bluuebunny/crossref_metadata_2025 huggingface dataset:
Hall effect in n-type InP crystals: Thermal activation energy and influence of compensation
Authors: Leloup J. , Djerassi H. , Albany J. H. , Mullin J. B.
Published: February 2003

Hall coefficient results between 10 and 300 K are reported on n-type InP crystals with room-temperature carrier concentrations ranging between 3.4×1014 and 5.2×1017 cm−3. The thermal activation energy Ed was deduced, particularly for samples in the isolated impurity range. It was found to decrease from about 6.3 to 2 meV in samples with carrier concentration increasing from 3.4×1014 to 1.6×1016 cm−3. The decrease in activation energy was observed to be influenced by compensation (Nd−Na) and to follow approximately the relation Ed=7.2[1−3×10−6(Nd−Na)1/3] meV. This decrease was also discussed on the basis of a more refined approach, leading to a degeneracy concentration in reasonable agreement with the experimental results.
Hot-wire pyrometry
Authors: Ferguson Colin R. , Keck James C.
Published: February 2003

A hot-wire pyrometer for measuring gas temperatures with a high sensitivity has been developed. The method can easily be extended to measurements of surface temperature. The principal elements of a hot-wire pyrometer are a fine wire inserted into the gas and a photomultiplier for measuring the radiation emitted from it. The output voltage V of the photomultiplier is shown both theoretically and experimentally to be the following function of wire temperature T: V=σT7/4 exp(−γT−1/2), where σ and γ are the calibration constants unique to a particular system.
Flux method for semiconductors in the presence of a temperature gradient
Authors: Thomchick John
Published: February 2003

A flux method, which has been used to treat diffusion-recombination transport problems in semiconductors, is extended to include the case of charge-carrier transport in the presence of a temperature gradient. Reflection and transmission coefficients for carriers entering a bulk region of a semiconductor are calculated as a function of the bulk-layer thickness, as well as in terms of ’’microscopic’’ backscattering and absorption probabilities. The analysis is carried out for the case where the temperature gradient and electric field are constant and small.
High-conductivity high-specific-heat copper for cryogenic applications
Authors: Steyert W. A.
Published: February 2003

Residual resistance ratios have been measured for five different types of copper after various mechanical and thermal treatments. Inexpensive methods of fabricating wires with ratios greater than 1000 are proposed. The development of copper with a very high specific heat at 4 K as well as high electrical and thermal conductivity is reported.
Radiative emission during the threshold on-state of a chalcogenide amorphous semiconductor
Authors: Vezzoli Gary C.
Published: February 2003

The technique for measuring the radiation emitted during the on-state of a chalcogenide amorphous semiconductor threshold device is described. The implications of the radiation emission are described and the limitations of interpretive conclusions are pointed out.
1/f noise in the variance of Johnson noise
Authors: Beck H. G. E. , Spruit W. P.
Published: February 2003

A criterion is derived for the detection limit of 1/f noise in the variance of the Johnson noise in thermal equilibrium. Experiments confirm the derived criterion. The results support the idea that in thermal equilibrium the resistance shows 1/f noise.
Temperature dependence of the relaxation of injected charge at the polycrystalline-silicon–SiO2 interface
Authors: Hickmott T. W.
Published: February 2003

Electron injection can occur at the polycrystalline-silicon–SiO2 interface of a polycrystalline-silicon gate MOS capacitor when relatively low negative voltages are applied to the gate. If the interface is improperly annealed, the flat-band shift due to injected electrons can be several hundred millivolts for 350-Å-thick oxides. The temperature and voltage dependence of the relaxation of injected negative charge has been measured. The amount of charge injected is higher and its relaxation is faster at higher temperatures. The moment of charge can shift towards the substrate silicon-SiO2 interface at negative gate voltages whose absolute magnitudes are less than the flat-band voltage of the capacitor.
Current transfer in multifilamentary superconductors. II. Experimental results
Authors: Ekin J. W. , Clark A. F. , Ho J. C.
Published: February 2003

Measurements are reported of the current-transfer effect in a 0.58×0.68-mm NbTi (180 filament) copper-matrix wire, and in a 0.33×0.66-mm Nb3Sn (3553 filament) bronze-matrix wire at magnetic fields from 2 to 8 T. With a voltage sensitivity of 100 nV, the effect of current transfer in the copper : NbTi wire was too small to be measured at a distance 1 cm from the current contact. In the bronze : Nb3Sn wire, however, the effect was relatively large and resulted in voltage-current characteristics which had an extensive linear region. The slope of the linear region decreased with distance x from the current contact as x−2±0.3 and reached a value of 10−12 Ω cm, for example, at a distance of 3±0.5 cm. Both the magnitude and functional dependence of the measured current-transfer effects correspond closely to that predicted by theory.
Computations of the micromagnetic dynamics in domain walls
Authors: Shir C. C.
Published: February 2003

A numerical model was developed to compute the temporal and spatial variations of the detailed micromagnetic structures of domain walls by numerical integration of the Landau-Lifshitz-Gilbert equation. The fundamental interactions due to anisotropy, exchange, and demagnetization are included. Preliminary results of the structure of a planar domain wall indicate that the wall width is much larger near the film surface than at the center of the film, because the demagnetization fields are significant near the surface and the side boundaries of the domain wall. The instabilities of the numerical integration of the LLG equation are investigated. Several methods were developed to cope with the stiffness which arises when the damping parameter becomes small. The effects of nondimensional film thickness and anisotropy parameters are similar and are less than 10%, with these parameters varying by a factor of 2. On the other hand, the effects of an ion-implantation layer in the film on the wall structure are found to be very significant.
Thermoluminescence and emission spectra of uv-grade Al2O3 from 90 to 500 K
Authors: Cooke D. Wayne , Roberts Hilary E. , Alexander Chester
Published: February 2003

Thermoluminescence (TL) from uv-dosimetry-grade Al2O3 has been studied over the temperature range from 90 to 500 K. Two intense glow peaks are observed at 270 and 435 K as a result of uv irradiation. Thermal activation energies and frequency factors for the 270 and 435 K peaks were determined to be E=0.69 eV and s=3.5×1010 sec−1; and E=1.11 eV and s=7.0×1010 sec−1, respectively. The 270 and 435 K peaks yield identical emission spectra consisting of a broadband (FWHM=90 nm) with a maximum at 420 nm. Also, they both exhibit emission in the red region of the spectrum. Photobleaching experiments revealed that both glow peaks could be readily photobleached by irradiation with either 230 or 410-nm radiation. The glow peak at 435 K is attributed to the thermal annealing of V−OH centers (a hole trapped on an oxygen ion adjacent to a cation vacancy with an OH ion nearby), and it is suggested that the 270 K peak is possibly due to the thermal annealing of V0OH centers (two holes trapped at adjacent oxygen ions next to a cation vacancy with an OH ion nearby). X irradiation produces two additional TL glow peaks at 210 and 385 K and a knee at 300 K. Thermal activation energies and frequency factors obtained for the 210 and 385 K glow peaks are E=0.47 eV and s=1.6×109 sec−1, and E=1.05 eV, s=3.6×1012 sec−1, respectively. Spectral distribution of the emission from these two peaks was identical, consisting of a broadband (FWHM=90 nm) that peaked at 310 nm. Two other types of Al2O3 crystals were investigated. One contained 0.05% chromium + 0.1% titanium by weight and yielded no TL upon uv or x irradiation. A sample containing 0.05% titanium by weight yielded a glow curve with peaks at 280 and 425 K. Trap parameters were determined to be E=0.77 eV and s=4.5×1011 sec−1, and E=1.06 eV and s=1.5×1012 sec−1, respectively. X irradiation produced additional glow peaks at 215 and 355 K and a knee at 265 K. The 215 K peak was the only additional peak sufficiently resolved to allow determination of activation energy (E=0.49 eV) and frequency factor (s=3.3×1010 sec−1). The 280 K emission spectrum peaks at 500 nm (FWHM=135 nm) and also exhibits emission near 310 nm. Spectral distribution of the TL resulting from the 425 K peak indicated a band (FWHM=135 nm) with a maximum at 490 nm.
SnO2/Si solar cells—heterostructure or Schottky-barrier or MIS-type device
Authors: Ghosh A. K. , Fishman C. , Feng T.
Published: February 2003

The performance of SnO2/Si solar cells has been measured and analyzed in detail. This has given us an insight into cell characteristics never revealed in previous studies. Though the device is a junction between two semiconducting materials, SnO2 and Si, it performs like an MIS device and in the thin-oxide limit as a Schottky-barrier device. The dark I-V characteristics are attributed to a combination of thermionic and diffusion processes. The diode constant associated with the former is close to 2 or higher and that associated with the latter is unity. It has been demonstrated that under certain conditions the diode constant can be independent of the reverse-saturation current. An MIS-type model can explain the spectral-response curve, the short-circuit photocurrent, the open-circuit photovoltage, and the light and dark I-V characteristics. A theoretical limit of the efficiency is estimated for the device.
Comparative radiation resistance calculation for graded- and constant-composition n AlxGa1−xAs–p AlzGa1−zAs solar cells
Authors: Hutchby James A.
Published: February 2003

The performance and radiation resistance of a new double-graded-band-gap n AlxGa1−xAs–p AlzGa1−zAs solar cell are theoretically determined. The performance of this device is similar to that of the single-graded-band-gap cell. The power-conversion efficiencies of both graded-band-gap structures are shown to be less sensitive to minority-carrier lifetime degradation than a similar constant-composition n AlxGa1−xAs–p GaAs heteroface cell.
A simple theory of back surface field (BSF) solar cells
Authors: von Roos Oldwig
Published: February 2003

A theory of an n-p-p+ junction is developed, entirely based on Shockley’s depletion layer approximation. Under the further assumption of uniform doping the electrical characteristics of solar cells as a function of all relevant parameters (cell thickness, diffusion lengths, etc.) can quickly be ascertained with a minimum of computer time. Two effects contribute to the superior performance of a BSF cell (n-p-p+ junction) as compared to an ordinary solar cell (n-p junction). The sharing of the applied voltage among the two junctions (the n-p and the p-p+ junction) decreases the dark current and the reflection of minority carriers by the builtin electric field of the p-p+ junction increases the short-circuit current. The theory predicts an increase in the open-circuit voltage (VOC) with a decrease in cell thickness. Although the short-circuit current decreases at the same time, the efficiency of the cell is virtually unaltered in going from a thickness of 200 μm to a thickness of 50 μm. The importance of this fact for space missions where large power-to-weight ratios are required is obvious.
Infrared spectral detectivity of Cr-doped GaAs
Authors: Look D. C.
Published: February 2003

The room-temperature spectral detectivity of Cr-doped GaAs has been examined in the impurity excitation region out to 1.7 μ, a range which includes the wavelengths of several important lasers as well as low-loss optical fibers. The results include values of D* greater than 1011 cm Hz1/2/W in the photoconductive mode, and 1010 cm Hz1/2/W in the photomagnetoelectric mode. Small carrier lifetimes, ∼10−8 sec, offer the potential of high-speed operation; however, the measured response times are much larger, ∼10−3–10−2 sec, because of very high input impedances. Formulas are presented to show the variation of D* with relevant parameters, and means of improving the performance are discussed.
Computer simulation of interacting dislocation motion resisted by pointlike barriers
Authors: Hanson K. , Morris J. W.
Published: February 2003

We consider interacting dislocations of like Burgers vectors in glide through random arrays of pointlike barriers. Two configurations are considered: first, many dislocations in the same glide plane; second, many dislocations on parallel glide planes, initially configured in a low-angle-tilt boundary. In our simulation, the glide plane(s) are periodic in all directions. In previous work, we determined the dimensionless athermal critical resolved shear stress for a single dislocation. The present results show that the athermal critical resolved shear stress for glide of a system of interacting dislocations τa* is related to that for a single dislocation system τ0* by the equation τa*=τ0* exp{−(π/h)[1/3λ (βc)1/2]1/2}, where h is a dimensionless average dislocation spacing, λ is a dimensionless dislocation line tension, and βc is a dimensionless barrier strength. The resulting dislocation morphologies can be explained in terms of the above parameters. Also, the stability of a moving low-angle-tilt boundary can be predicted.
Single-crystal elastic constants of Al2Cu
Authors: Eshelman F. R. , Smith J. F.
Published: February 2003

The single-crystal elastic constants of tetragonal Al2Cu have been measured over the temperature range 4.2–300 K by the pulse-echo-overlap technique. The directly measured constants show a normal monotonic decrease in magnitude with increasing temperature but with C44 showing the least change. The anisotropy ratios C33/C11, C12/C13, and C44/C66 show only small percentage changes between 4.2 and 300 K, but 2C44/(C11−C12) changes by nearly a factor of 2. Comparison of data for Zr2Ni with that for Al2Cu indicates some importance of atomic size effects. A Debye temperature of 402 K was evaluated from the elastic constants at 4.2 K.
The influence of structural relaxation on the density and Young’s modulus of metallic glasses
Authors: Chen H. S.
Published: February 2003

The Young’s modulus E of metallic glasses increases by ∼7% while the density ρ increases by only ∼0.5% upon annealing near the glass transition temperature. ρ and E of an ’’ideal’’ glass are calculated to approach the crystalline values within 0.5 and 10%, respectively. The large decrease in E of ∼30% observed upon vitrification of many glass-forming alloys may be attributed mainly to the frozen-in excess volume. The rates of increase in E associated with decrease in volume V, −d lnE/d lnV, during structural relaxation, crystallization, and thermal expansion are large and ∼15, 17, and 10, respectively. Structural reconstruction and consequent electron redistribution near the Fermi surface are suggested to be responsible for the large −d lnE/d lnV observed.
Epitaxial deposition of GaAs and GaAsP on Ge substrates
Authors: Jäger H. , Seipp E.
Published: February 2003

The successful deposition of GaAsP epitaxial layers on (001) -Ge substrates is reported. The Tietjen and Amick vapor-phase epitaxial technique is applied without modification. Hence the deposition can be transferred to technical production. Autodoping, i.e., the incorporation of Ge atoms in the epitaxial layer, was suppressed by choosing adequate back-surface passivation layers and by proper control of the epitaxial program steps. Evidence for the suppression of autodoping was given by carrier concentration measurements and by photoluminescence spectroscopy of GaAs layers on Ge substrates. The latter revealed no signs of Ge acceptors in the GaAs epitaxial layers, which means the concentration of Ge must be lower than at least 5×1014 cm−3. Based on this result the deposition of GaAs1−xPx on Ge substrates was studied with x?0.38 as an aim. After having attained an acceptable state of progress the layers were tested by zinc diffusion to get p-n junctions and light-emitting diodes. Commercial GaAsP samples were simultaneously subjected to the same treatment for control. We finally succeeded in producing diodes emitting red light with a dominant band-to-band peak of 15 nm width at room temperature.
Epilayer-substrate interfaces of Ge-doped GaAs grown by liquid-phase epitaxy
Authors: Lum W. Y. , Clawson A. R. , Elder D. I. , Wieder H. H.
Published: February 2003

The interfaces between Ge-doped GaAs homoepitaxial layers grown by liquid-phase epitaxy and their semi-insulating substrates have been characterized by photoluminescence and charge-carrier transport measurements. Our data suggest that a portion of the thermally generated As vacancies in the immediate vicinity of the interface are occupied by Ge atoms; this leads to a reduction in the deep-level complexes attributed to CAs–VAs associated with the thermally induced degradation of the substrate surface prior to epitaxial growth.
Thermal- and optical-excitation processes in GaP : Cu
Authors: Fagerström P. O. , Grimmeiss H. G. , Titze H.
Published: February 2003

The properties of two deep-level centers caused by Cu doping of GaP have been investigated in p+n diodes and photoconductors by photocurrent methods. Spectra of the cross sections for optical transitions from the valence band to the impurity levels are presented. The band-gap energy and the threshold energy of the deeper level (Ev+0.7 eV) show a similar temperature dependence from 85 to 300 K. The possible influence of other impurities on the optical threshold energy of this center is discussed. The absolute magnitude of the optical cross section for excitation from the valence band to this deep level is temperature dependent. Thermal excitation from the valence band to the shallower level (Ev+0.5 eV) is characterized by an activation energy of 0.54 eV, deduced from the temperature dependence of the thermal-emission rate. A value of about 10−13 cm2 is estimated for the thermal hole-capture cross section at 200 K.
Deep trapping effects at the GaAs-GaAs : Cr interface in GaAs FET structures
Authors: Houng Y. M. , Pearson G. L.
Published: February 2003

Transient capacitance measurements were made in order to study the interface properties of FET-type devices with and without LPE buffer layers. No detectable traps were found in the buffered devices, whereas two deep hole traps, located 0.58 and 0.81 eV above the valence band, were detected in the unbuffered FET devices when the gate-depletion region approached the substrate interface. The trap concentrations were 1×1016 and 2×1015 cm−3, respectively. An interface model was developed and used to show that the minority-carrier trapping effects which appeared in the active layer are actually due to the image effect of majority-carrier traps in the Cr-doped substrate acting through the interface space-charge region.
High-frequency Stark effect on optically excited atoms of a plasma in the static magnetic field
Authors: Kim S. H.
Published: February 2003

The effect of three-dimensional high-frequency turbulent electric fields on the σ+, σ−, and π components of the allowed 11S0-31P1 line and the forbidden 11S0-31D2 lines in the laser absorption spectra of a magnetoactive He I plasma is investigated by means of the coupled equations for the probability amplitudes of atomic states. The spectral shifts of σ+, σ−, and π components and the satellites about the forbidden lines are derived. The calculation reveals that the ratio of the intensity of the near satellite to that of the far satellite is different from the one obtained by second-order perturbation theory or the three-level rotating-wave approximation. The observations of the line shifts permit a quantitative determination of the intensity of the stochastic electric field, the average electron density, and the relative direction of the local magnetic field with respect to the linearly polarized laser field.
The high-pressure absorption spectra of the CO2 10.6- and 9.4-μm laser bands
Authors: Miller J. L.
Published: February 2003

A density matrix formulation of the interaction of radiation with bands of pressure-broadened overlapping spectral lines is described which includes the effects of interaction between neighboring lines due to collisions. A measurement of the abosrption coefficients at the centers of several lines of the 10.6- and 9.4-μm bands of CO2 for CO2 and mixtures of CO2 and N2 and He at absolute pressures to 18 atm is reported. The calculated spectra of these bands are given for the two limiting forms of overlapping line theory: one which maximizes line interaction and another which neglects it, calculating the spectra as sums of Lorentzian-shaped lines. The data are shown to be in good agreement with the theory which maximizes the line interaction.
Effect of preacceleration voltage upon ion-beam divergence
Authors: Whealton J. H. , Grisham L. R. , Tsai C. C. , Stirling W. L.
Published: February 2003

The effect of an insulator coating on the plasma electrode of a duoPIGatron ion source on ion-beam optics was examined theoretically and experimentally. The effect of a preacceleration potential, applied between the insulated electrode and the target cathode of the source plasma, on ion optics was also examined. A principal result is that this electrode arrangement with precel gives a much lower beam divergence than the same arrangement without precel. Detailed comparisons between the data and calculations are presented.
Direct recording of optical-gain spectra from ZnO
Authors: Hvam J. M.
Published: February 2003

Optical-gain spectra from ZnO at 300 and 1.8 K have been recorded by a new modulation technique. The gain is extracted from amplified spontaneous emission by modulation of the excitation length and synchronous detection. The method is particularly suited for measuring gain coefficients in the range −100<g<500 cm−1. The observed gain spectra from ZnO are interpreted in terms of exciton-exciton collision processes (300 K) and excitonic molecule transitions (1.8 K).
Fabrication and evaluation of erosion-resistant multispectral optical windows
Authors: Hopkins R. H. , Kramer W. E. , Brandt G. B. , Schruben J. S. , Hoffman R. A. , Steinbruegge K. B. , Peterson T. L.
Published: February 2003

Thin ZnS claddings can be bonded to ZnSe substrates to form a composite window designed to display rain-erosion resistance equivalent to ZnS alone, but with broadband transmittance and scattering levels comparable to ZnSe. Joining of the window components is achieved by means of a thin As-S-Se glass layer, using a technique we have termed optical brazing. Optical path differences in the composite window are primarily due to heterogeneities in the ZnS and ZnSe components; no degradation in optical quality due to the glass bond is evident. Rain-erosion data confirm that the composite window is as resistant to multiple drop impact damage as monolithic ZnS.
Red-emitting Ga(As,P)/(In,Ga)P heterojunction lasers
Authors: Kressel H. , Nuese C. J. , Olsen G. H.
Published: February 2003

This paper describes in detail the properties of vapor-grown double-heterojunction lasers of Ga(As,P)/(In,Ga)P with room-temperature threshold current densities as low as 3400 A/cm2 at 7000 Å and 6600 A/cm2 at 6800 Å. These thresholds are three to eight times smaller than those of (Al,Ga)As lasers in this wavelength range due to the shorter-wavelength direct-indirect transition in Ga(As,P). The optical and electrical characteristics of the Ga(As,P)/(In,Ga)P lasers are found to be similar to those of (Al,Ga)As, with fundamental transverse-mode operation to 70 °C, and spontaneous carrier lifetimes between 5 and 8 nsec typically observed at low current densities.
Effect of Mg diffusion on Ti-diffused LiNbO3 waveguides
Authors: Noda Juichi , Fukuma Masaharu , Saito Shoichi
Published: February 2003

A method for compensation of the index increment yielded by Li out-diffusion during Ti diffusion for the LiNbO3 waveguide formation is presented. Mg diffusion decreases the extraordinary refractive index, and its diffusion rate is far faster than that of Ti diffusion. An appropriate Mg diffusion condition is determined for eliminating the Li out-diffusion influence. Excellent optical confinement in the Ti-diffused LiNbO3 Y-cut strip waveguide is demonstrated with Mg diffusion.
Nonreciprocal reflection of electromagnetic waves from magnetized ferrite
Authors: Srivastava N. C.
Published: February 2003

The reflection of a uniform plane wave from a ferrite magnetized normal to the plane of incidence has been investigated. The conditions for the occurrence of ordinary and total reflection from a lossless planar ferrite have been tabulated for all possible combinations of the relevant parameters. The phase shift on total reflection from a lossless ferrite is found to be nonreciprocal and magnetically tunable. The absorption of electromagnetic power on reflection from a lossy ferrite is also nonreciprocal. The dependence of differential phase shift and reflection loss on various parameters has been numerically investigated. The results indicate the utility of magnetized ferrite in reflection-beam differential phase shifter and isolater, operated in the millimeter-wavelength region.
Adiabatic and pendulum approximations to the retarded Josephson equation
Authors: Schlup W. A.
Published: February 2003

The retarded Josephson equation, which is a second-order differential-integral equation, can be approximated by differential equations in different ways. There are the well-known adiabatic approximations which are justifiable for small ac-voltage amplitudes and in the slow-motion regime. Another type of approximation makes use of the pendulum analogy, where the arguments of the functions entering in the adiabatic current phase relation are replaced by time averages. Several modifications of this average pendulum approximation will be discussed. In particular, the characteristics of these different approximations are compared with the exact result in a limit where the agreement should be rather good. In the same limit the solutions are also investigated by asymptotic expansions under very general conditions.
Field theory for interdigital transducers
Authors: Zuliani M. J. , Ristic V. M.
Published: February 2003

The analysis of quasiacoustic-wave excitation by the uniform interdigital transducer is approached from a field point of view. Fields within the transducer are expressed in terms of a set of normal-mode functions which have been defined specifically for the interdigital array. Dispersion relations for these normal-mode functions are found to display band-gap regions with complex wave numbers. The complex wave number is responsible for the excitation process and permits a solution of the boundary conditions at both ends of the transducer structure. It is shown that the radiation fields excited by the transducer grow according to the dictates of a sine hyperbolic function from one end of the transducer to the other.
Cathodoluminescence of AlxGa1−xAs grown by liquid-phase epitaxy
Authors: Levin E. R. , Ladany I.
Published: February 2003

Small-area contrast fluctuations observed in cathodoluminescence-mode SEM images of thin AlxGa1−xAs layers grown by liquid-phase epitaxy on GaAs : Cr substrates are attributed to local variations in alloy composition. Quantitative estimates of the composition excursions are obtained from the variations in CL intensity by calibration against compositions known from electron-probe microanalysis. In a typical sample, the CL variations are shown to correspond to peak-to-peak fluctuations of about 1 at.% of Al and occur over irregular regions generally in the range 6–20 μm in diameter.
Broadband GaAs transmission photocathode
Authors: Antypas G. A. , Escher J. S. , Edgecumbe J. , Enck R. S.
Published: February 2003

The operational range of the glass-sealed negative-electron-affinity GaAs photocathode has been extended to 3.0 eV by increasing the Al concentration of the GaAlAs passivation layer and decreasing its thickness to approximately 0.3 μm.
Switching measurements on Josephson memory loops
Authors: Lum W. Y. , Chan H. W. K. , Van Duzer T.
Published: February 2003

This paper corrects and clarifies a previously reported dependence of current-transfer time on loop and junction parameters for Josephson-junction memory cells.
Deuterated polyethylene microspheres of variable density for laser-fusion targets
Authors: Halpern Gerald M. , Kim Hyo-Gun
Published: February 2003

This paper describes the experimental procedure we have developed for producing spherical deuterated polyethylene targets with a continuum of densities in the range 20–60% that of solid (ρsolid?1.0 g/cm3). These spheres (termed ’’microsponges’’) are typically 80–300 μm in diameter and are highly porous networks with average pore sizes of a few microns or smaller. The technique consists of (i) forming solid (i.e., normal density) microspheres by pulverizing and spheroidizing the (CD2)n starting material, (ii) cross linking the polyethylene chains in a γ-ray flux, (iii) swelling the cross-linked network in an appropriate hot solvent such as p-xylene, and (iv) rapidly extracting the solvent to ’’freeze-in’’ the expanded structure in the final target. A quantitative model based upon the theory of swollen networks has been employed to correlate the measured densities with the experimental parameters, such as radiation dosage, solvent type, and swelling temperature.
Variations in composition in binary and ternary semiconductors utilizing electrolyte electroreflectance: A topographical investigation
Authors: Pollak Fred H. , Okeke Cajetan E. , Vanier P. E. , Raccah Paul M.
Published: February 2003

Utilizing electrolyte electroreflectance, we have developed a unique approach for determining the variations in composition x across the face of binary and ternary alloy semiconductors. This technique is based on the fact that the energies of features in the optical spectra of semiconducting alloys depend on x in a continuous manner. Any shift in energy of a particular electroreflectance peak is measured using a small scanned light spot. Corresponding variations in x can be determined to within about 1% with a spatial resolution of about 100 μm. This technique is nondestructive and can readily be employed under atmospheric conditions at room temperature. Results are presented for a number of alloys, including Hg1−xCdxTe, Ga1−xAlxAs, InAsxSb1−x, and Pb1−xSnxTe. The advantages of our approach in relation to microprobe or luminescence methods is discussed.
A model of densification with simultaneous grain growth
Authors: Ikegami Takayasu , Tsutsumi Masayuki , Matsuda Shin-ichi , Shirasaki Shin-ichi , Suzuki Hiroshige
Published: February 2003

A densification model in which grain growth and densification progress simultaneously in a powdered compact produced the relation between the relative density ρ and average particle/grain size R, logρ (1−ρ0)/ρ0(1−ρ) =k4KG log(R/R0), where R0 is the initial particle size, ρ0 is the green density, KG is the dimensionless parameter dependent on the spread of the distribution of particle/grain size in the compact, and k4=SS/(1−ρ) S (SS is the pore surface area of the compact and S is the total area of particles/grains). Sintering data of BaCl2- and halogen-doped MgO compacts deviated slightly from the theoretically calculated relation. This discrepancy is interpreted in terms of the heterogeneously packed structure of particles/grains.
Crystallographic study of semi-insulating polycrystalline silicon (SIPOS) doped with oxygen atoms
Authors: Hamasaki M. , Adachi T. , Wakayama S. , Kikuchi M.
Published: February 2003

Thermally deposited silicon films doped with oxygen atoms and used as passivation films on silicon devices have been studied with transmission electron microscopy, x-ray diffraction, and ESCA. The films contain at least two phases, silicon microcrystals and silicon oxide. The size of the microcrystals in as-deposited films was dependent both on the deposition temperature and on the oxygen concentration. Heat treatment caused crystal growth which depended mainly on the annealing temperature and weakly on the annealing time. The lattice constant of the microcrystals was directly related to their size. The silicon oxide phase in as-deposited films was found to be SiO1.4. The results suggest ’’mosaic’’ model of the films which are amorphous when the diameter of the silicon microcrystals was less than 10 Å.
Differential studies of dual-dielectric charge-storage cells
Authors: Thornber K. K. , Kahng D. , Boulin D. M. , Neppell C. T. , Sundburg W. J.
Published: February 2003

By means of novel differential techniques, we have studied the writing and erasing dynamics of DDC cells and, in the process, uncovered a number of unexpected phenomena which play an important role in these processes. For example, we find writing currents qualitatively similar to, but considerably in excess of, those predicted earlier by Fowler-Nordheim studies on similar MOS structures. We find that these devices can be written with high and undiminished efficiency to 7–10 V of flatband shift depending on insulator thickness, and we determine the limiting source of efficiency degradation beyond these levels. In erase, we find an interesting enhancement due, we believe, to electron-electron repulsion of the net stored charge. By studying the reversible motion of the stored-charge centroid at high temperatures, we determine that the effect of the interfacial dopant on the outer insulator extends about 80 Å into this layer. Other studies indicate an effect on the thin oxide to be less than 20 Å. Low-field long-time charging results point to a Fowler-Nordheim–like writing current versus oxide field extending at least from 4.2 to 10 MV/cm, a range of no less than 109 in current density for oxide thicknesses of 80 Å or more. All these features and others were found and investigated using quite standard flatband measurements, albeit, by the use of novel patterns of writing and erasing.
Transient velocity characteristics of electrons in GaAs with Γ-L-X conduction band ordering
Authors: Kratzer S. , Frey Jeffrey
Published: February 2003

The transient velocity characteristics of electrons in GaAs have been calculated for uniform electric fields at room temperature. Three-level band-structure data have been used with a Monte Carlo simulation program to predict electron drift velocity, temperature, and valley population fractions as functions of position and electric field. Results for two three-level band-structure models are compared with those for the previously accepted two-level model. Transient and steady-state properties are seen to be sensitive to some material parameters whose values are still in dispute.
Carrier transport in oxygen-rich polycrystalline-silicon films
Authors: Tarng M. L.
Published: February 2003

A symmetrical-Schottky-barrier (SSB) band model is proposed for the carrier transport in oxygen-rich polycrystalline-silicon films. Semiquantitative analyses were made, comparing a one-dimensional depletion approximation, with voltage and temperature-dependent current measurements. The band gap is found to be similar to that of single-crystalline Si, with electrons as the majority carriers. A net donor state density of 2.3×1019 cm−3, 0.12 eV below the conduction band edge, exists in the grains of the polycrystalline silicon, and these donors are completely ionized in the presence of large grain-boundary surface states. This results in a grain-boundary surface-charge density of −2.3×1013q/cm2, setting up overlapped space-charge regions which give rise to the SSB band structure with a maximum band bending of 0.44 eV. The Fermi level is found to be pinned at the midgap at the grain boundaries—suggesting the existence of an amorphous intergrain layer. At and above 373 K, the carrier transport is by thermionic emission, TE. Below 373 K, it is dominated increasingly by a tunneling process, i.e., thermionic field emission, TFE. The current increases with applied voltage according to a sinh function. A calculated effective Richardson constant A** of ∼70 A cm−2 K−2 and a lower quantum-mechanical reflection, but higher electron-optical phonon backscattering than those of a metal-Si Schottky barrier, are found in the TE regime. The grain size deduced from the model agrees with that measured with a TEM: 100±41 Å. The band picture also agrees with the photoelectric threshold measurement.
Resistivity and microstructure of polycrystalline Au films deposited by rf bias-diode and triode sputtering
Authors: Cornely R. H. , Ali T. A.
Published: February 2003

Two different sputtering deposition methods, rf bias-diode and triode sputtering, were used to prepare highly polycrystalline films with mean crystallite size between 38 and 85 Å. The bias-sputtered films were metallically conductive at 20 Å nominal film thickness and had a large component of electrical resistivity independent of temperature. Films prepared with more than 5% rf bias had atomically roughened surfaces that showed completely diffused surface scattering. The reflection coefficient for grain-boundary scattering was found experimentally to be 0.27 and it was verified that the Mayadas-Shatzkes theory for polycrystalline metal films can be applied even when the mean crystallite size is as small as 40 Å.
Si-CdS heterojunction memory diodes
Authors: Duncan W. , Smellie A. R.
Published: February 2003

The I-V characterisitcs of pSi-nCdS heterojunction diodes have been investigated, the diodes being fabricated by growing epitaxial CdS films on silicon substrates under UHV conditions. Under certain fabrication conditions, viz., a substrate-acceptor doping ∼1019 cm−3, a CdS film resistivity ∼102Ω cm, and Schottky contacts to the CdS, it has been observed that the diode possesses two resistance states. For one of the states, the high-resistance state, the current is an exponential function of bias voltage, whereas for the other, the low-resistance state, the current is a linear function of voltage. Switching from the high to the low state occurs with a few V reverse bias applied to the heterojunction and will remain in this state with the bias voltage reduced to zero, and remain thus for a few weeks, i.e., no hold-on voltage is required. To revert to the high state, a forward-bias voltage is applied to the heterojunction and the diode switches to its initial state when a circuit current of a few mA flows. A binary-memory array of pSi-nCdS diodes has been constructed with a bit density ≳103 cm−2, and when operated under pulsed-bias conditions, continuous switching at 5×103 Hz has been obtained and the number of switching cycles ∼107 before any degradation takes place. A descriptive model of the diode has been developed which attempts to show that trap defects within the CdS film are responsible for the memory and switching characteristics.
Superconducting thin-film gradiometer
Authors: Ketchen Mark B. , Goubau Wolfgang M. , Clarke John , Donaldson Gordon B.
Published: February 2003

We describe the design, fabrication, and performance of planar thin-film dc SQUID’s and planar gradiometers in which a dc SQUID is incorporated as a null detector. Each gradiometer was fabricated on a planar substrate and measured an off-diagonal component of changes in the magnetic field gradient. The gradiometer with the highest sensitivity had 127×33-mm loops that could be connected in parallel or in series: The sensitivities were 2.1×10−13 and 3.7×10−13 T m−1 Hz−1/2, respectively. The intrinsic balance of the gradiometers was about 100 ppm for fields parallel to their plane, and a balance of about 1 ppm could be achieved for fields perpendicular to their plane. When the series-loop gradiometer was rotated through 360° in the earth’s field, the output returned to its initial value to within an amount corresponding to a balance of 1 ppm. Possible improvements in sensitivity are discussed.
Point-contact Josephson mixers at 130 GHz
Authors: Claassen J. H. , Richards P. L.
Published: February 2003

The properties of point-contact Josephson junctions operated as mixers with an external local oscillator at 130 GHz have been studied, and the results compared with predictions of the resistively shunted junction model. It was found that the junction’s output noise could be within a factor of 1.5 of the model prediction based on the thermal-driving noise. When the coupling to the rf source was optimized, a factor of 2 discrepancy was typical. The measured conversion efficiency agreed with the model, within the experimental uncertainty in the equivalent microwave circuit. The best coupling was achieved in full-height waveguide. The best overall performance, measured using the hot/cold source technique, was a single sideband conversion efficiency of 0.30 and a mixer-noise temperature of 180 K (both ±20%). The best junctions were made of Nb, with carefully prepared points. Nonideal behavior in other junctions is ascribed to heating effects. There is some evidence that junctions whose resistance exceeds a threshold value of ∼60 Ω are no longer well described by the RSJ model. A discussion is given of possible improvements in performance with better junctions or improved rf matching.
Magnetic precipitation hardening and Bloch-wall pinning in an 85Co-12Fe-3Nb alloy
Authors: Prokop G. S. , Soffa W. A.
Published: February 2003

The development of intrinsic coercivity during isothermal aging of a solution treated and quenched 85Co-12Fe-3Nb alloy was studied. The hysteresis loops, initial susceptibility, and magnetization were also measured and provided information for identifying the mechanism of coercivity development. Successive hysteresis loops clearly demonstrate that Bloch-wall pinning dominates the reversal mechanism in this alloy. The maximum coercivities found during isothermal aging were 21.5, 33, and 37 Oe at 800, 750, and 700 °C, respectively. The microstructure at maximum coercivity consisted of Widmanstätten plates of a phase similar to Co3Nb which formed along the {111} planes of the ferromagnetic matrix. At the lowest aging temperature, 700 °C, a metastable ordered L12 γ′ phase formed during the early aging times resulting in a significant increase in the coercivity compared to the solution-treated samples. The periodic microstructure associated with the γ′ phase also resulted in an extremely low initial susceptibility. After prolonged aging, the γ′ was replaced by the Widmanstätten precipitates. The decrease in coercivity for long aging times at 750 and 800 °C was the result of continued coarsening of the Widmanstätten morphology. The alloys magnetically hardened by the periodic γ′ microstructure exhibited hysteresis behavior indicative of homogeneous wall pinning, whereas the alloys hardened by the Widmanstätten precipitate showed the behavior characteristic of inhomogeneous wall pinning.
Multistep ionization in the positive column of low-pressure Na-Ne and Ne discharges
Authors: Vriens L.
Published: February 2003

Model calculations on the positive column of low-pressure metal-vapor–noble-gas and noble-gas discharges usually account for direct and two-step electron-impact ionization. The poor agreement between experiment and model calculations for certain discharge conditions has led us to a detailed analysis of the ion formation in a metal-vapor–noble-gas (Na-Ne) and a noble-gas (Ne) positive column. Multistep electron-impact ionization via many higher excited states is found to become a dominant process already at much lower pressures and current densities than considered so far. The multistage ionization will have the effect of lowering the electric field strength. Its highly nonlinear dependence on discharge current will further strongly favor the contraction observed, e.g., in noble-gas discharges.
A comparative study of laser and thermal annealing of boron-implanted silicon
Authors: Narayan J. , Young R. T. , White C. W.
Published: February 2003

Transmission electron microscopy has been used to study the effects of high-power laser pulses on as-grown and boron-implanted silicon. No defects (dislocations, dislocation loops, and stacking faults) were observed in either as-grown or boron-implanted (doses 3×1015 and 2×1016 ions cm−2) silicon after pulsed laser treatment. In thermally annealed specimens, on the other hand, a significant amount of damage was retained even after annealing at 1100 °C for 30 min. After thermally annealing the implanted laser-treated specimens at 600 and 900 °C for 30 min, no defects were observed for low-dose specimens; however, in high-dose specimens, precipitation of boron occurred after 600 °C annealing and it increased after annealing at 900 °C. These results and the electrical measurements on these samples suggest that the boron atoms in the precipitates are electrically inactive.
Channeled-ion implantation of group-III and group-V ions into silicon
Authors: Furuya T. , Nishi H. , Inada T. , Sakurai T.
Published: February 2003

Implantation of group-III and group-V ions along [111] and [110] axes of silicon have been performed using a backscattering technique, and the depth profiles of implanted ions have been measured by the C-V method. The range of channeled Ga ions is the largest among the present data, and a p-type layer of about 6 μm is obtained by implantation at only 150 keV. The carrier profiles of channeled Al and Ga ions with deep ranges do not show any distinguishable channeled peak contrasting with the B, P, and As channeling which gives a well-defined peak. The electronic stopping cross section (Se) of channeled P ions agree well with the results of Eisen and Reddi, but in B channeling, the discrepancies of 10–20% are observed among Se values obtained experimentally by three different groups.
Theoretical analysis of heat flow in horizontal ribbon growth from a melt
Authors: Zoutendyk John A.
Published: February 2003

A theoretical heat flow analysis for horizontal ribbon growth is presented. Equations are derived relating pull speed, ribbon thickness, thermal gradient in the melt, and melt temperature for limiting cases of heat removal by radiation only and isothermal heat removal from the solid surface over the melt. Geometrical cross sections of the growth zone are shown to be triangular and nearly parabolic for the two respective cases. Theoretical pull speed for silicon ribbon 0.01 cm thick, where the loss of latent heat of fusion is by radiation to ambient temperature (300 K) only, is shown to be 1 cm/sec for horizontal growth extending 2 cm over the melt and with no heat conduction either to or from the melt. Further enhancement of ribbon growth rate by placing cooling blocks adjacent to the top surface is shown to be theoretically possible.
Acoustical determination of the shear relaxation functions for polymethyl methacrylate and Epon 828-Z
Authors: Sutherland H. J.
Published: February 2003

A differential-path ultrasonic technique is used to obtain the acoustic propagation characteristics of shear waves in polymethyl methacrylate (PMMA) and Epon 828-Z. The acoustic velocity and attenuation are measured at 0.5, 1, and 2 MHz over a temperature range of −60 to 70 °C. Time-temperature superposition is used to transform these data into their ’’master curve’’ form. Using this representation, the shear-stress relaxation modulus is then deduced and combined with the previously determined longitudinal data to form a complete characterization of the short-time linear response of these two homogeneous and isotropic viscoelastic polymers.