bluuebunny/crossref_metadata_2025 huggingface dataset:
Liquid phase epitaxy of high-purity GaAs on conducting n-type substrates
Authors: Shealy J. R.
Published: February 2003

The liquid phase epitaxial technique for the deposition of lightly doped n-type GaAs on conducting n-type substrates is described. The effect of the starting materials, in particular the substrates and the undoped source crystal, on the epitaxial layer properties has been observed for a fixed set of growth conditions. Schottky barriers fabricated on this material exhibit near ideal current-voltage characteristics with breakdown voltages approaching the theoretical limit.
Effective masses for nonparabolic bands in p-type silicon
Authors: Madarasz Frank L. , Lang Joseph E. , Hemeger Patrick M.
Published: February 2003

The nonparabolic nature of the valence bands of silicon gives rise to an explicit temperature dependence in the density of states effective mass as defined through the carrier concentration as well as an energy dependence in the mass defined through the density of states itself. Both masses are important to those researchers interested in fitting electronic transport data. In the past the temperature dependent effective mass of Barber has been most commonly used. The approximations that have gone into the Barber mass are somewhat oversimplified in that he only approximated the actual band structure. We present a more complete calculation, and compare it with the results of Barber for nondegenerate p-type silicon. There is a significant difference, a factor of about 1.4, between our results and his in the temperature range 300–600 K. The difference is quite noticeable in calculating electronic transport quantities such as carrier concentration or conductivity mobility.
Beryllium doping in Ga0.47In0.53As and Al0.48In0.52As grown by molecular-beam epitaxy
Authors: Cheng K. Y. , Cho A. Y. , Bonner W. A.
Published: February 2003

Beryllium-doped Ga0.47In0.53As and Al0.48In0.52As epitaxial layers lattice matched to InP substrates have been grown by molecular-beam epitaxy (MBE). Doping levels as high as 2.5×1019 cm−3 have been achieved for both p-type Ga0.47In0.53As and Al0.48In0.52As. The maximum carrier concentration is an order of magnitude higher for these Be-doped layers than for those doped with Mn. The carrier concentration varies proportionally with the arrival rate of Be and the sticking coefficient of Be is estimated to be unity. Under our growth conditions, the carrier concentrations in Ga0.47In0.53As and Al0.48In0.52As layers are identical for the same Be arrival rate. Mobility studies showed that MBE grown Be-doped Ga0.47In0.53As layers are comparable to the best reported results obtained with liquid-phase epitaxy. When Sn was used as the n-type dopant, both Ga0.47In0.53As and Al0.48In0.52As p-n junction diodes were fabricated and evaluated.
The nature of intrinsic hole traps in thermal silicon dioxide
Authors: Manchanda L. , Vasi J. , Bhattacharyya A. B.
Published: February 2003

The energy and spatial distribution of intrinsic hole traps in dry thermal silicon dioxide have been determined. Thermal detrapping was used for the determination of energy levels of the traps and the etch-back technique was used to find the spatial location of the traps. These traps are distributed in energy from 1.0 to 1.5 eV with respect to the valence band edge of the silicon dioxide. Their centroid is located at approximately 120 Å from the Si–SiO2 interface. Results of various postoxidation annealing treatments show that the density of traps is significantly dependent on the process conditions. Like fixed charge Qf, these traps seem to be related to the lattice imperfections in SiO2 near the interface; however, the hole trap density and Qf vary in opposite directions due to the process changes. N2 annealing increases the trap density and O2 annealing, which reduces the hole trap density, increases the electron trap density in SiO2. Based on these results we support the trivalent silicon model for the traps and we postulate that nonbridging oxygen acts as an electron trap in SiO2. These results also support Raider and Berman’s model for fixed charge Qf.
Capacitance-voltage characteristics of Al-plasma anodic Al2O3-GaAs diodes
Authors: Hirayama Y. , Koshiga F. , Sugano T.
Published: February 2003

Metal-insulator-semiconductor diodes were fabricated on an n-type GaAs substrate by means of plasma anodic oxidation of aluminum film evaporated on the GaAs substrate. The capacitance-voltage (C-V) characteristics of these diodes were significantly affected by the deposition rate of the aluminum onto the GaAs substrate. Depth profiles revealed by Auger electron spectroscopy show that the amount of gallium atoms migrated from the GaAs surface through the aluminum oxide film increases with decreasing the deposition rate of the aluminum. At the appropriate deposition rate, the C-V curves show the increase of capacitance in negative-bias (polarity of inversion) region at low frequency.
Magnetostatic field effect on threshold current in a GaAs/AlyGA1-yAs double-heterostructure laser
Authors: Hsieh H. C. , Lee G. Y.
Published: February 2003

The magnetostatic field dependence of the threshold current density in a GaAs/AlyGA1-yAs double-heterostructure laser is investigated with the aid of the solution of the electron diffusion equation. The reduction of the threshold current density by increasing the magnetic field strength can be significant when the difference in the energy band gap of the active and inactive layers at the heterojunction is small.
Theoretical characteristics of 16-μm CO2 gasdynamic laser
Authors: Saito S. , Obara M. , Fujioka T.
Published: February 2003

In a CO2 gasdynamic laser (GDL), a small signal gain and an output of 16 μm have been theoretically examined in detail by solving the rate equations with the population of each vibrational level against the 9.4-μm stimulating field. The eight levels of CO2 up to the (001) level including the (110) and the (030) levels, and the 31 reactions involving the V-T reactions are taken into account in this model. With a 9.4-μm [P(14)] pulse of 10-MW input power, 8-mm-diam spot size, and 100-nsec pulse width, a 16-μm [P(15)] pulse of 27-μJ/pulse/cm3 extractable energy and 5.7-kW maximum power is obtained from an active length of 0.1 m. It indicates that by using a Q-switch technique, high-repetition-rate operation of 200 kHz can produce an average output power of 5 W/cm3. Finally, a 16-μm continuous lasing by injecting the 9.4-μm beam continuously is analyzed.
Photolytically pumped XeF (C→A) laser studies
Authors: Bischel W. K. , Eckstrom D. J. , Walker H. C. , Tilton R. A.
Published: February 2003

Properties of the visible XeF (C→A) photolytically pumped laser system have been investigated in detail. The research covers four main areas: (1) absolute fluorescence intensities from the C and B states, (2) C→A fluorescence spectra as a function of pressure and buffer gas, (3) gain/absorption measurements from 400–650 nm, and (4) demonstration of tunable laser operation over the 454–525-nm range. All results reported here indicate that the XeF (C→A) laser could be a highly efficient visible laser system.
An estimation theory of physical variable in noisy observation process
Authors: Agu Masahiro
Published: February 2003

An estimation theory of the physical variable observed by the system carrying its own fluctuations is developed. The dynamics of the observation system is assumed to be described by a nonlinear Langevin equation. It is shown how the information entropy of the estimation process is decreased through the accumulation of observed data.
Study of the 427.5-nm radiation in Kr and Kr-SF6 mixtures following intense electron-beam pulses
Authors: Luches A. , Nassisi V. , Perrone A. , Perrone M. R.
Published: February 2003

The 427.5-nm radiation emitted from the 6p‖3/2‖2→5s‖3/2‖2 transition of krypton was studied using time-resolved spectroscopic techniques at pressures up to 10 Torr, following excitation with an intense (25 kA) and short (15 ns) burst of 500-keV electrons. The spontaneous emission probability A and the two-body deactivation rate constant k1 of the 6p‖3/2‖2 level by ground-state krypton were found to be 2×107 s−1 and 2×10−10 cm3 s−1, respectively. By adding SF6 to Kr, at concentrations ranging from 0.05 to 1%, the quenching effect of the 6p‖3/2‖2 level by SF6 was studied.
Extension of Langmuir space-charge theory into the accelerating field range
Authors: Scott J. B.
Published: February 2003

The paper takes the space-charge theory developed by Langmuir and applies it to the accelerating-field range along with the image-potential theory suggested by Schottky. The combined theory produces a current-voltage curve which begins at the zero-field current and voltage calculated from space-charge theory, and then gradually approaches the curve generated by Schottky theory. The paper summarizes in a single equation the solution procedure outlined by Langmuir. Based on this equation, the paper discusses the behavior of the current-voltage curve at the transition points from the exponential range into the space-charge range and from the space-charge range into the accelerating field range.
A proposed electron spectrometer using a concave electrostatic mirror
Authors: van der Merwe J. P.
Published: February 2003

It is shown that a concave axially symmetric electrostatic mirror can be found with a high enough ratio of chromatic aberration to spherical aberration to allow it to be used as an electron spectrometer. The potential field is given in terms of a finite Fourier-Bessel series. Using only three nonzero Fourier coefficients, a field can be specified that allows—in the case of a point source located within the mirror field—an energy resolution of 0.003% [full width at half maximum (FWHM)] and a transmission of 0.6% of 2π steradians to be obtained. This field can be used as a starting point in an optimizing procedure reported earlier by the author, to increase the transmission or adapt the spectrometer for use with sources of finite dimensions.
Cylindrically converging blast waves in air
Authors: Matsuo Hideo , Nakamura Yuichi
Published: February 2003

Cylindrically converging shock waves are produced by utilizing the detonation of cylindrical explosive shells. The production and the propagation of shock waves are observed by framing and streak camera photographs, and the trajectory of shock propagations is determined by using an electrical ionization probing system. The effect of the quantity of explosives on the stability, or the axial symmetry, of shock fronts and on the strength of shocks produced is investigated. It has been shown that, for practical purposes, the approximation of shock trajectories by Guderley’s formulas would be sufficiently acceptable in an unexpectedly wide region near the implosion center, and that the axial symmetry of the shock front is improved by increasing the quantity of explosives, and thus, strong shocks are produced by merely increasing the quantity of explosives. The reflected diverging shock seems to be very stable. Piezoelectric elements have also been used to detect reflected diverging waves.
Analysis of the wide band gyrotron amplifier in a dielectric loaded waveguide
Authors: Choe Joon Y. , Uhm Han S. , Ahn Saeyoung
Published: February 2003

The effect of broadening the bandwidth with a dielectric load in a cylindrical gyrotron is investigated for a hollow electron beam. The linear dispersion relation for the azimuthally symmetric, transverse electric (TE) modes is obtained by the method of the wave impedance matching. It is found that the TE perturbations exhibit three unstable modes characterized by their phase velocities vph : one fast wave, the long wavelength mode (LWM, vph ≳c), and two slow waves, the intermediate (IWM, c≳vph ≳cε−1/2) and the short (SWM, vph <cε−1/2) wavelength modes. The optimum conditions for the wide band operation are obtained individually for each mode. Although the bandwidth in excess of 40% is possible for the slow waves (IWM, SWM) at a small axial momentum spread, it decreases rapidly as the spread increases. On the other hand, the LWM yields approximately 10% of the bandwidth insensitive to the spread. It is also shown that for a small spread (<5%), the slow wave (IWM) is preferable for the wide band operation, whereas for a large spread (≳5%) the fast wave (LWM) is desirable.
Dynamics of magnetically stabilized laser discharge
Authors: Capjack C. E. , Antoniuk D. M. , Seguin H. J. J.
Published: February 2003

The dynamics of a rotating plasma in a transverse electrode geometry appropriate to high power CO2 laser discharge pumping is examined. The magneto-gas-dynamic fluid model used reveals that the spatially nonuniform electric and magnetic fields within the discharge cause the plasma and neutral gas rotational velocities to be strongly sheared within the cathode fall and the positive column regions. This sheared rotation serves to both stabilize the discharge against glow to arc transitions and to drive a centrifugal neutral gas flow within the volume. The concomitant bulk gas cooling effect so produced is particularly beneficial in a high powered CO2 electrical discharge laser as it inhibits thermal bottle necking. An order of magnitude increase in discharge power loading has been achieved utilizing a simple ’’magnetic electrode’’ discharge configuration.
Constraints imposed upon theories of the vacuum arc cathode region by specific ion energy measurements
Authors: Miller H. Craig
Published: February 2003

The presence of high-energy ions (with potentials greater than the overall arc voltage) in the flux from the cathode region of vacuum arcs has been well established. While much excellent theoretical work has been done on the cathode region of a vacuum arc, only a modest amount of such work has predicted the energies of the ions leaving the cathode region. Two vacuum arc cathode theories which do predict the ion energies are the potential hump theory—where a positive space charge at the cathode spot accelerates the ions electrostatically, and the gas dynamic theory—where the ions are accelerated by a flow process. Few theorists have taken advantage of the available mass spectrometric data concerning individual ion energies. In this paper I compare such data with theoretical predictions. The best confirmed ion energy data is that for a copper cathode. Additional data are presented concerning the ion flux from a vacuum arc with a ten percent Bi/Cu cathode. Comparison of the copper and bismuth/copper data with the theoretical predictions shows that the potential hump and gas dynamic theories are in rough agreement with experiment, but are definitely not correct. Modifying the potential hump and gas dynamic theories by considering time-dependent phenomena (i.e., incorporating nonequilibrium states into the theory) is shown to offer the promise of bringing either theory into better agreement with experiment. I conclude that the available data on the energies of the ions leaving the cathode region of a vacuum arc can serve as strong constraints on theoretical analyses.
Current-voltage characteristics of low βc tunnel junctions with magnetically suppressed critical currents
Authors: Smith L. N. , Jillie D. W.
Published: February 2003

Low βc tunnel junctions have current-voltage characteristics which deviate from the intrinsic quasiparticle characteristic because of the ac Josephson effect. This effect has previously been analyzed for the special case of a pointlike junction in zero applied field. We demonstrate that deviations still occur when the critical current is suppressed by an applied field to a small fraction of its zero field value. The effects are significant for junctions whose length l is comparable to the Josephson penetration length λJ. These are often the junctions of practical interest. We present a simple model to explain the physical origin of these deviations, and also present detailed computer simulations using up to nine segments to model the distributed junction. For l = λJ, and an applied magnetic field which corresponds to the first minimum of the junction threshold characteristic, we find time-averaged voltages which deviate from the quasiparticle characteristic by up to 5%. Their magnitude is proportional to (l/λJ)2 and inversely proportional to the square of the applied field. This dependence can be used experimentally to confirm the observation of the effect.
A study of the ferroelectric field effect in Te films on lead germanate, triglycine sulphate, and triglycine selenate substrates
Authors: Mansingh Abhai , Krupanidhi S. B.
Published: February 2003

Ferroelectric field effect was studied in three devices using lead germanate (Pb5Ge3O11), triglycine sulphate (TGS), and triglycine selenate (TGSe) as ferroelectric substrates with tellurium (Te) semiconductor films at different temperatures between 90 K and the transition temperature of the ferroelectric substrates. The devices exhibit merit factors (ratio of ON and OFF conductivities) in the range of 103–105 at 0 °C. However, the device performance seems to be governed by the traps at the ferroelectric-semiconductor interface and in the semiconductor film. The surface states and the density of charges responsible for conductivity modulation are evaluated by both Crawford’s method and an integration method, and a reasonable agreement is observed in the numerical magnitudes. The activation energies obtained from the variation of drain-source conductance with temperature in both ON and OFF states are considerably higher than those measured for a Te film on a glass substrate. The merit factor showed a decrease both at low temperatures and near the transition temperatures. The decreases at high temperatures is consistent with the decrease in the polarization. The decreases in merit factor at low temperatures and the higher activation energy for conductance under field effect may be attributed to the trapping phenomenon.
Reflectance and optical constants of CdIn2Se4 crystals
Authors: Trykozko Rajmund , Huffman Donald R.
Published: February 2003

CdIn2Se4 crystals have been prepared by means of chemical transport reactions using iodine as a transport agent. The reflectance of CdIn2Se4 has been measured at room temperature and at liquid-nitrogen temperature in the range 1.5–20 eV using synchrotron radiation. Optical constants have been determined by means of Kramers-Kronig analysis. Comparison of experimental results with existing band structure calculations has been made, and some of the observed transitions and their localization in the Brillouin zone are discussed.
Infrared reflectance spectra of thin epitaxial silicon layers
Authors: Senitzky B. , Weeks S. P.
Published: February 2003

IR reflectance spectra of thin (0.5–3.0 μm) epitaxial layers on substrates containing n-type buried layers are investigated in the 5–50-μm wavelength range. From measurements on uniformly doped wafers it is found that the Drude model should be used to compute the optical constants of the buried layers. The reflectance spectra can then be used to determine epitaxial layer thickness, peak concentration of the buried layer, and the thickness of the buried layer. For our process conditions the optically measured epitaxial thickness and peak concentration are in close agreement to measurements performed with a secondary ion microprobe.
Determining the field emitter temperature during laser irradiation in the pulsed laser atom probe
Authors: Kellogg G. L.
Published: February 2003

Three methods are discussed for determining the field emitter temperature during laser irradiation in the recently developed Pulsed Laser Atom Probe. A procedure based on the reduction of the lattice evaporation field with increasing emitter temperature is found to be the most convenient and reliable method between 60 and 500 K. Calibration curves (plots of the evaporation field versus temperature) are presented for dc and pulsed field evaporation of W, Mo, and Rh. These results show directly the important influence of the evaporation rate on the temperature dependence of the evaporation field. The possibility of a temperature calibration based on the ionic charge state distribution of field evaporated lattice atoms is also discussed. The shift in the charge state distributions which occurs when the emitter temperature is increased and the applied field strength is decreased at a constant rate of evaporation is shown to be due to the changing field and not the changing temperature. Nevertheless, the emitter temperature can be deduced from the charge state distribution for a specified evaporation rate. Charge state distributions as a function of field strength and temperature are presented for the same three materials. Finally, a preliminary experiment is reported which shows that the emitter temperature can be determined from field ion microscope observations of single atom surface diffusion over low index crystal planes. This last calibration procedure is shown to be very useful at higher temperatures (≳600 K) where the other two methods become unreliable.
Properties of tungsten silicide film on polycrystalline silicon
Authors: Tsai M. Y. , d’Heurle F. M. , Petersson C. S. , Johnson R. W.
Published: February 2003

Tungsten silicide on polycrystalline Si becomes increasingly important as interconnections and gate electrodes for metal-oxide-semiconductor field-effect transistor(MOSFET) integrated circuits. Annealing behaviors of coevaporatd tungsten silicide on P-doped poly-Si are studied by x-ray diffraction, He+-backscattering, transmission electron microscopy (TEM), and secondary ion mass spectroscopy (SIMS). High-temperature annealing of silicides results in crystallization and homogenization of tungsten silicide as well as phosphorus out-diffusion from the poly-Si. Their effect on device fabrication is also discussed.
Crack extension in a double cantilevered beam model
Authors: Dowell E. H.
Published: February 2003

A simple, phenomenological model is presented for crack extension in a double cantilevered beam model. It invokes a continuum description of the beam per se, but postulates a discrete spring mechanism (which bonds the two halves to the beam) to provide a model of local failure. This in turn allows the prediction of global failure. Solutions to the mathematical model are obtained by the Rayleigh-Ritz method. Several interesting physical phenomena, which have been observed by previous investigators in wholly discrete models, are also predicted by the present model. These include lattice trapping, rapid fracture, and spontaneous bond healing.
Temperature dependence of the rate constants for three-body quenching reactions in the KrF* laser system
Authors: Klimek D. , Hsia J. C.
Published: February 2003

The KrF* and Kr2F* fluorescence emissions from e-beam excited F2/Kr/Ar mixtures were measured over the temperature range of 315°–420 °K, at total densities of 1, 2, and 3 amagat. These data were used in conjunction with kinetic model calculations to evaluate the temperature dependence of three-body quenching reactions of the type: KrF*+R+M→RKrF*+M, where R≡Ar, Kr, and M≡Ar, Kr. The decrease in the three-body rates with increasing temperature deduced from the experimental data, agrees to within 15% of that calculated by using classical phase-space theory.
Asymptotic formula for the resonant frequencies of a circular microstrip antenna
Authors: Chew W. C. , Kong J. A.
Published: February 2003

The resonant frequencies of both the axial and nonaxial symmetric modes of a circular microstrip antenna or resonator are solved asymptotically. The technique used is matched asymptotic expansions which is widely used in fluid mechanics but little used in electromagnetism. In this technique, the region around the open resonator is divided into the exterior region, the edge region, and the interior region. Leading order solution is derived in each region and matched to each other asymptotically. This provides an asymptotic eigenequation which can be solved approximately to give an asymptotic formula. The asymptotic formula agrees well with previous numerical methods, especially when the ratio of the dielectric substrate thickness to disk radius is d/a→0.
Small-angle x-ray and electron scattering from (SN)x
Authors: Schultz J. M. , Bentley J. , Hendricks R. W. , Lin J. S. , Petermann J.
Published: February 2003

Small-angle x-ray and electron scattering from (SN)x crystals is reported. Analysis of the scattering curves yields identification of rodlike scatterers with diameters of 50–100 nm and a density different from that of the matrix (SN)x. No scattering from microscopically observed fibrillar entities with diameters less than 10 nm was detected, indicating that these features bear approximately the same density as the matrix.
Double layer oxide film formation on elemental metals by anion interstitial diffusion
Authors: Fromhold A. T.
Published: February 2003

A development for the simultaneous formation of two-layered oxide phases on an elemental metal by means of anion interstitial diffusion is presented.
On the formation of binary compounds in Au/InP system
Authors: Piotrowska A. , Auvray P. , Guivarc’h A. , Pelous G. , Henoc P.
Published: February 2003

The formation and identification of binary compounds in Au-InP system has been reported. The contact reaction was investigated in the temperature range 320–360 °C by the combined use of 2-MeV He+ ions backscattering spectrometry, x-ray diffraction, TEM, and SEM. The results give evidence that both In and P form compounds with gold; formation of oxides has not been observed. A model of metallurgical structure of Au/InP contacts annealed at temperatures below or equal to 360 °C has been proposed.
In-depth profiles of deep-trap concentration in Fe-implanted n-type silicon
Authors: Kumagai Osamu , Kaneko Kunio
Published: February 2003

A peak of deep-level transient-spectroscopy spectrum obtained from iron-implanted n-type silicon was investigated, and it was found that the apparent energy level of the trap varied as the distance from the implanted layer increased. This is due to a change, with the distance, of the concentration ratio of two kinds of traps, an implantation-induced (E3:Ec −0.50 eV) and an iron-associated center (E2:Ec −0.58 eV). The E2 trap concentration showed an L-shaped in-depth profile. In the sample with a p+-diffused layer on the surface opposite of the iron-implanted layer, the in-depth profile of the E2 trap concentration was U shaped. These in-depth profiles can be explained in terms of interstitial-substitutional diffusion of iron atoms.
Deep level transient spectroscopy studies of trapping parameters for centers in indium-doped silicon
Authors: Jones Colin E. , Johnson Gregory E.
Published: February 2003

Deep level transient spectroscopy (DLTS) has been used to measure the low-temperature trapping parameters of defects in indium-doped silicon. Substitutional indium at Ev +0.15 eV, the indium–X center at Ev +0.11 eV, and two deeper indium related centers at Ev +0.31 eV and Ev +0.45 eV were studied. Electric fields have been found to lower the activation energies and increase the emission rates for the substitutional indium and the indium–X center. Theoretical models, including the field effect on the barrier and thermally assisted tunneling, have been used to fit the data. The capture coefficients near liquid-nitrogen temperature have been estimated as being for substitutional indium, C (In) = 7.6×10−9 cm3/sec exp (0.031 eV/kT); for the indium–X center, C(InX) = 7.7×10−8 cm3/sec exp (+0.006 eV/kT); for the Ev +0.31-eV center, C(H1) = 2×10−9 cm3/sec; and for the Ev +0.45-eV center C(H2) = 1.2×10−8 cm3/sec.
Experimental determination of the phonon and electron components of the thermal conductivity of bcc iron
Authors: Williams R. K. , Yarbrough D. W. , Masey J. W. , Holder T. K. , Graves R. S.
Published: February 2003

A study of the factors which affect the thermal conductivity of αFe and its solutions is described. The results of these experiments define the phonon and electronic components of the thermal conductivity of pure αFe fairly well between 90 and 400 K. Also, the phonon conductivity can be analyzed to identify the strengths of electron-phonon and phonon-phonon scattering, and the latter resistance is in good agreement with theoretical estimates. The scattering of phonons by electrons is intermediate between the small values for noble metals and the strong scattering found in Nb and Ta. An experimental estimate of the electron-phonon mass enhancement factor, 0.4, is derived from the results. Finally, reexamination of the data for ten solid solution alloys suggests that both phonon-scattering mechanisms are influenced by the alloying elements.
Electrical response of a copper-Constantan sheet couple to shock compression up to 81 GPA
Authors: Mashimo Tsutomu , Hanaoka Yasuharu , Manabe Ituo , Fujita Masahiro , Nagayama Kunihito , Sawaoka Akira
Published: February 2003

The response of a copper-Constantan sheet couple 50–60 μm thick to shock compression up to 81 GPa is studied. The results are consistent with the bulk junction results of Bloomquist et al. at pressures up to about 40 GPa, and with ones obtained from the calculated shock temperature above this pressure with an error of less than 15%.
Experimental determination of minority-carrier lifetime and recombination mechanisms in p-type Hg1−xCdxTe
Authors: Polla D. L. , Tobin S. P. , Reine M. B. , Sood A. K.
Published: February 2003

This paper presents an experimental study of minority-carrier lifetime and recombination mechanisms in n+-on-pHg1−xCdxTe photodiodes. Diode pulse recovery lifetime measurements have been carried out as a function of temperature, net acceptor concentration, and excess carriers in the alloy composition range 0.2<x<0.4. Based upon these measurements Shockley-Read recombination involving a deep center located close to midgap is shown to be the dominant recombination mechanism in the photodiodes studied. Minority-carrier lifetime measured by diode pulse recovery and minority-carrier diffusion length measured by the electron beam induced current (EBIC) technique are further correlated with Hg1−xCdxTe photodiode performance.
Current-voltage characteristics of AlxGa1−xAs Schottky barriers and p-n junctions
Authors: Lee S. C. , Pearson G. L.
Published: February 2003

Studies of temperature-dependent current-voltage (I-V) characteristics of AlxGa1−xAs Schottky barriers and p-n junctions indicate a gradual departure from theoretical behavior with decrease in temperature. The diode ideality factor n, which takes values between 1 and 2 at room temperature, increases to values between 1.5 and 4 at 94 K. It is shown that, if the ideality factor-ambient temperature product is replaced by an appropriate effective temperature T*, the I-V data appear to obey the theoretical formula at all temperatures. It is also shown that the 1-kT I-V characteristic of a p-n diode can be described either by standard diffusion or thermionic emission theory. This enables one to determine the barrier heights of p-n diodes from their 1-kT I-V plots.
The effect of dopant diffusion vapor pressure on the properties of sulfur and selenium doped silicon infrared detectors
Authors: Sclar N.
Published: February 2003

The n-type Si:S and Si:Se photoconductors with peak infrared response at about 5.5 and 3.5 μm and wavelength cutoffs at 6.8 and 4.1 μm, respectively, were prepared by diffusing sulfur and selenium into high-purity boron doped silicon wafers in closed tubes. The diffusions were performed at 1200 °C and the diffusion vapor pressures were varied by controlling the mass of volatile diffusants. The measured thermal impurity activation energies, the spectral responses, and the detector performance with temperature were found to depend on diffusion pressure. Optimum Si:S detectivity at ∼5.5 μm was obtained by using a diffusion pressure of 1 atm. Optimum Si:Se detectivity of 2.2×1011 cm Hz1/2 W−1 at 3.5 μm out to about 120 K was obtained using a diffusion pressure of 2 atm. This represents the highest operating temperature of any 3–5 μm silicon detector. For the higher pressures, increased spectral response contributions were found at peak wavelengths of 11 and 5.5 μm with cutoffs at about 12.0 and 6.2 μm for the Si:S and Si:Se, respectively. This response is identified with the contribution from impurity molecules whose population increases with diffusion pressure and which have lower ionization energies than the isolated impurities.
New features of the temperature dependence of photoconductivity in plasma-deposited hydrogenated amorphous silicon alloys
Authors: Vanier P. E. , Delahoy A. E. , Griffith R. W.
Published: February 2003

The temperature and flux dependences of photoconductivity have been investigated for plasma-deposited hydrogenated amorphous silicon alloys produced under a variety of processing conditions. In undoped films, new features such as thermal quenching and supralinearity are observed. Such behavior is critically dependent on the position of the Fermi level, and is not observed in alloys doped by the addition to the plasma of PH3, B2H6, O2+N2 mixtures, or air. Interpretation of the data is based on a model of competing recombination centers.
Shallow PtSi-Si Schottky barrier contacts formed by a multilayer metallization technique
Authors: Tsaur B-Y. , Silversmith D. J. , Mountain R. W. , Hung L. S. , Lau S. S. , Sheng T. T.
Published: February 2003

Shallow PtSi-Si Schottky barrier contacts have been formed by heat treatment at 400–500 °C of structures prepared by vacuum deposition of thin alternating Pt and Si layers on n-type (100) Si substrates. This multilayer technique permits the formation of very shallow contacts without placing any limitation on the thickness of the PtSi layer. For a layer of given thickness the contact (PtSi-Si) interface is more uniform than the interface for a PtSi layer of the same thickness formed by annealing a single layer of Pt on Si. The interfacial uniformity is independent of PtSi thickness for shallow PtSi-Si contacts produced from multilayer samples, while that for conventional PtSi-Si contacts produced from single-layer samples degrades as the thickness of PtSi increases. Large-area (9.4×10−3 cm2) diodes utilizing shallow PtSi-Si contacts about 200 Å deep have been fabricated without guard rings. These diodes exhibit near-ideal forward I-V characteristics, low reverse-leakage currents (less than 10 nA at −10 V) and high breakdown voltages (over −70 V). These characteristics are superior to those of conventional diodes formed by heat treatment of structures prepared by depositing a single Pt layer on Si.
The superposition principle for semiconductor-electrolyte junction solar cells
Authors: El Guibaly F. , Colbow Konrad
Published: February 2003

The superposition principle of currents in a solar cell states that the current flowing in an illuminated device subject to a forward bias V is given by the algebraic sum of the short circuit photocurrent and the current which would flow at bias V in the dark. We investigate this principle here in detail for the case of semiconductor-electrolyte solar cells. However, the results are also applicable to Schottky-barrier solar cells. It is concluded that the density of photoexcitable surface states and the surface transfer velocity for minority carriers from the semiconductor into the electrolyte are two important parameters that determine the validity of applying the superposition principle as well as in determining the current-voltage (J-V) characteristic of the device.
Regime of vortex flow in short Nb variable-thickness bridges
Authors: Kuriki S. , Goto K.
Published: February 2003

In the characteristics of short (l ? 0.2 μm) variable-thickness bridges made of Nb films we have found a transition into a regime of vortex flow when the thickness of the weak-coupling region is varied. The vortex flow is favored below a thickness of the order of the size of Nb grains. It is confirmed that the weak-coupling region exceeds the size of the vortex core because of the decrease in coherence length. A linear variation of the critical current with temperature and a linear or quadratic voltage increase in the I-V characteristic are observed in the vortex flow regime in agreement with theory. However, some disagreement is found in the microwave response.
Ultrasonic leaky waves in the presence of a thin layer
Authors: Nayfeh A. H. , Chimenti D. E. , Adler Laszlo , Crane R. L.
Published: February 2003

This paper presents theoretical and experimental results on the problem of bounded acoustic beam reflection at the Rayleigh angle from a fluid-solid interface which is loaded by a thin solid layer. The theoretical developement exploits the framework of existing theory to yield a simple, analytic model which is reasonably accurate for thin layers. It is shown that the influence of the layer is contained entirely in the dispersive Rayleigh wavespeed and the thickness-dependent displacement parameter Δs . Measurements of the reflected acoustic field amplitude have been performed on several samples of stainless steel loaded with a copper layer. We have found reasonably good agreement between the theoretical model calculations and experimental measurements for ratios of the layer thickness to the Rayleigh wavelength as large as 0.3. Beyond this value, some disparity is observed, particularly in the calculation of the thickness-dependent Rayleigh wavespeed.
Laser heating of semiconductors—effect of carrier diffusion in nonlinear dynamic heat transport process
Authors: Kim Dae M. , Kwong D. L. , Shah Rajiv R. , Crosthwait D. Lloyd
Published: February 2003

An analytic theory is presented to describe the nonlinear dynamic heat transport process in a semiconductor irradiated by a pulsed laser beam. The input rate of laser energy to the lattice is sensitively influenced by the ambipolar diffusion of the dense, laser-produced excess charge carriers. Additionally, the high heating rate of the laser beam significantly changes the material transport coefficients during the pulse. This nonlinear laser beam-solid interaction is examined from the viewpoint of the transport process, using a parametrized perturbation technique in Green′s function formulation. An explicit, analytical solution of the lattice temperature rise is presented and the threshold pulse energy for the onset of surface melting for the case of amorphous Si is calculated as a function of laser beam intensity as well as the carrier diffusion length. Our results are compared with both the melting and nonthermal models for laser annealing.
Spectroscopic studies of laser-produced carbon plasma in the visible region
Authors: Sinha B. K.
Published: February 2003

Spectra of laser-produced carbon plasma, using a 1-GW-5.5 ns, Nd:glass laser, were observed in the visible region between 3900 and 5900 Å. Most of the lines observed are new and, hitherto, unreported in laser plasma experiments. These lines originate predominantly from lower ionization stages. The relative intensities of these lines with respect to the strongest line are given. The results are discussed with reference to Corona model for ionization states.
Criteria for automatic x-ray absorption fine structure background removal
Authors: Cook J. W. , Sayers D. E.
Published: February 2003

Criteria for terminating smoothing to remove a cubic spline background from the x-ray absorption coefficient are stated in terms of three parameters obtained from the k3 weighted Fourier transform of the resulting x-ray absorption fine structure data. The three parameters are HR, the average value of the transform magnitude between 0 and 0.25 Å, HM, the maximum value in the transform magnitude between 1 and 5 Å, and HN, the average value of the transform magnitude between 9 and 10 Å. The termination criteria are HR−HN ⩾0.05HM; or if HN ≳0.1HM, then HR ⩾0.1HM. The incorporation of the criteria into a computer program to facilitate automatic background removal is discussed. Examples of application of the technique to copper, β-PtO2, and ferritin samples are presented.
Spin dependent electron absorption in gold
Authors: Erbudak M. , Ravano G.
Published: February 2003

The absorption of electrons by a polycrystalline gold target depends on the energy, the angle of incidence, and the spin polarization of the primary electrons. The latter dependence is due to the spin-orbit coupling of electrons in elastic scattering. The anisotropy in the diffuse scattering determines the gross features of the angular behavior of the spin dependent absorption which can exceed 1.5% of the primary beam intensity. Therefore a polycrystalline gold target is a simple and efficient detector for electron spin polarization.
Transient population distribution of SF6 gas excited by a CO2 laser
Authors: Koren G. , Levin I.
Published: February 2003

A method is developed for the calculation of the transient molecular population distribution of a gas excited by a laser pulse or any other means. This method allows the calculation of the vibrational energy distribution from the observed infrared fluorescence or absorption spectrum, and vice versa. First, two sample calculations for SF6 were performed: one in which the weak intensity absorption spectrum at 300 K was calculated using a thermal population distribution function (PDF), and the results were compared to the measured data, and the other in which the measured spectrum was used to calculate the PDF and the results were compared to the thermal PDF. Satisfactory agreement was obtained in both cases. Then we calculated the PDF of SF6 from its infrared fluorescence spectrum which was measured immediately after a CO2 laser excitation. The results show that at fairly low excitation levels (〈n〉≊1.5) there is a nonthermal PDF in the gas, which has a prominent maximum at high vibrational energies in addition to the maximum at low energies.
Analytical and numerical studies of foilless diodes
Authors: Jones Michael E. , Mostrom Michael A. , Thode Lester E.
Published: February 2003

The generation of intense annular beams by foilless diodes is studied through analytic equilibrium models and particle-in-cell simulation. In the high-voltage regime, the foilless diode operates below the space-charge limit and the impedance is nearly independent of the voltage. The current density is proportional to the current and to the square of the external magnetic field. From a kinetic theory equilibrium model, the beam scattering angle is found to be inversely proportional to the diode voltage, external magnetic field strength, and cathode radius. The predicted scaling is in good agreement with the simulation results. Criteria for adiabatic expansion and cooling of the beam, supported by simulation results, have also been considered.
Influence of self-absorption on output power characteristics of a high-pressure cw CO2 laser
Authors: Hishii M. , Nagai H. , Nagai A. , Akiba T.
Published: February 2003

Absorption of intracavity radiation by CO2 molecules in an unexcited region has detrimental effects on output power characteristics, especially above a certain level of output power, i.e., the threshold level. These absorption effects have been investigated experimentally in detail. The threshold level depends both on CO2 concentration of the laser gas and on the mirror transmission of the optical cavity. It is found from these dependences that the absorption effect becomes serious above ∼0.2 W/cm3, which is the density of optical power absorbed by the unexcited CO2 molecules. The influence of self-absorption on the laser efficiency and the oscillating line of 10.4-μm band can be explained well by a usual theory for laser oscillation. Furthermore, a novel method for monitoring the concentration of CO2 molecules is demonstrated.
Displaced hysteresis loop of Cu-Mn-Al alloy
Authors: Narita Kenji , Koga Shinji , Motowaki Yoshihiro
Published: February 2003

The 44.7Cu-20.6Mn-34.7Al (at. %) alloy, which exhibits a very high coercive force after aging at 300 °C, has been found to show a displaced hysteresis loop when it is cooled to 77 K in a magnetic field. The hysteresis loop of the sample which aged for more than 60 min at 300 °C is shifted along the magnetization axis instead of along the field axis. The magnetization measured at 300 K for a maximum applied field of 15 kOe becomes larger than that at 77 K after aging for 45 min at 300 °C. In the magnetization versus temperature curves of the sample aged for more than 45 min at 300 °C, the magnetization decreases monotonically with decreasing temperature. The increase of coercive force, which is obtained in the sample aged for more than 45 min at 300 °C, corresponds to the increase of the displacement of the hysteresis loop. These magnetic behaviors are considered to be caused by the exchange anisotropy interaction between the regions of ferromagnetic Heusler or Mn-poor phase and ferrimagnetic or antiferromagnetic Mn-rich phase.
Photoluminescence of AlxGa1−xAs grown by molecular beam epitaxy
Authors: Wicks G. , Wang W. I. , Wood C. E. C. , Eastman L. F. , Rathbun L.
Published: February 2003

Reduction of background oxygen containing species, higher substrate temperature, and low arsenic fluxes during growth have all been found critical to improve the luminescence of molecular beam epitaxy AlxGa1−xAs alloys. Attention to these parameters has allowed greatly improved quality films to be grown which show strong exciton recombination for the first time. The main unintentional acceptor impurity was then found to be carbon.
Soft x-ray diagnostic for a z-pinch discharge
Authors: Popil R. , Meyer J.
Published: February 2003

The electron temperature of a z-pinch discharge was determined using the familiar foil absorber method. Details of the x-ray detector used are described and the results obtained are presented. The measured electron temperature agrees well with the previously determined value of 40 eV obtained by ruby laser Thomson scattering.
The anode transition in a hydrogen glow discharge
Authors: Clothiaux E. J. , Askew R. F. , Spencer H. W.
Published: February 2003

A large volume, short tube hydrogen glow discharge, operating in the abnormal region without positive column, has been studied for the anode transition between no anode glow and anode glow, where a plateau appears in the V-I characteristic curve and an anode fall develops. The location of the plateau is found to be very sensitive to small changes in pressures. Measurements made at constant pressure give a linear dependence of anode fall potential on the discharge current.
A study of the ionization rates of electrons and holes in GaAs using a computer analysis of the properties of GaAs IMPATTs
Authors: Mazumder N. , Sridharan M. , Roy S. K.
Published: February 2003

Investigations by Stillman et al. [Appl. Phys. Lett. 24, 471 (1974)] and Ito et al. [J. Appl. Phys. 49, 4607 (1978)], mainly based on photomultiplication measurements, suggest that in GaAs the ionization rates of electrons and holes are not identical. Though the results of the two investigations are in qualitative agreement, there is a considerable difference in the numerical values of the ionization rates. A computer study of the dc properties of the linearly graded and high-low type GaAs IMPATT diodes using the ionization rate data of Stillman et al. and Ito et al. has been carried out, and it has been found that the data of Ito et al. are in closer agreement with the experimental breakdown voltage data.
Transport properties of thin metal films with energy-dependent relaxation time
Authors: Rahman Ijaz-ur-
Published: February 2003

Analytical expressions for the electrical and thermal current densities have been obtained previously for thin metal films having unlike surface properties. Those expressions assumed that the relaxation time τ is constant. In this paper an analysis of the transport properties has been carried out using a general energy dependence of the relaxation time τ = aEn. By measuring σF/σB and QF/QB as a function of the thickness of the film, the value of n, the energy dependence parameter, can be estimated. An estimate of n reveals information about the energy dependence of the electron mean free path.
A transparent-conducting coating for a-Si:H based devices
Authors: Ovadyahu Z. , Wiesmann H.
Published: February 2003

A simple procedure for the application of a transparent-conducting coating onto a-Si:H devices is described. Results pertaining to a-Si:H solar-cell heterojunctions incorporating such coatings are given and discussed.