bluuebunny/crossref_metadata_2025 huggingface dataset:
Dual dielectric silicon metal-oxide-semiconductor field-effect transistors as radiation sensors
Authors: Hughes R. C. , Dawes W. R. , Meyer W. J. , Yoon S. W.
Published: July 2002

A new design for radiation-sensing field-effect transistors (RADFETs) is presented, involving the use of very thick silicon nitride layers deposited on top of a high-quality thermal silicon dioxide. In contrast to previous RADFET fabrication procedures, no attempt was made to introduce hole traps into the thermal oxide. Instead the trapping layer at the nitride oxide interface was used to store the positive charge which forms the basis for operation of the RADFET. Data is presented which shows hole transport in the thermal oxide. Models explaining the field dependence of the response and the saturation behavior of the dual dielectric device are given. These RADFETs are more stable than any previously described in the literature and have a sensitivity of 86 μV/rad dose at room temperature.
Action of a static magnetic field on an argon discharge produced by a traveling wave
Authors: Pasquiers S. , Boisse-Laporte C. , Granier A. , Bloyet E. , Leprince P. , Marec J.
Published: July 2002

This paper deals with a low-pressure argon microwave discharge (5–100 mTorr), created and sustained by a traveling wave (390 MHz), in the presence of an axial static magnetic field (up to 550 G). First, the propagation characteristics of the wave (wave number, wave collisional damping, radial distribution of the electromagnetic energy) have been computed from the numerical resolution of the dispersion equation. It has been emphasized that the plasma is sustained either by a surface wave, or by a volume wave, according to the electron density and magnetic field values. Second, the electron density, the effective electron-neutral collision frequency ν for momentum transfer, the mean power θ required to maintain an electron in the discharge, and the effective electric field Eeff for the discharge maintaining have been experimentally determined, versus the pressure and the magnetic field. At a fixed pressure, the power required to maintain the discharge decreases as the magnetic field increases. It has been shown that this experimental result is consistent with simple theoretical modeling, describing the decrease of the electron loss by diffusion and recombination on the discharge tube walls.
Investigation of elastic properties of ZnO films by Brillouin scattering
Authors: Carlotti G. , Socino G. , Verona E.
Published: July 2002

The elastic properties of ZnO films have been investigated by means of the Brillouin scattering technique. Measurements were made of the phase velocity of surface phonons propagating on ZnO films ≊0.2 μm thick, deposited on both Si and Al2O3 substrates. A comparison of the experimental results with theoretical predictions shows that the elastic properties of the films, although appreciably different from those of the bulk material, are fairly close, however, to the properties observed in films almost two orders of magnitude thicker.
Property of amplified spontaneous emission and saturable absorber for a terawatt XeCl laser system
Authors: Watanabe M. , Endoh A. , Sarukura N. , Watanabe S.
Published: July 2002

A peak power of 1 TW has been obtained in XeCl with a pulse width of 310 fs and the amplified spontaneous emission (ASE) less than 3% in energy. The property of ASE was analyzed for different gains. Based on this analysis, the ASE coupling between stages was suppressed by using an appropriate spatial filter along with operating at a low-gain level. The saturation characteristics of UV dyes were investigated and analyzed for subpicosecond pulses. BBQ [4,4’’’di(2-butyl-octoxy-1)-p-quarter-phenyl)] in cyclohexane showed the satisfactory performance for a saturable absorber in contrast and transmission.
Digital image analysis of droplet patterns in polymer systems: Point pattern
Authors: Tanaka Hajime , Hayashi Takafumi , Nishi Toshio
Published: July 2002

New techniques of digital image analysis which are especially suitable for analyzing particle-distribution patterns are presented. Statistical mathematical methods are applied to the quantitative analysis of a spatial distribution of points in polymer systems. The techniques are useful for studying the spatial patterns of particles or droplets which are commonly observed in nucleation-growth-type phase separation and late-stage spinodal decomposition in polymer mixtures, crystallization process, microphase separation in block copolymers, incompatible polymer alloys, and composite materials, etc. We can divide point patterns into three typical point patterns: the Poisson pattern, the clustered pattern, and the regular pattern. The kind and strength of interaction or force between points can be determined from spatial point-distribution patterns. The point-pattern analysis has been applied to phase-separated structures of a polymer mixture, and it has been revealed that the pattern belongs to the regular pattern. The appearance of the regular pattern is probably a result of the Brownian coalescence mechanism for the droplet growth and it might also be due to a long-range interaction among droplets through diffusion field.
A constitutive model for the shock Hugoniot of porous materials in the incomplete compaction regime
Authors: Oh Ki-Hwan , Persson Per-Anders
Published: July 2002

A constitutive model is developed for the shock Hugoniot of porous materials in the incomplete compaction regime. The model is based on a comparison between the shock compaction and quasi-isostatic compaction and utilizes empirical data of material strength and compaction characteristics. The model requires only well-documented material constants as inputs. It accurately predicts porous Hugoniots for a wide range of materials.
New contactless measurement of photoeffects in semiconductors
Authors: Hlávka Jan
Published: July 2002

The magnetic field induced by a current which flows in a semiconductor during charge redistribution when photoeffect relaxation takes place is measured in a contactless way. The experimental results presented verify the above explanation of the contactless measurement and illustrate how to utilize it.
An efficient method for the analysis of electron waveguides
Authors: Frohne H. Rob , McLennan Michael J. , Datta Supriyo
Published: July 2002

Recent experiments in mesoscopic systems have demonstrated a striking similarity between electronic devices and optical or microwave waveguides. In the absence of impurities and phase-breaking scattering, the geometry of such devices determines their behavior. These devices, which are usually composed of a network of guiding channels, can be analyzed in a manner similar to that used for electromagnetic waveguides. Sections of a device can be represented by scattering matrices, and individual scattering matrices can be combined, to determine the scattering matrix for an entire device. An efficient method is presented for the calculation of scattering matrices for devices with an arbitrary geometry. The method is applied to the analysis of a quantum reflection transistor, in which current is modulated between source and drain by a remote gate.
Properties of plasma-deposited hydrogenated amorphous silicon prepared under visible light illumination
Authors: Sakata I. , Yamanaka M. , Hayashi Y.
Published: July 2002

Properties of hydrogenated amorphous silicon (a-Si:H) prepared by glow discharge decomposition of silane with visible light illumination on a growing surface have been described. The visible light illumination during growth has resulted in smaller light-induced changes, slightly lower photoconductivity before the prolonged illumination, lower content of bonded hydrogen, and lower ratio of the number of silicon dihydrides to that of total silicon-hydrogen bonds. Formation of Si network and consequent structural disorder of SiSi bonds, on the other hand, has not been affected by the illumination during the growth. The improved stability against the long exposure to light can be ascribed to the lower bonded hydrogen content and the reduced density of SiH2 bonds, while the structural disorder of the Si network does not have a direct relationship with the light-induced changes.
Mixture-dependent electron densities in x-ray preionized Ne-Xe-HCl mixtures
Authors: Gerritsen J. W. , Godfried H. P. , Bonnie R. J. M.
Published: July 2002

Preionization electron densities have been studied in an x-ray preionized XeCl laser as a function of the gas composition. Also the influence of emission of photoelectrons from the electrode surfaces on the initial electron density has been determined. For low Xe partial pressures, an excited neon bottleneck in the Penning ionization process of Xe is found. For higher Xe pressures, the preionization density increases linearly with the Xe concentration. A simple model gives a satisfactory agreement with the measurements over more than two decades of Xe partial pressure. We also determine the density of Ne* following x-ray irradiation. Measurements in mixtures containing HCl show that due to electron attachment no initial value of the electron density can be assigned. The method used here will give a lower estimate for the total charge density in these mixtures.
Reversed magnetic anisotropy in deformed (100) Cu/Ni/Cu structures
Authors: Chang Chin-An
Published: July 2002

Using (100) Cu(1000 Å) /Ni/Cu(1000 Å) structures with a different Ni thickness, a complete reversal in magnetic anisotropy is observed between the structures with 1000 and 50 Å Ni, respectively. The structures were deposited on (100) Si, with the first Cu layer in the (100) orientation as the seed, followed by epitaxial Ni and another Cu layer. Comparing the magnetization for the field applied parallel to the film plane, M∥, with that perpendicular to it, M⊥, M⊥ is found to increase and M∥, to decrease with decreasing Ni thickness. At a Ni thickness of 50 Å, a squared hysteresis loop is observed for M⊥. The M∥ curve, on the other hand, changes from a normal one at 1000 Å Ni to one with little hysteresis at 50 Å Ni. These are accompanied by an increasing deformation of the (100)Ni cubic lattice into a tetragonal one with decreasing Ni thickness, due to its mismatch with Cu. The deformation is discussed to assess the roles of stress in the observed reversal in magnetic anisotropy.
Effect of the confining potential on the magneto-optical spectrum of a quantum dot
Authors: Geerinckx F. , Peeters F. M. , Devreese J. T.
Published: July 2002

The energy levels of electrons confined to a circular quantum well with hard walls are calculated in the presence of a perpendicular magnetic field. The results are compared with the case of soft-wall confinement (parabolic potential). There are important differences in the transition energies of the magneto-optical spectrum: (i) in contrast to the parabolic case where only two transition energies are found, in the hard-wall case there are many transitions possible which have different energies. Only a small number of them however have sufficient oscillator strength to be observable; (ii) with increasing magnetic field the energies approach the two-dimensional results much faster than for the soft-wall case. In quantum dots with many electrons we calculate the Fermi energy as a function of the magnetic field.
Pump considerations for gain switched diode lasers
Authors: MacFarlane D. L.
Published: July 2002

We calculate the conditions under which a gain switched diode laser is optimized with respect to the width of the injection current pump pulse. We find, for both biased and unbiased operations, that a current pulse of approximately 20 ps corresponds to a Dirac delta function, a situation which yields the shortest, most intense output pulses.
A new argon-ion laser based on an electrodeless plasma
Authors: Zhu Peiyuan , Boswell R. W.
Published: July 2002

A new argon-ion laser based on an electrodeless magnetoplasma with tube diameter of 45 mm has been developed, and optimal operation conditions were experimentally studied. The plasma is thought to be generated by helicon waves excited by an external antenna. Selected excitation of the upper lasing level of Ar ii due to Landau damping of the helicon waves plays an important role in the mechanics of the population inversion in this laser. The plasma is excited externally by radio frequencies, and the lasing active medium does not directly touch the plasma wall, minimizing the problems associated with impurities from both the electrodes and the tube wall. A peak laser output power of 0.5 W with 10−4 efficiency has been reached, although the operation condition was not far from that of the lasing threshold.
Fractal surface scattering: A generalized Rayleigh solution
Authors: Jaggard Dwight L. , Sun Xiaoguang
Published: July 2002

We consider the scattering of electromagnetic waves from perfectly conducting fractal surfaces. The surface is modeled by a multiscaled bandlimited continuous fractal function. We analytically develop a generalized Rayleigh solution for electromagnetic wave scattering from such fractal surfaces. After an examination of the convergence of the Rayleigh systems, we numerically calculate the coupling strengths and relate the angular scattering energy distribution to the fractal descriptors of the surface. We find that the slope of the coupling strengths as a function of their corresponding spatial frequencies on a logarithmic scale depends monotonically on the fractal dimension of the scattering surface.
Quantum-dot size-distribution analysis and precipitation stages in semiconductor doped glasses
Authors: Liu Li-Chi , Risbud Subhash H.
Published: July 2002

The sequence of stages during precipitation of semiconductor (e.g., CdS, CdSe) clusters from supersaturated glasses exhibiting quantum-confinement effects was investigated. The rate of formation of nanometer-size ‘‘quantum dots’’ distributed in a continuous glass matrix is critically determined by the time and temperature of the heat treatment given to the quenched glasses. The entire precipitation process was analyzed in terms of several decomposition stages: nucleation, normal growth, coalescence of quantum dots, and devitrification of the glass matrix itself. Experimental data obtained by differential thermal analysis were utilized to identify the heat-treatment temperature range associated with the precipitation stages. The size distribution of CdSe quantum-dot clusters was analyzed using our transmission electron microscopy data. The data of Ekimov et al. [Solid State Commun. 56, 921 (1975)] was reduced to time-temperature master plots useful for precipitating quantum dots of a given size in glasses.
Soft magnetic properties and film structures of Fe-C/Ta multilayered films
Authors: Kobayashi Toshio , Nakamura Hitoshi , Nakatani Ryoichi
Published: July 2002

Fe-C/Ta multilayered films with low Ta diffusion into Fe are examined to find thermally stable soft magnetic Fe-based multilayers. Although coercivities of Fe-C/Ta multilayered films increase after heat treatment at 300–400 °C, they decrease to <200 A/m after heat treatment at 500–600 °C. Relative permeabilities of the multilayers with C concentrations of 5–7 at. % are 3000 at 500–600 °C, corresponding to the low coercivities. The magnetostriction constant changes from positive to negative as the heat-treatment temperature increases. Fe-C/Ta multilayered films show clear periodic structures at 300–600 °C. However, the periodic structure disappears and Fe crystallite growth occurs at 700 °C.
Effective conductivity of aggregates of anisotropic grains
Authors: Helsing Johan , Helte Andreas
Published: July 2002

General expressions for the effective conductivity σeff of overall isotropic aggregates of grains are derived within the average field approximation. The grains are modeled by ellipsoids with possibly anisotropic conductivity tensors. Explicit expressions for σeff are stated for a polycrystal, which corrects an earlier result of Bolotin and Moskalenko [V. V. Bolotin and V. N. Moskalenko, J. Appl. Mech. Tech. Phys. 8, 3 (1967)], and for systems resembling the structure of nodular and grey cast iron. Percolation of randomly distributed two-dimensional disks in a three-dimensional continuous medium is studied. The percolation threshold for the number density of disks of radius unity is numerically determined to be 0.233±0.002 per unit volume.
Room-temperature optical nonlinearities in strained (InAs)2(GaAs)5 superlattice quantum wells
Authors: McCallum D. S. , Huang X. R. , Boggess Thomas F. , Dawson Martin D. , Smirl Arthur L. , Hasenberg T. C.
Published: July 2002

We report room-temperature measurements of the nonlinear absorption cross section, σeh, and the nonlinear refraction coefficient, neh, associated with saturation of excitonic absorption and bandfilling, for high-quality multiple quantum well (MQW) structures in which each well consists of a highly strained, all binary (InAs)2(GaAs)5 short-period superlattice. The three samples studied, which have effective well thicknesses of 10.7, 14.8, and 18.8 nm, respectively, each display clearly resolved excitonic resonances at room temperature. Picosecond nonlinear transmission and transient grating measurements were performed on each sample in the spectral vicinity of the n = 1 heavy-hole excitonic resonance. The peak values of neh and σeh extracted from these measurements are comparable to those measured in high-quality GaAs/AlGaAs and unstrained InGaAs/InP MQWs. We determine the dependence of σeh and neh on the width of the quantum wells, and we discuss the fluence dependence of the nonlinearities. Consistency between the differential transmission and transient grating diffraction efficiency is demonstrated via a Kramers–Kronig analysis of the differential transmission spectra.
Chemical etch rates in HF solutions as a function of thickness of thermal SiO2 and buried SiO2 formed by oxygen implantation
Authors: Vanheusden K. , Stesmans A.
Published: July 2002

A comparative study of chemical etch rates in diluted HF or a mixture of HF, H2O, and HNO3 (P etch) was performed on conventional thermal silicon oxides (1050–1120 °C; O2 pressure ≊1.1 atm; one type with addition of 0.02% C2H3Cl3) and buried oxide layers. The latter were formed by single or multiple implanting n- and p-type (100) Si maintained at ≊600 °C with 150–200-keV O+ ions to a dose of ≊1.8×1018 cm−2, and subsequent annealing at 1250–1325 °C. The multi-implanted samples had three implants of a dose of 0.5–0.8×1018 O+ ions cm−2 each, separated by anneals but no final anneal. One of the thermal oxides was additionally irradiated with As+ ions to a dose of 1014 cm−2. Accurate mechanical thickness measurements revealed variations in etch rate between the different oxides, which provide direct evidence for a structural and/or stoichiometrical difference between thermal and buried oxides. The data indicate that the buried oxide is in a densified state as compared to thermal oxide. Also O+ and As+ irradiation-induced bond strain was clearly observed in buried oxide and thermally grown oxide, respectively. Additionally, plots of the etch rate as a function of oxide thickness reveal detailed information on structural variations of the oxide layers as a function of thickness. This is in contrast with the generally assumed homogeneity of most of these layers.
Thermal oxidation of amorphous ternary Ta36Si14N50 thin films
Authors: Pokela P. J. , Reid J. S. , Kwok C.-K. , Kolawa E. , Nicolet M.-A.
Published: July 2002

The oxidation kinetics of reactively sputtered amorphous Ta36Si14N50 thin films are studied in dry and wet ambient in the temperature range of 650–850 °C by backscattering spectrometry, Dektak profilometer, and x-ray diffraction analyses. The dry oxidation is well described by a parabolic time dependence which corresponds to a process controlled by the diffusion of the oxidant in the oxide. The growth of the oxide in wet ambient is initially very rapid and then proceeds linearly which means that the process is reaction limited. Both oxidation rates are thermally activated. The activation energies are 2.0 eV for dry and 1.4 eV for wet ambient. The pre-exponential factors are 0.17×1016 Å2/min and 7.4×108 Å/min, respectively. Both the dry and wet oxidation of the amorphous ternary Ta36Si14N50 film result in the formation of an x-ray amorphous Ta14Si5.5O80 layer.
An improved ionized-impurity scattering model for Monte Carlo simulations
Authors: Kay L. E. , Tang T.-W.
Published: July 2002

An improved Monte Carlo model for ionized-impurity scattering is developed and used to calculate majority- and minority-electron mobilities in silicon. The model includes scattering cross sections derived from phase-shift analysis, implementation of the Friedel sum rule, and a simple phenomenological model for multiple-potential scattering. This model provides a very good fit to experiment using a single adjustable parameter. Electron mobilities in n- and p-type Si are calculated and fit to experimental data at 300 and 77 K. Experimental results for Si of μn(NA)/μn(ND) ≊ 2 at 300 K are reproduced and a value of 3 < μn(NA)/μn(ND) < 4 is predicted at 77 K.
Shock-induced fluorescence shift of rhodamine-6G dye in ethanol solution
Authors: Shen X. A. , Gupta Y. M.
Published: July 2002

An experimental method is described to measure the time-resolved fluorescence spectrum of a dye in a liquid subjected to shock wave, uniaxial strain compression. Data are reported for rhodamine-6G in ethanol solution shocked to 19 kbar and compared to hydrostatic measurements [Appl. Opt. 24, 2779 (1985)]. Unlike the hydrostatic measurements, a continuous red shift of the fluorescence band with pressure was observed over the entire pressure range. In addition, the shock data show a larger shift rate than the hydrostatic data below 2.6 kbar and a comparable rate above this pressure, resulting in an overall larger shift with pressure. Implications of the present results for examining microscopic response of shocked liquids are discussed.
Device application and structure observation for hemispherical-grained Si
Authors: Watanabe Hirohito , Aoto Nahomi , Adachi Saburo , Kikkawa Takamaro
Published: July 2002

A polycrystalline-silicon surface with hemispherical grains (HSG) is deposited by low-pressure chemical vapor deposition at 590 °C. At the temperature, 590 °C, the structure of the Si film just after deposition is amorphous, but crystallization of the amorphous Si occurs to produce HSG-Si during annealing after deposition. The HSG-Si is formed by the nuclei generation on the clean amorphous-Si surface and by the crystalline growth during annealing. The surface area of the HSG-Si film is about twice as large as Si films deposited at other temperatures. By applying the HSG-Si film as the storage electrode for a 64-M-bit dynamic random access memories (DRAM) stacked-capacitor with a SiO2/Si3N4 dielectric film, a capacitance of twice the value is obtained. The increase of the capacitance makes it possible to reduce the DRAM cell area, even by using a relatively thick dielectric film for higher reliability.
Study of dynamics of diffusion and cluster formation of copper deposition on polyimide by optical second-harmonic generation
Authors: Zhang J. Y. , Shen Y. R. , Soane D. S.
Published: July 2002

We demonstrate that optical second-harmonic generation (SHG) can be successfully used for in situ study of metal/polymer interfaces. With this SHG technique, Cu cluster formation on polyimide by surface diffusion and Cu diffusion into polyimide have been investigated. The diffusion coefficients of Cu clusters into polyimide at various temperatures have been determined from the measured decay of SHG signal with time. The effects of temperature, cluster size, and surface modification on diffusion have also been examined. For T < Tg, the surface diffusion of Cu on polyimide to form clusters dominates over the diffusion into the bulk. The latter process becomes competitive with increasing temperature. When T ≳ Tg, few large-size Cu clusters can be formed on the polyimide surface. Cu diffusion into polyimide bulk can be greatly impeded by either a monolayer of Ti or by Cu clusters implanted in polyimide beforehand. In this case, Cu can wet the modified surface and form an interface between Cu and polyimide with good adhesion.
Electrically active defects in deep preamorphized single-crystal silicon layers
Authors: Ayres J. R. , Brotherton S. D.
Published: July 2002

High-energy Si and Ge implantations have been used to form thick (∼1 μm) amorphous films which permit direct electrical characterization of the layers after solid phase regrowth. The dislocation loops observed at the original amorphous–crystalline boundary after regrowth are fundamental to the preamorphization process and three dominant deep levels at Ec−0.40 eV, Ev + 0.47 eV, and Ev + 0.26 eV have been found to be spatially localized in the same region as the dislocation loops. The level at Ev+0.47 eV is most likely to be responsible for the spatially localized generation current also arising from the same region. The level at Ev+0.26 eV and a level, which was less dominant in the deep level transient spectroscopy measurements, at Ec−0.19 eV show features consistent with a defect displaying charge state controlled metastability. The density of these levels implied a high degree of reconstruction around the perimeter of the loops. The effects due to nitrogen decoration of the dislocations have also been investigated. The deep levels found within the regrown layers are believed to be associated with other dislocations which have not typically been seen in shallower preamorphized layers.
Heteroepitaxial growth of single crystalline 3C-SiC on Si substrates by gas source molecular beam epitaxy
Authors: Yoshinobu Tatsuo , Mitsui Hideaki , Tarui Yoichiro , Fuyuki Takashi , Matsunami Hiroyuki
Published: July 2002

Heteroepitaxial growth of 3C-SiC on Si substrates by gas source molecular beam epitaxy was investigated. Both Si(001) and Si(111) surfaces were carbonized using a C2H2 gas molecular beam to convert the surface region into single crystalline 3C-SiC prior to crystal growth. The supply of C2H2 was started at 400 °C, and the substrate temperature was raised at a rate of 7 °C/min. An amorphous-like layer was observed at 870 °C. Raising the temperature at a rate of 2 °C/min from 870 to 970 °C, a single crystalline 3C-SiC layer was obtained. In the case of Si(001), increase of C2H2 supply resulted in improvement of crystallinity, because of a thin (∼50 Å) 3C-SiC layer formed at an early stage of carbonization, which prevented outdiffusion of Si atoms. The thickness of the 3C-SiC layer did not increase for prolonged time of carbonization after formation of the thin layer. In the case of Si(111), the increase of C2H2 supply resulted in a thicker layer of 3C-SiC with a rough surface, because the channels of Si outdiffusion were not sealed off. Epitaxial growth of 3C-SiC was carried out using alternate supply of Si2H6 and C2H2 gas molecular beams on 3C-SiC layers obtained by carbonization under optimum conditions. Single crystalline 3C-SiC layers were obtained at 1075 °C, both on (001) and (111) surfaces.
Solutions of the heat conduction equation in multilayers for photothermal deflection experiments
Authors: McGahan William A. , Cole K. D.
Published: July 2002

Exact expressions are presented for the deflection of a laser beam passing parallel to and above the surface of a sample heated by a periodically modulated axisymmetric laser beam. The sample may consist of any number of planar films on a thick substrate. These exact expressions are derived from a local Green’s function treatment of the heat conduction equation, and contain an exact analytical treatment of the absorption of energy in the multilayered system from the heating laser. The method is based on calculation of the normal component of the heat fluxes across the layer boundaries, from which either the beam deflections or the temperature anywhere in space can be easily found. A central part of the calculation is a tridiagonal matrix equation for the N+1 normal boundary fluxes, where N equals the number of films in the sample, with the beam deflections given as simple functions of the normal heat flux through the top surface of the sample. Even though any layer or layers in the sample (including the substrate) can be optically absorbing, the final results are remarkably simple both in form and ease of calculation, even for large numbers of layers. In the case of an infinitesimal probe beam, the beam deflections are given by an expression involving a single numerical integration which can be eliminated for data analysis by Fourier transforming the experimental data. A general expression for the measured signals for the case of four-quadrant detection is also presented and compared to previous calculations of detector response for finite probe beams.
A secondary-ion-mass-spectrometry study of low-energy ion-beam mixing of Au-Pt interfaces
Authors: Likonen J. , Hautala M. , Koponen I.
Published: July 2002

Pt-Au multilayers deposited on a Si substrate were profiled with 2.5, 5, and 8 keV Ar+ ions in order to gain information on the influence of atomic mixing on secondary-ion-mass-spectrometry depth resolution. Collisional mixing and thermal spike mixing of metallic interfaces have been calculated with no adjustable parameters. The collisional mixing is calculated by Monte Carlo simulation and the thermal spike model based on well-established solid-state models is used to describe the late phase of the cascade. Experimentally observed broadening of the Au/Pt and Pt/Au interfaces as a function of primary-ion energy is predicted by the model. The experimental and calculated decay lengths of the trailing edge in Au are greater than in Pt by a factor of 2–3. This difference in interface broadening in Pt compared to that in Au is due to more efficient electron-phonon coupling and thus more rapid quenching of thermal spikes in Pt than in Au.
Transport properties of Cu/Mn multilayer films at low temperatures
Authors: Nallamshetty K. , Angadi M. A.
Published: July 2002

The electrical resistivity and the temperature coefficient of resistance (TCR) of Cu/Mn multilayer films have been reported for the bilayer wavelengths (Λ) in the range 4–12 nm by varying the number of double layers (n) from 5 to 30 in the temperature range 12 to 300 K. The most striking feature is the change in sign of the TCR as the bilayer wavelength is varied. The dependence of the room-temperature resistivity (ρRT) and TCR on the bilayer wavelength exhibits oscillatory behavior. The resistivity is found to be proportional to the inverse of the bilayer wavelength. The experimental results are analyzed, taking into account the effects of electron scattering at grain boundaries within the layers as well as scattering at interface boundaries between Cu and Mn layers.
Carbon diffusion in uncoated and titanium nitride coated iron substrates during microwave plasma assisted chemical vapor deposition of diamond
Authors: Weiser Paul S. , Prawer Steven , Hoffman Alon , Manory Rafael R. , Paterson Peter J. K. , Stuart Sue-Anne
Published: July 2002

Auger electron spectroscopy has been employed to investigate the effectiveness of thin films of TiN as barriers to carbon diffusion during chemical vapor deposition (CVD) of diamond onto Fe substrates. Auger depth profiling was used to monitor the C concentration in the TiN layer, through the interface and into the substrate both before and after CVD diamond deposition. The results show that a layer of TiN only 250 Å thick is sufficient to inhibit soot formation on the Fe surface and C diffusion into the Fe bulk.
Electrical characteristics of layer semiconductor p-GaSe doped with Cd
Authors: Shigetomi S. , Ikari T. , Nakashima H.
Published: July 2002

The electrical properties of Cd-doped GaSe have been investigated by using Hall-effect and deep-level transient spectroscopy (DLTS). The temperature dependence of hole concentration shows the characteristic of a partially compensated p-type semiconductor. The moderately deep acceptor level at about 0.28 eV above the valence band is detected by using both Hall-effect and DLTS measurements. We find that the acceptor level is associated with Cd-related defects formed by the dopant atoms.
Annealing studies of vacancies in proton irradiated silicon
Authors: Dannefaer S. , Mascher P. , Kerr D.
Published: July 2002

Annealing of vacancies produced by heavy proton irradiation of float-zone (Fz) and P-doped Czochralski-grown (Cz) silicon has been investigated by positron lifetime spectroscopy. In Fz-Si divacancies are retained after irradiation, and these defects are completely annealed out at 700 °C. In Cz P-doped silicon, impurities are found to enhance both the amount of retained vacancies as well as the tendency for vacancy clustering. Two annealing stages appear at 100 °C and close to 450 °C which seem to be a result of interstitial migration. Vacancy migration takes place in a wide temperature range between 100 and 1000 °C.
Determination of the plane stress elastic constants of thin films from substrate curvature measurements: Applications to amorphous metals
Authors: Witvrouw Ann , Spaepen Frans
Published: July 2002

A new method for measuring the static plane stress elastic constants of thin films on a substrate is described. It is based on measurements of the principal curvatures of two identical samples deposited on substrates with different preset curvatures. It is accurate if the deposition stress is no larger than the stress due to the bending of the substrates. Young’s modulus and Poisson’s ratio of amorphous Pd78Si22 were found to be the same as those of melt-spun material. The biaxial modulus of amorphous PdSi/PdSiFe multilayers was found to be independent of the bilayer repeat length.
The determination of valence band discontinuities in Si/Si1−xGex/Si heterojunctions by capacitance-voltage techniques
Authors: Brighten J. C. , Hawkins I. D. , Peaker A. R. , Parker E. H. C. , Whall T. E.
Published: July 2002

Capacitance-voltage (C-V) profiling has been used to measure the apparent carrier concentration profiles in Si/Si1−xGex/Si structures for a range of Ge percentages. Using Kroemers analysis, good agreement has been found between theoretical valence band offsets and those determined from the experimental data. The validity of Kroemers analysis has been assessed in the presence of traps using a C-V simulation program. Under certain circumstances, large errors occur in the extracted valence band offset due to distortion of the apparent carrier concentration profile by traps. It is proposed that the experimental data presented here falls into a regime where minimal distortion is to be expected and is reflected by the accuracy of the extracted valence band offsets.
Relaxation phenomena in the vicinity of the glass transition of poly (p-phenylene sulfide)
Authors: Shimizu Hiroshi , Nakayama Kazuo
Published: July 2002

Thermally stimulated depolarization current (TSDC), thermal sampling (TS) TSDC, and dielectric spectra of poly(p-phenylene sulfide) (PPS) were measured in the vicinity of the glass transition temperature Tg. The global TSDC spectra of amorphous PPS with varying the poling temperature revealed the presence of two TSDC peaks. Only a very intense peak associated with the α relaxation (the glass transition) was observed at 367 K in the global TSDC spectra poled at above 360 K, while an additional peak was observed at around 330 K in those spectra poled at below 355 K. This additional peak observed at below Tg was considered to be originated from the secondary sub-Tg relaxation. Both the sub-Tg and the α relaxations were analyzed from elementary TSDC spectra obtained by the TS technique. It was found that the temperature dependence of the relaxation times in both relaxations was ruled by the same compensation law. The physical meaning of the compensation temperature is discussed in relation to the thermal-expansion coefficient. Moreover, the dielectric constant ε′ and dielectric loss factor ε″ of amorphous PPS are calculated using the relaxation parameters derived from the TS-TSDC analysis. Numerical results of dielectric data are represented by three-dimensional and/or two-dimensional spectra and are compared with the available experimental data. The simulated dielectric spectra forecast that the sub-Tg relaxation should appear as a peak or shoulder of ε″ at lower-temperature and ultra-low-frequency regions in the ac measurements.
1H atomic motion in proton-exchanged LiNbO3
Authors: Engelsberg M. , do Nascimento George C. , Pacobahyba L. H.
Published: July 2002

1H nuclear magnetic resonance measurements in proton-exchanged LiNbO3 crystallites prepared with sulfuric acid as a proton donor, indicate the presence of two different motional regimes as a function of temperature. The low temperature regime appears to be especially revealing since it suggests a to-and-fro motion between a normal and an interstitial site which is very fast at ambient temperature. This may be evidence of a substantial population of interstitial sites and may help explain the unusual optical properties of this material.
Quasi permanent superconducting magnet of very high field
Authors: Ren Y. , Liu J. , Weinstein R. , Chen I. G. , Parks D. , Xu J. , Obot V. , Foster C.
Published: July 2002

We report on persistent field in a quasipermanent magnet made of high temperature superconductor. The material has an average of 40% molar excess of Y, relative to Y1Ba2Cu3O7 and has been irradiated with high energy light ions at 200 MeV. The magnet, which traps 1.52 T at 77.3 K, traps nearly 4 T at 64.5 K. No evidence of giant flux jump or sample cracking was observed.
Hole injection in AlGaAs Schottky barriers: Influence on the DX center occupation
Authors: Mosca R. , Gombia E. , Bosacchi A. , Franchi S. , Ghezzi C. , Frigeri P.
Published: July 2002

It is shown that current instabilities, which are frequently observed at low temperatures in forward biased Schottky barriers on n-type AlGaAs, result from changes in the distribution of negatively charged donors (DX centers) near the metal contact. These changes cannot be ascribed to sample-heating effects, but they originate from hole injection in the barrier during forward biasing. The dominant mechanisms which are expected to induce the observed distortions in the DX center profile are (i) direct capture of the injected holes by the DX center and (ii) radiative electron-hole recombination resulting in DX center photoionization. The role of the two mechanisms is discussed.
Many-electron effects on transport through two-dimensional quantum structures
Authors: Wang Jian , Wang Yongjiang , Guo Hong
Published: July 2002

A two-dimensional Thomas–Fermi–Dirac–von Weizsacker formalism is derived using a local density approximation to study ballistic transport in quantum structures. The effective potential of the two-dimensional system is calculated by minimizing the energy using a conjugate gradient technique. This method enables us to study the effects of exchange and correlation, in addition to the direct Coulomb interaction, on quantum transport. We have applied this method to calculate the transport property of a T-shaped two-dimensional quantum wire in the presence of the effective potential.
Effect of substrate roughness on microstructure, uniaxial anisotropy, and coercivity of Co/Pt multilayer thin films
Authors: Chang Chung-Hee , Kryder Mark H.
Published: July 2002

We studied the microstructure and magnetic properties of Co/Pt multilayer thin films sputtered onto glass and Si substrates with different surface roughness caused by different methods of substrate preparation. The microstructure determined by high-resolution electron microscopy and x-ray scattering could be correlated to the observed magnetic properties. Better (111) texture and smoother layer structures produced on smoother glass substrate surfaces produced higher uniaxial anisotropy. Coercivity, on the other hand, was enhanced by either pinning of the domain walls caused by substrate surface roughness or stronger columnar structure. Although Si substrates exhibited slightly different roughness under the same preparation conditions, the dependence of magnetic properties on the substrate surface was consistent with the trends using glass substrates.
Linear and nonlinear analysis of microwave power generation in submicrometer n+nn+ InP diodes
Authors: Gruz̆inskis V. , Starikov E. , Shiktorov P. , Reggiani L. , Varani L.
Published: July 2002

A closed hydrodynamic model and the associated numerical procedures are developed for simulating hot-carrier transport in submicron semiconductor devices. To check the validity of the model, the steady-state characteristics of near-micron n+nn+ InP diodes are compared with a standard Monte Carlo approach. The excellent agreement found fully validates the physical reliability of our model which has been further developed to investigate linear and nonlinear time-dependent characteristics. The contribution of each part of the device, when operating as microwave power-generation, is analyzed through the spatial profiles of the impedance-field spectrum. The usual subdivision of the n-region into a passive (dead-zone) and active zone is carried out. The dead zone is found to manifest itself as a purely real resistance which is practically independent of the frequency. One or more spatial zones which are responsible for the generation are shown to be formed in the active region of the diode. By reducing the length of the n-region, under the condition that the total current is constant in time, the additivity of the contributions from each part of the device into the generation spectrum is proven. The predictions of the linear analysis are compared with a direct simulation of the diode performance in the external resonant circuit. A wide-band tuning of the generation frequency from 100 up to 200 GHz is demonstrated. The microwave power generation is shown by both hydrodynamic and Monte Carlo simulation to be caused by the formation and propagation through the diode of accumulation layers. Theoretical results are found to compare well with available experiments.
Magnetic anisotropy and giant magnetostriction of amorphous TbDyFe films
Authors: Schatz F. , Hirscher M. , Schnell M. , Flik G. , Kronmüller H.
Published: July 2002

The influence of internal stress on the magnetic anisotropy and the magnetostriction was investigated in sputter-deposited amorphous (Tb0.27Dy0.73)0.42Fe0.58 films. Films with tensile stress show in-plane anisotropy and giant magnetostriction of λ∥=400×10−6 at 1 T measured in a field parallel to the film plane at room temperature. The magnetostriction rises rapidly to λ∥=200×10−6 at 0.05 T and the coercivity is less than 0.01 T. On the other hand films with compressive stress show perpendicular anisotropy and still higher magnetostriction of λ∥=540×10−6 at 1 T; however, this is by far a slower increase of magnetostriction at small fields. This different behavior is explained by considering the nature of magnetization processes, i.e., domain-wall motion and spin rotation.
Gate bias controlled charge distribution in the subbands of In0.29Al0.71As/In0.3Ga0.7As modulation doped heterostructures
Authors: Chen Jianhui , Wieder H. H. , Young A. P.
Published: July 2002

The gate voltage dependent charge distribution within the quantum wells of modulation δ-doped In0.29Al0.71As/In0.3Ga0.7As heterostructures, grown by molecular beam epitaxy and fabricated into front-gated, six-arm, Hall bar configurations, were evaluated by means of resistivity, Hall effect, and Shubnikov–de Haas (SdH) oscillatory magnetoresistance measurements. δ-doping the barrier layer with Si to 6×1012/cm2 leads to an apparent electron density, as obtained from Hall measurement made at 1.6 K, ns=2.65×1012/cm2. The SdH spectra exhibit a gate voltage-dependent transition from one subband to two subbands and the total electron density is in good agreement with that obtained from the Hall data. From a fast Fourier transform of the SdH data and low field magnetoresistance measurements the electron densities and mobilities of the two subbands at Vg=0 were found to be ns1=2.39×1012 cm−2, μ1=21 800 cm2/V s and ns2=3.96×1011 cm−2, μ2=16 000 cm2/V s, respectively.
Structural and optoelectronic properties of Ge-rich hydrogenated amorphous silicon-germanium alloys
Authors: Graeff C. F. O. , Chambouleyron I.
Published: July 2002

In this work the structural and opto-electronic properties of rf sputtered germanium-rich hydrogenated amorphous silicon germanium alloys (a-SixGe1−x:H) are presented. It has been found that for x≤0.1, the Si incorporation does not appreciably affect, either the density of localized states in the pseudo-gap, or the structural properties of the films. However the Tauc’s optical gap shifts from 1.04 eV (x=0.0) to ≊1.13 eV (x=0.1). A concomitant two orders of magnitude decrease of the dark conductivity is measured, whereas the photoconductivity remains essentially unchanged. In other words, the incorporation of small amounts of Si in the hydrogenated amorphous germanium (a-Ge:H) network produces a noticeable increase of the photosensitivity of the samples. These results are discussed in the framework of present models of amorphous semiconductor alloys.
Electromigration failure by shape change of voids in bamboo lines
Authors: Arzt E. , Kraft O. , Nix W. D. , Sanchez J. E.
Published: July 2002

The behavior of electromigration-induced voids in narrow, unpassivated aluminum interconnects is examined, using scanning electron microscopy. Some electromigration tests were interrupted several times in order to observe void nucleation, void growth, and finally the failure of the conductor line. It is found that voids which opened the line have a specific asymmetric shape with respect to the electron flow direction. Besides void nucleation and void growth, void shape changes can consume a major part of the lifetime of the conductor line. A first attempt to model these processes on the basis of diffusion along the void surface shows that voids with a noncircular initial shape tend to produce the fatal asymmetry due to electron wind effects, with the anisotropy of surface energy possibly playing only a minor role.
Effect of crystal growth on Ti3+ centers in KTiOPO4
Authors: Scripsick M. P. , Edwards G. J. , Halliburton L. E. , Belt R. F. , Loiacono G. M.
Published: July 2002

A series of Ti3+ centers have been formed in hydrothermally grown and flux-grown potassium titanyl phosphate (KTiOPO4 or KTP). These 3d1 defects (S=1/2) were created with 60 kV x rays at 77 K, and electron paramagnetic resonance and electron-nuclear double-resonance (ENDOR) data were taken below 30 K. The ENDOR spectra show that the two Ti3+ centers having the largest concentrations in hydrothermally grown KTP have a neighboring proton, presumably in the form of an adjacent OH− ion. In contrast, ENDOR spectra show that neither of the two Ti3+ centers having the largest concentrations in flux-grown KTP have a neighboring proton. These significant differences in the local environment of the Ti3+ centers may help explain why KTP crystals have shown differing susceptibilities to gray tracking.
Materials and processing aspects of CoCrTa/Cr longitudinal recording media. I. Processing and magnetic properties
Authors: Shen Y. , Laughlin D. E. , Lambeth D. N.
Published: July 2002

In this study, we correlate various processing conditions with the magnetic properties of CoCrTa/Cr films by varying the substrate preheating, the substrate bias, and the composition of the magnetic target. High Hc CoCrTa/Cr films with thin Cr underlayers were produced by either preheating the substrate or by rf bias sputtering. We found that the sputtering temperature of the magnetic layer plays a far more important role in reducing intergranular exchange coupling and increasing Hc than does the CoCrTa/Cr crystallographic texture. The optimum condition for preparing high Hc films depends on the magnetic target composition. Even though the crystallographic texture does not control Hc, it does have an effect on the ΔM curve which is related to the noise properties of CoCrTa/Cr media. ΔM measurements indicate that {11̄01}Co /{110}Cr textured films may have slightly better noise properties than the films with {112̄0}Co /{200}Cr texture with similar Hc.