bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectric relaxation functions and models
Authors: Gross Bernhard
Published: July 2002

The dielectric relaxation function is defined as the transient current generated by the application of a unit voltage. In analogy with viscoelasticity, a second relaxation function can be defined as the transient voltage generated by the application of a unit current. Each of these functions generates its own distribution function of relaxation times. If one of the distribution functions is truncated, the other has been found to contain single lines apparently devoid of physical significance. Using a particular test function derived from the Curie–von Schweidler law1,2 [Ann. Chim. Phys. 18, 20 (1899); Handbuch der Elektrizitaet und des Magnetisms (Barth, Leipzig, 1918), p. 286] it is shown here that such lines do not appear in all instances. On the other hand, the relaxation function, as a monotonously decreasing function, frequently is believed to contain only two types of parameters, one energy dissipative and another energy storing. However, using the same test function as above, one can prove that a relaxation function can contain all three types of parameters, one dissipative and two energy-storing ones. Therefore, a relaxation system cannot, in general, be defined as a two-parameter system. An energy-dissipative parameter represents resistive elements, while energy-storing parameters represent capacitive and inductive elements.
Surface plasmon optical characterization of lipid monolayers at 5 μm lateral resolution
Authors: Hickel W. , Knoll W.
Published: July 2002

Surface plasmon microscopic pictures recorded as a function of the angle of incidence of the coupling laser beam can be quantitatively evaluated and yield optical thicknesses of ultrathin coatings with an areal resolution of 5×5 μm2. This is demonstrated for a lipid monolayer transferred to a solid support in its phase transition region. The coexisting amorphous and crystalline domains can be analyzed simultaneously.
Diffusion of color centers generated by two-photon absorption at 532 nm in cubic zirconia
Authors: Mansour Nastaran , Mansour Kamjou , Van Stryland E. W. , Soileau M. J.
Published: July 2002

We have recently reported the formation of color centers in stabilized cubic zirconia (ZrO2, 18% Y2O3) by two-photon absorption at 532 nm. Here we present the results of measurements of the transmission of the colored samples as a function of time at room temperature. The results are found to be in good agreement with theory that assumes the color centers diffuse out of the irradiated region. The initial distribution of centers is assumed to have a Gaussian profile. For this model, the diffusion equation was solved exactly and the diffusion constant obtained (∼3.4×10−8 cm2/s).
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o micromagnetic calculations for particles (invited)
Authors: Fredkin D. R. , Koehler T. R.
Published: July 2002

We present the results of first-principles calculations of the magnetic behavior of particles of varying shapes (sphere, prolate spheroid, and rectangular particles of various aspect ratios) and sizes ranging from ≊0.1 to 10 μm. We use a numerical implementation of micromagnetics in which the only input quantities, aside from the particle geometry, are the material parameters and the magnetic history. We have obtained quantitative agreement with theory for spherical particles and qualitative agreement with experiment in the case of rectangular objects, and we have observed a variety of interesting reversible and irreversible phenomena accompanying magnetic reversal in all objects. We describe key aspects of the numerical implementation and survey selected results.
Photoluminescence in GaAs/AlGaAs heterojunction bipolar transistors: An investigation of the properties of the Mg acceptor
Authors: Humer-Hager T. , Tews H.
Published: July 2002

Detailed 77-K and temperature-dependent photoluminescence (PL) investigations of heterojunction bipolar transistor (HBT) structures grown by low-pressure metalorganic vapor-phase epitaxy are presented. HBT layer sequences with GaAs base and with AlxGa1−xAs base graded in the Al content are investigated. Different peaks belonging to GaAs and AlGaAs layers within the HBT structure are identified. It is shown that the PL spectrum is not only the superposition of single-layer signals, but also provides additional information about the incorporation of the base dopant Mg into the emitter and collector regions of the HBT during epitaxial growth. The presence of Mg in the collector leads to a signal absent in PL of single-layer GaAs doped merely with Si. It is interpreted as a free-to-bound Mg acceptor transition, and its intensity scales with the amount of diffused Mg. Two additional AlGaAs PL peaks besides that from the usual band-gap recombination are found to be correlated with Mg in the emitter. Their signal strength is dependent on the Mg concentration level. It will be shown that careful evaluation of the HBT spectra can help to decide whether a certain structure under investigation meets the requirements for further device processing.
Verification of the localized-wave transmission effect
Authors: Ziolkowski Richard W. , Lewis D. Kent
Published: July 2002

An acoustic array driven with a designed set of localized-wave (LW) solutions of the scalar-wave equation generates a robust, well-behaved, transient pencil beam of ultrasound in water. The performance of the LW-pulse-driven array theoretically and experimentally exceeds a tenfold improvement over related continuous-wave excitations of the same array.
Characteristics of Be+ and O+ or H+ co-implantation in GaAs/AlGaAs heterojunction bipolar transistor structures
Authors: Pearton S. J. , Ren F. , Wisk P. W. , Fullowan T. R. , Kopf R. F. , Kuo J.-M. , Hobson W. S. , Abernathy C. R.
Published: July 2002

The simultaneous formation of buried external collector and extrinsic base regions in GaAs/AlGaAs heterojunction bipolar transistor (HBT) structures by co-implantation of Be+ together with O+ or H+ ions is described. Oxygen implants at doses of ≥ 1012 cm−2, or proton implants at doses ≥ 1014 cm−2, followed by annealing at 500–550 °C, create fully depleted collector regions, while similar anneals lead to significant Be activation and lowered base resistance. Higher annealing temperatures improve this Be activation but restore the initial doping level in the implanted collector region. For Be+ ion doses ≤ 5≤5× 1014 cm−2 there are no defects visible by transmission electron microscopy in the HBT structure for annealing temperatures below 800 °C.
Cl2 reactive ion etching mechanisms studied by in situ determination of ion energy and ion flux
Authors: Manenschijn A. , van der Drift E. , Janssen G. C. A. M. , Radelaar S.
Published: July 2002

An experimental study of etching mechanisms in Cl2 reactive ion etching is reported. The ion-impact energy distribution and ion current density have been measured in situ at the rf electrode of a parallel-plate reactive ion etcher. This diagnostic method has been used for the first time to unravel etch characteristics in a practical etching environment. Samples of Si, SiO2, Ti, and TiSi2 have been etched both in Cl2 and Ar discharges, and the etch rates have been related to the ion flux and impact energy distribution. The angular impact energy distribution for both ions and neutrals has been calculated numerically in order to study the contribution of fast neutrals and the angular distribution of impinging species to the etch rate. Sputter yields have been determined from the observed etch rate and the ion current density, taking into account the (angular) energy distributions of bombarding ions and neutrals. Comparison of the obtained sputter yields in Ar and Cl2 discharges with corresponding data from (chemically assisted) ion-beam sputtering gives further insight into the etching mechanisms of Si, SiO2, Ti, and TiSi2.
Diffusion mechanism of zinc and beryllium in gallium arsenide
Authors: Yu S. , Tan T. Y. , Gösele U.
Published: July 2002

The outstanding features associated with Zn and Be diffusion in GaAs substrates and GaAs/AlGaAs superlattices are explained either quantitatively or semiquantitatively using the kick-out mechanism, in which it is assumed that the doubly positively charged Ga self-interstitial governs Ga self-diffusion. These features include (i) the dependence of the Zn solubility upon the pressures of the As and Zn vapor phases, (ii) the square power-law dependence of the Zn diffusivity on its own background concentrations under Zn isoconcentration diffusion conditions, (iii) the different shapes of the Zn in-diffusion profiles, (iv) the much lower diffusivities of Zn and Be under out-diffusion conditions than under in-diffusion conditions, and (v) the tremendous enhancement effect of Zn in-diffusion on GaAs/AlGaAs superlattice disordering and the undetectable effect of Be under out-diffusion conditions. Some useful quantitative information has been obtained. Strictly on a qualitative basis, we have found that the Longini mechanism is also able to explain the above features (i)–(iv) fairly well. The predicted effects of the Longini mechanism on Ga self-diffusion are, however, contrary to experimental results associated with superlattice disordering.
Raman-microprobe study of stress and crystal orientation in laser-crystallized silicon
Authors: Kolb G. , Salbert Th. , Abstreiter G.
Published: July 2002

The spatial variation of stress and crystal orientation in laser-crystallized silicon-on-insulator films has been determined using the Raman-microprobe technique. The spatial resolution achieved is better than 1 μm. The phonon shift relative to unstressed silicon is in the range of −1.5 cm−1 which corresponds to a tensile stress of 380 MPa and is in good agreement with theoretical analysis. Using a laser plasma line as an online reference, the peak position of the phonon signal has been measured with a resolution better than ±0.02 cm−1. Our results also show a 4°-backward tilt of the crystal orientation along a crystallization path length of 90 μm. This has been determined using a new polarization sensitive intensity-monitoring method on cross-cut specimens which features an angular resolution of ±1° independent of surface roughness.
Time-resolved electron energy distribution function measurements in a pulsed magnetic multipole hydrogen discharge
Authors: Hopkins M. B. , Graham W. G.
Published: July 2002

The time evolution of measured plasma parameters, including the electron energy distribution function (EEDF), in the discharge and post-discharge regime of a pulsed hydrogen magnetic multipole plasma is presented. The time necessary for the plasma to reach equilibrium has been established as 160 μs. The present results clarify the mechanisms which initiate the discharge. The decay rates of the charged-particle density and energy in the post-discharge have been measured. These measurements indicate that particle transport to the wall is the dominant loss mechanism for both charged-particle density and energy. The time-resolved EEDF is found to be non-Maxwellian in the discharge and Maxwellian in the late post-discharge.
Valence-band discontinuities at semiconductor heterojunctions
Authors: Pollard William
Published: July 2002

A realistic model for predicting valence-band discontinuities at semiconductor heterojunctions is presented. The proposed model is based on a simple picture of the semiconductor interfaces which takes into account charge transfer at the interface. Applications are made to a number of different heterojunctions and chemical trends are examined. Comparisons with experiment and with other model theories are discussed.
Photoluminescence studies on over-passivations of (NH4)2Sx-treated GaAs
Authors: Shikata S. , Hayashi H.
Published: July 2002

Over-passivation films of silicon nitride (SiN) and silicon dioxide (SiO2) on (NH4)2Sx-treated GaAs deposited by various kinds of systems were studied with photoluminescence measurements. Among the various kinds of systems commonly used in semiconductor device fabrication processes, electron cyclotron resonance chemical vapor deposition (ECR-CVD) produces undamaged over-passivation films and it appears to be a promising system. The silicon nitride and silicon dioxide deposited at room temperature by ECR-CVD have the same PL intensity. For SiN, the effect of the treatment is enhanced by annealing while a gradual degradation with increasing temperature is observed for SiO2. By using ECR-CVD SiN for sulfur-treated GaAs passivation, the luminescences of free excitons and donor bound excitons are observed even for bulk-grown GaAs at 4.2 K, which indicates the reduction of the recombination centers at the surface.
Thin-film interdiffusions in Cu/Pd, Cu/Pt, Cu/Ni, Cu/NiB, Cu/Co, Cu/Cr, Cu/Ti, and Cu/TiN bilayer films: Correlations of sheet resistance with Rutherford backscattering spectrometries
Authors: Shih D.-Y. , Chang C.-A. , Paraszczak J. , Nunes S. , Cataldo J.
Published: July 2002

Interdiffusion in the Cu-based Cu/Pd, Cu/Pt, Cu/Ni, Cu/NiB, Cu/Co, Cu/Cr, Cu/Ti, and Cu/TiN bilayer films has been investigated for anneal temperatures ranging from 150 to 400 °C in forming gas (N2-10%H2). The diffusion of Pd, Pt, and Ni into Cu has resulted in a significant increase in the sheet resistance of the film, which is correlated with the concentration profiles obtained from Rutherford backscattering spectrometries. In contrast, the diffusion of Co or Cr into Cu is negligible, probably due to the lack of solubility of Co or Cr in Cu at temperature ≤400 °C. Outdiffused Cu species were detected on the Pd, Pt, Ni, NiB, Ti, and Co surfaces, while that of Cu through Cr or TiN was negligible. The increases in film resistivities are mostly due to the increase of electron-impurity scattering centers as solute atoms diffuse into Cu. As a result, factors such as the use of different overcoated metals, annealing temperature, thickness of the Cu film, and the grain size of Cu all played a critical role in affecting the resistivity of the Cu films. The driving force for interdiffusion in these binary systems appears to be dominated by the mutual solubility between the bilayer films. Interdiffusion between the bilayer films can be suppressed by interposing a diffusion barrier layer of Cr, Ti, Zr, or TiN between Cu and the overcoated films. The trilayer structures are thermally stable up to 400 °C.
cw femtosecond pulses tunable in the near- and midinfrared
Authors: Wachman E. S. , Pelouch W. S. , Tang C. L.
Published: July 2002

Continuous tuning of a cw femtosecond optical parametric oscillator (OPO) is demonstrated from 0.755–1.04 μm for the signal branch, and from 1.5–3.2 μm for the idler branch, covering most of the potential tuning range of the device. Transform-limited pulses under 120 fs in duration are found throughout the signal tuning, and idler pulsewidth measurements suggest pulses of less than 215 fs should be possible throughout the idler tuning. These results have been achieved using a new walkoff compensation scheme in the OPO. Preliminary results of transmission correlation measurements of carrier relaxation in InGaAs are presented using the parametric oscillator as a tunable excitation source.
Spin-glass-like nature in Fe/DyFe multilayers
Authors: Honda S. , Ohtsu M. , Kusuda T.
Published: July 2002

Fe/DyFe multilayers were prepared by radio-frequency magnetron sputtering, where DyFe layers were amorphous and nonmagnetic at room temperature. When the Fe layer thickness dFe decreases, the crystallographic structure of the Fe layer changes from body-centered-cubic to amorphous at around 20 Å. At this critical thickness, the spontaneous magnetization and the Kerr rotation angle are nearly zero and the magnetization curve does not show hysteresis or saturation indicating its spin-glass-like or superparamagnetic nature. For dFe < 20 Å, the saturation magnetization and the Kerr rotation angle increase again due to the Fe-rich-DyFe amorphous alloy formed at the vicinity of the layer boundary with decreasing dFe. The perpendicular anisotropy increases with decreasing dFe because of the interfacial anisotropy Ks = 0.62 erg/cm2 in the crystalline region of dFe ≳ 20 Å.
Calculations of the microwave conductivity of high-T
c superconducting thin films from power transmission measurements
Authors: Wu P. H. , Min Qian
Published: July 2002

To calculate the complex conductivity σ=σ1−jσ2, and thus the surface resistance Rs and penetration depth λL, of high Tc superconducting thin films from microwave power transmission measurements, new expressions are derived taking into account the film thickness. Numerical examples are given to show that, compared with the calculations which neglect the film thickness, corrections in σ1, σ2, Rs, and λL are a few percent for film thickness ranging between 0.65 and 0.46 λL and that corrections in σ1 and σ2 are greater than those in Rs and λL. Using the newly derived expressions, maximum errors in Rs and λL are estimated to be about 30% and 3%, respectively, if errors between −10% and +10% are tolerated in the measurements of the magnitude and phase shift of microwave transmission.
Analytical relations between the phase of the photothermal signal and the thermal wavelength
Authors: Figari Angelamaria
Published: July 2002

Analytical expressions are derived for the photothermal signal, as the probe beam explores the thermal wave generated by the pump beam in the sample, grazing along its surface at a distance x from the heating spot. The relation between the phase of the signal and the thermal wavelength λth is pointed out, providing an analytical foundation to a refined photothermal technique for measuring the thermal diffusivity α. In particular, the analysis shows that both λth and α can be measured using arbitrary phase shifts relative to the heating spot center, which improves the measurement accuracy and the resolution in the application of this technique to imaging.
Line x-ray emissions from highly ionized plasmas of various species irradiated by compact solid-state lasers
Authors: Zeng G. M. , Daido H. , Murai K. , Kato Y. , Nakatsuka M. , Nakai S.
Published: July 2002

X-ray emissions in the spectral range of 2–13 nm from 21 kinds of material (carbon through tin) irradiated either by a 4 J/35 ns slab Nd:glass laser or by a 0.5 J/8 ns Nd:YAG laser were recorded with a grazing incidence spectrometer equipped with a microchannel plate detector. The absolute photon intensities of the spectra from these materials were determined. The variation of the molybdenum spectrum with laser irradiance was also investigated. Finally, the spectra ranging from 2 to 13 nm produced by the Nd:YAG laser of both the fundamental (1.06 μm) and its second-harmonic (0.53 μm) wavelengths are compared.
Deep implantation of nitrogen into GaAs for selective three-dimensional microstructuring
Authors: Würfl Joachim , Miao Jianmin , Rück Dorothee , Hartnagel Hans L.
Published: July 2002

Results are presented for deep implantation of nitrogen into n-type GaAs. The main purpose of these investigations is to clarify whether deep implantation can be a suitable process to create buried, selectively etchable layers for the fabrication of micromechanical structures in GaAs. The implanted layers have been characterized by x-ray photoelectron spectroscopy (XPS) combined with sputter profiling, electrical measurements using test Schottky diodes, and selected etching techniques. XPS depth profiling shows the formation of a GaAs1−xNy layer with y<x that can be etched with high selectivity with respect to the GaAs using alkaline agents. The degree of radiation damage introduced during implantation is determined by planar test diodes located at different depth levels in the implanted structure. It can be shown that implantation damage recovers to a certain extent after annealing at a temperature of about 750 °C although the optimum annealing conditions have not yet been found.
Measurements of interdiffusion in electrodeposited nickel-phosphorus multilayers
Authors: Ross C. A. , Wu D. T. , Goldman L. M. , Spaepen F.
Published: July 2002

The interdiffusivity within multilayered electrodeposited thin films of NiPx/NiPy has been measured using an x-ray technique. The NiPx, which can be deposited in the range 0≤x≤25 at. %, is crystalline at low phosphorus content but amorphous at high phosphorus content, so that films with a range of crystalline and amorphous structures could be prepared. Measurements on fully amorphous multilayers, where x,y≳18 at. %, give an interdiffusivity of order 10−22 m2 s−1 at 120 °C, which decreases with time, probably due to structural relaxation. The diffusivity decreases with decreasing repeat length of the films, with a critical repeat length of 40 Å. Crystalline/amorphous films show qualitatively different behavior, with the low-phosphorus layer governing the extent of a more limited diffusion phenomenon. This has been interpreted as the diffusion of phosphorus into a limited number of sites within the grain boundaries of the crystalline layers.
Characterization of YBa2Cu3O7, including critical current density J
c, by trapped magnetic field
Authors: Chen In-Gann , Liu Jianxiong , Weinstein Roy , Lau Kwong
Published: July 2002

Spatial distributions of persistent magnetic field trapped by sintered and melt-textured ceramic-type high-temperature superconductor (HTS) samples have been studied. The trapped field can be reproduced by a model of the current consisting of two components: (i) a surface current Js and (ii) a uniform volume current Jv. This Js + Jv model gives a satisfactory account of the spatial distribution of the magnetic field trapped by different types of HTS samples. The magnetic moment can be calculated, based on the Js + Jv model, and the result agrees well with that measured by standard vibrating sample magnetometer (VSM). As a consequence, Jc predicted by VSM methods agrees with Jc predicted from the Js + Jv model. The field mapping method described is also useful to reveal the granular structure of large HTS samples and regions of weak links.
Observation of thermal switching of a single ferromagnetic particle
Authors: Lederman M. , Gibson G. A. , Schultz S.
Published: July 2002

A magnetic force microscope (MFM) has been shown to be able to detect fields emanating from submicrometer permalloy particles with magnetic moments as low as 10−13 emu. We have used this MFM equiped with an in situ electromagnet to study the angular dependence of the switching field Hs(θ), and the probability of thermal switching of a single-domain permalloy particle as a function of the time duration of an applied magnetic field H. The angular dependence of Hs(θ) is significantly different from that expected for coherent rotation. For applied magnetic fields close to Hs, the time dependence of the probability for not switching cannot be fit with a simple exponential. These data indicate that multiple-energy barriers of similar height are involved in the thermally activated process responsible for the reversal.
Inverse problem of simultaneously estimating the timewise-varying strengths of two plane heat sources
Authors: Silva Neto A. J. , Özişik M. N.
Published: July 2002

An inverse analysis utilizing the conjugate gradient method of minimization and the adjoint equation is used for simultaneously estimating the timewise-varying strengths of two plane surface heat sources located inside a plate with insulated boundaries. No prior information is used for the functional forms of timewise variation of the source strength. Transient temperature recordings taken at the boundaries of the region, modified by addition of random errors, served as the simulated experimental data for the inverse analysis. In order to examine the accuracy of the estimation under most strict conditions, timewise variation of the source strength is chosen in the form of rectangular, triangular, and sinusoidal functions. Several different combinations of pulse shapes and location of the heat sources were studied. For situations in which the two heat sources were located close to each other, difficulty was experienced in the estimation of source strengths.
Equivalent circuit and capacitance of double barrier resonant tunneling diode
Authors: Wei T. , Stapleton S. , Berolo E.
Published: July 2002

By measuring the scattering parameters (S parameters) with on-wafer probing techniques, the small signal impedances of double barrier resonant tunneling diodes up to 18 GHz have been obtained. The high-frequency impedance found can be successfully reproduced by a parallel R-C circuit along with a series R-L circuit. Our study indicates that the double barrier quantum well structure can be represented by the parallel R-C circuit alone, while the inductance results from the air-bridge lines to the probe contacts. The capacitance-voltage (C-V) relationship is also obtained. Well-defined structures corresponding to the tunneling effect are found. An increase in capacitance after tunneling is found in the C-V curve, and it is attributed to the charge accumulation at the quasibounded state within the quantum well.
Pressure-induced rocksalt phase of aluminum nitride: A metastable structure at ambient condition
Authors: Xia Qing , Xia Hui , Ruoff Arthur L.
Published: July 2002

Energy-dispersive x-ray diffraction studies were carried out on the III-V compound aluminum nitride to 65 GPa using a synchrotron x-ray source. A pressure-induced first-order phase transition from a wurtzite structure to a rocksalt structure was observed. The first peaks of the high-pressure phase appeared at 14 GPa. On further loading of the diamond anvil cell, the wurtzite peaks disappeared by 20 GPa. After unloading the cell to atmospheric pressure, the rocksalt structure persisted. The equilibrium transformation pressure lies on the interval 0–14 GPa.
Underdetermined system theory applied to quantitative analysis of responses caused by unsteady smooth-plane waves
Authors: Sano Yukio
Published: July 2002

The mechanical responses of rate-dependent media caused by unsteady smooth-plane waves are quantitatively analyzed by an underdetermined system of equations without using any constitutive relation of the media; that is, by using the particle velocity field expressed by an algebraic equation that is derived from the mass conservation equation, and the stress field expressed by an algebraic equation that is derived from the momentum conservation equation. First of all, this approach for analyzing unsteady wave motion is justified by the verification of various inferences such as the existence of the nonindependent elementary waves by Sano [J. Appl. Phys. 65, 3857(1989)] and the degradation process by Sano [J. Appl. Phys. 67, 4072(1990)]. Second, the situation under which a spike arises in particle velocity–time and stress–time profiles, and the reason for the arising are clarified. Third, the influence of the spike on stress-particle velocity and stress–strain paths is examined. The spike induced in the profiles by a growing wave greatly influences the paths near the impacted surface. Finally, calculated particle velocity–time profiles are compared with experimental data.
Network structure of tellurite phosphate glasses: Optical absorption and infrared spectra
Authors: Abdel-Kader A. , El-Mallawany R. , ElKholy M. M.
Published: July 2002

A series of binary tellurite-phosphate glasses in the form [TeO2]0.81[P2O5]0.19 doped with different rare-earth oxides were prepared. The rare-earth oxides were: La2O3, CeO2, Pr2O3, Nd2O3, Sm2O3, and Yb2O3. The optical absorption coefficient and infrared spectra were measured in the ranges 200–900 nm and 200–1000 cm−1, respectively. It is found that the fundamental absorption edge depends upon the kind of the dopant cation. The infrared spectra of these doped glasses indicate that the rare-earth oxides are connected to the chains of TeO4.
Optical characterizations of photo-induced chemical vapor deposition produced SiO2 films in vacuum ultraviolet, ultraviolet, and visible region
Authors: Kanashima Takeshi , Nagayoshi Ryoichi , Okuyama Masanori , Hamakawa Yoshihiro
Published: July 2002

Photoluminescence and absorption properties of photo-induced chemical vapor deposition produced SiO2 films have been studied to identify the defects and the other imperfections. Two kinds of distinct absorption peak have been found which lie at 6.3 eV for low temperature deposition (around 30 °C), and at 7.6 eV for high temperature deposition (around 300 °C). Photoluminescence peaks at 2.7, 3.6–3.8, and 4.4 eV are found in the film deposited at high temperature, but the 4.4 eV peak is not seen in film deposited at low temperature. Intensity changes of the photoluminescence and absorption peaks have been obtained in various films which were deposited at different gas-flow-rate-ratios of Si2H6/O2 and were annealed in O2 and N2 ambients. It is considered from the treatment dependence of these peaks that the absorption peak at 7.6 eV and photoluminescence peak at 2.7 eV are attributable to oxygen-vacancies, but the absorption peak at 6.3 eV relates to oxygen-excess defects.
Comparisons of one- and two-dimensional three-moment fluid models for rf glow discharges
Authors: Young Fongray Frank , Wu Chwan-Hwa ‘‘John’’
Published: July 2002

Self-consistent nonequilibrium fluid models of both the two-dimension (2D) and one-dimension (1D) are presented. In the 2D simulations, the models evaluate the quantitative effects of both radial and axial flow dynamics inside a cylindrically symmetric parallel-plate geometry. The 1D model assumes that the radius of the electrode is much larger than the electrode gap and the moment distributions are uniform along the radial direction. The models are based on the first three moments of the Boltzmann equation and Poisson’s equation. Radio frequency (rf) glow discharge simulations from those two fluid models are presented and compared in this study. The comparisons are presented in terms of plasma density, electric field, mean energy, and ionization rate. Results of the 1D fluid model are close to those at the center of the reactor from the 2D simulations. Nonuniform profiles along the radial direction are obtained from the 2D simulations due to the radial dynamics. Higher electron mean energy in the middle region of the radial sheath is observed. The maximum ionization rate is located in the radial sheath region and agrees with the experimental observation.
Photoreflectance studies of lattice-matched and strained InGaAs/InAlAs single quantum wells
Authors: Monéger S. , Baltagi Y. , Benyattou T. , Tabata A. , Ragot B. , Guillot G. , Georgakilas A. , Zekentes K. , Halkias G.
Published: July 2002

Lattice-matched and strained InxGa1−xAs/In0.52Al0.48As single quantum wells with x=0.53 and x=0.60 have been studied by the optical modulation technique of photoreflectance (PR) at room temperature. The measurements have allowed the observation of interband transitions from the heavy- and light-hole valence subbands to the conduction subbands. The PR data have been adjusted with a least-squares fit to the first-derivative functional form. The energetic positions of the optical transitions deduced from the fit have been compared with theoretical values obtained by an envelope function model calculation including strain effects. The best adjustment allowed the determination of the conduction-band offset parameter Qc which is found equal to 0.71±0.07 for the lattice-matched and strained compositions.
Effect of polymer matrices on charge transport in molecularly doped polymers
Authors: Hirao A. , Nishizawa H. , Sugiuchi M.
Published: July 2002

Hole mobilities have been measured in diethylamino-benzaldehyde-diphenylhydrazone (DEH)-doped polymers as a function of the polymer composition, temperature, and electric field. It was found that the electric field dependence on the mobility was a strong function of the binder polymer employed. In all cases, the electric field dependence E can be described as exp(βE1/2T−1). β2 is related to the density of photoinduced spins in the molecularly doped polymers, which are related to the interaction between DEH and the polymer.
Interfacial reactions on annealing Cu/Al multilayer thin films
Authors: Jiang H. G. , Dai J. Y. , Tong H. Y. , Ding B. Z. , Song Q. H. , Hu Z. Q.
Published: July 2002

Thin film reactions of Cu/Al multilayer films were investigated by differential scanning calorimetry and transmission electron microscopy. Sequential intermetallic compound formation was found in the temperature range from 300 to 620 K. With excess copper present in the as-deposited trilayer and multilayer films, the observed sequence was CuAl2 and Cu9Al4, and the interfacial reactions were controlled by interfacial and grain boundary diffusion. The activation energies for the formation of CuAl2 and Cu9Al4 are 0.78±0.11 and 0.83±0.2 eV, respectively.
Micromagnetics of GMR spin-valve heads
Authors: Yuan Samuel W. , Bertram H. Neal
Published: July 2002

Three-dimensional micromagnetic modeling of shielded giant magnetoresistive heads with a spin-valve sensor is presented. If the pinning field from the exchange layer is not large enough, partial unsaturation of the pinned layer occurs upon excitation from the medium, which may cause down-track output noise. Increasing the pinning strength diminishes the playback instability, however, a larger sensor height is then desirable for the ease of proper biasing, but at the expense of on-track signal level. The free layer magnetization is nominally horizontal, reducing off-track asymmetry compared to heads with smaller sensor height.
Micromagnetic computation for wall and Bloch line coercivity in thin films with perpendicular anisotropy
Authors: Asada H. , Matsuyama K. , Gamachi M. , Taniguchi K.
Published: July 2002

Wall and vertical Bloch line (VBL) coercivity arising from spatial nonuniformity in the material parameters has been investigated for a typical 5-μm bubble garnet film by means of a two-dimensional micromagnetic computation. Two-dimensional sinusoidal modulations in the magnitude of the uniaxial anisotropy were assumed as a model for a compositional nonuniformity. Nonuniformities with a spatial wavelength comparable to the wall width were found to exert the largest pinning effect. The typical computed value for the wall and VBL coercivity were 0.7 and 2.2 Oe, respectively, where 10% variation and wavelength of 0.47 μm were assumed. The tendency, that the VBL coercivity is larger than that for the domain wall, agrees with the experimental results reported previously. The wall and VBL coercivity caused by a nonuniform exchange constant have also been computed and compared to the analytical solutions due to the step-like variation of wall and VBL energies, respectively. The larger VBL coercivity compared to that for the wall was observed for a local modulation with the size less than wall width and period more than 1 μm.
Behavior of a rectifying junction at the interface between porous silicon and its substrate
Authors: Pulsford N. J. , Rikken G. L. J. A. , Kessener Y. A. R. R. , Lous E. J. , Venhuizen A. H. J.
Published: July 2002

The current injection into metal/porous Si/bulk Si diodes is investigated by transport and photoresponse measurements. Under low forward bias, the diode current is determined by the space charge region at the porous Si/bulk Si interface. The activation energy of the photovoltage shows that holes are injected into porous Si states which have little quantum confinement. This is discussed in terms of the confinement model for porous Si photoluminescence.
Elastic stress relaxation in SiGe epilayers on patterned Si substrates
Authors: Fischer A. , Richter H.
Published: July 2002

A two-dimensional analysis of the in-plane misfit stress and its elastic relaxation in rectangular patterned heteroepitaxial SiGe/Si multilayer structures on Si substrate is presented. Based on the model of relaxing film stress the distribution of the misfit stress versus distance from the free surface of a multilayered mesa edge is calculated. By superposition of the isolated stress fields of the mesa edges, the biaxial misfit stress distribution in a finite heteroepitaxial thin-film structure on thick substrate is obtained. The formalism developed permits the determination of the variation of misfit stress values as a function of material and size characteristics of the patterned multilayer-substrate system. An elementary application of the theoretical analysis of the biaxial state of stress existing in the structured layer system is discussed briefly.
Stress relaxation in laterally small strained semiconductor epilayers
Authors: Van Mieghem P. , Jain S. C. , Nijs J. , Van Overstraeten R.
Published: July 2002

The stress field in laterally small strained semiconductor epilayers has been studied by the finite element method. The reaction of the epilayer on the substrate and the bulging-out effect caused by shear forces in the side wall boundaries play an important role. Analytical approximate methods are shown to be deficient. The normal stresses relax faster than a simple exponential with height z and virtually complete relaxation occurs at a height heff≊ √ab/2 (where a and b are the width and length, respectively, of the parallellopipidial epilayer) which is in good agreement with recent experiments. An equivalent lattice spacing fm as a function of z/√ab is defined and calculated.
Lower critical field and surface barrier in sintered Bi2Sr2CaCu2O8+δ superconductor
Authors: Chen D.-X. , Hernando A. , Conde F. , Ramírez J. , González-Calbet J. M. , Vallet M.
Published: July 2002

The saturated magnetization curves of a sintered Bi2Sr2CaCu2O8+δ superconductor are measured at different temperatures below Tc. The data are fitted by an extended critical-state model, so that the lower critical field, Hc1, and the first field for vortex entry, H1, are obtained. With decreasing temperature, Hc1 increases almost linearly whereas H1≳Hc1 below 50 K. Above 50 K, Bean–Livingston surface barriers disappear and the M(H) curves show anomalies that suggest that the critical-state model is not valid.
Positive charge and interface state generation in a thin gate oxide (30 nm) metal-oxide-semiconductor capacitor
Authors: El-Hdiy Abdelillah
Published: July 2002

The study of the positive oxide charge and the interface state creation in aluminium gate metal-oxide-silicon capacitors subjected to Fowler–Nordheim electron injection from the aluminium gate is performed. Band-gap ionization and emission of trapped electrons from initially neutral traps seem unlikely in these samples. The positive charge formation is linked to the relaxed hydrogen related species. Interface states are directly created by hot electrons, and by the conversion of a few holes to interface states during a warm-up to room temperature. But these interface states are especially due to the relaxation of the atomic or molecular hydrogen.
Numerical modeling of the optical properties of hydrogenated amorphous-silicon-based p-i-n solar cells deposited on rough transparent conducting oxide substrates
Authors: Leblanc F. , Perrin J. , Schmitt J.
Published: July 2002

Hydrogenated amorphous-silicon (a-Si:H) -based solar cells consist of two electrodes and a p-i-n structure, deposited on glass substrates. Depositing the p-i-n layers and the back metallic electrode on an optically rough transparent conducting oxide (TCO) electrode enhances the absorption of the incident light in the active i layer: Light is scattered at the rough front interface and is partially trapped in the high refraction index layer, as in a waveguide. In addition TCO roughness increases the front transmission coefficient, increasing the amount of light in the active layer. TCO texture yields a relative increase of the conversion efficiency up to 30%. A semiempirical model of thin-film solar-cell optics is presented, taking into account the interface roughness by introducing experimentally derived scattering coefficients and treating the propagation of specular light in a rigorous way. Numerically simulated spectral response and total reflectance of standard solar cells deposited on different TCO textures are compared to experimental data. The results show a better fit to measured characteristics than simulations obtained by previous semiempirical modeling. Improvements mainly come from the light propagation calculation. According to the model, the number of passes incident light may make through the active i layer reaches six for the most efficient cell. As an example of the model’s main application, the enhancement of the conversion efficiency that would be expected from an optimized TCO layer is calculated for each texture studied and for different back metallizations.
Anisotropy of the magnetic and magnetooptic properties of HoIG:Al single crystals (low and high magnetic field)
Authors: Ostoréro J. , Guillot M.
Published: July 2002

Magnetization and Faraday rotation measurements at 1152 nm have been performed on Ho3Fe5−zAlzO12 (z=0.45) single crystals as a function of temperature and magnetic field oriented along the 3 crystallographic axes [100], [110], and [111] in both experiments. A strong anisotropy is observed at low temperature (T<100 K), although the Faraday susceptibility remains anisotropic until Tcomp=185 K. High field magnetization measurements (H up to 200 kOe) show that the FR anisotropy is mainly of magnetic origin. The results are interpreted on the basis of the Dionne-refined Néel model of ferrimagnetic garnets using a field dependent canting angle.
Magnetic properties of an Fe/Cu granular multilayer
Authors: Rubinstein Mark , Tejada J. , Zhang X. X.
Published: July 2002

A Cu/Fe granular film, formed from a multilayer film and composed of particles of Fe imbedded in Cu, has had several of its important properties investigated. Measurements include ferromagentic resonance, magnetoresistance, Mössbauer effect, magnetic viscosity, and magnetization. The two-phase behavior of these immiscible alloy systems, and the effect of multilayering on the shape of the magnetic precipitates, can explain some of these properties. An explanation of the ferromagnetic resonance line shape is proffered. An extraordinary macroscopic quantum tunneling effect is found to govern the magnetic relaxation at the lowest temperatures.
Origin of n-type conductivity of low-temperature grown InP
Authors: Chen W. M. , Dreszer P. , Prasad A. , Kurpiewski A. , Walukiewicz W. , Weber E. R. , Sörman E. , Monemar B. , Liang B. W. , Tu C. W.
Published: July 2002

It is shown with correlated magnetic resonance and electrical measurements that the PIn antisite is the prevailing defect in InP grown by molecular-beam epitaxy at low temperature. The first ionization level of the PIn antisite is resonant with the conduction band, which makes the material n-type conducting due to autoionization of the PIn antisite.
Interfacial characterization of ion-beam-deposited a-C films on Ge
Authors: Bruce T. , Bello I. , Huang L. J. , Lau W. M. , High M. , Strnad V. , Panchhi P.
Published: July 2002

Diamondlike carbon films were deposited on germanium crystals with a mass-separated C+ ion beam in ultrahigh vacuum over the energy range 20–275 eV, and the interfaces were characterized with x-ray photoelectron spectroscopy. It was found that ion bombardment induced a carbide phase on the germanium surface. Further carbon accumulation then led to the growth of an amorphous carbon overlayer. The carbide phase was identified by a rather low C 1s binding energy (at about 283.8 eV) and small positive shift of the Ge 3p peak (about 0.4 eV). The valence-band spectra of these samples also suggested that germanium carbide formed with a pure carbon beam for the bombardment energy range considered has a band gap between germanium and diamondlike carbon.
Local structure and bonding states in a-Si1−xCx:H
Authors: van Swaaij R. A. C. M. M. , Berntsen A. J. M. , van Sark W. G. J. H. M. , Herremans H. , Bezemer J. , van der Weg W. F.
Published: July 2002

Infrared spectra of a-Si1−xCx:H deposited in a glow discharge of a silane/methane mixture have been measured. Comparison with elastic recoil detection and Rutherford backscattering spectrometry shows that the mean number of hydrogen atoms attached to silicon per silicon atom ([HSi]/[Si]) increases with higher carbon content and that more Si—H2 bonding configurations are formed. Hydrogen is preferentially bonded in (Si—H2)n clusters, which partly explains the observed apparent shift of the Si—H stretching mode to higher energy. The remaining contribution to this shift is believed to result from Si—H on surfaces of voids instead of an inductive effect. From composition measurements we observe that for each carbon atom, three hydrogen atoms are incorporated in the material, suggesting that during deposition carbon is initially incorporated in CH3 groups. However, the mean number of C—H bonds per carbon atom decreases from about 2.2±0.4 to 1.4±0.3 with increasing carbon content, indicating that the majority of the carbon atoms is two- or threefold coordinated to silicon.
Low-energy electron transport in alkali halides
Authors: Akkerman A. , Boutboul T. , Breskin A. , Chechik R. , Gibrekhterman A.
Published: July 2002

A model of electron transport in alkali halides, below 10 eV, is described. It is based on theoretically calculated microscopic cross sections of electron interactions with lattice phonons. Both acoustic and optical scatterings are taken into account, the former being also treated as a quasielastic process that randomizes the electron motion. Monte Carlo calculations based on the model simulate the UV-induced photoelectron emission from CsI. The calculated quantum efficiency and energy spectra are in good agreement with experimental data, in the photon energy range of 6.3–8.6 eV. The probability for an electron to escape from CsI, NaCl, and KCl is provided as a function of its energy and creation depth. A comparison is made between our approach and other phenomenological models.
Precipitation and relaxation in strained Si1−yCy/Si heterostructures
Authors: Strane J. W. , Stein H. J. , Lee S. R. , Picraux S. T. , Watanabe J. K. , Mayer J. W.
Published: July 2002

We have studied the thermal stability of Si1−yCy/Si (y=0.007 and 0.014) heterostructures formed by solid phase epitaxial regrowth of C implanted layers. The loss of substitutional C was monitored over a temperature range of 810–925 °C using Fourier transform infrared absorbance spectroscopy. Concurrent strain measurements were performed using rocking curve x-ray diffraction to correlate strain relaxation with the loss of substitutional C from the lattice. Loss of C from the lattice was initiated immediately without an incubation period, indicative of a low barrier to C clustering. The activation energy as calculated from a time to 50% completion analysis (3.3±5 eV) is near the activation energy for the diffusion of C in Si. Over the entire temperature range studied, annealing to complete loss of substitutional C resulted in the precipitation of C into β-SiC. The precipitates are nearly spherical with diameters of 2–4 nm. These precipitates have the same crystallographic orientation as the Si matrix but the interfaces between the Si and β-SiC precipitates are incoherent. During the initial stages of precipitation, however, C-rich clusters form which maintain coherency with the Si matrix so the biaxial strain in the heterostructure is partially retained.
Identification of defects and impurities in chemical-vapor-deposited diamond through infrared spectroscopy
Authors: McNamara K. M. , Williams B. E. , Gleason K. K. , Scruggs B. E.
Published: July 2002

Hydrogen-, oxygen-, and nitrogen-related defects in chemical-vapor-deposited (CVD) diamond have been observed by infrared spectroscopy and found to affect optical absorptions in spectral regions of commercial interest. The origin of absorptions in the infrared spectrum at 2820 and 2833 cm−1, which have been observed previously without being understood, have been assigned. The presence of these absorptions and the evidence of oxygen and nitrogen incorporation in CVD diamond have important implications for both the design of CVD diamond growth systems and the design of processes involving oxygen addition. In films which contain high hydrogen concentrations (≳0.2 at. %), some evidence has been found indicating the presence of a hydrogen environment, not present in films with lower hydrogen contents, which may be related to sp2-bonded carbon.