bluuebunny/crossref_metadata_2025 huggingface dataset:
Accurate evaluations of thermally stimulated current curves and defect parameters for CdTe crystals
Authors: Elkomoss S. G. , Samimi M. , Hage-Ali M. , Siffert P.
Published: July 2002

More accurate expressions for the evaluations of the trap depth E and the capture cross section S related to the thermally stimulated current process are developed. The different T−1, T−2, T−3, and T−4 dependencies of S on the temperature T have been considered for the slow retrapping case. In the fast retrapping case, the energy E and the product τNT have been expressed independently, where τ is the lifetime of the free electron and NT the total trap density. The calculations depend on the temperatures Tm and T1 that correspond to the peak and the half-height of the current, respectively. A new experimental method providing the determination of Tm and T1 with high precision has been developed that allows extensive experimental examination of thermally stimulated current curves in high-resistivity CdTe crystals. Application to defect parameters of fourteen levels in CdTe has been carried out in the slow and fast retrapping limits. In the slow retrapping case, the results differ from those obtained by the widely used Grossweiner formula. For the fast retrapping limit the values of E corresponding to different sets of Tm and T1 are calculated independently of τNT. This again has not been the case published by the different authors.
Surface polaritons on a small amplitude grating
Authors: Seshadri S. R.
Published: July 2002

The dispersion characteristics of the surface polaritons in the neighborhood of the band gap occurring near the edge of the first Brillouin zone are deduced and used in determining the reflectivity of the surface polaritons incident normally on a small amplitude grating of finite length.
Static and computer-simulated dynamic model approaches to effective elastic properties of noncubic polycrystals
Authors: Middya T. R. , Paul Mala , Basu A. N.
Published: July 2002

Based on the static deformation scheme envisaged by the effective medium theory developed by Zeller and Dederichs [Phys. Status Solidi B 55, 831 (1973)] formally similar to that of the quantum mechanical multiple scattering method, we have deduced a general expression for determining the effective elastic properties of any single component polycrystalline substance. From these general formulas using appropriate symmetry for the component crystallite the expressions for cubic, hexagonal, tetragonal, trigonal, and orthorhombic polycrystals may be easily derived. Two sets of approximate formulae are given and their ranges of validity discussed. For comparison with this static approach, we have also calculated the same quantities by simulating the polycrystal on a computer using the dynamic model developed by Middya, Basu, and Sengupta [J. Appl. Phys. 57, 1844 (1985)]. The results obtained by these two approaches based on entirely different assumptions are remarkably close to each other and to experiment for twenty-four different noncubic polycrystalline specimens considered in the present investigation. In fact, for the effective rigidity modulus, the agreement between the two methods is within 1% in all cases except for two specimens. The reasons for this discrepancy are discussed. However, while the computer simulation provides a very simple method for evaluating the effective elastic properties of polycrystals with high accuracy, it raises a question regarding the relation between the apparently contradictory assumptions on which the static and the dynamic methods are based. Finally, an experiment is suggested that may be helpful in resolving this difficulty.
Nature of the 1.5040–1.5110-eV emission band in GaAs
Authors: Beye Aboubaker C. , Neu Gérard
Published: July 2002

A structural analysis of the luminescence spectra of molecular-beam-epitaxy grown GaAs layer, in the energy range 1.5040–1.5110 eV (g-v lines) is reported. At least two distinct recombination processes are distinguished from the selectively excited photoluminescence, not the excitation spectra and the luminescence polarization measurements. The relation of several lines in this emission band with oriented complex defects is established and suggested acting as isoelectronic centers.
High T
c superconducting NbN films deposited at room temperature
Authors: Thakoor S. , Lamb J. L. , Thakoor A. P. , Khanna S. K.
Published: July 2002

Thin films of niobium nitride with superconducting transition temperature (Tc ) of 15.7 K have been deposited on a variety of amorphous as well as crystalline substrates including glass, glazed ceramic, fused quartz, and sapphire, maintained at room temperature, by dc reactive magnetron sputtering in a mixture of Ar and N2 gases. The effects of the deposition conditions, particularly the carrier gas pressure and composition, on the film crystal structure, orientation, and resistivity have been studied in an effort to maximize the superconducting transition temperature. A study of the variation of nitrogen consumption with nitrogen injection pressures for constant background argon pressures is conducted and found to be an absolute indicator of the NbN formation systematics. Initially, the consumption increases linearly with the injection pressure but beyond a certain threshold, it shows a distinct drop. The desired high Tc  NbN with B1 crystal structure is formed in the vicinity of this turning point of the reactive gas consumption-injection characteristic. High Tc films possess B1 (fcc, NaCl-type) crystal structure as revealed by their x-ray diffraction patterns. An initial increase in the injection pressure of the reactive gas (N2) results in a remarkable increase in the (111) diffraction line intensity along with an increase in the film Tc. This trend continues up to the turning point of consumption-injection characteristic, beyond which the crystal structure distorts into the substoichiometric tetragonal phase with a consequent reduction in the transition temperature. A general protocol for studying the formation systematics of transition metal nitrides has thus emerged.
Correlation between degradation and device characteristic changes in InGaAsP/InP buried heterostructure lasers
Authors: Fukuda Mitsuo , Iwane Genzo
Published: July 2002

Correlations between degradation and device characteristics are investigated in InGaAsP/InP buried heterostructure lasers. The logarithm of threshold-current increase rates is confirmed to be proportional to the voltage decrease at low current when injected carrier lifetime decreases during aging. When leakage current increases during aging, devices having a low initial voltage also tend to degrade to a large extent. These correlations hold within an operating range limited by the device structure and the material used during fabrication.
Comprehensive study of AuMn p-type ohmic contact for GaAs/GaAlAs heterojunction bipolar transistors
Authors: Dubon-Chevallier C. , Gauneau M. , Bresse J. F. , Izrael A. , Ankri D.
Published: July 2002

A comprehensive study of AuMn ohmic contact for p-type GaAs is presented using electrical testing, scanning electron microscopy, Auger electron spectroscopy, and secondary ion-mass spectroscopy. The contact fabrication—Mn proportion against Au, alloying cycle—was optimized taking into account the results of the electrical tests. Contact resistivity values are presented for different doping levels. Unalloyed AuMn contact was found to give a good contact resistivity on samples with an ultrahigh doping level of 2 × 1020 cm−3. The reliability of the contact was also studied, the reproducibility was found to be perfect and the surface morphology smooth. The contact metallurgy has also been investigated. The Mn diffusion was shown to be a shallow one. The contact formation has been demonstrated combining the classical mechanism of Ga vacancies filled with Mn acceptors and the out-diffusion of the dopant (Be) from the epitaxial layer toward the metal/GaAs interface due to the presence of Mn at this interface.
Calculation of warm electron transport in AlGaAs/GaAs single heterostructures using a Monte Carlo method
Authors: Yokoyama Kiyoyuki , Hess Karl
Published: July 2002

A simulation of electronic transport in AlGaAs/GaAs single-well structures including multisubband conduction has been performed based upon an ensemble Monte Carlo method. During the transient calculation, the electronic states of the quantum well are calculated in a fully self-consistent manner by including the influence of the changes in the energy distribution on the quantum well potential. The numerically obtained wave functions and energy levels are also used to update the major scattering matrix elements. The increase in electron energy with time and the corresponding changes of matrix elements and self-consistent field (through dependence of screening on the electron energy distribution) lead to a decrease in both velocity overshoot effects and steady-state drift velocity in low electrical fields at a low lattice temperature.
A simple method to determine the pretilt angle of nematic guest-host liquid crystals
Authors: Yang K. H. , Ong H. L. , Howard W. E.
Published: July 2002

The phase retardation-extremum method offers a fast and simple way to measure the pretilt angle of nematic liquid crystal (NLC) cells. Due to optical absorption of the dissolved dyes, such a method is not suitable to measure the pretilt angle of a guest-host (GH) NLC cell. We have obtained a simple and fast method to determine the pretilt angle of a GH NLC cell from the incident angle corresponding to the minimum transmission intensity of a polarized light passing through the GH cell. Using this simple method, we have measured the pretilt angles of GH NLC cells with different dye concentrations, and compared them with the pretilt angles of the corresponding host NLCs measured by the retardation-extremum method. Excellent agreement between the two methods was observed with a dye concentration of not more than 1%. Within our experimental errors, dye concentration of up to 5.8% (by weight) seems not to change the pretilt angle of the GH NLC from that of the corresponding host NLC.
Light-modulated Hall effect for extending characterization of semiconductor materials
Authors: Schacham S. E. , Finkman E.
Published: July 2002

A new technique for deriving the electron mobility as minority carriers in semiconductor materials is introduced. The technique is based on the modulation of the Hall voltage through the introduction of a low-level optical injection. The photogenerated excess carriers produce a signal which is a function of the magnetic field, the carrier mobilities and concentrations, and the concentration of excess carriers and thus to their lifetime. The measurement is easy to implement and it can be performed along with the measurement of the Hall coefficient and the conductivity. The only modification needed in a conventional galvanomagnetic setup is the introduction of a chopped low-intensity laser. Using these three simultaneous measurements, we determined the equilibrium carrier concentrations, the two mobilities, and the effective excess carrier lifetime of p-type HgCdTe narrow gap semiconductor. This novel technique allows us to present the mobility of electrons as minority-carrier throughout the temperature range of 13.6–300.2 K in this material.
Simulations of electron impact ionization rate in GaAs in nonuniform electric fields
Authors: Kim K. , Hess K.
Published: July 2002

A Monte Carlo simulation code has been developed to study the electron impact ionization in GaAs subject to nonuniform electric fields. Results are presented for the spatial evolution of the ionization rate and the average electron energy through a p+-n junction or Schottky barrier. We show that the dead space is significantly longer than estimated by simple ballistic models. For field variations typical for p+-n junctions or Schottky barriers, the results for the region after the dead space agree closely with steady-state calculations. Appropriate definition of the impact ionization rate in transient problems is discussed along with the Keldysh model.
Trap generation and occupation dynamics in SiO2 under charge injection stress
Authors: Nissan-Cohen Y. , Shappir J. , Frohman-Bentchkowsky D.
Published: July 2002

The effect of enduring charge injection on the physical properties of the SiO2 layer of a metal-oxide-semiconductor structure is studied by means of a novel characterization method. It is based on the observation reported previously, that under charge injection conditions the density of occupied oxide traps reaches a value which is only a fraction of the total trap density. This trap occupation level is strongly dependent on the oxide electric field. The oxide trap density can be evaluated by measuring this field dependence, using a relatively small amount of charge injection. This method is used to distinguish between the process of trap generation and electron trapping in the generated traps, under conditions of continuous charge injection up to levels of more than 50 C/cm2. The trap generation rate is found to be proportional to the flux of the injected charge, and to increase exponentially with the oxide electric field. At high oxide field only a small fraction of the newly generated traps are occupied; consequently, the measured oxide charge buildup does not reflect the actual increase in the density of generated traps. The density of the generated traps reaches high values of the order of 1020 cm−3. It is suggested that these high values of oxide traps may be the cause of the SiO2 ‘‘wear out’’ type breakdown, by forming a new path of conductance by electron tunneling between closely spaced generated traps.
Hydrogenation and annealing kinetics in boron- and aluminum-doped silicon
Authors: Dadgar Suzanne , Hsu Charles Ching-Hsiang , Pan Samuel Cheng-Sheng , Sah Chih-Tang
Published: July 2002

Hydrogenation kinetics of the aluminum and boron acceptors in oxidized silicon have been obtained during constant current avalanche electron injection stress in contrast to constant voltage stress reported previously by us. The annealing kinetics have been measured at eight new temperatures for Al-doped metal–oxide–semiconductor capacitors over the range 120–205 °C. Four phases were observed during the thermal activation of the aluminum acceptor. The first phase consisted of an initial drop of the hole concentration. Phase two was associated with the first-order hydrogen-acceptor bond-breaking reaction. The last two phases were attributed to the second-order kinetics of the hydrogen molecule formation and breakup reaction. The thermal activation energy for the aluminum acceptor was 1.6 eV in contrast to our previous 2.2 eV based on fewer (three) annealing temperatures, giving more firmly the chemical trend, B(1.1 eV)<Al(1.6 eV)<Ga(2.2 eV).
Room-temperature optically pumped laser oscillation at 2.07 μm from Ga0.85In0.15As0.13Sb0.87/ Al0.4Ga0.6As0.035Sb0.965 double heterostructures grown by molecular-beam epitaxy on GaSb substrates
Authors: van der Ziel J. P. , Chiu T. H. , Tsang W. T.
Published: July 2002

The growth by molecular-beam epitaxy of high-quality Ga0.85In0.15As0.13Sb0.87 active layers with Al0.4Ga0.6As0.035Sb0.965 cladding layers on GaSb substrates by molecular-beam epitaxy is reported. The lattice match of the active layer to the substrate is Δa/a ∼4 ×10−3. Optically pumped laser oscillation was observed from 80 to 300 K with T0=55 K for T<225 K and T0=32 K for 225<T<300 K.
Cross-sectional transmission electron microscope study of solid phase epitaxial growth in BF+2 -implanted (001)Si
Authors: Nieh C. W. , Chen L. J.
Published: July 2002

A cross-sectional transmission electron microscope (XTEM) study of solid phase epitaxial growth in BF+2 -implanted (001)Si has been carried out. It is demonstrated that XTEM is unique in providing accurate, high-resolution data on the regrowth of implantation-amorphous layer. The activation energy for the regrowth was measured to be 3.0±0.1 eV. Uncertainties in the XTEM measurements of solid phase regrowth rate are discussed.
Liquid-phase-epitaxial InAsySb1−y on GaSb substrates using GaInAsSb buffer layers: Growth, characterization, and application to mid-IR photodiodes
Authors: Zyskind J. L. , Srivastava A. K. , DeWinter J. C. , Pollack M. A. , Sulhoff J. W.
Published: July 2002

The growth of device quality InAsySb1−y on (100)-oriented GaSb substrates has been achieved by the use of intermediate buffer layers of Ga0.82In0.18As0.17Sb0.83 to minimize the dissolution of the subtrate by the ternary solution. Characterization of these layers by x-ray diffraction, compositional analysis, low-temperature photoluminescence, and electrical measurements indicates their high quality. Spectral response measurements of InAsSb/GaInAsSb/GaSb back-illuminated photodiodes give a 6%–7% quantum efficiency between wavelengths of 2.5 and 4.2 μm at room temperature.
Cs+-electron recombination in the presence of N2, O2, and CO2 at 300 K
Authors: Pritt A. T.
Published: July 2002

The mechanism and rate constants associated with three-body recombination of Cs+ and electrons have been determined by monitoring the disappearance of electrons using a movable double Langmuir probe in a flowtube apparatus. The ambipolar diffusion rate constant for the dilute plasma in argon and helium was measured to be 380±30 cm2 s−1 and 650±200 cm2 s−1, respectively. Electron-ion recombination was measured in the presence of molecular nitrogen, oxygen, and carbon dioxide. From the kinetics of the electron disappearance along the flowtube, plasma recombination in nitrogen can be explained by the formation of a complex ion, recombination in oxygen proceeds through the formation of the O−2 followed by dissociative attachment in which the latter step is the rate determining step, and recombination in CO2 can be attributed to a direct three-body process.
Comparative study of the growth processes of GaAs, AlGaAs, InGaAs, and InAlAs lattice matched and nonlattice matched semiconductors using high-energy electron diffraction
Authors: Berger Paul R. , Bhattacharya Pallab K. , Singh Jasprit
Published: July 2002

We have examined the effect of growth temperature and growth interruption time on molecular-beam-epitaxial growth of GaAs, Al0.3Ga0.7As, and InxGa1−xAs on GaAs substrates and In0.53Ga0.47As and In0.52Al0.48As on InP substrates using dynamical reflection high-energy electron diffraction as an in situ probe. We have studied the time taken for a rough growth front to recover in the absence of growth as a function of growth temperature for these compounds. It is found that while GaAs and InGaAs surfaces can recover in 15–20 s under ideal growth conditions, Al0.3Ga0.7As surfaces take ≊45 s, and In0.52Al0.48As surfaces take several minutes to recover. Our results also suggest that smoothening of the growth front occurs by rearrangement of the surface atoms, rather than by re-evaporation. We have also studied the effect of strain induced by mismatch on growth modes in the case of InxGa1−xAs on GaAs. Our studies suggest that the presence of strain inhibits the surface migration of adatoms during growth and thus tends to generate a rougher growth front.
Comparison of compositionally graded to abrupt emitter-base junctions used in the heterojunction bipolar transistor
Authors: Enquist P. M. , Ramberg L. P. , Eastman L. F.
Published: July 2002

This article describes an experimental study which compares compositionally graded to abrupt emitter-base junctions which are used in the heterojunction bipolar transistor (HBT). It is found that the larger current gains are obtained in devices with abrupt emitter-base junctions. Measurements of electroluminescence emitted from the base region and temperature-dependent current gain indicate that the larger current gain in the abrupt devices is due to a larger base-transport factor. The data presented provide evidence that the injection of hot electrons from an abrupt emitter-base junction is realizable and can result in improved performance of the HBT.
Exceptionally large enhancement of InP (110) oxidation rate by cesium catalyst
Authors: Soukiassian P. , Bakshi M. H. , Hurych Z.
Published: July 2002

Core level photoemission spectroscopy experiments using synchrotron radiation were performed to study the catalytic role of cesium in the oxidation of InP (110). At room temperature, we found an exceptional increase of the oxidation rate by a factor of 1013 in the presence of one monolayer of cesium on InP (110) surface. The oxide mainly consisted of phosphates as InPO4.
Anomalous substrate and annealing temperature dependencies of heavily boron-doped hydrogenated amorphous silicon
Authors: Jang Jin , Kim Sung Chul
Published: July 2002

The 1% boron-doped hydrogenated amorphous silicon (a-Si:H) has a sharp absorption edge, a low density of gap states, and a large optical gap of 1.82 eV when the substrate temperature is around 90 °C. The photoconductivity of these samples is nearly independent of substrate and annealing temperatures, while the conductivity activation energy decreases with increasing the substrate (or annealing) temperature. The difference between the conduction band edge and the Fermi level decreases up to 250 °C, and then nearly saturates with an increase of the substrate temperature. This result can be applied to fabricate the high open-circuit voltage a-Si:H n-i-p solar cells.
Influence of thermal effects on the eigenmodes of gain-guided diode laser arrays
Authors: Hadley G. R. , Hohimer J. P. , Owyoung A.
Published: July 2002

We show that the inclusion of junction-heating effects in the numerical modeling of a gain-guided diode laser array produces significant changes in the mode characteristics of such devices. This is evidenced as alterations in the near- and far-field emission patterns and modal gains of the high-order array eigenmodes. Our experimental measurements of the emission patterns from free-running and injection-seeded gain-guided diode laser arrays show very good agreement with the results of our model and illustrate the influence of these thermal effects.
Lattice strain and lattice dynamics of ZnSe-ZnTe strained-layer superlattices
Authors: Kobayashi Masakazu , Konagai Makoto , Takahashi Kiyoshi , Urabe Kazuyori
Published: July 2002

Lattice strain and lattice dynamics of ZnSe-ZnTe strained-layer superlattices (SLSs) were examined by means of transmission electron microscopy and Raman scattering. Superlattice structures were confirmed from both transmission electron diffraction patterns and bright field images of the samples. Lattice distortions which originated from misfit strains were observed by the lattice image mode. The crystallinity of the adjacent layers was degraded when the layer thickness became large and polycrystalline structures were observed when the layer thickness exceeded the critical layer thickness. Raman scattering was used to assess the magnitude of the strain in the SLSs. Optical phonon frequencies of the components in SLSs were different from those frequencies of the bulk materials. The frequency shifts were used to quantify the strains in the SLSs. The observed shifts corresponded to the calculated values.
Band structure of superlattice with graded interfaces
Authors: Jiang H. X. , Lin J. Y.
Published: July 2002

The electron-energy levels in the GaAs-Ga1−xAlxAs superlattice with finite thicknesses of interfaces between the layers, instead of sharp discontinuities across the interfaces, have been investigated. This model is more realistic for superlattices. A linearly increased (decreased) potential across the interfaces was assumed and a dispersion relation was derived to the second order of the thickness of the interface. The miniband structure, the shifting of the ground-state energy of the electron, and the effective-energy gap as functions of this thickness are presented.
An analysis of the heat-pulse method for thermal-transport measurements of thin films
Authors: Bortner L. J. , Newrock R. S. , Resnick D. J.
Published: July 2002

We analyzed the heat-pulse method of measuring the thermal conductivity and specific heat of thin films. The method, which separates the effects of the addenda from those of the film, fails because of problems of measurement accuracy. Our calculations show ways of treating the data that yield the thermal conductivity, specific heat, and thermal diffusivity to about 1% accuracy, if the addenda coefficients can be estimated to about 10%.
Electron holography to image magnetic domains (invited)
Authors: Tonomura Akira
Published: July 2002

The principles of electron holography were formulated 40 years ago. Recently, this technique has reached the level of practical application with the development of a coherent field-emission electron beam. In this method, magnetic lines of force are quantitatively observed in h/e flux units in an interference electron micrograph. Several applications of this method are introduced.
Magnetic studies in multilayer Ni-C films
Authors: Krishnan R. , Youn K. B. , Sella C.
Published: July 2002

Multilayer Ni-C films have been prepared using dc triode sputtering with a fixed C layer of 2 nm thick and with a Ni layer varying from 3 to 10 nm thick. The C layer is amorphous and the structure of the Ni layer is hexagonal for 3 nm thick but becomes fcc when the thickness is above 6 nm. The magnetization is strongly reduced which is attributed to the presence of nonmagnetic layers at each interface. These layers could be Ni3C. FMR indicates an easy perpendicular axis for t(Ni)>20 nm, but for t(Ni)<7 nm, the films develop an easy plane anisotropy. The Hc and the linewidth increases for t(Ni)<7 nm. Annealing at 473 K in vacuum leads to an increase in 4πM, indicating that C atoms are segregating out of the Ni layer and that the Ni film crystallizes better. The perpendicular anisotropy also develops strongly after annealing. The results are discussed.
Noise dependence on the thickness of plated disks
Authors: Judge J. S. , Seagle D. , Speliotis D. E.
Published: July 2002

Noise is as important a system performance determinant as signal, and yet in many recording system designs it is ignored in the erroneous pursuit of maximizing output signal regardless of the associated media noise. The dominant noise in thin metallic films used in high recording density applications is modulation noise, arising from the zig-zag magnetization pattern in the transition regions, which in turn may arise from strong exchange coupling between the crystallites of the film. In this study we investigated the dependence of the signal, the noise, and the signal-to-noise ratio in chemically deposited thin films as a function of their thickness which was varied from 0.02 to 0.16 μm, while the magnetic parameters of the films varied only in a narrow range (Hc: 480–580 Oe; SQ: ∼0.7; Ms=138 emu/g, and SFD: 0.06–0.13). The low density signal output increases monotonically with thickness in this range. The high density output (15–20 KFCI) shows a pronounced peak at a thickness of 0.05–0.07 μm. The peak modulation noise was found to increase with thickness, from a low value of 3 μV (RMS) to a high value of 13 μV (over 12 dB). Consequently, the high density signal-to-noise ratio of these films decreases monotonically with increasing thickness. The implications of these results on the optimization of thin-film media for high recording density applications are discussed.
Observation of laser-written magnetic domains in amorphous TbFe films by Lorentz microscopy (invited)
Authors: Suits J. C. , Geiss R. H. , Lin C. J. , Rugar D. , Bell A. E.
Published: July 2002

A review is given of Lorentz microscopy and its application to the study of laser-written domains in amorphous rare-earth/transition-metal–type materials. Domains, or regions of reverse magnetization, were written under various conditions of laser power and applied magnetic field in TbxFe1−x films where x varies in the range 0.14–0.32. Upon examination by Lorentz microscopy, and under certain conditions, these written regions show highly detailed magnetic structures. One condition for obtaining good images is the avoidance of oxidized surface layers showing in-plane magnetization. Another condition is tilting of the film plane in the transmission electron microscope to enhance image contrast. A variety of domain structures have been observed ranging from fully saturated regions with both highly regular and irregular boundaries, to fully demagnetized regions. An example of correlation between the field dependence of the microstructure and measurements of magneto-optical signal is given for the x=0.32 composition. Results are presented of carrier signal and noise measurements made on a film on a rotating disk.
Comparison of transient thermal conduction in tellurium and organic dye based digital optical storage media
Authors: Burgess A. N. , Evans K. E. , Mackay M. , Abbott S. J.
Published: July 2002

Considerable research and development has been done, in recent years, on combinations of optically absorbing thin films and substrates for digital optical storage media. Recent theoretical models have considered the formation of pits, by laser heating, in such media in two stages: (i) a preinitiation stage before pit formation; (ii) a pit growth stage. To compare the validity of suggested mechanisms for initiation accurate temperature calculations are required. In this paper the full transient thermal conduction equation is solved by finite element methods for both a tellurium and an organic dye layer system and the results compared.
A new protective film for magneto-optical TbFeCo media
Authors: Miyazaki M. , Shibata I. , Okada S. , Ito K. , Ogawa S.
Published: July 2002

A new protective film, Tb-SiO2, was developed to increase the lifetime of TbFeCo magneto-optical disks. Since Tb, a rare-earth metal, is quite easily oxidizable, an efficient protective layer is essential to assure the stability of magneto-optical disks. Given that vacuum-deposited SiO2 film acts as an oxidation-inducing layer, unlike SiO2 on a thermally oxidized silicon wafer, we invented a new protective film, Tb-SiO2, in which Tb is intended to trap active oxygen in the vacuum-deposited SiO2. The results were excellent and we estimate the lifetime of TbFeCo disks with Tb-SiO2 as an underlayer and overlayer, at more than 20 years at 40 °C, 90% relative humidity. The properties and protection effects of Tb-SiO2 are described.
Thermal behavior and strength of continuous filament Cu-Nb composites
Authors: Klein J. D. , Rose R. M.
Published: July 2002

Microfilamentary composites of continuous Nb fibers in Cu matrices prepared by the stack-and-draw method were tested for normal-state electrical conductivity, residual stress state, and tensile properties. Composite wires having nominal filament diameters of about 0.1 μm were characterized by elevated matrix annealing temperatures, large Nb residual strains, and high tensile strengths. In the fine-filament regime, finer wire sizes result in larger matrix resistivities, higher residual fiber strains, and higher tensile strengths with little effect on matrix annealing temperatures.
Filamentation instability in an inhomogeneous laser-produced plasma
Authors: Sharma A. K. , Mishra G.
Published: July 2002

A laser beam propagating along the density gradient in a laser-produced plasma is unstable to a transverse density perturbation. When ambient density scale length is comparable to growth length, spatial growth is faster than the exponential. For a linear density profile the amplitude of the filament varies with z as an Airy’s function, whereas for an exponential profile it goes as a Bessel function of imaginary order and argument. In both cases the growth rate increases with the transverse wave vector of the perturbation.
Fundamental differences between thick and thin oxides subjected to high electric fields
Authors: Warren William L. , Lenahan P. M.
Published: July 2002

We observe atomic scale differences in the response of thin and thick oxides subjected to high electric fields. In stressed thick oxides, we observe the generation of a ‘‘trivalent silicon’’ trapped hole center, termed E′; in stressed thin oxides no E′ centers were detected. We believe that our results indicate the absence of impact ionization in stressed thin oxides.
Bulk properties of composite media. II. Evaluation of bounds on the shear modulus of suspensions of impenetrable spheres
Authors: Sen Asok K. , Lado F. , Torquato S.
Published: July 2002

We evaluate third-order bounds due to Milton and Phan-Thien on the effective shear modulus Ge of a random dispersion of identical impenetrable spheres in a matrix up to sphere-volume fractions near the random close-packing value. The third-order bounds, which incorporate two parameters, ζ2 and η2, that depend upon the three-point probability function of the composite medium, are shown to significantly improve upon the second-order Hashin–Shtrikman (or, more general, Walpole) bounds which do not utilize this information, for a wide range of volume fraction and phase property values. The physical significance of the microstructural parameter η2 for general microstructures is briefly discussed. The third-order bounds on Ge are found to be sharp enough to yield good estimates of the effective shear modulus for a wide range of sphere-volume fractions, even when the individual shear moduli differ by as much as two orders of magnitude. Moreover, when the spheres are highly rigid relative to the matrix, the third-order lower bound on the effective property provides a useful estimate of it. The third-order bounds are compared with experimental data for the shear modulus of composites composed of glass spheres in an epoxy matrix and the shear viscosity of suspensions of bituminous particles in water. In general, the third-order lower bound (rather than the upper bound) on Ge tends to provide a good estimate of the data.
AlGaAs/GaAs quantum wells with high carrier confinement and luminescence efficiencies by organometallic chemical vapor deposition
Authors: Bertolet Daniel C. , Hsu Jung-Kuei , Lau Kei May
Published: July 2002

Single and multiple quantum wells with well widths ranging from 10 to 135 Å were grown by atmospheric pressure organometallic chemical vapor deposition and characterized by photoluminescence (PL) and electrical measurements. Compared with single layers of high-purity GaAs and AlGaAs which have high intensity near band-edge excitonic transitions, the quantum well (QW) structures exhibit very strong luminescence of the discrete QW eigenstates. The intense QW signals indicate that the carrier confinement efficiency of the wells is very high, which is also supported by significant mobility enhancement in the samples. The sharp PL lines suggest high quality and smoothness of the well interfaces.
Measurement of phase and coupling parameters in magneto-optic coupled mode waveguides
Authors: Okamura Yasuyuki , Inuzuka Hirosei , Yamamoto Sadahiko
Published: July 2002

A method for measuring the phase constant difference between the orthogonally polarized modes and the coupling coefficient in a magneto-optic coupled mode waveguide is described and demonstrated. It is based on measurements of polarization of the output light of the resulting ellipse due to the waveguide dispersion without the perturbation, the external magnetic field, and the variation of the mode conversion efficiency with the alternating perturbation. A reasonable Faraday rotation angle, which corresponds to the saturated coupling coefficient for a waveguide far from cutoff, has been obtained.
Effects on InP surface trap states of i
n s
i
t
u etching and phosphorus-nitride deposition
Authors: Jeong Yoon-Ha , Takagi Shinichi , Arai Fusako , Sugano Takuo
Published: July 2002

Effects of in situ etching of InP surfaces with PCl3 followed by low-temperature in situ chemical vapor deposition of phosphorus-nitride in a phosphorus-rich ambiance using NH3/PCl3/H2 on trap states of the interfaces were studied. The breakdown field of the phosphorus-nitride films was as high as 1×107 V cm−1 and the films showed trap-assisted conduction in high electric field with resistivity higher than 1×1014 Ω cm near the electric field of 1×107 V cm−1. Interface properties were found to be critically dependent upon PCl3 molar fraction, both the etching and deposition time, and the etching and deposition temperature. The frequency dispersion of capacitance-voltage characteristics in accumulation was about 3.3% for the frequency range from 10 kHz to 1 MHz. The hysteresis was as low as 0.17 V for the field electrode voltage swept between −6 and +6 V. The density of interface trap states, Nss, was 2×1011 cm−2 eV−1 at about 0.3 eV below the conduction-band edge of InP and was 8×1011 cm−2 eV−1 near the bulk Fermi level.
Electronic states at the interface between thin films of ZnS and crystalline p-silicon
Authors: Sands David , Brunson Kevin M. , Thomas Clive B.
Published: July 2002

Thin films of zinc sulfide have been evaporated onto p−-p+ silicon substrates and metal-insulator-semiconductor diodes fabricated. Capacitance-voltage characteristics have been analyzed qualitatively and quantitative measurement of the density of interface states has been made using the conductance technique developed by Nicollian and Goetzberger [Bell Syst. Tech. J. 46, 1055 (1967)]. Similarities between this interface and that between sputtered zinc sulfide are noted. A model is developed to explain the high densities of interface states observed (≥1012 cm−2 eV−1) and the suitability of these films for use in electroluminescent devices is discussed.
Defect-property correlations in garnet crystals. III. The electrical conductivity and defect structure of luminescent nickel-doped yttrium aluminum garnet
Authors: Rotman S. R. , Tuller H. L.
Published: July 2002

The conduction mechanisms in nickel-doped yttrium aluminum garnet (Ni:YAG) have been studied as a function of temperature and partial pressue of oxygen. ac conductivity and ionic transference measurements show that Ni:YAG is a mixed ionic-electronic conductor with an ionic mobility characterized by an activation energy of 2.0–2.2 eV. The reduction of Ni+3 to Ni+2 causes an increase in the oxygen vacancy concentration and a concurrent rise in the magnitude of the ionic conductivity. Codoping with zirconium, on the other hand, fixes the nickel in the divalent state, increases the n-type conductivity, and lowers the degree of ionic conductivity. A defect model is presented which is consistent with all of these observations.
Silicide formation with codeposited titanium-tantalum alloys on silicon
Authors: Capio C. D. , Williams D. S. , Murarka S. P.
Published: July 2002

The formation of disilicides of titanium and tantalum from Ti-Ta alloys codeposited on silicon and polycrystalline silicon have been investigated using x-ray diffraction techniques, resistance measurements, and Auger electron spectroscopy. Titanium and tantalum in the Ti-Ta alloy interacted independently with silicon. There was no titanium/tantalum compound formation and no ternary was detected. The growth of each metal silicide was sustained by continuous out-diffusion of silicon into the Ti-Ta alloy film until the metals were consumed in the silicide transformation. This behavior may account for the absence of phase separation and component accumulation. An initial reaction was observed after the 600 °C, 30 min anneal. The stable end phases formed at temperatures ≥800 °C are TiSi2 and TaSi2. High molecular weight intermetallics such as Ta5Si3 and Ti5Si3 that are normally not detected in Ta-Si and Ti-Si interaction studies were detected, suggesting a stabilizing effect of the impurities. The sheet resistance of the heat-treated samples is: (a) a strong function of the titanium content of the Ti-Ta alloy (low for Ti-rich alloys); (b) lower on silicon substrates; (c) invariant at temperatures >900 °C. The etch rate of the heat-treated samples in buffered hydrofluoric acid increased with increasing titanium content in the film.
Analysis of barrier transmission in resonant tunneling diodes
Authors: Araki Kinichiro
Published: July 2002

With use of the matrix deduced by Tsu and Esaki [Appl. Phys. Lett. 22, 562 (1973)], ‖M22‖2, the square of an absolute value for one of the matrix elements, which together represent a whole resonant tunneling double-barrier diode, is calculated by inserting tabulated products of two partial-diode matrix elements into the respective terms for ‖M22‖2. The same calculation method is then also applied to a calculation of ‖M22‖2 for a triple-barrier diode. From the calculated ‖M22‖2 the fundamental quantities that determine the resonant tunneling diode characteristics—transmission coefficients, resonant conditions, and full widths at half maximum of resonant peaks—are calculated for double- and triple-barrier diodes. These calculated formulas are rather simple, and so they are useful tools for understanding the physical mechanisms of the resonant tunneling diode and for developing other theoretical applications. Furthermore, the method of calculating ‖M22‖2 could be applied to diodes more complex than the triple-barrier diode treated here.
Nonparabolicity as a tool in band-gap engineering
Authors: Landsberg Peter T. , Yu Young-June
Published: July 2002

A new analytical, but still approximate, formula for the threshold energy of electron-electron-hole impact ionization is given for the case of parabolic valence and conduction bands of the simple Kane type. It is shown for the first time that impact ionization in this system can be ‘‘switched off’’ if the ratio of electron to hole effective mass is large enough. The condition for this to happen is given by a new formula which is exact within this model.
Ballistic transport in semiconductor alloys
Authors: Krishnamurthy Srinivasan , Berding M. A. , Sher A. , Chen A.-B.
Published: July 2002

The electronic structure of semiconductor compounds GaAs, InAs, and InP and alloys Ga0.5In0.5As, Ga0.7Al0.3As, and InP0.5As0.5, obtained in the coherent potential approximation, is used to calculate the group velocity and velocity relaxation time limited by longitudinal optical phonons, alloy disorder, and ionized impurities as a function of electron energy at 300 K. The nonparabolic nature of the band structure is found to severely limit the electron mean free path. With the types of interactions considered to date, the presence of L valleys does not limit the mean free path of electrons moving in the 〈100〉 direction. At 1018-cm−3 doping, electron-electron interactions reduce the mean free path by only 15% to 20%. InAs and GaInAs alloys offer advantages over all the other materials for devices with base widths greater than 500 Å; however, for thinner devices, ∼100 Å, no material is appreciably better than GaAs, the III-V compound currently under best control. The ballistic device-related properties of several II-VI systems compare favorably with the III-V alloys studied here. However, the II-VI compounds are less robust structural materials leading us to recommend the III-V compounds.
An evaluation of horizontal Bridgman-grown, undoped, semi-insulating GaAs
Authors: Gray M. L. , Sargent L. , Burke K. M. , Grim K. A. , Blakemore J. S.
Published: July 2002

An undoped, semi-insulating GaAs crystal grown by the horizontal Bridgman method has been characterized by axial and radial resistivity and mobility measurements. Due to lower thermal gradients, defect densities for wafers from this crystal are less than those observed for liquid-encapsulated Czochralski crystals. Cathodoluminescent images display uniform luminescent intensity around dislocated regions indicating an absence of impurity gettering in these areas. Concentrations of neutral EL2, a native defect and principal deep donor in undoped GaAs, are reported for seed, middle, and tail-end wafers. The distribution of EL2 over the area of each wafer is shown. Wafers were also implanted with 29Si and furnace annealed to form shallow n layers. Capacitance-voltage profiles demonstrate reproducible peak carrier concentrations and penetration depths.
Ultrasonic second-harmonic generation in various crystalline systems: Coupling parameters in terms of elastic moduli and propagation directions
Authors: Gerlich D. , Breazeale M. A.
Published: July 2002

The ultrasonic second- and third-order coupling parameters, K2 and K3, determined by ultrasonic second-harmonic generation, are evaluated in terms of the second- and third-order elastic moduli, for a number of crystalline systems. It is shown that K2 and K3 turn out simply to be the values of the elastic moduli C11 and C111, transformed into the direction of propagation. The possibility of evaluating the complete set of third-order elastic moduli from measurements of second-harmonic generation and hydrostatic pressure dependence of the sound velocity for pure mode propagation is discussed. Symmetries considered: cubic, hexagonal, rhombohedral, tetragonal, and orthorhombic.
A time-temperature-transformation diagram for the orthorhombic to tetragonal phase transition in YBa2Cu3O7−∂
Authors: Shi D. , Capone II D. W. , Goretta K. C. , Zhang K. , Goudey G. T.
Published: July 2002

An isothermal transformation curve marking the orthorhombic (O) to tetragonal (T) phase transition boundary has been established over a wide temperature range. There exists within the time-temperature-transformation diagram two distinct and separate regions containing superconducting samples with narrow 90- and 60-K transition temperatures, respectively. An oxygen diffusion coefficient at 300 °C in these materials is estimated based on isothermal data. The kinetic process of the T-O transformation is studied. It is found, at all temperatures investigated, that extended annealing reduces the normal-state conductivity of the material and that the best samples are produced for intermediate annealing times.
Minority-carrier lifetime in n-Al0.38Ga0.62As
Authors: Ahrenkiel R. K. , Dunlavy D. J. , Loo R. Y. , Kamath G. S.
Published: July 2002

The minority-carrier lifetime in n-Al0.38Ga0.62As has been investigated by laser-induced photoluminescence. A variety of device structures were used to reduce interface recombination effects, including double heterostructures. Bulk lifetimes of about 18 ns were seen at doping levels of 1×1016 cm−3 or less. These data suggest that minority-carrier devices are feasible in high aluminum AlGaAs, contrary to the suggestion of earlier work.
Magnetic correlations in amorphous Fe-Zr alloys
Authors: Rhyne J. J. , Erwin R. W. , Fernandez-Baca J. A. , Fish G. E.
Published: July 2002

Results of high-resolution small-angle neutron scattering (SANS) studies on amorphous alloys of composition FexZr100−x, x=90, 91, 92, show that ferromagnetic correlations exist below Tc, but that conventional long-range order is destroyed by competing exchange interactions. The transition temperatures drop with increasing iron concentration (Tc ≊226 K for Fe90Zr10 down to Tc ≊175 K for Fe92Zr8). Data taken at very low Q (0.008 Å−1<Q<0.02 Å−1) provide evidence of relatively large (≊200–≊400 Å) static spin clusters which do not disorder at Tc. Superposed on this is an ordering with a second shorter length scale which shows a cusp (not divergent) at the bulk Tc. The data were fitted to a combination of a Lorentzian and a power of a Lorentzian, the latter of which represents scattering from clusters with a Maxwellian distribution of sizes.
Short-range Ising spin glasses in general dimensions
Authors: Singh Rajiv R. P. , Fisher Michael E.
Published: July 2002

The equilibrium properties of nearest-neighbor Ising spin glasses on hypercubic lattices are studied as a function of d, the dimensionality. An expansion of Tc(d) to fifth order in inverse powers of d, augmented by high-temperature series estimates for d=3 and 4, yields the critical temperature for all d and for general, symmetric distributions of coupling strengths, Jij. By extrapolation of Tc to zero, the lower borderline dimensionality is estimated as dl ≂2.5. High-temperature expansions for the spin-glass susceptibility of the ±J model in powers of w=tanh2(J/kBT) and u=tanh2(H/kBT), where H is the magnetic field, yield estimates of the magnetic field crossover exponent Δ for d=3 to 8.