn cm−2; stretches up to twice the original length) in vertically or horizontally suspended latex tubes and in such tubes floating on a pillow of pressurized air. The agreement between theory and experiment is satisfactory. The phase velocity increases with the stretch, but decreases with an increase of the fluid viscosity. The damping decreases with an increase of the stretch. At the higher frequencies the damping increases with an increase of the viscosity of the fluid, but at the lower frequencies the opposite is the case. The influence of pressure both on phase velocity and damping proved small in the pressure range that was considered (0–4×105 dyn cm−2).
Radiative heat transfer through composite materials
Authors: Klemens P. G. , Greenberg I. N.
Published: February 2004

Radiative heat transfer in inhomogeneous materials is governed by the photon mean free path. For long-wave photons, the mean free path depends on the size and shape of the individual grains and, where applicable, of the voids. Long-wave photons have long mean free paths and play an important role in the heat transfer. In some cases they cause the radiative thermal conductivity at moderately high temperatures to be larger than one would expect by extrapolating from highest temperatures (above 2000 °K) according to a T3 law. Some special cases are treated including polycrystalline solids, densely packed powders, foams, and fibrous aggregates.
Reaction of iodine vapor with silver films in the β-AgI phase region
Authors: Shiojiri M. , Hasegawa Y. , Konishi K.
Published: February 2004

The reaction of iodine with silver at temperatures from 25 to 150 °C has been studied with a quartz crystal microbalance and by x-ray diffraction. The reaction approximately obeys the parabolic law and the reaction rate decreases with increasing temperature up to 146 °C, the transformation temperature of AgI. Crystals of β-AgI grow with various orientations on the silver surface at 25 °C, but gradually grow with the basal planes parallel to the film surface with increasing temperature. It is concluded that the diffusion of iodine atoms through the iodide films is rate determining, and that the adsorption of iodine gas and the oriented growth of the AgI film influence the diffusion and lead to the observed temperature dependence of the reaction.
Cataphoretic segregation effects in Ne–Hg and Ne–Xe–Hg mixtures
Authors: Tombers Reid B. , Chanin L. M.
Published: February 2004

Ion-sampling measurements have been made from the positive columns of dc discharges for 0.01% Hg in Ne at various discharge currents and pressures. Ion species detected included Ne+, Ne2+, Hg+, and Hg2+. Optical measurements of the 5461-Å line intensities of Hg were used to confirm the axial dependencies determined from the ion results. The degree of ionization of Hg was found to be considerably larger than for binary noble-gas mixtures. Measurements in Ne–Xe–Hg mixtures indicated a normal cataphoretic dependence on discharge current. No complex ions were detected in the tertiary mixture.
Parametric study of superradiant laser action in molecular nitrogen excited by a high-energy electron beam
Authors: Patterson E. L.
Published: February 2004

Excitation of the molecular nitrogen laser by a high-energy electron beam is shown to be controlled by E/p in a manner similar to other forms of electrical excitation. The electric field is produced by the increasing net current. Both the beam current and the nitrogen pressure for maximum laser power are found to vary directly as the laser diameter for the two diameters considered. Scaling of laser power with length is found to be limited by the high optical gain of the laser transition which causes the active medium to become superradiant before the full length is excited.
Optical spectra of Ce3+ and Ce3+-sensitized fluorescence in YAlO3
Authors: Weber M. J.
Published: February 2004

Infrared and ultraviolet absorption spectra arising from f→f and f→d transitions of Ce3+ in YAlO3 crystals are presented and used to derive the 4f and 5d energy levels. Excitation and fluorescence spectra of 5d→4f emission are also reported. The 5d fluorescence has a decay time of 16 nsec and a radiative quantum efficiency of near unity at 300 °K. Possible use of Ce3+ as a sensitizer for rare-earth and iron-group ion fluorescence in YAlO3 is surveyed; included is an investigation of energy transfer in a Ce, Nd, Cr-codoped crystal.
Depth-resolved cathodoluminescence in undamaged and ion-implanted GaAs, ZnS, and CdS
Authors: Norris C. B. , Barnes C. E. , Beezhold W.
Published: February 2004

Here we report a variety of results obtained by using sequences of luminescence spectra excited by 1–20-keV electron irradiation to carry out in situ studies of depth-dependent optical activity in luminescent crystals. Data are shown for various samples subjected to localized damage from ion implantation: GaAs implanted with Cu+, ZnS implanted with Ar+ and Cu+, and CdS implanted with Ar+ and H+. Semiquantitative interpretation of the results shows that the depth-resolved cathodoluminescence measurements can have unique value in characterizing the effects of ion-implantation lattice damage. In this case cathodoluminescence can be excited from depths ranging from much shallower to much deeper than typical implant depths. In addition, the use of depth-resolved measurements on nominally undamaged ZnS crystals reveals the presence of weak near-surface luminescence bands despite careful surface preparation. This result makes it clear that luminescent center profiling by layer removal methods can lead to erroneous results when recurring spectral features result from inherent near-surface conditions. More importantly, in several ZnS and CdS samples we find that unexpectedly sharp near-surface depth resolution (of the order of several hundred Å) can be obtained even though bulk carrier diffusion lengths are of the order of microns. While this effect is presently not understood in detail, the result should permit depth-resolved measurements on sputtering damage and very shallow implants. The various samples we have studied show that modifications in spectrum from injection-level effects (particularly GaAs) or from exposure to electron irradiation (particularly CdS) may appear in depth-resolved or other luminescence measurements. Finally, the depth-resolved cathodoluminescence measurements are compared with single-wavelength photoluminescence spectra on the same samples for cases where the photoexcitation light is or is not strongly absorbed. It is pointed out that the cathodoluminescence measurements are more adaptable to in situ depth profiling because the irradiation energy (excitation depth) and current (injection level) can be easily varied over wide ranges, and because the excitation depth is not affected by the optical absorption coefficient (which is often uncertain, particularly in implanted layers). In addition, we find that cathodoluminescence can be more sensitive than photoluminescence for studying optical centers introduced by shallow implants, even when the sample is strongly absorbing to the photoexcitation light.
Eigenmode analysis of wave propagation in optical waveguides deposited on gyrotropic and anisotropic substrates
Authors: Wang Shyh , Crow John D. , Wong Sik-Lam , Shah Manhar
Published: February 2004

Wave propagation in optical waveguides deposited on gyrotropic and anisotropic substrates is analyzed in terms of the eigenmodes of the guide. The field composition and the phase velocity of the eigenmodes are determined. The results of the analysis are applied to waveguide modulators and distributed-feedback lasers for use in integrated optics. Based on the eigenmode analysis, coupled-wave equations are set up to facilitate the analysis of integrated-optics problems which involve the use of gyrotropic and anisotropic waveguides.
Maintenance of threshold on-state of an amorphous semiconductor by cw bias: Effects of temperature, frequency, and bias interruption
Authors: Vezzoli G. C. , Doremus L. William
Published: February 2004

Threshold chalcogenide switching devices have been maintained in an on-state using cw functions in conjunction with the original set pulse. The on-state is distinct from a memory state in that the off-state can be recovered by lowering the signal amplitude (or frequency) without the need of a high current reset pulse. Once set on, the maintained or preserved on-state shows no switching discontinuity. Essentially zero current is observed (in either polarity) until a critical voltage level is reached, defined as the barrier voltage, beyond which the current rises almost vertically. The I-V curve of the preserved on-state displays its most pronounced temperature dependence at frequencies just above the value at which the device turns off but is relatively temperature independent at significantly higher frequencies (1 MHz and above). The temperature dependence has been investigated near the turn-off frequency from 500 down to about 20 °K, and consistently shows a maximum in barrier voltage vs ambient temperature at about 35 °K. At room and liquid-nitrogen ambients, barrier voltage increases superlinearly with decreasing frequency from about 1 MHz to the turn-off value. With a cw source, the turn-off which is caused by decreasing frequency appears to be due to allowing a current less than the minimum holding value to persist for a critical time period. Studies of interruptions of the pulse-switched on-state show that when the on-state voltage is forced to zero for a time in excess of about 0.4 μsec the device will turn off. As the interruption time increases, the reswitching voltage also increases until the original threshold is recovered at interruption times of about 1.5 μsec. A similar dependence has been found in the reswitching voltage for interruptions which do not force the on-voltage to zero but simply reduce it.
Plasma creation from thin aluminum targets by a TEA-CO2 laser
Authors: Dick K. , Pépin H. , Martineau J. , Parbhakar K. , Thibaudeau A.
Published: February 2004

The results of a study of the plasma produced by focused TEA-CO2 laser radiation on aluminum foil targets are presented. Streak photography, interferometry, and charge collection measurements are used to describe the time and space evolution of the plasma. A maximum plasma temperature of 30 eV, deduced from the ion expansion energy, was obtained for an incident flux of 1010 W/cm2. The electron density remained below cutoff throughout the interaction. For thick targets the plasma production can be described by using a self-regulating process. For thin foils the plasma becomes transparent during the laser pulse and the hydrodynamic expansion can influence the results. In this latter case temperature scaling laws based on an integrated inhomogeneous spherical model give good agreement with the experiment.
Electron-beam penetration in GaAs
Authors: Martinelli Ramon U. , Wang C. C.
Published: February 2004

Measurements of the primary electron-beam penetration depth R in single-crystal GaAs have been made over the electron-beam energy range of 3–17 kV. The penetration depth is defined as the GaAs film thickness at which primary electrons of a given energy Ep just begin to emerge from the exit surface of the film with an energy of several hundred eV. The relationship between R and Ep is R=a(Ep)b μm, with a=0.027±0.003 and b=1.46±0.05. Ep is given in kV.
Thermal activation energy of manganese acceptors in gallium arsenide as a function of impurity spacing
Authors: Blakemore J. S. , Brown Winfield J. , Stass Merrill L. , Woodbury Dustin A.
Published: February 2004

The thermal ionization energy for Mn acceptors in GaAs decreases with increasing density of either Mn atoms or compensators. Measurements of the correlation of Ea with Na or Nd are complicated by impurity inhomogeneity. Envelope functions fitted to the data show the same energy (0.11 eV) for the infinite dilution asymptotic value as is found for the optical activation threshold.
Interfacial screw dislocations in anisotropic two-phase media
Authors: Chou Y. T. , Pande C. S.
Published: February 2004

A simple analysis is presented of the elastic field of an interfacial screw dislocation in an anisotropic two-phase medium. Explicit expressions for the stress components of a single dislocation and of a dislocation wall are given.
Interference fringes due to magnetic domains in FeBO3
Authors: Haisma J. , Stacy W. T.
Published: February 2004

Polarization interference fringes caused by magnetic domain walls have been observed in FeBO3 at specimen temperatures below 190 °K. A simple model, based on the observed magnetic field dependence and orientation of the fringes, suggests that the domain walls are the 120 ° Bloch type, lying a few degrees oblique to the basal plane.
Structure and thermal stability of sputtered Au–Ta films
Authors: Christou A. , Day H.
Published: February 2004

The structure and thermal stability of bimetallic Au-Ta films has been studied by x-ray diffraction, electrical resistivity, and by microscopy. Annealing above 450 °C forms a TaAu compound. The growth of the TaAu layer at the Au–Ta interface follows a parabolic rate law. A low-temperature depletion of gold at tantalum grain boundaries occurs below 350 °C with an activation energy of 0.41 eV. Grain growth occurs with an activation energy of 0.50–0.55 eV for gold and 0.40–0.50 eV for tantalum. Thermal stresses of the order of 1.0×109 dyn/cm2 exist in the sputtered films.
Elastic properties of tantalum over the temperature range 4–300 K
Authors: Leisure R. G. , Hsu D. K. , Seiber B. A.
Published: February 2004

The elastic properties of tantalum have been investigated over the temperature range 4.2–300 K. The values of the adiabatic elastic constants C11, C44, and CL=(1/2) (C11+C12+2C44) at 4.2 K in units of 1012 dyn/cm2 are, respectively, 2.70, 0.873, and 3.02. The Debye temperature was calculated from the elastic constants and found to have the value of 265 K at low temperature. The elastic constants become temperature independent at low temperatures and approach linear behavior at high temperatures. In contrast to the normal behavior of the elastic constants, nuclear acoustic resonance experiments show anomalous line broadening.
Kinetics of WSi2 formation in the thin-film system W/PtSi/Si
Authors: Sinha A. K. , Smith T. E.
Published: February 2004

Alloying kinetics data on thin-film materials systems of interest in large-scale integration (LSI) technology are useful in the design of high-temperature processing schemes. In the present work, we have investigated the kinetics and mechanism of WSi2 formation in the thin-film system W/PtSi/Si, which is encountered in the Ohmic contact and Schottky barrier areas of silicon integrated circuits. In situ x-ray diffractometer measurements were carried out on various thin-film samples in the temperature range 690–840 °C. All the samples consisted of 2000-Å W film on 900-Å PtSi on 10-mils-thick n-type (100) Si doped with arsenic to a resistivity of 10 Ω cm. The amount of WSi2 formed was found to be equal to the amount of W consumed, indicating that an excess of Si atoms (diffusing species) is present at the reaction interface. The rate of transformation of W to WSi2 first increases with time and then it decreases. The data can be represented in terms of the generalized kinetic law: x = 1-exp[−K(T)tn], where x is the volume fraction of W transformed, K(T) is a temperature-dependent rate constant, t is time, and the index n is experimentally found to be equal to [inverted lazy s]1.35 in most cases of W/PtSi/Si samples annealed between 690 and 840 °C. A relatively high thermal activation energy of [inverted lazy s]4.4 eV/mole was deduced from an Arrhenius plot of half-time for transformation vs reciprocal of the annealing temperature. A comparison of the present results with those available on a W–Si thin-film system indicates that an intermediate layer of PtSi substantially accelerates the rate of formation of WSi2 and that PtSi may be also affecting the thermodynamic processes involved in WSi2 formation. It is suggested that the WSi2 nucleation process may involve, simultaneously, creation of W–Si bonds at the expense of Pt–Si bonds and restoration of the latter by out-diffusing silicon atoms. All the WSi2 nucleation sites at the W/PtSi interface are probably saturated before appreciable growth occurs.
Electrical and mechanical features of the platinum silicide-aluminum reaction
Authors: Hosack H. H.
Published: February 2004

The electrical and mechanical features of a thermally induced interaction between platinum silicide and aluminum have been investigated. It has been found that a diffusion-controlled reaction occurs between these two materials which results in conversion of platinum silicide to the intermetallic PtAl2. The activation energy for this process is found to be 0.77 eV. As platinum silicide Schottky diodes with aluminum contacts are sintered for increasing time periods, this reaction propagates to the platinum silicide-silicon interface and the effective barrier height of the metal-semiconductor junction is observed to drop sharply to a value below that of aluminum-silicon Schottky diodes. As longer sinter cycles are performed the effective barrier height rises to a value characteristic of aluminum-silicon contacts. This effect is shown to be a result of diffusion of aluminum through the reacted material and the formation of an essentially aluminum-silicon contact at the silicon substrate. The mechanical features of the platinum silicide-aluminum reaction observed on test devices are correlated with the electrical effects of this reaction noted on Schottky diodes.
Doubly charged ions in decaying plasmas in neon and argon
Authors: de Hoog F. J. , Oskam H. J.
Published: February 2004

Doubly charged ions were observed during the decay period of plasmas produced in neon as well as in argon at reduced gas pressures ranging from 0.14 to 1 Torr. The measured time dependence of both the Ne2+ ion density and the Ar2+ ion density were corrected for the effect of diffusion cooling of the electrons. The reaction rate constant for the partial charge exchange reaction Ne2++Ne→Ne++Ne+ was found to be k=(9 ± 2) × 10−14 cm3 sec−1. For the reaction rate of the similar reaction in argon, only an upper limit could be obtained. The value of the mobility of Ne2+ in neon was found to be μ(Ne2+)=6 ± 1 cm2/V sec. The value of the mobility of Ar2+ in argon was consistent with previously published data.
Space-charge effects upon unipolar conduction in semiconductor regions
Authors: Dascalu D.
Published: February 2004

The effect of space charge upon unipolar drift currents in uniformly doped semiconductor regions is studied. The geometry is assumed one dimensional and diffusion is neglected. Both majority- and minority-carrier injection is considered. First, the carrier mobility is taken to be constant. The current and voltage are expressed as functions of the injection level and the normalized carrier transit time, not regarding the actual boundary condition (at the injecting electrode). A space-charge factor which indicates the nonuniformity of the electric field is also defined and computed. Then, various physical situations, such as the space-charge-limited current diode, the shallow-barrier contact diode, the Schottky emission diode, and the emitter-current-limited injection can be studied. Universal diagrams for majority- and minority-carrier injection, respectively, allow evaluation of the space-charge effects and calculation of the J-V dependence by taking into account the proper boundary condition. Finally, an arbitrary velocity-field dependence and the possibility of a negative conductance on the static characteristic is discussed.
Laser damage in triglycine sulfate: Experimental results and thermal analysis
Authors: Bartoli F. , Kruer M. , Esterowitz L. , Allen R.
Published: February 2004

An investigation of the effects of 10.6-μm laser radiation on triglycine-sulfate (TGS) crystals determined that the primary irreversible damage mechanisms in TGS pyroelectric detectors are cracking and thermal decomposition (charring). Irradiation thresholds for cracking and charring were determined for TGS crystals of typical detector dimensions as a function of laser power density and irradiation time. These energy density thresholds exhibit two distinct regions of behavior: For short irradiation times E0 is independent of τ while for long times E0 varies as τ1/2. The thresholds are given empirically by E0 (crack) = [0.65 + 22(τ)1/2] J/cm2 and E0(char) = [4.0 + 34 (τ)1/2] J/cm2. A theoretical model describing thermally induced damage in irradiated crystals is presented. The energy density damage thresholds obtained from this model are compared to the experimental results. These results on material damage are used to predict damage thresholds in operating TGS detectors. These predictions are in good agreement with experimentally determined detector thresholds.
Correction of eddy current errors in electron beam deflection
Authors: Wardly G. A.
Published: February 2004

When electron beams are to be rapidly and accurately deflected by magnetic means, there are some cases in which the deflection yoke is surrounded by a conducting magnetic tube. Eddy currents are set up in the tube which result in time-dependent positional errors. A simplified treatment of the problem shows how the positional errors can be reduced by means of compensating coil pairs or hybridized saddle-toroidal yokes.
Source of error in foil thickness calibration by x-ray transmission
Authors: Boster Thomas A.
Published: February 2004

It is convenient to measure foil weight and area and use known values of density to calculate an average thickness. It is also possible to measure the transmission of monochromatic x rays through the foil and use accepted values of the absorption coefficient to determine foil thickness. If this x-ray transmission measurement is performed over a large area of an irregular foil, the resulting calculation of average foil thickness will not be in agreement with the weight-area method. The purpose of this paper is to indicate the error introduced in the average thickness measurement by examining the disparity in transmission between a uniform foil and several nonuniform foils having the same average thickness.
Lattice parameter of a crystal containing large perfect dislocation loops
Authors: Kelly P. M.
Published: February 2004

This paper shows that, contrary to some previously published work, large perfect dislocation loops do not alter the lattice parameter of a crystal. This conclusion has been verified by optical diffraction experiments using an elastic model of a dislocation loop.
Lattice parameter and volume of crystals containing prismatic dislocation loops
Authors: Keating D. T. , Goland A. N.
Published: February 2004

Contrary to the conclusion in the preceding communication, elasticity theory predicts a lattice parameter change due to the presence of a uniform distribution of prismatic dislocation loops. This result, previously derived by us on the basis of isotropic elasticity theory, has been shown by others to be valid for an anisotropic medium as well. That is, a random distribution of prismatic dislocation loops all with Burgers vector b produces a mean strain and lattice dilatation in the direction b. In this communication we review the steps leading to this result.
Comments on ``Electrode polarization of ionic conductors''
Authors: Mitoff S. P. , Charles R. J.
Published: February 2004

Macdonald analyzes the results and interpretations of an earlier experimental work by Mitoff and Charles, in which it was concluded that observed capacitances were too large to be explained by space-charge polarization due to blocking of a single mobile ion. These comments indicate the difficulties and uncertainties that arise in attempts to apply to this case two mobile ion models, in which the possibility of allowing the mobility of one of the ions to become zero is not explicitly accounted for.
The compensation bubble: A new type of magnetic bubble
Authors: Krumme Jens-Peter , Hansen Peter
Published: February 2004

A new type of magnetic bubble, which we call ``compensation bubble'', is observed as a limiting case of a Bloch wall bubble in (111) wafers of Y3Fe5−tGatO12 with a cylindrical compensation plane that arises from a radial gradient of the Ga content t. The relevant material parameters are measured and the structure of the compensation wall forming the compensation bubble is investigated.
Applicability of exponentially attractive and repulsive interactomic potential functions in the description of cubic crystals
Authors: Milstein Frederick
Published: February 2004

The well-known Morse function φ(r) = D {exp [−2α(r−r0)] −2 exp [−α(r−r0)]} can be considered to be a particular case of the general family of potential functions with exponential attraction and exponential repulsion, viz., φm(r) = [D/(m−1)] {exp[−mα(r−r0)] −m × exp[−α(r−r0)]}. This study examines the suitability of applying the functions φm (r) to the description of mechanical properties of cubic crystals. For bcc lattices, the ratio C11/C12 for the theoretical model of the crystal made up of atoms with φm (r) interatomic interactions is shown to be too small to provide a realistic description of bcc metals; also, the bcc crystals are found to be inherently unstable for larger values of αa0, where a0 is the lattice parameter of the crystal. For fcc lattices, however, the theoretical model of the crystal is found to be mechanically stable for arbitrary (i.e., m>1) exponentially attractive and repulsive interactions and the elastic moduli C11 and C12 of the theoretical fcc crystals are found to be capable of conforming to the respective experimental values of fcc metals. The results are in agreement with Born's analyses of lattice stability. Numerical values of D, α, and r0 are calculated for several different values of the parameter m for fcc Ni using experimental values of C11, C12, and lattice parameter. The element Ni is selected because, among the fcc metals, Ni most closely obeys the Cauchy condition C12 = C44. The functions φm are then used to calculate theoretical pressure versus volume (P-V) behavior (at pressures large enough to produce considerable anharmonicity) and the results are compared with experiment; good agreement is found between the calculated and experimental P-V relations.
On the electroacoustic waves guided by a cylindrical piezoelectric interface
Authors: Chen C. L.
Published: February 2004

The characteristics of electroacoustic surface waves supported by a curved piezoelectric-vacuum boundary are studied. A coaxial structure with a piezoelectric insulator as the inner cylinder and an electric conductor as the outer cylinder is considered. A dispersion relation for electroacoustic surface waves circulating around the periphery of the piezoelectric cylinder is obtained. Asymptotic solutions are compared with numerical solutions. Profiles for the mechanical displacement and electric potential for various modes are presented. Possible application as delay lines with long-time delay is indicated.
Vapor-phase growth and electrical conductivity of pure and impurity-doped ammonium halide crystals
Authors: Radhakrishna S. , Sharma B. D.
Published: February 2004

Ideal growth parameters for obtaining large transparent crystals of NH4Cl and NH4Br by vapor-phase technique are described. The electrical conductivity of such cystals and crystals grown from solution are reported. In pure NH4Cl crystals two regions with slopes 1.26 and 0.8 eV are obtained in the logσT vs 1/T plot. In impurity-doped NH4Cl crystals a third region with slope 1.04 eV is also observed. In pure NH4Br crystals two regions with slopes 1.06 and 0.66 eV are obtained.
Kinetics of the formation of hafnium silicides on silicon
Authors: Ziegler J. F. , Mayer J. W. , Kircher C. J. , Tu K. N.
Published: February 2004

We have investigated the composition and growth kinetics of hafnium silicides (HfSi and HfSi2) formed from thin films of hafnium sputter deposited on silicon. Backscattering of MeV He ions was used to monitor the growth of the silicide phases and to determine the Si/Hf concentration ratios. Seemann-Bohlin x-ray diffraction techniques provided identification of the phases and an estimate of the crystallite size of the films. The stable-phase HfSi forms in the temperature region 550–650 °C. The reaction initiates at the Hf/Si interface and the thickness of the HfSi increases proportional to the square root of time. The HfSi grows by diffusion of Si through the already formed phase with an interdiffusion constant D ≃ 2.4 exp(−EA/k T) cm2/sec with EA = 2.5 eV. Different behavior is observed for the formation of the HfSi2. In this case the silicide forms simultaneously throughout the HfSi layer at temperatures above 750 °C. We propose that the HfSi2 nucleates at the grain boundaries of the HfSi, rather than at the Si/HfSi interface. The transition to HfSi2 is completed rapidly because of the large density of nucleation sites and the small grain size of the film.
Elastic constants of praseodymium single crystals in the temperature range 4.2–300 K
Authors: Greiner J. D. , Schiltz R. J. , Tonnies J. J. , Spedding F. H. , Smith J. F.
Published: February 2004

The elastic constants of single crystals of double hcp allotrope of praseodymium have been measured over the temperature range 4.2–300 K. Maxima are observed near 100 K in the temperature dependences of C11, C33, and (C11 − C12)/2, and minima are observed near 30 K. The maxima correlate with the upper temperature limit of an anomalous contribution which has been reported in the heat capacity. The minima correlate with peculiar behavior which has been observed in other physical phenomena. Inference may be drawn from the elasticity data that the thermal expansion behavior of praseodymium at low temperatures is very highly anisotropic. Comparison of the elastic constants of praseodymium with available data for the other rare earths shows that the praseodymium data fit a general pattern. Evaluation from the elastic constants shows that the Debye temperature of praseodymium remains nearly constant throughout the temperature range of measurement within ± 2 K of 152 K.