bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and performance of magnetic heads for magneto-optic recording with magnetic field modulation
Authors: Ruigrok J. J. M. , Greidanus F. J. A. M. , Godlieb W. F. , Spruit J. H. M.
Published: July 2002

In magneto-optic recording, the most direct way to overwrite stored information is to switch the magnetization in a laser-heated region of the magneto-optic layer by means of an alternating magnetic field generated by a magnetic head. The heat dissipation in the head and the necessary voltage and current amplitude associated with fast switching, the desired high field, and a large head-to-medium distance make high demands upon the head design and the current source, respectively. Design criteria and numerical and experimental results for some circularly symmetric head configurations are presented.
A texture study of anisotropic sintered Nd-Fe-B magnets
Authors: Chang W. C. , Wu T. B. , Liu K. S.
Published: July 2002

An x-ray pole figure technique was used to study the development of magnetocrystalline texture in the sintering of Nd-Fe-B magnets. The effect of excess Nd on the texture and remanence is emphasized. It is found that a medium content of excess Nd enhances the (006) texture and remanence. However, a high content of excess Nd may deteriorate both texture and remanence, and in addition, the tilt of texture away from the prealigned direction also becomes more significant. It is believed that the floating and rotation of grains on the thick layer of liquid phase during sintering cause the deterioration.
Effects of magnetic history on the domain structure of small NiFe shapes
Authors: Corb B. W.
Published: July 2002

Buckled domain structures, usually with charge on both surfaces and domain walls, are created after applying a large field (historic field Ĥh) to rectangles and other odd-shaped elements and returning to the remnant state. The type of domain structure can be predicted by imposing the boundary condition that Ĥh⋅ Medge ≥0, where Medge is the magnetization at the edge of the shape. The origin of the boundary condition comes from the high demagnetizing energy necessary to reverse the magnetization at the edges of a thin film. Details of the metastable state are determined by wall and anisotropy energies as well as the demagnetizing energy from surface and domain wall charging.
Annealing effect on microstructure and magnetic properties in Fe-Cr sputtered films
Authors: Ohkoshi Masatoshi
Published: July 2002

Interactions between microstructure and magnetic properties in Fe-Cr sputtered films were investigated in the composition range 40–60 at. % Cr by studying films annealed after deposition. Saturation magnetization, perpendicular magnetic anisotropy, and perpendicular coercivity increase remarkably by annealing in the Fe-Cr films deposited at high Ar pressure. Film structure and magnetic properties of the Fe-Cr films depend strongly both on the Ar pressure and on the substrate bias during sputtering. If the energy of the incident particles is low, phase separation to the α and σ phases is prominent, and saturation magnetization is small. An increase in Ms, Ku, and Hc with annealing is associated with the further precipitation of Fe, changing saturation magnetization of the α phase.
Influence of boron related defects on activation of silicon implanted into undoped semi-insulating GaAs
Authors: Orito Fumio , Kawabata Shin-ichiro , Yamada Yutaka , Okada Yasumasa
Published: July 2002

The dependence of sheet carrier concentration of a Si-implanted layer on lattice parameters of undoped liquid encapsulated Czochralski GaAs was investigated. Crystals were grown from near-stoichiometric melts with varying boron concentrations. Sheet carrier concentration increases with an increase in lattice parameters due to the reduced boron concentration. An anomalous reduction in the lattice parameter suggests that native defects such as BGa VAs are responsible for the increase in the occupancy of implanted Si atoms on As sites.
Ultraviolet emission spectra from formed-ferrite plasma sources
Authors: Kashiwabara S. , Watanabe K. , Fujimoto R.
Published: July 2002

Emission spectra from a high-current line plasma produced by means of a formed-ferrite plasma source have been measured in the ultraviolet spectral region 225–400 nm with emphasis on the ambient gas pressure dependence. A long distance, linear plasma of 13 cm was produced in a test chamber filled with CF4, N2, and Ar gases at various pressures ranging from 760 down to 10−5 Torr. The formed-ferrite plasma source was driven by a 2-μF capacitor bank charged at 15–25 kV. When the line plasma was created in a high vacuum of 10−5 Torr, several emission lines caused by singly ionized atomic species such as FeII and NiII which originated from the ferrite material appeared in the shorter wavelength region near 250 nm. This finding implies possible generation of vacuum ultraviolet, extreme ultraviolet, and soft x-ray photons based on the higher ionized atomic species by the formed-ferrite plasma source operating in such a high vacuum.
Charge-transfer dipole moments at the Si–SiO2 interface
Authors: Massoud Hisham Z.
Published: July 2002

A first-order model has been developed to calculate the magnitude of the dipole moment at the Si–SiO2 interface resulting from partial charge transfer that takes place upon the formation of interface bonds. The charge transfer occurs because of the difference in electronegativity between the two species across the interface, namely silicon atoms and SiO2 molecules. This approach is similar to that introduced to describe the modification of band lineup at the Si–SiO2 interface by means of an intralayer of H or Cs. The charge-transfer estimation uses the principle of electronegativity equalization, and results obtained for (100) and (111) silicon substrates indicate that the magnitude of the interface dipole is orientation dependent. Dipole moments at the Si–SiO2 and gate–SiO2 interfaces should be included in the definition of the flatband voltage VFB of metal-oxide-semiconductor structures. The metal-semiconductor work function difference φms determined from capacitance-voltage measurements on (100) and (111) silicon oxidized in dry oxygen and metallized with Al agree well in magnitude and sign with the predictions of this model. Other types of interface dipoles and their processing dependence will be examined.
Schottky barrier height of single-crystal nickel disilicide/silicon interfaces
Authors: Kikuchi Akira , Ohshima Takashi , Shiraki Yasuhiro
Published: July 2002

Nickel disilicide (NiSi2) was formed on Si(100) and Si(111) substrates by the codeposition of Ni and Si. The Schottky barrier height was about 0.65 eV for NiSi2 on Si(100), independent of NiSi2 film thickness. By contrast, the Schottky barrier height for type-B NiSi2 on Si(111) depended on NiSi2 film thickness. Schottky barrier height decreased with increasing NiSi2 film thickness. It became constant (0.65 eV) above 50-nm-thick NiSi2. The Schottky barrier height determined by extrapolating NiSi2 film thickness to 1–2 layers of the NiSi2 film was 0.78–0.79 eV.
The study of critical current in YBaCuO thin films
Authors: Yuan C. W. , Zhao B. R. , Zhang Y. Z. , Zhao Y. Y. , Lu Y. , Wang H. S. , Shi Y. H. , Gao J. , Li L.
Published: July 2002

The magnetron sputtering method has been used for fabricating YBa2Cu3O7−y superconducting thin films. Their critical current and superconducting phase with relation to temperature have been investigated. Experimental results show, for some samples, the proportionality between critical current Ic and temperature as (1−T/Tc)3/2 in the vicinity of Tc and the typical proximity tunneling effect. While at temperatures much lower than Tc, the current-temperature relation corresponds well with the Ambegaokar–Baratoff theory.
The effect of Frenkel defect formation on spherical SiO2 precipitate growth in silicon wafers
Authors: Tiller William A. , Oh Seajin
Published: July 2002

A general analytic solution is given to the sphere-growth problem which includes (1) oxygen and point defect transport, (2) interface reaction kinetics, (3) surface energy, and (4) strain energy storage. Short, intermediate, and long time behaviors are given. In the long time domain, where the Peclet number for oxygen is constant provided the far field conditions are constant, the growth rate is dominated at low and intermediate temperatures primarily by silicon interstitial formation and somewhat by strain energy storage. At high temperatures (≳1150 °C), these effects become small and the interface begins to approach the thermodynamic equilibrium state. However, at all lower temperatures, the supersaturation of silicon interstitials at the SiO2/Si interface is very large and the interface is far from the thermodynamic equilibrium. Extension of the mathematical approach to precipitates of other shapes is also given.
The elastic interaction between screw dislocations and cracks emanating from an elliptic hole
Authors: Shiue Sham-Tsong , Lee Sanboh
Published: July 2002

Based on the solution of an internal crack, we have investigated the elastic interaction of a screw dislocation and cracks emanating from an elliptic hole by using a conformal mapping technique. We have derived the stress field, the image force on the dislocation, the stress intensity factor at the crack tip, and the crack extension force. From the image force, we find the unstable equilibrium positions of dislocation. It is possible to form a plastic zone from the region containing the unstable equilibrium position by collecting dislocations. By extending the concept of the unstable equilibrium position, we also develop the dislocation emission criterion. It is found that the critical applied stress for dislocation emission is dependent on the geometry of the crack. In addition, we also find that the elliptic hole prefers to emanate double cracks. Finally, it is worthwhile to mention that the mapping function cannot be arbitrarily chosen.
The effects of a high-temperature anneal on the electrical and optical properties of bulk CdTe:In
Authors: Giles N. C. , Hwang S. , Schetzina J. F. , McDevitt S. , Johnson C. J.
Published: July 2002

The electrical and optical properties of bulk CdTe:In have been studied by means of van der Pauw-Hall-effect measurements and low-temperature photoluminescence (PL). As-grown, the bulk CdTe:In samples exhibited high resistivity (ρ>108 Ω cm). Following a high-temperature anneal at 900 °C in a Cd overpressure, the CdTe samples became n-type (n∼1016 −1017 cm−3 at 300 K). The carrier concentration was found to depend on the anneal time. The PL spectra from as-grown samples are dominated by edge emission at 1.583–1.584 eV, the nature of which is determined from the optical measurements. As a result of the anneal, PL emission above 1.606 eV (the band gap of CdTe at 4.5 K) is observed. Excitation PL measurements, along with studies of the temperature and power dependencies of the PL emissions from the annealed samples, suggest an increase in band gap to 1.632 eV has occurred, which we believe is due to the incorporation of interstitial Cd into the lattice. Our study provides a correlation between the electrical and optical properties of bulk CdTe:In which, upon annealing, may be used as a conducting II-VI substrate in epitaxial film growth.
Oxygen- and carbon-related defects in edge-defined film-fed growth silicon ribbon
Authors: Pivac B. , Desnica U. V.
Published: July 2002

In this communication we report on infrared analysis of the SiOx-like defects segregated close to the surface of the edge-defined film-fed growth polycrystalline ribbons. These defects cause an absorption band very similar to that of the SiOx phase, but they are thermally unstable, and can be annealed by 650 °C thermal treatment. It is concluded that they are quenched high-temperature defects formed during the film growth. Possible nucleation centers for those defects are found to be C and/or SiC aggregates close to the surface.
The effects of high-fluence neutron irradiation on the superconducting properties of magnetron sputtered NbN films
Authors: Gregshammer P. , Weber H. W. , Kampwirth R. T. , Gray K. E.
Published: July 2002

Neutron irradiation experiments on sputtered NbN films up to a fluence of 1023 m−2 (E>0.1 MeV) are reported. Both the transition temperatures Tc and the normal state resistivities change only slightly with neutron fluence. While the critical current densities degrade (up to 30%) in an intermediate field range (6–14 T), the high field data show virtually no change of Jc due to the radiation-induced increase of Bc2 and the occurrence of peak effects near the upper critical field. It is therefore proven experimentally that NbN is an extremely radiation-hard high field superconductor.
Photoluminescence of GaAs films grown by vacuum chemical epitaxy
Authors: Bernussi A. A. , Barreto C. L. , Carvalho M. M. G. , Motisuke P.
Published: July 2002

GaAs layers grown by vacuum chemical epitaxy (VCE) are investigated by low-temperature photoluminescence. A qualitative relation between the growth parameters and the shallow-impurity-incorporation mechanism is established. It was observed that the predominant shallow acceptor is carbon, and its incorporation during the growth process decreases with the As:Ga ratio, increases with growth temperature until 750 °C, and then it diminishes. In this work we compare the characteristics observed in the VCE system with those in conventional molecular-beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD). Our results show that this system contains some advantages from both the MBE and MOCVD systems. The photoluminescence spectra also show that at low As:Ga ratios the generation of As vacancies or its complexes is strongly enhanced.
Effects of high carbon concentration upon oxygen precipitation and related phenomena in CzSi
Authors: Hahn S. , Arst M. , Ritz K. N. , Shatas S. , Stein H. J. , Rek Z. U. , Tiller W. A.
Published: July 2002

Effects of high carbon concentration upon oxygen precipitation and related phenomena in Czochralski (Cz) silicon have been investigated by combining various furnace and rapid thermal anneals. Our data show that oxide precipitate (OP) density, estimated from changes in interstitial oxygen concentration (ΔOi), increases with increasing substitutional carbon concentration, Cs, while thermal donor (TD) formation is inhibited at high Cs. Even though ΔOi increases monotonically with Cs, synchrotron radiation section topographs of processed high carbon content wafers (Cs∼4 ppma) exhibit Pendellösung fringes, indicating a strain-free bulk state. Our transmission electron microscope and optical microscopic data also show very few resolvable structural defects associated with precipitates inside the bulk Si. Using a thermodynamic and kinetic model, we attempt to explain: (1) reduced thermal donor formation, (2) lack of bulk stress notwithstanding high ΔOi, and (3) predominantly polyhedral precipitate morphologies in high carbon content CzSi.
Laser action of YAG-laser-vaporized metal-vapor laser
Authors: Hirata K. , Ninomiya H.
Published: July 2002

Laser oscillation has been observed on the copper 510.6-nm (2P3/2-2D5/2) transition. A YAG laser is used to produce the metal vapor by irradiating a metal plate, and the metal atoms are excited by pulsed discharge.
Propagation of a relativistic electron beam along an array of conductors
Authors: Rambo P. W. , Denavit J.
Published: July 2002

The propagation of a relativistic electron beam parallel to an array of parallel conductors, which provide charge and current neutralization of the beam, is investigated. Two geometries are studied: uniformly spaced planar foils or screens, and a matrix of parallel wires. The degree of charge and current neutralization and the resulting parallel and transverse fields are calculated for a uniform density pulse. The self-consistent transverse equilibrium is derived for the planar foil geometry. The effects of injection perpendicular to a planar cathode are investigated. Particle simulations in planar and cylindrical geometries are presented to confirm the analysis and to study edge effects and containment of the beam within the array. Comparison to vacuum drift tube operation shows that such arrays of conductors may allow beam transport with currents far exceeding the vacuum limit.
Xenon excited-state densities in electron-beam pumped XeCl and XeF
Authors: Kannari F. , Kimura W. D. , Seamans J. F. , Guyer Dean R.
Published: July 2002

Understanding of the neutral channel formation kinetics in excimer laser gas mixtures has been limited by the lack of data on the pertinent excited-state populations in these mixtures. Presented are time-dependent measurements of the lower level xenon excited-state densities in electron-beam (e-beam) pumped XeCl and XeF laser mixtures (neon diluent). Measurements are obtained using hook interferometry under nonlasing conditions at an average excitation rate of ≊250 kW/cm3 and e-beam pulse lengths of 0.4 and 1 μs. The population differences, ΔN*, between four different electronic transitions [three in the Xe*(6s)-Xe**(6p) manifold, and one in the Xe**(6s′)-Xe***(6p′) manifold] are examined as a function of halogen concentration. For both XeCl and XeF at high initial halogen concentrations (>4 Torr), the ΔN* densities of the Xe*(6s) and Xe**(6s′) transitions are relatively constant during the 0.4-μs e-beam pulse [for ΔN*(6s-6p): ≊4×1014 cm−3 for XeCl, and ≊1.5×1014 cm−3 for XeF]. At lower initial halogen concentrations, the ΔN* densities of 6s-6p and 6s′-6p′ start at the beginning of the pulse at approximately the same densities as the richer halogen mixtures, but at a certain point during the pulse, the ΔN* densities abruptly increase. This increase can be >10 times for very lean halogen mixtures (1–2 Torr), and occurs at earlier times as the initial halogen concentration is reduced. From other measurements, this increase appears related to the depletion of the halogen. The observed lifetime of the Xe*(6s) densities is ≊2 μs for the low initital halogen concentration mixtures. Additional density data for halogen-free Ne/Xe and Ar/Xe mixtures are also presented.
Excited states of the Mg acceptor in GaAs
Authors: Cavins J. R. , Yeo Y. K. , Hengehold R. L.
Published: July 2002

Selective pair luminescence (SPL) has been used to measure the excited states of shallow acceptors in undoped vapor-phase epitaxial (VPE) grown GaAs and Mg-implanted VPE GaAs. A set of experimental data for Mg excited states in GaAs is presented here. The results show that the 2P3/2 -, 2S3/2 -, and 2P5/2 -1S3/2 energy differences are 17.0, 20.0, and 21.0 meV, respectively. The value of the 2S3/2 state agrees very well with the previously reported two-hole transition luminescence result, and the other two values for the excited states agree very well with those reported for far-infrared Fourier transform spectroscopy. This assignment was further confirmed by making SPL measurements on Mg-implanted GaAs.
Structure and properties of diamondlike carbon coatings deposited in rf plasma from benzene and monosubstituted benzenes
Authors: Joshi Asawari , Gangal S. A. , Kulkarni S. K.
Published: July 2002

Properties of diamondlike coatings deposited in a modified design of the plasma reactor system are reported. Benzene and monosubstituted benzenes are used as the source gases. The films have been analyzed using scanning electron microscopy, glancing angle x-ray diffraction, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy techniques. Large crystallites (∼30 μm) are observed. The x-ray diffraction and x-ray photoelectron spectroscopy have been utilized to identify the physicochemical nature of the deposited films. Fourier transform infrared spectroscopy results suggest sp3 type of bonding in the films. Films are colorless, electrically insulating (≥109 Ω cm), and corrosion resistant.
Copper passivation of dislocations in silicon
Authors: Lee Jae-Gwang , Morrison S. Roy
Published: July 2002

The J-V characteristics of metal-insulator-semiconductor solar cells fabricated on Si samples which are damaged (lapped) with 1-μm grit size of Al2O3 are substantially degraded. The introduction of copper at 250–400 °C passivates the dislocations. The copper is diffused in from the surface. Anodic oxidation followed by etching in aqua regia and 48% HF was used to remove excess copper remaining on the damaged surface and to etch away controlled amounts of the silicon wafers. The experimental results are compared to the model of Divigalpitiya and Morrison [J. Appl. Phys. 60, 406 (1986)]. It is concluded using the model that copper passivation reduces the product of the density of hole traps and the capture cross section of hole traps and may also increase the specific conductance of the dislocations. Results for samples lapped with finer-grit alumina (0.3 μm) seem qualitatively different from those with 1-μm alumina. The variation in dislocation density as a function of depth into the surface is used to explain the difference qualitatively. The dislocation density decreases rapidly with distance from the damaged surface.
Electron transport in zinc telluride films
Authors: Athwal I. S. , Bedi R. K.
Published: July 2002

ZnTe films have been prepared by hot wall epitaxy onto glass and single-crystal potassium chloride substrates. The electron transport properties in polycrystalline and single-crystal films have been reported. The electrical resistivity decreases very slowly up to dopant concentrations 1016 at./cm3 followed by a steep fall. The drift mobility appears to be fairly constant over a wide range of dopant concentrations, while it shows rapid decline on heavy doping.
Brillouin light scattering studies on an iron whisker
Authors: Dutcher J. R. , Cochran J. F. , Heinrich B. , Arrott A. S.
Published: July 2002

We have made Brillouin light scattering measurements on a (001) iron whisker that was covered with epitaxial gold and with epitaxial silver under ultrahigh vacuum conditions. The surface mode frequencies have been measured to within ±0.03 GHz, allowing very careful comparisons of experiment with light scattering calculations. Observation of the 180° domain wall enabled an accurate determination of the surface spin pinning coefficient: Ks =0.54 ergs/cm2 for the gold covered whisker and Ks =0.79 ergs/cm2 for the silver covered whisker, with the easy axis perpendicular to the sample surface. An accurate measure of the sample heating due to the incident laser light was also obtained.
Boron-modified 2:17-type Sm(Co,Fe,Cu,Zr)z sintered magnets
Authors: Mukai T. , Fujimoto T.
Published: July 2002

The addition of a small amount of boron (8–380 ppm by weight) to the alloy with composition Co-25 wt. % Sm-19 wt. % Fe-6 wt. % Cu-2.5 wt. % Zr caused a remarkable increase in the coercive force (iHc) of the sintered magnets: iHc=13.7 kOe for 140-ppm B relative to iHc =7.1 kOe for 0-ppm B under the same aging condition. For the B-free alloy, a heterogeneous precipitation of the Cu-rich Sm2 Co7 -type phase (2:7 phase) was observed. The addition of B above 80 ppm completely suppressed the precipitation of the 2:7 phase. Boron was found to segregate at grain boundaries and subgrain boundaries. The results suggest that B substitutes for Co in the 1:5 phase and stabilizes a fine-scale cellular microstructure which consists of the 2:17 and 1:5 phases.
Critical temperature of iron derived from total energy calculations
Authors: Peng S. S. , Jansen H. J. F.
Published: July 2002

We have performed total energy calculations for iron in the ferromagnetic and in several antiferromagnetic configurations. It is assumed that the functional describing exchange and correlation is the same for the ferromagnetic ground state and the antiferromagnetic states. The calculated total energies are used to obtain the interaction parameters in a Heisenberg model. From this Heisenberg model we derive excited state properties, where one has to keep in mind that the model parameters are directly based on the ground-state ab initio results. The nearest-neighbor interaction is ferromagnetic and a model which includes only nearest-neighbor interactions yields a transition temperature of 1685 K. The next-nearest-neighbor interaction, however, is antiferromagnetic and reduces the critical temperature to 895 K. Several other physical quantities derived from our model Heisenberg Hamiltonian are discussed.
Irreversible flux losses of Nd-Fe-B magnets at elevated temperatures: Errors due to sample geometry
Authors: Strnat K. J. , Xiao Y. , Mildrum H. F.
Published: July 2002

Irreversible flux losses during thermal cycling or aging are commonly measured in open circuit on axially magnetized cylinders or square prisms. The reported results are usually tied to a mean operating-point permeance P derived from a dimensional ratio for the sample on the often unstated assumption that definable demagnetizing factors exist for both geometries. Experimental results on several shapes of different Nd-Fe-type magnets show that this can be misleading. Prisms always show a significantly better apparent stability than cylinders of presumably equivalent P. This means that loss data from different sources cannot be easily compared. Investigators should always precisely describe the sample shapes and coil configurations they used. Dimensional ratio rather than just P should be specified. Standardization to tests on cylinders is recommended.
Observation of auto-oscillations and chaos in subsidiary absorption in yttrium iron garnet
Authors: Srinivasan G. , Chen M. , Patton C. E.
Published: July 2002

Auto-oscillations of the dynamic magnetization and routes to chaos for the first-order transverse pump spin-wave instability have been studied in single-crystal yttrium-iron-garnet (YIG) films. The measurements reported here were made on a 20.8-μm-thick YIG film at 9.4 GHz with the static and microwave fields in the plane of the film. Auto-oscillations at 100–400 kHz were observed in the power absorbed by the film over a relatively narrow static field range of 1100–1460 Oe, compared to the first-order instability (FOI) range of 0–1630 Oe. The auto-oscillation frequency and threshold microwave field amplitude were both strongly field dependent. The threshold amplitudes were about a factor of 2 larger than the FOI threshold amplitudes. At even higher power levels and for an even narrower field range of 1300–1380 Oe, the auto-oscillations showed frequency changes indicative of chaotic behavior. Several different subharmonic bifurcation routes to chaos were observed for different fields within the chaotic region.
Optimization of magnetostriction in metallic glasses
Authors: Gibbs M. R. J. , Squire P. T. , Hayes A. , Vincent J. H.
Published: July 2002

We demonstrate the enhancement of magnetostrictive response due to surface crystallites for a range of Fe-based metallic glasses. The data are interpreted in terms of the strain fields of the crystallites.
Magnetoelastic effects in amorphous wires and amorphous ribbons with nonmagnetic thin-film coatings
Authors: Wun-Fogle M. , Savage H. T. , Kabacoff L.T. , Hathaway K. B. , Merchant J. M. , Beihoff B.
Published: July 2002

We have measured the magnetomechanical coupling in amorphous 2605SC ribbons which have been coated by magnetron sputtering on one or both sides with copper films between 31 and 186 nm in thickness. Coating on one side produces an additional resonance mode which may be a coupling of an extensional and flexural mode. Coating on both sides greatly increases the anisotropy and reduces the coupling factor. Analysis indicates that these effects are due to stresses imposed by the coating on the ribbon and can be ameliorated by control of deposition parameters. In transverse-field annealed amorphous Fe77.5B15Si7.5 wire material we find a lower coercive force and lower values of applied fields required for saturation than in our ribbon investigations. This is probably due to a lower surface-to-volume ratio for the amorphous wire, i.e., surface defects play a lesser role in the wire geometry. We find a different magnetization process. Values of magnetomechanical coupling approach ribbon values. Saturation values of magnetostriction are equivalent. Values of the transverse anisotropy in the wire material are lower than what we have previously obtained in our ribbon material. We conclude that the amorphous wire will be a good sensor material.
Laser-induced gas breakdown in the presence of a static electric field
Authors: Kumar V. , Thareja R. K.
Published: July 2002

The breakdown of Ne, Ar, and Xe gases at different pressures is studied by focusing a XeCl excimer laser in the presence of a static electric field transverse to the laser focus.
Nonlinear optical absorption in GaAs doping superlattices
Authors: Danner A. D. , Dapkus P. D. , Kost A. , Garmire E.
Published: July 2002

The first direct nonlinear absorption measurements at energies below and above the band gap of GaAs doping superlattices are reported. Large period, lightly doped structures exhibit properties that are consistent with the Franz–Keldysh oscillations seen in bulk material. Very small period heavily doped structures show absorption features that reflect the quasi-two-dimensional nature of the conduction-band energy spectrum in such a system. The dependence on excitation of the nonlinear absorption in these systems is described.
Effect of light-induced defects on the short wavelength quantum efficiencies of amorphous silicon solar cell structures
Authors: Fortmann C. M. , Lange S. , Hicks M. , Wronski C. R.
Published: July 2002

Light-induced defects in intrinsic hydrogenated amorphous silicon (a-Si:H) are found to have a large effect on the short wavelength quantum efficiencies (SWQE) of a-Si:H solar cell structures. The dependence of SWQE on cell structure thickness, volume absorbed bias illumination, and externally applied voltage has been studied. The results on thick cell structures (≳0.5 μm) can be explained by a simple model which yields light-induced defects with hole capture cross sections of about 10−11 –10−12 cm2 and densities consistent with other measurements.
A model for the surface chemical kinetics of GaAs deposition by chemical-beam epitaxy
Authors: Robertson A. , Chiu T. H. , Tsang W. T. , Cunningham J. E.
Published: July 2002

Recently we have reported the measurement of reflection high-energy electron diffraction intensity oscillations during chemical-beam epitaxy of GaAs using triethylgallium (TEG) and As2 derived from an arsine cracker [Appl. Phys. Lett. 50, 19 (1987)]. In this study we observed a significant variation of the GaAs growth rate with substrate temperature at constant TEG flux. In addition, the variation of growth rate with incident flux at constant temperature was found to be nonlinear below approximately 500 °C and linear above 500 °C for incident fluxes yielding maximum growth rates between 0.2 and 1.8 monolayers/s. We have developed a model of the surface pyrolysis of triethylgallium which explains the qualitative behavior of the above data. The model assumes the existence of adsorbed triethyl, diethyl, and monoethyl gallium species as well as adsorbed ethyl radicals. As a starting point, the rate limiting step to epitaxial incorporation of atomic gallium is assumed to be cleavage of the second ethyl–gallium bond. Elimination of atomic hydrogen from adsorbed ethyl groups to form ethylene is also included in the model, as is recombination of one ethyl group and a diethylgallium to form adsorbed triethylgallium. Assuming Arrhenius behavior for the rate constants of the elementary steps of the reaction mechanism and steady-state behavior an expression for the temperature dependence of the growth rate is derived. Using realistic values for the preexponential factors and activation energies of the elementary steps a reasonable fit to the experimental data was obtained. The model reproduces the nonlinear dependence of growth rate on incident flux below 500 °C and the fall-off growth rate at higher temperature. The nonlinearity is due to the second-order recombination of an adsorbed diethyl gallium radical with an adsorbed ethyl radical followed by desorption of triethylgallium. The fall-off in growth rate above 500 °C is due to desorption of diethyl gallium radicals.
Depth profiles of vacancy-type defect in Si+-implanted GaAs resulting from rapid thermal annealing
Authors: Lee Jong-Lam , Shim Kyu-Hwan , Kim Jin Sup , Park Hyung Moo , Ma Dong Sung , Tanigawa S. , Uedono A.
Published: July 2002

Depth profiles of vacancy-type defects in the active region of annealed Si+-implanted GaAs were measured by means of the monoenergetic positron beam measurements. Parabolic-type distributions for vacancy-type defects in the depth below the surface were observed in two-step annealed Si+-implanted GaAs. Activation properties by Hall measurements were improved by a two-step rapid thermal annealing technique, whereas the concentration of vacancy defects in active layer below the surface is not changed.
Improved material properties of amorphous silicon from silane by fluorine implantation: Application to thin-film transistors
Authors: Schropp Ruud E. I.
Published: July 2002

In this paper it is reported for the first time that the material properties of hydrogenated amorphous-silicon films deposited from a pure silane plasma can be improved by a low-dose fluorine implantation. It is shown that the field-effect density of states is reduced after implantation and appropriate annealing. The implanted material shows a better photostability as well as a better resistance against prolonged electric field application and against exposure to temperatures above deposition temperature.
Thermally stable ohmic contacts to n-type GaAs. IV. Role of Ni on NiInW contacts
Authors: Shih Yih-Cheng , Murakami Masanori , Price W. H.
Published: July 2002

Recently, thermally stable, low resistance NiInW ohmic contacts to n-type GaAs have been developed using a conventional evaporation and lift-off technique and annealing the contacts by a rapid thermal annealing method. This contact material has great potential for use in GaAs integrated circuits. In the present paper, the microstructure of the NiInW contact material has been studied extensively by cross-sectional transmission electron microscopy. Special attention was paid to understanding the role of Ni in the NiInW contacts by analyzing samples prepared by different deposition sequences. In order to prepare the contacts with a large fractional coverage of InxGa1−xAs phases at the metal/GaAs interface, which is essential to produce low resistance contacts, Ni must prevent In from spreading vertically into the GaAs substrate during the heating process. The formation of a uniform Ni2GaAs layer at the GaAs surface and suppression of In diffusion toward the GaAs by intermixing In with Ni at the initial stages of annealing were found to be critical to prepare such contacts with large fractional coverage of the InxGa1−xAs phases. In addition, Ni2GaAs phases seem to remove native oxides at the GaAs substrate, which is also important in attaining good coverage by InxGa1−xAs phases at the GaAs surface. Also, excess In was found to form high melting point Ni3In compounds which improved thermal stability.
Electro-optical response characteristics of rare-earth-doped alkaline-earth-sulfide electroluminescent devices
Authors: Ando Masahiko , Ono Yoshimasa A.
Published: July 2002

Electro-optical response characteristics of rare-earth-doped alkaline-earth-sulfide electroluminescent (EL) devices were studied. From the measurement of luminance and transferred charge response characteristics of CaS:Eu, CaS:Ce, SrS:Eu, and SrS:Ce EL devices, rare-earth luminescent centers were found to play a decisive role in controlling electro-optical response characteristics rather than alkaline-earth-sulfide phosphor materials were. Especially, it was found that slow luminance response and slow transferred-charge response were due to the Eu luminescent center. These response characteristics in CaS:Eu were improved to a practical level by codoping a small amount of Ce.
Inverse ac Josephson effect at terahertz frequencies
Authors: Danchi W. C. , Golightly W. J. , Sutton E. C.
Published: July 2002

The inverse ac Josephson effect occurs when a Josephson junction driven by a microwave source of frequency  f  produces constant-voltage steps at integer multiples of hf/2e. For low-leakage current hysteretic junctions driven at microwave frequencies below about 100 GHz, some of these steps can cross the zero dc bias current axis. These zero-crossing steps allow modern series array voltage standards to operate without individually biasing the junctions in the array. We reexamine the theory behind these steps and show that they can exist at frequencies much higher than thought previously. The Riedel singularity in the supercurrent response allows this effect to exist even up to terahertz frequencies. We describe a set of analytical calculations which provide limits on the amount of rounding of the Riedel peak which can be permitted while still allowing these zero-crossing steps to occur. We also discuss practical considerations such as microwave power levels required and parameters for device fabrication. This analysis is supported by numerical frequency-domain computations and time-domain simulations for a number of realistic I-V curves with rounded Riedel singularities and with quasiparticle subgap leakage currents.
Material properties of InP-on-Si grown by low-pressure organometallic vapor-phase epitaxy
Authors: Wuu D. S. , Tung H. H. , Horng R. H. , Lee M. K.
Published: July 2002

Undoped InP epilayers have been grown directly on (100) Si substrates by low-pressure organometallic vapor-phase epitaxy. The surface morphology, x-ray diffraction peak width, and ion backscattering yield each improve substantially with InP thickness (0.1–3 μm). X-ray and photoluminescence (PL) measurements demonstrate that the InP heteroepilayers are under biaxial tensile strain in the surface parallel direction. The carrier concentration profile shows that the carrier distribution in the InP layer is very uniform, while an apparent reduction in concentration occurs at the InP/n-type Si interface. The 77-K PL spectrum reveals a strong near-band-edge emission with a full width at half maximum of 14 meV. Post-growth thermal annealing at 780 °C was confirmed to be effective in improving the overall quality of InP-on-Si. The results presented are superior to those reported previously for InP/Si heteroepitaxy.
Controlled conductivity in iodine-doped ZnSe films grown by metalorganic vapor-phase epitaxy
Authors: Yoshikawa Akihiko , Nomura Hiroshi , Yamaga Shigeki , Kasai Haruo
Published: July 2002

Iodine-doped ZnSe films have been grown on GaAs by low-pressure metalorganic vapor-phase epitaxy using dimethylzinc and hydrogen selenide as reactants. In order to accomplish an accurate control of the carrier concentration in the films over a wide range, ethyliodide diluted to 1000 ppm was used as a dopant source. It has been shown that the carrier concentration can be changed in the range from 1015 to 1019 cm−3 by varying the flow rate of ethyliodide. Furthermore, the films with carrier concentrations below 1018 cm−3 exhibit strong blue emission with suppressed deep level emissions. The origin of blue emission has been ascribed to the iodine donors incorporated during growth. According to the results shown, it has been concluded that iodine is a superior donor dopant for ZnSe from a standpoint of the controllability and reproducibility of electrical and photoluminescence properties of the n-type films over a wide range.
Silicide doping technology in formation of TiSi2 /n+ p shallow junction by salicide process
Authors: Yang Jeng-Rern , Lue Juh Tzeng
Published: July 2002

The fabrication of a shallow n+ p junction by diffusing arsenic atoms from the As+ -implanted TiSi2 into the underlying silicon has been developed. The amendment of the radiation damage and the activation of impurities can be fulfilled in one annealing process in conjunction with the dopant drive-in. The junction depth below the TiSi2 /Si interface is about 0.11 μm, and is insensitive to the values of implanted ion energy and the annealing condition as long as the dopants remain in the TiSi2 film. The dopant concentration near the surface in the n+ region can be added up to 2×1019 /cm3 for an implanted dose of 5×1015 /cm2 .
Nonalloyed and alloyed low-resistance ohmic contacts with good morphology for GaAs using a graded InGaAs cap layer
Authors: Mehdi I. , Reddy U. K. , Oh J. , East J. R. , Haddad G. I.
Published: July 2002

Using a thin graded layer of InGaAs starting on GaAs and becoming InAs on the top, low-resistance alloyed and nonalloyed ohmic contacts have been achieved on n+-GaAs epilayers grown by molecular-beam epitaxy on a semi-insulating GaAs substrate. In addition, by a suitable choice of the multilayer ohmic metals and by an optimization of the alloying process, good surface morphology was obtained. The transmission-line model is used to extrapolate contact resistances from measurements on test patterns with multiple gap spacings varying from 1 to 10 μm. The nonalloyed contact resistance is found to be 0.025 Ω mm for a GaAs layer doped to 1×1018 with a 500-Å graded InGaAs layer. Alloying the contact at 475 °C for 60 s produces a contact resistance of 0.019 Ω mm. This represents a substantial improvement over the contact resistances obtained by just using an ungraded cap layer of InAs on GaAs. Assuming that the sheet resistance under the contact is the same as the sheet resistance in the top semiconductor layer (this is not strictly true), the nominal value of the specific contact resistance for the nonalloyed situation is 5.32×10−7 Ω cm2, while for the alloyed case the specific contact resistance is 2.56×10−7 Ω cm2. The metal scheme used for the contact is Ni/Ge/Au/Ti/Au.
Effects of rapid thermal processing on electron traps in molecular-beam-epitaxial GaAs
Authors: Kitagawa Akio , Usami Akira , Wada Takao , Tokuda Yutaka , Kano Hiroyuki
Published: July 2002

Variations of deep levels in Si-doped molecular-beam-epitaxial (MBE) n-GaAs layers by rapid thermal processing (RTP) using halogen lamps were investigated by deep level transient spectroscopy. RTP was performed at 700, 800, and 900 °C with the face-to-face configuration. Native deep levels M1 (Ec−0.18 eV), M3 (Ec−0.33 eV), and M4 (Ec−0.51 eV) in MBE n-GaAs are annealed out by RTP at 900 °C. The metastable electron trap N1 (Ec−0.5∼0.7 eV) and the midgap electron trap EL2 (Ec−0.82 eV) are produced by RTP at 700, 800, and 900 °C. Two electron traps N2 (Ec−0.36 eV) and N3 (Ec−0.49 eV) are produced by RTP at 900 °C. The peculiar spatial distribution of N1 and EL2 are observed across the RTP layers. In particular, the EL2 distribution is found to be a W-shaped pattern. It is supposed that this peculiar shape of the spatial variation is consistent with that of the thermal stress induced by RTP. In addition the spatial variations of EL2 are suppressed by use of the guard ring composed of GaAs pieces, since it prevents the thermal stress during RTP, but EL2 remains at uniform concentration of ∼1014 cm−3 across the RTP layer. It seems that the thermal stress enhances the production of the trap EL2. On the other hand, the trap N1 is found to disappear by the use of the guard ring composed of GaAs pieces. We also discuss the difference of deep levels between MBE and bulk GaAs after RTP.
Effects of phonon confinement on electron transport in superlattices
Authors: Shigekawa Naoteru , Mizutani Takashi , Yokoyama Kiyoyuki
Published: July 2002

The effect of LO-phonon confinement within each layer of semiconductor superlattices on electron transport parallel to their interfaces at room temperature is evaluated numerically using Monte Carlo methods on a GaAs/AlAs superlattice and bulk GaAs. The calculated results for the superlattice with 50-Å-thick GaAs layers show that the electron mobility is enhanced by a factor of 2.5, and that the effective high-field velocity in a 0.35-μm-long channel is 25% greater in the superlattice than in bulk GaAs because the velocity-overshoot effect is more evident in the superlattice.
Electron liberation from negative ions as a means of laser preionization
Authors: Osborne M. R. , Winfield R. J. , Green J. M.
Published: July 2002

An analysis is made of the possible methods of liberation of electrons from atomic negative halide ions in the context of providing sufficient preionization for discharge-pumped rare-gas-halide excimer lasers. Some previous treatments of collisional detachment are shown to be in error by several orders of magnitude. Ion and electron impact detachment of electrons is found to produce a negligible preionization electron number density. Photodetachment is shown to be the dominant electron liberation mechanism, and to be capable of producing electron densities adequate for preionization of the excimer laser discharge.
Minority-electron mobility in p-type GaAs
Authors: Ito Hiroshi , Ishibashi Tadao
Published: July 2002

The mobility of photoinduced minority electrons in molecular-beam epitaxially grown p-GaAs has been measured directly by the Hall method. The electron mobility in a 1×1017 cm−3 Be-doped sample was about 3500 cm2 /V s at room temperature. Temperature dependence of minority electron mobility is clearly different from that of majority-hole mobility in the same sample. This result indicates the difference in dominant scattering mechanisms for electrons and holes in p-type GaAs.
Achievement of low-resistivity p-type ZnSe and the role of twinning
Authors: Neumark G. F.
Published: July 2002

Past literature is replete with reports of well-conducting p-type ZnSe; however, such reports have either been poorly reproducible and/or have shown puzzling features which are incompatible with accepted semiconductor theory (e.g., p-type behavior via n-type dopants, better light emitting diodes from high-resistivity material, etc.). We have recently noted that ‘‘good’’ p-type material available to us has been heavily twinned, and moreover has shown ‘‘nonstandard’’ electrical behavior such as a negative differential resistivity. In the present paper the earlier literature is reanalyzed based on the concept that to date such p-type material has probably always been heavily twinned. A far improved understanding of the earlier work is obtained via the insight gained from these recent (twinning) results.
Hole trapping in reoxidized nitrided silicon dioxide
Authors: Dunn G. J.
Published: July 2002

Radiation-induced hole trapping in nitrided oxides and reoxidized nitrided oxides was investigated. Midgap voltage shift in reoxidized nitrided oxide capacitors was observed to saturate rapidly with dose, while the voltage shift in nitrided oxide capacitors continues to increase. Reoxidized nitrided oxide capacitors exhibited the unusual characteristic of greater voltage shifts when irradiated under negative bias. It is proposed that a high density of small cross-section traps exists in the nitrided oxide, while the traps in reoxidized samples are larger in cross section and concentrated in the upper half of the dielectric. An etch-off experiment demonstrated that the majority of these traps lie within ∼7 nm of the gate.
New approaches to the synthesis of acicular α-FeOOH and cobalt-modified iron oxide particles
Authors: Kuo P. C. , Tsai T. S.
Published: July 2002

Formation of acicular α-FeOOH particles from the reaction system of FeCl2 -NaOH is studied. It is found that acicular α-FeOOH particles with a particle size of about 0.5 μm and axial ratio of about 10 can be obtained by oxidizing the mixed solution of FeCl2 and NaOH with a molar ratio of NaOH/FeCl2 larger than 2. New acicular Co-γ-Fe2 O3 particles are synthesized by absorbing Co2+ ions on the surface of acicular α-FeOOH particles followed by dehydrating, reduction, and oxidation. We find that using N2 as dehydrating atmosphere is better than air or H2. After reduction, variations of the coercivity of Co-Fe3 O4 particles with various cooling rates are investigated. The transformation temperature of Co-Fe3 O4 →Co-γ-Fe2 O3 is about 300 °C for the particles with cobalt content (Co/Co+Fe)<12 mol %. Distributions of Co2+ and Fe2+ ions in the particles are measured by the dissolution method. Coercivity of the acicular Co-γ-Fe2 O3 particles between 400 and 1200 Oe can be controlled by the cobalt content and additional anneal in N2.