bluuebunny/crossref_metadata_2025 huggingface dataset:
The formation of hydrogen passivated silicon single-crystal surfaces using ultraviolet cleaning and HF etching
Authors: Takahagi T. , Nagai I. , Ishitani A. , Kuroda H. , Nagasawa Y.
Published: July 2002

We have tried to develop a new procedure to prepare the clean surface of a silicon single crystal. We successfully prepared the contamination free bare silicon surface with ultraviolet cleaning followed by HF dipping with low concentration HF obtained by dilution by organic free ultrapure water, at room temperature under the atmospheric condition. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and ultraviolet photoelectron spectroscopy measurements proved thus prepared surface has a hydrogen monoatomic layer terminating the dangling bonds of silicon. The hydrogen termination was found to have remarkable passivation effect against surface oxidation reaction. A silicon thin-film epitaxially grown on the prepared surface was confirmed to have perfect crystal structure and high-purity level by scanning electron microscopy, reflection high-energy electron diffraction, Raman spectroscopy and secondary ion mass spectroscopy.
A simplified method for quantum size effect analysis in submicron devices
Authors: Lui Wayne W. , Frey Jeffrey
Published: July 2002

The Wigner-transformed Bloch equation is used to analyze the quantum size effects which occur in very small semiconductor devices. In this approach, instead of solving the Schrödinger equation, the diagonal elements of the density matrix are calculated directly. As a result, the eigenvalue problem is avoided, thereby greatly reducing computation time. A simple algorithm suitable for two-dimensional device simulation including quantum size effects is also developed.
Breakdown phenomena of gas-insulated gaps with nanosecond pulses
Authors: Kawada Yukimitsu , Hosokawa Tatsuzo
Published: July 2002

Breakdown phenomena of gas-insulated gaps with nanosecond pulses were examined under the spot illumination of the ultraviolet rays on the cathode surface in the atmospheric gases such as air, N2, and O2. Our investigation reveals that the 50% probability of flashover voltage obtained under the spot illumination of the ultraviolet rays shows very close values under the entire illumination on the cathode surface, and the observed time lag of flashover may be explained by the conventional avalanche-to-streamer development theory.
Transition from amorphous to crystal growth of boron films in plasma-enhanced chemical vapor deposition with B2H6+He
Authors: Komatsu Shojiro , Moriyoshi Yusuke
Published: July 2002

A temperature-dependent transition from amorphous to crystal growth was found to accompany a change in its apparent activation energy in plasma-enhanced chemical vapor deposition of boron films made from B2H6+He at substrate temperatures (Ts) of 923–1163 K and a pressure of 200 Pa. The transition temperatures (Tc) as well as the activation energies (ΔE1 and ΔE2 at higher and lower Ts, respectively) were found to depend on the plasma power. The Tc (K), ΔE1 (kcal/mol), and ΔE2 (kcal/mol) are 1018, 7.5, and −3.6 for 600 W, 1074, 20, and −2.7 for 800 W, and 1003, 4.2, and −2.0 for 1 kW, respectively.
Model for infrared absorption and transmission of liquid-phase epitaxy HgCdTe
Authors: Hougen C. A.
Published: July 2002

Infrared absorption and transmission in n-type Hg-melt liquid-phase epitaxial Hg1−x CdxTe is modeled using empirical expressions for the absorption coefficient. It is shown that the composition profile and photoconductive relative response can be predicted using room-temperature transmission data alone. This model, having a total of four independent variable parameters, takes into account composition profile, detector thickness, surface nonuniformities, and detector-back reflections. Unlike previous techniques used to predict the relative-response cutoff, this model does not arbitrarily define an energy gap.
Chemical and structural characterization of physical-vapor deposited CuInSe2 for solar cell applications
Authors: Tseng B.-H. , Rockett A. , Lommasson T. C. , Yang L. C. , Wert C. A. , Thornton J. A.
Published: July 2002

This paper reports the results of a comparative study of chalcopyrite-structure CuInSe2 deposited by three techniques, three-source evaporation, reactive sputtering and a hybrid sputtering, and evaporation method. All films exhibit comparable microstructures and microchemistries. Evaporated and hybrid-process films include significant porosity. All layers show dislocations, twins, and stacking faults. No second phases were observed in layers deposited by any of the techniques, independent of film composition. Data supporting this conclusion include average and single-grain energy-dispersive x-ray fluorescence spectroscopy measurements, diffraction studies of the film structure, and transmission electron microscopy images of the films. Finally, grain sizes can be increased by annealing films at temperatures above 400 °C.
1/f noise in double-heterojunction AlGaAs/GaAs laser diodes on GaAs and on Si substrates
Authors: Fang R. Z. , van Rheenen A. D. , van der Ziel A. , Young A. C. , van der Ziel J. P.
Published: July 2002

Low-frequency electrical current noise measurements are reported on double-heterojunction AlGaAs/GaAs laser diodes fabricated on GaAs and on Si substrates. The noise spectra show a frequency dependence proportional with f−γ with γ close to unity. The spectral intensity is proportional to the current for smaller currents (<0.1 mA) and levels off at larger currents (>1 mA). The diodes built on the GaAs substrate are 50 times less noisy than the ones built on the Si substrate. This effect is attributed to the fact that the density of dislocations at the Si interface is much larger than at the GaAs substrate/device interface.
Optimization of annealing parameters for the growth of epitaxial Ba2YCu3O7−x films on LaAlO3(100)
Authors: Siegal Michael P. , Phillips Julia M. , van Dover R. B. , Tiefel T. H. , Marshall J. H.
Published: July 2002

The superconducting and structural properties of Ba2YCu3O7−x (BYCO) films on LaAlO3(100) substrates can be improved by carefully optimizing the post-deposition annealing parameters. Films are grown by co-deposition of BaF2, Y, and Cu in the correct stoichiometric ratio to within 1% of 2:1:3. Annealing parameters in an ex situ furnace, including the ambient, annealing temperature, oxidation temperature, and duration of anneals are systematically studied. Films are characterized for epitaxial quality (χmin), morphology, critical temperature (Tc), sharpness of the superconducting transition (ΔT), and critical current density (Jc). For example, beyond simply dissociating BaF2, the use of wet O2 appears to prevent the agglomeration of oxides during the initial heating process, and then act to thermodynamically stabilize the basic BYCO film structure at high temperatures after being formed. Comparisons are made with the best single-crystal BYCO structural and electrical data available. The optimized films have relatively smooth morphology with χmin<3%, Tc>90 K, ΔT<0.5 K, and Jc>106 A/cm2 in essentially zero magnetic field at 77 K.
Pressure and frequency dependence of ion bombardment energy distributions from rf discharges
Authors: Toups M. F. , Ernie D. W.
Published: July 2002

Experimental measurements of the energy distribution and flux of ions bombarding an electrode of a parallel-plate rf reactor were performed in argon, neon, and a 95% helium-5% argon mixture using a hemispherical retarding grid energy analyzer. Quadrupole mass analysis was performed to identify the ions which were bombarding the electrode. Frequencies from 2.5 to 20 MHz and pressures from 0.025 to 1.6 Torr were studied. For a given amplitude of the applied rf potential, the ratio of the frequency of the applied rf potential to the reactor gas pressure was found to be the critical parameter in determining the shape of the measured ion bombardment energy distributions. The total ion flux to the electrode surface was found to be proportional to the square of the frequency and insensitive to the reactor gas pressure, for a fixed amplitude of the applied rf potential. These results are discussed with reference to the physics of rf gas discharges.
X-ray transmission calculations for an aluminum plasma
Authors: Abdallah Joseph , Clark Robert E. H.
Published: July 2002

Computer programs developed recently at Los Alamos have been used to calculate the transmission of x rays through an aluminum plasma. Theoretical energy levels, oscillator strengths, and photoionization cross sections were combined with the local thermodynamic equilibrium population model to calculate the plasma absorption coefficient as a function of photon energy. The transmission spectrum is simulated by accounting for the plasma depth and spectrometer characteristics. These results are compared to spectra observed during recent experiments; excellent agreement is obtained.
Random telegraph signals and low-frequency voltage noise in Y-Ba-Cu-O thin films
Authors: Jung G. , Vitale S. , Konopka J. , Bonaldi M.
Published: July 2002

Excess low-frequency noise extending to MHz frequencies was observed in dc current biased granular high-Tc thin films. At particular bias conditions random telegraph signal produced by a single, fast two-level fluctuator dominated the noise properties of the sample. Lifetimes of the low- and high-voltage states of the fluctuating system were found to be exponentially distributed. Power spectra of the excess noise signal could be well fitted with a single Lorentzian contribution. Duty cycle dependence of the random telegraph signal on bias conditions was used to get an insight into physical mechanism causing the fluctuations. Charge trapping events in the intergranular intrinsic Josephson junctions and trapped flux hopping were identified as possible alternative sources of the observed noise.
Theoretical calculation of exciton optical-absorption intensity in III-V and II-VI semiconductor quantum wells
Authors: Sugawara Mitsuru
Published: July 2002

The integrated intensity of the optical-absorption spectrum of ground-state electron-heavy-hole exciton resonances in III-V and II-VI semiconductor quantum wells is calculated based on an effective-mass approximation. The intensity increased significantly with the band gap of the well materials, primarily due to the shrinkage of the two-dimensional exciton radius. This result shows the high potential of wide-gap II-VI semiconductor quantum wells for optoelectronic devices.
Magnetic-field effects on vacuum insulator flashover
Authors: Lehr M. , Korzekwa R. , Krompholz H. , Kristiansen M.
Published: July 2002

The influence of magnetic fields (both dc and pulsed) on dielectric surface breakdown in vacuum and simulated low-earth-orbit conditions has been investigated using pulsed test voltages. Predictions from the saturated secondary electron emission avalanche breakdown model and the experimental results both show magnetic insulation effects (i.e., an increase in flashover voltage) at magnetic-field amplitudes as low as 0.1 T. The most favorable configuration for magnetic insulation is with the magnetic field oriented parallel to the insulator surface and perpendicular to the electric field. An increase in flashover voltage with increasing magnetic field is seen when the vector E×B points away from the surface, while a decrease followed by an increase in flashover voltage is seen for E×B into the surface. The magnitude of the insulation effect depends on the dielectric material, ambient pressure, surface roughness, and the presence of background plasma. Predictions from single-particle computer simulations of the secondary electron avalanche process, using nonuniform fields, point to the importance of conditions at the cathode in producing magnetic insulation effects. It was found that it is sufficient to apply the magnetic field in the cathode region only, and that significant magnetic insulation effects can be observed using small, lightweight permanent magnets. An applied magnetic field will also increase the flashover voltage in a low-density (ne ≊ 104 cm−3) plasma environment. The dependence of the flashover voltage on electrode separation (gap distance) is observed to remain sublinear with the application of an insulating magnetic field. Prebreakdown luminance measurements are presented which further support the saturated secondary electron emission avalanche model.
Current response in semiconductor heterostructures within the independent-electron picture
Authors: Pötz W.
Published: July 2002

The principle of maximum entropy is used to construct carrier distribution functions for dc transport simulations of tunneling structures within the independent particle picture. The external circuit is introduced via macroscopic constraints which are implemented into the density operator by the principle of maximum entropy. Application to (resonant) tunneling structures is presented.
Calculation of impact ionization coefficients with a third-order Legendre polynomial expansion of the distribution function
Authors: Wang Shiuh-Luen , Goldsman Neil , Hennacy Kenneth
Published: July 2002

Values for impact ionization coefficients are calculated from the electron momentum distribution function. The distribution function is found by solving the Boltzmann transport equation. The solution is obtained by combining a third-order Legendre polynomial expansion with numerical methods which employ finite differences and sparse-matrix algebra. The calculated values for impact ionization agree with experiment and Monte Carlo simulations. Results obtained while using three versus two Legendre polynomials are compared. Calculations performed using three Legendre polynomials predict one half the impact ionization rate given by similar calculations using only two polynomials. Calculations predict that phonon scattering plays a much more significant role in carrier transport than does impact ionization.
Analytical formulation of ionization source term for discharge models in argon, helium, nitrogen, and silane
Authors: Pérès I. , Ouadoudi N. , Pitchford L. C. , Boeuf J. P.
Published: July 2002

Simple analytical representations of the ionization source terms in argon, helium, nitrogen, and silane dc glow discharges for steady-state and quasisteady-state conditions are presented. These analytical forms express well the highly nonequilibrium nature of the ionization in the cathode fall and negative glow regions which cannot be described by a Townsend ionization coefficient depending on the local value of the reduced electric field. These source terms can be easily incorporated into fluid models of gas discharges.
Deposition and analysis of lithium niobate and other lithium niobium oxides by rf magnetron sputtering
Authors: Rost Timothy A. , Lin He , Rabson Thomas A. , Baumann Robert C. , Callahan Daniel L.
Published: July 2002

The deposition of thin films of lithium niobate (LiNbO3) on silicon with rf magnetron sputtering has been investigated. A matrix of experiments was designed to determine the effect of several parameters on the resulting film quality. Under optimized conditions, oriented polycrystalline films of LiNbO3 are produced that exhibit a columnar grain structure with the polar axis normal to the substrate surface. Deviations from sputtering parameters optimized for producing LiNbO3, have been shown to produce films of varying proportions of either LiNb3O8 or Li3NbO4 with LiNbO3. The stoichiometry, microstructure, and electrical properties of selected films have been investigated with Rutherford backscattering, diffractometry, transmission electron microscopy, and a variety of electrical measurement techniques.
A model for spin-wave auto-oscillations in finite-size magnetic samples
Authors: Cherepanov V. B. , Slavin A. N.
Published: July 2002

A theory of collective oscillations in a system of spin waves parametrically excited by homogeneous parallel pumping in a finite-size ferromagnetic sample is developed. This theory is an extension of the well-known S theory of spin-wave collective oscillations in an infinite ferromagnetic medium for the case when the boundary conditions in a magnetic sample of finite size D are taken into account. We explain the following experimentally observed properties of spin-wave auto-oscillations that were not explained by the existing models of this phenomenon. (i) The difference between the threshold of parametric excitation of spin waves hth and the threshold of auto-oscillations hosc. (ii) The finite value of the auto-oscillation frequency fosc at the threshold of auto-oscillations. (iii) The dependences of the threshold hosc and the frequency fosc of the spin-wave auto-oscillations on the size of the ferromagnetic sample. The results of the theory are in a good qualitative agreement with experimental results.
A neutron scattering study of the quasi-one-dimensional, dilute Ising-like antiferromagnet CsCo0.83Mg0.17Br3
Authors: Rogge R. B. , Yang Y. S. , Tun Z. , Gaulin B. D. , Fernandez-Baca J. A. , Nicklow R. M. , Harrison A.
Published: July 2002

Neutron scattering measurements have been performed on a single-crystal sample of CsCo0.83Mg0.17Br3, a quasi-one-dimensional, Ising-like antiferromagnet. Residual three- dimensional interactions between the dilute magnetic chains precipitate a phase transition to long-range order at TN∼9.0 K, and short-range correlations persist as high as 40 K. Relatively high-energy inelastic scattering from both ‘‘bulk’’ spin-wave modes and ‘‘end’’ modes is observed from the finite chains. The low-energy inelastic spectrum is dominated by soliton scattering due to antiphase domain walls propagating along the finite chains.
Molecular beam epitaxial growth and evaluation of intrinsic and extrinsically doped Hg0.8Cd0.2Te on (100) Cd0.96Zn0.04Te
Authors: He L. , Becker C. R. , Bicknell-Tassius R. N. , Scholl S. , Landwehr G.
Published: July 2002

The structural and electrical properties of (100) Hg1−xCdxTe epilayers grown by molecular beam epitaxy have been systematically investigated for different Hg/Te flux ratios. The hillock density, electron concentration and the electron mobility depend strongly on the Hg/Te flux ratio. A minimum in the hillock density correlates well with the highest mobilities and the lowest concentrations. As is well known electrical properties are strongly influenced by structural defects. Structural defects such as twins and defects due to nonstoichiometry can be largely reduced by optimizing the Hg/Te flux ratio. It is shown that an optimum Hg/Te flux ratio exists within a narrow range between 270 and 360 at the growth temperature of 180 °C, in contrast with the larger range of the Hg/Te flux ratio over which single crystalline growth could be maintained. The difficulties encountered in the x value determination from normal transmission curves, i.e., from E0(x), due to the Burstein–Moss shift are discussed. In order to overcome these difficulties, the x values of the Hg1−xCdxTe epilayers were also determined from E1(x). A calibration of E1(x) resulted in small but significant discrepancies with the literature. Extrinsic As doping using the δ doping technique is demonstrated and a very high atomic sheet density of 1.2×1013 cm−2 is obtained.
Theoretical studies of pulsed photothermal phenomena in semiconductors
Authors: Cheng Jian-chun , Zhang Shu-yi
Published: July 2002

This paper presents a thorough theoretical study of pulsed photothermal phenomena in semiconductors. The explicit expressions of the temporal distributions of plasma wave, thermal wave, and displacement field within a finite semiconductor sample, excited by an incidence of the pulsed laser, are derived analytically. We simulate numerically the time evolutions of the pulsed photothermal optical reflectance, the pulsed photothermal optical beam deflection (i.e., Mirage effect), and the pulsed photothermal displacement signals for different characterized parameters of semiconductor samples. The theoretical works are significant to provide a quantitative time- and space-resolved study of dynamic deexcitation processes and characterization of parameters of semiconductor samples under normal experimental conditions by the pulsed photothermal techniques.
Electron transport across a wide AlGaAs barrier
Authors: Daniels M. E. , Bishop P. J. , Jensen K. O. , Ridley B. K. , Ritchie D. A. , Grimshaw M. , Linfield E. H. , Jones G. A. C. , Smith G. W.
Published: July 2002

An experimental and theoretical study has been made of electron transport over a wide AlGaAs barrier with graded interfaces sandwiched between GaAs contact layers. The width of the central barrier region was varied between 700 and 2100 Å. Two series of samples with nominally identical structures but from different sources were investigated. Extensive measurements of both the voltage and temperature dependence of the current were made, as well as measurements of capacitance and magnetoresistance. Drift-diffusion thermionic emission theory has been used to interpret the data. Both numerical and analytical solutions of the model have been developed and were found to be in good agreement with each other. The presence of space charge in the barrier region, which has the effect of increasing the barrier height, was seen to be crucial to an understanding of the data. When the effect of space charge was included in the model good agreement was obtained between theory and experiment for electric fields up to 10 kV cm−1. The numerical solution required only one adjustable parameter, namely the value of the space-charge density. The parameters used in the analytical model were all derived from the experimental data.
Suppression of intersubband nonradiative transitions by a magnetic field in quantum well laser devices
Authors: Blank Alexander , Feng Shechao
Published: July 2002

It is suggested that a perpendicular magnetic field can strongly suppress the most important nonradiative intersubband transition processes, namely Auger recombination and optical phonon transitions, in an intersubband infrared laser device that has recently been proposed using multiple quantum wells. The present analysis suggests that the fabrication of such a novel laser device is quite realistic using present III-V technologies.
The achievement of near-theoretical-minimum contact resistance to InP
Authors: Fatemi Navid S. , Weizer Victor G.
Published: July 2002

We have investigated the electrical and metallurgical behavior of the InP/Au/Ni contact system. We show that when a layer of Au, 100 Å or more in thickness, is introduced between n-InP and Ni contact metallization, specific contact resistivity Rc values in the low 10−8 Ω cm2 range are achieved after sintering. It is suggested that these ultralow values of Rc are due to the presence, at the metal-InP interface, of a Ni3P layer combined with a stoichiometry change in the InP surface. We show, in addition, that it is possible to achieve very low Rc values with this system without incurring device destroying sinter-induced metallurgical interdiffusion.
Validity of actinometry to monitor oxygen atom concentration in microwave discharges created by surface wave in O2-N2 mixtures
Authors: Granier A. , Chéreau D. , Henda K. , Safari R. , Leprince P.
Published: July 2002

The validity of actinometry to monitor oxygen atom concentration in O2-N2 microwave discharges created by surface wave is investigated. The plasma is created with a gas flow in a quartz tube of inner diameter 16 mm at pressures in the Torr range. First, it is shown that the reliability of actinometry can be deduced from the longitudinal profile of the actinometry signal. Second, absolute concentrations of oxygen atoms are estimated from the experimental actinometry signal and agree satisfactorily with concentrations simultaneously measured by vacuum ultraviolet (VUV) absorption downstream from the plasma. Moreover, upon varying the nitrogen percentage (0%–100%), it is evidenced that the actinometry signal is proportional to the concentration measured by VUV absorption. Furthermore, it is evidenced that the oxygen dissociation rate is only 2% in pure oxygen plasmas, while it reaches 15% (433 MHz) or 30% (2450 MHz) for mixtures containing more than 20% of nitrogen. This drastic increase in [O] upon the addition of N2 is extensively discussed and, finally, attributed to a decrease in the recombination frequency of oxygen atoms on the quartz wall, in the presence of nitrogen.
Mechanism of leakage current through the nanoscale SiO2 layer
Authors: Nagano Seido , Tsukiji Masaru , Ando Koichi , Hasegawa Eiji , Ishitani Akihiko
Published: July 2002

We clarify the mechanism of leakage current through the nanoscale ultrathin silicon dioxide (SiO2) layer in a metal-insulator-semiconductor structure based on the multiple scattering theory when technologically important phosphorus doped polycrystalline silicon is adopted as the gate electrode. We also derive an analytic expression for the direct tunneling current, and show that its measurement presents an excellent opportunity to determine the effective mass of an electron in the SiO2.
Physical characterization of ultrathin anodic silicon oxide films
Authors: Clark K. B. , Bardwell J. A. , Baribeau J.-M.
Published: July 2002

Ultrathin oxides formed on p-type (100) Si using anodic oxidation in dilute aqueous NH4OH solution have been characterized by Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS), and x-ray reflectometry. The aim of the work was to optimize the growth and annealing conditions for fabrication of ultrathin gate oxides. Two alternate growth conditions (potentiostatic and galvanostatic) could be used to grow oxides of thickness between 3 and 16 nm. There was very little difference between the two types of oxides; however, the FTIR asymmetric stretch maximum νm was at slightly higher frequencies and this band was slightly narrower for potentiostatic oxides compared to galvanostatic oxides of the same thickness. For both types of films, νm increased with film thickness, while the corresponding full width at half-maximum decreased. As-grown ∼11-nm-thick films of both types contain 3.8±0.3% -OH (bound as isolated silanol) and 5.0±0.4% -OH (bound as H2O and/or associated silanol) by mass, and have a density of 2.05±0.03 g cm−3 compared with a density of 2.27±0.03 g cm−3 measured for thermal oxides. Thus, the composition of the as-grown anodic oxides can be written as SiO1.93(OH)0.14⋅0.18H2O. Discounting the H content, this converts to an O/Si ratio of 2.25±0.02, which can be compared to the O/Si ratio of 2.27±0.06 measured for as-grown films by XPS. Potentiostatically grown ∼11-nm-thick films were annealed at temperatures between 300 and 900 °C in forming gas. Two different stages were observed as a function of anneal temperature. At temperatures below 500 °C, water and/or associated silanol was ejected from the films. This resulted in a maximum in the stress and/or disorder in the oxides at anneal temperatures of 500 °C. At temperatures above 500 °C, the remainder of the silanol was removed from the films; some kind of stress relief occurred. The oxides became stoichiometric at temperatures 700 °C and above.
Thermoelastic response of pulsed photothermal deformation of thin plates
Authors: Cheng Jian-chun , Wu Lei , Zhang Shu-yi
Published: July 2002

A theoretical investigation of the dynamic thermoelastic response of pulsed photothermal deformation (PTD) deflection detections for some Q-switch laser pulses and finite thickness samples has been presented. The results show that signals can be characterized by a quasistatic process when the laser pulse rise time is on the order of 1 μs and the sample thickness is in submillimeter range (typically for semiconductor wafers). However, as the pulse rise time decreases or the sample thickness increases, the dynamic wave behavior gradually becomes apparent, and the quasistatic approximation gives only a contour curve of the dynamic time evolution. When the rise time decreases on the order of 10 ns or less for the same kind of the samples, the PTD deflection signal reflects a totally dynamic wave behavior.
Analyses of localized confinement potential in semiconductor strained wires and dots buried in lattice-mismatched materials
Authors: Nishi Kenichi , Yamaguchi A. Atsushi , Ahopelto Jouni , Usui Akira , Sakaki Hiroyuki
Published: July 2002

Analytical and finite-element-method calculations have been conducted for obtaining strain distributions and consequent carrier confinement potential changes in semiconductor strained wires and dots made of lattice-mismatched materials. The inhomogeneous strain distribution modifies the confinement potentials locally, which causes carrier wave function localization. First, to obtain a fundamental strain distribution and band-structure change semiquantitatively, analytical calculations are performed in simple, symmetrical structures such as an InP cylinder and an InP ball buried in GaAs or InGaP matrices assuming isotropic valence bands and isotropic elastic characteristics. Here, strain is found to exist in the surrounding matrices as well as in the wires and dots. This effect is peculiar to the strained wire and dot because in pseudomorphic strained layers there is no strain in surrounding matrices. Thus, the band structures are found to be greatly modified in the surrounding matrix as well as in the wire or dot. Hole effective masses at the band edge are also calculated by diagonalizing a 4×4 orbital strain Hamiltonian. Furthermore, to calculate the effects in a realistic structure, finite-element-method calculations are performed for a triangle-shaped InP wire along the 〈110〉 direction, including anisotropic elastic characteristics. Calculated nonuniform strain within the wire is found to modify the confinement potential, which localizes electrons near the base. Valence subbands are largely split near the vertices. From these results, the strained wires and dots are found to be applicable for quantum wires and dots, in which the quantum confinement effect will be enhanced by the modified confinement potential due to the inhomogeneous strain.
Giant magnetoresistance in spinodally decomposed Cu–Ni–Fe films
Authors: Chen L. H. , Jin S. , Tiefel T. H. , Wu T. C.
Published: July 2002

We report the observation of the GMR effect in spinodally decomposed Cu–20Ni–20Fe thin films. A ΔR/R value as high as 6.5% was observed at room temperature. In contrast to the commonly observed temperature-dependent behavior of ΔR/R increasing at low temperature; thin film shows a decrease in ΔR/R at 4.2 K. The dependence of the GMR effect on various deposition parameters, such as substrate temperature has been studied. The observed giant magnetoresistance behavior in Cu–20Ni–20Fe films is most likely related to the field-induced decrease in electron scattering in a pseudosuperparamagnetic material, as well as the spin-dependent scattering at the two-phase interface and in the ferromagnetic phase.
Simulation of transformations of thin metal films heated by nanosecond laser pulses
Authors: Balandin V. Yu. , Niedrig R. , Bostanjoglo O.
Published: July 2002

The ablation of free-standing thin aluminum films by a nanosecond laser pulse was investigated by time-resolved transmission electron microscopy and numerical simulation. It was established that thin film geometry is particularly suited to furnish information on the mechanism of evaporation and the surface tension of the melt. In the case of aluminum the surface tension σ as function of temperature can be approximated by two linear sections with a coefficient −0.3×10−3 N/K m from the melting point 933 K up to 3000 K and −0.02×10−3 N/K m above 3000 K, respectively, with σ(933 K)=0.9 N/m and σ(8500 K)=0. At lower pulse energies the films disintegrated predominantly by thermocapillary flow. Higher pulse energies produced volume evaporation, and a nonmonotonous flow, explained by recoil from evaporating atoms and thermocapillarity. The familiar equations of energy and motion, which presuppose separate and coherent vapor and liquid phases, were not adequate to describe the ablation of the hottest zone. Surface evaporation seemed to be marginal at all laser pulse energies used.
Oxygen precipitation in silicon
Authors: Borghesi A. , Pivac B. , Sassella A. , Stella A.
Published: July 2002

A review is presented of the recent advances in the study of oxygen precipitation and of the main properties of oxide precipitates in silicon. After a general overview of the system ‘‘oxygen in silicon,’’ the thermodynamics and the kinetics of the precipitate formation are treated in detail, with major emphasis on the phenomenology; subsequently, the most important techniques for the characterization of the precipitates are illustrated together with the most interesting and recent results. Finally, the possible influence of oxygen precipitation on technological applications is stressed, with particular attention to recent results regarding device yield. Actually, the essential novelty of this review rests on the attempt to give an extended picture of what has been recently clarified by means of highly sophisticated diagnostic methods and of the influence of precipitation on the properties of semiconductor devices.
Experimental studies of the fingering phenomena in two dimensions and simulation using a modified invasion percolation model
Authors: Onody R. N. , Posadas A. N. D. , Crestana S.
Published: July 2002

Experiments of water infiltration in a vertical plane through layered soils were carried out in the laboratory. We have followed the fingering dynamics by using image techniques. The fractal theory has been applied to describe the fingering phenomena. We also have simulated a modified site gradient invasion percolation model where most of the physical ingredients relevant to the problem have been incorporated. In contrast to what occurs with the standard gradient invasion percolation model, we have found the formation of many fingers. Taking into account the bond number, the number of fingers, and the wetted area of the experiments, we have fitted the parameters of our model. This opens the possibility of a theoretical prediction of the pore size distribution of the soil. The results are then compared with the experimental data.
Fast positronium formation and dissociation at surfaces
Authors: Gidley D. W. , McKinsey D. N. , Zitzewitz P. W.
Published: July 2002

The origin of short-lived components in the annihilation lifetime spectrum of positronium (Ps) is shown to be due to fast Ps that is collisionally dissociating at the surfaces of the surrounding confinement cavity. The results are consistent with a model of fast (10–100 eV) Ps production by backscattered positrons from the incident beam. It is found that the typical lifetime of dissociating Ps scales with the mean free path of the cavity, and the relative formation intensity depends inversely on the incident positron beam energy. This ubiquitous effect will be present in any Ps formation experiment involving a free surface and can only be eliminated at beam energies less than 10 eV. More practical methods of minimizing the undesirable systematic effects of fast Ps quenching in depth-profiled positron lifetime spectroscopy and in precision Ps decay rate measurements will be discussed.
Theoretical investigation of current-noise characteristics in finite semiconductor superlattice with correlated thickness randomness
Authors: Xiong Shi-Jie
Published: July 2002

Using a transmission probability formalism, we perform theoretical calculations for the current-noise characteristics of a finite semiconductor superlattice with correlated thickness randomness in which the thicknesses of barriers are regular but those of wells are partially random. The transmission probability is calculated by the use of an exact Airy-function formalism combined with a transfer matrix technique. We show that the tunneling resonance, owing to the existence of reflectionless electron waves in the absence of electric field, is sensitively suppressed by the applied field, leading to a special region of negative differential resistivity at low bias voltages in the I-V curve. The current fluctuations near the peak of the I-V curve are decreased from the usual shot-noise values due to the large transmission of the reflectionless waves. The results may shed light on the possibility of exploiting the structure in designing resonant-tunneling systems that require optimum sensitivity to applied electric field.
Thermographic analysis of electromigration phenomena in aluminum metallization
Authors: Kondo Seiichi , Ogasawara Koutaro , Hinode Kenji
Published: July 2002

Electromigration-induced void growth in Al metallization was investigated by comparing it with the electrical resistance change and the thermographically measured change in temperature distribution. Constant current flowing through two different-width interconnects in series consistently induced void growth at their junction so that it could be observed with high resolution in the fixed fields of an infrared microscope and an optical microscope. The electrical resistance change occurring as a result of an electromigration test was found to directly reflect a local temperature change resulting from the void growth: a pulse phenomenon in the electrical resistance corresponds to a temperature increase of more than 200 °C around the void-growing area. This phenomenon can be attributed to a local melting induced by the void growth and to a void healing process after recrystallization of the adjacent Al grains.
Reverse recovery of a GaAs optoelectronic thyristor
Authors: Korobov V. , Mitin V.
Published: July 2002

Results of numerical simulation of reverse recovery processes in a two-terminal GaAs optothyristor are presented. In the highly conducting ON state there are many excess carriers in the inner layers of the device. Reversing the anode voltage removes these carriers, turning the device off. The behavior of a PnpN structure after reversing the anode voltage essentially depends on the width of the n base. For a wide n base, negative anode voltage has little effect on carrier removal. In the case of a narrow n region, penetration of an electric field into the p base is responsible for a fast removal of slowly diffusing holes from the device. This allows decrease in turn-off times by several orders of magnitude over traditional two-terminal devices. The thyristor is switched off completely after the time interval, when all holes have been evacuated from the p base. Reverse-recovery time for this regime of ‘‘n-base punchthrough’’ is calculated in terms of device parameters.
Magnetic field effect on interface profile between immiscible nonmagnetic liquids—Enhanced Moses effect
Authors: Sugawara Hiroharu , Hirota Noriyuki , Homma Takuro , Ohta Masayuki , Kitazawa Koichi , Yokoi Hiroyuki , Kakudate Yozo , Fujiwara Shuzo , Kawamura Mitsutaka , Ueno Shoogo , Iwasaka Masakazu
Published: July 2002

The change in the interface profile between immiscible nonmagnetic liquids was investigated quantitatively in a superconducting magnet with a large horizontal bore. The interface profile changed into concave down or up at the field center accordingly to the balance of magnetic susceptibilities between the lower and upper liquids. A flat interface was also demonstrated when the susceptibilities were balanced. It was found that modification of the interface profile was significantly amplified under an applied field as low as 1 T when the densities of the two liquids were quite close. The morphological change induced by the applied magnetic field can be used to remove a boundary, which initially separates two liquids without the field, and to initiate a mixing process or a chemical reaction between the two liquids.
Formation of Ni silicide from Ni(Au) films on (111)Si
Authors: Mangelinck D. , Gas P. , Grob A. , Pichaud B. , Thomas O.
Published: July 2002

The solid state reaction between a Ni (7 at. % Au) film and a Si substrate at temperatures ranging from 250 to 800 °C is examined by scanning electron microscopy, x-ray diffraction, and Rutherford backscattering spectrometry. Compared to the usual features for thin film reaction of Ni with Si, we observed the following. (i) The simultaneous growth of Ni2Si and NiSi, and the growth of NiSi at the expense of both Ni2Si and Ni. This is related to Au accumulation in the metal layer. (ii) Au precipitation at 300 °C followed by the dissolution of the clusters thus created above the Au–Si eutectic temperature (370 °C). (iii) A decrease of the temperature of formation of NiSi2 and the appearance of thickness oscillations that are characteristic of nucleation. These different effects are interpreted by taking into account the metallurgy of the system: segregation of Au in the Ni film, Au solubility in the different silicides, change in surface and interface energies, and chemical interactions with Si.
Laser ablation and the unzipping of addition polymer
Authors: Blanchet Graciela B.
Published: July 2002

Ability to control decomposition path and products for addition polymers is important in many applications ranging from thin film fabrication and basic understanding of reaction kinetics to evaluating the feasibility of thermal routes for the recycling of addition polymers. Laser ablation, a technique widely used to deposit thin films of a variety of inorganic materials, can also be used as a simple and highly versatile method for the deposition of thin polymer films of materials that are difficult to process and studying decomposition kinetics as well. In situ studies of the products formed by the laser/polymer interaction suggest that, as in standard pyrolysis, decomposition of poly(tetrafluoroethylene), poly(methylmethacrylate), and poly(α-methyl styrene) proceeds via chain unzipping leading to monomer. Unexpectedly, high monomer yields are also observed for addition polymers that pyrolyze by random scission producing little or no monomer. Examples of such materials presented here include poly(vinylfluoride) and polypropylene.
Probing solvent dynamics in concentrated polymer films with a high-frequency shear mode quartz resonator
Authors: Katz Alexander , Ward Michael D.
Published: July 2002

Solvent reorientational dynamics in concentrated polymer films have been probed with a new experimental method based on a linear electromechanical model and a AT-cut high-frequency quartz resonator. This method is unique in that the viscoelastic characteristics of a composite resonator comprising the viscoelastic film and the quartz resonator are probed at the frequency of minimum resonator amplitude (fYmin) rather than at fYmax, thus permitting measurements under conditions where a linear electromechanical model is most applicable. The method involves measurement of the admittance characteristics of the unloaded quartz resonator and the composite resonator, transformation of the admittance data near fYmin into a linear form that provides accurate determination of the resonant conductance and susceptance, and use of Newton–Raphson numerical iteration to determine the viscoelastic characteristics from these values. This procedure enables real-time investigation of dynamic processes in polymer films, as demonstrated here by the simultaneous determination of the film thickness, storage modulus, and loss modulus during the drying of a spin-coated film containing polystyrene and 2-chlorotoluene solvent. The viscoelastic characteristics are investigated at a resonant frequency near 5 MHz under ambient conditions as the solvent mass fraction continuously decreases from its initial value of 15%. The trends in the measured storage and loss moduli are consistent with a single relaxation process, namely rotational relaxation of the 2-chlorotoluene solvent molecules. The solvent relaxation time increases with decreasing solvent content owing to the increasing influence of the polymer chains on the solvent reorientational dynamics. A plateau in the relaxation time at low solvent content (<2%) suggests the presence of a solvent glass transition. The results demonstrate that shear mode quartz resonators can be used to investigate solvent dynamics in polymer films at high concentrations that are inaccessible by other experimental methods.
Structural and optical characterization of InP/GaxIn1−xAsyP1−y quantum wells and interfacial layers
Authors: Roth A. P. , Lévesque P. , Syme R. W. G. , Lockwood D. J. , Aers G. C. , Rao T. S. , Lacelle C.
Published: July 2002

Several multiquantum wells of InP/GaxIn1−xAsyP1−y grown by chemical-beam epitaxy have been studied by high-resolution x-ray diffraction, low-temperature photoluminescence, and Raman scattering to characterize interfacial layers between the barriers and the wells. These interfacial layers are created during the initial stage of growth of the quaternary material as a result of the longer transient for the saturation of the group-III elements flux. The combination of x-ray diffraction and photoluminescence allows a precise determination of the interfacial layer thickness and composition grading and shows that interface roughness is of the order of 1 monolayer. Raman scattering confirms these results and is used to determine values of the sound velocity and of the index of refraction in the quaternary alloy material.
Chemical synthesis, microstructure, and magnetic properties of chains composed of ultrafine Fe–Co–B particles
Authors: Zhang L. , Manthiram A.
Published: July 2002

An inexpensive chemical method was used to obtain ferromagnetic chains composed of nanometer size spheres of Fe–Co–B. The method involves a controlled reduction with KBH4 in aqueous as well as water-ethanol media of Fe2+ and Co2+ in the presence of an applied magnetic field. The chemical composition, particle size, crystallinity, and microstructure are characterized by inductively coupled plasma analysis, transmission electron microscopy, and x-ray diffraction. The magnetic properties are evaluated with superconducting quantum interference device magnetometer. The particle size and crystallinity decrease by increasing both the Co content and the amount of ethanol in the reaction medium. The observed magnetic properties are correlated to the degree of crystallinity and chemical composition. The magnetic properties are improved significantly by a subsequent annealing step at 400–500 °C in an Ar–H2 mixture. Moreover, the experiments carried out to verify the magnetization reversal mechanism support the chain of spheres model.
Characterization of boron silicide layer deposited by ultrahigh-vacuum chemical-vapor deposition
Authors: Tseng H.-C. , Pan F. M. , Chang C. Y.
Published: July 2002

Deposition of a boron-containing layer using B2H6 diluted with H2 on a Si(001) surface has been carried out in an ultrahigh-vacuum chemical-vapor-deposition (UHV-CVD) system. The deposited boron-containing layers were characterized by atomic force microscope and Auger electron spectroscopy (AES), and the junction depth was determined by secondary-ion-mass spectroscopy. Effective doping is accomplished before perceivable nucleation is initiated. Islands are first formed on the substrate surface at a small dose of diborane, and the grains coalesce to form a rough film for higher doses. At growth temperature above 800 °C, the film is composed of possibly SiB6, according to AES depth profiles. Correlation between the junction depth and the sheet resistance of the UHV-CVD-deposited specimens prepared under various conditions is discussed. Postdeposition rapid thermal annealing was performed to study the effect of subsequent thermal cycles on the junction depth and sheet resistance.