bluuebunny/crossref_metadata_2025 huggingface dataset:
Incorporation of carbon dioxide laser-grown oxide layers into conventional metal-oxide-silicon devices
Authors: Boyd Ian W.
Published: February 2003

The dielectric breakdown strength of CO2 laser-grown oxides is measured and compared with other SiO2 films grown by well-established techniques. For the first time, the successful application of laser technology with existing Integrated Circuit preparation techniques to manufacture simple Metal-Oxide-Silicon devices is reported. Optimum processing conditions for CO2 laser oxidation of Si are described which eliminate such common laser-induced faults as slip dislocation and wafer warpage. The average field strength exhibited by the first capacitor to break down from several batches of 100 incorporating a laser-grown oxide layer was found to be 8.3 MV cm−1.
Effect of oxidizing and reducing atmospheres at elevated temperatures on the electrical properties of zinc oxide varistors
Authors: Sonder E. , Austin M. M. , Kinser D. L.
Published: February 2003

Voltage–current characteristics have been measured for varistors that have been heated in reducing or oxidizing gases. Reducing environments produced large decreases in the leakage resistance. However, the original varistor characteristics could be restored by subsequent heating in oxidizing ambients. The oxygen partial pressure below which degradation occurred is 100 Pa at 800 °C. Degradation by reducing ambients occurred at much lower temperatures (150–500 °C) than did restoration of the varistor characteristics by oxidizing ambients (500–700 °C). An explanation of the observed behavior is proposed.
Proximity effect correction for electron beam lithography by equalization of background dose
Authors: Owen Geraint , Rissman Paul
Published: February 2003

Compensation for the proximity effect in electron lithography can be achieved by equalization of the backscattered dose received by all pattern points. This is accomplished by exposing the reverse tone of the required pattern with a beam diameter dc=2σb ×(1+ηe)−1/4 and dose Qc=Qe ×[ηe/(1+ηe)], where σb is the radius of the Gaussian spatial distribution function of backscattered electrons at normally exposed pixels, ηe is the ratio of backscattered to forwardscattered energy, and Qe is the dose delivered to normally exposed pixels. This correction method has been confirmed to work for 500-nm features by computer simulation of electron beam exposure and development and by experiment on a raster scan electron beam lithography system.
Effects of detector coil size and configuration on measurements of the magnetoencephalogram
Authors: Cuffin B. Neil , Cohen David
Published: February 2003

Estimates of the location and strength of electrical sources in the brain can be made using the magnetoencephalogram (MEG) which is the measurement of the brain’s magnetic field. Since the size and configuration of the field-sensing coils used in MEG detectors can affect these measurements, the effects must be known and taken into consideration in making these estimates. This paper uses computer modeling methods to determine the effects of coil size and configuration on measurements of a dipolar source in a spherical model of the head. The measurements are as follows: a magnetometer, which uses a single coil; a first-order, in-line gradiometer, which uses two coils at different distances from the head; and a first-order, side-by-side gradiometer, which uses two side-by-side coils at the same distance from the head. For the magnetometer it is found that the effects of coil size are large enough that the source depth can be overestimated by as much as 0.65 cm and its strength underestimated by as much as 31%. For the in-line gradiometer, the effects of the back coil on measurements of sources near the surface of the sphere are small as compared to the effects of the finite size of the front coil; for deeper sources, the effects are found to be large but nearly independent of the size of the back coil. For the side-by-side gradiometer, the effects of coil size are large enough that the dipole depth can be overestimated by as much as 0.45 cm and its strength underestimated by as much as 37%. In addition, the effects of tilting the two coils used in the side-by-side gradiometer are investigated. It is found that this tilting does not cause the measurements to be more localized over the source. Finally, the effects of coil size on estimates of source depth made from side-by-side gradiometer measurements of the falloff of field amplitude with distance from the sphere are determined. It is found that the effects are large enough to cause the depth to be overestimated by as much as 0.5 cm.
Density and temperature variations in pulsed discharge lasers
Authors: Milonni P. W.
Published: February 2003

Approximate expressions are derived for the density and temperature variations in a pulsed discharge laser. The analysis is specialized to the case of the electron-beam-excited CO2 laser. In particular, a procedure is suggested for including the refractive index variations in computer codes modeling loaded resonator characteristics of high-power pulsed lasers.
1.3-μm InGaAsP continuous-wave lasers vapor grown on (311) and (511) InP substrates
Authors: Olsen G. H. , Zamerowski T. J. , DiGiuseppe N. J.
Published: February 2003

Continuous-wave (cw) lasing behavior has been observed with 1.3-μm InGaAsP lasers grown on (311) and (511) InP substrates. Threshold current densities of (311) devices were 30% lower than those on comparable (100) devices (1000 vs 1300 A/cm2). The photoluminescence intensity from p+–InGaAsP ‘‘cap’’ layers is more than an order of magnitude greater than on (100) devices.
High pressure studies of Ge using synchrotron radiation
Authors: Qadri S. B. , Skelton E. F. , Webb A. W.
Published: February 2003

Compressibility studies have been carried out on Ge–I (diamond-cubic structure) to 12.0 GPa; the results are in very good agreement with previous work. We confirm the recent report of a substantial lowering of the Ge I–II transition pressure in a nonhydrostatic pressure environment. We observe the Ge–II (200)-peak at 10.5±0.2 GPa in a more hydrostatic pressure environment and as low as 6.7 GPa when shear stresses are present. On release of pressure from above 11 GPa, we find that Ge–II converts predominantly into Ge–III when Ge–I and shear stresses are present and completely into Ge–III in the absence of Ge–I in a more hydrostatic pressure environment. This is contrary to what had been previously presumed.
Investigation of the complex permittivity of n-type silicon at millimeter wavelengths
Authors: Kinasewitz Robert T. , Senitzky B.
Published: February 2003

Measurements of the complex permittivity at 107.3 GHz of n-type silicon specimens in the 5–50 Ω cm resistivity range were made using a free space reflection/transmission technique. Reflectance measurements on specimens in the 0.004–5 Ω cm range were obtained. All measurements were compared with a single relaxation time Drude model and a more complete model that was developed which includes Fermi–Dirac statistics and energy dependent lattice and impurity scattering. Although the Drude model was found to reliably predict the complex permittivity of n-type silicon over a specified range of resistivity, it has limitations which are discussed.
Polarization and depolarization behavior of hot pressed lead lanthanum zirconate titanate ceramics
Authors: Xi Yao , Zhili Chen , Cross L. E.
Published: February 2003

A detailed study of the polarization and depolarization behavior of 7:65:35 and 8:65:35 lead lathanum zirconate titanate transparent ceramics under dc bias and constant heating rates has been carried out. The dielectric permittivity exhibits a new anomaly near 0 °C in freshly thermally depoled samples which is associated with a buildup of macrodomains and the development of a remanent polarization. From continuity of the dispersive behaviors it is suggested that the dielectric change at the so-called α–β transition Td is not a conventional phase change, but rather is a loss of macro-ordering and a decay back to a disordered microdomain texture.
New photoluminescence lines in GaAs layers grown by metalorganic vapor phase epitaxy
Authors: Roth A. P. , Goodchild R. G. , Charbonneau S. , Williams D. F.
Published: February 2003

A set of luminescence lines previously observed only in GaAs layers grown by molecular beam epitaxy (MBE) has been observed for the first time in layers grown by metalorganic vapor phase epitaxy (MOVPE). The lines which appear between 1.5515 and 1.504 eV are more evident in samples grown with low arsine concentrations and low substrate temperatures. It appears that these additional lines are due to recombinations involving native defects. Unlike the MBE case, extrinsic impurities from the reactants are incorporated in the layers during the growth, thus reducing the concentration of native defects responsible for the additional lines.
Isotope dependence of the breakdown strength of gases
Authors: Christophorou L. G. , Mathis R. A. , James D. R.
Published: February 2003

It has been found that while the highly nonuniform direct current breakdown voltage Vs of H2 exceeds that of D2, the Vs of CH4 is substantially lower than that of CD4. The former (direct) and the latter (inverse) isotope effects are discussed, respectively, in connection with differences in the ionization coefficients and electron-impact-induced dissociation processes of the isotopic pairs of molecules.
Temperature dependence of the nonlinearity constant and ultrasonic attenuation in pure silicon and germanium
Authors: Rajagopalan S. , Joharapurkar D. N.
Published: February 2003

The temperature dependence of the nonlinearity constant in pure silicon and germanium have been studied for longitudinal waves along the 〈100〉 axis in the temperature range 73–293 K. The estimated temperature dependence has been compared with that obtained from the experimental values of attenuation. Attenuation of 480 and 286 MHz ultrasonic waves for silicon and of 306 MHz ultrasonic waves for germanium have been evaluated, using a temperature dependent nonlinearity constant D, and compared with experimental values of attenuation available in the literature. The results are found to be in good agreement with the experimental values for silicon and germanium.
Pulsed laser annealing of GaAs and Si: Combined reflectivity and time-of-flight measurements
Authors: Pospieszczyk A. , Harith M. Abdel , Stritzker B.
Published: February 2003

Both GaAs and Si single crystals were laser annealed with a 20-ns ruby laser pulse. By means of a time-of-flight measurement the velocity distribution and the density variation of evaporated Ga or As and Si atoms were determined for different energy densities. Simultaneously the reflectivity of the crystal surface was measured time-resolved. The data show consistently that the molten phase occurs at energy densities ≳0.35 J cm−2 for GaAs and ≳0.8 J cm−2 for Si. The results are in agreement with a purely thermal model for laser annealing.
Band-gap narrowing from luminescence in p-type Si
Authors: Dumke William P.
Published: February 2003

The luminescence data of Schmid, Thewalt, and Dumke on heavily doped p-type Si has been analyzed to provide the effective band gap for the n⋅p product at room temperature in p+Si. The results are in very good agreement with the measurements of Slotboom and DeGraaff, and extend the acceptor concentrations for which the effective band gap is available by a factor of four. The disagreement of these results with the values obtained from infrared absorption measurements is further evidence of a nonrigid band-gap shift.
Mobility-lifetime product and interface property in amorphous silicon solar cells
Authors: Okamoto H. , Kida H. , Nonomura S. , Fukumoto K. , Hamakawa Y.
Published: February 2003

The mobility-lifetime products ( μτ) and interface property have been examined through the photovoltaic studies in actual hydrogenated amorphous silicon (a–Si:H) p–i–n junction solar cells. A small amount of boron atoms included in a–Si:H enhances the μτ products of both electrons and holes up to the order of 10−7 cm2/V, which corresponds to the carrier diffusion length in excess of 5000 Å. The doped window layer possessing inferior photoelectric property works as the recombination region for photocarriers generated in the active i layer, and practically dominates the interface property together with the surface recombination velocity S0 at the electrode/doped layer interface. The S0 at the SnO2/p a–Si:H interface is estimated to be about 3×102 cm/s with an assumption of the electron mobility at 0.1 cm2/Vs. Prolonged light exposure causes a reversible change of the μτ products in every layer composing the p–i–n junction. These experimental results are discussed in connection with photovoltaic performances.
High-power KrF laser transmission through optical fibers and its application to the triggering of gas switches
Authors: Itoh Yasuyuki , Kunitomo Kouichi , Obara Minoru , Fujioka Tomoo
Published: February 2003

The fundamental transmission characteristics of KrF laser radiation (248 nm) through the step-index-type fused quartz fiber have been determined. For the step-index-type fused quartz fiber used the transmission loss is about 0.5 dB/m at power densities up to 3.9 MW/cm2 and 2 dB/m at 100 MW/cm2. One of the applications of this intense UV KrF laser transmission via optical fibers is the development of a gas insulated spark-gap switch trigger by a KrF laser through a 2-m-long optical fiber. As a result, at a voltage 90% of the self-breakdown voltage and at an illumination power density of 1.2 MW/cm2, a full trigger jitter of less than 5 ns is realized and it corresponds to a 1-σ jitter of less than 1 ns. The illumination energy is as low as 10 μJ/shot.
Granular effective medium approximation
Authors: Yonezawa F. , Cohen M. H.
Published: February 2003

This article analyzes the structure of the so-called self-similar effective medium approximation (SSEMA) which has been proposed for the effective permittivities in multicomponent inhomogeneous materials such as sedimentary rocks. In particular, our interest lies in understanding what kind of geometry is represented by the SSEMA. We show that, in the case of binary disorder, the first constituent is treated in the SSEMA in such a way that its geometrical continuity in space is guaranteed all the way down to the limit of zero proportion while the second constituent remains disjoint. This accounts for the zero percolation thresholds manifest in Archie’s law.
Conduction mechanism and 1/f noise in ZnO varistors
Authors: Kusy A. , Kleinpenning T. G. M.
Published: February 2003

The conduction mechanism in ZnO varistors has been studied assuming thermionic emission as the only way of charge transport. A model elaborated on that basis has been satisfactorily applied to the approximation of the I–U and C–U characteristics and has made it possible to determine the barrier height Φb(300 K)=0.86 V, the donor concentration ND≂1019 cm−3, the effective number of grains between the electrodes g≂20, the position of the Fermi level EC−EF≂0.07 eV, and the donor level EC−ED≂0.20 eV. The relative power spectral density of 1/f current fluctuations SI/I2 in the varistors in the ohmic region has been calculated, starting from the mobility fluctuation approach of the 1/f noise. The calculated linear relationship between SI/I2 and the varistor resistance in the ohmic region has been confirmed by the experimental results. The calculated 1/f noise density is in agreement with the observed density.
Calculated Auger rates and temperature dependence of threshold for semiconductor lasers emitting at 1.3 and 1.55 μm
Authors: Nelson R. J. , Dutta N. K.
Published: February 2003

A set of generalized calculated results are presented for both radiative and Auger rates in direct gap semiconductors. Emphasis is on materials with band gaps of 1.3 and 1.55 μm. The radiative and Auger components of the lifetime at threshold are calculated for several possible materials for a semiconductor laser at these wavelengths based on the best available data for the band structure of these materials. We find that the calculated T0 for these materials lie in the range 49 K–92 K.
Analysis of multielement semiconductor lasers
Authors: Ebeling K. J. , Coldren L. A.
Published: February 2003

An analysis of laser action in a multielement resonator structure is presented. Resonance wavelengths, threshold gains, energy density distributions, and quality of the modes are obtained from a linear model. A multimode rate equation approach then describes the dynamical behavior and gives absolute values for the modal output. It is shown that structures with only a few active elements can have a high mode selectivity providing single-longitudinal-mode operation of semiconductor lasers under high-frequency current modulation. For example, the suppression of unwanted secondary modes in an eight-element laser can be larger than 23 dB.
Threshold-temperature characteristics in (GaAl)As visible laser diodes emitting below 750 nm
Authors: Hayakawa T. , Suyama T. , Yamamoto S. , Hayashi H. , Yano S. , Hijikata T.
Published: February 2003

The temperature dependence of the threshold current Ith has been measured for (GaAl)As v-channeled substrate inner stripe lasers emitting in the wavelength range of 781–697 nm. Ith (350 K)/Ith (300 K) is found to increase below 750 nm with decreasing wavelength in spite of the fairly large heterojunction step height Δx of 0.4. This is well explained by the model of carrier leakage due to unconfined carriers in the active layer. The calculation indicates that the threshold-temperature sensitivity below 750 nm is almost determined by the carrier leakage in the cladding layer when Δx is smaller than ∼0.4, and it is determined by the temperature dependence of the fraction of the total electrons in the direct conduction band of the active layer when Δx is larger than ∼0.6.
A high power D2O laser optimized for microsecond pulse duration
Authors: Behn R. , Kjelberg I. , Morgan P. D. , Okada T. , Siegrist M. R.
Published: February 2003

A high power D2O laser, pumped by a single mode CO2 laser, has been optimized to produce 1 μs pulses at 385 μm. Pump energies up to 100 J were available using an e-beam preionized CO2 amplifier at 2.5 atm. Far infrared pulse energies of 140 mJ in multimode and 40 mJ in single mode operation have been obtained from a 4-m unstable resonator. During parametric studies the influence of operating pressure, spatially inhomogeneous pump intensity, resonator feedback as well as saturation effects have been investigated.
Theory of transient self-focusing of a CO2 laser pulse in a cold dense plasma
Authors: Schmitt A. , Ong R. S. B.
Published: February 2003

The self-focusing of laser pulses in a plasma is theoretically investigated for the situation in which the refractive index change is not in equilibrium with the pulse. In particular, the analysis models a CO2 laser–plasma interaction experiment in which the ponderomotive and thermal conduction dominated mechanisms of self-focusing are dominant. The moment method and the Gaussian shape ansatz are used to describe the laser pulse propagation. Threshold powers are derived for the transient self-focusing process, which reveals that self-focusing can occur even for times much less than the characteristic dielectric relaxation time. Because of the behavior of the pulse heating, thermal conduction dominated self-focusing is inherently a transient phenomenon without a true steady state limit. The governing equations are also numerically solved, revealing the existence of ion acoustic waves created by the action of moving focal spots. These transversely propagating waves may be responsible for breakup or filamentation of the laser pulse.
Determination of in-plane residual stress states in plates using horizontally polarized shear waves
Authors: King R. B. , Fortunko C. M.
Published: February 2003

In this paper a new approach for using acoustic measurements to evaluate residual stresses in the presence of unknown material property variation is presented. Procedures previously applied to the evaluation of stress with acoustic measurements are reviewed, and it is shown that these involve using measurements with bulk waves propagating along the normal to the surface of a plate and do not provide sufficient information to separate the influences of stress and material property variations. To overcome this fundamental limitation, an alternative theory is developed that governs the propagation of shear waves polarized horizontally with respect to the surface of a plate (SH waves), but propagating at oblique angles with respect to the surface normal. The question of separating the effects of residual stress and material properties on acoustic velocity is addressed in detail. A practical experimental procedure is developed that permits the evaluation of the in-plane components of the principal stresses in a plate exhibiting an unknown inhomogeneous initial anisotropy caused by material texture or microstructure. The procedure is then verified experimentally using an aluminum specimen with a known residual stress state, but unknown initial anisotropy.
Solitons in distensible tubes
Authors: Thielheim K. O.
Published: February 2003

The unsteady flow of an incompressible fluid in distensible tubes is investigated by means of solutions of a nonlinear wave equation. The formalism applied is related to the theory of flat water waves; the propagation of impulses is described as solitons. Relations connecting parameters describing the propagation and the physical properties, respectively, are given. Various orders of approximation are compared. Dispersion relations of the linearized version are considered; flow patterns are calculated for typical cases.
Effect of hydrogen impurity on the electrical characteristics of neon-argon gas mixtures. I. Measurement of ionization coefficients
Authors: Bhattacharya A. K.
Published: February 2003

The effect of H2 on the breakdown potential and Townsend ionization coefficients for Ne-A mixtures were measured by the luminous-flux method. Both argon and hydrogen form Penning mixtures with neon. The breakdown potentials for Ne-A gas mixtures are determined by the Penning reaction, Nem+A→Ne+e+A+, between metastable neon (Nem) and ground state A atoms. At low H2 concentrations (<0.1%) the breakdown potentials and Townsend ionization coefficients are unaffected. At higher H2 levels (>0.1%), increase in breakdown potential caused by the lowering of the Townsend ionization coefficients depends upon the value of the product, pd, of the fill pressure ( p) and the electrode separation (d). This is due to (1) lowering of electron average energy which determines Nem density, and (2) nonionizing reaction, Nem+H2→H*(n=3)+H+Ne, competing with the Penning reaction between Nem and A atoms.
Role of photodetachment in initiation of electric discharges in SF6 and O2
Authors: Van Brunt R. J. , Misakian M.
Published: February 2003

The role of photodetachment in the initiation of electron avalanches near a positive point electrode was investigated for a discharge gap in which the negative ion flux was controlled by UV irradiation of the cathode. For irradiation of the anode region with light beams up to 500 mW, photodetachment was found to make a negligible contribution to avalanche initiation in SF6 and O2 at pressures from 50 to 500 kPA (∼0.5 to 5 atm). The conditions under which the role of photodetachment might be observed are discussed, and it is shown that for the conditions considered here the expected dominant electron release mechanism in the gap is through collisional detachment of stable negative ions. Previously reported enhancements in avalanche rates resulting from irradiation of a positive point can be explained as arising from increases in negative ion densities due to attachment of photoelectrons ejected by scattered radiation.
Measurement of spatially resolved gas-phase plasma temperatures by optical emission and laser-induced fluorescence spectroscopy
Authors: Davis Glenn P. , Gottscho Richard A.
Published: February 2003

Knowledge of the energy distributions of particles in glow discharges is crucial to the understanding and modeling of plasma reactors used in microelectronic manufacturing. Reaction rates, available product channels, and transport phenomena all depend upon the partitioning of energy in the discharge. Because of the nonequilibrium nature of glow discharges, however, the distribution of energy among different species and among different degrees of freedom cannot be characterized simply by one temperature. The extent to which different temperatures are needed for each degree of freedom and for each species is not known completely. How plasma operating conditions affect these energy distributions is also an unanswered question. We have investigated the temperatures of radicals, ions, and neutrals in CCl4, CCl4/N2 (2%), and N2 discharges. In the CCl4 systems, we probed the CCl rotational and vibrational energy distributions by laser-induced fluorescence spectroscopy. The rotational distribution always appeared to be thermal but under identical operating conditions was found to be ≊400 K colder than the vibrational distribution. The rotational temperature at any point in the discharge was strongly dependent upon both applied power and surface temperature. Thermal gradients as large as 102 K mm−1 were observed near electrode surfaces but the bulk plasmas were isothermal. When 2% N2 was added to a CCl4 discharge, N2 second positive emission was observed and used to estimate the N2 rotational temperature. The results suggest that emission from molecular actinometers can be used to measure plasma temperatures, providing such measurements are not made in close proximity to surfaces.
Minority carrier lifetime improvement by HCl oxidation and argon ion implantation of silicon
Authors: Engel P. M. , de Souza J. P.
Published: February 2003

The gettering of metallic impurities was investigated by means of the C-t measurement technique using MOS capacitors. A combination of gettering techniques by HCl oxidation and backside argon ion implantation proved to be suitable to produce high minority carrier lifetime with good uniformity over the gettered regions.
Enhanced diffusion processes during ion implantation: A numerical analysis
Authors: Miotello A. , Mazzoldi P.
Published: February 2003

Previously reported experimental results on time evolution of Si/Pt profiles during Ar ion implantation have been analyzed on the basis of a theoretical model which accounts for the preferential sputtering and enhanced diffusion of Si atoms. Si sputtering yield reflects the energy dependence of the Ar nuclear stopping power at the SiPt mobile surface. Comparison with experimental results on metallic and dielectric systems has been performed in order to clarify the mechanism which induces the enhanced diffusion process.
Growth of CdTe films on silicon by molecular beam epitaxy
Authors: Lo Yawcheng , Bicknell R. N. , Myers T. H. , Schetzina J. F. , Stadelmaier H. H.
Published: February 2003

Results of initial attempts to grow cubic-phase CdTe films on (111) and (100) Si substrates by molecular beam epitaxy are reported. Substrate temperatures in the range 200–400 °C were employed along with deposition rates of 1–9 Å/s. Films grown at temperatures below 300 °C exhibited streaked x-ray diffraction patterns which contained extra hexagonal-phase features. Sharp cubic-phase epitaxy was obtained for CdTe films grown on (111) Si substrates at 330–350 °C. Similar depositions on (100) Si substrates also produced epitaxial CdTe films. However, the (100) epilayers displayed unusual x-ray diffraction patterns which are suggestive of twin formation. Nomarski micrographs revealed the epitaxial CdTe films to be uniformly free of voids and microcracks despite the large difference in lattice constant and thermal expansion coefficient for these materials.
Creation and annealing kinetics of magnetic oxygen vacancy centers in SiO2
Authors: Devine R. A. B. , Golanski A.
Published: February 2003

Dose and energy dependence of the E′1 defect density/cm2 created in SiO2 by implantation of Ar ions has been determined by electron paramagnetic resonance. A dose dependent region followed by a saturated, dose independent region is found for all energies studied (50–150 keV). In the low dose limit for 100-keV Ar ions we estimate E1 creation to be 35/implant ion. The defect density/cm2 is found to be a linear function of the longitudinal atomic collisional damage distribution consistent with a picture of overlapping lateral damage distributions. A simple model for defect creation and annihilation gives a good quantitative explanation of the observed energy and dose dependence of the defect density. Isothermal annealing studies have been performed and the results do not follow those expected for a simple exponentially activated process. A model assuming correlated defect/interstitial recovery gives a better description of the experimental results and suggests an activation energy for recovery of approximately 0.85 eV.
Grain boundary phenomena in n-type CdTe films grown by hot wall vacuum evaporation
Authors: Huber Walter , Fahrenbruch Alan L. , Fortmann Charles , Bube Richard H.
Published: February 2003

Films of n-type CdTe doped by coevaporation of indium have been deposited by hot wall vacuum evaporation on 7059 Corning glass and BaF2 single crystal substrates. Layers deposited on glass show a dark resistivity of the order of 105 Ω cm and a light resistivity of 500 Ω cm under AM1.5; photoexcitation increases the electron density but does not affect the electron mobility. Layers deposited on BaF2 show a dark resistivity of about 3 Ω cm and a light resistivity of about 2 Ω cm, corresponding to an electron density of 3.9×1016 cm−3 and an electron mobility of 48 cm2/V s; illumination of these layers on BaF2 increases the electron mobility but not the electron density. A quantitative model for grain boundary transport in polycrystalline materials is shown to give good agreement with the experimental data.
Superconducting transition temperature versus thickness of Nb film on various substrates
Authors: Kodama Jun-ichi , Itoh Mineo , Hirai Heihachiro
Published: February 2003

Dependence of superconducting transition temperature on the thickness of Nb films deposited upon several kinds of substrates by means of rf sputtering was studied in search of rudimental data necessary in fabricating variable thickness microbridge type Josephson junctions. The transition temperature was found to lower with the decrease of Nb film thickness. The lowering characteristics of the transition temperature were found to vary in accordance with whether the substrate surface was amorphous or crystalline. The cause of the variance was studied on thin films with the aid of x-ray diffraction pattern analysis and measurement of film resistance.
Low power nonlinear effects in the ferromagnetic resonance of Zn2Y and MnZnY hexagonal ferrites
Authors: Silber L. M. , Patton C. E. , Naqvi H. F.
Published: February 2003

The room temperature ferromagnetic resonance (FMR) absorption at 8.9–11.2 GHz in two planar hexagonal ferrites, Zn2Y and MnZnY, has been found to exhibit strong nonlinear behavior at low power levels corresponding to microwave field amplitudes on the order of 10 mOe. For somewhat larger amplitudes, 20–50 mOe, the asymmetric resonance curves show pronounced foldover effects. With increasing static field, the absorption increases gradually to a steep cutoff at a field several hundred Oe above the position of the low power FMR. With decreasing field, a sharp spike occurs coincident with the high field tail of the low power FMR line, followed by a gradual decrease which tracks the upsweep absorption. The detailed shapes of these curves depend strongly on sweep rate. Steady-state absorption curves at the highest powers employed, with 350 mW incident power and a microwave field amplitude of 58 mOe, result only for very slow sweep rates of 20 Oe/min or less.
Forces and torques acting on plane and cylindrical electrets in slot-effect transducers
Authors: Abazi Alajdin , Jefimenko Oleg D.
Published: February 2003

A theoretical discussion of forces and torques acting on electrets in slot-effect transducers of plane and cylindrical geometry is presented. Both bipolar and monopolar electrets are considered. The electrets are assumed to carry arbitrary internal and surface charges. The dependence of forces and torques on the magnitude and location of the charges and on other electret parameters is analyzed.
Thermal dielectric breakdown with cylindrical electrodes
Authors: Beers B. L. , O’Dwyer J. J.
Published: February 2003

Solutions to the equations of thermal breakdown are computed for cylindrical electrodes with different boundary conditions. The development of the electric field and the temperature distributions are followed as functions of time, consequent on the application of a constant interelectrode voltage. The implications for possible breakdown by modes other than thermal are briefly discussed.
Complete calculation of the electric potential produced by a pair of current source and sink energizing a circular finite-length cylinder
Authors: Lambin Ph. , Troquet J.
Published: February 2003

Green’s function for the solution of Poisson’s equation in cylindrical coordinates is calculated using the underlying Sturm–Liouville problem. The potential distribution produced by an arbitrarily oriented eccentric dipole located in a homogeneous conducting circular finite-length cylinder is given; three alternative forms are presented, which enable us to compute the potential everywhere in the cylinder. Previous works devoted to this subject were incomplete in the sense that the formulas which were presented there do not converge everywhere. For our expressions of the Green function,we show that Gabor and Nelson’s theorem applies for the present geometry. We also consider the case where the current source and sink are remote from each other in order to check the consistency between Gabor and Nelson’s theorem and Helmholtz’s principle. Applications of our formulas are presented in a situation which is representative of the human trunk activated by the heart and discussion of the results is made in relation with electrocardiology. It is shown that the eccentricity of the dipole is responsible for curving the line of the greatest potentials and for wrapping the zero equipotential plane.
Photoelectrochemistry of microcrystalline chlorophyll a films
Authors: Inganäs Olle , Lundström Ingemar
Published: February 2003

Thin films of microcrystalline chlorophyll a in contact with electrolytes have been studied. It is shown that the electrode acts as a photocathode, as indicated by the dependence of photoeffect on electrode potential and redox potential of electrolyte. Impedance measurements at low frequencies show that a space charge is formed at the electrode/electrolyte interface. The chlorophyll photocathode is in principle capable of reducing water to hydrogen, even though a very high overpotential kinetically blocks this. All these photoelectrochemical properties are compatible with the picture of the organic photoelectrode as a p-type semiconductor.
E
1′ defect profiles in Ar implanted SiO2
Authors: Devine R. A. B. , Debroux M. H.
Published: February 2003

The technique of electron paramagnetic resonance has been used to obtain atomic displacement damage profiles in SiO2 implanted with Ar ions at 125 keV. Measured damage projected range and profile width are both 27% larger than expected from calculations. Results for isochronally annealed samples suggest that annealing proceeds uniformly without a profile redistribution.
Structure and coherence of NbAl multilayer films
Authors: McWhan D. B. , Gurvitch M. , Rowell J. M. , Walker L. R.
Published: February 2003

NbnAlm multilayer films grown on oxidized Si(100) at room temperature by magnetron sputtering have Nb[110] and A[111] texture. The films have ∼1% coherency strains which decrease with increasing modulation wavelength. The composition modulation is approximately a trapezoidal wave with interfacial regions ∼11 Å thick as a result of grain boundary diffusion.
Measurement of concentration and photoionization cross section of indium in silicon
Authors: Parker G. J. , Brotherton S. D. , Gale I. , Gill A.
Published: February 2003

Variable-temperature Hall-effect measurements, capacitance–voltage (C–V) measurements and flameless atomic absorption have been used to assess the concentration of indium in indium-doped silicon (Si:In) crystals. It was found that the flameless atomic absorption and C–V results were in very good agreement, but the extraction of an indium concentration from Hall-effect data was not a straightforward exercise due to the fact that the indium did not enter the ‘‘exhaustion’’ region. However, by analyzing the Hall data using a recent determination of the hole effective mass, and by using a physically reasonable value for the Hall scattering factor, the Hall data gave indium concentrations in very good agreement with the other two techniques. The Si:In substrates were also characterized optically using infrared absorption. These results, together with the indium concentrations determined above, yielded a peak indium photoionization cross section of (1.55±0.25)×10−16 cm2 at a 4-μm wavelength.
Quantum-chemical modeling of boron and noble gas dopants in silicon
Authors: Aronowitz Sheldon
Published: February 2003

The electronic effects of the presence of boron and noble gas dopants in a model silicon lattice were investigated using a self-consistent charge extended Hückel program. The extent of electronic interaction of the noble gas with the lattice is given by: Kr>Ar>Ne. Theoretically, boron diffusion in the presence of neon, argon or krypton was examined using a self-consistent charge extended Hückel program. The net energy of interaction between boron and neon is strongly repulsive while argon–boron exhibits a region of relative stability; krypton exhibits behavior similar to argon though no region of stability was found for the range of separations used in the calculations. Finally, it is noted, from the relative energy of the topmost filled molecular orbital associated with boron (in an interstitial position), that activation of the boron does not require boron movement but can be accomplished by indirect transitions.
Hall effect studies in germanium doped AlxGa1−xAs
Authors: Nelson A. W. , Robson P. N.
Published: February 2003

Germanium doping of AlxGa1−xAs has been studied over the range x=0.22–0.40 by measuring the Hall effect in epitaxial layers grown by liquid phase epitaxy. Hall measurements were carried out in the temperature range 70–300 K and the resulting mobilities and carrier densities were analyzed as a function of temperature. These analyses have shown that the Hall to drift mobility ratio in this material, previously assumed to be around unity, is ∼0.6 and that Ge produces two acceptor levels in AlxGa1−xAs. The dominant acceptor level has an activation energy which increases monotonically with x and has a value of ∼160 meV at x=0.40. A shallow level of much lower concentration has also been found at an energy of 20–40 meV above the valence band edge. In addition we have found the level of compensation in our material to be low.
Thermoelectric power of aluminum films
Authors: De D. , Bandyopadhyay S. K. , Chaudhuri S. , Pal A. K.
Published: February 2003

The thermoelectric power (TEP) of aluminum film was measured in the thickness range of 300–1600 Å. From the size effect of electron diffusion term, the energy dependence of the mean free path of conduction electrons (U) and the Fermi surface area (V) were calculated to be U=0.957 and V=1.322. The phonon-drag part of TEP also exhibited a size effect from which the mean free path of the dominant phonon mode was estimated to be 400 Å. The effect of grain boundary scattering on thermoelectric power was also studied.
Impedance of thin semiconductor films in low electric field
Authors: Lee Kwyro , Shur Michael S.
Published: February 2003

Impedance and admittance of a thin semiconductor film in the direction perpendicular to the film is calculated as a function of the sample length, doping, and temperature for voltages smaller than the thermal voltage. The calculation is based on the approximate solution of the Boltzmann equation in the relaxation time approximation. When the sample length is smaller than the mean free path, the conductance becomes independent of the sample length. In this limit the inductive susceptance is proportional to the sample length. When the sample length becomes comparable to the mean free path, the inductive susceptance reaches the maximum value, and then decreases. Our calculation shows that for high mobility GaAs samples at 77 K, the size effect may be important for films thinner than 5 μm. The results of the calculation are interpreted in the frame of a simple equivalent circuit which includes the bulk resistance, in series with the resistance due to the finiteness of the sample length, in series with the inductance L due to the inertia effect of the carrier transport, and all in parallel with the geometric capacitance C. The sample inductance L is approximately equal to (ω2pC)−1 where ωp is the plasma frequency. This simple model agrees fairly well with the results of the numerical calculation. The calculation, based on the model demonstrates that the predicted effects can be observed for realistic values of the contact resistance.
A new self-limiting process for the production of thin submicron semiconductor films
Authors: Lee Kevin C. , Silcox J. , Lee C. A.
Published: February 2003

This paper describes a new anodic etching technique for the fabrication of device quality, self-limited, thin submicron semiconductor films. The technique relies upon the creation of a thin slightly damaged surface layer in the semiconductor by low dosage ion implantation. Evidence is presented to show that the lifetime of holes in this layer is drastically reduced causing the etching rate to decrease by a factor of several thousand when the damaged layer is exposed to the anodic etching solution.
Comparison of N2, Xe, Kr, and ArF excimer flashlamps with respect to their suitability for pumping TlI
Authors: Gerber T. , Lüthy W. , Schmiele R. , Henchoz P.-D.
Published: February 2003

The far UV spectra of a flashlamp with a rise time of 30 ns filled with either N2, Xe, Kr, or Ar, F2, He mixtures at 1 bar have been recorded. Emission of these flashlamps are compared in a band ranging from 190 to 220 nm. It is shown that the N2 and ArF flashlamps produce an nearly identical output and are best suited for TlI photodissociation. The light energy in this band with respect to the total emission from 190 nm to 4.5  μm amounts to 7% for N2 and 15%–25% for ArF.
Bonding pad induced stresses in (Al,Ga)As double heterostructure lasers
Authors: Swaminathan V. , Wagner W. R. , Anthony P. J. , Henein G. , Koszi L. A.
Published: February 2003

We have studied Au bonding pad induced stresses in (AlGa)As double heterostructure lasers by photoluminescence, x-ray Automatic Bragg Angle Control measurements, and infrared and optical microscopy. Examination of several devices which have thick (10–12 μm) plated Au bonding pads indicates that stresses approaching the fracture stress can exist in such devices. The high stress induces aggregates of microcracks along 〈100〉 directions in the epitaxial layers. Regions in the stripe where the cracks intersect are nonradiative, causing failure of the device.
Effect of surface relaxation on stress failure in laser-irradiated glass
Authors: Batteh Jad H.
Published: February 2003

An analytic study is conducted to determine the effect of stress and structural relaxation on stress failure in laser-irradiated BK-7 glass. Both short (10 μs) and long (1 s) pulses of CO2 and DF laser radiation are considered. The model for the glass temperature consists of the one-dimensional diffusion equation with a source term to account for absorption of energy from the laser beam. Stresses are calculated from an analysis which includes the effect of relaxation at the irradiated surface. The model indicates that the surface stress is strongly dependent on the absorption coefficient of the glass at the laser wavelength and on the laser pulse duration. The implication of these results as to the failure mode in glass subjected to high intensity CO2 and DF radiation is discussed.
An analysis of the asymmetric part of electron–electron Boltzmann integral
Authors: Kunc Joseph A.
Published: February 2003

A numerical analysis of the asymmetric part of electron–electron collision integral is presented. The results are given in the form of graphs for two commonly considered plasma situations: the collision-dominated case (symmetric part of electron distribution is Maxwellian) and the field-dominated case (symmetric part of electron distribution is Druyvesteynian). The importance of the asymmetric part of e-e collision integral in the Boltzmann equation is also discussed.
Nonlinear Landau damping of a whistler in a current-carrying plasma
Authors: Tewari D. P. , Sharma A. K.
Published: February 2003

A high-amplitude whistler wave propagating through a current-carrying plasma decays into a low-frequency resistive quasimode and frequency-upshifted scattered whistler. In this process of nonlinear Landau damping a pump-wave photon absorbs a quantum of energy from the drifting electrons to generate an upshifted whistler photon. Upconversion occurs only when the drift velocity of electrons exceeds the phase velocity of the quasimode (ω<k⋅vd).
Uniformity of energy deposition for laser driven fusion
Authors: Skupsky Stanley , Lee Kotik
Published: February 2003

Laser driven fusion requires a high degree of uniformity in laser energy deposition in order to achieve the high density compressions required for sustaining a thermonuclear burn. The characteristic nonuniformities produced by laser irradiation, with multiple overlapping beams, are examined for a variety of laser-target configurations. Conditions are found for which the rms variation in uniformity is less than 1%. The analysis is facilitated by separating the contributions from (1) the geometrical effects related to the number and orientation of the laser beams and (2) the details of ray trajectories for the overlapping beams. Emphasis is placed on the wavelength of the nonuniformities in addition to their magnitudes, as the shorter wavelength nonuniformities are more easily smoothed by thermal condution within the target. It is demonstrated how the geometrical symmetry of the laser system effectively eliminates the longer wavelengths, and how shorter wavelength nonuniformities can be ‘‘tuned out’’ by varying parameters such as the focal position and the radial intensity profile of the beam. The distance required for adequate thermal smoothing of the irradiation nonuniformities is found to be 2 to 3 times smaller than previously estimated due mainly to the relatively small spatial wavelength of the nonuniformities. This is a consequence of the geometrical symmetry of the laser system and is relatively insensitive to the details of overlapping beams. The results are particularly important for irradiation with short wavelength laser light (e.g., 0.35 μm), as the small smoothing distances anticipated for moderate laser intensities are found to produce adequate attenuation of the calculated nonuniformities.
Particle sizing in two-phase flows from scattered laser power spectra and laser attenuation
Authors: Eversole J. D. , Hulsizer S. C.
Published: February 2003

Diagnostic measurements have been made on a two-phase flow of carbon particles suspended in nitrogen gas, in conjunction with another experiment. Experimental data on particle size distribution were obtained from scanning electron microscopy of samples, laser extinction, and laser scattering in the flow. Two independent nonintrusive laser measurements indicated ‘‘average’’ particle diameters of 1.5 and 3.4 μm. Predictive calculations show that these experimental measurements can be used to indicate the degree of agglomeration in the flow and provide restrictive boundaries to a priori size distributions which are computationally consistent with the observed data.