bluuebunny/crossref_metadata_2025 huggingface dataset:
The measurement of effective complex refractive indices for selected metal silicides
Authors: Frampton R. D. , Irene E. A. , d’Heurle F. M.
Published: July 2002

The measurement of thermally grown silicon dioxide films on selected metal silicides (CoSi2, CrSi2, Ir3Si5, NiSi2, Ru2Si3, and WSi2) via ellipsometry has been investigated. The oxide-thickness calculation requires a knowledge of the complex refractive index of the metal-silicide substrate which can be measured independently by ellipsometry on bare silicide substrates. In order to check the measured refractive indices for the silicide substrates, the thicknesses of thermally grown SiO2 films were compared from ellipsometry which used the measured refractive indices, Rutherford backscattering, and step-height thickness measurements. It is shown that, despite considerable complexities introduced by various surface treatments, procedures have been found so that effective refractive indices for the silicide substrates can be obtained, which in some instances require removal of the oxide and measurement of the complex refractive index of the silicide after oxidation.
Electron energy distribution functions in carbon monoxide discharge and post-discharge conditions: The role of superelastic electronic collisions from CO(A3Π) state
Authors: Gorse C. , Paniccia F. , Bretagne J. , Capitelli M.
Published: July 2002

The influence of superelastic electronic collisions from the metastable CO(A3Π) state on the electron energy distribution functions (EDF’s) of CO in both discharge and post-discharge conditions has been studied by solving the Boltzmann equation with different concentrations (cm) of CO(A3Π). The results show that the role of CO(A3Π) becomes more important as the reduced electric field (E/N) is lowered. Very small concentrations of CO(A3Π) (cm  ≂ 10−7) are sufficient to affect EDF in the post-discharge regime (E/N=0). Superelastic electronic collisions are such that they create different plateaus in EDF, each one spaced approximately every 6.2 eV, which represents the energy threshold of the metastable electronic state.
Determination of density of localized states in amorphous silicon alloys from the low field conductance of thin n-i-n diodes
Authors: Shur Michael , Hack Michael
Published: July 2002

We describe a new technique to determine the density of localized states in the energy gap of amorphous silicon alloys from the temperature dependence of the low field conductance of n-i-n diodes. This new technique allows us to determine the bulk density of states in the center of a device. It involves fewer assumptions than other established techniques, and by varying the intrinsic layer thickness the density of states within approximately 400 meV of midgap can be determined. We measured the temperature dependence of the low field conductance of amorphous silicon alloy n-i-n diodes with intrinsic layer thicknesses of 0.55, 0.45, and 0.15 μm and deduced the density of localized states to be approximately 5×1016 cm−3 eV−1 at 0.45 eV and 5×1017 cm−3 eV−1 at 0.24 eV below the bottom of the conduction band.
Photovoltaic decay and its temperature dependence on amorphous silicon solar cells
Authors: Fang P. H. , McCabe P. , Wu Xing-hui , Kinnier J. H.
Published: July 2002

In the investigation of characteristics of amorphous-microcrystal combined silicon solar cells prepared by a vacuum evaporation, we found that (1) the photovoltaic voltage which decays as a function of continuous illumination time satisfies the Scher–Montroll function [Phys. Rev. B 12, 2455 (1975)] derived from stochastic hoping model and (2) the steady-state photovoltage as a function of temperature is found to be described by an empirical function of Vogel–Fulcher [Phys. Z. 22, 645 (1921); J. Am. Ceram. Soc. 8, 339 (1925)].
Magnetic effects in eddy current nondestructive method
Authors: Yi Jae-yel , Lee Sekyung
Published: July 2002

Magnetic effects in eddy current nondestructive method are studied employing an extension of the general ideas of Globus for the magnetization processes of polycrystalline materials. The reversible permeability depends on the residual magnetization of the material. The relation between these two quantities is derived from the Globus model. An expression is derived for the impedance of a single-turn coil above a ferromagnetic conducting half-space. From this expression, flaw effects and liftoff effects are analyzed, and theoretical treatment for the evaluation of residual magnetization is described.
Effect of stray inductance on capacitive-voltage divider
Authors: Wong C. S.
Published: July 2002

The effect of stray circuit inductance on the response of a capacitive-voltage divider to fast-rising voltage pulses is investigated. Results obtained from the analysis of the capacitive divider’s equivalent circuit indicate an upper-frequency limit of only 1% of the natural frequency of the circuit.
Conversion electron Mössbauer spectroscopic study of ion-beam mixing at Fe-Mo interface
Authors: Joshee Rekha , Phase D. M. , Ghaisas S. V. , Kanetkar S. M. , Ogale S. B. , Bhide V. G.
Published: July 2002

Ion beam induced atomic mixing at Fe-Mo interface has been studied by using the technique of conversion electron Mössbauer spectroscopy (CEMS). Use has been made of a thin (∼50 Å) layer of Fe57 isotope (enriched to 95.4%) at the interface to obtain the Mössbauer information selectively from this region. A noninterface sensitive measurement has also been performed to reveal the magnetic hyperfine interactions in the entire region of the iron overlayer. It is shown that a deposition induced reaction between the molybdenum substrate (having a thin coating of native oxide) and the Fe57 layer renders a graded nature to the interface, which is transformed upon ion bombardment (100-keV Kr+, dose ∼1016 ions/cm2) into a disordered alloy. The dominant nonmagnetic component corresponding to the interface of the ion beam mixed sample happens to be a quadrupole doublet, which represents the presence of Fe57 atoms in Fe2+ charge state. The appearance of this contribution is attributed to formation of an oxygen coordinated ternary compound in the interface layer during ion bombardment. On the basis of the comparison of the results of the interface-sensitive and non-interface-sensitive studies it is established that the inclusion of oxygen in the ion mixed sample is mainly confined to the near interface region and that the region of the overlayer contains a metastable alloy of the binary Fe-Mo system. The influence of thermal annealing at various temperatures between 200 °C and 500 °C on the ion beam mixed state has also been studied by monitoring the changes in the hyperfine interaction parameters. It is shown that the oxygen-incorporated regions of the disordered alloy retain the nonmagnetic Fe2+ charge state subsequent to annealing at 500 °C, while other regions lead to precipitation of α-Fe and Fe2Mo phases.
Surface layers in yttrium iron garnet by annealing in H2 atmosphere
Authors: Balestrino G. , Lagomarsino S. , Tucciarone A.
Published: July 2002

Formation of a surface layer was studied in pure yttrium iron garnet (YIG) by annealing in H2 atmosphere at temperatures above 450 °C. Double-crystal x-ray diffraction from the surface layer shows interference fringes in analogy with the ion-implantation case. From an analysis of the fringes based on the kinematical theory, the strain profile was determined. It appears that the surface layer has a well-defined negative lattice mismatch with respect to the underlying film bulk, and that a transition region exists with a decreasing absolute value of mismatch. Analogies and differences with respect to the ion implantation are pointed out.
The role of reflectivity change in optically induced recrystallization of thin silicon films
Authors: Grigoropoulos Costas P. , Buckholz Richard H. , Domoto Gerald A.
Published: July 2002

In this paper we study a simplified model of the fundamental mechanisms governing the radiatively induced recrystallization of a thin polysilicon layer on a heat-sink structure. It has been observed that instabilities in laser induced crystal growth on thin polysilicon layers do occur. To study these solidification instabilities we use a linear stability analysis. The reflectivity difference between the liquid and the solid phases is shown to be a source of thermal instability.
Electrical properties of Schottky diodes of Ti on highly doped GaAs
Authors: Zussman A.
Published: July 2002

I-V and C-V characteristics of Schottky diodes prepared by Au/Pt/Ti evaporation and by Ti sputtering on GaAs substrates with electron concentrations of 1.5×1017, 4.5×1017, and 3.5×1018 cm−3 were measured as a function of temperature between 77 and 300 K. The ideality factor was found to follow the theory of thermionic field emission. Closer agreement with that theory was observed for evaporated and annealed diodes and for sputtered diodes than for evaporated, as-deposited devices. The sputtered diodes exhibited the best I-V characteristics with an ideality factor n=1.04 and a reverse current lower by more than two orders of magnitude than that of the evaporated devices at 300 K. This behavior was attributed to the presence of an interfacial oxide layer in the evaporated devices. Departure from the thermionic field emission theory was observed in devices with Nd≥4.5×1017 cm−3 at low forward bias and was attributed to current transport due to a mechanism of multistep recombination tunneling through defects.
Characterization of EL2 distribution on semi-insulating GaAs wafer by optically assisted imperfection profile
Authors: Wang Faa-Ching
Published: July 2002

An improved nondestructive characterization technique is developed to measure the relative density distribution of the EL2 level in undoped semi-insulating (SI) GaAs wafers at room temperature. Experimentally, the resistance of a small area of the wafer is measured twice, first with greater than band-gap illumination outside a small masked area and then with a narrow-band optical filter centered at 1074 nm in place of the masked area. The difference of the two measured resistances is shown to be proportional to the density of the EL2 level. By moving the masked area across the wafer while taking resistance measurements, the relative density variation of EL2 can be determined. A theoretical discussion based on the commonly used compensation model for undoped SI GaAs materials is presented to interpret the experimental data. A technique for applying electrical contacts to SI GaAs materials by ultrasonic soldering has been developed to achieve reproducible measurements. Although only GaAs materials were investigated, this optically assisted imperfection profile can be applied to study other high-resistivity semiconductors.
A technique to improve the epitaxial growth of some fcc and bcc metals on rock salt
Authors: Köster S. , Herres N. , Rey M. , Reichelt K.
Published: July 2002

It has been found that by the deposition of a thin layer of LiF on rock-salt cleavage faces the epitaxial growth of Ag, Al, Cu, Cr, Fe, V, and Mo will be improved markedly. The simultaneous growth of the metals on air-cleaved rock-salt substrates and on air-cleaved rock-salt faces covered with a LiF interlayer before the metal deposition have been compared by transmission electron microscopy and x-ray rocking curves.
Observation of radiative surface plasmons in metal-oxide-metal tunnel junctions
Authors: Donohue J. F. , Wang E. Y.
Published: July 2002

A peak in the ultraviolet (UV) region of the spectrum of light emitted from metal-oxide-metal (MOM) tunnel junctions has been observed at room temperature. Both the amplitude and wavelength of the peak are sensitive to applied junction bias. The UV peak corresponds to the normal or radiative surface plasmon mode while a visible peak, also present in our spectra and reported in past MOM literature, is due to the tangential or nonradiative mode. The radiative mode requires no surface roughness or gratings for photon coupling. The results show that it is possible to obtain radiative surface plasmon production followed by a direct decay into photons with MOM tunnel diodes. A MOM diode with a double anode structure is found to emit light associated only with the nonradiative mode. The thickness dependence of the UV peak along with the experimental results of the double anode MOM diode and the ratio of the UV peak to visible peak support our contention that the UV light emission is indeed due to the radiative surface plasmon.
Impulse photoconductance of thin-film polycrystalline silicon
Authors: Hammond R. B. , Johnson N. M.
Published: July 2002

Using optoelectronic correlation and sampling oscilloscope techniques we measured impulse photoconductance of polycrystalline-Si thin-film photoconductors excited by femtosecond dye-laser pulses. We studied as-deposited micrograin films as well as annealed, H-passivated, and H-passivated/annealed films. Results yielded photoexcited carrier mobilities of 6.8 and 104 cm2/V s, respectively in as-deposited and 1150 °C-annealed films. The photoconductance decays of as-deposited films showed an initial fast decay time of ∼22 ps followed by a primary decay time of ∼150 ps. Photoconductance decays of annealed films showed similar primary decay times but no initial fast decay transient. H passivation of both as-deposited and annealed films produced no changes in carrier mobilities. However, H passivation of as-deposited films eliminated the initial fast decay transient and increased the primary decay time to ∼800 ps. H passivation of annealed films increased decay time only slightly. Results suggest that grain boundaries control decays in as-deposited films but not in annealed films, and that H passivation does not reduce carrier scattering.
Influence of residual gases and surface contaminants on the aging behavior of island silver films
Authors: Das V. Damodara , Sastry M. S. Murali
Published: July 2002

The aging of island silver films deposited on glass at room temperature and at a pressure of 2×10−5 Torr was studied by monitoring the dc electrical resistance of the films. Films in the resistance range 1–11 MΩ/⧠ were studied under different conditions to ascertain the role of the residual gases and surface contaminants on the agglomeration rate. It was found that residual gases do not significantly affect the agglomeration rate, but a film of water vapor adsorbed on the glass surface retards the agglomeration to a great extent. An expression is arrived at for the functional dependence of the interisland spacing with time for the different conditions of study, assuming that the conduction in these island films is by quantum mechanical tunneling.
Propagation of light in an optically active electro-optic crystal of Bi12SiO20: Measurement of the electro-optic coefficient
Authors: Henry M. , Mallick S. , Rouède D. , Celaya L. E. , Garcia Weidner A.
Published: July 2002

We have studied the phenomenon of light propagation in an optically active linearly birefringent medium with particular reference to the electro-optic crystal of Bi12SiO20. Analytic expressions are given for the ellipticity and the orientation of the emerging light vibration when linearly polarized light is incident normally on the crystal. From these expressions we derive the interesting results that there exists an orientation of the incident light vector for which the output beam is linearly polarized and that the input and output linear vibrations are then symmetrically oriented with respect to the principal birefringent axes of the crystal. This particular angle of orientation is expressed in terms of the linear and circular birefringence of the crystal. Since ellipticity is a function of the electric-field-induced linear birefringence and hence of the electro-optic coefficient of the crystal, we have determined the electro-optic coefficient r41 from a measured value of the ellipticity. The coefficient r41 is found to be (4.1±0.1)×10−12 m/V.
Ellipsometry measurements of nickel silicides
Authors: Chen Hong-Wen , Lue Juh-Tzeng
Published: July 2002

The real (n) and imaginary (k) parts of the refraction index of Ni2Si, NiSi, and NiSi2 silicides are measured by an ellipsometer in the optical range of 4000–7000 Å. The n and k are within the values of 2.0–3.5 for the high-temperature annealed nickel silicides.
Lifetimes, ionization energies, and discussion of the emission lines in the 1.5040–1.5110-eV range in GaAs
Authors: Reynolds D. C. , Bajaj K. K. , Litton C. W. , Peters G. , Yu P. W. , Fischer R. , Huang D. , Morkoç H.
Published: July 2002

We have calculated the recombination lifetimes for donor-acceptor (D-A) pairs having separations of 50–70 Å and find very good agreement with measured lifetimes. We have also measured the ionization energies of the transitions in the same spectral region using the temperature dependence of line intensity. The estimated ionization energies of D-A pairs in this spectral region agree very well with the measured ionization energies. A model has been presented for the g lines, which accounts for the origin of the g lines in both GaAs and InP.
Model and diagnostics of the high-pressure mercury discharge with sodium iodide additives
Authors: Dakin James T. , Gilliard Richard P.
Published: July 2002

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.
Discharge constriction, photodetachment, and ionization instabilities in electron-beam-sustained discharge excimer lasers
Authors: Kushner M. J. , Pindroh A. L.
Published: July 2002

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.
Effects of impurities on radiation damage in InP
Authors: Yamaguchi Masafumi , Ando Koushi
Published: July 2002

Strong impurity effects upon introduction and annealing behavior of radiation-induced defects in InP irradiated with 1-MeV electrons have been found. The main defect center of  0.37-eV hole trap H4 in p-InP, which must be due to a point defect, is annealed even at room temperature. Its annealing rate is found to be proportional to the 2/3 power of the preirradiation carrier concentration in InP. Moreover, the density of the hole trap H5 (Ev+0.52 eV) in p-InP, which must be due to a point defect–impurity complex, increases with increase in the InP carrier concentration. These results suggest that the radiation-induced defects in InP must recover through long-range diffusion mediated by impurity atoms. A model is proposed in which point defects diffuse to sinks through impurities so as to disappear or bind impurities so as to form point defect–impurity complexes. In addition to the long-range diffusion mechanism, the possibility of charge-state effects responsible for the thermal annealing of radiation-induced defects in InP is also discussed.
Be+/O+-ion implantation in GaAs–AlGaAs heterojunctions
Authors: Adachi Sadao
Published: July 2002

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).
Formation of silicides by rapid thermal annealing over polycrystalline silicon
Authors: Narayan J. , Stephenson T. A. , Brat T. , Fathy D. , Pennycook S. J.
Published: July 2002

We have investigated the formation of titanium silicide by rapid thermal annealing in nitrogen and argon ambients over polycrystalline silicon. A sheet resistance of about 3 Ω per square for a 300-Å Ti layer was achieved after 900 °C/10-s annealing treatment, which decreased to about 2 Ω per square after 1100 °C/10-s treatment. The silicides were found to be stable during rapid thermal annealing up to 1100 °C/10 s with no or negligible migration of titanium along the grain boundaries in polycrystalline silicon. An external layer (titanium rich, mixture of titanium oxide and nitride) was observed to form during rapid thermal annealing treatment in the nitrogen ambient, but the surface remained clean in the argon ambient.
Electronic and optical properties of Fe-doped InP prepared by organometallic vapor-phase epitaxy
Authors: Huang K. , Wessels B. W.
Published: July 2002

The incorporation of Fe into InP grown by organometallic vapor-phase epitaxy using ferrocene as the dopant source has been studied. Room temperature resistivity of the doped epitaxial layers varied from 0.14 to 7×104 Ω cm. Photoluminescence measurements at 10 K indicated that the predominant deep radiative transition in the doped InP was at 1.07 eV. The relative intensity of this band depended on the ferrocene partial pressure.
Ion beam damage-induced masking for photoelectrochemical etching of III-V semiconductors
Authors: Chi G. C. , Ostermayer F. W. , Cummings K. D. , Harriott L. R.
Published: July 2002

Ion implantation damage has been used as a mask for patterning III-V semiconductors by photoelectrochemical etching. The damage inhibits etching and the optical absorption of the semiconductor prevents light from penetrating through the damaged layer. Patterns of ion implantation damage have been produced on the surface of InP, InGaAs, and InGaAsP by implantation of 50 and 150-keV Be+ ions through a photoresist mask and with a focused beam of 20-keV Ga+ ions. Subsequent photoelectrochemical etching produces surface relief features corresponding to the damage pattern. The effect of the electrolyte and the spectral composition of the light on the resolution are described. Micron size features have been delineated and the technique may be preferable to alternate masking methods (metallization or projection) in certain applications.
Ferromagnetic relaxation in LPE-grown Eu-Ga substituted yttrium iron garnet films
Authors: Rao B. Uma Maheshwar , Mukhopadhyay P. , Srivastava C. M.
Published: July 2002

The magnetization, geff and linewidth ΔH∥ and ΔH⊥ for liquid-phase-epitaxially grown thin films of EuxY3−xFe5−yGayO12 (0.2≤x≤1.2; y=1.0) have been investigated in the temperature range 85–420 K. ΔH versus temperature curves show maxima which occur at about the same temperature as that observed in bulk single crystals of EuIG, but the width of the curves is narrower in the LPE films. The temperature and composition dependence of geff and ΔH have been explained on the basis of the three sublattice model and a new relaxation mechanism based on anisotropic exchange.
Mössbauer spectroscopy of Sn-doped GaAs grown by liquid-phase epitaxy
Authors: Williamson D. L.
Published: July 2002

Gallium arsenide single-crystal layers, doped with 119Sn-enriched tin, have been prepared by liquid-phase epitaxy and characterized by 119Sn Mössbauer spectroscopy (MS) and Hall measurements. Two Sn sites are observed by MS, and the population of one of these (site A) matches the carrier concentration in as-grown material, therefore allowing the MS parameters of this site to be positively identified as those of the SnGa donor in GaAs, and thereby showing no evidence for compensation. The population of the second type of Sn (site B) increases with the total Sn concentration, and this site is clearly electrically inactive. The site B MS parameters are similar to those of Sn3As2, SnAs, and β-Sn, thereby demonstrating that microprecipitates of these phases may often exist in heavily Sn-doped liquid-phase-epitaxial GaAs. Site B could also be due to clusters of Sn and/or Sn-As that are precursors to the formation of distinct precipitates of Sn3As, SnAs, or β-Sn. Annealing experiments yield a Sn-related acceptor that is very likely of the form SnGaVGa. In addition, precise MS parameters are reported for the intermetallic phases SnAs and Sn3As2.
Material and device properties of GaAs on sapphire grown by metalorganic chemical vapor deposition
Authors: Kasai Kazumi , Nakai Kenya , Ozeki Masashi
Published: July 2002

Surface morphology, electron mobility, and photoluminescence (PL) spectrum have been investigated for the epitaxial layers of GaAs on (0001) sapphire grown at several temperatures. The optimum growth temperature range is determined to be around 690 °C. The mobility and the PL intensity efficiency are improved by increasing the layer thickness, due to the decrease of defect density. The structure related to the defects is located at a wavelength of 1.04 μm in the PL spectra. We fabricate the first field-effect transistor on GaAs on sapphire, and it has a transconductance of 20 mS/mm for a gate length of 2.5 μm.
Thermal stability of TiSi2 on mono- and polycrystalline silicon
Authors: Wong C. Y. , Wang L. K. , McFarland P. A. , Ting C. Y.
Published: July 2002

Thermal stability of TiSi2 on mono- and polycrystalline silicon was investigated by cross-sectional transmission electron microscopy and high-resolution electron energy loss spectroscopy. Additional heat treatments after silicide formation result in a rough silicide/silicon interface, discontinuity of the metal silicide film, and a penetration of silicide into silicon/polycrystalline silicon substrates. Plausible explanations for these observations are presented.
Origin of thickness oscillations in nucleated thin-film silicides
Authors: Bradley R. Mark
Published: July 2002

A theory of the origin of thickness oscillations in nucleated metal silicide thin films is presented. It is shown that under certain conditions the uniformly growing state is unstable against small perturbations, and that the interface velocity oscillates periodically in time once the steady state is perturbed. These oscillations lead to the observed thickness and grain size modulations. A morphological instability can also occur, resulting in patterns of concentric rings with wavy perimeters.
Application of the Bergman–Milton theory of bounds to the permittivity of rocks
Authors: Korringa J. , LaTorraca G. A.
Published: July 2002

The permittivity of brine-saturated porous rocks below 2 GHz varies with frequency in a way that is linked closely to the pore geometry. The theories of bounds of the permittivity by Bergman and by Milton, based on Bergman’s work on two-component composites, impose restrictions on this frequency dependence. We give a detailed and systematic analysis of these restrictions for this special case. We show to what extent the conductivity at low frequencies, combined with a measured value of the permittivity at an intermediate frequency, restricts the permittivity at all other frequencies. We establish a scaling law, according to which the permittivity depends on the brine conductivity σ2 and the frequency ω, only through the ratio σ2/ω, to a good approximation. We apply the analysis to data on sandstones by Poley, Nooteboom, and de Waal. As a further application of this theory, we derive bounds for the electrical or thermal conductivity of a two-component composite using the values that this same property would have if either of the components were an insulator.
Influence of film-growth conditions on c-axis orientation in sputtered Co-Cr thin films
Authors: Niimura Y. , Nakagawa S. , Kitamoto Y. , Naoe M.
Published: July 2002

Double- and multiple-layered Co-Cr thin films have been prepared to clarify the dominant factors in the c-axis orientation at the early stage of the film growth. The optimized process condition in the facing-targets sputtering system is likely to promote the c-axis self-orientation in the films since they can grow on the plasma-bombardment-free substrate. This effect was confirmed by depositing the films on the poorly oriented Co-Cr film as the underlayer. Meanwhile, when the well-oriented Co-Cr thin film was used as the underlayer, a continuous growth of crystallites resulted in the improvement of the c-axis orientation in the growing film even under process conditions unfavorable for depositing the well-oriented films. This Co-Cr underlayer effect continues until the thickness of the depositing film reaches about 2000 Å, suppressing the influence of the unfavorable sputtering condition.
Effect of hydrogen on the properties of magnetron sputtering of hydrogenated amorphous silicon carbon alloy films
Authors: Saito Nobuo
Published: July 2002

Hydrogenated amorphous silicon carbon alloy films have been prepared by magnetron sputtering of silicon in methane-hydrogen-argon gas mixtures, and the dependence of film properties on hydrogen partial pressure (PH) as well as methane partial pressure against total gas pressure has been investigated. With increasing PH, the concentration of carbon increases, accompanied with the increase in the number of Si–C bonds, in spite of the unchanging partial pressure of methane. Following this, the optical band gap and activation energies of dc conductivities increase, and the photoconductivity as well as the dark conductivity decreases. The intensity of Si–H bonds is almost unchanged, while that of C–H bonds increases. These results are discussed mainly from the standpoint of the change of deposition process composed of the chemical decomposition of methane and the physical sputtering of silicon.
Transport in double-barrier resonant tunneling structures
Authors: Goldman V. J. , Tsui D. C. , Cunningham J. E. , Tsang W. T.
Published: July 2002

We report measurements of current-voltage characteristics of AlGaAs/GaAs double-barrier resonant tunneling structure (DBRTS) with current peak-to-valley ratio exceeding 13:1 at 77 K. We also show that space-charge layers formed in a biased device influence significantly the charge transport in DBRTS.
Experimental study of propagation of intense relativistic electron beams in nonconducting vacuum drift tubes after passage through a localized plasma source
Authors: Destler W. W. , O’Shea P. G. , Segalov Z.
Published: July 2002

The propagation of intense relativistic electron beams into evacuated nonconducting drift tubes after passage through a localized plasma source has been experimentally studied. Time-integrated photographs of the propagation process have been obtained, as well as quantitative measurements of the propagated beam current and energy.
Nucleation and growth of titanium silicide studied by i
n s
i
t
u annealing in a transmission electron microscope
Authors: Raaijmakers I. J. M. M. , Reader A. H. , van Houtum H. J. W.
Published: July 2002

We have studied the crystallization of sputter-deposited amorphous Ti-Si alloy thin films of different compositions. A versatile means of discriminating between phenomena occurring in the nucleation and subsequent growth stages was offered by in situ annealing in a transmission electron microscope. Nucleation of TiSi2 with the ZrSi2 structure was observed for all alloys studied (Ti:Si=1:2 to Ti:Si=1:3). The activation energy for nucleation was independent of composition. TiSi2 crystallites appeared to possess a rather high density of stacking faults, predominantly concentrated in the center of the crystallites. The character of these stacking faults was analyzed. The growth of TiSi2 was anisotropic in amorphous alloys up to a composition of Ti:Si=1:2.5; more silicon-rich alloys yielded isotropic growth. The anisotropy in growth rate, and the resulting morphology of the crystallites were related to the crystal structure. The crystallization of the amorphous alloy with the composition Ti:Si=1:2 proceeded via a polymorphous phase transformation. The Si-rich alloys crystallized through eutectic decomposition. This was clearly evidenced by a difference in the activation enthalpy for growth. Since the activation enthalpy for growth differed from the activation energy for nucleation, an influence of the heating rate on the microstructure of the completely crystallized alloy could be predicted. This, in turn, might affect the resistivity, roughness and transformation temperature to the C54 TiSi2 equilibrium phase.
Optical admittance spectroscopy: A new method for deep level characterization
Authors: Dueñas S. , Jaraiz M. , Vicente J. , Rubio E. , Bailón L. , Barbolla J.
Published: July 2002

A new method for the optical cross-section measurement of deep levels in junctions is presented. It is based on the measurement of the capacitance and conductance of the junction under illumination, as a function of the photon energy hν and the frequency of the measuring signal. This technique has been applied to the measurement of the optical capture cross section σon of the Au acceptor level corresponding to the emission of electrons to the conduction band.
Characterization of hydrogenated amorphous silicon by capacitance-voltage and surface photovoltage measurements using liquid Schottky barriers
Authors: Sakata I. , Ishida T. , Okazaki S. , Saitoh T. , Yamanaka M. , Hayashi Y.
Published: July 2002

Experimental studies have been made on the electrical properties of hydrogenated amorphous silicon (a-Si:H) using liquid Schottky barriers. We have found that the quasi-static capacitance-voltage (C-V) method can be applied to the a-Si:H/quinone-hydroquinone (Q-HQ) liquid Schottky junction. This method enables us to determine the net density of positive space charge due to ionized traps and impurities in a-Si:H (Ne), the built-in potential (Vb), and the width of the surface space-charge layer (W), of this liquid junction. The barrier height of an undoped a-Si:H/Q-HQ junction has been estimated to be more than 1 eV from the value of Vb thus obtained. By C-V and surface photovoltage (SPV) measurements on the same samples, we have studied the changes in the properties of a-Si:H with doping and with prolonged illumination. It has been found that phosphorous (P) doping drastically decreases the hole diffusion length measured by the SPV method and increases the value of Ne. Slight boron (B) doping increases the ambipolar diffusion length L1 and the field assisted carrier collection length L2, both of which have been determined by SPV. These results explain the observed enhancement of the photovoltaic properties of a-Si:H p-i-n solar cells with the slight B doping to the i layers. The values of L1 and L2 have a distinct correlation with the photo-voltaic properties in the slightly B-doped samples, which has confirmed the effectiveness of the SPV method in characterizing a-Si:H as a photovoltaic material. We have found that the increase in Ne and the decrease in L1 occur simultaneously in undoped a-Si:H with prolonged illumination. On the other hand, the increase in Ne does not always accompany the decrease in L1 in the photoinduced changes in P-doped or slightly B-doped a-Si:H, which suggests the difference in the mechanism of the changes between undoped and doped samples.
Negative differential conductivity in electron-beam irradiated Ar-HCl mixtures
Authors: Lando M. , Rozenberg Z. , Rokni M.
Published: July 2002

The drift velocity of secondary electrons in electron-beam irradiated Ar/HCl gas mixtures was obtained by measuring both the current and electron densities as a function of an externally applied electric field. The measurements were performed for a variety of HCl concentrations between 0.1% and 5.0% and electric-field strengths between 0.1 and 10 Td (1 Td=10−17 V cm2). The electron-beam pulse was 350 ns long, at an energy of 150 keV and current density between 4.2 and 0.017 A/cm2. The electron density was measured by time-resolved infrared interferometry at 9.6 μm. The results show that the Ar/HCl system exhibits negative differential conductivity.
Ferromagnetic multilayers of Permalloy and TiN
Authors: Maritato L. , Falco Charles M. , Aboaf J. , Paul D. I.
Published: July 2002

Ferromagnetic multilayers of Permalloy (Ni 81%, Fe 19%) alternated with TiN were prepared by magnetically confined plasma dc sputtering. Rutherford backscattering spectroscopy and x-ray diffraction analysis showed high structural quality for our samples. The easy- and hard-coercivity field values and the anisotropy field values were reduced by the lamination and were almost independent of the number of layers. Electrical resistivity versus temperature and resistivity ratio measurements were also made.
A new model for dielectric-breakdown phenomenon in silicon dioxide films
Authors: Chen D. N. , Cheng Y. C.
Published: July 2002

A new model is proposed to interpret the breakdown phenomenon of dielectric thin films such as SiO2 films over the whole range of an applied field. It is suggested that two main mechanisms are responsible for the dielectric breakdown which is influenced by the geomorphic and physical parameters, and the examination conditions. One of the mechanisms is the avalanche breakdown, the so-called intrinsic type, which is caused by impact ionization. The other, the extrinsic type, is the filament-heating transport which induces a destructive breakdown. A simple mathematical model invoking the role of photon absorption is constructed to describe the effects of the band gap and the insulator thickness on the dielectric breakdown. It can be deduced from the model that (i) the mean distance of impact ionization is equivalent to the minimum thickness of the film generating the impact ionization and (ii) the probability of impact ionization is a function of the width of the band gap of the insulator under an applied field. Finally, effects of various processing conditions on the breakdown mechanisms and the dielectric strength are discussed.
Characterization of depth profiles and redistribution during thermal processing of aluminum implanted into silicon
Authors: Wilson R. G.
Published: July 2002

We report the results of a study of atom and acceptor depth profiles of unannealed and annealed Al implants into Si. We describe three regimes of Al redistribution during annealing, the characteristics of which depend on the density of the Al and associated defects. We also report as-implanted and annealed Al depth distributions, range parameters, and profile-shape factors for Al implanted into crystalline Si for energies from 20 to 600 keV and fluences from 3×1012 to 3×1016 cm−2.
Independent verification of the values of electroelastic constants of alpha quartz
Authors: Hruska Carl K.
Published: July 2002

The component values of the cumulative electroelastic tensor of quartz found by C. K. Hruska (Proceedings of the 31st Annual Frequency Control Symposium, June 1977, pp. 159–170; available from NTIS, Springfield, VA, as document AD A088221) by means of the resonator method are independently confirmed by G. A. Reider, E. Kittinger, and J. Tichy [J. Appl. Phys. 53, 8716 (1982)] using a time delay experiment. The disagreement of several orders of magnitude existing with other authors who also used the resonator method is explained and removed. There can be no doubt that the magnitude of the electroelastic tensor components is in the range of 1 and 10−1 N/(V m) and that the standard errors of their determined values can be as small as several percent.
Impulse coupling to aluminum resulting from Nd:glass laser irradiation induced material removal
Authors: Bass M. , Nassar M. A. , Swimm R. T.
Published: July 2002

The properties of the impulse coupling coefficient for long-pulse Nd:glass laser irradiation to aluminum are reported. Most significant is an anticorrelation between this coefficient and the mass of the material removed by the irradiation. A model is suggested which shows that this property may be related to the convergence or divergence of the laser beam as it penetrates the material. When using long-pulse irradiation, the impulse coupling coefficient does not depend on the initial conditions of the surface finish. Data are presented which also demonstrate the dependence of the impulse coupling coefficient on both the incident intensity and energy density.
Quenching and recovery spectra of midgap levels (EL2) in semi-insulating GaAs measured by double-beam photoconductivity
Authors: Hariu Takashi , Sato Tomoru , Komori Hiroshi , Matsushita Koichi
Published: July 2002

Optical cross sections for transition of midgap donor levels (EL2) from normal states to metastable states and vice versa, were determined in semi-insulating GaAs by double-beam photoconductivity technique. The photoconductivity response to secondary light is quenched with one or two time constants depending upon the occupancy of normal states at thermal equilibrium, and optical quenching spectra are obtained from the larger time constant. Optical recovery measurement indicated that only a certain fraction of total quenching is recovered optically and that this fraction depends upon wafers. A new model of EL2, AsGa in association with any acceptor, is proposed based upon the observed results on different liquid-encapsulated Czochralski and metalorganic chemical vapor deposition semi-insulating wafers and other results reported so far.
dc electroluminescence in copper-free ZnS:Mn thin films. II. A dielectric breakdown theory of instability
Authors: Cattell A. F. , Inkson J. C. , Kirton J.
Published: July 2002

The occurrence of localized destructive breakdown (LDB) is a feature of direct coupled thin-film electroluminescence (DCTFEL) which has been attributed in the past to variations in applied field or threshold voltage caused by geometrical artifacts introduced during film deposition. However, in a companion paper it has been reported that this view of LDB is inconsistent with observations; instead there are strong indications that both LDB and DCTFEL are natural consequences of dielectric breakdown in ZnS:Mn. In this paper, the O’Dwyer theory of dielectric breakdown is applied to DCTFEL in ZnS:Mn with the aid of a simple computational equilibrium model. It is found that with reasonable assumed values for basic electronic parameters, current-controlled negative resistance (CCNDR) is expected in the normal DCTFEL current density regime. Localized (filamentary) conduction is, of course, a well-known consequence of CCNDR and the profound implications of this for EL are explored in some detail. It becomes clear that a number of poorly understood features of practical DCEL devices arise quite naturally from this dielectric breakdown theory; examples are premature brightness saturation at near maximum efficiency, the coexistence of DCTFEL and LDB, and the factors affecting the balance of that coexistence. It is concluded that while the dielectric breakdown model of DCTFEL presently rests precariously on assumed parameter values, the qualitative predictive power of the theory gives it significant weight. In view of this, some of the implications for DCTFEL device design are explored.
Incorporation of strain hardening in piezoresistance analysis: Application to ytterbium foils in a PMMA matrix
Authors: Gupta Y. M. , Gupta Satish C.
Published: July 2002

The results of an earlier paper are extended to include strain hardening in the analytic model for piezoresistance. This development is necessary to model the gauge hysteresis observed in the experimental data. Analytic developments to incorporate strain hardening in the theoretical formalism and procedures to calculate the gauge response are described. The analytic model is used to calculate the response of ytterbium (Yb) foils in a polymethylmethacrylate matrix in both shock wave and quasi-static experiments. Good agreement is observed between the model predictions and experimental results. Difficulties in calculating the lateral gauge response when the matrix material is inelastic are discussed.
Theory of high-temperature oxide decomposition at the SiO2/Si interface
Authors: Bradley R. Mark
Published: July 2002

The ultra-high vacuum decomposition of a thin oxide layer on a resistively heated silicon substrate proceeds by the formation and lateral growth of holes in the oxide layer. It is shown that the hole radii grow linearly with time on a uniformly heated substrate, in contrast to the experimental result R2∝t−t0. To account for the observed growth law, it is argued that defects in resistively heated wafers act as localized heat sources and so tend to nucleate holes. Under the assumption that the hole growth is reaction limited, we obtain the observed R2∝t−t0 behavior. A simple experimental test of the theory is proposed.
Characterization of superlattices based on amorphous silicon
Authors: Hundhausen M. , Santos P. , Ley L. , Habraken F. , Beyer W. , Primig R. , Gorges G.
Published: July 2002

We have characterized the structure of superlattices (SL’s) based on amorphous silicon by optical interference microscopy and secondary electron micrographs. Differences in the etch rate of a-Si:H and a-SiNx:H in CP6 create a series of terraces and steps in a-Si:H/a-SiNx:H superlattices that show up clearly in interference contrast micrographs and allow an assessment of the quality of the SL. Secondary electron microscopy images of doping superlattices (npnp or nini) of a-Si:H reveal after plasma etching the layered nature of the samples. The necessary contrast is provided by differences in the etch rate of the two interfaces (i.e., n→p vs p→n). Evidence for structural differences of the interfaces of nini multilayers stems from secondary ion mass spectrometry and 15N depth profiles of hydrogen that show an extra amount of H of the order of 1015 cm−2 only at that interface where intrinsic a-Si:H is growing on top of the n-type material. We explain these results in terms of a growth model which entails a hydrogen enrichment over its bulk concentration that is not limited to the surface but extends into a subsurface region during the film deposition.