ALBERT

Notes: In this work, we have numerically integrated in space and time the effective mass Schrödinger equation for an exciton in a semiconductor quantum-well structure. Considering a Coulomb interaction between the electron-hole pair and an external electric field, we have studied the excitonic tunneling escape process from semiconductor quantum wells. Our method of calculation has been applied to types-I, -II, and -III quantum-well superlattices. In addition, we present the calculated excitonic lifetimes for the GaAs/GaAlAs, InAs/GaSb, and HgTe/HgCdTe systems under an external electric field. In the HgTe/CdTe system, the possibility of having similar electron and hole lifetime values is also found if the applied electric field is large enough.

Notes: A self-consistent two-dimensional (2D) model of large volume inhomogeneously preionized transient high-pressure glows as used in XeCl lasers is described. The basic concept is to use a curvilinear orthogonal coordinate system generated by conformal mapping of a cartesian system. The model uses the local field approximation and is based on a cartesian 2D model of J.-P. Boeuf and L. C. Pitchford [IEEE Trans. Plasma Sci. 19, 286 (1991)]. As only direct ionization is taken into account, applications are limited to the ignition phase. Application to a discharge between cylindrical rods predicts a high degree of E-field homogenization due to space charges and demonstrates the limits of parallel resistor models. Inside the cathode sheath an explosive formation of a very thin highly ionized layer is predicted. This sheath ignition is also seen in experiments.

Notes: The fractal dimensions of five fractional Brownian motion (fBm) surfaces of 257×257 pixel size, with Hurst exponent H ranging from 0.1 to 0.9, were computed by profile, contour, and surface area analyses. A technique was deemed reliable if it demonstrated accuracy, consistency and sensitivity. Of all the techniques examined, surface area analysis methods, namely, two-dimensional pyramid and Peleg methods, were found to be most reliable and efficient for the data size studied. Hence, these were employed in a preliminary fractal analysis of poly(methyl methacrylate) and poly(styrene) fracture surfaces. The surfaces were imaged at scan sizes ranging from 1–6.5 μm by atomic force microscopy (AFM). The images indicated the existence of fractal structure and a high degree of roughness at microstructural scales for both the surfaces. These observations were supported by the results of the two surface area analysis techniques. A more conclusive study was prevented by severe scoring of the surfaces by the AFM tip at smaller scan sizes and the availability of only a narrow range of scan sizes.

Notes: We have investigated in detail the influence of interlayer structures on nonalloyed ohmic contact resistance (ρc), in terms of the crystalline defects and the potential barrier at the interlayer/GaAs interface. The interlayer structures are a graded-band-gap InAs/GaAs strained-layer superlattice (graded SLS), a graded-band-gap InGaAs, and conventional SLSs without graded band gaps. A two-layer transmission line model indicates that the barrier resistance in the interlayer highly depends on the interlayer structure: ≤5×10−8 Ω cm2 for the graded SLS and graded InGaAs interlayers and 10−5–10−6 Ω cm2 for the conventional SLS interlayers. To explain the large dependence of the interlayer structure, first, the density and distribution of the misfit dislocations and stacking faults caused by the large lattice mismatch between InAs and GaAs have been investigated in detail by high-resolution transmission electron microscopy. In the graded SLS and conventional SLS interlayers, the influence of the high-density depletion regions spread near the crystalline defects is found to be negligible because of the high doping concentrations (∼1019 cm−3) in the interlayers. Second, the potential barrier at the interlayer/GaAs interface has been investigated by simulating the barrier resistance. The potential barrier profile is calculated self-consistently with Poisson's equation and the Schrödinger equation. Tunneling current through the barrier is analyzed using the Wentzel–Kramers–Brillouin approximation or the numerical wave solution to the Schrödinger equation. The graded SLS interlayer has the effectively smooth conduction band profile without the barriers, which is similar to that of the graded InGaAs interlayer, because of its short period SLS. In the conventional SLS interlayers, the reasonable barrier heights of 0.14–0.26 eV obtained by this simulation indicates that these barriers are the dominant factor which increases the contact resistances. For the low-resistance nonalloyed ohmic contact, therefore, a smooth conduction band profile without band discontinuity is more predominant than the reduction in the crystalline defect density.

Notes: The fracture characteristics of metal/polymer line structures formed by depositing Au/Cr lines on a semiflexible polyimide, pyromellitic dianhydride-oxydianiline (PMDA-ODA), substrate have been investigated using a stretch deformation technique. The delamination behavior, fracture morphology, fracture energy, and energy dissipation rate have been determined as a function of line width and thickness. The metal dimension was found to influence the crack formation mode and morphology. The experimental studies were supplemented by finite-element analysis to evaluate the stress distribution and deformation energetics of the line structure, which takes into account the plastic deformation of the metal and the polymer. Results from this analysis show that the observed fracture characteristics can be attributed to the edge and thickness effects induced by metal confinement. Essentially, the deformation behavior is determined by the mechanical environment induced by metal confinement at the interface. Plastic deformation of both metal and polymer plays an important role in controlling the stress distributions as well as the deformation energetics. The fracture energy of the metal-polyimide interface determined by an overall energy balance method was consistent with that obtained from energy dissipation rate. The average value is 25 J/m2 for the Au/Cr/PMDA-ODA line structure.

Notes: In situ resistance measurements, x-ray diffraction, Rutherford backscattering spectrometry, transmission electron microscopy, isothermal and constant heating rate differential scanning calorimetry and Auger electron spectrometry depth profiles have been used to investigate the interactions in copper and magnesium thin films leading to the growth of Cu2Mg and CuMg2 intermetallics. The effect of exposing the reacting interfaces to controlled exposure of oxygen on the nucleation and growth kinetics of such intermetallics was also investigated. It is found that the first phase to form is CuMg2, at about 200–215 °C. It is determined that the formation of CuMg2 occurs by a two step process consisting of nucleation and growth. The nucleation of CuMg2 takes place in a region composed of a Cu/Mg solid solution. The nuclei form at certain preferred sites and grow in directions both parallel and perpendicular to the surface, eventually leading to a continuous CuMg2 layer. The growth of CuMg2 nuclei in the plane of the original interface occurs at a constant rate, whereas the growth in a direction perpendicular to the original interface is found to be diffusion limited. In the presence of excess copper Cu2Mg forms at higher temperatures, with complete conversion to Cu2Mg occurring at about 380 °C. When the Cu surface is dosed with oxygen prior to Mg deposition, ramp rate differential scanning calorimetry (DSC) shows that the nucleation and growth of CuMg2 as well as the growth of Cu2Mg are not disturbed. Dosing the Mg surface with oxygen results in significant changes in the growth of the two phases. In this case a thin MgO layer is formed at the oxygen dosed surface, lateral growth of CuMg2 is unaffected, but vertical growth of CuMg2 across the oxygen dosed interfaces is delayed by 25–30 °C. The growth of Cu2Mg is also shown to be delayed, by 22–54 °C due to the interfacial oxygen dose.

Notes: Thin-film reactions between nickel and silicon are investigated by differential scanning calorimetry and transmission electron microscopy on evaporated bilayers with different compositions and thicknesses. The thermograms are interpreted by a computer modeling, based on diffusion-controlled growth. Experiments and simulation reveal the simultaneous formation of crystalline Ni2Si and of an amorphous phase of composition probably near NiSi. The derived kinetic data confirm literature values from isothermal experiments.

Notes: Polar angle distributions of core level photoemission intensities recorded on YbAs/GaAs(001) and ScAs/GaAs(001) heterostructures are presented. They allow first the surface roughness of thin YbAs overlayers to be seen, second to estimate the tetragonal distortion of a strained ScAs film and, third, the most interesting point, to demonstrate in a direct fashion that the mixed (Yb-As) (010) planes of YbAs grow in the prolongation of the As planes of GaAs. The results are compared to those obtained by other authors with various techniques. The main advantage of the photoelectron diffraction method over the other techniques is that it can be performed on very thin epitaxial films (some monolayers) directly in situ under ultrahigh vacuum.

Notes: We attempt to establish the mathematical expression of the current and the magnetic field in a metallized capacitor. The expression of the impedance of this capacitor is also presented. The distribution of the current is discussed through the variation of the capacitor impedance and compared to experimental ones. There is good agreement between experimental and theoretical results. The analytical expressions of the magnetic field and the current also show a dependence on parameter δ2 akin to the skin depth in conductors. δ2 also depends on frequency. When δ2 is smaller than the outer radius of the capacitor, the current distribution becomes inhomogeneous.

Notes: High purity InP layers have been grown by chemical beam epitaxy using H2 as the carrier gas for transporting the metal alkyl trimethylindium into the growth chamber. InP layers exhibiting Hall mobility as high as 238 000 cm2/V s at 77 K and with a peak value of 311 000 cm2/V s at 50 K and residual Hall concentration of 6×1013 cm−3 at 77 K were grown at 500 °C using a low V/III ratio (2.2) and a phosphine (PH3) cracking cell temperature of 950 °C. The 4.2 K photoluminescence spectra were dominated by donor bound exciton (D0,X)n up to n=6 and free exciton (X) transitions for InP layers grown above 500 °C. All the InP samples exhibited very weak acceptor related photoluminescence transitions indicating very low concentration of acceptors. The energy of these transitions suggests that Mg is the major residual acceptor. Donor impurity identification by high resolution magnetophotoluminescence indicated that S and Si are the major impurities. PH3 has been found to be the major source of S impurities in the present study.

Notes: Normal and superconducting properties of PtSi films with thicknesses of d=2–20 nm have been investigated. The superconducting transition has been observed on the thin films down to d=4 nm. The systematic reduction of the transition temperature with decreasing d (increasing the sheet resistance) has been explained by the localization and Coulomb interaction effects on superconductivity. The temperature dependence of the upper critical field indicates that the PtSi films behave as homogeneous superconductors.

Notes: Magnetic and structural properties of sputtered CoNiPt(SiO2) alloy films have been studied for high-density longitudinal recording media. In-plane coercivity remarkably increases from 1400 to 2500 Oe with an increase of SiO2 content up to 4 at. % and coercive squareness S* slightly decreases from 0.90 to 0.87, while the perpendicular magnetic anisotropy is not changed significantly. Media noise is markedly reduced by the addition of SiO2. Si in the film is shown to be in the form of SiO2 by x-ray photoelectron spectroscopy. In x-ray diffraction, hcp-CoNiPt lattice is observed and the lattice constants of this hcp structure are expanded by the SiO2 addition. Relative integrated intensities of the diffraction peaks from (100) and (002) planes to (101) plane are not dependent on the SiO2 content, which indicates that the average orientation of the c axis of the hcp lattice is not influenced by the SiO2 addition. This agrees with the result that the perpendicular anisotropy is not significantly changed. From the transmission electron microscopy and high-resolution scanning electron microscopy analyses, grain size decreases with the SiO2 addition. Moreover, the outline and shape of crystal grains become sharper with the SiO2 addition of 2 at. % than those in pure CoNiPt. With the 4 at. % SiO2, clear separation among each crystal grain is observed. These changes of the grain structure by the SiO2 addition are attributed to the chemical segregation of the SiO2 at the grain boundary. It is concluded that the development of this grain separation is a major reason for remarkable increase in the coercivity and reduction of the media noise by the SiO2 addition.

Notes: A new model is presented which quantitatively describes the reversible magnetization process and its contribution to the magnetization curve in soft amorphous ribbons. It takes into account the role of the coherent moment rotations, through analysis of the orientation distribution of the magnetization vector Is in the sample cross section and its evolution with the applied field. Such analysis relies on the assumption, dictated by magnetic domains observations, of a spatial distribution of local anisotropies, whose intensity and direction are mainly determined by the long-range random stresses quenched in during the process of rapid solidification. The reversible I(H) curve is obtained by integrating the local magnetization contributions with respect to their angular distribution, according to a minimum energy condition involving the Zeeman, the local anisotropy, and the macroscopic anisotropy terms. It is shown that a relatively simple analytical expression for I(H) can be worked out. The model is applied to experimental I(H) recoil curves, which have been determined as a function of the stress-induced anisotropy in positive magnetostriction (Fe81B14Si3C2) and negative magnetostriction (Co80B10Si10) amorphous ribbons. It is shown that the shape of I(H) and its evolution with the applied tensile/compressive stress are correctly predicted by the theory.

Notes: An rf nitrogen (N) plasma source has been used to achieve p-type conductivity in molecular beam epitaxy CdTe layers grown with a Cd overpressure. Photoluminescence and secondary ion mass spectrometry measurements have confirmed the incorporation of the N species, and evidence for the resulting p-type conductivity has been obtained using capacitance-voltage and current-voltage techniques. Net hole concentrations as high as 2×1017 cm−3 have so far been achieved, which contrasts with the normally n-type nature of our undoped CdTe layers.

Notes: The fluorescence phenomena of nanostructured Al2O3 without doping and after doping of nano-Fe2O3 (4.61 and 48.01 wt %) were systematically investigated. The results show that a new fluorescence band with a peak position of about 17 500 cm−1 occurs for boehmite, η-Al2O3 and γ-Al2O3 and it disappears for α-Al2O3. This band can be attributed to fluorescence of Fe3+ in the systems with low-order degree (boehmite, η- and γ-Al2O3 and interfaces), which arises from 6A1→4T1 d5 electron transitions of Fe3+.

Notes: The frequency-dependent conductivity and dielectric constant of a salt-water-saturated porous glass specimen have been measured. The measurements cover the full frequency range of the Maxwell–Wagner dispersion. The experimental results have been compared with the recently introduced local porosity theory and with previous theories. For the purpose of comparing with the local porosity theory experimental measurements of local porosity distributions from digitized pore space images are presented. These experimental porosity distributions are then used for a first experimental test of local porosity theory. The comparison with previous theoretical expressions for the frequency-dependent effective dielectric function shows that local porosity theory constitutes a significant improvement in the quantitative agreement.

Notes: Results are presented on the wet thermal oxidation of AlxGa1−xAs. The growth of wet thermal oxides of AlxGa1−xAs is shown to be linear with time. An O2 carrier gas was found to form a self-terminating oxide for compositions investigated (x(approximately-greater-than)0.4), but required elevated temperatures for substantial growth. The use of a medium oxygen concentration (∼20%) in a N2 carrier formed nonuniform oxides for all compositions investigated. A low O2 concentration (0.1%) in the N2 carrier was found to reduce the activation energy of the oxidation process for Al0.6Ga0.4As from 1.9 to 1.0 eV while increasing the activation energy of Al0.8Ga0.2As from 1.6 to 1.75 eV. For these wet thermal oxides it is observed that lateral oxidation at heterojunction interfaces is enhanced. This enhanced lateral oxidation can be attributed to local stress due to the smaller volume of the growing oxide compared to the volume of the consumed semiconductor.

Notes: The optimum particle size distribution of an electrorheological fluid (ERF) is studied theoretically by the cubic particle chain model developed by the authors. For simplification purposes, the study is limited to a mixture that consists of two different particle sizes, i.e., small particles and large particles, but of the same permittivity. We adopt periodic boundary conditions with two chains in the unit cell. Static yield stress is calculated for three particle configurations. In the first configuration, each chain contains only one particle size, either small or large. The other configurations use chains which are constructed from small and large particles, arranged alternately. However, whereas the second requires particles of neighboring chains to be complementary, the third requires an alternating arrangement. The relative magnitude of the calculated yield stress in these the situations is τ2〈τ3〈τ1. In the first configuration calculated yield stress is independent of the particle size ratio. However in the second configuration, the yield stress increases as the size ratio approaches unity. From the results of these typical cases, we conclude that the ERF consisting of only the same particles gives the largest static yield stress. Also interactions among the chains as a description of the many-body effect is discussed.

Notes: High-power millimeter wave generators can induce electron cyclotron waves in a plasma which can fulfill many functions (plasma breakdown, heating, current drive) in fusion plasma reactors including both tokamak and stellarator concepts. All these applications require tens of megawatts of power in the frequency range 100–300 GHz and power 0.5–1.5 MW per unit. Among various microwave sources gyrotrons are the most developed source. Because of the heat losses in resonator walls at such high frequencies and powers oversized cavities must be used. In such cavities the mode competition becomes a severe problem. The most advanced theory of mode competition in gyrotrons is the nonstationary nonlinear theory. In the present article we extend this theory by allowing for inhomogeneity of the guiding magnetic field. The importance of this generalized theory is illustrated in the case of a 3 MW 140 GHz gyrotron with a coaxial cavity working in the TE21,13 mode.

Notes: Ultrahigh-vacuum scanning tunneling spectroscopy and tunneling spectroscopy measurements of polypyrrole-vacuum-metal and polypyrrole-vacuum-polypyrrole tunneling junctions indicates the existence of three characteristic energy levels, 0.60, −0.40, and −0.65 eV near the Fermi level of an as-grown polypyrrole films. The measured energy levels of −0.40 and −0.65 eV could be attributed to localized filled states and mobility edge, respectively.

Notes: A nonsaturable component to the 980 nm excited state absorption (ESA) is found in Er3+-doped silica glass fibers. This anomalous behavior of the ESA provides a way of quantitatively characterizing the degree of clustering in these glasses. It is found that the degree of clustering is greater for higher Er3+ concentrations, and is significantly reduced with the addition of aluminum to the glass. With this method it is also found to be possible to distinguish between true clustering and the occurrence of closely spaced Er3+ pairs in a random distribution.

Notes: Optical absorption spectroscopy has been applied to measure the absolute population densities of the first excited levels of atomic hydrogen H*(n=2) and argon Ar*(4s) in an expanding cascaded arc plasma in hydrogen-argon mixture. It is demonstrated that the method allows us to determine both H*(n=2) and Ar*(4s) absolute density radial profiles for H2 admixtures in Ar ranging from 0.7% to 10% with good accuracy. The measured H*(n=2) densities are in the 1014–1016 m−3 range, and Ar*(4s) densities are in the range of 1015–1018 m−3. It has been shown, that the density of hydrogen excited atoms H*(n=2) serves as an indicator of the presence of argon ions and hydrogen molecules in the expanding plasma. A kinetic model is used to understand evolution of H*(n=2) density in the expansion, and to estimate the total atomic hydrogen population density and hydrogen dissociation degree in sub- and supersonic regions of the plasma.

Notes: The characteristics of Cu precipitation on various types of defects associated with oxygen precipitation in Czochralski-grown silicon are investigated by transmission electron microscopy and the electron-beam-induced-current technique. Specimens containing dominantly either punched-out dislocations or bulk stacking faults were intentionally contaminated with Cu at various temperatures and cooled at three different rates. Colonies of Cu precipitates developed irrespective of cooling rate, apparently originating from punched-out dislocations developed around oxygen precipitates. In heavily contaminated specimens cooled fast from the contamination temperature, Cu also precipitates on Frank partial dislocations bounding stacking faults. During slow cooling, precipitation of Cu takes place on Frank partials only in lightly contaminated specimens but never in heavily contaminated specimens. Cu precipitates in colonies are thermally more stable than those formed on Frank partials. It is concluded that punched-out dislocations are more favorable precipitation sites for Cu than Frank partials.

Notes: The coefficient of thermal expansion of electrodeposited Ni/Cu multilayers was obtained by measuring the evolution of membrane resonances and hence the tension as a function of temperature. The apparent thermal expansion coefficient of the multilayer membranes increases as the interface density of the multilayers increases. This increase is analyzed in terms of stress relaxation resulting from sliding of nonperfectly bonded interfaces. The analysis permits the normalization of all thermal expansion data of the Cu/Ni multilayers with layer thicknesses ranging from 20 to 800 nm but not of the thinnest layers, 2 nm thick. The results are consistent with the idea that interfacial adhesion improves as the layer thickness becomes very small, favoring epitaxial growth.

Notes: The application of the elastic recoil detection technique utilizing heavy ions for the analysis of semiconductor samples is demonstrated. With this technique the depth profiles of the primary constituents as well as profiles of all impurities can be measured in one spectrum. Depending on the target material, a depth resolution down to 20 nm can be achieved. All elements except hydrogen can be detected with almost the same sensitivity, namely ∼1×1015 at/cm2 with 136 MeV I in a 30° recoil geometry. For hydrogen, the sensitivity is about four times better.

Notes: A model for the growth and shrinkage of stacking faults in silicon is presented. It accounts for interstitial traps and a nonuniform concentration of intrinsic point defects. The complete system of balance equations of intrinsic point defects is solved numerically to simulate the kinetics of stacking faults during oxidation under the assumption that float-zone silicon contains less interstitial traps than Czochralski silicon. Investigation of the influence of different interstitial trap concentrations on the growth and shrinkage of surface stacking faults shows that the kinetics of surface stacking faults is not strongly affected by the presence of interstitial traps. Surface stacking faults are expected to grow in float-zone and Czochralski silicon in a similar way.

Notes: Experimental observations of dopant diffusion and defect formation are reported as a function of implant temperature in Si implanted GaAs. The diffusion of Si during post-implant annealing decreases by a factor of 2.5 as the implant temperature increases from −2 to 40 °C. In this same temperature range, the maximum depth and density of extrinsic dislocation loops increase by factors of 3 and 4, respectively. Rutherford backscattering channeling measurements indicate that Si implanted GaAs undergoes an amorphous to crystalline transition at Si implant temperatures between −51 and 40 °C. A unified explanation of the effects of implant temperature on both diffusion and dislocation formation is proposed based on the known differences in sputter yields between crystalline and amorphous semiconductors. The model assumes that the sputter yield is enhanced by amorphization in the lower temperatures, thus increasing the excess vacancy concentration. Estimates of excess vacancy concentration are obtained by simulations of the diffusion profiles and are quantitatively consistent with a realistic sputter yield enhancement.

Notes: In this paper we discuss two models of environmental degradation of adhesive joints developed from experimental observation of the joint failure mode. It is found that after severe degradation, failure is dominated by the interfacial mode, i.e., by failure at the interface between adhesive and adherend. The fraction of failure in the interfacial mode was found to be related to the joint strength and to be proportional to the frequency shift of a minimum in the spectrum of the reflected ultrasonic signal. One model considers an interface as an interphase in the form of a nonhomogeneous layer composed of two phases: "soft'' which is viscoelastic (degraded part of the interphase) and "stiff'' corresponding to the nondamaged interphase. Increase of the "soft'' phase fraction corresponds to the process of degradation in the interphase. The second model describes degradation in a form of disbonds filled by absorbed water at the interface. The disbonded interface is modeled by transverse spring boundary conditions, with the complex spring stiffness representing the quality of the bond. The influence of different disbond growth scenarios is considered. Advantages and drawbacks of these models are discussed.

Notes: We present calculations of conductance in a multiply connected nanostructure with a quantum box geometry. Well-defined conductance oscillations appear which are attributed to the quantum interference effect in the presence of a controllable impurity in the quantum box. As the strength of the impurity potential is modulated, conductance oscillations arise from the constructive and destructive interference for the two electronic paths around the centrally located impurity and a third tunneling path through the impurity. We discuss the dependence of these oscillations on the size of the impurity, in terms of circulating or bound states in the quantum box formed by multiple reflections of the phase-coherent electron. The conductance oscillations are predicted to be strong for realistic structural parameters and robust against increasing temperature.

Notes: Carrier concentration and mobility of unintentionally doped InP layers, grown directly on Si using metal-organic vapor-phase epitaxy, have been studied. The formation of antiphase domains (APDs) was found to depend on annealing of the Si substrate in an AsH3 flow prior to epitaxial growth. Dislocation densities determined by the wet chemical delineation technique were (8±1)×107 cm−3, seemingly uncorrelated to APDs in the layers. In addition to a shallow donor and a compensating acceptor, a deep donor was observed affecting the temperature dependence of the free-electron concentration between 77 and 300 K. The electron mobility in this temperature range could be described in terms of the scattering mechanisms which are dominant in homoepitaxial InP, namely, scattering due to polar optical phonons, to ionized impurities, and to space charges. Electron scattering due to either of these mechanisms was strongly influenced by the occurrence of antiphase boundaries (APBs). The space-charge density as well as the degree of compensation of the epitaxial layers increases with the density of APBs. Degraded 300 K mobilities were obtained indicating the effect of local stress at the APB.

Notes: The transport processes in phosphorus-doped polycrystalline silicon thin films are examined by standard six-electrode Hall effect and conductivity measurements over a wide temperature range, 100–400 K. These films were deposited by a novel layer-by-layer technique at very low substrate temperatures (300–360 °C) using fluorinated precursors, SiFmHn (m+n≤3). The analysis indicated that the grain boundaries are the major barriers to carrier transport. The grain boundary carrier transport is controlled by thermionic emission at high temperatures, whereas at low temperatures, it is dominated by a tunneling process through the barriers. The electrical properties of these films were found to vary as a function of the film thickness. It appears that the grain boundary defects are passivated to a large degree by this novel deposition technique and that the grain boundary barriers are consequently smaller than those in films prepared by other growth schemes.

Notes: Hole mobility in strained Si1−xGex/Si(001) layers is calculated as functions of temperature and doping concentration for various Ge contents using a Monte Carlo technique. In the Monte Carlo simulation, the band structure is computed by using a bond orbital model, which combines the k⋅p and the tight-binding methods with a strain Hamiltonian. The Fermi–Dirac distribution is employed for heavily doped impurity scattering. The alloy interaction potential of 1.0 eV for the Monte Carlo model is obtained by fitting the measured velocity-field characteristics in strained Si1−xGex alloys. The calculated hole mobilities compare well with experimental results. The strain effect on hole transport is also evaluated.

Notes: Semiconductor lasers under large-signal direct modulation by a square waveform are found to exhibit a transition from a power spectrum characterized by a fundamental frequency and FM sidebands to a continuous spectrum with a catastrophically broadened linewidth of the order of several GHz. The interesting feature of the phenomenon is that the photon output remains periodic apart from noise-induced fluctuations, and the broadening of the power spectrum is attributed to the sensitivity of the phase of the optical field to a large difference in the relaxation oscillation frequencies in the on and off states as well as the coupling between motions at the intrinsic resonance frequency of the system and the externally-imposed modulation frequency. It is shown that under deep modulation by a periodic injection current, the optical phase becomes aperiodic generating a wide range of new frequencies in the power spectrum. It is also demonstrated that by confining the excursions of the injection current to the region of almost-linear optical response, linewidth broadening may be avoided. Quantitative criteria for determining the boundary of the broadened-linewidth region are presented for several modulation frequencies.

Notes: The thermal diffusivities of mercury cadmium telluride, (Hg1−xCdx)1−yTey, and mercury zinc telluride, (Hg1−xZnx)1−yTey, with 0.55≤y≤1.0 and 0.0125≤x≤0.054 65, and of pure Te were measured from 350 to 850 °C by the laser flash technique. The diffusivity of near-pseudobinary Hg1−xCdxTe solids decreased more rapidly with temperature approaching the melting point than did pseudobinary solids previously reported: The solid diffusivity for x=0.028 17 and y=0.55 was 0.83 mm2/s at 371 °C, decreasing to 0.22 mm2/s at 614 °C. The diffusivity of Te-rich (Hg1−xCdx)1−yTey melt increased with x and with temperature: The melt diffusivity for x=0.039 36 and y=0.782 was 0.91 mm2/s at 485 °C, increasing to 4.93 mm2/s at 851 °C. For Te-rich (Hg1−xZnx)1−yTey melt with x=0.0125 and y=0.7944 there appeared to be a minimum diffusivity of about 2.6 mm2/s near 690 °C. The thermal diffusivity of pure Te solid was 0.97 mm2/s at 300 °C and decreases to 0.64 mm2/s at 439 °C. The melt diffusivity of pure Te was 1.52 mm2/s at 486 °C, increased to 3.48 mm2/s at 584 °C. Experimental data presented can be used to calculate the thermal conductivity needed for designing systems capable of growing a better quality single crystal of these materials.

Notes: A simple model of foam drainage is introduced in which the Plateau borders and quadruple junctions are identified with pools that discharge through channels to pools underneath. The flow is driven by gravity and there are friction losses in the exhausting channels. The equation of Bernoulli combined with the Hagen–Poiseuille equation is applied to describe the flow. The area of the cross section of the exhausting channels can be taken as a constant or may vary during drainage. The predictions of the model are compared with standard drainage curves and with the results of a recently reported experiment in which additional liquid is supplied at the top of the froth.

Notes: Confocal fluorescence microscopy has been used to measure the three-dimensional distribution of the H3 color center produced in type IIa natural diamonds by 5 MeV He+ irradiation at a total fluence of 8×1015 cm−2. The peak of the H3 emission occurs 16 μm below the surface of the irradiated side of the diamond, which is in fair agreement with the peak of the vacancy distribution predicted by a Monte Carlo calculation (transport of ions in matter or trim). The H3 distribution is broader in the direction normal to the surface (10 μm full width at half maximum) than the trim calculation. This is attributed to diffusion of vacancies caused by self-annealing during irradiation.

Notes: A specimen of Cu50Fe50 equiatomic composition was mechanically alloyed (MA) by ball milling starting from the pure elements, which are immiscible according to the equilibrium phase diagram. Structural analysis by x-ray and neutron diffraction has shown that the mechanical process initially reduces the crystallite size of both elements as a function of the milling time. The diffraction data show that the bcc iron phase is subsequently consumed, due to progressive incorporation of the iron atoms into the fcc copper matrix. The Mössbauer spectra of a specimen MA for 16 h has a broad magnetic profile typical of a Fe-Cu extended solid solution, with some evidence of two local environments of the iron atoms and a small admixture of the γ-Fe. The annealing of these MA treated specimens effects a decomposition of the extended solid solution into FCC copper and both α- and γ-iron allotropes. This decomposition process is discussed in relation to spinodal decomposition and to nucleation-and-growth mechanisms.

Notes: Using an optimized bond breaking algorithm, we simulated the failure of three-dimensional networks composed of two randomly interspersed components. We studied the strength and the number of bonds broken prior to the failure instability (the damage). When one phase is of low concentration, damage mostly occurs when the dilute phase is very weak and fails prematurely, although a limited "matrix damage'' mechanism does exist. In contrast, when the composite is a 50/50 mixture and the two phases are macroscopically interpenetrating (both phases percolate), the ability to absorb damage is greatly enhanced. In the interpenetrating phase regime the strength of the composite is, in some cases, enhanced beyond that of the analogous particle reinforced composite. These features suggest that interpenetrating phase composites can have improved properties in comparison to conventional "particulate'' composites. Analysis of the composite is neatly summarized in "damage maps'' which give a quick indication of the regions in which the ability to absorb damage is enhanced. Using lattices of up to linear dimension L=40 we also study the finite-size-scaling laws for the average strength and damage of the networks.

Notes: The crystal structure of LaFe9Si4 intermetallic compound equilibrated at 1173 K has been determined by the x-ray powder diffraction and refined by the Rietveld technique. The crystal structure belongs to the tetragonal symmetry with space group I4/mcm, which can be derived from the cubic NaZn13-type structure. Each unit cell contains four formula units of LaFe9Si4. The lattice parameters are a=7.932(1) A(ring) and c=11.677(2) A(ring). The calculated density is Dx=6.86(4) g/cm3. In the structure there are five kinds of equivalent positions, i.e., 4a, 16l(1), 16k, 16l(2), and 4d, which are occupied by 4La, 16Fe(1), 16Fe(2), 16Si, and 4Fe(3) atoms, respectively.

Notes: A nondestructive method is introduced to determine the effective elastic moduli of fiber-matrix interphases from measured composite moduli. The composite moduli are obtained by measuring the angular dependences of ultrasonic longitudinal and transverse phase velocities in planes along and perpendicular to the fibers. Three independent interphase effective moduli are found using micromechanical multiphase models which were applied after averaging composite transverse moduli to account for the composite orthotropy. Sensitivity analysis shows that errors in the calculated interphasial moduli are approximately ten times those in the composite moduli. Experiments are performed on Si3N4 ceramic and Ti-24Al-11Nb intermetallic matrix composites reinforced with carbon coated silicon carbide fibers. The experimental interphasial moduli for the intermetallic composites agree with literature data after accounting for the interphase microstructure. The interphasial moduli for ceramic composites are lower than those for the intermetallic composite due to imperfect mechanical contact between the interphase and the porous matrix. The use of the method to assess the interphase degradation is demonstrated for interphasial oxidation damage. The analysis helps to determine the morphology of the damaged interphase.

Notes: Space-charge dipole domain dynamics theory has been used to investigate the frequency locking, quasiperiodicity, and chaos in extrinsic Ge. Our numerical results agree with the experimental phenomena.

Notes: The surface roughness of polished InP (001) wafers were examined by x-ray reflectivity and crystal truncation rod (CTR) measurements. The root-mean-square roughness and the lateral correlation scale were obtained by both methods. The scattering intensities in the scans transverse to the specular reflection rod were found to contain two components. A simple surface model of surface faceting is proposed to explain the experimental data. The sensitivities of the two methods to the surface structure and the role of the resolution functions in the CTR measurements are discussed.

Notes: Monte Carlo methods which have been widely used for studying high field electron and hole transport, so far have not been applied to the complex problem of Ohmic hole transport. We present a versatile generalization of the Monte Carlo approach for Ohmic hole mobility studies and apply it to pure silicon and germanium. In particular, we examine the role of the optical phonon deformation potential d0 in controlling the temperature dependence of the mobility.

Notes: Thermal emission of charges has been studied in Si3N4-GaAs structures which were prepared using direct plasma-enhanced chemical-vapor deposition. A comparison has been made of the effects of predeposition plasma treatments using hydrogen, argon, and a mixture of the two. Channel current transient spectroscopy was used in the temperature range 77–350 K. All of the samples exhibited electron emission from an interface-state continuum with energies that were consistent with the interface-state-band model proposed by Hasegawa. When argon and hydrogen were used together two extra processes were observed. One of these was due to an electron trap with an activation energy of 0.05 eV; this response was from states at the remote edge of the depletion region several thousand angstroms from the interface. The necessity for argon and hydrogen suggests that argon had created structural damage permitting the entry of hydrogen atoms to form electrically active complexes in the damaged region. The second process which had an activation energy of 0.05 eV resembled hole emission but, because hole injection was an unlikely process, this observation has been attributed to an interfacial polarization process exhibiting thermally activated relaxation. The corresponding dipole moment per unit area was 1.0×1011 C m. Since this mechanism also required the action of argon and hydrogen it was concluded that this was damage related, with electrical activity produced by the hydrogen atoms.

Notes: We investigate acoustic-phonon scattering in quantum wires subject to a periodic potential along the propagating direction. A technique for modeling the electronic structure of the periodic system is introduced using the imaginary time propagation method. The acoustic-phonon scattering rate is evaluated by taking umklapp processes into account. We found umklapp processes can cause a significant increase in intersubband scattering but is negligible for intrasubband scattering. Overall, the exact treatment of the electron dispersion relation improves the acoustic-phonon limited mobility compared to earlier estimates [H. Noguchi, J. P. Leburton, and H. Sakaki, Phys. Rev. B 47, 15593 (1993)].

Notes: Mapping of the magnetic flux distribution in a square-shaped superconducting YBa2Cu3O7 thin film was carried out using a scanning micro-Hall probe with a spatial resolution of about 25 μm. Calculation procedures for converting the measured flux map to the film current distribution are discussed. The flux penetration with the applied field perpendicular to the film surface was studied in initially zero-field-cooled samples. With full flux penetration, the film sheet currents follow the sample edges, whereas with partial flux penetration, the sheet currents are more complex and include multiply connected patterns. In both cases the sheet currents change their flow direction abruptly along the sample diagonals where the shielding is more effective, and this results in distinctive minima of the flux penetration. The saturation magnetization for a square-shaped sample of side 2a was found to be identical to that for disc and cylindrical samples of radius a. It is shown that the multiply connected current patterns corresponding to various parts of the hysteresis cycle can be reconstructed from the superposition of two appropriate virgin current distributions. The critical current density was dependent on magnetic flux density, and it was found to follow the Kim model.

Notes: Electron paramagnetic resonance (EPR) of centers produced in porous silicon (PS) by heat treatment in air is investigated. The properties of these centers are compared with the defects present in as-prepared PS or activated by treatment of the specimens with ethanol. The native defects of PS and those produced by thermal annealing show different saturation behavior of the EPR spectra when the microwave power is increased. Also, their spin-dependent recombination processes are different. The dependence of the EPR line intensity on the thermal annealing time at temperatures of 150–500 °C obeys a law characteristic to a diffusion process with an activation energy of 0.9 eV. This value is close to the activation energy of oxidation of crystalline silicon surfaces with atomic oxygen.

Notes: Results of measurements in situ of electrostrictive strain, dielectric polarization, dielectric constant, and crystallographic parameters as functions of applied electric field in the temperature range 20–200 °C of Pb0.97La0.02(Zr0.66Ti0.11Sn0.23)O3 composition are reported. The antiferroelectric to ferroelectric phase transition with large volume change ΔV=0.35 A(ring)3 is shown to be the dominant mechanism of the field-induced strain. The microscopic nature of the switching mechanism and the variation of the strain versus polarization squared at various temperatures are discussed.

Notes: Li-doped LiBO2 and LiNbO3 thin films have been studied and their optical and electrical properties determined. With doping the ionic conductivity of the films was found to increase substantially. The highest conductivity obtained with the doped films was about 4.5×10−6 S cm−1. All the films exhibited a high degree of transmission in the spectral region from 350 to 2500 nm. The remarkable increase in the ionic conductivity coupled to the preservation of a high optical transmission makes this doping technique highly attractive for devising ion conductors that can be used in transmissive solid-state electrochromic systems or the so-called "smart windows.''

Notes: The transition from rhombohedral phase to tetragonal in screen-printed lead zirconate titanate (PZT) thick films was studied using Raman-scattering spectroscopy, and the results were compared with those of x-ray-diffractometry investigations. The unfired films were subjected to rapid firing in an air atmosphere at temperatures ranging from 960 to 1150 °C. During firing the composition of the films changed gradually as lead evaporated, which moved the composition of films to the ZrO2-PZT region and resulted in precipitation of ZrO2. This caused the original rhombohedral structure to be converted to tetragonal. Correspondingly, the Raman spectra also changed with increasing firing temperature. The variation in Raman spectra was characterized by three frequency regions, denoted as the low-, intermediate-, and high-frequency region, respectively, which are related to three cubic T1u modes. Moreover, it was also observed that the appearance of tetragonal modes was delayed from the formation of tetragonal structure during the process. This discrepancy suggested the existence of a certain "mismatch'' in structure.

Notes: A refrigerator is described that is based upon thermionic emission. Room-temperature refrigeration is efficient when the work function of the anode is about 0.3–0.4 eV but those low values are unattainable. The refrigerator only operates at higher temperatures.

Notes: The use of a low oxidation state Ti compound, cyclopentadienyl cycloheptatrienyl titanium, (C5H5) Ti(C7H7) (CPCHT), as a potential source for TiN and Ti in plasma enhanced chemical vapor deposition processes has been investigated. This precursor provides us with a new chemical vapor deposition route to TiN films that offer an interesting contrast to films deposited from Ti(IV) precursors. Film depositions were carried out by introducing CPCHT, with H2 carrier gas, into the downstream region of a NH3, N2, H2, or mixed H2/N2 plasma. Low resistivity (100–250 μΩ cm) nitrogen-rich TiN films with little carbon or oxygen incorporation and good conformality were deposited with activated N2 or NH3 at deposition temperatures of 300–600 °C, inclusive. Mixed H2/N2 plasmas resulted in more stoichiometric TiN films with similar properties. The most striking feature of these films is the absence of columnar grain growth, in contrast to TiN films deposited using TiCl4 or Ti(NR2)4. Although the film texture was influenced by the plasma gas, the average grain size of the films deposited using activated N2 and NH3 was similar. The TiN films that we deposited were effective diffusion barriers between aluminum and silicon up to 575 °C. Depositions using activated H2 resulted in films with significantly less carbon than CPCHT, but still having a minimum of 2.7:1 C:Ti. The lower oxidation state of the precursor did not facilitate the deposition of a Ti-rich film. No depositions were observed with any of the reactant gases in the absence of plasma activation.

Notes: A theoretical framework for the design of asymmetrically doped n-type n-i-p-i- superlattices for subband detector applications in the 10 μm spectral range is described. Excellent agreement is found with the subband absorption spectra measured in a series of GaAs n-type n-i-p-i- samples and oscillator strengths, transition energies, and dipole matrix elements comparable with conventional quantum-well heterostructure detectors are found. Pronounced IR-absorption modulation by optical pumping with band-gap radiation is seen, due to the enhanced interband recombination time resulting from the type-II n-i-p-i- potential. The prospective advantages of n-type n-i-p-i- devices for the detection and modulation of 10 μm radiation are discussed.

Notes: Current voltage characteristics of narrow-gap Hg1−xCdxTe photodiodes, fabricated on liquid phase epitaxy and metalorganic chemical vapor deposition grown layers, have been investigated. It is shown that the tunneling-recombination process is the dominant mechanism that determines the dark current at forward and at low reverse bias. This mechanism also determines the junction zero-bias resistance.

Notes: We have performed a detailed study of two-dimensional grating coupling for quantum well infrared photodetectors in the very long wavelength spectral region λ∼16–17 μm. Using calculations based on the modal expansion method we quantitatively explain the double peaked responsivity spectrum. By optimizing the grating parameters we achieve a normal incidence responsivity and detectivity which are three times larger than the 45° angle of incidence geometry.

Notes: We characterize the photorefractive behavior of a photorefractive multicomponent polymer composite of PVK-TCP:C60:DEANST. Efficient plasticization of the host polymeric matrix and utilization of a nonlinear chromophore with a large dipole moment provide a large poling-induced electro-optic coefficient. Diffraction efficiencies as high as 40% and asymmetric net two-beam coupling gain coefficients in excess of 130 cm−1, surpassing those of known inorganic single-crystalline photorefractive media, are reported.

Notes: Friction between graphite and diamond surfaces against a sharp silicon nitride tip was measured using a friction force microscope (FFM). Atomic-scale friction images of a freshly cleaved highly oriented pyrolytic graphite exhibited the same periodicity as that of the graphite surface; however, the peaks in friction profiles and those in corresponding topography profiles were displaced relative to each other. Using the Fourier expansion of the interaction potential, the conservative interatomic forces between the FFM tip and the graphite surface have been calculated. It is shown that the variations in atomic-scale friction and the observed displacement between the peaks in the frictional (or lateral) force and those in the corresponding topography can be explained by the variations in interatomic forces in the normal and lateral directions. Thus, the observed variation in friction force may not necessarily occur as a result of the commonly believed atomic-scale stick-slip process, but can be due to variation in the intrinsic lateral force between the sample and the FFM tip. At large scan sizes (50×50 nm2 or larger), the variation of friction for graphite and a single-crystal (IIa) diamond was found to correlate with the variations in the local slope of the sample surface, suggesting that a ratchet mechanism is responsible for variations in microscale friction.

Notes: Amorphous diamondlike carbon (DLC) films grown by low-energy mass-selected ion-beam deposition have been examined by electron-energy-loss spectroscopy (EELS). Films grown using deposition energies of 50, 120, and 300 eV have been studied. For these deposition energies, all films exhibit similar EELS characteristics indicating a very high degree of sp3 bonding. The bulk plasmon resonance is intermediate between that of graphite and that of diamond; however, the properties of the low-energy-loss spectra of the DLC films are more similar to those of diamond. The near-K-edge carbon EELS data from the films exhibit a π* feature which is much smaller than that of graphite or evaporated carbon. The use of previously proposed computational methods on the near-K-edge EELS data indicates that over 80% of the carbon atoms are sp3 bonded. The size of the π* feature is larger for smaller plasmon energies, as expected. The present data are in accord with other analyses of similar films that indicate a broad (∼30–300 eV) energy window for diamondlike film formation.

Notes: A detailed study of Fe implantation and damage annealing in indium phosphide is presented. The technological goal was to obtain thermally stable semi-insulating layers in n-type InP. Different characterization techniques were employed, including structural (x-ray diffraction, Rutherford backscattering spectrometry, and transmission electron microscopy), chemical (secondary ions mass spectrometry), and electrical (current-voltage) measurements. Both undoped and n-type (Sn) doped substrates were implanted with Fe doses ranging from 5×1011 to 2.2×1014 cm−2 and annealed at a temperature of 650 °C. The high doses used to compensate n+ doping caused amorphization of the material. The reordering process of the amorphous layers and its influence on the Fe redistribution properties were studied in detail. The activation of the implanted Fe atoms after annealing was derived. Although the recovery process of the amorphized layer appears to be rather complex, our results show that good crystal quality and full compensation can be reached also for n+ doped substrates, leading to resistivity values above 2×107 Ω cm, even starting from an initial doping level as high as 1.4×1018 cm−3.

Notes: Degradation of top electrodes is one of the most important factors to determine the lifetimes of organic electroluminescence (EL) devices. An organic EL device [indium thin oxide (ITO)/N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4, 4'-diamine (TPD)/tris(8-hydroxy- quinoline)aluminum (Alq3)/Al] was prepared and a morphological change of the Al top electrode was observed during and/or after applying voltage by atomic force microscopy and scanning electron microscopy (SEM). The change in the electrode surface, i.e., the increase in surface roughness was observed during the current flow. The degradation process started from faint dark core parts and propagated into disks with different rates depending on the magnitude of applied voltage. Degraded sites of the Al electrode, which were analyzed as aluminum oxide by Auger electron spectroscopy, protruded into the air on the organic layers. In SEM images of a life-end electrode, discontinuities due to crevasse formation in the organic layers sandwiched by the ITO base and the metal top electrodes were observed in many places. These results confirm that one of the most crucial factors of the degradation process was deformation of metal and organic layers due to heat, gas evolution, and oxidation caused by applied voltage.

Notes: The effect of pressure gradients that develop in diffusion systems consisting of particulates dispersed in a continuous fluid is considered. It is shown that the gradient of chemical potential which drives the diffusion flux induces a pressure gradient that opposes this flux. This effect, which exists in addition to the induced bulk flow, is expressed in terms of a diffusive buoyancy force (DBF). For dispersions consisting of monodisperse particulates in a single-component fluid, the net driving force is the negative product of the volume fraction occupied by the fluid and the gradient of the chemical potential of the particulates. For polydisperse particulates, the DBF is the negative product of the total volume fraction occupied by the particulates and the expectation of gradient of their chemical potential. The joint effect of the DBF and the hydrodynamic hindrance is expressed in terms of a concentration-dependent diffusion coefficient. It is shown that the effect of the DBF yields a fundamental diffusion coefficient Dφ, which is the product of the volume fraction occupied by the fluid 1−φ, and the Stokes–Einstein diffusion coefficient D. The intrinsic diffusion coefficient, which is defined as the product of 1−φ and Dφ, thus becomes the product of the square of 1−φ and D. At steady state the concentration profile cannot be analytically linear unless the buoyancy and hydrodynamic effects are offset by changes of size, energy per particulate and the activity coefficient. Finally, implications regarding the diffusion equation and effects of combined fields on the DBF are considered.

Notes: The kinetics associated with the breakdown of epitaxy at low temperatures are studied for growth onto a number of Si surfaces, including (001), (117), (115), and (113). These surfaces are all initially generated at trench edges on a single patterned substrate. Growth on each of these surfaces at low temperatures is shown to result in a well-defined crystalline-to-amorphous transition. The epitaxial thicknesses hepi have been measured over a range of substrate temperatures below 280 °C, and activation energies characteristic of this transition were determined. In general, the breakdown in epitaxy occurs such that hepi(001)(approximately-greater-than)hepi(117)(approximately-greater-than)hepi(115)(approximately-greater-than)hepi(113). Growth at slightly higher temperatures, Tsubstrate(approximately-greater-than)300 °C, shows a different microstructure than that at lower temperatures. Epitaxial growth continues for longer times on (113) facets, as compared with (001). These results are discussed in terms of a recently proposed model explaining the breakdown of epitaxy at lower temperatures and an epitaxial temperature for Si.

Notes: Thermal stability and crystallization of amorphous Si:P alloy thin films consisting of 20–44 at. % P have been studied in this work. The results show that the alloys have crystallization temperatures ranging from 850 to 1150 °C, which are all higher than that of pure amorphous Si, and that the variation of resistivity of the alloys during the 120 h aging at 300 °C is small (0.6%). These results indicate that the alloys have a high thermal stability, which is in agreement with the thermodynamic prediction we have made. It has also been observed that the crystallization products for these alloys are different. A new silicon phosphide phase has been observed in the 30 at. % alloy sample and suggested to be possibly a hexagonal Si7P3 phase which has lattice parameters a=5.32 A(ring) and c=13.3 A(ring). The alloy films were deposited onto quartz substrates and Si wafers by coevaporation of Si and P. X-ray diffractometry and transmission electron microscopy were utilized to investigate the crystallization temperature and product of the amorphous alloys.

Notes: The use of Ar dilution in a N plasma source has been used to achieve control of both electrical and optical properties of p-type ZnTe:N grown by molecular-beam epitaxy. Photoluminescence data are presented that show the transition from "pure'' ZnTe emission to that indicative of heavily N-doped ZnTe. A new principal bound-exciton line associated with N impurities is observed at 2.3685 eV. An anomalous red shift in the corresponding donor-acceptor pair peak energy with increasing N concentration is observed at high N concentration and is attributed to the effects of N impurity banding. Trends in p-type conductivity confirmed the ability to control hole concentrations using Ar dilution.

Notes: The electrical conductivities of n-doped silicon and, in particular Si:Bi, have been investigated for doping levels greater than the impurity critical concentration Nc for the metal-nonmetal transitions. A general feature of the conductivity for concentration normalized to Nc is presented in the order σ(Bi)(approximately-greater-than)σ(As)(approximately-greater-than)σ(P)(approximately-greater-than)σ(Sb). For Si:Bi, the value of Nc is calculated for different criteria. The mobility of electrons presents a lower value compared to Si:P. The results for Si:P and Si:As are compared to the experimental data available in the literature.

Notes: Time-dependent p-n junction characteristics (junction depth: xj∼0.2 μm) underneath TiN/Ti contact metal have been determined in terms of contact interface crystallinity. Reverse bias (≥6.0 V) soft-breakdown characteristics result in a leakage current increase during reverse bias and temperature aging stress. It has been elucidated that this degradation is dependent on the crystallinity of Ti-Si interdiffused layers at the contact interface and the p-n junction polarity. The degradation is observed only in amorphous Ti-Si contacted n+-p junctions. Nevertheless, in amorphous Ti-Si contacted p+-n junctions and crystalline TiSi2 contacted n+-p and p+-n junctions, the degradation does not appear. In the case of the amorphous Ti-Si contacted n+-p junction, it is concluded that the time-dependent degradation is caused by diffusion of positively ionized Ti enhanced by the applied electric field.

Notes: A systematic comparative study between the electronic and optical properties of the strain layer superlattices (Si)10−n/(Ge)n coherently grown on a Si1−n/10Gen/10(001) alloy surface and those of the corresponding bulk alloys Si1−n/10Gen/10 is presented. We find that the superlattices have a smaller fundamental gap than the corresponding alloys; also for energies smaller than 1.5 eV and polarization along the growth plane, the real part of the dielectric function, ε1, for the SLS is larger than that of the corresponding alloy, while for perpendicular polarization, the two dielectric functions practically coincide. The utilization of this property for the construction of planar waveguides is investigated. In particular, the transverse electric modes of a waveguide consisting of a finite thickness SLS (Si)6/(Ge)4, sandwiched between two layers of the alloy Si0.6Ge0.4, are studied. No transverse magnetic modes exist in this structure.

Notes: Carrier energy relaxation rates via carrier-polar optical-phonon interactions with hot phonon effects are theoretically studied in multisubband quantum well structures. The effects of changing the width and depth of quantum wells on the carrier energy relaxation rate are discussed. Compared to the result of the bulk, we find that the difference in the energy relaxation rate between quantum wells and bulk is rather small. Reducing the lifetime of longitudinal-optical phonons will effectively enhance the carrier energy relaxation rate. The implications in designing high-speed quantum well lasers are also suggested.

Notes: A method for imaging magnetic domain structures in the transmission electron microscope is described. Coherent Foucault imaging provides a direct means of producing a magnetic interferogram which reveals the quantitative distribution of magnetic induction across the specimen. The technique requires the high coherence of a field-emission gun system and the ability to position an aperture accurately to cut part of the diffraction pattern. A simple analytical theory, together with computer simulations and experimental results, is presented to demonstrate the power of the technique.

Notes: The influence of internal stress on the magnetic anisotropy and the magnetostriction was investigated in sputter-deposited amorphous (Tb0.27Dy0.73)0.42Fe0.58 films. Films with tensile stress show in-plane anisotropy and giant magnetostriction of λ(parallel)=400×10−6 at 1 T measured in a field parallel to the film plane at room temperature. The magnetostriction rises rapidly to λ(parallel)=200×10−6 at 0.05 T and the coercivity is less than 0.01 T. On the other hand films with compressive stress show perpendicular anisotropy and still higher magnetostriction of λ(parallel)=540×10−6 at 1 T; however, this is by far a slower increase of magnetostriction at small fields. This different behavior is explained by considering the nature of magnetization processes, i.e., domain-wall motion and spin rotation.

Notes: Due to dipole interaction, the molecular polarization brought about by an external field is significantly lower in condensed matter (liquids) than in a gas. In addition to this, the response of interacting dipoles to stepwise changes of the external field does not follow a simple time exponential. Instead, a spectrum of relaxation times is required to describe such a response. Debye and Ramm [Ann. Phys. 28, 28 (1937)] have attempted to describe the effects associated with rotational hindrances due to dipole-dipole interaction by the following differential equation: ∂f/∂t =(kT/ρ)Δf+(1/ρ)div(f grad u), where f denotes the distribution function specifying the number of dipoles pointing in a certain solid angle, t the time, ρ a friction coefficient, and u the potential of the forces acting on the dipoles. The latter quantity depends both on the external field and on the contribution from the dipole-dipole interaction (internal field). Although unable to solve the above equation explicitly, Debye and Ramm (DR) made some predictions about the solution, concluding, among other things, that the inclusion of an internal field E would yield a process with a discrete spectrum of relaxation times. Finding such prospect highly interesting, we subjected the DR equation to a close study using some advanced mathematical tools (Fourier integral operators etc.). Contrary to the conclusions of DR, we found that the above equation cannot be solved in the way originally described, and that the conjectured eigenfunctions and eigenvalues do not exist. Furthermore, we show that, in contrast to DR's statements, the above equation is not solved by certain classical expressions relating to free-rotating dipoles (no internal field). The lack of physical content of this equation appears to be due to a number of not permissible simplifications.

Notes: Photoreflectance and photoluminescence were used to study GaAs/AlGaAs quantum wells (QWs) as they were partially intermixed using SiO2 capped rapid thermal annealing. As the annealing temperature was increased, the experimental photoreflectance results showed spectral features moving to higher energies and merging to form broad peaks. This is explained by changes in the shapes of the originally square wells, which result in a convergence of their subbands around certain energies. The interpretation of these changes showed that the partially intermixed QWs were well described by an error-function profile.

Notes: The low-pressure chemical-vapor deposition of phosphorus-doped silicon film on glass at 550 °C was investigated as a function of silane pressure (1–100 Pa) and phosphine/silane mole ratio ranging between 4×10−6 and 4×10−4. At this low temperature the film is homogeneous in thickness and the silicon is amorphous except for low pressure (1 Pa). Phosphorus concentration varies linearly with mole ratio in amorphous deposited films. The resistivity of films annealed at 600 °C decreases while the incorporation of phosphorus (mole ratio) increases, and varies with phosphorus concentration from 101 to 10−3 Ω cm. For the same phosphorus content, the resistivity is lower if the silicon film is amorphous deposited and subsequently crystallized, than if the film is polycrystalline deposited. Carrier concentration and mobility are measured using the Hall method. Doping efficiency and electrical properties are discussed.

Notes: A technique for growing ultrathin silicon oxides of superior quality at low temperatures is indispensable for future submicron device applications. Fundamental characteristics such as the oxide breakdown fields, oxide charges, and interface-state densities of various ultrathin silicon oxides (≤8 nm) grown by microwave plasma afterglow oxidation at low temperatures (400 and 600 °C) were investigated. Fluorination (HF soaking) and low-temperature N2O plasma annealing were employed to improve the properties of the oxides. The breakdown fields of the as-grown silicon oxides were enhanced and the interface-state densities were reduced. The effect of N2O annealing time on the interface-state density was also investigated. A longer annealing time ((approximately-greater-than)1 h) was required to reduce the interface-state density. The effective oxide charge density of 600 °C as-grown oxide was as low as 6×1010 cm−2. Additionally, the breakdown field of the thin silicon oxide grown at 600 °C with 15 min N2O plasma annealing was 12 MV/cm.

Notes: The principle of minimum available noise energy is used to calculate the quasipotential over the state space of a nonhysteretic Josephson junction driven by a rf bias. This potential surface provides an intuitive picture of the dynamics of phase lock and defines a stability parameter, the activation energy for thermally induced phase slippage, which determines the optimum operating conditions for a proposed programmable voltage standard.

Notes: This article studies the mesoscopic transport of electrically controllable inversion layers of Si metal-oxide-semiconductor field-effect transistors that use a dual-gate structure. We have developed two kinds of devices: a quasi-one-dimensional device (1D-FET) and a Coulomb blockade device (CB-FET). In both devices, the field effect is used to change the channel structure by introducing potential barriers in the narrow inversion channel. The 1D-FET changes a long diffusive quantum wire into a short ballistic one. Strong oscillations in differential conductance, even negative differential conductance, have been observed at 4.2 K, indicating enhanced modulation of electron mobility by intersubband scattering suppression. The CB-FET, on the other hand, transforms a simple quantum wire into a coupled quantum-dot array. A clear change in transport properties is observed with changes in the barrier height at low temperatures. The experimental results are consistent with the theory of one-dimensional subbands and the Coulomb blockade of single-electron tunneling.

Notes: The Au/n-Si Schottky barrier (SB) which contains hydrogen has a 0.10 eV lower SB height (SBH) than that without hydrogen. For the hydrogen-containing SB, zero bias annealing (ZBA) decreases the SBH while reverse bias annealing (RBA) increases it. In addition, ZBA and RBA cycling experiments have been made which reveal a reversible change of the SBH within at least four cycles. The annealing temperature of ZBA and especially of RBA influences the SBH. We interpret the above effect in terms of an interaction between hydrogen and metal-semiconductor interface states.

Notes: We measured the increase in threshold currents due to lateral carrier diffusion in InGaAs/AlGaAs quantum-well ridge-waveguide laser diodes. The ridge stripes were fabricated by using both in situ monitored pure Cl2 reactive ion etching and selective wet etching to completely eliminate the spreading current in the conductive upper cladding layer while keeping the ridge sidewalls straight. After comparing the threshold data with a theoretical model, the ambipolar diffusion coefficient is found to be 22 cm2/s in the population-inverted InGaAs layer. This model is based on the calculated optical gain curve and the ambipolar carrier transport in the quantum-well and waveguiding layers. The dependence of carrier lifetime on the local carrier concentration is included in the calculation. Moreover, from another set of devices with the portions of the active layer outside the ridge stripes etched away, the surface recombination velocity is found to be around 1–2×105 cm/s.

Notes: Ion and electron densities have been measured in long, low pressure, cylindrical nitrogen and helium dc discharges using computer-controlled Langmuir probes. Cylindrical probe data have been analyzed with a variety of theories in order to determine the latter's accuracy. Electron densities were obtained from the electron saturation currents using orbital motion limited (OML) theories, and from the electron retardation region of the probe trace by integration of the second derivative of the probe current. Ion densities were obtained from both OML and radial motion analysis of the ion saturation currents. Line integrated microwave interferometry and discharge current continuity considerations in the positive column have been used to obtain two independent electron density measurements. While both probe electron density methods agree very well with each other and reasonably well with the independent density measurements, the OML theory applied to the ions overestimates the plasma density by up to a factor of 10. The radial motion theory yields ion densities that show considerably better agreement with the electron densities than the OML theory. Ion and electron densities have also been measured with planar probes, but they were found to perturb the surrounding plasma more than the cylindrical ones.

Notes: Abnormal (100) grain growth has been characterized in predominantly (111)-textured Cu thin films as a function of deposition temperature, annealing temperature and the presence of a Ta or W underlayer. For films deposited at room temperature, bimodal grain size distributions are observed at annealing temperatures at or above 150 °C for Cu on Ta and 100 °C for Cu on W. Suppression of (100) abnormal grain growth was achieved by depositing Cu on either barrier layer at 150 °C. A bimodal grain size distribution was still observed for the film deposited on W at 150 °C but the large grains forming this distribution were found to be (111) oriented. These results are explained as the result of competition between strain energy minimization and surface and interface energy minimization. The (100) growth is shown to be driven by a reduction of the orientation-dependent strain energy that builds up due to the elastic anisotropy of Cu. Films deposited at higher temperatures have a lower yield stress which limits the achievable strain energy driving force, thereby suppressing the (100) growth. Surface energy minimization drives the (111) abnormal growth.

Notes: Age-momentum measurements and positron lifetime measurements were carried out in order to investigate vacancy-type defects produced in 3 MeV electron irradiated synthetic silica glasses, in which 1 ppm and 300 ppm of –OH bonds were contained. A high formation probability of positronium (Ps) was found for unirradiated specimens. These Ps atoms were considered to be formed in open-volume defects (∼7×10−2 nm3). The formation probability of Ps was drastically decreased by the electron irradiation, especially for the specimens which contained 1 ppm of –OH bonds, even though the size of the open-volume defects and the momentum distribution of electrons at the open-volume defects are independent on the –OH concentration and on the electron irradiation. Since the values of second lifetime components of positron lifetime spectra were ∼300 ps and very close to the estimated value of the lifetime of the positrons which are considered to be trapped in the mono- or divacancies, the decrease of formation probability of Ps can be attributed to an increase of positron annihilation in vacancy-type defects generated by the electron irradiation. Positrons were suspected to be trapped in such defects.

Notes: Hot-stage high-voltage (1.5 MeV) transmission electron microscopy was used to directly observe CdS nanocrystals precipitated in a silicate glass and a theoretical framework of nanocrystal coarsening kinetics more appropriate than the popularly used Lifshitz–Slyozov–Wagner theory was developed. Nanocrystallite nucleation and coarsening were monitored in situ by video taping of bright-field images of the edges of thin (less than 2 μm) glass fragments heated in the hot stage; crystallite size distribution was obtained from the taped experimental observations. The effects of electron-beam heating and diffusion out of the nanocrystals were included in developing the theoretical analysis of coarsening kinetics which were used, in turn, to interpret the experimental size distribution curves.

Notes: Barium titanate thin films were fabricated by the sol-gel technique from two different precursors, one using barium 2-ethyl haxanoate and other using barium hydroxide dissolved in methoxy ethanol as barium source. The films were examined at different curing temperatures using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, optical transmission spectroscopy, and x-ray diffraction. The films prepared from an ethyl hexanoate precursor were found to crystallize around 550 °C into tetragonal polycrystalline form, whereas those prepared from a barium hydroxide precursor were crystallized into cubic form around 600 °C. The films prepared from the ethyl hexanoate precursor showed larger shrinkage during heat treatment and were more porous than those made from the hydroxide precursor. The changes in thickness, refractive index, and band gap of the films annealed at different temperatures were correlated with chemical modifications of the precursor film as well as structural and microstructural changes occurring during the formation of the final barium titanate thin film. FTIR spectroscopy and electron microscopy were used to support these observations.

Notes: A structural study of the initial interface region formed by zirconium on silicon (111) was undertaken. Thin films (100 A(ring)) of zirconium were deposited in ultrahigh-vacuum conditions onto atomically, clean silicon (111) wafers and annealed in situ at 25 °C intervals between 300 and 425 °C, over which range Auger spectroscopy indicated silicon diffusion to the surface. Structural characterization of the evolving interface was performed primarily via extended x-ray-absorption fine-structure (EXAFS) measurements. Results indicate that a major structural rearrangement takes place between 350 and 375 °C. EXAFS fitting analysis reveals this transition to be from a disordered-intermixed phase to a more ordered state having interatomic distances closely resembling those of ZrSi, but lower coordination numbers. Ordering continues with progressively higher annealing temperatures until the interface region assumes the ZrSi structure at ∼425 °C. The results are discussed in terms of the free energy and strain of the interface film.

Notes: A model of electron transport in alkali halides, below 10 eV, is described. It is based on theoretically calculated microscopic cross sections of electron interactions with lattice phonons. Both acoustic and optical scatterings are taken into account, the former being also treated as a quasielastic process that randomizes the electron motion. Monte Carlo calculations based on the model simulate the UV-induced photoelectron emission from CsI. The calculated quantum efficiency and energy spectra are in good agreement with experimental data, in the photon energy range of 6.3–8.6 eV. The probability for an electron to escape from CsI, NaCl, and KCl is provided as a function of its energy and creation depth. A comparison is made between our approach and other phenomenological models.

Notes: The structural, electrical, and piezoresistive properties of in situ boron-doped thin silicon layers deposited by plasma-enhanced chemical-vapor deposition at 320 °C on oxidized silicon substrates and subjected to a rapid thermal anneal (1100 °C for 20 s) have been investigated. Macroscopic electrical parameters derived from resistivity and Hall-effect measurements were compared to microscopic characteristics deduced from optical data to explain the low-temperature coefficients of resistance measured on this polycrystalline material. Finally, the piezoresistivity gauge factors of these heavily doped layers are discussed in view of their internal stress state and of other structural characteristics.

Notes: The electrical properties of Pd/Zn/Pd/Au ohmic contacts to p-type In0.47Ga0.53As/InP have been investigated as a function of the ratio of the interfacial Pd and Zn layers and the annealing treatment. For as-deposited contacts, the presence of an increasing thickness of interfacial Zn and Pd to ∼300 A(ring) in the metallization resulted in a reduction in specific contact resistance, ρc, to a low value of 1.2×10−5 Ω cm2. Annealing of all of the contact configurations except the Zn=0 and 20 A(ring) structures produced a reduction in ρc to a minimum value of 7.5×10−6 Ω cm2 at 500 °C. A critical thickness of the Zn≥50 A(ring) and Pd≥100 A(ring) interfacial layers was required in order to produce a significant reduction in ρc during annealing. These results have been interpreted in terms of the reaction between Pd and In0.47Ga0.53As and an associated doping at the near surface region by Zn atoms. Annealing of the contacts at temperatures of ≥450 °C resulted in significant intermixing of the metal layers and the In0.47Ga0.53As as revealed by Rutherford backscattering spectrometry and Auger depth profiling.

Notes: We find that sandwich films of the form Co50 A(ring)/Cu (t)/Co50 A(ring) with a CoO overlayer have large negative magnetoresistance [(MR)—up to 15% at T=4.2 K] for Cu thickness t(approximately-greater-than)10 A(ring). The MR correlates with a plateau in the magnetization curve which indicates antiparallel magnetization directions of the Co layers as caused by exchange coupling from the antiferromagnetic CoO overlayer. The addition of Co layers 2 or 4 A(ring) thick inserted midway in the Cu spacer can increase or decrease the MR depending on Cu spacer thickness. When comparing sandwich films with and without the insert layer, MR agrees in magnitude if 1/2 the total Cu thickness is used for the insert film. This means that it is only necessary to have a 2 or 4 A(ring) Co layer to scatter spin polarized electrons and implies that interface scattering at a boundary between Co and Cu may dominate over bulk scattering. For films with or without Co insert layers, a metallic Cu overlayer of 20 A(ring) thickness, causes the magnetization plateau to disappear and reduces the MR to less than 1%.

Notes: Nb/Al-AlOx/Nb superconducting tunnel junctions for the application of radiation detectors were fabricated using dc magnetron sputtering. The surface morphology of polycrystalline Nb films was observed using an atomic force microscope. Junctions with various Al film thicknesses were fabricated. The leakage current of the junctions is found to decrease as the Al thickness increases, indicating an improvement of the Al film coverage over the Nb surface. X rays were detected with the junctions prepared and the low leakage property across the junction makes possible x-ray detection with various size junctions up to 200×200 μm2.

Notes: YBa2Cu3O7−x (YBCO) films deposited by pulsed laser ablation on unbuffered and CeO2-buffered yttria-stabilized zirconia (YSZ) substrates were studied by x-ray diffraction and transmission electron microscopy to investigate film orientation. From φ scans it was determined that the unbuffered films possess two major in-plane orientation relationships with the substrate. Both have (001)YBCO(parallel)(001)YSZ, with either [100]YBCO(parallel)[100]YSZ or [110]YBCO(parallel)[100]YSZ, a 0° or 45° orientation, respectively. As deposition temperature increases, satellite peaks that straddle the 0° or 45° orientations develop. The Σ boundary and near coincident site lattice descriptions are applied to the discussion of these misorientations. In general the CeO2-buffered YBCO films align with to the 45° orientation to the CeO2 buffer layer. Out-of-plane film orientation was investigated for both unbuffered and CeO2-buffered YBCO films and expressed as a ratio of the amount of c⊥ material to a⊥ material. Buffered films exhibited c⊥ material to a⊥ material ratios approximately twice those of unbuffered films. Transmission electron microscopy combined with the x-ray data was used to develop an explanation for the trends in the variation of the c⊥/a⊥ ratio with film deposition temperature.

Notes: Rectangular current pulses of duration 0.14 μs, flowing across Bloch domain walls in Ni81Fe19 films, cause displacements Δx of these walls, observable by Kerr-contrast microscopy. In zero magnetic field, Δx reaches (approximately-equal-to)14 μm/pulse at current densities (approximately-equal-to)30% above the value jc where wall motion starts. This critical current density is jc(approximately-equal-to)1.2×1010 A/m2 for a film thickness w=263 nm. We have measured jc versus film thickness for w=120–740 nm, and find jc∝w−2.1. This suggests strongly that the observed wall motion is associated with an S-shaped distortion of the wall by the circumferential magnetic field of the current. This wall distortion is limited by the wall surface tension. The wall structure becomes that of the so-called asymmetric Néel wall. Through wall distortion, the current pulse pumps kinetic energy and momentum into the wall. This kinetic energy is then dissipated during ballistic wall motion happening largely after the end of the pulse. We also find jc to be independent of pulse duration.

Notes: The densification behavior, microstructure, and electrical properties of ZnO-V2O5 ceramics were studied with V2O5 as the only additive ranging from 0.01 to 1.0 mol %. The addition of V2O5 to zinc oxide shows a tendency to enhance the densification rate and promote grain growth. However, a microstructure that consisted of anomalously grown grains was found for the specimens containing V2O5≥0.05 mol % when sintered at 1100 °C for 2 h. The x-ray diffraction and SEM-EDS microanalysis revealed that the sintered specimens had a two-phase microstructure, i.e., a vanadium-rich intergranular phase formed between ZnO grains. The formation of the grain boundary barrier layer was confirmed by the non-ohmic I-V behavior and the quick drop of apparent dielectric constant with increasing frequency of the ceramics. A nonlinearity coefficient of 2.4–2.8 was obtained at a current density of 10 mA/cm2 for a series ZnO-V2O5 ceramics, and a Schottky barrier height of 0.44–0.47 eV (at 25 °C) was determined from the I-V and C-V experimental data, based on the thermionic emission theory, and the model of back-to-back double Schottky barriers.

Notes: The change in electromagnetic impedance of a conductor due to the presence of a long, perpendicular surface-breaking crack in a normally incident, uniform electric field is calculated in closed form in the high-frequency limit. At high frequencies, where the skin depth is much smaller than the depth of the crack, the fields near the edge and corners of the crack are effectively decoupled. This means that the solution may be formulated as the sum of contributions from the corners, faces, and edge of the crack. Simple analytical expressions for the electric field are found and used to calculate the impedance due to the crack in the high-frequency limit without resorting to numerical methods.

Notes: The morphological stability of the solid-liquid interface in the solidification of a dilute binary alloy is analyzed using linear and nonlinear perturbation analyses. The energy-balance condition at the interface is modified to incorporate the effects of surface excess energy. The Landau coefficient, which represents the nonlinear growth rate, is calculated using the direct method of undetermined coefficients. The results are applied to practical metallic and nonmetallic systems. The proposed surface energy correction is found to be significant at large growth velocities and low frequencies of interface perturbation: Linear stability is obtained over a larger range of frequencies and velocities; while the correction restricts the frequency range of nonlinear stability, the Landau coefficients obtained are larger and indicate greater stability over this range.

Notes: We report a measurement of the total photoelectron yield of gold as a function of the incident x-ray polarization. Polarized x rays with energies of 2.5, 2.7, and 4.0 keV were used to excite a gold photocathode at a glancing incidence angle between 5° and 50°. Contrary to a previous report, we found no measurable polarization dependence for all three x-ray energies. We conclude that the modulation factor, i.e., the fractional change of the total yield when the polarization state is varied, is less than 4%.

Notes: Thin films of carbon nitride have been grown on various substrates using low power radio frequency reactive sputtering of graphite in pure nitrogen plasma. A quantitative composition analysis using Rutherford backscattering spectrometry shows that the film contains about 51 at. % C, 44 at. % N, and 5 at. % O. The study of the microstructure of the films using cross-sectional scanning electron microscopy reveals highly oriented columnar structures.

Notes: We report the engineering of sets of mesas on lead-substituted single crystals of Bi2Sr2CaCu2Oy. Each mesa behaves as a series array of intrinsic Josephson junctions with, up to 70 K, "two states'' hysteretic I(V) characteristics, free of branching, whose RnIc products can be tuned through geometrical patterning and adjustment of the lead contents. RnIc values as high as 550 mV at 4.2 K have been reached. The tuning through lead substitution is attributed to the decrease of the anisotropy with increasing lead content.

Notes: We present Monte Carlo simulations for the dynamic response of a submicron linearly graded AlxGa1−xN metal-semiconductor-metal (MSM) structure, and compare it with a uniform GaN MSM device. Both electron and hole transport, as well as circuit elements are comprehensively included. Our results demonstrate enhancement in speed and frequency bandwidth. The improved response, despite additional alloy and multi-mode scattering, arises from the capability of rapid hole removal from the device. The 20% reduction in the turn-off time for a 0.25 μm device could, in principle, be further enhanced through the use of more complex nonuniform grading profiles.

Notes: Double-sided Y1Ba2Cu3Ox films are prepared on MgO(100) substrates for KrF excimer laser deposition and their electrical properties, both direct current and microwave frequencies, are examined. Double-sided Y1Ba2Cu3Ox films show zero resistivity at temperatures higher than 88 K and ρ(300K)/ρ(100 K) higher than 2.7. Using a niobium shield, a double-sided Y1Ba2Cu3Ox films microstrip line resonator at 5.7 GHz shows an unloaded Q value of 2.6×104 at 77 K and 1.1×105 at 4.2 K. These are the highest class of unloaded Q known to be reported for planar-type resonators.

Notes: Conditions for Hopf bifurcations and associated current oscillations are presented for a standard model of a resonant tunneling diode circuit. We derive a simple analytic formula for the Hopf bifurcation type (subcritical or supercritical) and discuss how this affects circuit operation, e.g., whether or not hysteresis and bistability are observed in current-voltage curves.