bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanosecond pulse discharges in C3F8-Ar mixtures
Authors: Kunhardt E. E. , White M. G.
Published: February 2003

In this paper we present results from experiments to determine the behavior of C3F8-Ar mixtures as filling gases in a uniform-field spark gap subjected to high voltage, nanosecond pulses. The gas pressure ranges from 500 to 960 Torr and the overvoltage ranges from 50% to 300%. The electrode separation is 1 cm. U-V irradiation has been used prior to the arrival of the pulse to the gap. In general, the discharge consists of very large numbers of closely packed filaments with the overall diameter being less than or equal to approximately 1 cm. The initial rate of current rise at the load is large (∼1012 A/sec). Subsequently, a phase of relatively constant current is observed the length of which changes with the concentration of C3F8. This phase has large resistance and the energy deposited into the discharge ranges from 6% to 20% of the energy in the incident pulse, as the concentration of C3F8 increased from 30% to 100%. The final state of conduction of the discharge is an arc. In light of these observations, the behavior of self- and nonself-sustained discharges is discussed.
Breakdown in air-filled microwave waveguides during pulsed operation
Authors: Anderson D. , Lisak M. , Lewin T.
Published: February 2003

A theoretical investigation is made of the threshold condition for breakdown in air-filled high power microwave waveguides during pulsed operation. The analysis concentrates on a parameter range characterized by microwave frequencies in the GHz range and pressures larger than 100 Torr. In particular, explicit analytical expressions are obtained for the dependence of breakdown field on pulse length and pulse repetition frequency.
Secondary ion mass spectrometry: Depth profiling of shallow As implants in silicon and silicon dioxide
Authors: Vandervorst W. , Maes H. E. , De Keersmaecker R. F.
Published: February 2003

The usefulness of secondary ion mass spectrometry as a process control tool in integrated circuit applications has been investigated. As a test case, shallow As implants (4–40 keV) in silicon and silicon dioxide are measured and the range parameters (projected range, range straggling, skewness, and kurtosis) are derived. In this work it is shown that the measurements of these shallow profiles are extremely sensitive to disturbing effects such as collisional mixing and/or radiation-enhanced diffusion. The effect of the primary energy and of the primary mass on the measured profiles is discussed in terms of these two mechanisms. In agreement with previous investigations it is found that low primary energies are mandatory for measuring shallow profiles without disturbing effects. However a lower limit for oxygen bombardment is encountered below which the ionization rate of the As atoms is drastically reduced over more than one order of magnitude. This limits the use of lower primary energies in the SIMS analysis of the As profiles.
Vibrational properties of HgCdTe system
Authors: Talwar D. N. , Vandevyver M.
Published: February 2003

The results of reflection spectra at 300 °K in the far-infrared region (100–400 cm−1) are reported due to low concentration of Hg atoms in the Cd-rich CdHgTe mixed crystals. A gap mode is observed at 131 cm−1 due to isolated Hg occupying Cd in CdTe. The experimental results are analyzed theoretically using the well-know Green’s function technique. The perturbation caused by low concentration of Cd(Hg) is described by the mass change at the impurity site as well as local variation of impurity-host interactions. In the nearest neighbor approximation, all the involved Green’s function matrix elements have been computed numerically by incorporating the lattice phonons from an eleven parameter rigid-ion model fitted to recent neutron data of HgTe and CdTe. We find that different substitutional defects in Hg-Cd tellurides can give rise to well-defined symmetry vibrations both within the gap and outside the maximum phonon frequency regions. Our calculations suggest that a gap mode of Hg substituted to Te is likely to be the possible explanation for the origin of the observed Ω2 mode in HgTe. In the cases of known experimental data (viz., CdTe:Hg and HgTe:Cd) we have estimated the nature of force perturbations and the results are compared and discussed with those obtained from a modified-random-element isodisplacement model.
Hydrogen dissolution in palladium: A resistometric study under pressure
Authors: Magnouche A. , Fromageau R.
Published: February 2003

The hydrogen solubility in palladium in equilibrium with H2 gas has been measured, between room temperature and 540 °C, using a resistometric method, for pressures ranging between 0.01 and 10 MPa. In these conditions, the experimentally determined values of the solubility and of the dissolution enthalpy exhibit very close agreement with those obtained by other methods (calorimetry, volumetry, etc.), or after electrolytic charging. This good agreement demonstrates the validity of the resistometric method for determination of the solubility of hydrogen in metals.
An atom-probe field-ion microscope study of 200-eV 1H+2 ions implanted in tungsten at 29 K
Authors: Macrander Albert T. , Seidman David N.
Published: February 2003

The atom-probe field-ion microscope (FIM) technique was used to study the low-temperature diffusive behavior of hydrogen (1H) in tungsten. Tungsten FIM specimens were implanted in situ with 200-eV 1H+2 ions, at a specimen temperature of 29 K. The specimens were analyzed chemically on an atomic scale, via the atom-probe FIM technique, during the controlled pulse field evaporation of the (110) planes. No hydrogen events were detected at depths below the surface which corresponded to the calculated mean projected range of either 1H or 1H2. The mean projected ranges were calculated employing a modified version of Biersack’s and Haggmark’s Monte Carlo program entitled trim (Transport of Ions in Matter). The experimental results set a lower bound of (1–10)×10−18 cm2 s−1 on the diffusivity of hydrogen (1H) in tungsten at 29 K. This extremely high diffusivity of hydrogen in tungsten at 29 K, when compared with the value extrapolated from ∼1100 K on an Arrhenius plot, suggests strongly that the diffusion of hydrogen in tungsten should be described by a nonclassical model. In addition, experiments were performed which demonstrated the adsorption of hydrogen on the surface of tungsten FIM tips (initially cleaned atomically by field evaporation) from the ambient pressure in the FIM.
Laser-induced resonant carrier lifetimes in n-InSb
Authors: McClure S. W. , Seiler D. G. , Littler C. L.
Published: February 2003

Transient carrier lifetimes of high-purity n-InSb are found to exhibit a two-stage decay in the photoconductive response. Resonant increases in the first stage decay occur at the same magnetic field strengths as resonant interband two-photon magnetoabsorption between Landau levels. The presence of shallow Te donors is shown to control both the observed resonant and transient behavior.
Inhomogeneity of liquid-phase-epitaxial InGaAsP lattice matched on InP: Effects of transient growth
Authors: Brunemeier P. E. , Roth T. J. , Holonyak N. , Stillman G. E.
Published: February 2003

Band-gap and lattice constant data are presented characterizing the transient composition that occurs at the onset of liquid-phase-epitaxial growth of InGaAsP on InP substrates. This compositional inhomogeneity, a region of significantly different band gap and lattice constant than that of the remainder of the layer, is a result of the extreme nonequilibrium conditions that exist in the first milliseconds of growth. The consequences of a thin, strained, and band-gap-graded layer within a practical device are considered, and a method of producing crystals free of this basic inhomogeneity is demonstrated. The data permit a calculation of the changes in solidus atomic fraction of each atomic species present in the diffusion-limited growth, clarifying some aspects of incorporation kinetic effects. A mechanism for the transient growth is considered, based on new data and data of previous work.
Schottky contact barrier height modification by ion implantation of Al into GaAs
Authors: Aina O. , Pande K. P.
Published: February 2003

The barrier height of Al/GaAs Schottky contacts have been increased from 0.82 to 0.99 eV by the ion implantation of Al into GaAs prior to metal deposition. The contacts have lower leakage currents and higher breakdown voltages than contacts made on unimplanted samples. I-V, C-V, and photoresponse data will be presented to show clear evidence of barrier height increase. Carrier concentration profiling, scanning electron microscopy (SEM) and Auger analysis will also be used to show that the barrier height increase is due to the formation of a thin layer of AlGaAs by the Al implantation.
Theory of defect scattering in two-dimensional multisubband electronic systems on III-V compound semiconductors
Authors: Yamaguchi Eiichi
Published: February 2003

A theory of defect scattering has been developed for two-dimensional electron gas in metal-insulator-semiconductor field-effect transistors (MISFETs) on III-V compound semiconductors. An analytic formula has been obtained for the transport relaxation time limited by the defect scattering with intra- and intersubband transitions. The theory has been able to phenomenologically explain the experimental results for temperature dependence and Ninv (inversion electron concentration) dependence of the mobility on InAs and InP MISFETs. The abrupt decrease observed in the mobility at 1.2×1012 cm−2 of Ninv on InAs has been found to be due to the intersubband defect-scattering effect on ground subband electrons.
Enhanced diffusion and precipitation of iron in gold-doped polycrystalline silicon
Authors: Miremadi Bijan K. , Morrison S. Roy
Published: February 2003

Decoration of grain boundaries by iron has been found possible at low temperature (600 °C and above) only if gold is present in the polycrystalline silicon sample. Evidence is presented that the gold increases the solubility of the iron rather than its diffusion constant. Without the gold present, the solubility of the iron is apparently too low. The presence of the iron is detected by the resulting high conductivity at low temperature along the grain boundary, with characteristics similar to impurity band conductivity. The effect is analogous to ‘‘piping’’ of gold-doped silicon during the diffusion of some donor impurities to form diodes or transistors.
Ion-beam and laser mixing of nickel overlayers on silicon carbide
Authors: Narayan J. , Fathy D. , Holland O. W. , Appleton B. R. , Davis R. F. , Becher P. F.
Published: February 2003

We have investigated ion-beam and laser mixing of Ni overlayers on silicon carbide substrates using cross-section and analytical techniques of electron microscopy, and ion scattering and channeling techniques. The thickness of the overlayers was varied from 200 to 500 Å on both crystalline and polycrystalline substrates of silicon carbide. The thickness of the ion-beam mixed region was found to increase with increasing dose of the implanted ions. The laser mixing was obtained only within a critical window of the pulse energy density (1.15±1.25 J cm−2) of a ruby laser (wavelength 0.693 μm, and pulse duration 28×10−9 s). The structure of the mixed region was found to be amorphous, with occasional presence of crystalline nickel silicide (Ni2Si) islands. The laser-mixed SiC specimens showed a considerable improvement (>35%) in their fracture strength.
X-ray rocking curve analysis of superlattices
Authors: Speriosu V. S. , Vreeland T.
Published: February 2003

We present detailed analyses of x-ray double-crystal rocking curve measurements of superlattices. The technique measures depth profiles of structure factor, and profiles of perpendicular and parallel strains relative to the underlying substrate. In addition to providing a detailed picture of the state of stress, the profiles are a direct measure of the composition modulation. The thickness of the period of modulation and the average strain are determined with a precision of ∼1%. The detailed structure of the period is determined to ∼5%. We obtain an expression relating the structure of the rocking curve to the structure of the period. This expression allows analytic determination of the structure without Fourier transformation or computer fitting. We show the influence of small random fluctuations in layer thicknesses and strains. The technique is applied to a 15-period GaAlAs/GaAs and a ten-period AlSb/GaSb superlattice grown on 〈100〉 GaAs and 〈100〉 GaSb substrates, respectively. In the former, the thickness of the period was 676 Å and the perpendicular strain varied between zero for the GaAs layer and 0.249% for the layer with peak (93%) Al concentration. Transition regions, ∼100 Å thick, with continuously varying composition, were found between the GaAs and the Ga0.07 Al0.93As layers. Fluctuations in structural properties were less than 5% of the average. The AlSb/GaSb superlattice had a period of 610 Å with sharp transition regions between the layers and negligible fluctuations from period to period. The perpendicular strains were −0.03% and 1.25%, respectively, for the GaSb and AlSb layers. A uniform parallel strain of 0.03% was found throughout the superlattice. Nonzero parallel strain indicates that a small fraction of the misfit between the superlattice and the substrate is plastically accommodated by net edge dislocations lying in a narrow region (a few hundred Å thick) at the interface with the substrate. The net number of edge dislocations was calculated to be ∼1×104/cm2. The measured perpendicular strains were in excellent agreement with the values calculated from bulk lattice parameters, elastic properties, and the parallel strain. For both superlattices, the standard deviation of random atomic displacements away from perfect crystal sites was below 0.1 Å, in agreement with reported ion channeling and electron diffraction measurements of superlattices. The rocking curve method is a major tool for quantitative analysis of superlattices.
Negative electron affinity gallium arsenide photocathode grown by molecular beam epitaxy
Authors: Narayanan A. A. , Fisher D. G. , Erickson L. P. , O’Clock G. D.
Published: February 2003

The molecular-beam-epitaxial technique has been used to grow a high-quality GaAs negative electron affinity photocathode structure with a p-type beryllium doping concentration of 3×1019 cm−3. The reflection mode photoemission characteristics such as the white light sensitivity, the quantum efficiency, the minority carrier (electron) diffusion length, and the electron surface escape probability measured on such a cathode are described. The growth technique followed, offers a precise control over the layer thickness and doping level.
Improvements in the determination of interface state density using deep level transient spectroscopy
Authors: Eades Wendell D. , Swanson Richard M.
Published: February 2003

Deep level transient spectroscopy (DLTS) in the current transient mode has been applied to the measurement of the trap density at the silicon-silicon dioxide interface. Application of Shockley–Read–Hall theory to the analysis of DLTS data indicates that if the energy dependence of the majority carrier capture cross section is strong, then it is necessary to take it into account if accurate interface state density values are to be obtained. We have used the small pulse trap filling technique to estimate the degeneracy factor and measure the capture cross sections of the interface states, and then applied this information in the calculation of the interface trap density from a conventional large pulse DLTS temperature scan. Very good agreement is obtained with the values extracted from high-low frequency capacitance-voltage measurements.
Photoluminescence and infrared spectroscopy of acceptors in GaAs
Authors: Bishop S. G. , Shanabrook B. V. , Moore W. J.
Published: February 2003

Time-resolved and continuous wave (cw) photoluminescence studies and infrared absorption spectroscopy have been carried out on bulk liquid-encapsulated Czochralski crystals of GaAs grown from Ga-rich and stoichiometric melts. These samples all exhibited the 78-meV residual acceptor which has been attributed previously to the neutral state of the GaAs antisite double-acceptor defect. The temperature dependence and time-resolved studies of the ∼1.44-eV photoluminescence band associated with the 78-meV residual acceptor in these samples demonstrates conclusively that the luminescence bands reported by various workers in the 1.441–1.443 eV range are all attributable to a donor-acceptor pair transition involving the same acceptor level. Two distinctly different photoluminescence bands at 1.283 eV (236-meV level) and 1.316 eV (203-meV level) can be distinguished on the basis of peak energies, temperature dependence, and time decay characteristics. The difference between these two bands was not recognized previously and both have been attributed by independent workers to the negative charge state of the GaAs antisite defect. While the quantitative correlation of the relative intensities of the ∼1.44- and 1.283-eV photoluminescence bands from sample to sample and as a function of exciting light intensity implies some relationship between these two bands, far-infrared intracenter absorption measurements indicate that this relationship cannot be as simple as that between the neutral and negative charge states of a double acceptor. However, infrared spectroscopy of the sample which exhibits the strongest 1.316-eV luminescence spectrum revealed a shallow acceptor with 203-meV binding energy and with D and C absorption line separation characteristic of a hole bound to a negatively charged (double) acceptor. This fact and a measured decay rate for the 1.316-eV luminescence band which is ∼10 times slower than that of the ∼1.44-eV band are consistent with the suggestion that the 203-meV level is the negative charge state of a 78-meV double acceptor.
Effect of surface recombination on the decay of excess minority carriers in semiconductors induced by finely focused picosecond pulsed laser beams
Authors: Ioannou D. E. , Gledhill R. J.
Published: February 2003

A study is carried out of the effect of surface recombination on the decay of the excess minority carrier population induced in a semiconductor sample by a very short pulse of a finely focused laser beam. An expression is obtained for this decay in a substantially simplified form, which can be readily computed numerically. Some sample calculations are presented, which show that, in agreement with previous experimental observations, this effect is important only for the initial part of the decay and only for large values of surface recombination velocity (>104 cm/sec) and absorption coefficient. If the initial fast portion of the decay is neglected, the minority carrier lifetime can be determined fairly accurately from the average slope of the remaining part of the decay, the resultant error being typically up to 15%.
Phase transformation and impurity redistribution during pulsed laser irradiation of amorphous silicon layers
Authors: Narayan J. , White C. W. , Holland O. W. , Aziz M. J.
Published: February 2003

Microstructural changes and impurity redistribution have been studied in 30Si+-, 75As+-, 63Cu+-, and 115In+-implanted, laser-annealed amorphous silicon layers for various pulse energy densities. Electron microscopy showed the formation of two distinct polycrystalline regions after irradiation with pulse energy densities below the threshold for ‘‘defect-free’’ annealing. A large polycrystalline (LP) region is found at the surface; a fine polycrystalline (FP) region lies below the LP and any remaining amorphous material. The extent of impurity redistribution, determined by Rutherford backscattering measurements, was much greater in the LP region than in the FP region, indicating a very short melt lifetime in the latter. Accumulation of Cu and In at the free surface was found, indicating motion of an interface towards the free surface during growth of the large polycrystals. Similarly, accumulation was found at the FP-amorphous Si boundary, indicating motion of an interface away from the free surface during growth of the fine polycrystals. The LP thickness was found to correspond to the maximum depth of melting calculated by a heat-flow program. These results indicate that the FP layer forms by explosive crystallization.
Modeling of electrical response for semiconducting ferrite
Authors: Cheng Hsiu-Fung
Published: February 2003

The electrical properties of semiconducting ferrite materials are investigated. A simplified model, consisting of bulk material separated by highly resistive grain boundary layers, is proposed. The nature of grain boundary on its electrical behavior is also discussed. Complex impedance technique is used to analyze the electrical response of polycrystalline specimens. The characteristics of the complex impedance dispersion curves for MnZn-ferrite specimens are affected by the sintering and annealing conditions. All the complex impedance plots differ from idealized semicircles, but can be fitted by circular arcs very well. An experimental equivalent circuit is proposed to explain the observed R-X dispersion. The tremendous increase in the grain boundary resistivity due to controlled-atmosphere sintering is ascribed to the preferential oxidation. The decrease in the apparent resistance of the specimens in the high-frequency region arises from the polarization effect. This is attributed to the special microstructure of such material, namely, semiconducting bulk material with insulating grain boundaries.
Bias-temperature stress on metal-oxide-semiconductor structures as compared to ionizing irradiation and tunnel injection
Authors: Haller G. , Knoll M. , Bräunig D. , Wulf F. , Fahrner W. R.
Published: February 2003

This paper presents the change of the midgap voltage ΔVMG and the surface state density Dit caused by bias temperature (BT) stress, ionizing irradiation, and tunnel injection experiments on metal-oxide-semiconductor capacitors. The irradiation tests and the tunnel injection experiments are carried out to find correlations of the degradation mechanisms among the three stress procedures. The BT stress is performed on n- and p-type samples with applied positive and negative fields (1–5 MV/cm). The stress temperatures are 100, 150, and 200 °C; the maximum aging time is 30 h. After BT stress, n- and p-type samples exhibit the same degradations of the midgap voltage VMG and of the interface state density Dit, respectively. The increase of ‖VMG‖ and Dit for negative BT stress is significantly larger than in the case of positive BT stress. An analytical expression which describes the changes of VMG and Dit for negative BT stress is developed. Drastic changes of VMG and Dit are observed after switching the stress voltage from negative values to positive ones or to ground. The ratio of (trapped hole) charges in the oxide and in the interface states is identical in all three experiments.
Influence of clustering on the mobility of III-V semiconductor alloys
Authors: Blood P. , Grassie A. D. C.
Published: February 2003

Using published structural data we estimate that the conduction band in GaInAsP alloys matched to InP has a spatial variation with an amplitude of about 0.08 eV as a result of partial segregation into clusters. We argue that the electrons may be located in isolated ‘‘lakes’’ and that since the conduction band fluctuation is larger than kT at room temperature and below, current conduction may be inhomogeneous and may be restricted to percolation paths. This could account for reported differences in mobility of alloys grown within and outside the miscibility gap.
Study on grain boundary Josephson junctions in BaPb1−xBixO3 thin films
Authors: Suzuki Minoru , Enomoto Youichi , Murakami Toshiaki
Published: February 2003

Several characteristics have been experimentally investigated for the grain boundary Josephson junctions inherently formed at every grain boundary of polycrystalline sputtered BaPb1−xBixO3 superconducting thin films, where x=0.2, 0.25, and 0.3. The origin of the boundary Josephson junction barrier is ascribed to the low carrier density, the structure sensitiveness, and surface states originating from the Bi ions in the grain boundary region, all of which this superconducting oxide posesses at the same time. The grain boundary Josephson junction exhibits tunneling-type I-V characteristics, which progressively change to those of a weak link in the temperature range near the superconducting transition temperature. The gap voltage observed is less than the value given by the Bardeen–Cooper–Schrieffer theory, except for x=0.3. The temperature dependence of the maximum Josephson current deviates from the Ambegaokar–Baratoff theory in the same temperature range. All these tendencies are interpreted in terms of the McMillan tunneling model for a proximity sandwich, based on a model of a parabolic grain boundary potential barrier. Qualitative agreements are attained for the composition dependence of these characteristics. Relations between the Bi content and the junction barrier properties are also discussed, partly in relation to the strong coupling tendency in this oxide system.
Influence of radiative and convective transfers in a photothermal experiment
Authors: Rousset G. , Charbonnier F. , Lepoutre F.
Published: February 2003

Mirage effect results obtained with samples at high temperature are in disagreement at low frequencies with the photothermal theory which only takes into account conductive transfer in the surrounding gas. The radiative and convective transfers are analyzed. The calculated orders of magnitude show that, for our experimental conditions, the convective effects are predominant.
Channeling studies in graphite
Authors: Elman B. S. , Braunstein G. , Dresselhaus M. S. , Dresselhaus G. , Venkatesan T. , Wilkens B.
Published: February 2003

The channeling characteristics of helium ions in the polycrystalline semimetal graphite have been studied using Rutherford Backscattering Spectrometry in the 1.2–2.4 MeV energy range. Axial channeling is investigated in the geometry where the ion beam is parallel to the highly preferred c-axis direction of a sample of highly-oriented pyrolytic graphite (HOPG). Assuming a Gaussian distribution of crystallite orientations and measuring the energy and angular dependencies of the backscattering yield, it was possible to extract the minimum yield and the critical angle for channeling in single-crystal graphite, and the standard deviation for the spread in c-axis crystallite orientations. An unusual increase of the measured angular width for channeling with depth was observed, and is attributed to the polycrystalline nature of HOPG.
Emission spectra and etching of polymers and graphite irradiated by excimer lasers
Authors: Koren G. , Yeh J. T. C.
Published: February 2003

Emission spectra in the visible and ultraviolet range, scanning electron microscopy of various polymers [polyimide, Mylar, and polymethyl-methacrylate (PMMA)], and graphite exposed to 193-, 248-, and 351-nm laser radiation were used to investigate the laser etching process. Measurements were performed under vacuum and in air and He environments. At low laser fluence, which depends on the sample and laser wavelength, an unresolved continuum emission was observed. At higher fluences clear C2, C, and in some cases also CN emissions were found in addition to the continuum. At still higher fluences ionic carbon emissions became dominant. It was found that laser-produced plasma processes are responsible for most of the observed emissions. Rough and smooth etched surfaces were obtained at different laser fluences depending on the linear absorption coefficient of the sample at the laser wavelength. In polyimide, a rough-to-smooth surface transition versus the laser fluence was found to occur exactly when the C2 and C emissions appeared on top of the continuum. It is suggested that the laser etching mechanism is mostly a statistical thermodynamic process, but without complete energy randomization.
Interactions of absorbing aerosols with intense light beams
Authors: Armstrong R. L.
Published: February 2003

The establishment of steady-state, developed vaporization regimes in intensely irradiated aerosol particles is investigated. This analysis is aided by the identification of several characteristic interaction times which serve to identify, after a given irradiation time, the dominant aerosol-beam interactions. An approximate treatment of the approach to steady-state conditions is also given. Finally, the aerosol vaporization model developed here is applied to the description of aerosol-enhanced breakdown using a theory developed elsewhere.
Mixing of Sn with nitrogen implantation in Al, Ti, and steel
Authors: Anttila A. , Hirvonen J. , Koskinen J.
Published: February 2003

The ion-beam mixing mechanism has been studied for the case where an easily evaporated heavy element is mixed by implanting light ions into the bulk material. Here Sn was mixed by implanting 400-keV N+2 into Al, Ti, and steel. The implantations were performed using both low- and high-intensity beams and with different doses. The samples were heated during and after implantation. Mixing of the bulk material with Sn occurred in the high-intensity implantation. On the contrary, the low-intensity implantations had no discernible ion-mixing effect. Annealing measurements carried out after the implantations demonstrated that the N implantation retards diffusion of Sn into the bulk material and that the nitrogen sites have no tendency to trap diffusing Sn atoms.
Au/Ti resistors used for Nb/Pb-alloy Josephson junctions. I. Electrical stability
Authors: Murakami Masanori , Alessandrini E. I. , Kim K. K.
Published: February 2003

Bilayered Au/Ti films are very attractive for use as resistor materials of experimental Nb/Pb-alloy Josephson junction devices. In order to predict the electrical stability of the Au/Ti resistors during storage at room temperature, changes in microstructure and electrical resistivity of Ti and Au/Ti films during isothermal annealing at temperatures ranging from 298–473 K were studied using transmission electron microscopy, x-ray diffraction, and electrical measurements. Growth of Ti grains during annealing was observed in these films. The activation energy for the grain growth was determined to be 1.51 eV. Decreases in the sheet resistance measured at 4.2 K were observed at the early stages of isothermal annealing. By analyzing the annealing temperature dependence of rates of resistance changes, the activation energy of 1.49 eV was obtained. This energy value is very close to that obtained for the grain growth and, therefore, one of the main causes in the resistance decrease is believed to be due to the growth of Ti grains. Based on the present results, a model to predict the electrical resistance change for the Au/Ti films during storage at room temperature was established. The model predicted that change in the resistance can be significantly reduced by preannealing the resistors at an elevated temperature. The prediction was supported by the experiment and an excellent quantitative agreement between measured resistance values and those predicted by the model was obtained. Based on this model, the change was predicted to be −1.5% after about 3 years at room temperature, if the resistors were preannealed at 353 K for 10 h. This resistor stability is satisfactory for designing logic and memory circuits of Josephson devices, and it can be increased simply by preannealing for longer times at 353 K.
Temperature dependence of the threshold current density in InP-Ga0.28In0.72As0.6P0.4 (λ=1.3 μm) double heterostructure lasers
Authors: Casey H. C.
Published: February 2003

The experimental threshold current density Jth(T) in InP-Ga0.28In0.72As0.6P0.4(λ=1.3 μm) double heterostructure lasers varies with temperature as exp(T/T0) with T0≂100 K for 100 K <T<250 K and with T≂65 K for 250 K<T<350 K. Numerous mechanisms have been suggested to explain this observed temperature dependence. The temperature dependence of gain gives T0≂100 K for T between 100 and 250 K, and T0≂200 K for T between 250 and 350 K. Inclusion of the temperature dependence of the Auger recombination and carrier concentration at threshold reduces T0 to ∼100 K in the 250 to 350 K temperature range. A leakage current of one-third of the total current at 300 K is required to reduce T0 to 65 K for 250 K<T<350 K. This leakage current is due to the hot carriers that result from Auger recombination and some of these carriers do not lose sufficient energy by interactions with the lattice to be confined by the heterojunction barriers. Previous experimental measurements found that the leakage current was 10–30% of the total current at room temperature. Another suggested cause of the small T0 is intervalence-band absorption. Extension of results for intervalence-band absorption in InP to Ga0.28In0.72As0.6P0.4 demonstrates that intervalence-band absorption is not significant.
Schottky barrier restricted AlGaAs laser with an etched mesa ohmic contact
Authors: Reynolds C. L. , Holbrook W. R. , Nygren S. F. , Shimer J. A. , Logan R. A. , Temkin H.
Published: February 2003

A gain-guided AlGaAs double heterostructure laser which employs a Schottky barrier in conjunction with a p-GaAs etched mesa contact for current isolation has been fabricated. This Schottky barrier restricted structure provides a device whose electrical and optical characteristics are comparable to that of other gain-guided lasers and which is simple to fabricate. Preliminary aging data indicate high reliability of the Schottky barrier restriction.
Integral equation formulation for heat conduction in closed regions with arbitrarily shaped boundary surfaces
Authors: Morita N.
Published: February 2003

An integral equation formulation is given for investigating time-dependent temperature distribution in the regions enclosed with arbitrarily shaped boundary surfaces. Only the temperature on the boundary surfaces is taken as the unknown which is determined by solving the surface integral equations numerically. Once the temperature on the boundary surfaces becomes known, that in the volume regions can be calculated through the integral expressions. Surface integral equations are derived for the two cases of surface boundary condition; one is the ‘‘radiation’’ boundary condition and the other is the condition of intimate contact of two media. The application of the first case is given for the problem of heat conduction in the human abdomen region subject to both electromagnetic heating and surface cooling from outside the body during hyperthermia therapy.
Plastic instability and particulation in stretching metal jets
Authors: Walsh J. M.
Published: February 2003

Metal jets (or rods) that are plastically stretching eventually undergo a particulation process that arrests the plastic elongation and thus limits the target penetration that is to be achieved by the jet. The particulation process is found to depend upon the perturbation structure and upon a single dimensionless flow parameter φ. Statistical definitions are introduced for the perturbation magnitudes (jet roughness magnitude, velocity irregularity function, yield strength irregularity function). Then the jet length Lb at breakup is determined as a function of φ0 and these perturbation magnitudes. Jet yield strength σ, density ρ, and initial velocity gradient Ux occur in the definition of φ0 so that the effects of σ, ρ, and Ux upon Lb are also determined.
Hybrid finite element method for scalar wave refraction into three-dimensional bodies
Authors: Meijer Paul H. E. , Cowart Gregory A. H.
Published: February 2003

The hybrid finite element method is a combination of the finite element method in a closed domain and an analytic solution outside this domain. The analytic solution is used in the region of homogeneous dielectric constant, while the finite element method is applied to the region of heterogeneous dielectric constant. Matching conditions, expressed in the form of nonlocal boundary conditions that were described in a previous article by P. H. E. Meijer, Gregory A. H. Cowart, and Stanley M. Neuder [Appl. Sci. Res. 40, 97 (1983)], are used to obtain equations for the scalar amplitudes of the wave function refracted into a heterogeneous object of arbitrary shape. The problem is described by means of a functional, containing integrals over the volume and surface of a spherical domain which completely encloses the physical scattering object. The integrals are approximated and the variation of the functional results in a system of linear equations in the unknown wave functions at the nodal points of the domain. The new aspect of the method is the use of cubature formulas to reduce the surface integrals to sums. The formulation is tested by comparing results with the analytic solution for refraction into a homogeneous sphere.
Direct measurement of temperature in shock-loaded polymethylmethacrylate with very thin copper thermistors
Authors: Rosenberg Z. , Partom Y.
Published: February 2003

We present direct measurements of the temperature of shock-loaded polymethylmethacrylate (PMMA) in the 0.5 – 3.0-GPa range. The experimental technique is based on embedding a very thin (1 μm thick or less) copper thermistor in the shocked sample and recording its resistance changes during the 5–8 μs of a dynamic experiment. Due to the small thickness of the gauge thermal equilibrium between gauge and specimen can be reached in these short times. The measured temperatures of shock-loaded PMMA are in good agreement with the calculated values. Moreover, the measured temperature-time histories confirm the viscoelastic behavior of PMMA, shock loaded in the 0–2.0 GPa, which was found by others using particle velocity measurements.
Thermionically electron emitting matrix cathodes for magnetohydrodynamic generators: Analytical model
Authors: Maken N. J. S. , Raju G. V. R. , Gupta Bhumesh
Published: February 2003

Current and voltage drop calculations have been made for matrix cathodes having a number of sharp pins projecting out from its surface in open-cycle magnetohydrodynamic plasmas. It is assumed that from the cathode surface to the cathode sheath edge, the current flows in current tubes formed around the projected pins. The effect of high electric field on the work function of the tip has been taken into account and calculations are made for a variable number of tips and tip area. Work functions of the tip and the slant surface are taken to be different. The current and voltage characteristics have been obtained by solving the current continuity and Poisson’s equations in spherical coordinate geometry. It is observed that the current increases with an increase in the number of pins per unit area and tip area. The theoretical results have been compared with the experimental observations.
Two-stream instability in a self-pinched relativistic electron beam
Authors: Uhm Han S.
Published: February 2003

The two-stream stability properties are investigated for a self-pinched relativistic electron beam propagating through a weakly ionized plasma channel. The analysis is carried out within the framework of a macroscopic cold-fluid model, and electrostatic stability properties are investigated for the case of rectangular beam and channel density profiles. Depending upon the ionization condition of the channel, either the beam electron-ion two-stream or the beam electron-plasma electron two-stream instability is excited. In either case, the critical beam current for instability is obtained. In contrast with the one-dimensional analysis of the two-stream instability, the stabilizing influence of a self-pinched beam originates from the finite beam radius. From the critical current, it is shown that for an appropriate choice of physical parameters, the electron beam is free from the two-stream instability. Moreover, the growth rate of instability under unstable conditions can be drastically reduced for a small axial wave number.
Long-wavelength lattice dynamics of In1−xGaxAsyP1−y alloys
Authors: Inoshita Takeshi
Published: February 2003

The first investigation of the lattice dynamics of In1−xGaxAsyP1−y quaternary semiconductor alloys lattice matched to GaAs has been made by Raman scattering. The spectra in the optical frequency range consist of two separate bands, each having a peak at the high-frequency end. These two peaks are shown to be GaP-like and GaAs-like, respectively. The cell-isodisplacement theory for the long-wavelength lattice dynamics by Zinger, Ipatova, and Subashiev [Sov. Phys. Semicond. 10, 286 (1976)] is reexamined in detail. It is improved upon by consistently treating the renormalization of the intracell force constants and then applied to InGaAsP. This improvement gives remarkably better fitting of the calculated phonon frequencies to the existing experiments in the entire composition range 0≤x, y≤1 and enables the construction of a coherent model for the long-wavelength lattice dynamics of InGaAsP. The results of the Raman measurements are discussed in the light of the calculation. The oscillator strengths are also calculated and compared with the infrared experiment.
Effect of potential fluctuations on the transport properties and the photoconductivity of compensated semiconductors. Application to semi-insulating GaAs. I. Semiconductor under equilibrium conditions
Authors: Pistoulet B. , Girard P. , Hamamdjian G.
Published: February 2003

In highly compensated semiconductors, the potential fluctuations due to inhomogeneous distribution of impurities lead to fluctuations in the density of carriers and ionized deep levels (donor or acceptor). The result is that the local neutrality condition is no longer obeyed and only averaged quantities over a sample are experimentally attainable. We describe a statistical model of long range fluctuations, writing down an averaged neutrality equation. The Fermi energy, the dc free carrier density, and its activation energy, are very much dependent on the magnitude of the fluctuations and on the degree of compensation of the deep level. These variations are shown in the case of semi-insulating GaAs. A method of quantitative evaluation of the fluctuations and of the degree of compensation is given. It is applied to explain the data on non-Cr-doped semi-insulating GaAs samples.
Double-carrier injection and recombination in insulators, including diffusion effects
Authors: Torpey Peter A.
Published: February 2003

A theory describing the double-carrier injection and recombination in thin insulating crystals is developed and applied to the case of current flow in anthracene. The diffusion-free analysis indicates that the scaling J∝V2/d3 holds, even when recombination effects are present for any crystal thickness. The same scaling is shown to be valid when diffusion effects are present, if the injecting contacts are not limiting. The individual effects of recombination, diffusion, contacts, and crystal thickness are studied and discussed.
The kinetics of pressure-induced fcc-bcc transformation in ytterbium
Authors: Divakar C. , Mohan Murali , Singh A. K.
Published: February 2003

The kinetics data for the pressure induced fcc→bcc transformation in ytterbium under isobaric-isothermal conditions in the pressure range 3.3–4.6 GPa have been reported. The kinetics data satisfy Avrami equation: ζ=1−exp−(t/τ)n, where τ and n are constants at a given pressure. Both τ and n decrease with increase in pressure, as given by the following relations: ln τ=(36.2±1)−(6.8±0.3)p, and n=1.36+0.55p−0.168p2, where p is pressure (GPa). The activation free energy for the combined process of nucleation and growth has been estimated from the τ −p data and is found to decrease with increase in pressure. The activation free energy varies from 16 kcal mol−1 at 3.3 GPa to 11 kcal mol−1 at 4.6 GPa. The activation enthalpies at 3.3, 3.6, and 3.8 GPa have been determined by measuring τ at different temperatures. The activation volume is −17 cm3 mol−1 at 300 K. It is estimated from the τ −p data that fcc-bcc transformation under shock loading will occur at about 7 GPa.
dc magnetron production of amorphous silicon solar cells
Authors: McKenzie D. R.
Published: February 2003

The operation of a dc cylindrical magnetron with a stainless-steel cathode in silane gas was investigated. Coating rates up to 0.15 μm/min were obtained for hydrogenated amorphous silicon (a-Si:H). The photoconductivity of the films was slightly dependent on coating rate. The optical properties of the films were investigated and found to be an indicator of film quality. The infrared spectra and photoconductive properties of doped films were also studied. Solar cells of the p-n type in which the p layer is either a-Si:H or a-SixC1−x:H were made and their performance studied. It was concluded that the dc magnetron is capable of producing good cells with higher deposition rates than previously obtainable.
Phosphorus out-diffusion during high temperature anneal of phosphorus-doped polycrystalline silicon and SiO2
Authors: Murarka S. P.
Published: February 2003

Loss of phosphorus by evaporation, from doped polysilicon and SiO2 films, due to high temperature anneals has been investigated by use of neutron activation analysis technique. It is found that large amounts of phosphorus, as much as 99%, are lost from polysilicon films during inert ambient anneals. The loss is dependent on the temperature and time of anneal and on the initial phosphorus concentration. There is no loss in oxidizing ambients. For P-glass films phosphorus is lost only from the top layers of the film. The top layer, when free of phosphorus, acts as diffusion barrier for further loss from underlying P glass. Also the maximum loss from P glass is ambient dependent, being ∼10% in oxygen, 20% in argon, and over 35% in steam. Mathematical modeling of the phosphorus out-diffusion from polysilicon and P-glass films is discussed.
Comment on ‘‘Focus wave modes in homogeneous Maxwell’s equations: Transverse electric mode’’
Authors: Wu Tai T. , King Ronold W. P.
Published: February 2003

The recent formulation by Brittingham [J. Appl. Phys. 54, 1179 (1983)] of a solitary electromagnetic wave called a ‘‘focus wave mode’’ in terms of three regions with discontinuities is found not to satisfy Maxwell’s equations across the discontinuities.
Second-harmonic generation with phase-matched long-range and short-range surface plasmons
Authors: Quail J. C. , Simon H. J.
Published: February 2003

We report the observation of enhanced optical second-harmonic generation in reflection with simultaneous phase-matched excitation of the fundamental short-range and the harmonic long-range surface plasmon modes. Resonant second-harmonic generation due to separate excitation of the fundamental long-range and short-range surface plasmon modes and harmonic long-range surface plasmon mode is also observed.
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7Fe Mössbauer effect in ThFe5 hydride
Authors: Gubbens P. C. M. , van der Kraan A. M. , Buschow K. H. J.
Published: February 2003

The hydrogen absorption in the CaCu5-type compound ThFe5 was studied by x-ray diffraction, magnetic measurements, and 57Fe Mössbauer spectroscopy. Hydrogen absorption leads to a 6% increase of the unit cell volume without change in crystal structure. There is only a slight change in magnetic properties. The 57Fe Mössbauer spectra of the ternary hydride are characterized by relatively sharp lines, an increase in hyperfine field, and an increase in isomer shift relative to the uncharged compound. The increase in 57Fe isomer shift invariably observed after charging of Fe compounds with hydrogen is explained in terms of the Miedema–van der Woude model. The relatively low tendency of the hydride of ThFe5 to decompose (disproportionate) as compared to some other Th-Fe hydrides is explained on the basis of a kinetic approach.