bluuebunny/crossref_metadata_2025 huggingface dataset:
Amorphous force transducers in ac applications
Authors: Meydan T. , Overshott K. J.
Published: February 2003

The high stress sensitivity and high yield stress properties of amorphous ribbon materials make them suitable for magnetic sensors and tranducer applications. Recently the authors have shown that ac systems eliminate the offset voltage and drift problems of the previously published dc systems. Further investigations proved that these transducers could be operated with a linear characteristic up to 1000 g in multiwrap toroidal configurations. The cause of the transducing behavior of the materials was proved to be variation of permeability with stress. It was previously suggested that the optimum operating frequency of the ac transducers is dependent on the physical configuration of the core. Further investigations have shown that the optimum operating frequency is linearly dependent on the amplitude of the input signal to the transducer. Double-core systems have been previously described in the literature where one core acts as a dummy core and the force is applied to the active core. The disadvantage of the double-core system is that aging of the active core changes the performance of the transducer by as much as 10%. A new system will be presented which uses an accurate analog memory to reduce the ageing effect to a fraction of one percent.
Sensitive bistable magnetic sensors using twisted amorphous magnetostrictive ribbons due to Matteucci effect
Authors: Mohri K. , Takeuchi S.
Published: February 2003

New sensitive magnetic-field sensors are presented using twisted amorphous magnetostrictive ribbons such as Fe80B20 and Fe81−xCrxB17Si2. Sharp voltage pulses are induced between ends of the ribbon of as short as 25 mm or at the terminals of the detecting coil against external fields of as low as 1 Oe and 0.01 Hz–6 kHz. The domain nucleation field at the bistable flux reversal is very constant for 130 °C, 600 h using Fe79Cr2B17Si2, and a possible maximum operating temperature is about 180 °C. Small sized magnetic sensors without any windings for detecting rotational speed, distance, and other mechanical quantities are realized using the twisted ribbons by combining with small magnets. These sensitive and reliable magnetic sensors with digital outputs are suitable for applications in industrial robots and automobiles controlled with microcomputers.
Two-ion anisotropic interaction from band f electron hybridization and magnetic ordering in uranium intermetallics
Authors: Thayamballi P. , Cooper B. R.
Published: February 2003

We have generalized the Coqblin-Schrieffer type two-ion anisotropic interaction to f2 and f3 configurations (U4+ and U3+). This interaction between ions occurs via the hybridization with the intervening sea of band electrons (i.e., via resonant mixing at each site with f component of band electrons when expressed in spherical waves about that site). With the addition of small antiferromagnetic Heisenberg (isotropic Ruderman-Kittel) interaction and crystal-field interaction, we obtain a 2k noncollinear ground state with a type I collinear antiferromagnetic state at slightly higher energy. It appears likely that this ordering of states will provide a transition with increasing temperature from a noncollinear 2k magnetic structure to a type I collinear structure as observed experimentally in UP and UAs.
Comment on ‘‘Phase transformation on and charged particle emission from a Si crystal surface induced by ps laser pulses’’
Authors: Vechten J. A. Van
Published: February 2003

The electron and positive ion emissions observed in the work cited are noted to be inconsistent with the Saha-Langmuir equation. Moreover, the observed exponential dependence of ion yield on incident laser energy is shown to be inconsistent with thermal evaporation in either the low or the high fluence regime. It is suggested that the most likely cause of this ion emission is multiple-photo-ion emission.
Diffusion of indium in silicon inert and oxidizing ambients
Authors: Antoniadis D. A. , Moskowitz I.
Published: February 2003

The diffusion of indium in silicon at 1000 °C has been measured in inert (dry nitrogen) and oxidizing (dry oxygen) ambients. It was found that, similarly to phosphorous, boron, and arsenic, indium experiences significant oxidation-enhanced diffusion. This result indicates that indium, like the other elements mentioned above, diffuses in silicon by a mixed interstitialcy and vacancy mechanism. It was also found that indium, similarly to gallium, segregates readily and diffuses rapidly in thermal silicon dioxide.
Liquid phase epitaxial growth of (Al,Ga)As double-heterostructure laser material in a sapphire boat
Authors: Reynolds C. L. , Tamargo M. C.
Published: February 2003

It is demonstrated that the use of a sapphire boat in the liquid phase epitaxial (LPE) growth of (Al,Ga)As double heterostructure (DH) laser material results in better layer-thickness uniformity and no edge growth. We attribute this improvement to control of thermal geometry within the melt. In addition, the wetting of Ga on sapphire results in laser material which has less prominent meniscus lines and is free of rake lines. The distribution of cw threshold currents represents a substantial improvement for LPE grown (Al,Ga)As and is comparable to that reported for MBE (Al,Ga)As DH lasers.
Effect of hydrogen on the deposition rate for planar rf magnetron sputtering of hydrogenated amorphous silicon
Authors: Webb James B.
Published: February 2003

The deposition rate for planar magnetron sputtered films of a-Si:H has been measured for a wide range of hydrogen and argon pressures and applied rf power. At high sputter pressures the rate decreases mainly from a loss of material due to scattering effects within the plasma, while for high H2/Ar ratios, a decrease is observed resulting from the low sputter efficiency of H+ ions. For the first time a model is presented which describes quantitatively the deposition rate as a function of these parameters. These results indicate that less than 0.5% of the added hydrogen is ionized by the rf discharge which accounts for the low sensitivity of the magnetron sputtering process to the presence of hydrogen.
Field ionization of deep levels in semiconductors with applications to Hg1−xCdxTe p-n junctions
Authors: Anderson W. W. , Hoffman H. J.
Published: February 2003

Deep level-to-band tunneling is investigated as a source of excess current in narrow band semiconductors with specific application to Hg1−xCdxTe. The theoretical modeling is carried out by analogy with the Oppenheimer approach to the field ionization of hydrogen and the resulting expression for the transmission matrix element is found to be an improved version of the one originally derived by Price and Sah. The tunneling rate characteristics are governed primarily by the exponential term which is calculated using ‘‘exact’’ E-k dispersion relations combined with a parabolic barrier field. The preexponential term displays a marked insensitivity to both deep level energy and choice of impurity potential for near midgap states. Application of the theory to find the generation-recombination rate for the process leads to the anticipated ‘‘bump’’ in the forward bias I-V characteristics of pn junctions for a suitably chosen range of device parameters. The first direct experimental observation of just such a bump in Hg1−xCdxTe diodes is also reported in this paper.
Interface state density in the interelectrode region of overlapping polycrystalline silicon gates
Authors: Zheng X. Q. , Hofmann K. , Schulz M. , Risch L.
Published: February 2003

Constant capacitance deep-level transient spectroscopy was applied to analyze the interface state density in the interelectrode region of metal-oxide-semiconductor (MOS) structures having over-lapping polycrystalline silicon gates. A dual-gate structure fabricated on an integrated circuit chip by the double polycrystalline silicon technology was used to vary the extent of the space-charge region in the boundary. The interface state density D*it per boundary length was determined in MOS structures on p-type silicon to D*it =3×106 cm−1 eV−1 at the energy EV +0.99 eV. The interface state density Dit per unit area increases from a value Dit ≊109 cm−2 eV−1 under the bulk gate to Dit ≊1011 cm−2 eV−1 in the boundary region.
A study of phase and losses in ferrites by the magnetomicrowave Kerr effect
Authors: Singh P. K. , Prasad Shiva , Singh Prabhat K. , Singh S. B.
Published: February 2003

The magnetomicrowave Kerr effect has been studied in polycrystalline samples of ferrite having various compositions and two different crystallographic structures, at 9.442 GHz in terms of R, the amplitude ratio of two orthogonal components of the elliptically polarized reflected wave from the magnetized sample, and δ, the phase difference between them. This paper reports for the first time the study of a phase parameter in ferrites. A new method has been suggested for the determination of the phase constant of the bridge. The value of the effective linewidth has been obtained both from R-H and δ-H curves. It has been found that the values of the effective line- width obtained from δ-H curves are in agreement with the values estimated from R-H curves. This suggests that the measurement of δ can also facilitate the determination of the effective line- width.
Dispersion relations for hot electrons
Authors: Price Peter J.
Published: February 2003

The analytical properties of the linear response functions, for perturbations of a system in a nonequilibrium steady state, are discussed with application to semiconductor hot-electron phenomena. The characteristics of the frequency dependence of the harmonic response coefficients are considered in terms of dispersion relations which are consequences of ‘‘causality,’’ and in terms of properties of the time-domain response functions. The possibility of materials with a real-part differential conductance which is negative in some range of frequencies, while remaining positive at zero frequency, is discussed.
Effects of cation contaminants in conductive TiO2 ceramics
Authors: Yan M. F. , Rhodes W. W.
Published: February 2003

Ten cation contaminants, namely Al, Ga, Co, Fe, Mg, Zn, Zr, Ca, Sr, and Ba were investigated for their effects on the electrical properties, microstructures, and discoloration of conductive TiO2 ceramics. It was found that Al, Ga, Co, Fe, and Mg cause discoloration and increase the electrical resistivity by a factor of 104 to 106 in Nb-doped TiO2 ceramics. The other dopants do not introduce such changes in TiO2. The electrical properties, microstructures, and discoloration were measured in specimens of AlxNb0.007Ti0.993−xO2 with 0≤x≤0.01. When the Al content exceeds a critical value, ranging from 0.48% at 1400 °C to 0.25% at 1200 °C, the electrical resistivities and grain size increase rapidly, and the specimen is discolored from the original black to an ivory white color. Color boundary migration induced by Al diffusion in Nb-doped TiO2 was quantitatively measured. From the kinetics of the boundary migration, the Al diffusivity (D) was calculated to be D=2.67 exp(−53.3 kcal/mole/RT) cm2/s in the temperature range of 1200 to 1400 °C. The rapid diffusion of the small cations, namely Al, Ga, Co, Fe, and Mg, results from an interstitial diffusion mechanism. However, other cations, having a radius larger than the interstitial channel (∼0.77 Å radius), cannot diffuse by this mechanism. Defect reactions are proposed to explain the increase in the electrical resistivity and microstructural changes due to Al diffusion. These defect reactions also show that the problem of acceptor contamination cannot be avoided by adding an excess quantity of donor dopant if the solubility of the donor is much less than that of the acceptor contaminant.
A mechanism of degradation in leakage currents through ZnO varistors
Authors: Sato Ken , Takada Yoshio , Takemura Taketoshi , Ototake Masafumi
Published: February 2003

Thermally stimulated currents through ZnO varistors subjected to the voltage stresses, dc, and square-wave voltages are analyzed on the base of carrier trappings in the depletion layers of ZnO grains. The analysis indicates that the field ionization of trapped carriers in a reverse-biased depletion layer plays an important role in the degradation phenomena, thereby suggesting that the current increase with time under the dc and ac stresses is due to the same origin. An Arrhenius relation to predict the life of varistors and a dependence of leakage current Jc on time t, ln Jc ∝t1/2, are derived from a carrier trapping model.
Antireflection layers for GaAs solar cells
Authors: Arora N. D. , Hauser J. R.
Published: February 2003

The results of reflectance and transmittance calculation for various single and double layer optical coatings on GaAs solar cells are presented. An optimization technique has been used to calculate the optimum thicknesses of the layers which result in maximum transmission of photons at the GaAs surface taking into consideration the solar spectrum in outer space (air mass zero illumination). The effect of angle of incidence of light is also discussed. The technique used is quite general and could be used for any system of multilayer thin films of absorbing or nonabsorbing type with light incident at any angle.
Diffusion length of minority carrier in n-type semiconductors: A photoelectrochemical determination in aqueous solvents
Authors: Etchebery Arnaud , Etman Mohamed , Fotouhi Bahman , Gautron Jacques , Sculfort Jean-Loup , Lemasson Philippe
Published: February 2003

Photoelectrochemical measurements with aqueous electrolyte-semiconductor junctions under monochromatic illumination for five n-type semiconductor compounds are presented: ZnSe, CdSe, CdTe (II-VI) and GaP, InP (III-V). The Schottky behavior of these junctions is demonstrated in the dark and under illumination. Only if conditions such as surface preparation, proper band bending, and doping level as well as energy of incident photons are achieved, the photocurrent versus potential characteristics are described using Gärtner’s equation. Values of the diffusion length L of holes are determined by an extrapolation and a fitting method. They depend on the particular properties of the samples, particularly the concentration of free electrons. Results obtained are: ZnSe (7×1017 cm−3) L=0.025 μm; CdSe (2.5×1018 cm−3) L=0.124 μm; CdTe (8.5×1017 cm−3) L=0.14 μm; GaP (4×1016 cm−3) L=0.24 μm; InP (3×1017 cm−3) L=0.15 μm.
Electron spin resonance in CdxZnyMnzTe alloys
Authors: Manoogian A. , Chan B. W. , Brun del Re R. , Donofrio T. , Woolley J. C.
Published: February 2003

Electron spin resonance (ESR) studies were made on the Mn2+ constituent of CdxZnyMnzTe (x+y+z=1) polycrystalline semimagnetic semiconductors, covering the whole range of solid solutions available, alloys with 0.10≤z≤0.75 being used. These materials exhibit spin-glass properties at low temperatures. The temperature dependence of the Mn2+ ESR linewidths were measured in the samples between 4.2 to 300 K, and it was found in each case that the linewidth increased with decreasing temperature, reaching a maximum value at a critical temperature Tc. The temperature variation of the linewidths were found to fit a theoretical expression of the form ΔH=A[Tc/(T−Tc)]α, where ΔH is the linewidth, A is a constant, Tc is the critical temperature and α is the critical exponent. The percolation limit for any ratio of x:y was found to be in the range 0.20≤z≤0.25. For values of z above this limit, Tc was found to vary smoothly with z for fixed x:y ratios, showing a linear variation in the limiting case of Zn1−zMnzTe , and all the lines extrapolated to a value of Tc=305 K for MnTe. For fixed values of z the values of Tc were found to increase linearly with y. The value of α was found in each case to fall within the range 0.33±0.08. In some samples an extra line of width ∼100 G was found superimposed on the main ESR line, and it is attributed to clustering of Mn2+ ions in the structures, with the resultant line from the cluster being exchange narrowed.
Use of low-frequency sinusoidal temperature waves to separate pyroelectric currents from nonpyroelectric currents. Part I. Theory
Authors: Garn Lynn E. , Sharp Edward J.
Published: February 2003

This is the first of two papers wherein a new method is described which allows the analysis and evaluation of electric currents, such as pyroelectric currents and thermally simulated conductivity or currents arising from heated dielectric materials. It is shown for certain temperature and frequency ranges that the ac current from a nonpyroelectric material is in phase with a small sinusoidal temperature wave superimposed on a constant heating rate used to warm the samples. In addition, the ac current of pyroelectric origin is shown to be π/2 radians out of phase with the same temperature wave. Possible sources of error, such as undesired phase shifts resulting from slowly varying background currents or harmonics in the sinusoidal temperature wave, are also discussed.
Use of low-frequency sinusoidal temperature waves to separate pyroelectric currents from nonpyroelectric currents. Part II. Experiment
Authors: Sharp Edward J. , Garn Lynn E.
Published: February 2003

Data are presented on several dielectric materials which typically possess varying degrees of pyroelectric response depending largely on the electrical (poling) and thermal (heating) conditioning of the materials. A measurement technique described in the preceding paper was used to analyze these materials. The results of these measurements are compared with those reported by other workers using different techniques. The strength and simplicity of this method is clearly demonstrated when analyzing materials such as poly(vinylidene fluoride) (PVF2), where the current arising from a heated sample stems from a combination of sources or mechanisms in the material.
Photovoltaic properties of ferroelectric BaTiO3 thin films rf sputter deposited on silicon
Authors: Dharmadhikari Vineet S. , Grannemann W. W.
Published: February 2003

Ferroelectric thin films of BaTiO3 have been successfully deposited on n-type silicon substrates at temperatures above 500 °C by rf sputtering in an O2/Ar atmosphere. Analysis by x-ray diffraction patterns show that films deposited at room temperature are amorphous. At temperatures above 500 °C, crystalline BaTiO3 films with a tetragonal structure are obtained. The polarization-electric field (P-E) hysteresis loops and a broad peak in the dielectric constant versus temperature curve at Curie point indicate that the rf sputtered BaTiO3 films are ferroelectric. An anomalous photovoltaic effect is observed in these thin films which is related to the remanent polarization of the material. The results on open-circuit and short-circuit measurements provide an important basis for a better understanding of the role of photovoltaic field, photovoltaic current, and the pyroelectric properties in photoferroelectric domain switching.
Interface structures during solid-phase-epitaxial growth in ion implanted semiconductors and a crystallization model
Authors: Narayan J.
Published: February 2003

We have investigated the interface structures during solid-phase-epitaxial (SPE) growth in ion implanted silicon and gallium arsenide using high-resolution, cross-section electron microscopy. The crystalline amorphous (c-a) interface during solid-phase-epitaxial growth on {001} faces in silicon was found to be planar with undulations of ∼5 Å over 200–500 Å intervals. However, above certain dopant concentrations that were much higher than the solubility limits, the SPE growth was completely halted, and the c-a interface was observed to become unstable by developing large undulations that resulted in the formation of twins. The solid-phase-epitaxial growth on {111} faces in Si contained atomically smooth interfaces at first. This was followed by the formation of twins. However, the growth on {001} faces of GaAs was found always to be accompanied by the formation of twins. A model of crystal growth in diamond cubic lattices is presented, which can account for the orientation dependence of SPE growth rates, the nature of interfacial instability, and the formation of twins during SPE growth in Si and GaAs.
Shrinkage and growth of oxidation stacking faults during thermal nitridation of silicon and oxidized silicon
Authors: Hayafuji Y. , Kajiwara K. , Usui S.
Published: February 2003

We have studied the shrinkage and growth of preexisting oxidation-induced stacking faults during thermal nitridation of silicon without oxide film and of oxidized silicon with oxide film 23 to 5600 Å thick. Nitridation was carried out at 1050 to 1200 °C under ammonia partial pressures of 10−3 to 4 kg/cm2. We observed that stacking faults in silicon without oxide film shrink linearly with nitridation time and their shrinkage rate increased as the partial pressure of ammonia increased. On the other hand, stacking faults in oxidized silicon with oxide film grew during nitridation and their growth rate increased with the increase of ammonia partial pressure after the pressure reached about 10−1 kg/cm2 and with the increase of the thickness of the oxide film. Based on these results, we have proposed a model which assumes that in the shrinkage phenomenon, an undersaturation of silicon self-interstitials occurs near the silicon surface because of silicon-cation migration from the silicon-nitride interface to the nitride surface. The model also assumes that the growth phenomenon occurs because of the supersaturation of silicon self-interstitials, which are generated by the reaction of ammonia with silicon dioxide and are injected into the bulk of silicon through the silicon-nitride interface. The projected results of this model agree reasonably well with the experimental results.
Electron irradiation effects in p-type GaAs
Authors: Loualiche S. , Nouailhat A. , Guillot G. , Gavand M. , Laugier A. , Bourgoin J. C.
Published: February 2003

Deep level centers produced by 1-MeV electron irradiation at room temperature on p-type GaAs (liquid- and vapor-phase epitaxial layers) have been studied by means of Deep Level Transient Spectroscopy and Deep Level Optical Spectroscopy. Activation energies, thermal and optical photoionization cross sections, and introduction rates have been measured for the main defects. The trap H1 is shown to have an introduciton rate (0.25 cm−1) different from that of the E3 center created in n-type GaAs. As previously reported H1 is found to be highly relaxed from the Franck-Condon shift parameter given by optical spectroscopy. New hole traps created with an introduction rate greater than 2 cm−1 have been detected for the first time by low-temperature transient spectroscopy measurements.
Compensation mechanisms related to boron implantation in GaAs
Authors: Martin G. M. , Secordel P. , Venger C.
Published: February 2003

Two different compensation mechanisms are shown to be responsible for the carrier removal observed after boron implantation in n-type GaAs: (i) Compensation due to complex lattice defects corresponding to implantation damage and which mainly give rise to two narrow bands in the band gap centered at Ec−0.55 eV and Ev+0.70 eV. These defects and the related compensation vanish after annealing for half an hour at temperatures between 350 and 550 °C by exodiffusion. (ii) Compensation due to chemical effects which consists in the formation of complexes between impurities already present in the wafer and the created defects or the boron atoms themselves. These complexes, which are not observed to exodiffuse, are stable at much higher temperatures, up to around 800 °C. It is shown that these complexes do not generate deep levels. Furthermore, it is established that a boron implantation at relatively high dose (1014 at cm−2) followed by an annealing at 860 °C, leads to a depletion of both the electrically active Cr atoms and the deep donor defect EL2 in the implanted region. The presence of boron does not seem to affect the electrical properties of implanted layers further annealed at 860 °C, as far as its concentration does not exceed 1–2×1017 cm−3. But larger concentrations, sometimes noticed in liquid-encapsulated Czochralski (LEC) semi-insulating substrates, might have a real influence.
Electroelastic effect in alpha quartz
Authors: Reider Georg A. , Kittinger Erwin , Tichý Jan
Published: February 2003

The electroelastic effect of α quartz is investigated by means of high-resolution measurements of ultrasonic transit times as a function of a superimposed biasing field. Experimental results are reported for 25 different configurations of wave normal, displacement, and electric field vectors. It is shown that these results may consistently by expressed in terms of an effective fifth-rank tensor with eight independent components.
Thermal properties of two low viscosity silicon oils as functions of temperature and pressure
Authors: Sandberg O. , Sundqvist B.
Published: February 2003

The thermal conductivity and the specific heat capacity per unit volume have been measured for two low viscosity grades of Dow Corning 200 fluid (polydimethyl siloxane) in the range 110 to 350 K and under pressures up to 2.0 GPa (20 kbar). Both the quantities studied are found to increase with increasing pressure in the liquid phase. From the measured data the phase diagrams are obtained. The 5 mm2/s (5 cSt) grade fluid does not crystallize, but undergoes a glass transition at 1.0 GPa at room temperature. The 1 mm2/s (1 cSt) grade has a more complicated phase diagram with a partly crystalline phase at low temperatures and pressures and two glass transitions at high temperatures and pressures.
Gain, saturation, and optimization of the XeF discharge laser
Authors: Sadighi-Bonabi R. , Lee F. W. , Collins C. B.
Published: February 2003

In this work a xenon-F2 plasma diluted in helium has been operated as a pulsed amplifier for the B→X transition of XeF. Two synchronously excited plasmas were produced by preionized discharges in atmospheric electrical avalanche devices switched by hydrogen thyratrons. The principle output obtained at 352 nm from the tube serving as an oscillator was optically delayed and then was threaded through the second discharge. Calibrated attenuation of this beam injected into the amplifier provided data on the overall amplification ratio. From these data effective saturation intensities of 620 and 860 kW/cm2 were found for operation at pressures of 2.7 and 3.7 atmospheres, respectively. Corresponding small signal gains were found to be moderately high, reaching 0.11 and 0.13 cm−1, for the two conditions, respectively. Based upon these results for the gain and saturation parameters, a self-excited oscillator was designed to be optimized simultaneously for energy density and efficiency. By matching the ringing time of the driving circuit to the characteristic time of the discharge a XeF device was realized which produced 10-ns output pulses representing an energy density of 2.7 J/liter and an efficiency relative to storage of 1.6%.
Pinched-beam ion-diode scaling on the Aurora pulser
Authors: Meger R. A. , Young F. C.
Published: February 2003

A pinched-beam ion diode has been operated on the Aurora pulser in positive polarity at impedances ranging from 10 to 35 Ω. Ion generation efficiencies of 20% were observed with ion energies ranging from 2.5 to 5 MeV. The ion current scaled inversely with the anode-cathode gap, and a peak value of 65 kA was measured for the smallest gap. A plasma erosion switch was used to decrease prepulse voltage and gap closure in the diode.
Measurement of ionization and attachment coefficients in SF6 and SF6+N2
Authors: Govinda Raju G. R. , Dincer M. S.
Published: February 2003

Prebreakdown ionization currents have been measured in SF6, N2, and SF6+N2 mixtures by the Townsend method over the E/p range 100–450 V cm−1 Torr−1. A digital computer analysis is used for evaluation of the ionization and attachment coefficients. The variation of (α−η)/p in SF6 and N2 mixtures is found to be nonlinear with the percentage mixture ratio. Sparkover voltage measurements are carried out for SF6, N2, and SF6+N2 mixtures in the pd interval of 3.5≤pd≤25 Torr cm. Furthermore, the apparent secondary ionization coefficients have been deduced in SF6+N2 mixtures. They decrease significantly with increasing partial pressure of SF6. The reduction observed in this coefficient is attributed to the increased photon absorption coefficient.
Interfacial reactions between aluminum and transition-metal nitride and carbide films
Authors: Wittmer Marc
Published: February 2003

Recently transition-metal nitrides and carbides have received great interest as diffusion barrier materials in contact structures for silicon semiconductor devices. Excellent stability of the contact structure is achievable through heat treatments of up to 600 °C when Ni is used as the top metal layer. However, the same transition-metal compounds show poor barrier properties with Al as the top layer if heat treated to 600 °C. We have therefore investigated the failure mechanism of transition-metal nitride and carbide barrier materials in Al overlayer metallizations. This knowledge has enabled us to develop high-temperature contact structures for silicon semiconductor devices by using an intermetallic compound of Al instead of plain Al for the top layer.
Electron mobility in single and multiple period modulation-doped (Al,Ga)As/GaAs heterostructures
Authors: Drummond T. J. , Kopp W. , Keever M. , Morkoç H. , Cho A. Y.
Published: February 2003

Single and multiple period modulation-doped (Al,Ga)As/GaAs heterostructures have been grown by molecular beam epitaxy (MBE) and characterized by Hall measurements. The basic structure consists of alternating layers of undoped GaAs and doped (Al,Ga)As separated by undoped ’’intrinsic’’ layers of (Al,Ga)As. The thickness of each of these layers was varied independently in a one, three, or nine period structure. Mobilities as high as 211 000, 95 500, and 8 360 cm2V−1 s−1 were obtained at 10 K, 78 K, and 300 K, respectively. The total sheet charge concentrations were about 2.25×1012 cm−2 in the highest mobility structures. Single period structures with an AlAs mole fraction of 0.33 typically had higher room-temperature mobilities while multiple period structures with an AlAs mole fraction of 0.2 gave better results at cryogenic temperatures. The enhanced mobilities are attributed to the separation of electrons and donors by the undoped (Al,Ga)As layers and the high quality interfaces obtainable by MBE. To our knowledge, these results on single and multiple period structures are comparable to the best values reported to date.
Influence of AlAs mole fraction on the electron mobility of (Al,Ga)As/GaAs heterostructures
Authors: Drummond T. J. , Kopp W. , Fischer R. , Morkoç H.
Published: February 2003

Single period (Al,Ga)As/GaAs heterostructures with doped (Al,Ga)As layers were prepared and characterized by Van der Pauw-Hall measurements between 10 and 300 K. The mobility and the concentration of the two dimensional electron gas at the heterojunction interface were studied with varying x AlAs mole fraction. The electron mobility goes through a peak at about the direct-indirect transition, x = 0.38 while the carrier concentration steadily decreases up to x = 0.38. Electron mobilities of 100 000 and 200 000 cm2/Vs were measured at 77 and 10 K, respectively. These results represent the best mobilities reported to date in single period structures.
Two-electron conduction in N-type Hg1−xCdxTe
Authors: Finkman E. , Nemirovsky Y.
Published: February 2003

The results of galvanomagnetic measurements in N-type Hg1−xCdxTe, as a function of magnetic field for the compositions x≃0.215 and x≃0.29 and over the temperature range 15⩽T⩽300 K are reported. A unified model is proposed which fits the magnetic field dependence of both the conductivity and the Hall coefficient. The most significant feature of the model is that two types of electrons are contributing to the transport properties and are responsible for the magnetic field dependence of the conductivity and the Hall coefficient. The two sets of electrons have mobilities which at the lowest measured temperature (15 K) differ by up to two orders of magnitude, and have concentrations which are of the same order of magnitude.
Voltage and thermal treatment of tunnel junctions
Authors: Hernández G. , Montalvo D. , Will T. A.
Published: February 2003

The effect on the zero-bias resistance of Al-Al oxide-Pb tunnel junctions subjected to a fixed voltage (at 77 and 300 K) and to thermal (300 K, open circuit) treatment was investigated. Variations in zero-bias resistance occurred only at 300 K, both with and without applied bias. An attempt was made to separate the voltage from the thermal effect by means of control junctions which, we suppose, show the same relative thermal effect as the biased ones. In thermally treated junctions we found a drastic variation within the first hour. These results are interpreted in terms of ionic mobility.
Nuclear magnetic relaxation and the internal geometry of sedimentary rocks
Authors: Cohen Morrel H. , Mendelson Kenneth S.
Published: February 2003

In this paper we study nuclear magnetic relaxation in the pore fluid within a detrital sedimentary rock. Bloch equations are introduced for the magnetization and solved for the case of uniform magnetization, yielding a single relaxation rate linearly related to the surface to volume ratio of the pore space. The surface magnetization is then eliminated and a closed set of equations for the bulk magnetization is developed. These equations are solved in detail in a spherical pore. The results show that local uniformity within a pore is set up rapidly. We show how to partition the pore space into individual pores separated by throats and obtain a set of coupled relaxation equations for the magnetization within each pore. The equations have the form encountered in the theory of disordered materials. When the throat size is sufficiently small, the relaxation function yields directly the probability distribution of the surface to volume ratios of individual pores. Otherwise, geometric information about pores and throats is enfolded in the relaxation function.
Stacking fault annihilation dependence on surface orientation in silicon
Authors: Hayafuji Yoshinori , Kawado Seiji
Published: February 2003

The annihilation of oxidation-induced stacking faults in silicon wafers with an orientation from 0° to 6° off the [001] axis along the [110] zone has been investigated. The density (DI) of stacking faults on the (111) and (111̄) planes was independent of the surface orientation and can be expressed in the form 1/DI−1/DIO∝t1.34, where DIO is the density in the initial stage of oxidation and t is the oxidation time. The mechanism of this type of stacking fault annihilation can be explained in terms of the unfaulting reaction caused by the impingement of two Frank partial dislocations. A model of the annealing out of the perfect dislocation loops formed by the unfaulting reaction is also proposed. On the other hand, a marked surface orientation dependence was observed in the density (DII) of stacking faults on the (1̄11) and (11̄1) planes. This density can be expressed as DII∝exp(−αt0.4) . The constant α is dependent on the surface orientation. α showed a maximum value of 3.5 h−0.4 for a 3.7°-off-(001) wafer and was nearly zero for a (001) wafer.
Comment on ’’Gettering of mobile oxygen and defect stability within back-surface damage regions in Si’’
Authors: Schaake H. F.
Published: February 2003

It is shown that the amount of oxygen detected in back-surface damaged regions of silicon wafers after annealing in vacuum is too great to have originated from the bulk of the wafer. Calculations show that residual water vapor in the ambient can account for the amount observed.
Electron diffusion lengths in liquid-phase epitaxial p-GaAs:Ge layers determined by electron-beam-induced current method
Authors: Shen C. C. , Pande K. P. , Pearson G. L.
Published: February 2003

The electron diffusion lengths in liquid-phase epitaxial (LPE) p-GaAs:Ge layers were determined by using the electron-beam-induced current method. The electron diffusion length is found to reduce gradually as the doping level of the epitaxial layer is increased. For four LPE p-GaAs:Ge layers with carrier concentration of 1.4×1016 cm−3, 2.0×1017 cm−3, 1.3×1018 cm−3, and 2.5×1019 cm−3, the electron diffusion lengths were determined to be 8.1, 6.7, 5.1, and 1.2 μm, respectively.
Validity of Raman and transmission data reaffirmed
Authors: Lee M. C. , Aydinli A. , Lo H. W. , Compaan A.
Published: February 2003

The simple experimental test of blocking the 1.15-μm cw probe beam shows that Si luminescence is not a problem in our time-resolved transmission measurements. The phonon wave vector probed in our Raman experiments is q = 1.5×106 cm−1, so that the Raman experiment is, in fact, sensitive to direct phonon heating by carrier relaxation.
Stimulated Raman scattering in a magnetoactive piezoelectric semiconductor
Authors: Apte N. , Ghosh S.
Published: February 2003

The stimulated Raman scattering of a large-amplitude, transversely polarized, electromagnetic pump wave from both the electron plasma wave and the molecular vibrations produced at a frequency equal to that of transverse optical phonon has been investigated in an n-type piezoelectric semiconductor. The general dispersion relation has been obtained considering only the Stoke’s component of the scattered electromagnetic wave in the presence of a large magnetostatic field applied at an arbitrary angle ϑ to the direction of propagation of the pump wave. The analysis has been applied to both cases of isotropic (B0 = 0) and magnetoactive (B0≠0) plasmas. The threshold electric field necessary for the onset of Raman instability and the growth rate of the unstable Raman mode well above the threshold have been studied. It is concluded that the threshold pump amplitude as well as the growth rate are strongly dependent on the orientation of the magnetostatic field with respect to the wave vectors k, k1 and its magnitude.
Calculation of the current-voltage-pressure characteristics of dc diode sputtering discharges
Authors: Maniv S. , Westwood W. D. , Scanlon P. J.
Published: February 2003

The relationship between current density, applied voltage, and pressure in dc diode discharges used for sputter deposition has been calculated using a model which considers the electron and ion currents within the cathode dark space. Electrons emitted from the target cause ionization primarily at the interface between the dark space and negative glow and ions crossing the dark space suffer symmetric charge exchange collisions with neutrals. The resulting expression for the characteristic is of the form J = B−2/3 (Va−V0)3/2, where V0 is the minimum voltage at which the discharge can be maintained. The values of B and V0 have been obtained by comparison with experimental data for argon and oxygen discharges with a Ta sputtering target. They vary approximately as (pressure)−4/3 and (pressure)−1, respectively. Values of B calculated from the experimental data for J and Va in argon and oxygen discharges agree with the values obtained from the model and measured values for the dark space distance. Comparison of the model with experimental data gives an estimate of the average value of Townsend’s ionization coefficient.
Irradiance scaling of fast ion expansion for CO2 laser produced plasmas
Authors: Church P. , Martin F. , Pépin H. , Decoste R.
Published: February 2003

Faraday collector and calorimeter measurements of the ion emission are obtained for short CO2 laser pulses irradiating planar polyethylene targets at intensities between 1012 and 2×1013 W cm−2. The fast ion angular distribution is more peaked towards target normal than the thermal ion distribution. The hot electron temperature inferred from both the slope of the fast ion velocity distribution and the maximum ion velocity scales as I0.25 and I0.9 for irradiances respectively above and below a critical value of Icr = 5×1012 W cm−2. The high irradiance scaling agrees with that of the hot electron temperature deduced from x-ray measurements. At low irradiance, the discrepancy between the ion and x-ray hot electron temperature scaling indicates that the expansion is nonisothermal resulting in a cooling of the hot electrons and in a colder fast ion velocity distribution.
An analytic model for the shock Hugoniot in porous materials
Authors: Simons Girard A. , Legner Hartmut H.
Published: February 2003

A simplified analytic model for the Shock Hugoniot in porous materials is developed. The model is most accurate in the limits in which the pressure is dominated by either the elasticity (low pressure) or by the thermal motion (high pressure). The compressed density is expressed as a function of the pressure, the initial solidity and density of the material, the cold compression coefficient (Young’s Modulus)−1, and the Grüneisen coefficient. The model is validated over a wide range of materials, pressures, and solidities.
A comparison of transverse and linear preionizing spark arrays in transversely excited atmospheric CO2 lasers
Authors: Cridland J. V. , Howells S.
Published: February 2003

Two spark array geometries are commonly used to initiate the glow discharge in a transversely excited Atmospheric CO2 laser. It is shown that the type of array used determines the laser output peak power as well as the amount of energy that can be deposited in the gas prior to arc formation.
The simulation of images in the field ion microscope: Specimens of arbitrary crystal structure and orientation
Authors: Eaton H. C. , Lee L.
Published: February 2003

A method is described which can be used to derive the lattice geometry and stacking sequence of any plane in any crystal structure. The scheme is used to develop an algorithm for simulating field ion microscope images. The simulations allow consideration of specimens of any crystal structure and orientation.
Electrical properties and photoluminescence of Te-doped GaAs grown by molecular beam epitaxy
Authors: De-Sheng Jiang , Makita Y. , Ploog K. , Queisser H. J.
Published: February 2003

The application of PbTe as a molecular tellurium source in the growth of n-type GaAs:Te by molecular beam epitaxy (MBE) has been investigated. We obtained free-carrier concentrations ranging from 2×1016 to 2×1019 cm−3. In particular in degenerate n-type material, excellent 77 K Hall mobilities were achieved. Even at high impurity concentrations (≳1018 cm−3), Te was not found to accumulate at the surface if a true Pb-saturated (n-type) starting material was used as dopant source. Using low-temperature photoluminescence measurements, we further studied the influence of the doping concentration on the shift of the Fermi level and on the radiative recombination across the fundamental gap in heavily n-doped GaAs:Te. Calculations based on the Burstein-Moss shift and on the band tailing effect, as well as a line shape analysis, were performed for a distinct interpretation of the observed luminescence behavior. At concentrations below 5×1017 electrons cm−3, band-acceptor transitions involving residual carbon acceptors act as dominant recombination process. Above 1018 electrons cm−3, however, the luminescence spectra can be well described by indirect transitions between free electrons in the conduction band and localized acceptor-like centers in the deeper tail states above the valence band edge.
Multilevel Si doping in GaAs using a single AsCl3:SiCl4 doping source
Authors: Eu V. , Feng M. , Zielinski T. , Whelan J. M.
Published: February 2003

Multilevel Si-doped GaAs epitaxial layers with abrupt interfaces can be grown using a single AsCl3:SiCl4 liquid doping source with a constant doping flow rate in an AsCl3/H2/Ga chemical vapor deposition system. Doping variations are achieved by adjustments in the HCl to H2 partial pressure ratios. The H2 is injected between the source and substrate to vary the HCl partial pressure. Si concentrations in these layers vary inversely as approximately the cube of the H2 to HCl partial pressure ratio for a fixed SiCl4 inlet flow.
Time response of a vertical electric dipole over a two-layer medium by the double deformation technique
Authors: Ezzeddine A. , Kong J. A. , Tsang L.
Published: February 2003

The time response of the aximuthal magnetic field due to a vertical electric dipole over a two-layer medium is obtained by application of the double deformation technique. The solutions are shown to obey the principle of casuality. Numerical results are illustrated with the complete time response for the cases of a slab of nonconducting dielectric and a conducting two-layer medium.
Ionic bond effects on the mean excitation energy for stopping power
Authors: Wilson J. W. , Chang C. K. , Xu Y. J. , Kamaratos E.
Published: February 2003

Molecular mean excitation energies for ionic bonded molecules calculated according to the local plasma approximation are compared to the Bragg rule. Adjustments of 15% are calculated for LiF in agreement with experiments while 6% adjustments are predicted for HF and 3% for LiH.
Comment on ’’Thermal oxidation of InP and properties of oxide film’’
Authors: Griffiths J. E. , Schwartz G. P. , Sunder W. A. , Schonhorn H.
Published: February 2003

In a recent paper, Yamaguchi and Ando [J. Appl. Phys. 51, 5007 (1980)] discussed the composition of thermally grown oxide films on InP. Reanalysis of their infrared absorption data in conjunction with Raman data shows that their assignments of oxide products are in error. The dominant product at T≳620 °C is indium orthophosphate.
Preparation and properties of superconducting BaPb1−xBixO3 thin films by sputtering
Authors: Suzuki Minoru , Enomoto Youichi , Murakami Toshiaki , Inamura Takahiro
Published: February 2003

Superconducting thin films of BaPb1−xBixO3 with transition temperature above 9 K were successfully prepared by rf diode sputtering and subsequent annealing. It was found that sputtered films tended to lack Pb and Bi during deposition, so that targets with excess Pb and Bi were used in order to achieve the film stoichiometry. Sufficient oxygen partial pressure during discharge was found to be requisite for obtaining thin films with low resistivity, high Tc, and sharp superconducting transition. The films admit optical transmission to a small extent in the wavelength range from 500 to 700 nm. Based on these results, some aspects of the band structure are discussed.
Dimerization of Zn vapor in a supersonic carrier gas
Authors: Flotte A. Reyes , Echt O. , Sattler K. , Recknagel E.
Published: February 2003

A source has been constructed for the generation of metal cluster beams. The particles are detected by electronic time of flight mass spectrometry which includes pulsed electron impact ionization. Condensation occurs in a supersonic carrier gas (H2, He, or Ar) and large dimer/monomer ratios are found, although the Zn1 vapor pressure before the expansion is only 10−3 mbar. The highest measured value of the dimer to monomer intensity ratio was 6.
Kinetic torque and dynamic behavior in a magnetic levitation device
Authors: Bird J. F.
Published: February 2003

A magnetic torque is induced by motions of a cylindrical metal shell that is being levitated around an alternating-current filament—a suspension device analyzed previously for the motionless case. This kinetic magnetic torque is calculated for shell-filament configurations in which the shell rotates on its own axis while revolving in circular orbits about the parallel current axis. The calculated torque is given numerically over a wide range of device parameters via a set of universal curves, with analytic formulae for limiting cases. The torque results are used to assess the dynamics of the suspension under various conditions, including external magnetic spin damping and extraneous orbital momentum generation.