bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies of stress compensated quartz resonators with ultralinear frequency-temperature responses
Authors: Nakazawa Mitsuo , Ballato Arthur , Lukaszek Theodore
Published: July 2002

Stress compensated quartz resonators having ultralinear frequency-temperature responses have been discovered, consisting of doubly rotated cuts whose orientations, defined in terms of the polar angles φ and θ, lie on a locus where the second-order temperature coefficients of frequency are zero in the range of φ=10 °±2 ° and θ=110 °±5 °. These angles of orientation are in close proximity to, or on the locus of, zero frequency coefficients of stress and are thus referred to as new linear and stress compensated (NLSC) cuts. In the vicinity of the NLSC cuts, a relatively strong 123̄1 x-ray plane exists at φ equal to 10.9 ° and θ equal to +106.6 °. This x-ray plane makes the manufacture of NLSC cuts easier and cheaper than ones previously reported. In this paper the theoretical and experimental values of the frequency-temperature responses and some physical features of NLSC cuts are discussed.
Explosive containment with spherically tamped powders
Authors: Glenn L. A.
Published: July 2002

An effective technique for maximizing the explosive charge that a given container can safely handle is to fill the space between the charge and the container walls with a porous medium or a powder. Using the wrong powder, however, can be worse than using no powder at all. Moreover, a powder-filled container that performs very well with a small charge may also be worse than a powderless system when the charge is increased. An analysis of this problem is developed with the aim of identifying appropriate buffer material properties and the conditions under which breakdown occurs. The results are compared with various experiments performed with graphite powder, coke chunks, granular salt, snow, and vermiculite.
Pit formation during laser marking of thin organic films
Authors: Chung Tai-Shung
Published: July 2002

The governing equations for the transitional fluid motion and pit contour induced by the laser marking and the thermocapillary are derived. The rate of thickness change is controlled by two factors: the surface tension force and the gravitation force; the former is much more important than the latter. The temperature rise in a thin optical layer is calculated based on the Poynting vector theorem. Calculated results indicate that the temperature profile follows a Gaussian distribution, and is in agreement with previous reports. Mathematical modeling shows that the rate of pit formation is strongly related to the surface tension, melt viscosity, layer thickness, and optical properties of the recording layer. The effects of the marking conditions, substrates, and convectional heat transfer on pit contour are also determined. In addition, the limitations of this model are discussed in detail.
Interface plasma excitations in step  p-n junctions
Authors: Pimpale Ashok , Paranjape B. V.
Published: July 2002

Localized interface plasma modes in  p-n junctions are studied by applying a hydrodynamic model taking full retardation effects into account. Using a Shockley model of the  p-n junction, the problem is analogous to that of an electron plasma and a hole plasma separated by a depletion region. The dispersion relation for the localized modes is obtained by using the continuity conditions for the electric and magnetic fields at the boundaries of the depletion region. The low-frequency plasma mode in the electrostatic limit has a dispersion relation ω≂(kW)1/2ωp for long wavelengths. It is shown that this mode does not couple with the electromagnetic radiation. These modes can interact with ultrasound and possible experiments are suggested. The maximum sound frequency that can be absorbed by this plasma mode is obtained. For sound waves below this maximum frequency absorption can occur at a particular angle of incidence of the sound wave. Typical numerical results have been given for the case of silicon.
Chaos and phase lock in long Josephson junctions
Authors: Cirillo M.
Published: July 2002

Results of extensive digital simulations of a long Josephson junction subject to the presence of dc and rf driving currents are reported. The dynamic behavior of this system is mapped as a function of rf amplitude and frequency of the parameter set which leads to fluxon oscillations in the absence of an rf drive. In response of the rf excitation the junction is shown to exhibit a variety of behaviors including periodic motion in which the fluxon oscillation is phase locked to the rf frequency, chaotic motion in which spatial structure persists, and spatially uniform periodic and chaotic motion.
InGaAsP (1.3 μm) grown by liquid-phase epitaxy in the V groove of a channeled InP substrate: A photoluminescence study
Authors: Swaminathan V. , Koos G. L. , Wilt D. P.
Published: July 2002

The photoluminescence characteristics of a 1.3-μm undoped n-type InGaAsP grown lattice matched by liquid-phase epitaxy in the V grooves of a channeled InP substrate are compared with that grown over a planar substrate. In the 5.5 K photoluminescence spectrum, for both types of growth the epitaxial layer exhibits two well-defined and sharp (FWHM∼7–8 meV) bands at 1.016 and 0.99 eV. Both peaks are assigned to band-edge luminescence arising from two different compositions in the epilayer, the 0.99-eV peak arising solely from a transient growth region present near the substrate–epi interface. It is found that the transient growth region can be enhanced in the V channels perhaps due to additional perturbations due to growth on nonplanar substrates.
Possibility of obtaining coherent radiation from a solid state undulator
Authors: Bogacz S. A. , Ketterson J. B.
Published: July 2002

The idea of using a crystal lattice or a superlattice as an undulator for a free electron laser is explored. A purely classical treatment of relativistic positrons channeling through the proposed structure is performed in a self-consistent fashion involving the wave equation for the radiating electromagnetic field and the kinetic equation for the positron distribution function. The (positive) gain coefficient for a forward radiating field is obtained in closed form. Matching the Kumakhov channeling resonance to the undulator frequency further enhances the gain. This result, combined with a feedback mechanism arising from Bragg diffraction within the basic crystal lattice, leads to an instability of the radiation inside the crystal. A simple threshold condition involving the atomic scattering factor and the net gain is formulated. Finally, a numerical estimate of the Kumakhov-enhanced gain coefficient is made for the (110) planar channeling in a strain-modulated Si superlattice.
CO2 laser spectroscopy of shallow and deep levels in n-InSb by photo-Hall techniques
Authors: Littler C. L. , Seiler D. G.
Published: July 2002

We report the first use of laser-induced photo-Hall techniques to investigate shallow and deep levels in n-InSb. From these measurements we show that photo-Hall techniques provide a very sensitive measure of the photoinduced changes in the free-electron concentration of InSb due to weak transitions from impurity or defect levels. As a result a new class of impurity transitions, referred to as LO phonon-assisted impurity cyclotron resonance harmonics, have been identified. In addition, time-resolved and intensity-dependent photo-Hall studies performed for temperatures between 3.6 and 20 K have resulted in the determination of absorption coefficients and recombination rates associated with the weak absorption of CO2 laser radiation by shallow and deep levels in n-InSb.
Analytic modeling of the discharge of a unipolar photoconductor
Authors: Young Ralph H.
Published: July 2002

The discharge of a photoconductor under open-circuit boundary conditions (e.g., xerographic discharge) is investigated for the case in which only one carrier (e.g., holes) is mobile. Bulk recombination is taken into account. A general solution for the electric field and analytic expressions for the surface potential are obtained for the case of flash illumination. The space and time evolution in the limit of low-intensity illumination exhibits remarkable scaling properties and is governed by a single nonlinear differential equation in one variable. A criterion is derived for predicting whether flash illumination will produce a larger or smaller discharge than a slower illumination with the same total number of photons.
Time-resolved Raman scattering measurement of photoexcited plasmon in GaP crystals
Authors: Yugami H. , Nakashima S. , Oka Y. , Hangyo M. , Mitsuishi A.
Published: July 2002

An overdamped plasmon-LO phonon coupled mode in undoped GaP crystals has been observed under high excitation condition. We have studied the relaxation process of the coupled mode in the time range of nonoseconds using a time-resolved Raman scattering technique at 81 K. The decay time of photocreated free carriers has been estimated from line-shape fitting of the coupled mode in the time-resolved Raman spectra. The decay time obtained from the Raman study has been compared with the value obtained from luminescence measurements. The plasmon hybridized with the LO phonon is found to be a gaslike electron-hole plasma.
Failure of tungsten ribbon filaments by formation and growth of hot spots
Authors: Walter John L.
Published: July 2002

The mechanism of formation and growth of hot spots was studied using filaments made of doped tungsten foil which were burned at constant voltage to incipient failure in vacuo and in half an atmosphere of nitrogen. The grain size and morphology of the filaments were set by controlling the heating rate to the initial operating temperature, 2300 °C. The nucleation and growth of hot spots were observed and measured by optical pyrometry. The rate of growth of the hot spot was initially linear and directly related to the grain size of the filament. Filament life was greater the smaller the grain size except for filaments with grain size approaching that of a single crystal. The position of the hot spot was fixed along the length of the filament and centered on a particular grain boundary or group of boundaries. From the linear rate of growth of the hot spot and from other evidence, it was concluded that the hot spot was generated by migration of vacancies to form voids at the potassium bubbles near a grain boundary. Growth and coalescence of these voids decreased the cross-section area of the filament, thus nucleating a hot spot. This mechanism explained all of the experimental observations.
Zn diffusion in GaAs obtained by a simple open-tube technique
Authors: Oren M. , Masum Choudhury A. N. M.
Published: July 2002

Zn diffusion into 2-in.-diam semi-insulating GaAs wafers has been carried out by a simple, open-tube diffusion method using a commercially available GaAsZn solid source and without surface coating or encapsulation. High-quality (μ=75–100 cm2/V s) layers with a flat carrier concentration and sharp cutoff Zn distribution have been obtained. The p-type layers obtained by this method are uniform across the wafer, and the technique can be easily scaled up. Selective diffusion of Zn was also demonstrated with this technique, using a plasma-deposited Si3N4 as a diffusion mask.
Performance of a magnetic susceptometer for thin films and surfaces
Authors: Meservey R. , Moodera J. S.
Published: July 2002

The design and performance of a magnetic susceptometer for thin films and surfaces is described. The device uses a 14-MHz resonant circuit driven by a tunnel diode oscillator with a superconducting meander line as the inductive element. Magnetic properties of thin films deposited near the line in ultrahigh vacuum at low temperature affect the inductance of the meander line and thus the frequency. The device can detect a susceptibility change equal to that of a change in Fe thickness of 0.03 atomic layers. The minimum detectable change in the diamagnetism of superconducting Pb corresponds to a thickness difference of 10−3 Å. The effect of 10−6 atomic layers of Fe can be detected by its depairing effect on a superconducting Pb film. The oscillator circuit including the film being studied is analyzed and the oscillation frequency calculated so that the effect of the various circuit elements can be determined. Suggestions for extending this technique are given.
Backscattering analysis of AuGe-Ni ohmic contacts of n-GaAs
Authors: Cohen D. D. , Kalkur T. S. , Sutherland G. J. , Nassibian A. G.
Published: July 2002

AuGe-Ni is widely used for the fabrication of ohmic contacts to n-GaAs. The alloying behavior of evaporated AuGe-Ni alloyed by furnace and scanning electron beam (SEB) is characterized by Rutherford backscattering with 2-MeV 4He+ ions. The redistribution and diffusion of constitutents involved in the ohmic contact formation is studied by comparing the experimental spectrum with theoretically computed spectra. The studies show that SEB-alloyed contacts undergo less redistribution of contact constituents compared with furnace-alloyed contacts. It is established that the penetration depth of Au for furnace-alloyed contacts increases with metallization thickness, whereas for SEB-alloyed contacts the penetration depth is independent of metallization thickness.
Oxidation behavior of nitrogen-ion implanted Fe50Ni50 alloy: A conversion electron Mössbauer spectroscopic study
Authors: Dorik Y. S. , Chaudhari S. M. , Ghaisas S. V. , Ogale S. B. , Bhide V. G.
Published: July 2002

The oxidation behavior of Fe50Ni50 alloy foils implanted with 80-keV N+2 ions at a dose of ∼1016 ions/cm2 is studied by using the technique of conversion electron Mössbauer spectroscopy (CEMS). The oxidation is carried out in air at various temperatures up to a maximum of 500 °C, for different intervals of time. It is shown that the as-implanted as well as implanted and annealed foils exhibit higher resistance to oxidation as compared to the virgin foils; the oxidation resistance being significantly higher in the case of the annealed foils. It is established that the reason for improvement in oxidation resistance is nickel enrichment of the surface layers leading to formation of diffusion-limiting nickel-rich NixFe3−xO4 phase at the oxide-metal interface during the early oxidation process. The presence of this phase in the oxidized samples is inferred from the hyperfine interactions exhibited by the corresponding CEMS spectra and also from x-ray diffraction measurements.
Characterization of ion-implantation doping of strained-layer superlattices. II. Optical and electrical properties
Authors: Myers D. R. , Biefeld R. M. , Gourley P. L. , Wiczer J. J. , Zipperian T. E. , Fritz I. J. , Barnes C. E. , Osbourn G. C.
Published: July 2002

We have investigated the properties of Ga(AsP)/GaP strained-layer superlattices (SLSs) that have been doped by implantation of 1×1015/cm2, 75 keV Be+ followed by controlled-atmosphere annealing at 825 °C for 10 min. Our results indicate that doping of these strained-layer superlattices without disordering is a viable process. Liquid-helium temperature photoluminescence suggests a binding energy for the implanted acceptors of 50 meV, consistent with that of beryllium in GaP-based alloys. The implantation-doped regions exhibit room-temperature electrical activation of 15% and hole mobilities of 20 cm2/V s, consistent with the values expected for type-converted GaP-based alloys. SLS diodes fabricated by this process exhibit excellent rectification properties, with a forward turn-on voltage of approximately 1.8 V and low values of room-temperature reverse leakage current densities. Diodes formed from SLSs with original n-type doping of 1×1017/cm3 have typical reverse leakage current densities of 1×10−7 A/cm2 at −10 V, despite the depletion region penetrating approximately ten interfaces of the SLS at this bias. Deep-level transient spectroscopy demonstrates the existence of defect centers, whose densities and signatures are similar to those found in ion-implanted GaP. The implanted photodiodes exhibit a wavelength-dependent photoresponse characteristic of grown-junction SLS photodetectors in the same chemical system. Examination of the spatial response of the photodiodes to a tightly focussed (FWHM=2.45 μm) laser beam at a wavelength of 488 nm indicates that the photoresponse from the device is uniform to within 10% for regions away from the edges of the implanted regions. Modelling of the wavelength-dependent and the spatially dependent photoresponse allows an estimate of minority-carrier diffusion lengths for electrons and holes of 1.0 μm parallel to the SLS layers and 0.1 μm perpendicular to the SLS layers. The excellent electrical and optical properties of the implanted and annealed SLS materials implies additional device applications for these novel materials.
An x-ray photoelectron spectroscopy study of the thermal nitridation of SiO2/Si
Authors: Vasquez R. P. , Madhukar A. , Grunthaner F. J. , Naiman M. L.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) has been used to study the dependence of the nitrogen distribution in thermally nitrided SiO2 films on the nitridation time and temperature. Intensity analysis of the XPS data, of which a detailed derivation is presented, in conjunction with chemical depth profiling, has been used to determine the compositional variation with depth in the nitrided film. The experimental results show that, for a nitridation temperature of 1000 °C, the maximum nitrogen concentration in the interfacial region occurs at the interface in the initial stages of nitridation (within 10 min), while at later times (30 min and longer) the maximum occurs 20–25 Å away from the interface. For a nitridation temperature of 1150 °C, the maximum interfacial nitrogen concentration occurs 20 Å from the interface for nitridation times as short as 5 min, but saturates at a lower value than that observed at 1000 °C. For a nitridation temperature of 800 °C, the maximum interfacial nitrogen concentration remains at the interface for nitridation times up to 4 h. These data can be understood within a previously developed kinetic model which explicitly considers the effect of interfacial strain on the nitridation kinetics. In addition, the intensity of a fluorine marker is found to correlate with the nitrogen concentration. It is postulated that the fluorine bonds preferentially to defects, and it is shown that this postulate and the measured fluorine intensities are consistent with a strain-dependent energy of formation of defects, proposed recently to explain electrical results.
Front surface passivation of silicon solar cells with antireflection coating
Authors: Crotty G. , Daud T. , Kachare R.
Published: July 2002

It is demonstrated that the deposition and postdeposition sintering of an antireflection (AR) coating in hydrogen acts to passivate silicon solar cells. Cells with and without an SiO2 passivating layer, coated with a TiOx/Al2O3 AR coating showed comparable enhancements in short-wavelength spectral response and in open-circuit voltage Voc after sintering at 400 °C for 5 min in a hydrogen ambient. The improvement in Voc of cells without SiO2 is attributed to front surface passivation by the AR coating during processing.
An approximate solution to the scattering integral for general interatomic potentials
Authors: Blanchard J. P. , Ghoniem N. M. , Chou S. P.
Published: July 2002

An approximation of the scattering integral is derived by expanding the potential about the distance of closest approach and truncating the expansion so that the integral can be performed analytically. The results are improved by using the approximate integrand only in the region near the closest approach, and assuming zero potential for large distances. The analytical solution, which requires little computation time relative to other solution methods, is shown to yield sufficient accuracy for a wide range of particle energies and impact parameters, using both the Moliere and ‘‘Universal’’ potentials.
Study of magnetic and recording properties of dc magnetron sputtered CoCr thin films
Authors: Ravipati Durga P. , Haines W. G. , Sivertsen J. M. , Judy J. H.
Published: July 2002

CoCr thin films were prepared by dc magnetron sputtering, on aluminum substrates in a dual-sided sputtering system. Ouchi and Iwasaki [J. Appl. Phys. 57, 4013 (1985)] have reported that for magnetron sputtered CoCr thin films on a substrate at constant temperature, the coercivity is dependent on the substrate temperature and not on the deposition rate. However, for applications in which no heat sinking is applied during deposition the temperature of the film and the substrate increases with time which produces a film with a coercivity gradient that affects both the magnetic and the recording properties. This report investigates the effects of this coercivity gradient on the recorded output amplitudes. The average perpendicular coercivity Hc(⊥) was observed to increase from 65 to 440 Oe, and then decrease with further increase in thickness. The average dispersion of the c axis, Δθ50, decreased from 6.5°, for the thin films, to 2.8° for the thick films. Coercivity measurements reveal a relatively soft film [Hc(⊥)<100 Oe] for the initial layers. The initial soft layer acts as a magnetic flux sink as does the underlayer in a double-layer media when recorded using a thin-film head. The films with thicker soft layers (100-Å/s deposition rate) show 30–40 % more output when compared to films with thin soft initial layers (lower deposition rates). Comparable recorded outputs were observed when the thick soft layer (1 μm thick at 100-Å/s deposition rate) was replaced with an Fe-Ni-Cr ferromagnetic alloy [Hc(⊥)<80 Oe].
On the coercivity of sputtered CoCr films (abstract)
Authors: Gau J.-S. , Cofield M. L.
Published: July 2002

CoCr films with the nominal composition of 20 at. % Cr were rf sputtered onto a glass substrate as a function of both substrate temperature (Ts) and argon pressure (PAr). By controlling the process parameters, both positive effective and in-plane anisotropy films can be obtained. The angular variation of the coercivities of these films (which serves as a test of the possible coercivity mechanisms) has been measured.1 We found that no unique correspondence exists between our experimental data and Wuori’s theoretical models of the reversal mechanism.2 By changing the substrate temperature, a family of monotonically decreasing, angular-dependent coercivity curves are obtained. The perpendicular film made at low Ts and PAr shows a slowly decreasing dependence of the coercivity as a function of the field angle. Furthermore, the easy-axis hysteresis loop displays a reentrant magnetization effect. The complexity of the magnetization reversal process is attributed to nonhomogeneous crystal structure. (All of these films exhibit evidence of a soft magnetic underlayer.) Ferromagnetic resonance (FMR) spectra measured at 9.8 and 35.2 GHz show multiple resonance structures. The anisotropy constant of the films become increasingly more negative with increasing argon pressure and/or substrate temperature. These results are consistent with bulk magnetic measurements made by vibrating sample magnetometry and microstructural observations using transmission electron microscopy.3 Details of the structural characterization by FMR and its implication on the coercivity mechanism will be presented.
Induced magnetic form factor of CeCu6
Authors: Vrtis M. L. , Loong C.-K. , Hinks D. G. , Stassis C. , Arthur J.
Published: July 2002

Polarized neutron scattering techniques have been used to study the spatial distribution and temperature dependence of the magnetization induced by an externally applied magnetic field in a single crystal of CeCu6, a heavy-fermion compound that remains paramagnetic and nonsuperconducting down to ∼10 mK. The measurements were performed at 4.2 K and 92 mK in an applied magnetic field of 50 kOe. We find that the induced magnetization is predominately of 4f electronic character and exhibits Pauli-like behavior in the 4.2 K–92 mK temperature region.
π-bonded model of an oxygen-vacancy center in SiO2
Authors: Baranowski J. M. , Strzalkowski I. , Marczewski M. , Kowalski M.
Published: July 2002

Tight-binding total energy calculations of the two possible states of the neutral oxygen-vacancy center in SiO2 have been performed within the bond orbital approximation. It has been shown that the lowest energy state is realized by a transfer of one electron from a nonbonding p oxygen orbital (next to the vacancy) into an opposite silicon dangling hybrid, and then by the formation of a π bond between the remaining oxygen p electron and the nearest silicon dangling hybrid. The new π-bonded model of the oxygen-vacancy center is discussed and the results obtained are compared with experimental data. The most important aspect of this work is the demonstration that for defects in SiO2, the π interactions are very important and should not be neglected in describing the physics of many problems in SiO2.
Relativistic quantum mechanical analysis of a free electron laser
Authors: Schächter L.
Published: July 2002

A free electron laser based on a magnetic undulator in its linear regime is analyzed using the Klein–Gordon equation to describe the electron dynamics. Special attention is paid to an electromagnetic wave with a general polarization and an arbitrary spectrum. The influence of high harmonics is investigated. The effect of decreasing periodicity of the wiggler on the analysis is investigated too.
〈110〉 channeled depth distributions and values of electronic stopping for the fourth-row transition elements (Z=19 – 28) in the silicon crystal
Authors: Wilson R. G.
Published: July 2002

We report experimentally measured depth distributions of the transitions elements of the fourth row of the periodic table channeled in the 〈110〉 direction of the Si crystal and calculate the corresponding values of electronic stopping Se. These values show the Z1-dependent nature of electronic stopping in this region of atomic number. The 〈110〉 channeled depth distributions of these transition (d shell) elements exhibit three peaks; the possible origin of the middle peak, which is not observed for the nontransition elements, is discussed.
Alteration of GaAs wafer heated locally by Nd:YAG laser beam
Authors: Kawamura Tsutomu , Kamejima Taibun
Published: July 2002

A GaAs wafer has been locally heated by Nd:YAG laser beam between 600 and 1240 °C (melting point of GaAs) in air. When the temperature gradient is very steep, diffuse streak patterns and fiberlike patterns, in addition to the reflections of GaAs substrate, rapidly and clearly appeared in in situ observation of x-ray Laue photographs from the periphery of the irradiated area by the laser beam. This altered phase material is assigned to the heavily mosaic structure of twelve-twinned β-Ga2O3 crystals, based on the results of x-ray precession photography and ion microprobe analysis. It is clarified, moreover, that the disordered phase of GaAs plays an important role for the formation of that mosaic oxide crystal. The formation mechanisms of these two altered phase materials are discussed. An effective suppression method of these altered phase materials is also presented.
Low-temperature plasma anodization of tantalum silicides
Authors: Perrière J. , Siejka J. , Climent A. , Navarro E. , Martinez-Duart J. M.
Published: July 2002

The low-temperature plasma anodization of cosputtered Ta silicide has been studied. The anodization parameters, oxide growth rate, electric field, and faradic efficiency showed a strong dependence on the silicide formation (with or without annealing). Rutherford backscattering techniques were employed to characterize the oxide films and it was found that the plasma oxides grown on as-deposited silicide are of uniform composition in the oxide bulk, but the near-surface region shows a slight Si oxide enrichment, and, thus, a Ta oxide depletion. On the contrary, for annealed (950 °C) silicides, when the hexagonal Si-enriched TaSi2 phase is formed, a high-surface enrichment in Ta oxide is observed in the plasma grown oxides. The insulating properties of the oxide films as determined by capacitance, electrical conductivity, and dielectric strength measurements also depend on the silicide formation, and these properties were correlated to the cation depth distributions in the oxide mixtures. A spectacular difference in the dielectric constant has been found between oxide formed on an as-deposited layer (∼12) and on an annealed one (∼6). This is a consequence of continuous (although nonconstant) cation’s mixture in the first case and layered structure in the second.
Reply to ‘‘Comment on ‘Rapid thermal annealing and regrowth of thermal donors’ ’’ [J. Appl. Phys. 5
9, 3495 (1986)]
Authors: Stein H. J. , Hahn S. K. , Shatas S. C.
Published: July 2002

An activation-energy determination from isothermal-annealing experiments without establishing an order for decay kinetics is discussed.
Comments on ‘‘Direct experimental determination of voltage across high-low junctions’’ [J. Appl. Phys. 5
9, 285 (1985)]
Authors: Bellone S. , Caruso A. , Vitale G.
Published: July 2002

Daud and Lindholm [J. Appl. Phys. 59, 285 (1985)] have recently proposed a method to measure the voltage across a high–low transition by using a three-terminal device structure. We dispute the validity of the asumptions on which their theoretical model is based and point out that a similar device structure was previously proposed to the same purpose.
Influence of {111} regrowth sidewall interfaces on the performance of 1.54 μm InGaAsP/InP etched-mesa-buried-heterostructure lasers
Authors: Chu S. N. G. , Logan R. A. , Temkin H.
Published: July 2002

The quality of {111} sidewall interfaces formed during liquid phase epitaxial regrowth around an etched mesa in an etched-mesa-buried-heterostructure laser device has been studied using cross-sectional transmission electron microscopy, cross-sectional transmission cathodoluminescence, and energy dispersive x-ray analysis. The results are correlated with the optical performance and electrical characteristics of the device before the aging test. It is found that the interfacial lattice imperfection will affect the device performance only when the defects are nonradiative recombination centers or they constitute a leakage path for the current. The possible causes for a defective interface will be discussed.
Defects dynamics in as-grown and electrodiffused quartz: An interpretation of the predose effect
Authors: Martini M. , Spinolo G. , Vedda A.
Published: July 2002

In the thermally stimulated luminescence (TSL) of quartz there is always a glow peak at T=100 °C, whose sensitivity (response to a unit irradiation dose) increases after repeated irradiations followed by heating. This phenomenon, known as predose, has been studied in synthetic quartzes, both as grown and deprived of alkali ions, this latter process being obtained by electrodiffusion (‘‘sweeping out’’). Evidence is given that only unswept or partially swept quartzes show the predose effect. Through the study of the combined effects of irradiation and thermal annealing, following two different procedures, a relation between the formation of Al-OH− centers and the 100 °C TSL intensity is established. We propose that the enhancement of luminescence happens through the modification of oxygen hole centers from precursors containing hydrogen to peroxy radicals (e.g., O−2 ions) which are responsible for the luminescence. The H+ ions, made available in such a process, are responsible for the Al-OH− centers formation.
Ranges and depth distributions of 200-keV He ions channeled in Si, Ge, and GaAs crystals
Authors: Wilson R. G.
Published: July 2002

We report depth distributions of 200-keV He ions channeled in the 〈100〉 and 〈110〉 directions of Si, Ge, and GaAs crystals and in a random orientation of each crystal, measured using secondary ion mass spectrometry. The 〈100〉 channeled profiles agree with the random profiles within experimental error. The 〈110〉 channeled profiles are about 1.7, 2.3, and 2.2 times as deep as the random peaks (projected range) for the three crystals, respectively. Assuming velocity-proportional electronic stopping, values of electronic stopping are calculated for He in Si, Ge, and GaAs. Fractions of He ions backscattered into the vacuum are estimated. Profiles for Ge and GaAs, with the same average atomic number, are compared. Range and profile shape parameters are tabulated.
Magneto-optical Kerr effect of rf-sputtered PtMnSb thin films
Authors: Ohyama Ryuji , Koyanagi Tsuyoshi , Matsubara Kakuei
Published: July 2002

Thin films of the C1b-phase Heusler alloy PtMnSb, prepared by rf sputtering and subsequent annealing, have been studied in order to assess the high magneto-optical Kerr effect of this compound. The room-temperature saturation magnetization (Ms) and coercive force (Hc) for PtMnSb thin films after being annealed at 500 °C were about 400 emu/cm3 and 110 Oe, respectively. The easy axis of magnetization was parallel to the film plane for all films. The polar Kerr rotation θK for the PtMnSb films with a C1b phase has a maximum value in excess of 1.8° at 710-nm wavelength in a 5-kOe external magnetic field perpendicular to the film plane. Thin films substituted with Ni for Pt, which are an admixture of PtMnSb and an isoelectronic compound NiMnSb, are also examined. The θK peak showed a red shift, in contrast with PtMnSb containing excess Pt concentration, where a blue shift was observed. The intensity reduced significantly with increasing Ni concentration in the films.
Electron swarm behavior in nonuniform fields in nitrogen
Authors: Moratz T. J. , Pitchford L. C. , Bardsley J. N.
Published: July 2002

The transport of electrons through a background nitrogen gas under the influence of a spatially varying electric field is studied through a Monte Carlo simulation. Nonhydrodynamic effects, i.e., a nonlocal dependence of the electron transport and rate coefficients on the ratio of the field strength to the neutral density, E/N, are observed. For example, the high-energy tail of the electron-energy distribution function is sluggish in responding to the spatially varying field, and hence the ionization coefficient lags the local field value. In addition, the spatially dependent vibrational-excitation-rate coefficient goes well beyond the range of values found in hydrodynamic calculations. The results are discussed in terms of recent formulations of nonhydrodynamic transport theory and are contrasted with previous results.
Transient thermoelectric effects in intercalation compounds MxTiS2 (M=3d transition metals)
Authors: Sasaki Minoru , Koyano Mikio , Inoue Masasi
Published: July 2002

Simultaneous measurements of thermal diffusion processes of electrons and phonons in 1T-TiS2 and intercalation compounds MxTiS2 (M=Mn, Fe, Co, and Ni; x=0.1–1/3) have been made in the temperature range 78–280 K using a pulsed laser-induced ‘‘transient thermoelectric (TTE)’’ or photodiffusion effect. The initial stage of the decay curves of TTE voltage observed solely in TiS2 gives the electron-hole recombination times τr, from which capture cross sections are evaluated. At the second stage, two relaxation times (τf and τs) are observed in all crystals; the fast and slow components are associated with the intra- and intervalley scatterings through electron-phonon interactions, respectively. The evaluation of the final stage yields the thermal diffusion coefficient DT and thermal conductivity κ of these materials. The effect of intercalation of the guest 3d metals on these quantities is qualitatively discussed.
Electromagnetic resonance enhanced photoabsorption in planar metal–oxide–metal tunnel junction detectors
Authors: Soole J. B. D. , Hughes H. P. , Apsley N.
Published: July 2002

We present calculations of surface plasmon and guided wave enhanced light absorption in the metal electrodes of planar aluminum–aluminum oxide–silver and aluminum–aluminum oxide–aluminum tunnel junctions. We consider excitation, under conditions of attenuated total reflection, of both the ‘‘fast’’ and ‘‘slow’’ surface plasmons of the junction, and of TE and TM guided modes supported by a dielectric film adjoining the junction. We find that >97% absorption may be obtained at resonance in a single electrode of a practical device, the thickness of which is only a fraction of the expected photocarrier mean free path, and show how the angular width of the absorption peak may be varied by changing the adjacent dielectric media. We also show how resonant absorption may be used in a biased planar device for the detection of radiation at normal incidence.
Load following characteristics of SiGe/GaP thermoelectric generators and their response to external heating
Authors: El-Genk Mohamed S. , Seo Jong T. , Buksa John J.
Published: July 2002

This paper discusses the load following characteristics of SiGe/GaP thermoelectric (TE) generators during both steady-state and transient changes of the external load. It also investigates the performance of TE generators as they are subjected to an external heating at their cold shoes. Results show that TE generators are load following within a narrow range of external load values and that external heating impairs their performance. The load following behavior of TE generators was found to be independent of the rate of changing the external load (steady state or ramp). For a constant hot shoe temperature, external heating of the TE generators caused their cold shoe temperature to rise and consequently increased the rate of heat rejection by radiation and decreased the electric power output. Because of the enhancement in the heat rejection by radiation during the external heating of the TE generators, a large heating rate is required for the generators to cease operation. The tolerance of TE generators to external heating can effectively be increased by initially raising the TE cold shoe temperature.
Hydrostatic pressure dependence of the optical absorption edge in Bi12SiO20
Authors: Toyoda T. , Nakanishi H. , Endo S. , Irie T.
Published: July 2002

The optical absorption coefficients in Bi12SiO20 have been measured precisely at various hydrostatic pressures up to 40 kbar at room temperature. The interband gap for the indirect allowed transition was found to have a pressure coefficient (∂Eg/∂P)T of −1.20×10−6 eV/bar. Using the result of the pressure coefficient, it was indicated that the electron-phonon interaction was dominant in the temperature dependence of the indirect energy gap in Bi12SiO20.
The coupling technique: A two-wave acoustic method for the study of dislocation dynamics
Authors: Gremaud G. , Bujard M. , Benoit W.
Published: July 2002

Progress in the study of dislocation dynamics has been achieved using a two-wave acoustic method, which has been called the coupling technique. In this method, the attenuation α and the velocity v of ultrasonic waves are measured in a sample submitted simultaneously to a harmonic stress σ of low frequency. Closed curves Δα(σ) and Δv/v(σ) are drawn during each cycle of the applied stress. The shapes of these curves and their evolution are characteristic of each dislocation motion mechanism which is activated by the low-frequency applied stress. For this reason, the closed curves Δα(σ) and Δv/v(σ) can be considered as signatures of the interaction mechanism which controls the low-frequency dislocation motion. In this paper, the concept of signature is presented and explained with some experimental examples. It will also be shown that theoretical models can be developed which explain very well the experimental results.
Formation mechanism of hydrogen-associated defect centers at silica optical fiber surfaces
Authors: Hibino Yoshinori , Hanafusa Hiroaki
Published: July 2002

As a result of studies on drawing-induced defect centers in GeO2-doped optical fibers using electron-spin-resonance techniques, a hydrogen-associated center with an 11.9-mT hyperfine splitting, in addition to Ge E′ centers, is observed in as-drawn optical fibers. The concentration of the 11.9-mT center increases when the optical fibers are immersed in water. Furthermore, an increase is observed in x-irradiated optical fibers, but not in irradiated preforms. Since water molecules have very small diffusion coefficients in silica glass and since drawing-induced residual strain exists in optical fibers, it is deduced that the 11.9-mT center is intrinsic to the optical fiber surface and that its formation is due to stress corrosion of the silica glass.
Pressure and temperature derivatives of the elastic moduli of some polycrystalline semiconducting compounds using single-crystal third-order elastic constant data and the elastic-constant pressure derivatives
Authors: Rao R. Ramji , Padmaja A.
Published: July 2002

The pressure and the temperature derivatives of the bulk, shear, and Young’s moduli and of the Poisson’s ratio of some 3-5 and 2-6 polycrystalline semiconducting compounds have been calculated from Hill’s approximation. The third-order elastic constants and the pressure derivatives of the second-order elastic constants of the corresponding single-crystal compounds have been employed in these calculations. Since the single-crystal input data are experimental, we would expect the present polycrystalline calculations to correspond to experimental measurements.
Epitaxial CaF2 on GaAs(100) after ambient transfer with arsenic overlayer
Authors: Sinharoy S. , Lin Y. F. , Rieger J. H.
Published: July 2002

By using an amorphous overlayer of arsenic, it is shown that a GaAs(100) wafer, with a layer of GaAs grown on it by molecular-beam epitaxy, can be satisfactorily transferred in the laboratory atmosphere from one ultrahigh vacuum chamber to another. The clean GaAs(100) surface is retrieved in the second chamber by low-temperature (350 °C) evaporation of the arsenic overlayer. An epitaxial layer of CaF2 was grown successfully on a smooth GaAs surface retrieved in this manner. This technique offers an opportunity to investigate GaAs/epifluoride/GaAs structures by transferring samples between the GaAs growth chamber and the fluoride growth chamber without subjecting them to a higher temperature (600 °C) cleaning process.
Feasibility of laser pumping with neutron fluxes from present-day large tokamaks
Authors: Jassby D. L.
Published: July 2002

The minimum fusion-neutron flux needed to observe nuclear-pumped lasing with tokamaks can be reduced substantially by optimizing neutron scattering into the laser cell, located between adjacent toroidal-field coils. The laser lines most readily pumped are probably the 3He-Ne lines at 0.633 μm and in the infrared, where the 3He-Ne gas is excited by energetic ions produced in the 3He(n,p)T reaction. These lines are expected to lase at the levels of D-T neutron flux foreseen for the TFTR (Tokamak Fusion Test Reactor) in 1990 (≫1012 n/cm2/s), while amplification should be observable at the existing levels of D-D neutron flux (∼1010 n/cm2/s). Lasing on the 1.73 and 2.63 μm transitions of Xe may be feasible at the maximum expected levels of D-T neutron flux in TFTR enhanced by scattering.
Elimination of residual image distortion in the stigmatic ion microscope
Authors: Bernius Mark T. , Ling Yong-Chien , Morrison George H.
Published: July 2002

A combination electrostatic octupole stigmator and cosine deflector has been incorporated into the secondary ion-optical lattice of the stigmatic ion microscope. Distortion-free images are obtained with a ∼15% improved image resolution and a ∼10% increased secondary ion signal measured at the detector, the latter improvement being beneficial also for depth-profile (ion microprobe) work. The details outlined in this paper, which are easy to implement, are offered to users of the CAMECA IMS-3f secondary ion mass spectrometer for a significant improvement in its imaging capability.
Electrical derivative characteristics of InGaAsP buried heterostructure lasers with a rectifying contact
Authors: Wright P. D.
Published: July 2002

Results of a study of the electrical derivative chartacteristics of 1.3-μm InGaAsP buried heterostructure lasers with rectifying (nonlinear) electrical contacts are presented. A physical device model and an equivalent circuit model, including a metal-semiconductor contact, have been developed. This model is also appropriate to light emitting diodes and photodiodes. Solutions for the electrical derivative characteristics, dv/di and i dv/di vs i, of the equivalent circuit model are obtained and used to calculate the characteristics of 1.3-μm InGaAsP buried heterostructure lasers both with and without a rectifying contact. The calculated electrical derivative characteristics are compared to measured data for our lasers. Excellent agreement between measured and modeled characteristics is obtained and the analysis is shown to be useful for extracting detailed metal-semiconductor and p-n junction characteristics with high accuracy. The physical basis for nonlinear contacts to optoelectronic devices made from relatively wide band-gap semiconductors such as InP and InGaAsP is described. The results of this study are useful for characterization, modeling, failure mode analysis, and process control improvement of these devices.
Optical time-of-flight investigation of the exciton transport in silicon
Authors: Laurich B. , Hillmer H. , Forchel A.
Published: July 2002

The transport of carriers created at the surface of a silicon sample by a short laser pulse is investigated by a new optical time-of-flight technique. This method is based on the excitation of charge carriers in a small region of the sample and the subsequent time-resolved detection of the carrier density at a well-defined distance. This provides direct access to the carrier velocity and the carrier density distribution. In the low-temperature regime investigated here the carrier transport is shown to be performed by free excitons. A comparison of the experiment with a hydrodynamic model yields an exciton diffusivity of D=300T−1/2 cm2/s. It is shown that acoustic-phonon scattering via the deformation potential is the dominating scattering process.
A computationally fast, two-dimensional vector hysteresis model
Authors: Koehler T. R.
Published: July 2002

A new, computationally fast, two-dimensional vector hyteresis model has been developed. While the model is similar in spirit to those which compute the local magnetization as the sum of the magnetizations of a collection noninteracting Stoner–Wohlfarth particles, it ultimately, after several features to provide computational speed and flexibility are introduced, has nothing in common with the latter except the ability to treat correctly the physics of hysteresis.
Mechanisms of carbon and oxygen incorporation into thin metal films grown by laser photolysis of carbonyls
Authors: Gluck N. S. , Wolga G. J. , Bartosch C. E. , Ho W. , Ying Z.
Published: July 2002

We report the results of a series of experiments studying metal film growth by low-power UV-laser photolysis of metal carbonyls. Small-area Mo, W, and Cr films were grown on Si substrates by photolysis in a background pressure of 0.1–0.2 Torr of the carbonyl. The different metals exhibited vastly different deposit morphologies. Elemental depth profiling by Auger electron spectroscopy (AES) revealed the presence of large amounts of carbon and oxygen in the films. Ultrahigh vacuum studies of the interaction of 257- and 514-nm radiation with multilayer coverages of Mo(CO)6 and W(CO)6 adsorbed on Si(111)7×7 using high-resolution electron energy-loss spectroscopy, laser-induced desorption, and AES were performed to clarify the mechanisms of adsorbed metal carbonyl decomposition and impurity incorporation into the films. Decomposition of both the adsorbed and gas-phase carbonyls proceeds through direct electronic excitation of the molecule by absorption of the 257-nm radiation; however, the photodecomposition products of the adsorbed carbonyls are different from the gas-phase decomposition products. The evidence suggests that both the surface and the previously deposited photofragments stabilize the partially photolyzed carbonyls, preventing removal of all the CO ligands from the adsorbed species.