bluuebunny/crossref_metadata_2025 huggingface dataset:
Piezoresistance in n-channel inversion layers of silicon films on sapphire
Authors: Zaima Shigeaki , Yasuda Yukio , Kawaguchi Seiji , Tsuneyoshi Manabu , Nakamura Tetsuro , Yoshida Akira
Published: July 2002

The piezoresistance effect in n-channel inversion layers of (001) silicon films on sapphire (SOS) and (001) bulk silicon has been studied at room temperature using metal-oxide-semiconductor field-effect transistors radially arranged on a diaphragm with 36 mm in diameter. The piezoresistance characteristics of inversion layers are markedly different between SOS and bulk silicon. Main features of the experimental results are interpreted on the basis of the deformation potential theory and the surface quantization effect in inversion layers, and it is concluded that the difference between SOS and bulk silicon can be mainly explained by the effect of residual strain in SOS. The piezoresistance coefficients of inversion layers on SOS have been determined experimentally, and have been found that π11≂−π12. In addition, the comparison of the experimental value of π11/π12 with the calculated value is suggested that the transverse mobility of electrons in the valley which have its longitudinal axis of ellipsoid perpendicular to the film surface is smaller as compared with that in the other valleys.
The density of localized states at the semi-insulating polycrystalline and single-crystal silicon interface
Authors: Brunson Kevin M. , Sands David , Thomas Clive B. , Reehal Hari S.
Published: July 2002

The density of localized states at the interface between as-deposited 51 at. % semi-insulating polycrystalline silicon and silicon has been measured using the conductance technique. Aluminum-gated metal-insulator-semiconductor structures were made on n-n+ and p-p+ epilayered silicon and full details of capacitance-voltage and conductance-voltage characteristics are given. The interface state response is shown to fit the statistical model and comparisons with the Si-SiO2 interface were made. The density of states is found to be between ∼6×1010 cm−2 eV−1 near midgap rising to ∼6×1011 cm−2 eV−1 at the band edges.
Phase transitions and ferroelectric behavior in Pb5M3O9F10(M=Mo, W) and phase transition in Pb5Ti3O3F16
Authors: Arquis-Canouet S. , Ravez J. , Chaminade J. P. , Hagenmuller P. , Abrahams S. C. , Marsh P.
Published: July 2002

Two new nonlinear optic lead transition-metal oxyfluorides have been prepared and characterized. Pb5W3O9F10 is tetragonal with a=14.583(3), c=7.365(1) Å and nonlinear dielectric susceptibility d33=0.025(5)10−12 V−1 m. The atomic arrangement permits reversal of the spontaneous polarization, with resulting maximum atomic displacements along the polar axis of about 0.4 Å. The Curie temperature predicted on the basis of the tungsten and associated oxygen atom displacements is about 840 K. The experimental phase transition temperature is 785(15) K. The dielectric permittivity reaches a maximum of 2.4×107 at 805(10) K as the loss tangent passes through a minimum. Pb5Mo3O9F10 is isostructural with Pb5W3O9F10 and exhibits similar properties. The PbF2–MoO3 system contains five distinct and newly characterized phases: cubic Pb1−xMoxO3xF2−2x with 0≤x≤0.15, orthorhombic Pb3MoO3F6 with distorted fluorite-type structure, the closely related α and β phases of tetragonal Pb5Mo3O9F10, and tetragonal PbMoO3F2. Pb5Ti3O3F16 is isostructural with Pb5W3O9F10, with a phase transition at 780(10) K and d33<10−16 V−1 m.
Cross-sectional transmission electron microscope study of residual defects in BF+2-implanted (001)Si
Authors: Nieh C. W. , Chen L. J.
Published: July 2002

A combined cross-sectional and plan-view transmission electron microscope study of residual defects in 110-keV, 5×1015/cm2 BF+2- implanted (001)Si has been carried out. Complete amorphization of the surface layer to a depth of about 1400 Å from the surface was found in as-implanted samples. The general trends of the amorphous/crystalline (a/c) regrowth were found to be similar in 550–900 °C annealed samples. ‘‘Paired’’ dislocations were observed in the first ∼600 Å of regrown layers. A high density of twins was found subsequently as the a/c interface advanced to the surface. Small defect clusters, irregular dislocations, equiaxial loops, and rodlike defects were observed to distribute in bands underneath the original a/c interface. The regrown layers were found to be almost dislocation- and twin-free in 1000–1100 °C annealed specimens. The regrown layer, however, contained a high density of fluorine bubbles. The bubbles were concentrated near the orignal a/c interface and the surface. Irregular dislocation networks were found to develop near the orignal a/c interface. The origins of residual defects and their possible influences on device applications are discussed.
Inversion criteria for the metal-insulator-semiconductor tunnel structures
Authors: Wang S. J. , Fang B. C. , Tzeng F. C. , Chen C. T. , Chang C. Y.
Published: July 2002

The conditions of strong surface inversion in the semiconductor surface of a metal-insulator-semiconductor (MIS) tunnel structure are studied. By employing the voltage equation which governs the potential distribution in the MIS diode and by defining a parameter θ which indicates the energy separation between the semiconductor minority-carrier quasi-Fermi level and the metal Fermi level at the insulator–semiconductor interface, the values of θ(inv) under strong surface inversion are calculated in terms of oxide thickness, metal work function, oxide and interface state charges, semiconductor doping concentration, and reverse bias voltage. There are three conditions, namely, (1) without the external injection of the minority-carrier current density Jinj (i.e., Jinj=0), (2) with it (i.e., Jinj is positive), and (3) where Jinj is negative (i.e., carrier extraction). The second condition can be attributed to the critical insulator thickness dcri below which the semiconductor surface cannot be inverted solely by applying a reverse bias voltage, hence an externally injected minority-carrier current Jinj(inv) is required to achieve strong surface inversion at certain bias and oxide thickness. It also reveals that Jinj(inv) increases with decreasing insulator layer thickness and is strongly dependent on the oxide and interface state charges. For the Al–SiO2–Si tunnel structure, the calculated value of dcri is about 30 Å, which is in good agreement with the reported experimental results of 28–35 Å.
Characterization of free jet expansion of SF6 molecules
Authors: Trava-Airoldi V. J. , Sbampato Maria Esther , dos Santos Alberto M. , Ghizoni C. C.
Published: July 2002

In this work we present experimental measurements of the mean velocity of SF6 molecules in a pulsed-free jet as a function of the distance from the expansion orifice. A pyroelectric detector was used to measure the time of flight of the molecules in the jet. A comparison of the experimental results with theoretical values for the mean velocity taking the temperature dependence of the specific-heat ratio into account leads to the conclusion that the freezing of rotational, vibrational, and translational temperature is reached at considerable distances from the expansion orifice.
Band-gap and spin-orbit splitting of the lattice-matched GaAsSb/InAs system
Authors: Mani H. , Joullie A. , Joullie A. M. , Girault B. , Alibert C.
Published: July 2002

The GaAsySb1−y solid solution was grown by liquid-phase epitaxy on an InAs substrate. The direct transitions E0 and E0+Δ0 of its band structure were determined by the electroreflectance method from 30 to 300 K. The measurements show that the band-gap energy E0 is equal to the spin-orbit splitting of the valence band Δ0 at 230 K for the perfectly InAs-lattice-matched GaAs0.09Sb0.91 alloy. The equality E0=Δ0 is predicted at room temperature for the GaAs0.83Sb0.17 ternary alloy.
Ge-Si alloy microstructure fabrication by direct-laser writing with analysis by Raman microprobe spectroscopy
Authors: Herman Irving P. , Magnotta Frank
Published: July 2002

Micron-dimension structures of germanium-silicon alloys of various compositions are formed by several direct-laser writing techniques, including pyrolytic deposition of silicon from silane on laser-melted germanium substrates and codeposition from silane/germane mixtures on different absorbing substrates. In situ composition analysis of these polycrystalline alloy microstructures is performed by Raman microprobe analysis. The measured Raman shifts and widths of the laser-deposited alloys are found to be in better agreement with published Raman data on germanium-silicon alloy films than with the Raman data on alloy bulk solids. In the codeposition of alloys, the decomposition of germane to form Ge is observed to be about six times faster than the decomposition of silane to form Si, independent of the silane/germane ratio, laser power, and substrate type.
The stability of a sample in a diamond anvil cell
Authors: Moss William C. , Goettel Kenneth A.
Published: July 2002

We have performed a theoretical analysis of the stability of a gasketed sample in a diamond anvil cell. Our analysis shows the stability of the sample depends principally on the yield strength and the thickness of the gasket, the bulk modulus and the radius of the sample, and the geometry of the culet. Our results yield a simple methodology that can be used to obtain stable samples in a diamond anvil cell.
Magnetic image effect in superconducting magnet and magnetization measurement
Authors: Miyajima Hideki , Otani Yoshichika , Varga Imre , Chikazumi Sōshin , Nakao Kōichi
Published: July 2002

The magnetic image effect in a superconducting magnet (SCM) distorts the distribution of the magnetic flux produced by the magnetized specimens, so that this effect must be taken in consideration for a precise measurement of magnetization. This effect depends on the intensity of magnetic fields, histories of the SCM magnet, and geometrical arrangements of the coil system. The magnetic flux distribution in a small SCM, into which a superconducting Pb tube shield is inserted, is measured for the purpose of comparison with the electromagnetic calculation. The image effect is also investigated experimentally using a high sensitive vibrating sample magnetometer and a 100 kOe SCM. The results calculated numerically are in good agreement with the experiments. In general, under the presence of the image effect, the susceptibility measured by a vibrating sample magnetometer tends to be overestimated, while magnetization tends to be rather underestimated. In a practical cryogenic system, however, the eddy current loss induced in the metallic wall around the specimens was found to play also an important role.
Amorphous (SiC)xGe1−x :H films prepared by rf sputtering: Optical and electrical properties
Authors: Girginoudi D. , Thanailakis A. , Christou A.
Published: July 2002

The optical absorption spectra, dc conductivity, thermal activation energy, photoluminescence, and the IR spectra of a(SiC)x Ge1−x :H films prepared by conventional rf sputtering have been measured. Changes in the optical band gap from about 1.0 up to 2.25 eV, with corresponding changes in dc dark conductivity from 10−3 to 10−11 Ω−1 cm−1 and in thermal activation energy from 0.23 up to 0.78 eV, may be observed by varying the Ge content and the hydrogen partial pressure. Band-edge luminescence is the main radiative transition mechanism, and phonon bands attributed to C–H vibration modes have for the first time been observed. Systematic shifts in the IR absorption spectrum have been attributed to the effect of carbon and germanium bonds
A stochastic model for dielectric breakdown in thin capacitors
Authors: Willming D. A. , Wu C. H.
Published: July 2002

A nontrivial two-dimensional stochastic model for dielectric breakdown within a parallel plate capacitor is presented for the first time. The model has been used to determine geometric properties of parallel plate discharges. Comparisons are made between these properties and known fractal properties of electrostatic discharges within cylindrical geometries. As the spacing between the plates of a capacitor increases, the value of the fractal dimension of the associated discharge structure increases from the minimum value of unity and approaches the limiting value corresponding to the case of infinite spacing. For any given spacing, this fractal exponent is equal to the exponent of first passage time for the discharge pattern to reach a given height. A study of various power law relationships governing the breakdown may provide insight into the breakdown mechanism and electrical insulating quality of various materials. The model is applicable to the breakdown of thin insulating layers of metal-oxide-semiconductor devices.
Epitaxial Fe films on GaAs for hybrid semiconductor-magnetic memories
Authors: Schloemann Ernst , Tustison Randal , Weissman Jehoshua , Van Hook H. Jerrold , Varitimos Thomas
Published: July 2002

The magnetic and structural properties of Fe films deposited by ion-beam sputtering (IBS) on (100)-oriented GaAs substrates are described. The films are between 30 and 600 nm thick and are characterized by a coercive field of approximately 3–6 Oe. The saturation magnetization and anisotropy field, inferred from vibrating sample magnetometer measurements agree substantially with the values expected for bulk Fe. Films deposited on the (100) substrate show the expected fourfold (or ‘‘biaxial’’) symmetry with no indication of a uniaxial anisotropy component. These properties make the films ideally suitable for the intended application in a hybrid semiconductor-magnetic memory, in which two magnetic remanent states with mutually orthogonal magnetization directions interact with an electronic flip-flop circuit.
Collisional-radiative ionization and recombination model for high-temperature air and its application to discharges
Authors: Taylor R. D. , Ali A. W.
Published: July 2002

A collisional-radiative (C-R) model for high-temperature air is developed. Ionization and recombination coefficients are presented for electron temperatures between 1.0 and 3.0 eV and electron densities between 1016 and 1019 cm−3. For an assumed airlike mixture of 80% nitrogen and 20% oxygen, these results are compared with C-R coefficients of nitrogen and oxygen plasmas developed separately and show little difference. The inclusion of charge-exchange effects does not alter the coefficients. Saha decrements for air are used to delineate the onset of local thermodynamic equilibrium (LTE) for the above conditions. These thresholds are compared to other criteria and show some difference. Finally, ratios of spectral line intensities are presented in terms of the Saha decrements as a means of diagnosing high-temperature air discharges, such as lightning channels, without requiring LTE.
Effective elastic and piezoelectric constants of superlattices
Authors: Akcakaya E. , Farnell G. W.
Published: July 2002

It is shown that the determination of a set of equivalent elastic constants for periodically layered anisotropic materials to predict the acoustic performance in the long wavelength limit can be extended on the one hand to include piezoelectricity of the component materials and on the other to allow multiple layers within each period. The necessary matrices are shown in a form which can be programmed easily. The validity of the use of these equivalent constants is shown by comparison of results obtained with them and with an exact layer-by-layer calculation both for bulk-wave slowness surfaces and for surface-wave propagation velocities in two quite different examples of material combinations.
General model for intrinsic dopant diffusion in silicon under nonequilibrium point-defect conditions
Authors: Cowern N. E. B.
Published: July 2002

A general expression for the intrinsic diffusivity of a substitutional impurity in silicon is derived in terms of the self-interstitial and vacancy concentrations. The vacancy mechanism, the exchange mechanism, and two processes associated with the motion of interstitial impurity atoms, the ‘‘kick-out’’ and ‘‘Frank–Turnbull’’ mechanisms, are included in the analysis. These last two contributions to the impurity diffusion are not additive under nonequilibrium point-defect conditions, and may partially cancel each other in certain cases. The general expression can be fitted to data on As diffusion in silicon under nitridation and oxidation conditions, which were previously unexplained. The results indicate the possible presence of substantial vacancy, pushout, and Frank–Turnbull terms, but no significant exchange term. Conditions are proposed for definitive experimental measurements to test the significance of the Frank–Turnbull contribution.
Effect of Schottky barrier height on EL2 measurement by deep-level transient spectroscopy
Authors: Ma Q. Y. , Schmidt M. T. , Wu X. , Evans H. L. , Yang E. S.
Published: July 2002

A systematic study of EL2 midgap trap in GaAs using deep-level transient spectroscopy (DLTS) is reported for contacts having a large range of Schottky barrier height. The results show that the DLTS signal of EL2 increases as the barrier height rises from 0.62 eV and saturates for barrier height above 0.83 eV. It is found, for the first time, that for Schottky barrier height lower than 0.62 eV the EL2 signal disappears. A model for calculation of the quasi-Fermi level in the depletion region is used to explain the variation and disappearance of the EL2 signal. This model may also apply to other electron traps near midgap.
Magnesium-doped In0.5Ga0.5P growth by liquid-phase epitaxy
Authors: Chang L. B. , Cheng K. Y. , Liu C. C.
Published: July 2002

The structural, electrical, and optical properties of Mg-doped In0.5Ga0.5P liquid-phase epitaxial layers, which were grown on (100) Cr-doped semi-insulating GaAs substrates with a supercooling method at 750 °C growth temperature, are reported. It has been found that the lattice mismatch between In0.5Ga0.5P epilayers and GaAs substrates are slightly increased with increasing Mg impurity concentration. The electrical properties of these epilayers were determined by Hall measurements in the temperature range between 77 and 300 K. The data show that both the room-temperature carrier concentration and the hole mobility of Mg-doped layers varied linearly from 3.5×1017 to 1.2×1019 cm−3 and from 50.5 to 15 cm2/V s, respectively, as a function of Mg dopant mole fraction from 1.0×10−4 to 1.5×10−3. The Mg acceptor ionization energy was evaluated as 21.3 meV. The photoluminescence results indicate that the Mg acceptor ionization energy in In0.5Ga0.5P is approximately 28–35 meV, which is different from the electrically determined value and is discussed in this report. The distribution coefficient is also determined in this report as a value of 0.12 for Mg in In0.5Ga0.5P liquid-phase epitaxy at 750 °C growth temperature.
Calculation of Brillouin light scattering intensities from pairs of exchange-coupled thin films
Authors: Cochran J. F. , Dutcher J. R.
Published: July 2002

A computer program has been developed that can be used to calculate the intensity of light scattered from thermal magnons in two planar exchange-coupled magnetic films. The static magnetizations have been assumed to be uniform and parallel with an applied magnetic field which lies in the plane of the films. The calculation includes exchange energies, cubic magnetocrystalline anisotropy energies, and surface pinning energies. The results of the calculation compare favorably with the data reported for iron films by Grünberg et al. [Phys. Rev. Lett. 57, 2442 (1986)].
Model of the field-effect quantum-well laser with free-carrier screening and valence band mixing
Authors: Ahn D. , Chuang S. L.
Published: July 2002

The effects of free-carrier screening and valence band mixing on gain-switching characteristics of the field-effect quantum-well laser are studied theoretically. Our analysis is based on the multiband effective mass theory and the density matrix formalism with the intraband relaxation taken into account. We calculate the electronic structure of the quantum well by solving simultaneously the multiband effective mass equations for the envelope functions with Poisson’s equation. It is found that the free-carrier screening affects considerably both electronic properties (band structure and wave functions) and gain-switching characteristics by reducing the electric field and charge separation in the quantum well when the gate field is applied across the quantum well.
Properties of metal-semiconductor and metal-insulator-semiconductor junctions on CdTe single crystals
Authors: Wang Frank F. , Fahrenbruch Alan L. , Bube Richard H.
Published: July 2002

Metal-semiconductor and metal-insulator-semiconductor junctions, involving the thermal oxide cadmium tellurite (CdTeO3), have been fabricated on both p- and n-type cadmium telluride (CdTe) single crystals. The oxide is effective in increasing the photovoltaic performance of these junctions only in the case of n-type material. For n-type CdTe, the oxide increases the open- circuit voltage over that of the Schottky barrier, whereas for p-type CdTe the oxide decreases the open-circuit voltage. These and several other junction properties may be understood in terms of proposed energy-band diagrams for Cr/CdTeO3/p-CdTe and Au/CdTeO3/n-CdTe structures
Impulsive generation of hypersonic waves: An application to the measurement of acoustic properties of poly-methyl-methacrylate
Authors: Blanchard D. , Casalegno R. , Pierre M. , Trommsdorff H. P.
Published: July 2002

Monochromatic hypersonic sound waves are efficiently generated by spatially periodic impulsive heating of a material with two interfering laser pulses. Their evolution can be monitored optically and the acoustic velocity and attenuation in the GHz frequency range can be measured. This method is particularly well adapted when external transducers are difficult to use: mechanical contact, strong attenuation, etc. This paper critically analyzes the use of the method and demonstrates its application to the study of a polymer material (PMMA) undergoing the glass-rubber phase transition.
Space-charge-limited current density as a function of electron flow duration in an emissive diode
Authors: Girardeau-Montaut Jean-Pierre , Girardeau-Montaut Claire
Published: July 2002

From basic laws governing the flow of electrons in a plane diode, we obtain combined relations about boundaries of space-charge-limited current density variations in an electronic-injector diode when duration of emission is varying. Although diode geometry of effective injectors is generally more complicated than that of a plane diode, we point out how the simplest relations can be used with a relatively good approximation. Then typical temporal modes of diode operation are analyzed. For each one, we give characteristic equations connecting peak intensity, maximum charge, and current duration in the diode, and we determine their applicability. Then we define a time that is a typical limit between the two principal temporal operating regimes. Utilization of reduced variables permits application of the main results to many practical situations such as comparison between working performances of photoinjectors assisted by laser, and prediction of maximum peak current available at the diode output for a given duration.
High-T
c superconducting lenses for relativistic electron beams
Authors: Matsuzawa H. , Ohmori O. , Yamazaki H. , Ueno J. , Furumizu A. , Saito A. , Takahashi T. , Akitsu T.
Published: July 2002

New types of focusing lenses for relativistic electron beams (REBs) are proposed, and preliminary experimental results are obtained. The principle of the lenses is as follows: When REBs are injected into the small apertures of cylindrical superconducting lenses, self-magnetic fields of the REBs are perfectly confined in a region between the REBs and the wall of the lenses. The REBs are focused by those compressed fields. The superiority of superconducting lenses was shown using foilless REB diodes which were operated at 0.15-Torr Ne and had high-Tc , cylindrical superconductor anodes made of Y-Ba-Cu-O compounds (axial lengths of 30 and 145 mm and an inner diameter of 20 mm). The focused REBs (0.8 kA, 270 keV, pulse widths of less than 5 ns) had main beam diameters less than 2 mm.
Low-temperature deposition of silicon dioxide films from electron cyclotron resonant microwave plasmas
Authors: Herak T. V. , Chau T. T. , Thomson D. J. , Mejia S. R. , Buchanan D. A. , Kao K. C.
Published: July 2002

Silicon dioxide films were deposited on crystalline silicon substrates by electron cyclotron resonant (ECR) microwave plasma-enhanced chemical vapor deposition (PECVD). Films were grown on Si〈100〉 substrates at temperatures of 140–600 °C, flow rates of 0.5–10 sccm SiH4, 10–30 sccm O2, and at a pressure of 10−3 Torr. Infrared absorption spectroscopy of the samples indicated no detectable SiH, OH, or SiOH groups. Neither an afterglow chemistry nor He dilution was required to eliminate H impurities as was previously reported for silicon oxide films deposited from rf plasmas. This suggests that significant differences exist between rf and ECR microwave plasma chemistries. We have found that the stoichiometry and index of refraction was not sensitive to oxidant ratio for a wide range of conditions in contrast to other studies. Stoichiometric SiO2 films, with good physical properties, were grown for a much wider range of oxidant ratios relative to those which are characteristic of the rf PECVD technique. In addition, films grown under optimal conditions had infrared absorption spectra nearly identical to those of thermally grown oxides and index of refraction of 1.456, as measured by ellipsometry. We concluded that by using an ECR microwave plasma, SiO2 films with optical and bonding properties comparable to oxides thermally grown at 1000 °C in dry oxygen can be deposited at a low temperature (350 °C) and a low pressure (10−3 Torr) in a O2/SiH4 reactant gas mixture without the need for a carrier gas.
Experimental study of the ionization front in pulsed-surface-wave-produced plasmas
Authors: Gamero A. , Sola A. , Cotrino J. , Colomer V.
Published: July 2002

The advance of the ionization front along the plasma column is studied during the formation process of plasmas produced by a surface wave. The experimental measurements have been performed in argon gas, for the 0.1–30-Torr pressure range, using pulsed microwave power at 2.45 GHz. The ionization front velocity decreases along the plasma column, from its maximum value at the launcher to the zero value at the stationary plasma column end, similarly to the surface-wave power diminution. This velocity can be expressed to depend only on the product collision frequency times tube radius and the surface-wave incident power along the plasma column.
A critical examination of the molecular-beam-epitaxial growth of InxGa1−xAs/GaAs strained quantum well structures
Authors: Pamulapati J. , Oh J. E. , Debbar N. , Bhattacharya P.
Published: July 2002

We have investigated the molecular-beam-epitaxial growth and optical properties of InxGa1−xAs/GaAs (0.07≤x≤0.20) single and multiple quantum well structures. Photoluminescence and absorption measurements were made to characterize the various structures. Low-temperature excitonic linewidths as small as 1.2–2.4 meV have been obtained in 80–120-Å InxGa1−xAs/GaAs (0.07≤x≤0.20) single and multiple quantum wells up to total thicknesses of 2.0 μm. The Stokes shift in these samples is ∼1–2 meV. This result is independent of the absence or presence of an intermediate composition buffer layer and indicates that the latter does not influence the optical properties of strained multiquantum wells. The growth kinetics and growth modes are more important factors in this respect.
Low-temperature surface cleaning method using low-energy reactive ionized species
Authors: Yamada Hiroshi
Published: July 2002

A new low-temperature Si substrate surface cleaning method using low-energy controlled ionized species produced from H2 or H2-SiH4 electron-cyclotron-resonance plasma is described. This method is based on the reactive ion beam deposition technique, which opened up the possibility for lowering the crystalline Si film growth temperature. By irradiating the 50–300-eV ionized species produced from H2-SiH4 plasma onto the single-crystal Si(111) and Si(100) substrates, thoroughly clean surfaces were obtained at the low temperature of 650 °C. These cleaned substrate surfaces exhibited superstructures, such as Si(111)-7×7 and Si(100)-two-domain-2×1.
Magnetoresistive measurement of the exchange constant in varied-thickness permalloy films
Authors: Smith Neil , Markham David , LaTourette David
Published: July 2002

A current passed through a thin ferromagnetic stripe, magnetized along the stripe (easy) axis, generates an inhomogeneous magnetic field that opposes exchange forces and fans the magnetization in opposite directions through the film thickness, forming a variable-angle Bloch wall parallel to the film plane. The magnitude of this effect is a strong function of film thickness and is readily detected magnetoresistively in Permalloy films. Comparison of experimental results with micromagnetic predictions allows determination of the exchange constant A. We have extended our previous measurement of A on a single 2800-Å-thick film to three film thicknesses in the range 2000–4000 Å. The overall agreement between theory and experiment is good, and is consistent with a value of A=1.05×10−6 erg/cm±10%, in full agreement with the earlier measurement.
High-barrier height metal-insulator-semiconductor diodes on n-InP
Authors: Lee Y. S. , Anderson W. A.
Published: July 2002

Metal-insulator-semiconductor diodes were fabricated using Pd, Ni, and Au contacts on n-InP covered by a 40-Å chemically grown oxide. The oxide had a refractive index of 1.4–1.6 with a composition of mainly In2O3+some InPO3 near the surface and mixed oxide+InP near the interface. Pd devices gave the highest-barrier height of 0.80 eV and the lowest reverse saturation current density of 3×10−8 A/cm2. Current-voltage-temperature and capacitance-voltage-temperature data gave temperature dependence of barrier height and revealed an interface state recombination current mechanism with surface states 0.4 eV above the valence-band level. Richardson plots gave good straight lines when empirically corrected using barrier height divided by ideality factor.
Diffusion and self-gettering of ion-implanted copper in polyimide
Authors: Das J. H. , Morris J. E.
Published: July 2002

The diffusion of ion-implanted Cu in Kapton films has been studied by Rutherford backscattering. At low temperatures, diffusion is thermally activated with an energy of 0.41 eV and a diffusion constant D of about 10−18 cm2/s at room temperature. Above 460 K the implanted profiles narrow dramatically instead of continuing to spread, a process interpreted in terms of cluster nucleation at the polymer’s β′ transition temperature. Subsequent diffusion of the clusters above 525 K has an activation energy of 1.91 eV. The ion implantation causes discernible surface damage to the polyimide.
Monte Carlo study of photogenerated carrier transport in GaAs surface space-charge fields
Authors: Zhou Xing , Hsiang Thomas Y. , Miller R. J. Dwayne
Published: July 2002

A self-consistent ensemble Monte Carlo particle model to simulate the dynamics of photogenerated carrier transport in GaAs surface space-charge fields is presented. Dependence of transport parameters, such as relaxation processes, carrier screening, and velocity overshoot, on pulse width, injection level, and excitation energy is investigated and related to the experimentally observable potential drop across the surface space-charge region. In the present study, the high-field conditions are produced by charged surface states, and are to be modified by the redistribution of injected carriers. The photocarrier-induced change in the electric field, which can be measured using electro-optic sampling techniques, is found to be due to the spatial separation of the electron-hole pairs. The simulation results show that at a high injection level a maximum potential drop would result due to complete carrier screening of the surface charge field. The rate of change of this potential drop also would increase with increasing level of injection. These results are in good qualitative agreement with experimental observations. The simulation predicts an enhanced degree of velocity overshoot at decreasing injection energies and, at below L-minima excitation, a second increase in the potential resulting from the redistribution of carriers in the bulk. In this way, it is indicated that the study of the onset of photoconductivity can be used to probe such transport properties in GaAs.
Reactive–fast-atom beam etching of GaAs using Cl2 gas
Authors: Shimokawa Fusao , Tanaka Hidenao , Uenishi Yuji , Sawada Renshi
Published: July 2002

GaAs dry etching using reactive–fast-atom beam etching to obtain an etched mirrorlike surface is investigated. An etch rate of 0.1–0.6 μm/min is obtained when Cl2 gas is used, which is 50–100 times faster than when Ar gas is used. The etch rate ratio between GaAs and photoresist AZ-1350J is more than 30. As a result, a trench with a depth of more than 10 μm and a width of less than 2 μm is easily fabricated under the etch conditions of a Cl2 gas pressure of 5–6.5×10−2 Pa, an accelerate voltage of 1.5–1.8 kV, and a substrate temperature of about 100 °C. The radiation damage caused by this etching is very small, and it is similar to that caused by wet chemical etching, in spite of the relatively higher accelerator voltage. The thickness of an induced damage layer is only 150 Å. It is found that the radiation damage induced by reactive–fast-atom beam etching decreased with an increase of the etch rate. It is confirmed that vertical, smooth, damage-free etching can be easily attained with reactive–fast-atom beam etching.
Parametric studies of x-ray preionized discharge XeCl laser at single shot and at high pulse rate frequency (1 kHz)
Authors: Sentis Marc L. , Delaporte Philipe , Forestier Bernard M. , Fontaine Bernard L.
Published: July 2002

The design and performance of a high repetition rate (1 kHz) and high average power (200 W) XeCl discharge pumped laser (λ=308 nm) using a cold cathode x-ray gun or a wire ion plasma gun for preionization are presented. The dependence of the output energy and of the average output power at low and high pulsed repetition frequency (PRF) on xenon partial pressure is studied. The discharge stability at high PRF is better with lower xenon partial pressure. The influence of preionization level and temporal delay between x-ray pulse and laser discharge is discussed, as well as the required preionization level at higher PRF.
Theoretical issues for critical currents of bulk polycrystalline YBa2Cu3O7−δ superconductors
Authors: Chen Lin , Zhang Yu-heng
Published: July 2002

The influence of grain orientation and weak-link coupling between grains on the critical current of polycrystalline Y-Ba-Cu-O superconductors has been investigated by numerical methods. The theoretical results indicate that there is size effect on jC in bulk polycrystals, and that it is not necessary to consider the influence of grain orientation when jC is less than 105 A/cm2.
Energy pooling and associative ionization following laser excitation of mercury vapor
Authors: Majetich Sara , Boczar Elisa Mangle , Wiesenfeld John R.
Published: July 2002

Laser excitation of the Hg(63P1←61S0) transition at 253.7 nm permits selective population of Hg(63P1). Subsequent quenching by N2 yields Hg(63P0). Observation of emission spectra and temporal profiles of emission features following laser excitation of Hg/Ar mixtures reveals that energy pooling of two Hg(63P1) yields Hg(61S0) plus mercury in the 93S1,73D3,71D2, and 81S0 states, all of which lie no more than 0.6 eV below 2×E[Hg(63P1)]. Collisions of Hg(63P1) with Hg(63P0) are dominated by associative ionization to yield Hg+2, dissociative recombination of which produces a long-lived tail in the atomic emission signals. This work confirms the high efficiency of associative ionization involving atoms in the 63P1 and 63P0 states. The atomic states observed following subsequent dissociative recombination agree well with those reported previously.
Spectral analysis with various beam propagation techniques
Authors: Yevick David , Hermansson Björn
Published: July 2002

We compare the modal electric field distributions and propagation constants of strongly guiding semiconductor rib waveguides obtained with several newly proposed beam propagation techniques to those of the standard beam propagation method.
Impact ionization of deep traps in semi-insulating GaAs substrates
Authors: Li Z. -M. , McAlister S. P. , McMullan W. G. , Hurd C. M. , Day D. J.
Published: July 2002

The behavior of the leakage current in the semi-insulating substrate of a GaAs device is more complicated than previously recognized. The voltage dependence of this current seen in a conventional voltage-controlled experiment has hysteresis, which arises from an S-type negative differential conductivity (S-NDC). This is incompatible with the conventional trap-fill-limited model, and we propose an alternative explanation based on the impact ionization of deep-level traps. We show how this simple model can account qualitatively for the S-NDC and the associated current instability, and how it can be extended when the deep traps are photoexcitable.
Elastic properties of reentrant spin glass
Authors: Mukhopadhyay P. K. , Raychaudhuri A. K.
Published: July 2002

Young’s modulus (E) and the sound velocity (v) of the alloy series Fe80−xNixCr20 were measured using a vibrating reed technique for 14≤x≤30 in the temperature range 1.5–300 K. The measurement, done over a large range of x and T, made it possible to study and compare the elastic manifestation of various magnetic transitions in a single alloys series, from long-range antiferromagnet (AFM) to long-range ferromagnet (FM) through intermediate phases of spin glass (SG) and reentrant spin glass (RSG). The magnetic contribution to E and v is found to be qualitatively similar in FM and RSG alloys (both positive) and that it tends to zero as x→xc, where xc is the critical nickel concentration for the onset of ferromagnetism. In the spin glass (x<xc), the magnetic contribution is negative and shows a minimum near the spin-glass transition. E has also been measured in an applied field H(=0.02 T) as a function of temperature (T<Tc) to study the contribution of magnetic domains to E in alloys with ferromagnetic and reentrant spin-glass transitions. It is found that in RSG alloys, the domain-related contribution to E vanishes below the reentrant transition.
Novel electron-beam lithography for i
n s
i
t
u patterning of GaAs using an oxidized surface thin layer as a resist
Authors: Taneya M. , Sugimoto Y. , Hidaka H. , Akita K.
Published: July 2002

The first demonstration of in situ electron-beam (EB) lithography is reported, where a photo-oxidized surface thin layer of GaAs is used for a resist. The in situ EB lithography sequence consists of five processes, i.e., preparation of a clean GaAs surface, photo-oxidation for a resist film formation, direct patterning of the oxide resist by EB-induced Cl2 etching, Cl2 gas etching of GaAs surface for pattern transfer, and thermal treatment in an arsenic ambient for resist removal and surface cleaning. The GaAs wafer is never exposed to air throughout all of the above processes to avoid an unintentional surface contamination. The minimum electron dose required for patterning of the GaAs oxide resist is about 5×1016 cm−2. An overgrown layer on the patterned GaAs surface shows a good surface morphology, which strongly indicates that this technology makes it possible to repeat crystal growth and surface patterning.
Electrical, physical, and chemical characteristics of plasma-assisted chemical-vapor deposited semi-insulating a-SiN:H and their use as a resistive field shield for high voltage integrated circuits
Authors: Osenbach J. W. , Zell J. L. , Knolle W. R. , Howard L. J.
Published: July 2002

The electrical, physical, and chemical characteristics of plasma-assisted chemical-vapor deposited semi-insulating a-SiN:H for use as a resistive field shield to passivate high voltage integrated circuits are summarized. The films were deposited onto the devices in a hot wall horizontal tube plasma reactor using NH3 and SiH4. The stoichiometry, refractive index, stress, structure, deposition rate, thermal stability, electrical properties, and sodium penetration resistance were determined. The chemical, physical, and mechanical properties of the film are controlled by the NH3/SiH4 flow ratio. The N/Si ratio decreased linearly from 1/2 at a 5/1 NH3/SiH4 flow ratio to 0.15/1 at a 1/2 NH3/SiH4 flow ratio. This decrease in nitrogen content manifests itself as an increase in the refractive index from 2.1 to 3.1. Using the random bonding model, we show that the bond strength decreases and effective bond length increases with decreasing N/Si ratio. The decrease in bond strength causes a decrease in the thermal stability of the film because hydrogen evolution is more easily achieved. The increase in bond length increases the magnitude of the compressive film stress. The electrical properties of the films are also controlled by the N/Si ratio. For example, the conductivity at 25 °C and 1 MV/cm increases from approximately 1×10−18(Ω cm)−1 to approximately 2×10−7(Ω cm)−1 when the N/Si ratio decreases from 1.1/1 to 0.15/1. The conductivity data are consistent with a Frenkel–Poole mechanism. SinSiN films with conductivities between 10−11 and 10−14 (Ω cm)−1 measured at 2.4×105 V/cm and 25 °C were successfully applied to high voltage ICs. These films did not affect the device yield, but did yield devices which were immune to surface ions. The average breakdown voltage of the high voltage devices passivated with semi-insulating a-SiN:H was increased by 20–40 V over those passivated with insulating a-SiN:H.
Resistance and 1/f noise of Au, Al, and Ge contacts to (Hg,Cd)Te
Authors: Beck W. A. , Davis G. D. , Goldberg A. C.
Published: July 2002

The resistance and 1/f noise of Au and Al contacts to ion-sputtered p-type Hg0.79Cd0.21Te and of Ge contacts to Hg0.7Cd0.3Te have been measured at temperatures of 12, 40, 77, and 295 K. The Au and Al contacts were ohmic at all temperatures whereas the Ge contacts were partially rectifying. The specific contact resistance for Au and Al varied by about a factor of 10 up to 9×10−4 Ω cm2 and 3×10−3 Ω cm2, respectively, at 295 K, and there was little variation in resistance down to 12 K. The 1/f noise of the Au and Al contacts could be described as a power spectral density of resistance fluctuations SR which varied with the contact diameter d as SR∝d−m, where 5≤m≤6 for Au and 2≤m≤3 for Al. The values of m suggest that whereas the 1/f noise of the Au contacts originated at the Au/(Hg,Cd)Te interface or in the underlying (Hg,Cd)Te, the 1/f noise of the Al contacts originated in a surface conduction layer next to the contact. The magnitude of the 1/f noise was significantly larger than expected for any fundamental 1/f noise source.
Characterization of x rays emitted from 351-nm laser-produced plasmas for x-ray shadowgraphy
Authors: Kondo K. , Nishimura H. , Kongo K. , Hasegawa H. , Kato Y. , Yamanaka T. , Nakai S. , Taniguchi K.
Published: July 2002

X-ray conversion efficiencies in 351-nm laser-produced plasmas are investigated. X-ray line emissions, which are useful for x-ray shadowgraphy, have been characterized by studying dependencies on laser pulse duration, irradiation intensity, target material, and target structure. The conversion efficiencies decrease with increasing x-ray energy and markedly decrease with increasing laser intensity. A microparticle on a plastic plate is tested in an attempt to develop a point x-ray source. This target shows a higher conversion rate than a microwire target due to reduction in energy dissipation through hydrodynamic expansion.
Dynamics of electron flow in extended planar-anode diode operating at 19 MV and 700 kA
Authors: Sanford T. W. L. , Halbleib J. A. , Poukey J. W. , Baldwin G. T. , Carlson G. A. , Stygar W. A. , Mastin G. A. , Sheridan T. , Mock R. , Alexander J. A. , Brock E. R. , Landron C. O.
Published: July 2002

The electron flow in a planar-anode diode having an extended anode-cathode gap operating on the HERMES III accelerator is characterized and compared with predictions of a computational model. The model combines a particle-in-cell code with Monte Carlo radiation transport. The comparisons confirm the model and show that the diode provides both a matched load and a versatile large-area source of γ rays for the study of nuclear radiation effects. Electrical and spatial parameters of the beam at the diode and the downstream radiation fields from a graphite target are presented as a function of the anode-cathode gap.
Optical spectroscopic study of mechanisms in CCl4 plasma etching of Si
Authors: Clarke P. E. , Field D. , Klemperer D. F.
Published: July 2002

The emission of Si, SiCl, Cl, Cl2, CCl, Cl+, and Cl+ 2 has been observed in a CCl4 rf discharge in the presence of Si(100) in a plasma etching system. Spectral intensities have been recorded over a wide range of process gas flow rates and rf powers. These data have been analyzed to show that (i) SiCl emission from the Ã state arises through chemiluminescent reactions of metastable (1S) Si and (ii) the species which leaves the Si surface in the etching process is SiClx (x=0, 1, or 2) rather than SiCl3 or SiCl4. To arrive at these conclusions, detailed chemical models are examined and shown quantitatively to reproduce our observed variations of emission with flow and power.
Monolayer resolution by means of x-ray interference in semiconductor heterostructures
Authors: Tapfer L. , Ospelt M. , von Känel H.
Published: July 2002

We show that the interference of x-ray wave fields in semiconductor heterostructures can be used to detect ultrathin layers having 1 monolayer thickness. A detailed theoretical and experimental investigation on Si/Six Ge1−x heterostructures is presented. The interference effect is studied experimentally by using a high-resolution double-crystal x-ray diffractometer. The diffraction patterns are recorded in symmetrical as well as asymmetrical Bragg geometries and are analyzed by using the dynamical x-ray diffraction theory for distorted crystals.
Simulation of magnetization reversal dynamics on the Connection Machine (invited) (abstract)
Authors: Mansuripur M. , Giles Roscoe
Published: July 2002

Magnetization reversal processes in thin magnetic films have been simulated on the Connection Machine (CM). The massive parallelism of the CM allows large lattices of dipoles to interact while following the dynamic equation of Landau–Lifshitz and Gilbert toward equilibrium. Our two-dimensional hexagonal lattice consists of 256×256 dipoles with local uniaxial anisotropy, nearest-neighbor Heisenberg exchange, and long-range dipole-dipole (demagnetizing) interactions. The demagnetizing field has been computed with the fast Fourier transform technique1 which is particularly suited for the CM environment. Two sets of material parameters are considered in these studies. The first set is representative of amorphous rare earth–transition metal (RE-TM) alloys, which are currently of interest for their application as the media of erasable optical data storage. The second set corresponds to polycrystalline cobalt alloys (such as CoCr and CoPt), which are high-quality materials for in-plane magnetic recording applications. The discrete models of the RE-TM films have a cell size of approximately 10 Å, accomodating the narrow wall width of these media. In contrast, the cell size for CoCr-type media is typically 500 Å, which is their average crystallite size. We present simulation results that show domain nucleation and growth processes during magnetization reversal. Hysteresis loops and torque curves have also been computed by simulation, and we show the close agreement between these results and those of experiments. Complex magnetic ripple structures are observed in CoCr-type media when random axis anisotropy competes with demagnetization. Some of the more interesting features of these simulation ripples will be described.