ALBERT

Notes: A description of the propagation of compression Biot waves in layered porous media in normal incidence with transfer matrices is given. An application of this model to prediction of surface impedance for a partially reticulated foam is given, with comparison with measured values.

Notes: Scanning electron microscope images of cross sections of several porous specimens have been digitized and analyzed using image processing techniques. The porosity and specific surface area may be estimated directly from measured two-point spatial correlation functions. The measured values of porosity and image specific surface were combined with known values of electrical formation factors to estimate fluid permeability using one version of the Kozeny-Carman empirical relation. For glass bead samples with measured permeability values in the range of a few darcies, our estimates agree well (±10–20%) with the measurements. For samples of Ironton-Galesville sandstone with a permeability in the range of hundreds of millidarcies, our best results agree with the laboratory measurements again within about 20%. For Berea sandstone with still lower permeability (tens of millidarcies), our predictions from the images agree within 10–30%. Best results for the sandstones were obtained by using the porosities obtained at magnifications of about 100× (since less resolution and better statistics are required) and the image specific surface obtained at magnifications of about 500× (since greater resolution is required).

Notes: A novel device, the "hollow oval magnetron,'' was designed and characterized. The device has a hollow electrode with an oval cross section. It sustains a large-area uniform plasma with low-energy ions under low pressure and moderate rf power (Ni ∼1011 cm−3, Γi ∼0.5 mA/cm2, Ei ∼30 eV, and P∼5 mTorr). The energy distribution of ion current onto the hollow electrode has a broad spread ΔEi /E¯i ∼1 in the rf mode, and a narrow peak ΔEi/ E¯i ∼0.1 with a low-energy tail in the dc mode. The device is a good candidate for low-energy high-rate plasma-material processing.

Notes: First- and second-order Raman scattering by Zn-implanted InP is investigated in order to determine critical fluences needed for a complete disturbance of the lattice and recovery temperature during thermal annealing. Disorder-activated first-order acoustical scattering and second-order optical scattering are shown to be highly sensitive probes.

Notes: Preionized plasma has been compared with vacuum and with neutral gas as a medium for the propagation of intense ion beams across magnetic fields. Two cusp-injection ion ring experiments have been used to study the effectiveness of these three cusp-fill media for space-charge neutralization, as shown by the subsequent spreading of the injected rings. In the ion ring experiment a (approximately-less-than)100-ns ion beam was injected into ∼20-eV plasma fills of (approximately-less-than)1012/cm3, giving much better propagation than vacuum, but not as good as 100-mTorr H2 gas. In the long-pulse ion ring experiment with (approximately-greater-than)200-ns beam rise time, plasma fill and vacuum gave similar propagation. The results suggest that for complete neutralization of space charge in ion beams propagating across magnetic fields, background media must be provided to meet certain minimum requirements of conductivity and collisionality which depend upon the beam current and rise time.

Notes: Electrical and microstructural changes of coevaporated V75Si25 alloy thin films have been studied as a function of temperature from room temperature to 830 °C. In situ resistivity measurements, hot-stage transmission electron microscopy, Rutherford backscattering spectroscopy and the Seeman–Bohlin glancing angle incidence x-ray diffraction technique were applied. Upon heat treatment at a heating rate of 8 °C/min, a sharp decrease in resistivity occurs at ∼670 °C which results from an amorphous to crystalline phase transformation. The crystallized phase was identified as V3Si. The mechanism of transformation is random nucleation at a rapidly decreasing rate and a fast quasi-isotropic growth. The kinetics of crystallization have been studied by utilizing electrical resistivity measurements during isothermal heat treatment. Six different temperatures between 570 °C and 630 °C were adopted. The apparent activation energy (∼3.6 eV) obtained from isothermal measurements was found to be in agreement with that obtained from nonisothermal treatments at varying rates of heating. The distinct change of the Avrami mode parameter from 4 to 2 at a constant value of t/τ during the process of crystallization is not immediately understood.

Notes: We consider a rf SQUID subjected to an external magnetic flux that includes dc, periodic, and stochastic components. Using a previously developed linearization technique, the response of the SQUID (below its hysteresis threshold) to this force is determined as a function of the internal parameters of the device. The measurement process, wherein the flux sensed by the SQUID is coupled to a tank circuit, is also considered. The results obtained, using the linearization technique referred to above, are compared with previously reported work on this subject. It is seen that, while not exact, this technique allows one to compute, analytically, the response (measured as an autocorrelation function or its associated spectral density) very accurately below the SQUID hysteresis threshold.

Notes: The resistivity and residual resistance ratio of 31-nm films of AuIn2+δ have been measured for a series of precision vacuum-deposited films covering the range of −0.04≤δ≤0.12. Both the resistivity and the resistance ratio exhibit a strongly peaked dependence on δ around δ=0. The results are analyzed in terms of the Mayadas–Shatzkes theory of scattering in thin films which includes the effects of both surface and grain boundary scattering. The dominant contribution to the resistivity is due to grain boundary scattering. The grain boundary scattering coefficient is unusually large compared to published results on single-phase metal films. These findings are interpreted in relation to the structure of the films and to the presence of second-phase material (AuIn or In) in the grain boundaries.

Notes: Amorphous silicon–tellurium alloy thin films were fabricated by coevaporation over the composition range of 0–82 at. % Te. The electronic and optical properties of these films were systematically investigated over this same range of composition. The optical gap of these films was found to decrease monotonically with increasing Te content. Conduction near room temperature was due to extended state conduction, while variable range hopping dominated below 250 K. The incorporation of Te in concentrations of less than 1 at. % was found to produce an increase in the density of localized states at the Fermi level and a decrease in the activation energy. This was attributed to the Te being incorporated as a substitutional, fourfold coordinated, double donor in a-Si. At approximately 60 at. % Te, a decrease in the density of localized states at the Fermi level, and an increase in the activation energy and photoresponse was indicated. This was attributed to the possible formation of a less defective a-Si:Te compound.

Notes: The electrical type, resistivity, and donor or acceptor concentration of CdTe films deposited electrochemically at various potentials were measured. The carrier mobilities of the films were determined from these results. The deposition potential dependence of the mobility was small and the deposition potential dependence of the resistivity was mainly controlled by the deposition potential dependence of the donor or acceptor concentration. The carrier mobilities were very small compared with those in single crystals due to the scattering of the carriers at grain boundaries.

Notes: Interface properties of plasma-enhanced chemical-vapor-deposited dielectric SiON on GaAs systems pretreated by NH3 plasma were studied. The effects of the process parameters in the NH3 plasma pretreatment, such as total pressure, radio-frequency power, substrate temperature, NH3 flow rate and pretreatment time, were investigated by the measurements of Auger electron spectroscopy, Raman spectroscopy, current-voltage, and capacitance-voltage characteristics. The transient region width and the surface strain field, surface leakage current, hysteresis, and degree of Fermi-level pinning evidently related to interface properties, are increased with increasing total pressure, decreased with increasing radio-frequency power, substrate temperature, and pretreatment time, and independent of NH3 flow rate. The physical and electrical properties of SiON/GaAs interface have been significantly improved under an optimum NH3 plasma pretreatment condition. The correlation of these parameters in pretreatment process with the interface properties including interdiffusion, surface strain field, surface leakage current, hysteresis, and Fermi-level pinning are discussed.

Notes: A hole diffusion length in liquid-encapsulated-czochralski (LEC) GaAs monocrystals (Si-doped, n(approximately-equal-to)1015–1016 cm−3) in the range (0.4–3.0) 10−4 cm, has been determined by photon and electron bombardment through semitransparent Au or Cr Schottky electrodes. A minority-carrier lieftime in the range (0.3–9.7) 10−9 s was estimated. Schottky barrier diodes with abrupt junctions giving optimum electrical characteristics were prepared. The absorption length of the examined samples was evaluated by optical transmission measurements. The diffusion length investigation, which was carried out by the steady-state surface photovoltage (SPV) and the scanning electron microscope electron-beam-induced current (SEM-EBIC) techniques, has been related to the spectral quantum efficiency of Schottky diodes. SPV and EBIC techniques are emphasized as complementary methods for the investigation of bulk photoelectronic properties.

Notes: Both the steady-state and transient solute (impurity) concentrations at the surface of a film during its deposition are calculated as a function of deposition rate, temperature, diffusivity, bulk film solute concentration, and segregation energy. The steady-state solute concentration at the surface is found to increase upon increasing either the solute diffusivity or the magnitude of the (negative) segregation energy, or upon decreasing the deposition rate. The transient concentration profile at the start of deposition relaxes toward the steady-state profile as 1/t. Implications of the present results for film growth mechanisms and methods to control the degree of segregation via manipulation of deposition parameters are discussed.

Notes: This paper presents a study on drawing condition dependences of optical absorption at 630 nm and nonbridging oxygen hole centers (NBOHCs) in optical fibers drawn from low-OH-content synthetic silica glass. The intensity of the 630-nm absorption is proportional to the NBOHC concentration, and the value of the oscillator strength for the NBOHC is 4.2×10−4, which nearly equals the theoretical values. These results confirm that the 630-nm absorption is due to the NBOHCs in low-OH-content silica glass. Furthermore, the 630-nm absorption increases with increasing drawing tension. This drawing tension dependence is explained by applying kinetics of the stress-induced crack growth in metal to the formation of the NBOHCs in the drawing process.

Notes: Infrared spectroscopy has been applied to the study of the kinetics of oxidation in high-pressure dc-sputtered amorphous silicon. The different spectra obtained during the evolution of the oxidation are processed by factor analysis. Two oxidation mechanisms have been found. Their associated infrared spectra and time evolution can be explained by a model that proposes the existence of a two-level microstructure. The spectra associated with each one of the oxidation mechanisms seems to correspond mainly to SiO2, modified by the presence of surface modes.

Notes: The effect of band bending near the interface of a-Si:H/a-SiNx:H layered structures has been investigated for various a-SiNx:H compositions by measuring in-plane dark current and photocurrent. The dark current of a-Si:H/a-SiNx:H layered structures increases about four orders of magnitude and the activation energy decreases with a decrease in x of a-SiNx:H. The photocurrent also increases about four orders of magnitude with a decrease in x. This photocurrent enhancement is larger in the shorter wavelength region, and this spectral change agrees with the photocurrent spectral change induced by an increase in gate bias in thin-film transistor structures. From these results it is found that the band bending toward electron accumulation in a-Si:H near the a-Si:H/a-SiNx:H interface increases with a decrease in x of a-SiNx:H, resulting in high photoconductivity.

Notes: The effects of gas ambient changes on the photoluminescence (PL) intensity and the conductivity of chemically cleaned (100) InP and GaAs have been investigated. The room-temperature PL intensity of n-type, p-type, and Fe-doped semi-insulating InP is found to be reversibly changed by the presence of various gases at the semiconductor surface. The resistivity of thin-film InP resistors is also found to be affected by gas ambient changes, both under illumination and in the dark. These measurements show that the surface Fermi level of InP is not tightly pinned and is reversibly changed by exposure to different ambients. The PL intensity and surface conductivity of GaAs are also found to be sensitive to the gas environment, though to a lesser degree than InP. The responses of InP and GaAs are of a different nature and suggest that the surface state densities of these materials are reversibly affected by the chemisorption of oxygen. This in turn suggests that there are adsorbate-induced surface states on InP and GaAs which arise as a result of the interaction of adsorbed oxygen with the semiconductor surface and that are not associated with intrinsic semiconductor defects.

Notes: Rietveld analyses of room-temperature neutron diffraction data for seven Nd2(CoxFe1−x)14B alloys (x=0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) are reported. Throughout the entire composition range the Nd2Fe14B-type tetragonal crystal structure is maintained, with the lattice constants decreasing significantly as the Co concentration x increases. We find that the j2-type transition-metal sites are preferentially occupied by Fe ions in the pseudoternary systems, a result which is analogous to the preferential Fe occupation of c sites we previously observed in hexagonal Nd2(CoxFe1−x)17 alloys.

Notes: An experimental setup is described which makes it possible to determine the particle number per unit length and the pressure in high-pressure mercury lamps. For this purpose the absorption of the frequency-doubled 514.5-nm line of an Ar+ laser by the mercury ground state is used. The method has been applied to measure the spatial variation of the particle number along the axial direction of a high-pressure arc and also to determine the time-dependent particle number during the warm-up and cool-down phases of a lamp. Furthermore the frequency dependence of the pressure fluctuations in a high-pressure lamp during an ac cycle has been measured for sinusoidal as well as pulsed supply voltage. The results are in agreement with calculations from a numerical model.

Notes: Simple analytic models have been developed to describe the current density and magnetic field profiles in a cylindrically symmetric plasma carrying a z-directional current. Solutions are obtained for time varying boundary magnetic fields characteristic of imploding liner and gas puff plasma implosions. The cylindrical models are compared with previously developed planar solutions. Applications to electromagnetically imploded plasma shells show a small variation in the magnetic field profiles at early times and large radius. These variations become more pronounced as the implosion moves to smaller radius. In general, the effects of cylindrical geometry become significant only when the outer radius reaches the same order as the magnetic field gradient scale length.

Notes: A negative potential well is found in front of a positively biased electron collecting plate in a low temperature laboratory plasma. The well parameters are governed by the Child–Langmuir condition and a necessary condition for the existence of such potential wells is the presence of an ion pumping mechanism which removes trapped ions from the wells. Here ion pumping was provided by the presence of negative electrically floating ceramic on the back of the plate.

Notes: A trapped distribution of low-energy electrons was used to alleviate spherical aberration in a solenoidal magnetic lens. The space-charge-correction method has potential application to the focusing of heavy, negatively charged particles such as H− ions. In the geometry investigated, the field contributions from trapped electrons cancel net electric fields along magnetic flux surfaces. The lens magnetic fields therefore define equipotential surfaces. Experimental results were obtained using a 10-keV electron beam as a nondestructive probe in a solenoid lens with 65-G peak field. Annular distributions of trapped electrons were achieved that were stable against the diochotron instability. Deflections of the probe beam were consistent with theoretical predictions. The peak focused current density of the 10-keV beam was improved twentyfold with the addition of trapped electrons in the lens.

Notes: A calculation is presented of spontaneous radiation emitted by an electron beam passing through a continuously rotating quadrupole magnetic undulator. It is shown that radiation spectrum emitted in forward direction of beam propagation has four peaks, corresponding to four betatron frequencies. Utilizing the Madey theorem, a stimulated emission is calculated and presented as gain versus frequency curves, for different values of the quadrupole magnetic field. A free-electron laser operating at two or three radiation frequencies with a quadrupole magnetic wiggler is suggested.

Notes: A method is developed to calculate the depth distribution of the local stoichiometric disturbance (SD) resulting from ion implantation in binary-compound substrates. The calculation includes first-order recoils considering projected range straggle of projectiles and recoils and lateral straggle of recoils. The method uses tabulated final-range statistics to infer the projectile range distributions at intermediate energies. This approach greatly simplifies the calculation with little compromise on accuracy as compared to existing procedures. As an illustration, the SD profile is calculated for implantation of boron, silicon, and aluminum in silicon carbide. The results for the latter case suggest that the SD may be responsible for otherwise unexplained distortions in the annealed aluminum profile. A comparison with calculations by other investigators using the Boltzmann transport equation shows good agreement.

Notes: The microstructure of a fiber-reinforced composite material can be characterized in terms of a set of n-point matrix probability functions Sn which give the probability of finding n points all in the matrix phase. From a knowledge of these functions one can place rigorous upper and lower bounds on effective thermal, electrical, and mechanical properties of the composite. Third- and fourth-order bounds derived by Milton involve threefold integrals over the three-point matrix function S3. Exact analytic determination of S3 is impossible except in idealized cases, and the highly oscillatory nature of the integrands makes numerical integration costly and time consuming. In this paper we discuss an approximation to S3 in terms of the two-point function S2, which is often quite easy to determine. We show that in this approximation the bounds can be expressed in terms of twofold integrals for which the integrands are mostly of one sign, and which can be evaluated very cheaply to a high degree of precision. For a model microstructure in which the inclusions consist of fully penetrable cylinders, we compare our approximate results with the exact results. Agreement is excellent.

Notes: Computer simulations of the intrinsic (400) reflecting power of In1−xGaxAs layers having graded compositions are presented. We find that multiple x-ray peaks can result from a linearly graded region which implies that an interpretation which ascribes individual peaks to sublayers having a constant lattice parameter may not always be correct. We find that, in general, the simulations are asymmetric and that they have a full width at half maximum less than ∼100 arcsec. We have simulated an actual rocking curve of a single In1−xGaxAs1−yPy layer grown on a (100) InP substrate by vapor-phase epitaxy which exhibited multiple peaks, and we find that a good fit is possible if the layer had a graded lattice parameter. Comparing dynamical to kinematical simulations for a 3-μm-thick linearly graded layer, we find that most of the features resulting from the grading can be explained using kinematical theory. However, only the dynamical simulations can properly account for the reflecting power in the vicinity of the substrate peak and for the lack of fine structure which is observed in the absence of a discontinuity in Bragg spacing at the layer/substrate interface.

Notes: The effect of excess phosphorus vapor during the process of MIS structures on InP is analyzed in detail. It is shown that the density of interface state distribution is considerably modified after in situ thermal precleaning of the substrate in phosphorus overpressure (suppression of the Fermi-level pinning and significant reduction of the density of surface states near midgap). Phosphorus overpressure also provides an efficient protection of the surface during the insulator deposition. Fermi-level pinning in the upper part of the gap is assigned to the uncontrolled native oxide left on the surface after a stay of InP substrate in ambient atmosphere.

Notes: A simple yet exact method of solving the Schrodinger equation across an arbitrary one-dimensional piecewise-linear potential is described. It is based on the analytical solution of the Schrodinger equation across a linear potential, where the solution can be expressed as a linear combination of the Airy functions. Proper boundary conditions are imposed at the interface between adjacent linear intervals of the potential, and a transfer-matrix procedure is utilized in the derivation. The quantum mechanical transmission coefficient across a potential barrier and eigenenergies of a potential well can also be easily calculated using this method.

Notes: Compositionally modulated Ni/Ni–P films, with wavelengths between 2.1 and 4.0 nm and an average P content around 12 at. %, have been prepared by alternating electrodeposition in a simple and inexpensive apparatus consisting of two baths of different composition. X-ray diffraction showed a single (000) satellite at low angles due to the presence of the modulation.

Notes: In situ ellipsometry measurements have been used to determine the optical structure of interfaces during the growth of a-Si@B:H/a-SiNx@B:H heterostructures. We have observed significant deviations of the ellipsometry data from calculations which assume both uniform growth and abrupt interfaces. For the growth of a-SiNx@B:H on a-Si:H such deviations are attributed to a 40 A(ring) layer, less absorbing than bulk a-SiNx@B:H, which is left behind at the interface. This layer appears to result from a higher void density or enhanced N incorporation in the initial 20 s of a-SiNx@B:H growth. It is also possible, however, that a thin layer on the a-Si:H surface is converted to a transparent nitride. In support of the latter possibility, the a-Si:H surface is found to be highly reactive in a N2 plasma: a 150 A(ring) nitride layer is formed during a 10-min exposure time at the same plasma power used for a-SiNx@B:H growth. For the growth of a-Si:H on a-SiNx@B:H, we have found that the interface structure is sensitive to the nitride preparation technique. The evolution of the surface roughness on a-Si:H alternate layers is obtained in real time during the preparation of an a-Si@B:H/a-SiNx@B:H multilayer structure. The implications of these observations for recent interpretations of optical measurements on multilayer structures is treated in detail.

Notes: Using Kane's energy–wave-vector relation (k.P model), it is shown that the nonparabolic band structure of binary compound polar semiconductors (BCPSCs) is, in fact, a perturbed parabolic band structure. The formula for this "parabolic'' band structure is used to derive current, carrier concentrations, Einstein equation, and others. The formula for the Einstein equation is found to be of the same form as that for wide-gap semiconductors. Simplified relations for nonparabolicity coefficients have been derived. It is shown that these coefficients compare well with similar coefficients derived earlier from different considerations. Numerical calculations of effective mass, density of states, Fermi energy, and electron-impurity interaction energy have been carried out for a number of representative compounds. Good correspondence of theoretical results with available experiments indicates that the present model is quite useful for describing properties of BCPSCs.

Notes: The noise power spectral density from 100 MHz to 88 GHz has been measured for forward-biased platinum n–n+–GaAs Schottky barrier diodes at room temperature. There appear to be five sources of noise: shot noise, Johnson noise, hot-electron noise, intervalley scattering noise, and trap noise. The magnitudes of these sources are dependent on the bias condition, frequency, and structural parameters as well as the quality of the material. A trap mechanism that may explain the frequency-dependent noise is suggested. The relative importance of each source is investigated for different diodes versus forward bias and frequency. The current-voltage characteristics were also investigated, and show features at high forward bias which are not predicted from simple theories.

Notes: The effects of HCl on trap generation in silicon dioxide layers at high electric fields are reported by comparing 700-A(ring), 200-A(ring), 9% HCl, and 0% HCl dry oxides stressed at constant avalanche electron injection currents and voltages. Experimental data indicate that HCl decreases the hydrogenation rate of boron acceptor in the silicon surface layer due to a high-density chlorine layer at the oxide/silicon interface but HCl increases the density of the peaked interface trap at 0.3 eV above the silicon midgap. A new chlorine-related positively charged electron trap in the oxide is observed and isolated from the chlorine-independent negatively charged oxide hole trap. Chlorine also reduces the density of the smaller cross-section oxide electron trap which gives the turn-around phenomena.

Notes: A new method for analyzing space-charge-limited currents (SCLC) has been presented. This is based on the step-by-step calculation of the density of state g(E) using Poisson's equation, which could reduce the relative error in determining g(E) encountered in various analyzing methods. The present method has been applied to deducing g(E) in hydrogenated amorphous silicon: The density of states at the Fermi level g(Ef) has been estimated to be 1×1015 cm−3 eV−1 and g(E) for deep states varies slowly with energy.

Notes: The effect on negative resistance of a small aluminum concentration in the outer GaAs layers of a GaAs-Ga1−xAlxAs double-barrier tunneling structure is calculated. The aluminum concentration can be chosen so that the alloy conduction-band minimum is slightly below the energy of the resonant tunneling level of the GaAs central well region. Less voltage is then needed to raise the incoming electrons into the resonant energy level. The decreased voltage across the structure has several beneficial effects. The electron transmission coefficient through the barriers on resonance increases, the total applied voltage across the device is reduced, and the current through parasitic parallel resistances is reduced. Significant improvements in peak-to-valley ratios are predicted, the improvement being dependent on the parameters of the structure.

Notes: An analysis of the frequency dependence of superconductor-insulator-normal (SIN) and superconductor-insulator-superconductor (SIS) quasiparticle mixers is presented. Power-law expressions for conversion loss and mixer shot-noise temperature for the double-sideband SIN mixer are derived from the Tucker theory for the case of a source conductance which is small compared to the conductance of the junction. For an ideal SIN tunnel junction at T=0 the mixer conversion efficiency is shown to decrease approximately linearly with frequency up to f=Δ/h. From f=Δ/h to 2Δ/h the conversion efficiency remains approximately constant, while above f=2Δ/h it rolls off as the inverse square of the frequency. Expressions for the shot-noise contribution to the mixer noise temperature are also derived. At frequencies up to f=Δ/h the noise temperature rises as the square root of the frequency. From f=Δ/h to f=2Δ/h the noise temperature of the mixer increases linearly with frequency, whereas above f=2Δ/h it rises as the cube of the frequency. Conversion efficiency and noise temperature are also calculated numerically for the SIN mixer. Good agreement is found between the frequency dependencies calculated analytically in the limit of small local oscillator power and the numerical calculations for optimal pumping. The frequency dependence of the nonideal SIS junction is also analyzed, and shown to yield similar results, with the characteristic frequencies Δ/h and 2Δ/h for a SIN mixer transformed into 2Δ/h and 4Δ/h, respectively. Expressions also are derived for the saturation power as a function of frequency.

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

Notes: To calculate the head field distribution first we pursue the Poisson integral approach3 using Fourier series method retaining up to 200 terms in the series. The parameters related to the rational approximation to the field equation for both ring heads and pole-keeper heads have been obtained and tabulated. The idea of the Poisson integral is then extended, denoted as Poisson integral II, to enable us to calculate the head fields both within and without the head gap regions. The first Poisson integral II involves eight parameters and enables us to calculate head fields in reasonably good agreement with the direct Fourier series calculations. The second Poisson integral II involves a self-consistent calculation, which is reducible to the rational field equations with five parameters and is highly capable of producing head field distribution anywhere with great accuracy at low spacings. Results of a comparison with a finite element method calculation are excellent.

Notes: It has been found that CuInSe2 polycrystalline material suitable for photoelectrochemical cells can be produced from low grade In, Se, and Cu. Low-energy electron diffraction (LEED) measurements on these samples show that well ordered (112) surfaces can be produced after 35 min Ar ion bombardment at ∼8 μA cm−2, 600 eV, followed by 30 min anneal at temperatures as low as 320 °C. Extra LEED spots are visible at some energies, indicating a clean surface but with possible nonstoichiometric areas. No effects of oxygen are observed at exposures up to 326×103 L.

Notes: The vacuum emission technique has been used to study electron transport and heating in silicon nitride and silicon oxynitride. The experimental results are compared to data for silicon dioxide in which all the conduction-band electrons can gain several eV of energy at electric fields greater than 2 MV/cm. Although average electron energy as a function of electric field curves are very similar to silicon dioxide, the total number of electrons which can be heated to energies greater than 2 eV is greatly reduced because of the increased trapping in these films. Reduction in hot electrons due to increased trapping is correlated to increasing nitrogen content through the oxynitride phases to silicon nitride. Trapping/detrapping on energetically shallow sites in the forbidden gap controls the bulk limited conduction in these films, and very few electrons are allowed to move freely in the conduction band.

Notes: The modifications of the electronic properties of cleaved GaAs (110) surfaces induced by the oxygen adsorption have been studied by contact potential difference measurement. The oxygen exposure induces acceptor and donor surface states which pin the surface Fermi level at approximately 0.45 and 0.7 eV above the valence band for n- and p-doped samples, respectively. Noticeable modifications Δχ of the electronic affinity are also produced. The features of the states and the possible origins of Δχ are discussed.

Notes: Ultralow-power, high-resolution, pulsed-laser photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies were carried out in molecular-beam-epitaxial GaAs/AlxGa1−xAs multi-quantum-well structures at 5 K. Fine structures were observed for the first time in the PLE spectra, both in the heavy-hole and light-hole excitonic regions. Most of the fine structures are considered to arise from monolayer fluctuations in the thicknesses of the GaAs wells. Dramatic changes in the line shapes and the peak positions of the PL and PLE spectra were observed by applying selective PL detection and excitation spectroscopic techniques.

Notes: Schottky-barrier diodes have been fabricated by evaporation of Pt on Si substrates followed by annealing at 500 °C to yield PtSi. Then V and Al were evaporated. The amount of oxygen intentionally incorporated in the V film during deposition was varied and the resulting effect on the diffusion barrier action of the vanadium film has been studied by I-V and C-V measurements of the diodes and by backscattering spectrometry of simultaneously prepared test samples. It is found that for V films with low oxygen concentrations annealing in the range 400–600 °C leads to the formation of VAl3 and subsequent barrier height change. For vanadium films containing 50-at. % oxygen there is no observable reaction between V and Al and the barrier height is preserved for annealing between 400 and 600 °C.

Notes: The magnetic field splitting and strain splitting of the emission lines in the 1.5040–1.5110 eV range in GaAs are reported. In the Voigt configuration the lines show doublet splittings in applied magnetic fields. In combined magnetic and strain fields four lines are observed in this configuration. All of the lines show a similar splitting. The splittings agree with what would be expected for shallow donor-acceptor pair centers in a zinc-blende structure.

Notes: The photoelastic effect, or the strain dependence of refractive index n0, essentially controls the details of light scattering in liquids, glasses, and crystals. Some knowledge of its behavior as a function of structure and chemical composition is therefore extremely valuable in a search for devices which seek to maximize or minimize such light scattering mechanisms. This paper derives a bond-orbital theory for the hydrostatic photoelastic effect (or the dependence of n0 on density ρ) for three-dimensionally coordinated crystalline structures (for which density fluctuations are directly related to primary bond length fluctuations) including four-, six-, and eightfold coordinated cations. The theory sets out the manner in which ∂n0/∂ρ depends on such fundamentals as valence, ionic radii, and degree of covalence, and highlights a term not previously derived in any prior theories of linear dielectric response. This term, involving relative anion to cation size, while not inconsequential in an evaluation of n0 itself, is absolutely essential for any understanding of ∂n0/∂ρ and completely dominates the latter in many more-ionic crystals. The final theory contains two parameters which are determined from experiment (essentially in the ionic and fully covalent limits, respectively). When complete it is tested on more than thirty halides, oxides, chalcogenides, and pnictides, for which reliable photoelastic data have been found in the literature. The agreement of theory with experiment is within experimental error for all except the tetrahedrally bonded halides for which direct interband activity by shallow-core d electrons places them outside the theory as presently constituted.

Notes: Spectroscopic data from a high-pressure mercury arc with sodium iodide additives are compared with model calculations. The fused silica arc tube was oriented horizontally, and rotated about its own axis at sufficiently high speed to center the arc. This mode of operation suppresses convective effects, creating a greater degree of axial symmetry and longitudinal homogeneity than is normally present in a metal halide arc. High-resolution line-of-sight spectra were recorded for all of the principal spectral features and for a series of offsets from the arc axis. Several independent measurements of the arc temperature are extracted from the spectra using standard techniques. The arc model assumes local thermodynamic equilibrium, axial symmetry, longitudinal homogeneity, absence of convection, and time independence. Equations associated with energy conservation, radiation transfer, chemical equilibrium, and multicomponent diffusion are solved simultaneously to determine a self-consistent arc temperature profile, radiation field, and distribution of chemical species. Boundary conditions on these calculations include the input power per unit length, the arc tube radius, the amount of mercury per unit length, and the sodium iodide vapor pressure at the wall. Direct comparisons between the data and the model are made for the high-resolution spectra at various offsets, and the arc temperature. Comparisons are also made for a similar arc without sodium iodide. The model is used to study the response of the discharge to independent variations in power loading and sodium iodide pressure.

Notes: Historically GaAlAs alloys grown by molecular-beam epitaxy have high deep level concentrations (〉1016 cm−3), low luminescent efficiency with broad peaks, and are difficult to dope controllably below mid 1016 cm−3. We report the effect that the low incident antimony molecule fluxes during growth appear to help reduce the density of deep levels below 1014 cm−3, which then allows reproducible doping control in the low 1015 cm−3 range. Exciton-dominated photoluminescence with half widths ∼4.0 meV are now routinely achieved using this technique. Further evidence for the quality improvement of AlGaAs by heavy atom (Sb) doping comes from high 4 K two-dimensional electron gas mobilities for low sheet electron densities, e.g., 1.3×106 cm2/V s for n=2×1011 cm−2. SIMS profiles of antimony content are presented and estimates of incorporated concentrations are given.

Notes: Positron lifetime and Doppler broadening investigations of oxygen in silicon (Cz silicon) have been performed. It was found that positrons may be trapped by defects yielding a positron lifetime of only 100 ps and a momentum distribution of the annihilation quanta which is wider than that for defect-free silicon. This unequivocally shows that clusters of oxygen constitute positron traps. The trapping process was found to be thermally activated in the 25–300 K range. Isochronal and isothermal annealing showed that the clusters alternate during growth between having an interstitial character and a vacancy character. At 450 and 500 °C, growth of oxygen clusters takes place with an activation energy of 1.5 eV, while at 650 and 714 °C, these clusters disappear with an activation energy of 1.1 eV. At 714 and 790 °C, growth of new clusters takes place with an activation energy of 2.6 eV.

Notes: The migration of Cr, Mn, Ni, and Xe implanted in sapphire during post-implantation thermal annealing is investigated by Rutherford backscattering (RBS)/channeling studies. Thermal annealing was performed in air or in vacuum. It is shown that the epitaxial recrystallization of the implantation-damaged region dominantly causes the migration of the implanted ions when there is little or no solid solubility of the ion species in sapphire. This migration mechanism strongly relates to the formation of oriented precipitates. When the implanted ions migrate toward the surface, surface precipitates of oxides are formed with annealing in air. On the other hand, when the implanted ions concentrate around the projected range at an elevated temperature, metals mainly precipitate in the substrate. The following crystallographic relations are found between the precipitates and the substrates: (111) MnAl2O4, (111) NiAl2O4, (111) Ni or (110) Cr(parallel)(0001) Al2O3, and (103) Mn3O4(parallel)(112¯0) Al2O3.

Notes: The preparation of an ion-conducting elastomeric solid based on a dimethylsiloxane-ethylene oxide copolymer complexed with a sodium salt is described. 23Na nuclear magnetic resonance measurements reveal the presence of both bound and mobile sodium species throughout the temperature range −120 to 100 °C. Electrical conductivity measurements over a similar temperature range are found to be consistent with the configurational entropy model for transport, with a T0 parameter about 50 °C below the "central'' glass transition temperature Tg.

Notes: We investigate here the influence of the crystallographic orientation of the CdTe substrate on the condensation coefficients of Hg, Cd, and Te during the growth of Hg1−xCdxTe and CdTe by molecular-beam epitaxy. We show that the Hg condensation coefficient is strongly influenced by the orientation. A CdTe (1¯1¯1¯)B face requires about one order of magnitude less mercury than a (111)A face when growth occurs at 185 °C. Whereas for a CdTe(100) face, the Hg condensation coefficient falls in between. Even though the effect is less dramatic for the condensation coefficient of cadmium, a similar tendency is observed. These results can be explained in terms of the bonding of the surface atoms and confirm once again that the surface plays an important role in the molecular-beam-epitaxial growth process.

Notes: The growth and characterization of GaxIn1−xP (x=0.51, 0.65, 0.69) are described in this paper. The organometallic vapor-phase epitaxial (OMVPE) growth was carried out in an atomospheric pressure reactor using trimethylgallium (TMGa), trimethylindium (TMIn), and phosphine (PH3). GaAs and commercially available hydride vapor-phase epitaxial GaAs0.70P0.30 and GaAs0.61P0.39 were used as the substrates. The influence of growth temperature and V/III ratio on the properties of the OMVPE epilayers was studied. This resulted in the determination of an optimum growth temperature of 625 °C and an optimum V/III ratio range of 40–50. The results of the mismatch due to the different lattice constants of the GaxIn1−xP epilayer and the substrate were investigated. It was found that high-quality GaxIn1−xP epilayers can be obtained only when the mismatch ||Δa/a0|| is less than 1×10−3. Under the conditions mentioned above, epilayers were reproducibly obtained with featureless surface morphologies, and photoluminescence (PL) with high intensities and narrow half-widths (41–43 meV at 300 K). The dislocation etch pit densities ρ of Ga0.65In0.35P and Ga0.69In0.31P epilayers were 7.4–8.6×104 cm−2, grown lattice matched to GaAs1−yPy ( y=0.30, 0.39) substrates with ρ=6.4–7.5×105 cm−2. The degradation of PL intensity after annealing at temperatures between 400 and 600 °C in H2 or N2 indicates an increase in the surface recombination velocity for GaInP epilayers. Etching 30 A(ring) from the surface was found to restore the original PL intensity.

Notes: Nonplanar morphology and compositional inhomogeneity are observed in GaAs1−xPx superlattices when the phosphorus content is substantially different in adjacent sublayers. The main characteristic feature of the distortion is a series of ribbonlike regions running through the superlattice which etch at a faster rate and contain more phosphorus than the surrounding material and are also the source of clusters of dislocations. Morphological stability and a general decrease in dislocation density can be effected by decreasing the interlayer strain, i.e., compositional difference, between the superlattice sublayers.

Notes: The pressure dependence of the optical phonons in LiNbO3 to 21 GPa and in LiTaO3 to 10 GPa has been investigated by Raman spectroscopy, using the diamond anvil cell. All the observed modes increase in frequency with pressure, and no mode softening occurs. This is in contrast to the behavior observed in BaTiO3 and PbTiO3, which are well-known displacive-type ferroelectric. It is suggested that this difference in pressure behavior may stem from a different type of phase transition in LiNbO3 and LiTaO3, namely the order-disorder type.

Notes: We report detailed optical absorption spectra for Mn2+ in CaF2. The spectra from unirradiated samples, reported here for the first time, enable the 495-nm luminescence emission to be clearly assigned to a transition from the first excited 4T1g (4G) level to the 6A1g (6S) ground state. On the basis of the absorption curves energy level assignments are made for all of the 4G, 4D, 4P, and 4F levels. Racah parameters are evaluated and the reduction of these from their free-ion values, due to covalency effects, is estimated. A value of Dq=420 cm−1 is calculated and an Orgel diagram for this system is constructed. Finally, oscillator strengths for each of the transitions are estimated from the absorption spectra. The optical absorption spectra from gamma irradiated samples show a complex array of overlapping bands, most of which can be shown to be related to the presence of Mn. The thermal annealing of the bands is associated with the production of thermoluminescence at an emission wavelength of 495 nm. Although no definite models can be offered for the defects involved in these processes, they are believed to be complexes of Mn and radiation-induced defects (e.g., Mn/F centers).

Notes: The magnetostatic energy of imperfect films having a two-dimensional square-lattice structure with voids between square islands of magnetic material is calculated for arbitrary ratios of thickness and island size to the period of the lattice. These calculations are relevant to the understanding of the uniaxial anisotropy observed in many thin films used as magnetic-storage media.

Notes: A new time-resolved electron spin resonance experiment is presented. This experiment allows us to evaluate an efficiency of different nonradiative recombination mechanisms responsible for the strong temperature dependence of the ZnS:Al visible photoluminescence.

Notes: Intense visible emission in the red, green, and blue has been observed from infrared to visible multiphoton Y1−xErxF3 upconversion phosphors pumped with 1.5-μm radiation from InGaAsP-laser sources. With 0.01〈x〈0.2, the dominant emission is in the green corresponding to transitions from the 4S3/2 level of Er3+. The addition of Tm3+ in the 0.001–0.02 range preferentially quenches the emission from the higher-energy Er3+ levels resulting in a red visible emission originating on the Er3+ 4F9/2 level. The phosphors are useful visible monitors of focused 1.5-μm semiconductor laser and unfocused F-center laser radiation. The unexpectedly high brightness in the visible may be attributed to thermal equilibration, where the excitation is trapped in the higher lying states after each upconversion step.

Notes: Polycrystalline silicon on insulator is laser-recrystallized using three different capping layer structures on separate wafers. The capping layer structures used include a 6-nm nitride layer, a combination of 64-nm nitride and 20-nm oxide layers, and 50-nm nitride antireflection periodic stripes oriented parallel to the direction of laser scanning. Electrical characteristics are measured by metal-oxide-semiconductor (MOS) silicon-on-insulator (SOI) test structures fabricated in the laser-recrystallized silicon films. Measurement of carrier mobilities, MOS interface properties, leakage currents, and ring oscillator delay times are compared for wafers having different capping layer structures. Stress in each case is characterized using a Raman spectrometer with microprobe.

Notes: It is shown that when account is taken of the attenuation of incident radiation into the bulk of a photoconductor, as a result of the absorption, the expressions for the responsivity and detectivity are modified. An earlier derivation [Infrared Phys. 20, 385 (1980)] attributed the difference in the operation of the detectors in the transverse and longitudinal geometries to carefully defined "effective'' quantum efficiencies. Here we show that a more physically motivated view attributes the difference to the different photoconductive gains for the two geometries. It is shown that the appropriate gains for the responsivity and detectivity are not the same.

Notes: A three-axis superconducting gravity gradiometer with a potential sensitivity better than 10−3 Eötvös Hz−1/2 is currently under development for applications in space. Although such a high sensitivity may be needed for only a limited number of terrestrial applications, superconductivity offers many extraordinary effects which can be used to obtain a gravity gradiometer with other characteristics necessary for operation in a hostile moving-base environment. Utilizing a number of recently devised techniques which rely on certain properties of superconductors, we have produced a design for a sensitive yet rugged gravity gradiometer with a high degree of stability and a common-mode rejection ratio greater than 109. With a base line of 0.11 m, a sensitivity of 0.1 Eötvös Hz−1/2 is expected in an environment monitored to a level of 10−2 m s−2 Hz−1/2 for linear vibration and 7×10−6 rad s−1 Hz−1/2 for angular vibration. A conventional stabilized platform can be used at this level. The intrinsic noise level, which is two orders of magnitude lower, could be achieved by monitoring the attitude with a superconducting angular accelerometer which is under development. In addition, the new gradiometer design has the versatility of adapting the instrument to different gravity biases by adjusting stored dc currents.

Notes: Radiation sensing field-effect transistors operated at zero bias show a low-dose response that is roughly linear in the thickness of the gate oxide. The same devices show a thickness squared dependence if a bias is applied during the irradiation. This effect can be explained by examining the effect of diffusion and electron trapping on the buildup of net positive charge in the gate oxide.

Notes: The interactions between Au and Cu across a Ni barrier layer have been studied using a wide range of Ni thickness. Above 300 °C, extensive interdiffusion between Au and Cu has been observed, with little involvement of the Ni layer. The interdiffusion between Au and Cu results in a nearly continuous change and uniform distribution in composition for both the parent Au and Cu layers, different from those of the binary Au/Cu system. Reaction mechanisms involved are suggested, and the impact of such interactions on the packaging metallurgy is discussed.

Notes: Effects of the heat treatment condition on the high-field superconducting performances of the surface diffusion processed V3Ga have been investigated. Ic at fields near Hc2 depends mainly on the layer thickness and Hc2 of V3Ga. The two-stage reaction process, which consists of the first reaction at the higher temperature to form a thick enough V3Ga layer and the subsequent second reaction at the lower temperature to achieve high values of Tc and Hc2, has been found to improve appreciably the Ic of SDP V3Ga in high magnetic fields. Overall Jc (including copper stabilizer) of about 2.0×104 A/cm2 at 19 T has been obtained for a ∼100-m-long V3Ga tape.

Notes: The activation energy for electromigration failure was determined for Al-4% Cu conductor stripes covered with polyimide. The activation energy was measured to be 0.88 eV, which is substantially higher than that measured previously for similar systems under glass. The difference in the activation energies is attributed to the possible presence of hydrogen in the Al–Cu grain boundaries.

Notes: We demonstrate laser emission by photopumping at room temperature from a distributed feedback structure for a surface-emitting laser constructed by alternating growths of a GaAs/AlGaAs multiquantum well and an Al0.7Ga0.3As layer using molecular-beam epitaxy. A threshold photoexcitation intensity lower than 3.1×105 W/cm2, a 34-nm longitudinal mode spacing, and a 2.3-nm peak width of the laser emission were observed for the 6-μm-thick multilayer.

Notes: Rare gas–halogen excimer lasers excited by electron-beam-sustained discharges (EBSD) will operate stably for only a limited length of time (hundreds of nanoseconds to a few microseconds). In this paper, results from a multidimensional model for an EBSD KrF laser are used to study various aspects of discharge ionization and geometric stability, and the relationship between the two. We examine the effects of photodetachment of electrons from the halogen negative ion, of circuit response, and of nonuniform e-beam power deposition upon the onset of discharge instabilities. We find that both spontaneous emission from KrF* and laser oscillation resulting in photodetachment of electrons from F− can initiate an ionization instability. By operating with high impedance electrical circuits, the tendency towards instabilities by this effect can be reduced. We also find that the spatial uniformity of the e-beam power deposition is directly correlated with both the rate of discharge constriction and the time at which the discharge suffers an ionization instability.

Notes: The time evolution of the energy balance in a nitrogen discharge during its early phases of development is simulated using a self-consistent calculation of the electron distribution function (EDF), the vibrational population (VP), and densities of some electronically excited states. The contribution of the V–T (vibration-to-translation), and V–V (vibration-to-vibration) energy exchanges is quantitatively analyzed. The contribution to the energy balance by self-quenching reactions of the N2(A3Σ+u) state is also analyzed. It is shown that the population of this state in a discharge and its contribution to the energy balance may be significant.

Notes: The technique of cross-sectional transmission electron microscopy has been applied to study the nature of the radiation damage in GaAs bombarded with 300 keV protons to total doses of 1015 and 5×1015 protons cm−2. The results indicate that upon annealing at temperatures of 500 °C and above, the precipitated damage becomes visible in the form of hydrogen platelets (i.e., hydrogen-filled edge vacancy loops) on the {110} cleavage planes of GaAs.

Notes: Be+/O+-ion implantation is performed in GaAs/AlGaAs heterojunction wafers. Secondary ion mass spectroscopy analysis shows that the oxygen profile is in good agreement with the theoretical profile (LSS) and that the beryllium profile is still deeper than the theoretical one. The electrical properties of the ion-implanted heterojunctions are studied by means of current-voltage (I-V) and capacitance-voltage (C-V) measurements and are found to strongly depend on the isochronal annealing temperature. A low-temperature anneal (≤400 °C) produces a high-resistivity isolation layer of about 0.4 μm thick in the heterojunctions. At annealing temperatures above 400 °C, the data indicates a pronounced decrease in the carrier concentration in AlGaAs regions as compared with their original doping, but a good recovery after a high-temperature anneal (800 °C).

Notes: The influence is described of several device parameters, i.e., the total director twist, the pretilt angle, and anchoring energy, on the director pattern in highly twisted samples with nonzero boundary tilt. A difference compared with previous approaches is the inclusion of a finite anchoring energy coefficient in the continuum equations. The results indicate a pronounced influence of the surface anchoring on the hysteresis in the midplane tilt angle as a function of an applied voltage.

Notes: The electrical impedance of a lossy conductor is a complicated function of time (or frequency) because of the skin effect. By solving the diffusion equation for magnetic fields in conductors of several prototypical shapes, the impedance can be calculated as a function of time for a step function of current. The solution suggests an electrical circuit representation that allows calculation of time-dependent voltages and currents of arbitrary waveforms. A technique using an operational amplifier to determine the current in such a conductor by measuring some external voltage is described. Useful analytical approximations to the results are derived.

Notes: A theoretical model is presented for the physical description of free-to-bound transitions to deep levels in semiconductors and for the synthesis of their fluorescence line shapes. The analysis takes account of broadening by emission and absorption of lattice quanta, by the continuum of initial electronic states, and by the random distribution of impurity sites or other inhomgeneous mechanisms. The vibrational contribution is developed for linear coupling to a single vibrational mode in the harmonic approximation, and for linear coupling to many modes having a range of vibrational frequencies, including the specialization of the latter results to the "narrow coupling'' limit. The electronic contribution is specified only for thermal broadening by conduction-band states. The contribution of inhomogeneous mechanisms is modeled by Gaussian distributions. Formulas for the line-shape function and its initial moments are provided for use in fitting and interpreting experimental photoluminescence data. Use of the "narrow coupling'' results to synthesize the temperature dependence of measured line shapes can prescribe the parameters of a single-frequency configurational-coordinate model.

Notes: A systematic photoluminescence (PL) study of a deep level in liquid-phase-epitaxy-grown GaAs:Sn is presented. Experimental details and results are reported on PL spectra and decay-time measurements in the temperature range T=4.2–300 K for selected carrier concentrations between n=6×1016 and 2×1018 cm−3. Qualitative interpretation of the measured data is shown to be consistent with a conduction-band-to-deep-acceptor transition. This interpretation was further supported by synthesis of the high-temperature line shapes, using general techniques developed for analyzing free-to-bound transitions. The effects of electron-lattice interaction in the narrow-coupling limit of the initial electronic state continuum, and of inhomogeneous broadening by the random distribution of impurities, are taken into account. Values predicted for the parameters of a three-state configuration-coordinate diagram for the transition correlate well with measured T and decay-time results, as well as with estimates obtained from a moment analysis of the line shapes.

Notes: This paper gives formulas for analyzing two curling regions which are magnetostatically coupled at film edges. Magnetostatic energy of coupled film edges having any given surface and volume charges can be calculated from the formulas. These formulas are expressed in terms of film width W, film thickness T1 and T2, saturation magnetization M1 and M2, curling length D1 and D2, and angle θ01 and θ02 between the magnetic moment and the film edge surface of the upper and under layers, respectively. Using these formulas, we have quantified the magnetization distribution in the coupled film edges and the decrease in energy caused by magnetostatic coupling and the conversion of surface charges into volume charges. The approximate formulas derived in the previous paper [J. Appl. Phys. 58, 1610 (1985)] are corrected in this paper.

Notes: The piezoresistance effect in n-channel inversion layers of (001) silicon films on sapphire (SOS) and (001) bulk silicon has been studied at room temperature using metal-oxide-semiconductor field-effect transistors radially arranged on a diaphragm with 36 mm in diameter. The piezoresistance characteristics of inversion layers are markedly different between SOS and bulk silicon. Main features of the experimental results are interpreted on the basis of the deformation potential theory and the surface quantization effect in inversion layers, and it is concluded that the difference between SOS and bulk silicon can be mainly explained by the effect of residual strain in SOS. The piezoresistance coefficients of inversion layers on SOS have been determined experimentally, and have been found that π11(approximately-equal-to)−π12. In addition, the comparison of the experimental value of π11/π12 with the calculated value is suggested that the transverse mobility of electrons in the valley which have its longitudinal axis of ellipsoid perpendicular to the film surface is smaller as compared with that in the other valleys.

Notes: The ionization and attachment coefficients for CCl2F2/SF6 mixtures were determined from measurements of prebreakdown ionization currents in a steady-state Townsend discharge at a pressure p25=4 Torr and temperature of 25 °C. The curves representing the ionization coefficient (α) for reduced fields in the range from 110 to 180 V cm−1 Torr−1 exhibit a small maximum at about 15% of CCl2F2, while those representing the attachment coefficient (η) flatten out between 0% and 50% CCl2F2 and decrease at higher partial densities. The limit field obtained using the condition α=η shows two extrema, i.e., a minimum at approximately 20% and a maximum at 75% of CCl2F2, while the curves obtained from the breakdown-potential measurements available in the literature show only a maximum, at roughly the same position. Theoretical values of the transport coefficients were obtained by numerically solving the Boltzmann equation using previously determined effective sets of electron collision cross sections [J. P. Novak and M. F. Fréchette, J. Appl. Phys. 55, 107 (1984); 57, 4368 (1985)]. The good agreement between the calculated and the experimental values provides supporting evidence for the applicability of the present calculation method and collisional cross sections to analyze electron swarms in the range of fields comparable in magnitude to the limit field.

Notes: An electron beam propagating nearly parallel to the interface between two materials of different mean inner Coulomb potential (V0) is deflected towards the material with the largest ||V0||. It is experimentally demonstrated that this effect can be used to determine which of the two materials at an interface has the largest V0 and to image interfaces. Examples are presented from the SiO2/Si (111) interface and from a thin sandwich comprising the Al/Cu/Cr/SiO2/Si(100) interface system. Electron energy-loss spectroscopy of electrons deflected at the Si(111)/vacuum interface shows a strong surface plasmon peak, and with some instrumental improvements this may be a useful spectroscopic technique on buried interfaces.

Notes: In this paper we present an optical method to control the geometry of buried layers in optoelectronic heterostructures. The technique uses an optical microscope equipped for infrared applications and relies on the fact that the different layers of the multilayer structure have different band gaps. Accordingly transmission/absorption, reflectance, and photoluminescence of the inidividual layers exhibit their characteristic near-band-gap spectral variations at different wavelengths. By appropriate selection of the wavelength range used for image formation, any layer of interest can be made visible. As an example we investigated a mushroom-type InGaAsP/InP 1500-nm laser structure with subsequent mass transport. Both technological steps, the formation of the mushroom by underetching, and the regrowth by mass transport represent critical processes in the fabrication of these index-guided lasers. Our results show clearly that the successful accomplishment of the process can be controlled by images of the selected buried layer. Contrast and resolution of the pictures are sufficient to show any irregularity in etching or regrowth. The main advantage of the method is that it offers the possibility of investigating whole wafers without sample preparation and in a nondestructive way, which is in marked contrast to observation with a scanning electron microscope, where only profiles along cleaved facets can be inspected.

Notes: We review work on In2O3:Sn films prepared by reactive e-beam evaporation of In2O3 with up to 9 mol % SnO2 onto heated glass. These films have excellent spectrally selective properties when the deposition rate is ∼0.2 nm/s, the substrate temperature is (approximately-greater-than)150 °C, and the oxygen pressure is ∼5×10−4 Torr. Optimized coatings have crystallite dimensions (approximately-greater-than)50 nm and a C-type rare-earth oxide structure. We cover electromagnetic properties as recorded by spectrophotometry in the 0.2–50-μm range, by X-band microwave reflectance, and by dc electrical measurements. Hall-effect data are included. An increase of the Sn content is shown to have several important effects: the semiconductor band gap is shifted towards the ultraviolet, the luminous transmittance remains high, the infrared reflectance increases to a high value beyond a certain wavelength which shifts towards the visible, phonon-induced infrared absorption bands vanish, the microwave reflectance goes up, and the dc resisitivity drops to ∼2×10−4 Ω cm. The corresponding mobility is ∼30 cm2/V s. The complex dielectric function ε is reported.These data were obtained from carefully selected combinations of spectrophotometric transmittance and reflectance data. It is found that ε can be reconciled with the Drude theory only by assuming a strongly frequency-dependent relaxation energy between the plasma energy and the band gap. We review a recently formulated quantitative theoretical model for the optical properties which explicitly includes the additive contributions to ε from valence electrons, free electrons, and phonons. The theory embodies an effective-mass model for n-doped semiconductors well above the Mott critical density. Because of the high doping, the Sn impurities are singly ionized and the associated electrons occupy the bottom of the conduction band in the form of an electron gas. The Sn ions behave approximately as point scatterers, which is consistent with pseudopotential arguments. Screening of the ions is described by the random phase approximation. This latter theory works well as a consequence of the small effective electron radii. Exchange and correlation in the electron gas are represented by the Hubbard and Singwi–Sjölander schemes. Phonon effects are included by three empirically determined damped Lorentz oscillators. Free-electron properties are found to govern the optical performance in the main spectral range. An analysis of the complex dynamic resistivity (directly related to ε) shows unambiguously that Sn ions are the most important scatterers, although grain-boundary scattering can play some role in the midvisible range.As a result of this analysis one concludes that the optical properties of the best films approach the theoretical limit. Band-gap shifts can be understood as the net result of two competing mechanisms: a widening due to the Burstein–Moss effect, and a narrowing due to electron-electron and electron-ion scattering. The transition width—including an Urbach tail—seems to be consistent with these notions. Window applications are treated theoretically from detailed computations of integrated luminous, solar, and thermal properties. It is found that In2O3:Sn films on glass can yield∼78% normal solar transmittance and ∼20% hemispherical thermal emittance. Substrate emission is found to be insignificant. Antireflection with evaporated MgF2 or high-rate sputtered aluminum oxyfluoride can give ∼95% normal luminous transmittance, ∼5% normal luminous reflectance, little perceived color and little increase in emittance. A color purity 〈1% in normal transmission and 〈10% in normal reflection is achievable for a daylight illuminant within extended ranges of film thickness.

Notes: Spatially resolved soft x-ray spectra were collected for neon plasmas produced by imploding hollow annular gas puffs with MA level driving currents. The Z-pinch imploded plasmas were studied for different risetime currents produced with or without the use of a plasma erosion opening switch (PEOS). Selected spectrograms were processed and analyzed to obtain absolute energies for the radiation emitted in the Ne ix and Ne x discrete transitions, as well as for total emission over the spectral range 900–1600 eV. The neon plasmas radiate 1–2.5 kJ in this energy range predominantly in the α transitions of both ions. The plasma uniformity inferred from spatially resolved spectral lines improves significantly using a faster rise-time driving current.

Notes: Results are presented for the radiation-induced transient darkening of thin organic polymer films normally used as Cerenkov light emissions sources. The radiation source is a 27-MeV, 10-μC, 200-ns electron beam generated by the PHERMEX accelerator. The typical dose for a single pulse is 5 Mrad. At this dose, the broadband time-resolved percent transmission above 520 nm was measured for four common polymers: polyimide (Kapton-H), polyethylene terephthalate (Mylar), cellulose acetate, and high-density polyethylene. Kapton was found to darken the most and polyethylene darkened the least. The recovery time to normal transmission for Kapton was found to be greater than 10–20 μs. The radiation-induced attenuation coefficient is shown to depend on electronic band energy separation. The results show that Kapton is not the material of choice for a Cerenkov light source.

Notes: The internal friction (IF) background of gold is studied in the kHz frequency range. Systematic measurements of IF as a function of frequency, strain amplitude, and temperature show that the IF is due to the superposition of two contributions: the thermoelastic effect and a dislocation effect. The thermoelastic effect is responsible for the IF background observed when the strain amplitude tends to zero. It is the only contribution to the IF background which is strain amplitude independent. On the contrary, the dislocation effect contributes only to the strain amplitude-dependent IF background. This effect is proportional to the strain amplitude. In particular, it is zero when the strain amplitude tends to zero. Furthermore, the dislocation contribution is frequency independent. The experimental results show that the dislocation effect cannot be explained by a viscous damping of dislocation motion, but must be related to an hysteretic and athermal motion of dislocations.

Notes: Secondary-ion-mass spectrometry, Hall-effect measurements, and dc I-V characteristics of 1-μm Ga0.47In0.53As-Al0.48In0.52As high-electron mobility transistor structures indicate that significant diffusion of Si can occur in these layers. The source of the Si is both the intentional Si used for modulation doping of the devices, and Si which is an unintentional impurity in the Fe-doped InP substrates on which the layer is grown. Preannealing and polishing the substrates can lessen the effect.

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

Notes: Diffusion of gases through porous media is often treated in the continuum approximation of fluid dynamics. However, when the pore diameter is of the same order of magnitude as the mean free path of the molecules in the gas, the continuum approximation is no longer valid because of incorrect collision counting. This paper presents the first theoretical solution of this problem by strict use of the kinetic theory of gases. The diffusion coefficient as calculated herein exhibits a coupling term not present in the continuous fluid treatment.

Notes: The difference in the operation of extraction geometry versus radial geometry Applied-B ion diodes is explained through the use of a general magnetic insulation condition for cylindrically symmetric ion diodes which is expressed in terms of the magnetic stream function. We find that Applied-B extraction geometries attempted so far have suffered from a magnetic field configuration defect which explains their rather poor performance. We present solutions to the extraction Applied-B ion diode problem, as well as 2D, electromagnetic particle-in-cell simulations of an example solution.

Notes: Because they are less susceptible to the hydromagnetic Rayleigh–Taylor instability than other fast Z-pinch imploding liner systems, gas puffs offer the possibility of higher implosion velocity. This higher specific energy appears necessary for optimizing high-energy x rays required in a photoionization-pumped soft x-ray laser. Nevertheless, large-scale-length nonuniformities created as the gas flows from the nozzle across the electrode gap are a potential problem. One- and two-dimensional calculations suggest that gas near the nozzle will implode before that which is further from the nozzle, leading to an effect described as "zippering.'' Because the number of such two-dimensional calculations that can be done is limited and because the density distribution of nozzles is uncertain, we have developed a simple quasi-two-dimensional interface code that is able to quickly survey the effect of arbitrary initial gas distributions on the implosion dynamics. Results of this survey suggest that zippering contributes significantly to thermalization time, and we propose two methods to counteract this problem. These techniques, each of which involves tailoring the initial density distribution to offset effects of nonuniformities, appear promising. Nevertheless, we will never completely eliminate these nonuniformities, therefore, they must be accounted for in x-ray laser target design.

Notes: Under ultrahigh vacuum conditions, molybdenum disilicide has been obtained by electron gun evaporation of molybdenum on heated monocrystalline silicon substrate. Depending on the deposition temperature, the resulting thin film is composed of tetragonal disilicide or of a mixture of hexagonal and tetragonal disilicide. Preferential orientations of MoSi2 have been observed for both phases grown on (100) silicon substrate heated at 550, 650, and 750 °C. Further annealing does not improve the crystallographic orientation of the materials.

Notes: The incorporation of nitrogen and hydrogen during nitridation of SiO2 was studied over the temperature range of 800–1000 °C and for ammonia pressures of 1, 5, and 10 atm. The nitrogen content of the nitrided films was determined with Rutherford-backscattering spectrometry and elastic-recoil detection. Nitrogen in-depth profiles were obtained applying Auger analysis combined with ion sputtering. Hydrogen profiles in the films were measured using nuclear-reaction analysis. Both the nitrogen and hydrogen incorporation were found to increase with temperature in this range. A higher ammonia pressure primarily increases nitridation of the bulk of the oxide films. Depending on the nitridation conditions, up to 10 at.% of hydrogen may be incorporated. As distinct from the nitrogen profiles, the hydrogen in-depth profiles are essentially flat. The concentration of hydrogen in the films, however, was always found to be smaller than that of nitrogen: measured H/N ratios varied between 0.25 and 0.85, the smaller values being obtained for the thinner oxides and higher nitridation temperatures. The model previously postulated to explain the nitrogen incorporation during atmospheric nitridation of SiO2 proves to be valid at higher pressures as well. By considering the role of OH as a reaction product of the nitridation process, the hydrogen results can be accommodated within the same concept. The model predicts a low H/N-incorporation ratio for a thin surface and interface layer and a substantially larger ratio for the bulk of the film. If this prediction is correct, which seems to be indicated by the etch-rate behavior of the nitrided oxides, then this would have considerable importance for the electrical properties of this material.

Notes: Cross-sectional high-resolution transmission electron microscopy (HRTEM) images of the crystalline Si/SiO2 interface have been computer simulated on the basis of various interface models in order to facilitate the interpretation of experimental HRTEM images. Continuous random networks of SiO2 have been constructed on crystalline Si substrates with different orientations and surface morphologies using plastic balls and spokes. The distortion energy introduced by artifacts in the model has been relaxed by modifying the atom positions, HRTEM images of the models have been calculated using the multislice dynamical electron scattering method. The apparent shift of the (111)Si/SiO2 interface into the SiO2 region has been observed due to the localization of first Si atoms in SiO2 region. The contrast of the crystalline Si image due to the amorphous SiO2 region in the wedge-shaped bilayer structure of the Si/SiO2 interface has been obscured. The undulated (100)Si/SiO2 interface delineated with {111} facets has given an unexpectedly flat periodic-nonperiodic interface image.

Notes: It is shown in semiconductor superlattices that slight fluctuations in layer thicknesses will result in localization of electronic states. It has been previously argued that this localization will hinder the formation of minibands. We show that these localized states have energy differences of much less than the thermal energy at room temperature. Therefore, the overall electronic state is a thermal average of the localized states. Because of this, slight fluctuations in layer thickness will not hinder the formation of minibands, except at low temperatures.

Notes: The Monte Carlo computer program trim is used to calculate the projected range, the standard deviation, the skewness, and the kurtosis of implanted boron ion distributions in silicon, silicon dioxide, molybdenum disilicide, tantalum disilicide, titanium disilicide, and tungsten disilicide. The boron implantation energy ranges from 10 to 500 keV.

Notes: Native oxides on the surface of Cd1−xMnxTe (0≤X≤0.7) have been analyzed on the basis of XPS measurements. Depth profile analysis revealed a significant increase in the thickness at higher Mn concentrations and a strong Mn segregation to the surface, respectively. Sputter-induced damage on cleaved (110)-oriented surfaces was analyzed by photoreflectance and photoluminescence measurements. The damage was found to be larger on CdTe than on the alloy. Thermal annealing showed nearly complete restoration for the surface of the alloy, while CdTe revealed irreversible modifications in the near-surface regime upon sputtering and post annealing.

Notes: We report an application of nuclear magnetic resonance (NMR) spectroscopy to the study of fluorine-doped silicate glass prepared by the modified chemical vapor deposition process, prior to drawing the rod into fibers. The silica contains 1.03-wt. % fluorine, as determined by the calibrated intensity of the 19F NMR spectrum. The isotropic chemical shift of the 19F spectrum shows that fluorine bonds only to silicon; there is no evidence of oxyfluorides. Analysis of the distribution of nuclear dipolar couplings between fluorine nuclei reveals that the relative populations of silicon monofluoride sites [Si(O–)3F] and species having near-neighbor fluorines, such as silicon difluoride sites [Si(O–)2F2], are nearly statistically random. That is, to a good approximation, the fluorine substitutes randomly into the oxygen sites of the silica network. There is no evidence of local clusters of fluorine sites, silicon trifluoride sites [Si(O–)F3], or silicon tetrafluoride (SiF4).

Notes: The field-ion microscope technique has been employed to study, on an atomic scale, the vacancy structure of individual depleted zones (DZs) in platinum specimens which had been created by 20-keV Kr+ ions. DZs are the final quiescent state of collision cascades. The irradiations were performed in situ at 60 K and the specimens were examined at this temperature by the pulse field-evaporation technique. The following experimental quantities were determined for each DZ: (a) the absolute number of vacancies (ν); (b) the average diameter; (c) the average vacancy concentration based on ν and the actual volume filled by the vacancies; (d) the radial distribution function of the vacancies out to the ninth nearest-neighbor; (e) the fraction of first-nearest-neighbor vacancies in clusters of size n; (f) the average depth (L) from the irradiated surface, measured along a direction parallel to the incident ion beam, at which each DZ was detected and its direction of elongation; and (g) the sputtering yield based on the number of vacancies detected in the near-surface region (〈5 A(ring) thick). All of the measured quantities are compared with corresponding quantities extracted from either an analytical model or a Monte Carlo computer code (Transport of Ions in Matter—trim) of radiation damage. We demonstrate that it is possible to transform a microscopic spatial distribution of vacancies to a continuous radiation damage profile with atomic resolution.

Notes: Group-III acceptors are deactivated by hydrogen released by 8 keV electrons in metal-oxide-silicon capacitors. The decay of the acceptor density during keV electron beam irradiation shows three conjoined phases: an initial delay, a short-time transient, and a long-time transient. This overlapping temporal characteristic is related to comparable rates of hydrogen bond breaking at the gate–oxide interface, hydrogen migration across the oxide, and emission and capture of proton at the group-III acceptor. Isothermal annealing data showed clearly two distinct annealing phases: an initial exponential rise and the long-time second-order recovery kinetics. The hydrogenation and annealing rate coefficients from these electron beam irradiated oxides are different from those obtained from avalanche electron injection (AEI) experiments. The difference suggests that the atomic structure surrounding the hydrogen-acceptor complex depends on the hydrogenation energetics. Compared with those electrons in the AEI experiments (tens eV), the higher-energy (keV) electrons can create more extended interfacial dangling bonds which are hydrogen or proton traps.

Notes: We present a detailed discussion of the physical significance of measurements of capacitance as a function of applied bias voltage to a Schottky barrier when the semiconductor involved contains not only shallow levels but also deep levels. Whether deep levels are affecting the capacitance can be determined by measuring the capacitance versus voltage as a function of frequency or of temperature, and observing the frequency or temperature dependence of the slope of a plot of inverse capacitance as a function of voltage compared to the frequency or temperature dependence of the slope of a plot of inverse squared capacitance as a function of voltage. The slope of the inverse capacitance as a function of voltage should not be a function of frequency or temperature regardless of whether deep levels are significant or not, whereas the slope of the inverse squared capacitance as a function of voltage should depend on frequency and/or temperature if deep levels are significant. Examples of this behavior are given from measurements on CdTe single crystals and thin films.

Notes: Distributions of stress, dislocations, and the EL2 midgap defect have been optically mapped in semi-insulating GaAs wafers, from [100]-grown crystals created by the liquid-encapsulated Czochralski method. The evolution of EL2 along the growth axis indicates that assessment of this property through the majority of the crystal volume is often poorly represented by wafers from near the two end regions. A comparison of maps for stress, dislocation and EL2 patterns as all measured with a given wafer does not support hypotheses that EL2 is a direct consequence either of stress or of dislocations. Other mechanisms, such as segregation and melt dynamics, thus appear more likely to control the formation and distribution of EL2.

Notes: The production of negative hydrogen ions sputtered from a low work function converter surface has been investigated. Hydrogen and cesium admitted into the vacuum chamber are chemisorbed on a polycrystalline molybdenum target. H−, Mo−, and e− are sputtered from this cathode by Cs+ ions in the energy range 150–1000 eV. Angular and parallel energy distributions of H−, Mo−, and e− are measured as a function of hydrogen gas pressure, cesium coverage, and incident ion energy. For optimum coverage, the H− ion temperature varies from 0.65% and 0.35% of the incident Cs+ bombarding energy for Cs+ ion energies of 250 and 1000 eV, respectively. The secondary electrons have a temperature of 0.04% of the bombarding energy almost independent of Cs+ energy. The spreads increase with decreasing target coverage and are independent of surface roughness. The optimum H−, Mo−, and e− yields are also measured as a function of hydrogen pressure and incident Cs+ bombarding energy. The optimum H− ion yield is 0.41 at a Cs+ ion energy of 750 eV. By extrapolating the H− ion yield at low Cs+ bombarding energy, a Cs+ ion threshold energy of 120 eV may be estimated. This indicates a binding energy of hydrogen smaller than 3.6 eV.