bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface segregation during deposition
Authors: Eykholt R. , Srolovitz D. J.
Published: July 2002

Both the steady-state and transient solute (impurity) concentrations at the surface of a film during its deposition are calculated as a function of deposition rate, temperature, diffusivity, bulk film solute concentration, and segregation energy. The steady-state solute concentration at the surface is found to increase upon increasing either the solute diffusivity or the magnitude of the (negative) segregation energy, or upon decreasing the deposition rate. The transient concentration profile at the start of deposition relaxes toward the steady-state profile as 1/t. Implications of the present results for film growth mechanisms and methods to control the degree of segregation via manipulation of deposition parameters are discussed.
Thermal etching of GaAs by hydrogen under arsenic overpressure
Authors: Okubora A. , Kasahara J. , Arai M. , Watanabe N.
Published: July 2002

GaAs was found to react directly with hydrogen at temperatures above 800 °C. This reaction resulted in etching of GaAs. An etching rate of 10–15 Å/min was observed after annealing at 900 °C in a H2/AsH3 ambient. On the other hand, no etching was observed after annealing in an Ar/AsH3 ambient. The etching rate was found to be proportional to the pressure of H2 to the 3/2 power. A smooth mirrorlike surface was obtained under excess As pressure, due to the resulting congruent loss of Ga and As. An Arrhenius plot of the etching rate gives an energy of 2.90 eV, which is in good agreement with the heat of evaporation of Ga, which indicates that the etching rate is determined by the rate of evaporation of Ga atoms at the surface.
State-of-the-art AlGaAs alloys by antimony doping
Authors: Wood C. E. C. , Kerr T. M. , McLean T. D. , Westwood D. I. , Medland J. D. , Blight S. , Davies R.
Published: July 2002

Historically GaAlAs alloys grown by molecular-beam epitaxy have high deep level concentrations (>1016 cm−3), low luminescent efficiency with broad peaks, and are difficult to dope controllably below mid 1016 cm−3. We report the effect that the low incident antimony molecule fluxes during growth appear to help reduce the density of deep levels below 1014 cm−3, which then allows reproducible doping control in the low 1015 cm−3 range. Exciton-dominated photoluminescence with half widths ∼4.0 meV are now routinely achieved using this technique. Further evidence for the quality improvement of AlGaAs by heavy atom (Sb) doping comes from high 4 K two-dimensional electron gas mobilities for low sheet electron densities, e.g., 1.3×106 cm2/V s for n=2×1011 cm−2. SIMS profiles of antimony content are presented and estimates of incorporated concentrations are given.
Observation of slip dislocations in (100) silicon wafers after BF2 ion implantation and rapid thermal annealing
Authors: Ritz K. N. , Delfino M. , Cooper C. B. , Powell R. A.
Published: July 2002

The generation of slip dislocations in BF2 ion-implanted, 100-mm-diam silicon wafers during rapid thermal annealing is investigated. Whole wafer x-ray topography shows that annealing at 1150 °C causes slip to initiate randomly at positions of maximum resolved stress at the wafer edges and over scribe marks made on the back surface prior to annealing. Lowering the annealing temperature by 20 °C, which corresponds to decreasing the silicon yield stress by less than 106 dyn cm−2, prevents slip from occurring and allows sufficient removal of implantation-induced defects from which junction diodes with good current-voltage characteristics are fabricated.
Voltage-induced modulation of Josephson current
Authors: Okabe Yoichi , Takeuchi Kiyoshi , Takatsu Motomu
Published: July 2002

Superelectrons passing through the weak link region of Josephson junctions are affected by the electric potential applied to this region, and are accelerated or decelerated. The effect would appear as the modulation of the supercurrent through the junction. The amount of the supercurrent is calculated using the time-dependent Ginzburg–Landau equation for the device structures of superconductor-insulator-normal conductor-insulator-superconductor where the intermediate normal region is used to introduce the electric potential.
Precipitation of SiO2 on dislocations in polycrystalline silicon with a high carbon concentration
Authors: Gervais A. , Moudda-Azzem T.
Published: July 2002

Transmission electron microscopy (TEM) observations are reported on defects induced in polycrystalline silicon ribbon during the burn-off of the carbon support and the diffusion process. Ribbon-shaped silicon crystals are characterized by a high carbon and oxygen content at their solubility limits. TEM investigations show that SiO2 is precipitated as either alpha or beta quartz on the dislocation cores during annealing in O2 atmosphere.
Observation of microwave Cerenkov radiation as a diffraction pattern
Authors: Maruyama X. K. , Neighbours J. R. , Buskirk F. R. , Snyder D. D. , Vujaklija M. , Bruce R. G.
Published: July 2002

Measurement of microwave Cerenkov radiation in air exhibits the diffraction pattern predicted in earlier work. The radiation appears only at harmonics of the frequency of periodic electron bunches. Angular distribution power measurements are presented for frequencies of 2.86, 5.71, 8.57, and 11.42 GHz corresponding to the fundamental and the first three harmonics of an S-band rf linac.
Laser and energy-beam annealing of mechanical damage in silicon caused by slicing and lapping
Authors: Lee El-Hang
Published: July 2002

We report for the first time an attempt to melt and recrystallize macroscopic (10–20 μm deep) silicon mechanical damage that originates from wafer modifications such as slicing and lapping. Recrystallized surfaces appear mirror shiny, with significantly improved surface smoothness, as compared to the grossly coarse texture of the original damaged surfaces. The crystallinity also appears good. Across the recrystallized layer was observed some indication of impurity migration caused by segregation in the melt. Recrystallized layers contained far fewer defects than the bulk underneath, sometimes evolving to denuded-zone-like layers. This aspect can be particularly useful in the practical use of this technique for wafer modifications.
Double-pass versus expanding-beam concept for very large excimer laser amplifiers
Authors: Lowenthal Dennis D.
Published: July 2002

In this communication, the scalability of large excimer laser amplifiers with nonsaturable absorption is examined in terms of two extraction geometries. These geometries include a single-pass expanding-beam concept, recently proposed as a means to extend the laser length beyond an absorption length product of unity, and a conventional double-pass rectilinear (nonexpanding) arrangement. It is shown that the double-pass configuration provides the same total-energy output with greater efficiency than the expanding-beam concept (assuming a constant expansion angle), but has an overall length that is smaller by a factor of ∼3.
Substrate temperature effect on crystallographic quality and surface morphology of zinc sulfide films on (100)-oriented silicon substrates by molecular-beam epitaxy
Authors: Yokoyama Meiso , Kashiro Ko-ichi , Ohta Shin-ichi
Published: July 2002

The crystallographic quality and the surface morphology of ZnS films on (100) Si substrates by molecular-beam epitaxy are profoundly dependent on the substrate temperature Ts. When the Ts was below 300 °C, single crystalline films with twins grew along 〈100〉 directions in the initial stage of growth. However, when the film thickness was increased, the growth orientation changed from 〈100〉 to two 〈511〉 directions of the Si substrate. Namely, the relation of growth orientations between overgrowth and substrate is ZnS(111)∥Si(511). When the Ts was set between 340 and 370 °C, the grown films were single crystal with twins appearing initially and grew with a 〈100〉 orientation, but decreased with increasing film thickness. Especially in the case of Ts=340 °C, the ZnS film became best crystallized and exhibited the twin-free streaky pattern in the reflection high-energy electron diffraction pattern with a smooth surface morphology.
Infrared interferometers at 10 μm
Authors: Lewandowski Jacques , Mongeau Bernard , Cormier Maurice , Lapierre Jean
Published: July 2002

The two infrared (10-μm) wave fronts of an interferometer (Michelson or Mach-Zehnder) interfere separately with a tilted reference beam on a dynamic recording medium consisting of a thin oil film on a glass substrate. Illumination of this twin hologram with a visible (He-Ne) beam reconstructs simultaneously, in the same direction, two wave fronts characteristic of each arm of the interferometer. Practical realization and experimental constraints, such as air turbulence and mechanical vibrations, are easily satisfied with these long-wavelength interferometers. Experimental results include air wedge determination, homogeneity test of a NaCl plate, step deposit evaluation and afocal assembly analysis. The real-time aspect of our recording medium also permits the visual observation of transient phenomena.
An analytical technique for calculating high-field transport parameters in semiconductors
Authors: Bandyopadhyay S. , Maziar C. M. , Datta S. , Lundstrom M. S.
Published: July 2002

This paper describes an analytical technique for calculating high-field steady-state transport parameters in semiconductors using the first, second, and third moments of the Boltzmann transport equation. The transport parameters for each individual conduction valley are found by solving the moment equations and the valley population ratio is determined by equating the intervalley scattering rates. Instead of the usual drifted Maxwellian approximation, we represent the distribution function in terms of Hermite functions. This causes the moment equations to decouple, thereby making it simpler to evaluate the transport parameters analytically. Moreover, we account for the electron temperature anisotropy by using two different temperatures: one for the distribution parallel to the applied field and another for the transverse direction. This leads to better accuracy in the calculation of transport parameters as well as the valley population ratio.
Surface current and hysteresis in fine filament NbTi superconductors
Authors: Carr W. J. , Wagner G. R.
Published: July 2002

Measurements of the hysteresis loops, the magnetic moments obtained by cooling in a constant field, and the critical current density of submicron NbTi filaments are consistent with the assumption that surface current is the principal mechanism of current flow in these filaments.
Influence of scribe damage on pits formed by immersion of Si in HF solution
Authors: Sawada R.
Published: July 2002

This paper describes the influence of deliberately applied scribe damage on pits formed in (001) Si wafers by immersion in a hydrofluoric acid solution. Immersion caused dense pitting, which correlates with stacking faults. However, a pit-poor region appears in the strained vicinity of the scribe damage. The strain introduced in the damage vicinity is thought to promote Si dissolution judging from the measurement of induced current and voltage for a wafer subjected to bending stress. For a wafer annealed subsequently to damage application, a pit-rich region is found to be propagated along the (111) and (001) intersection in the damage vicinity where gettering is presumed to have occurred. Both the pit-poor and pit-rich regions present for the respective wafers are ascertained to be wider by one order of magnitude than the dislocation formation region introduced in the damage area. The pit formation is strongly influenced by the elastic strain, which is formed around the damage, as well as by mechanical damage gettering.
Efficiency considerations for polycrystalline GaAs thin-film solar cells
Authors: Yamaguchi Masafumi , Itoh Yoshio
Published: July 2002

The effect of grain boundaries upon the efficiency of polycrystalline GaAs thin-film solar cells is analyzed. Solar-cell properties are calculated on a simple model where grain boundaries act as recombination centers to reduce the minority-carrier diffusion length in the solar cell’s active layer and increase the space-charge layer recombination current. An effective diffusion length is expressed in terms of grain size, allowing the calculation of short-circuit current density and open-circuit voltage. Excellent agreement is obtained between theory and experiment. The fabrication of thin-film GaAs solar cells with an efficiency greater than 18% appears to be possible if the grain size in the thin-film GaAs layer with thickness of 3 μm is larger than 1000 μm.
Effects of rapid thermal processing on thermal oxides of silicon
Authors: Lee S. K. , Kwong D. L. , Alvi N. S.
Published: July 2002

The effects of rapid thermal processing (RTP) on the electrical properties of thin gate oxides in metal-oxide-semiconductor (MOS) devices have been studied. MOS capacitors have been analyzed by current-voltage (I-V) and constant current stress techniques. MOS field-effect transistors (MOSFETs) have been fabricated using RTP for the post-implant anneal, and the transistor degradation due to hot carrier injection has also been investigated. No significant RTP-induced degradation was detected in any category of the device properties considered here. An abnormal trapping behavior was observed on the wafer annealed at high temperature and/or long duration.
Photochemical vapor deposition of hydrogenated amorphous silicon films from hydrogen diluted monosilane
Authors: Mutsukura Nobuki , Katoh Yoshiki , Machi Yoshio
Published: July 2002

Mercury-photosensitized photochemical vapor deposition of hydrogenated amorphous silicon films was carried out for H2-diluted SiH4 source material using 2537-Å light excitation. The deposition rate of the amorphous silicon film increased with increasing H2 volume in the source and exhibited a maximum for a 30% SiH4 source. Substrate temperature dependence in the deposition rate increased for a large amount of H2 in the source as compared with a pure SiH4 source. This result was applied to prevent transparency loss in a quartz window used to introduce the excitation light into the reaction zone.
Ohmic, superconducting, shallow AuGe/Nb contacts to GaAs
Authors: Gurvitch M. , Kastalsky A. , Schwarz S. , Hwang D. M. , Butherus D. , Pearton S. , Gardner C. R.
Published: July 2002

An emerging new class of superconductor-semiconductor devices requires Ohmic superconducting contacts which do not diffuse deeply into a semiconductor. We developed a contact to GaAs based on ∼150 Å of AuGe covered with ∼2000 Å of Nb annealed in reducing atmosphere at 390–420 °C for 1–5 s. The resulting contact has linear I-V characteristics at all temperatures down to 4.2 K, resistivity of ∼2×10−6 Ω cm2 (∼0.1 Ω mm), and superconducting transition temperature Tc ≳8 K. Secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM) studies revealed very shallow penetration of the active dopant Ge into GaAs; the upper limit for the thickness of the doped layer with Ge concentration over 1017 cm−3 is estimated as 200–300 Å. Gold, a nonactive dopant (deep level) drops to below 1018 cm−3 within the same distance, with the possible tail extending further. Morphology and uniformity of a contact, as revealed in TEM and optical microscopy, is good, owing to the Nb overlayer which prevents AuGe from ‘‘balling up’’ upon melting. These contacts can be used in low-temperature devices and conventional devices based on GaAs.
Voltage and light bias-dependent spectral response of the CuInSe2/Cd(Zn)S thin-film solar cell
Authors: Eron Murat
Published: July 2002

In this paper, experimental results of bias- and light-dependent spectral response measurements of CuInSe2/Cd(Zn)S thin-film solar cell and its consequences are discussed. The dc measurements are analyzed in light of new data and their consistency with chopped light measurements are reiterated. Experimental evidence also suggests that, at least in some cells, at high forward bias, reversal of photocurrent occurs. Present models for the bias- and light-dependent collection factor are also reviewed.
Laser-induced chemical reactions at the Al/III-V compound semiconductor interface
Authors: Richter H. W. , Brillson L. J. , Kelly M. K. , Daniels R. R. , Margaritondo G.
Published: July 2002

We have used pulsed laser annealing to promote and characterize highly localized chemical reactions at Al interfaces with III-V compound semiconductors. At successive stages of these laser-induced reactions, we have monitored atomic movement and chemical structure on a microscopic scale using soft x-ray photoemission spectroscopy and Auger electron spectroscopy. For Al on each of the six III-V compound semiconductors investigated, we have found a finite range of energy density above a characteristic threshold energy density such that a chemical reaction is produced without disrupting the surface morphology. The systematic change of threshold with different semiconductors indicates a thermally activated reaction occurring in the molten phase of the Al overlayer and a thin substrate layer. Heat flow calculations, which model the temperature profiles during and after the laser pulse, confirm this model and also account for the highly abrupt interface between the reacted ternary overlayer and the binary substrate. The excellent agreement between experiment and theory demonstrates that thermal properties of the semiconductor have a dominant influence on the interfacial temperature profile and threshold energy density for reaction.
Very low-threshold V-channeled substrate inner stripe lasers using high-resistive Al0.85Ga0.15As burying layer
Authors: Yamamoto Saburo , Hijikata Toshiki
Published: July 2002

A new V-channeled substrate inner stripe laser with a very low-current threshold has been devloped using a high-resistive Al0.85Ga0.15As burying layer. An optical waveguide is formed by making use of a V channel on the substrate in the mesa. Very low-current thresholds (Ith=10–15 mA, Jth=1 kA/cm2) and stable fundamental transverse mode operation up to 30 mW are achieved even for the structure with broad active-layer widths (5–6 μm). Little degradation is observed over 3000 h at 50 °C.
Influence of deposition conditions on the properties of sputter-deposited Co-V thin films
Authors: Thompson J. A. , Stevenson D. A.
Published: July 2002

In the present study, Co-V films (17 at. % V) were deposited by rf sputtering onto several substrates that are candidates for magnetic recording substrates: glass; SiO2/Si; Ni-P/Al; and Corning Fotoceram. Films were deposited through a range of deposition variables, and their magnetic properties were measured in the film plane and perpendicular to the film plane. Magnetic orientation ratios on the various substrates range from <0.10 to >0.50. The substrate bias was one of the most important deposition parameters, and the response of coercivity to the bias voltage was much greater on glass than on any other substrate. On glass the perpendicular coercivity increased from 238 to 1360 Oe as the bias increased from 0 to 100 V. X-ray diffraction showed the films to be either amorphous or crystalline with preferred orientation. In general, amorphous films were deposited with zero substrate bias, while crystalline films were more easily obtained under conditions of substrate bias. The degree of crystallinity is a major determining factor for the magnetic properties of these films.
Cerenkov and sub-Cerenkov radiation from a charged particle beam
Authors: Neighbours John R. , Buskirk Fred R. , Maruyama Xavier K.
Published: July 2002

As a consequence of the relaxation of the phasing condition between the moving charge and radiated wave for finite beam path lengths, the Cerenkov peak is broadened and the threshold energy is lowered. A criterion for the threshold energy is developed which is applicable to charged beams consisting of a single charge bunch of finite size, as well as beams consisting of periodically repeated bunches.
Short-range-order structure of an InGaAs compound semiconductor grown by liquid-phase epitaxy
Authors: Woronick S. C. , Canova E. , Kao Y. H. , Hills M. E. , Nee T. W. , Rehn Victor
Published: July 2002

Extended x-ray absorption fine structure has been measured in an In0.53Ga0.47As compound grown by liquid-phase epitaxy. The fluorescence measurement technique was used so as to preserve the integrity of the as-grown sample. Results indicate that the virtual crystal approximation is invalid in this system, and that the structure contains significant disorder in the cation and anion sublattices. The nearest-neighbor environment around each constituent atom, however, appears to be well ordered.
Controversy regarding the 0.85-eV deep hole level in GaP
Authors: Iqbal M. Zafar , Ahmad M. , Baber N. , Zafar N.
Published: July 2002

Thermal emission rate data have been obtained on a 0.85-eV deep hole level in liquid-phase-epitaxial GaP light-emitting diodes using dark capacitance transients. Published emission rate data on this level exist for vapor-phase-epitaxial GaP. Detailed comparison with available data reveals a wide spread in emission rates casting serious doubts on the hitherto presumed origin of this level.
Spatially resolved gain measurements in a discharge-pumped KrF laser amplifier
Authors: Hirst G. J. , Rivano V. , Webb C. E.
Published: July 2002

The small-signal energy gain of a discharge-pumped KrF laser amplifier has been measured as a function of position within the laser aperture, of gas-mixture composition, and of supply voltage and polarity. The spatial uniformity of the gain distribution has been examined, and gain perturbations associated with discharge nonuniformities have been observed.
Response of a metal-oxide-semiconductor field-effect transistor to a cosmic-ray ion track
Authors: Benumof Reuben , Zoutendyk John
Published: July 2002

A cosmic-ray ion track passing perpendicularly through the oxide layer of an enhancement-mode metal-oxide-semiconductor field-effect transistor (MOSFET) forms a conducting path, the resistance of which is proportional to the stopping power of the cosmic ion and independent of the cross-sectional area of the ion track. The voltage across the oxide capacitance may drop below the threshold voltage if the gate bias is sufficiently low or if the external resistance in the gate-source circuit is sufficiently high. The first of a pair of MOSFETs forming a flip-flop circuit may thus be turned off, and the second transistor may turn on, providing it has a sufficiently short delay time, thereby completing a single-event upset.
Effect of second harmonic generation of idler wave on difference frequency generation
Authors: Mehendale S. C. , Forysiak W. , Harrison R. G.
Published: July 2002

The effect of second harmonic generation of idler wave on the process of difference frequency generation is analyzed theoretically. It is shown that, in general, the presence of second harmonic generation has a favorable influence on the evolution of the difference frequency wave. When the two processes are exactly phase matched, the usual oscillations in the variation of generated wave intensity with the interaction length are almost completely eliminated while retaining nearly complete conversion.
Transmission electron microscopy of carbon-implanted {111} copper surfaces
Authors: Matthews L. M. , Ball C. A. B.
Published: July 2002

Carbon ions with an energy of 150 keV were implanted in {111} surfaces of copper single crystals at doses of 1016 C+ cm−2 and 1017 C+ cm−2. The radiation damage below the implanted surfaces was examined by transmission electron microscopy of cross sections of the surface regions. The effects of annealing for 30 min at 600 and 750 °C were also studied. Damage consisted of a band of small defect clusters, dislocation loops, and dislocations in the band and extending from it. The depth of this band is approximately 40% deeper than that predicted from ion range theory, and the reason for this is not clear. The range increases with larger dose. The dislocation structures are consistent with the strains due to swelling being accommodated by dislocations.
On the temperature dependence of the Mott–Schottky characteristics of high-barrier Ti–p-Si metal-insulator-semiconductor diodes
Authors: Lootens D. U. , Hanselaer P. L. , Laflère W. H. , Van Meirhaeghe R. L. , Cardon F.
Published: July 2002

Mott–Schottky characteristics of Ti–p-Si metal-oxide-semiconductor diodes have been studied as a function of temperature and doping concentration. It was concluded that the contact gives rise to a strongly inverted semiconductor surface. Under these conditions, it is known that the value of the voltage intercept associated with the Mott–Schottky characteristics is only an underestimation of the built-in voltage. This offers an explanation for the anomalous temperature dependence of the barrier height determined from Mott–Schottky plots, as reported by several authors.
Spin reorientation in Nd2(Fe0.9M0.1)14B (M=Co, Ni, Ru)
Authors: Yen L. S. , Chen J. C. , Ku H. C.
Published: July 2002

Low-temperature magnetic measurements have been made on pseudoternary compounds Nd2(Fe0.9M0.1)14 B(M=Co, Ni, Ru) in order to study the effect of partial replacement of Fe by other transition metals on the spin reorientation phenomena. The spin reorientation temperature (Tsr) decreases from 136 K for ternary Nd2Fe14B to 128 K for 10% Co replacement, to 118 K for 10% Ni replacement, and to 92 K for 10% nonmagnetic Ru replacement. The extrapolated 0 K tilting angle of easy magnetization from the tetragonal c axis decreases from 30° of Nd2Fe14B to 20° for M=Co, 19° for M=Ni, and 18° for M=Ru.
Transverse magnetoresistance in pyrrhotite for B⊥c
Authors: Vitoratos E. , Sakkopoulos S.
Published: July 2002

The transverse magnetoresistance was measured on natural pyrrhotite single crystals from 88 to 607 K, beyond the Curie point Tc ∼600 K. A magnetoresistance of the order of 10−3 with a complex oscillatory behavior was observed, which as the temperature increased, passed through a maximum and then diminished very rapidly. An explanation of this complex behavior is attempted, based on the influence of magnetic field and temperature on (a) the spatial fluctuations of magnetization produced by impurities and dislocations, (b) the spin-polarization of the carriers, and (c) the carrier concentration in the compound.
Surface-energy-driven grain growth during rapid thermal annealing (<10 s) of thin silicon films
Authors: Garrison S. M. , Cammarata R. C. , Thompson C. V. , Smith Henry I.
Published: July 2002

Surface-energy-driven grain growth in 70-nm-thick phosphorus-doped Si films is reported for anneals of less than 10 s over a temperature range of ∼1100 to 1225 °C. Secondary grains grow to sizes of 1 μm or larger and have (111) crystallographic texture, indicating surface energy minimization. A kinetic analysis of grain growth suggests that while the rate of grain boundary motion is limited by P diffusion, the initial growth rate can be high, 72 nm/s at 1100 °C.
Laser-induced grating characteristics in doped lithium niobate crystals
Authors: Arizmendi Luis , Kliewer Michael J. , Powell Richard C.
Published: July 2002

The properties of laser-induced gratings were characterized in doped LiNbO3 crystals using small-angle scattering pattern analysis, the analysis of erasure decay patterns, and two-beam mixing. The results show the usefulness of each of these types of experimental techniques in obtaining different types of information about the photorefractive response of the material. The samples investigated included crystals doped with copper, erbium, magnesium, and hydrogen. The results obtained on a series of Mg-doped crystals showed a strong increase in the charge relocation rate at high concentration levels resulting in a decrease in the grating modulation depth. The results of the two-beam mixing experiments are consistent with increased conductivity in the samples with high Mg concentrations.
Superlattice conduction in superlattice modulation-doped field-effect transistors
Authors: Arch D. K. , Shur M. , Abrokwah J. K. , Daniels R. R.
Published: July 2002

We fabricated superlattice modulation-doped field-effect transistors where the doping is concentrated in GaAs narrow quantum wells separated by undoped AlGaAs barriers. As the doped AlGaAs regions are eliminated from such a structure, the concentration of traps generally associated with doping of AlGaAs is low. We observed the threshold voltage shift of only 140 mV with temperature change from 77 to 300 K (which should be compared to the shift of 200–300 mV in conventional modulation-doped field-effect transistors). Peak transconductances of 310 mS/mm at 300 K and 321 mS/mm at 77 K have been obtained. An interesting feature of this device is the complicated dependence of the transconductance on the gate voltage which has two peaks at 77 K and one sharp peak at 300 K. These peaks are caused by the parallel conduction paths in the superlattice at high gate voltages and by the gate leakage current. This parallel conduction in GaAs-doped quantum wells may be used in order to achieve larger voltage swings in superlattice modulation-doped field-effect transistors.
Characterization of periodic composites by laser-beam diffraction
Authors: Berke Andreas , Neite Günter , Riehemann Werner , Nembach Eckhard
Published: July 2002

A method has been developed for deriving the characteristic lengths of periodic composites by diffracting a laser beam from their surface and analyzing the diffraction pattern. This method has been applied to two directionally solidified lamellar eutectics and to a fibrous composite produced by wire drawing. From the diffraction pattern the periodicity length, the width of the bright phase, and the effective fluctuation of these two lengths have been computed. The latter fluctuation characterizes the perfection of the composite.
The influence of an interposed titanium thin film on the formation of tungsten silicides
Authors: Wei C. S. , Setton M. , Van der Spiegel J. , Santiago J.
Published: July 2002

Thin films of tungsten silicides have been formed on samples of W(50 nm)/Ti(5 or 10 nm)/Si〈100〉 by rapid-thermal annealing. The results of the experiments show that by interposing a thin layer of Ti at the W-Si〈100〉 interface, the temperature at which WSi2 is first detected is lowered to 570–600 °C, and the W-Si reaction rate is increased, as compared to the W/Si〈100〉 samples. The resulting WSi2 film has an electrical resistivity of about 115 μΩ cm with a smooth surface. Neither the W-rich silicide phase, W5Si3, nor the hexagonal WSi2 phase is found in the annealed samples. The growth kinetics are monitored using a four-point probe, x-ray diffraction, scanning electron microscopy, and scanning Auger analysis.
Growth mechanism of amorphous silicon by evaporation containing hydrogen from radio-frequency discharge
Authors: Pang Da-Wen , Cui Shu-Fan , Mai Zhen-Hong , Chen Joseph H.
Published: July 2002

Amorphous silicon containing high concentrations of H was produced by Si evaporation and the simultaneous addition of H from rf discharge. The H content in the films is approximately 60–70% of that found in glow-discharge produced amorphous Si containing H. The optical gap was found to be 1.7 eV. Effectiveness in the reduction of the dangling bond density has been determined by electron spin resonance. It was found that the Si–H bond was primarily formed in the gaseous phase and subsequently condenses into the solid phase. Thermal annealing and infrared spectra indicate that films produced in this manner result in improved thermal stability when compared to samples produced by glow discharge.
The effect of nitrogen implantations on A15 phase formation in Nb3 Si
Authors: Clapp Mireille Treuil , Manzur Tariq
Published: July 2002

Amorphous ribbons of Nb79Si21 were formed using the melt spinning technique. These were then implanted with nitrogen ions to form uniform surface layers of 1 and 2 at. % N. The A15 phase formed between annealing temperatures of 650–750 °C. The lattice parameter was 0.514 nm and the superconducting transition temperature was 6 K. To our knowledge, previous attempts to synthesize A15 Nb3Si from amorphous solids have required the application of very high pressures.
Transient front and initial conditions in Maxwell’s theory
Authors: Lee Shih-Chang , Lee Hung-Mou
Published: July 2002

Through investigating the transient front, initial conditions are obtained from the time domain electromagnetic problem involving objects with edges or vertices. These conditions are required so that Maxwell’s divergence equations are satisfied away from a radiating surface. Via a simple example, it is demonstrated that when such idealized geometries are considered, the time dependence of the source in such a problem cannot be chosen arbitrarily under Maxwell’s theory.
Photo-Hall determination of acceptor densities in n-type HgCdTe
Authors: Hoffman C. A. , Bartoli F. J. , Meyer J. R.
Published: July 2002

A comprehensive photo-Hall investigation of compensation densities in n-type Hg1−xCdxTe (0.224<x<0.235) is reported. The technique consists of measuring the low-temperature electron mobility as a function of optically excited carrier density. Pulses of 25-μs duration from a CO2 laser yield excess electron-hole plasma densities of between 1013 and 1016 cm−3. At low excitation levels the mobility increases due to the neutralization of ionized acceptors by photoexcited holes, while at higher excitation levels the mobility slowly decreases due to electron-hole scattering. By comparing to a detailed theory for electron transport in photoexcited narrow-gap semiconductors, the density of compensating acceptors NA can be accurately determined. The theory is generalized to account for multi-ion scattering, carrier heating, surface conduction, and inhomogeneous excitation. Experimental refinements significantly extending the range of narrow-gap n-type samples for which compensation densities may be determined are discussed. The present study demonstrates the broad applicability of the technique by determining NA for samples with compensation ratios between 0.09 and 0.96 and with both single and double acceptors.
Nb-based A15 compound Josephson tunnel junctions fabricated using a CF4 cleaning process: II. Properties of magnetron-sputtered Nb3X(X=Al,Ge) films
Authors: Tanabe K. , Asano H. , Michikami O.
Published: July 2002

Josephson tunnel junctions with Pb counterelectrodes have been fabricated using a CF4 plasma cleaning process on A15 Nb3X(X=Al,Ge) thin films prepared by magnetron sputtering. The effects of deposition conditions on junction quality as well as superconducting parameters (gap, dc Josephson current, and magnetic penetration depth) of the films have been investigated. The junction quality is largely influenced by film deposition conditions, especially by substrate temperature. Junctions with base electrodes which are deposited on oxidized silicon (for Nb3Al) or sapphire (for Nb3Ge) radiatively heated above approximately 700 °C show high-quality I–V curves, while lower temperatures lead to increases in the excess conductance and the width of the sum-gap structure. High-quality junctions with large sum gaps (up to 4.05 mV at 4.2 K for Nb3Al/Pb and 5.05 mV for Nb3Ge/Pb) can be prepared on such films. Furthermore, systematic relationships between the superconducting parameters and the energy gaps are observed, which indicate a good homogeneity of the films. In contrast, all junctions on higher-Tc films prepared by means of self-epitaxial deposition or using a molybdenum substrate holder exhibit apparent current rise at lower voltages, indicating the coexistence of low-Tc materials. Systematic correlation between the junction quality and the residual resistivity ratio shows that such an inhomogeneity extends to the bulk of the films. Radiatively heated samples with the A15 phase composition near the boundary of the film homogeneity range exhibit favorable properties for electric applications such as large energy gaps and small magnetic penetration depths (∼150 nm). However, junctions using these films persistently exhibit nonidealities, such as a slight amount of excess conductance with onset at the Pb gap and a broadened current rise at the sum-gap in their optimized I–V curves, similar to those reported in the coevaporated films.
An alternative method for the performance analysis of silicon solar cells
Authors: Mohammad S. Noor
Published: July 2002

An approximate formula for electron-hole generation rate has been proposed. The proposed approximation is found to give good representation of the actual generation rate provided by Dunbar and Hauser and by Fossum. In order to determine the applicability of this approximation attempts have been made to calculate short-circuit current, open-circuit voltage, and solar cell efficiency of an n+p silicon solar cell. The calculations involve consideration of nonuniform doping, spatial dependence of the band, and drift field for the n+ region, and band gap narrowing, Shockley–Read–Hall recombination, and Auger recombination for both n+ and p regions. The variations of short-circuit current, open-circuit voltage, and solar cell efficiency with doping concentration of the substrate p region are found to be in good agreement with results obtained from experiments. The trend of the results indicates that proper optimization of the width and impurity concentration of the diffused n region, of the width and impurity concentration of the substrate p region, and of the front-surface recombination velocity is necessary for achieving the highest efficiency of a solar cell.
Compression and propagation of an intense ion beam in a strong magnetic field
Authors: Nakagawa Yoshiro , Enomoto Tamotsu
Published: July 2002

An intense pulsed ion beam (≳50 keV, ∼80 A/cm2, and ∼400 ns pulse length) from a magnetically insulated ion diode was injected axially into a strong magnetic field (up to 2.2 T). This long pulse, high-density proton beam was efficiently guided and compressed (2r=6.0 cm to 2r≲2.0 cm) by the magnetic field. The current density at the center of a beam under a maximum magnetic field (40 cm from the diode) was increased by a factor of 4 (up to 320 A/cm2). The beam radius, calculated by the snow-plow model, indicated that a more effective compression could be obtained by a strong magnetic field under ideal conditions. The observed large beam radius, compared with the radius expected from the model, could be attributed mainly to field penetration into the beam radius since the skin depth of the ion beam (c/ωp ∼0.4 cm) was not much smaller than the radius of the initial beam (r0 ∼3 cm). By applying a magnetic field that was greater than 0.8 T, the ion beam was propagated 50 cm without loss.
Distortions in optical deep level transient spectroscopy on semi-insulating GaAs with a conducting layer of finite thickness
Authors: Brierley Steven K.
Published: July 2002

The use of optical deep level transient spectroscopy with intrinsic illumination to characterize deep acceptor levels in thin conducting layers on semi-insulating GaAs is shown to generate a majority-carrierlike peak that is, in fact, erroneous. A quantitative model is presented which explains this peak in terms of conversion of the semi-insulating bulk GaAs below the active layer to p type due to the filling of unoccupied EL2 traps. This type of conversion induces a space-charge region at the active layer–bulk interface which increases the resistance in series with the Schottky-barrier depletion-layer capacitance. The relaxation of the series resistance to its unperturbed value appears as a change in the measured capacitance, thereby creating a false majority-carrier peak. It is emphasized that the false peak shifts the apparent position of nearby minority-carrier peaks, thus seriously distorting the true ODLTS spectrum and making the identification of key minority-carrier traps much more difficult.
A new sequentially etched quantum-yield technique for measuring surface recombination velocity and diffusion lengths of solar cells
Authors: Partain L. D. , Kuryla M. S. , Fraas L. M. , McLeod P. S. , Cape J. A.
Published: July 2002

We have developed a new technique to characterize the individual layers of high-efficiency solar cells. In general, the technique allows one to set lower bounds for diffusion lengths and upper and lower bounds for interface recombination velocity. This is sufficient to determine which parameter limits performance, and often the actual parameter values are also determined accurately. We obtain this information by fitting a theoretical model to quantum-yield spectra measured on a sample in its initial state, and after its window passivation and top active layers are sequentially etched away. With such data on two p on n GaAs solar cells with AlxGa1−xAs passivation, we determined minority-carrier hole diffusion lengths of 1.0±0.2 and 0.2±0.05 μ in the Te-doped n layers for first and second samples, respectively. We found lower limits for the minority-carrier electron diffusion lengths in the top p layers of 2.0 μ in the carbon-doped first sample and 4.0 μ in the Mg-doped second sample. We determined interface recombination velocities of 4.0±0.5 (105) cm/s at the carbon-doped p layer’s interface with its Al0.45Ga0.55As passivation layer, and between 500 and 104 cm/s for the Mg-doped layer’s interface with its Al0.9Ga0.1As passivation layer. After stripping the AlxGa1−xAs layer away, we measured surface recombination velocities of 8.0±2.0 (106) cm/s on the carbon-doped sample, and 1.0±0.2 (107) cm/s on the Mg-doped sample.
Rapid removal for photoresist by a large-area electron beam
Authors: Sun D. C. , Yu Z. Q. , Li F. M. , Du Y. C. , Wang H.
Published: July 2002

Rapid removal of photoresist assisted by a large-area electron beam in oxygen atmosphere has been performed. The removal rate depended upon the pressure, flow rate of oxygen, and the power density of the electron beam. The maximum removal rate of 2500 nm/min for photoresist was one order of magnitude higher than that of conventional plasma processes.
Long sequences of order–order transitions with a temperature-dependent rotation of the magnetization in anisotropic quartic spin Hamiltonians
Authors: Oliker J. , Kventsel G. F. , Katriel J.
Published: July 2002

The anisotropic spin Hamiltonian of the form H= 1/2 (axs2x +ays2y+azs2z) + 1/4 (bxs4x+bys4y +bzs4z) + 1/2 (cxs2ys2z +cys2zs2x +czs2xs2y) can give rise to eight different phases (isotropic; Ising-type in any one of the directions x, y, z; or xy-like in any one of the planes xy, yz, or zx; xyz phase). A comprehensive mean-field study of the possible sequences of phases and types of phase transitions, exhibited upon variation of the temperature for different choices of the Hamiltonian parameters, is presented. While the resultant magnetization is always a decreasing function of the temperature, each one of the components can have a different temperature dependence, giving rise to various orientations of the resultant magnetization.
Nature of transitions in uniformly frustrated two-dimensional planar spin systems
Authors: Berge B. , Diep H. T. , Ghazali A. , Lallemand P.
Published: July 2002

We have investigated a generalized Villain’s model by varying the strength η of the negative bond. We show that there exists a critical value ηc= (1)/(3) below which the twofold degeneracy disappears; the ground state becomes ferromagnetic. A detailed numerical study shows that, for a given η>ηc, the system exhibits in general, two distinct transitions: The low temperature one corresponds to Ising-type transition; the high temperature one corresponds to KT type. These two transitions seem to coincide in the Villain’s model (η=1). Comparison with recent related models is presented.
Bulk modulus of the solid solution of hydrogen in titanium at 673 K
Authors: Sakka Tetsuo , Naito Shizuo , Mabuchi Mahito , Hashino Tomoyasu
Published: July 2002

The bulk modulus of the solid solution of hydrogen in titanium is determined from the measurements of the modulus of rigidity and the Young’s modulus as a function of the hydrogen concentration at 673 K. These moduli give identical trends in their concentration dependence. As the hydrogen concentration increases, the moduli decrease steeply in the α-phase region, are almost constant in the (α+β)-coexisting-phase region, and increase less steeply in the β-phase region. On the other hand, the bulk modulus for the solid solution is evaluated in the electronic-band theory, in which the contribution of s-shell and d-shell electrons is considered. The spherical cellular model is applied to the calculation, in which the Wigner–Seitz radius is given as a function of the hydrogen concentration. The electronic contribution to the bulk modulus is represented by the effective mass parameter, which is determined by comparing the theoretical expression of the bulk modulus with the experimental data. The fact that there is a great dependence of the effective mass parameter on the hydrogen concentration suggests that the solid solution of hydrogen in titanium must be characterized in terms of its electronic structure.
Collective spin waves in Fe/Pd and Fe/W multilayers
Authors: Hillebrands B. , Baumgart P. , Mock R. , Güntherodt G. , Boufelfel A. , Falco C. M.
Published: July 2002

In Fe/Pd and Fe/W multilayers the complete, theoretically predicted band of collective magnetostatic spin-wave excitations has been observed. Despite the large number of bilayers (49–90) discrete spin-wave modes have been found in the upper half of the band. For Fe/Pd multilayers the saturation magnetization shows a monotonic reduction of up to 30% with decreasing modulation wavelength (down to 33 Å), which is not found in the Fe/W multilayer.
Field dependence of the flexural domain wall modes
Authors: Batra S. , Wigen P. E.
Published: July 2002

The domain wall oscillations have been investigated in the frequency range 10–150 MHz by using a magneto-optical spectrometer for the case of parallel stripe domains in the thin films of substituted YIG. The equations of motion are modified in a perturbation approach to include in-plane field and stray fields arising from the magnetic charges on the film surfaces. The inclusion of the stray fields makes the wall structure Bloch-like in the center and Néel-like close to the surface of the film. Under uniform excitation, the walls can flex and give rise to infinitely many resonance frequencies. The resonance frequencies and the wall profiles for different flexural modes are calculated by considering a small amplitude wall displacement about the equilibrium wall position. It is shown that the even modes are symmetric and odd modes are antisymmetric about the center of the film. Experimentally, three modes ν0, ν1, and ν2 have been observed as a function of the applied in-plane field. The field dependence of the ν0 is seen to be in very good agreement with the theory. For higher modes, a good qualitative agreement is observed. Unlike the rigid wall model, the present theory explains the finite values of the resonance frequencies for all values of an applied in-plane magnetic field up to the saturation fields.
Magnetization and FMR studies in amorphous Co-Fe-Nb films
Authors: Krishnan R. , Saint Martin F. , Sztern J. , Ounadjela K.
Published: July 2002

We have prepared amorphous Co87Fe2Nb11 films by rf sputtering. The effect of various deposition parameters on the properties have been studied. An in-plane field of 900 Oe was applied in the film plane during the film deposition in order to obtain samples with a well-defined easy in-plane axis with very little dispersion. Under optimal conditions we get Hc=0.1 Oe and HA=15 Oe. The magnetization amounts to 11 kG. The FMR spectra show standing spin waves and D has been calculated to be 300 meV A2. Increasing rf power and argon pressure lead to an increase in Hc and HA.