bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid thermal annealing of indium-implanted silicon single crystals
Authors: Shiryaev S. Yu. , Larsen A. Nylandsted , Safronov N.
Published: July 2002

Rapid thermal annealing of indium-implanted 〈100〉 silicon single crystals has been studied as a function of anneal time and temperature (5–25 s, 685–1060 °C) for two implanted In concentrations (6×1019 and 1.2×1020 cm−3). The combination of Rutherford backscattering spectrometry/channeling and transmission electron microscopy was used to characterize the crystals after annealing. There is found to be a correlation between the In redistribution processes and the dislocation structure. The In peak centered at the crystalline/amorphous interface after rapid thermal annealing at 800 °C is concluded to be due to pipe diffusion. The direct backscattering of α particles from dislocation cores is discussed, and it is demonstrated that maximum backscattering from the dislocation core in a silicon crystal is obtained for the Burgers vector orthogonal to the direction of the incoming beam.
Investigations of the SiO2/Si interface. I. Oxidation of a clean Si(100) surface using photoemission spectroscopy with synchrotron radiation
Authors: Nakazawa M. , Kawase S. , Sekiyama H.
Published: July 2002

The surface oxidation process of Si(100), and the distribution of intermediary oxidation states at the SiO2/Si interface have been extensively studied by high resolution (ΔE<0.3 eV) photoemission spectroscopy using synchrotron radiation. The results show that the ratio at the SiO2/Si interface for three intermediary states, Si3+, Si2+, and Si1+ (SiOx), is strongly dependent on SiO2 layer thickness. In particular, the proportion of Si3+ increases with the formation of the 0∼1 nm thick SiO2 layer. However, the three intermediary components at the interface are distributed with ratios of Si3+:Si2+:Si1+=7:2.5:1 in the oxidation stage where a SiO2 layer is formed over 1 nm.
Deep-level trap model of diode laser modulation: Significance of spontaneous emission and gain saturation
Authors: Bourkoff E. , Liu X. Y.
Published: July 2002

We have investigated the effects of deep-level traps on the high-speed modulation behavior of semiconductor diode lasers. A set of three coupled, nonlinear rate equations which model the dynamic behavior of the diode laser has been numerically solved. Our model includes not only the effects of deep-level traps, but also of gain saturation, spontaneous emission into the lasing mode, carrier and photon lifetimes, and varying injection current densities. We show how the laser modulation frequency decreases with increasing trap density and how this behavior depends upon other laser parameters. In particular, we discuss effects of the gain saturation and spontaneous emission factors in the presence of deep-level traps. It turns out that these two parameters do not affect the oscillation frequency (either relaxation oscillation or self-sustained pulsations) very significantly. However, they are found to have profound effects on other aspects of the dynamic response. We also provide, for the first time, an analytical expression for the threshold current density. The dc responses with and without traps are compared as well.
Metalorganic chemical vapor deposition of (ZnO)x(SiO2)1−x films
Authors: Lawrence David J. , Lee S.Tong , Blanton Thomas N.
Published: July 2002

The metalorganic chemical vapor deposition of (ZnO)x(SiO2)1−x films in the temperature range 300–450 °C is described. The deposition system is similar to those commonly used to deposit SiO2 and silicate glass films at atmospheric pressure. The source gases are dimethylzinc, silane, and oxygen. Rutherford backscattering spectrometry and x-ray diffraction have been used to characterize the films. The dependence of the film composition on the source gas composition is given. The films appear amorphous to the thin-film diffractometer for x<0.8. The ultraviolet absorption edge of (ZnO)x(SiO2)1−x varies continuously with the solid composition from x=0 (SiO2 ) to x=1 (ZnO).
Flow-rate modulation epitaxy of GaAs and AlGaAs
Authors: Kobayashi Naoki , Makimoto Toshiki , Yamauchi Yoshiharu , Horikoshi Yoshiji
Published: July 2002

Flow-rate modulation epitaxy (FME) is a new epitaxial growth method which can produce a very flat heterointerface and a sharp doping profile. This paper describes FME growth conditions and electrical and optical properties of FME-grown GaAs, AlGaAs layers, and GaAs/AlGaAs single-quantum-well heterostructures. FME can reduce growth temperatures without deteriorating the crystalline quality and can produce flatter heterointerfaces than the metalorganic chemical vapor deposition method. The catalytic decomposition of silane on the Ga atomic surface efficiently dopes silicon into GaAs and AlGaAs with sharp profiles. For p-type doping, trimethyl metalorganic sources produce carbon atomic layer doping with no memory effect and a low diffusion coefficient of carbon. Experiments using FME to grow modulation doped heterostructures and heterostructure bipolar transistors prove FME to be a promising method of producing III-V semiconductor devices with thin-layered structures.
Photoluminescence of Zn-diffused and annealed InP
Authors: Montie E. A. , van Gurp G. J.
Published: July 2002

Ampoule diffusion of Zn in InP gives rise to donor-acceptor photoluminescence transitions with peak positions dependent on the rate of cooling after diffusion. Subsequent annealing in an atmosphere without Zn causes a change in peak position. Luminescence peaks between 1.30 and 1.38 eV are found. These peaks are described as being due to transitions between various Zn interstitial donor levels and the Zn substitutional acceptor level. The luminescence results are correlated with results of secondary ion mass spectrometry and Schottky barrier capacitance-voltage measurements, and are consistent with an earlier model in which Zn diffuses as an interstitial donor and is incorporated both as an interstitial donor and as a substitutional acceptor.
A three-band model for liquid-crystal birefringence dispersion
Authors: Wu Shin-Tson , Wu Chiung-Sheng
Published: July 2002

A three-band model which consists of one σ→σ* and two major π→π* electronic transitions was developed to account for the birefringence dispersion of a uniaxial liquid crystal. By comparing theory with experimental results, the contribution of each band to the overall birefringence is evaluated. The effect of each band on birefringence dispersion depends strongly on the conjugation length of the molecule. This model reveals new physical insights for designing a liquid-crystal molecule with desirable birefringence.
Surface acoustic wave properties of aluminum gallium arsenide
Authors: Steel Victor E. , Hunt W. D. , Emanuel M. A. , Coleman J. J. , Hunsinger B. J.
Published: July 2002

Surface acoustic wave (SAW) properties are measured for {100}-cut, 〈100〉-propagating aluminum gallium arsenide (AlxGa1−xAs) with x=0.2 and 0.4. The parameters used to characterize these properties are SAW velocity, SAW attenuation, and piezoelectric coupling coefficient. The measured velocities are found to be substantially higher than those on GaAs in agreement with the theoretical predictions of Adachi. The attenuation is close to the corresponding attenuation on GaAs which is approximately 1 dB/μs. The piezoelectric coupling coefficient is measured using two independent methods and is found to be significantly higher than that of GaAs. This means that the transduction of energy from electrical to acoustical is more efficient and hence acoustic charge transport devices on AlxGa1−xAs substrates will require considerably less rf drive power. An extensive literature search has revealed no previous work, theoretical or experimental, characterizing attenuation or piezoelectric coupling of SAW on AlxGa1−xAs. The velocity has been predicted by Adachi based on a model formulated by Keyes, and has been measured by Sapriel, but the measured velocities reported herein correspond to the predicted values much better than the values measured by Sapriel. The measurement technique described has not, to the authors’ knowledge, been previously used for measurement of the piezoelectric coupling coefficient, and represents a convenient method of obtaining the SAW parameters experimentally.
Ion implanted waveguides in polymethylmethacrylate
Authors: Zhang L. , Townsend P. D. , Chandler P. J. , Kulisch J. R.
Published: July 2002

Optical waveguide profiles of He+ ion implanted polymethylmethacrylate have been analyzed. The surface index increases by up to 3% and the depth profile of the index is consistent with a diffusion limited decomposition of the target. This was confirmed by 77- or 300-K implants with a capping layer to inhibit decomposition.
Temperature and composition dependence of grain boundary segregation in La2−xSrxCuO4−y
Authors: Roshko A. , Chiang Y.-M.
Published: July 2002

The composition of grain boundaries in La2−x Srx CuO4−y has been mapped as a function of bulk composition and annealing temperature. It is found that the predominant composition change is an enrichment of Sr, that this segregation occurs primarily on the La sublattice, and that the segregation energy (0.03 to 0.1 eV) agrees with an elastic misfit strain energy estimate for Sr as a solute. Grain boundary segregation is shown to persist at annealing temperatures as high as 1000 °C, and to be relatively uniform from grain boundary to grain boundary in these untextured polycrystals. Compositional disorder is thus intrinsic to grain boundaries in La2−x Srx CuO4−y and must be considered along with structural disorder in understanding the nature of the weak links. While prospects for high-polycrystalline critical-current densities in this material appear poor based on these results, the ability to predict and control grain boundary segregation may conversely prove to be useful in applications that require specific grain boundary junction properties.
Influence of the screening effect onto the transport parameters of hot 2D electrons in n-GaAs square quantum wells
Authors: Zandler G. , Vass E.
Published: July 2002

The heating temperature ΔTe , the drift velocity vd , the average momentum-loss rate 〈−dℏkE/dt〉, and the average energy-loss rate 〈−dε/dt〉 of hot 2-D electrons interacting simultaneously with polar optical phonons and ionized impurities are calculated as a function of the lattice temperature T, the carrier concentration n, and the external electric field E. The calculations are carried out with unscreened and screened interaction matrix elements including plasmon-phonon coupling. A hot drifted Fermi–Dirac distribution is used to evaluate 〈−dℏkE/dt〉 and 〈−dε/dt〉, as well as the dielectric screening function in the random-phase approximation. The distribution-function parameters vd and Te are determined self-consistently by solving simultaneously the power- and force-balance equations.
Hg+ ion density in low-pressure Ar-Hg discharge used for a mercury lamp
Authors: Lin Tingsheng , Goto Toshio , Arai Toshihiko , Murayama Seiichi
Published: July 2002

The Hg+ ion density on the tube axis in the low-pressure Ar-Hg discharge lamp with 12 mm i.d. has been first measured under various bath temperatures and discharge currents with a modified absorption method. The radial distribution of the Hg+ ion density also has been determined.
Influence of oxygen concentration on processing YBa2Cu3O7−x
Authors: Chen Nan , Shi Donglu , Goretta K. C.
Published: July 2002

The sintering kinetics of YBa2Cu3O7−x have been studied from 870 to 930 °C in oxygen/argon mixtures ranging from 0.2% to 100% oxygen. For sintering at temperatures below that required for formation of any liquid phase, densification rates increased with decreasing oxygen concentration, and transport critical current densities increased with increasing density. The activation energy for sintering was 190±30 kJ/mol.
Characterization of Nb/AlOx-Al/Nb Josephson junctions by anodization profiles
Authors: Imamura Takeshi , Hasuo Shinya
Published: July 2002

The thin tunneling barrier in a Nb/AlOx-Al/Nb Josephson junction was characterized by anodization profiles. Our studies focused on Nb/AlOx and Al/Nb interfaces in Nb/AlOx-Al/Nb junctions made by varying certain process parameters. The interface quality was checked by the anodization profiles and was greatly affected by film thickness, layer sequence, annealing treatment, and the existence of a thin oxide. By comparing the profiles with the junction characteristics measured at 4.2 K, we confirmed that the interface sharpness in the profiles is related to the junction quality. The anodization profile is a useful tool to diagnose the tunneling barrier interfaces in Nb/AlOx-Al/Nb Josephson junctions, especially at room temperature during fabrication.
Rate-dependent plasticity of copper and stainless steel under shock compression
Authors: Tonks Davis L.
Published: July 2002

Experimental copper and stainless-steel particle velocity profiles are analyzed to determine the plastic strain, plastic strain rate, and deviatoric stress through the shock front. A steady-wave shock analysis is used, together with a numerical characteristics-code calculation to correct for reflections created when the steady wave passes through the sample-window interface. The results are well represented by power-law relations giving the plastic strain rate as powers of the deviatoric stress and plastic strain. The effects of the sample-window interface are found to be minor for windows closely matched in impedance to the sample. The effects of the window on the strain-rate relation are appreciable only near peak compression.
A model for the oxidation-enhanced diffusion of boron in extrinsic silicon
Authors: Tsoukalas D. , Chenevier P.
Published: July 2002

In this communication the authors propose a simple method for the estimation of the fractional interstitialcy component fI of boron that is based on the interpretation of oxidation-enhanced diffusion data in extrinsic conditions. The model developed explains satisfactorily the experimental results when the value of fI is 0.25. This result indicates an important contribution of vacancies to boron diffusion in silicon.
Modeling of a plasma column produced and sustained by a traveling electromagnetic surface wave
Authors: Zhelyazkov Ivan , Benova Evghenia
Published: July 2002

We present an improved model of a plasma column produced and sustained by a traveling azimuthally symmetric electromagnetic surface wave. The axial density profile of the column as well as the wave dispersion and field and power characteristics are now specified by five parameters: (i) the collision frequency for momentum transfer ν, ν<ω (ω being the wave angular frequency), (ii) the number σ=ωR/c (R is the plasma column radius, c the speed of light), (iii) the number β indicating the gas-discharge regime (B=0 for the diffusion regime and 0<β≤2 for the bulk recombination one), (iv) the permittivity of the container (glass tube) εd, and (v) the number γ=1+d/R (d denoting the thickness of the tube), the last two parameters having been neglected earlier. The influence of εd and γ on the wave dispersion properties and the axial profiles of the plasma density, wave power, and wave electric field components has been studied numerically. Our improved model is tested with the experimental data [A. Sola, A. Gamero, J. Cotrino, and V. Colomer, J. Appl. Phys. 64, 3419 (1988)] of argon plasmas produced by high-frequency surface waves in three different tubes and in a wide range of gas pressures. The agreement between the theory and experiment is very good. The model has been also applied to another particular experimental setup and the results are compared with the corresponding theoretical curves obtained by Sá and Ferreira (Europhysics Conference Abstracts ESCAMPIG 88, Vol. 12H, p. 191) and with the experimental data of Saada, Bloyet, Dervisevic, and Laporte [Université Paris Sud, Rapport L.P. 220 (1983)].
Electrical conduction in a tin-oxide–silicon interface prepared by spray pyrolysis
Authors: Chaudhuri Uma Ray , Ramkumar K. , Satyam M.
Published: July 2002

This paper describes the voltage-current characteristics of tin-oxide–silicon interfaces prepared by spray pyrolysis. A theoretical model for the explanation of the observed characteristics at low currents is also described.
Combined ac photocurrent and photothermal reflectance measurements in semiconducting p-n junctions. II
Authors: Mandelis Andreas , Ward Alan A. , Lee K. Timothy
Published: July 2002

The ac photocurrent (PC) and photothermal reflectance (PTR) spectroscopic response theory of a semiconducting p-n junction developed in part I [J. Appl. Phys. 66, ⧠⧠⧠⧠ (1989)] is applied to theoretical simulations to identify the influence of the various electronic and geometrical device parameters involved. The theory is further tested in an experimental configuration with a commercial solar cell. The experimental ac photocurrent and photothermal reflectance data exhibited satisfactory agreement with the theoretical model, and yielded, respectively, experimental values for the minority lifetimes τp and τn. A combination of PC and PTR data yielded reasonable Ln estimates.
Deposition of Co-Cr films with large magnetization on polyethylene naphthalate tape
Authors: Akiyama S. , Furuto Y. , Nakagawa S. , Naoe M.
Published: July 2002

It is difficult for Co-rich Co-Cr film to orient its magnetization moment perpendicularly because of large saturation magnetization Ms. The two-step sputtering method with the facing targets sputtering system was useful for depositing Co83Cr17 films with large Ms and the perpendicular magnetic anisotropy on the very thin Co79Cr21 underlayer with the good c-axis orientation continuously on the polyethylene naphthalate tape substrate. The underlayer was helpful for improving the perpendicular magnetic anisotropy of Co83Cr17 films.
Photoinduced absorption in calcium-doped yttrium iron garnet
Authors: Thavendrarajah A. , Pardavi-Horvath M. , Wigen P. E.
Published: July 2002

The equilibrium optical absorption and the near steady state photoinduced absorption measurements are performed on CaX:YIG (X=0, 0.10, 0.34) epitaxial thin films in the temperature range 10–300 K. The photoinduced effects show a broad region of induced absorption with two peaks near 2.6 and 1.9 eV and a strong photoinduced transmission (bleaching) in the region near the gap. The peaks near 2.6 and 1.9 eV are attributed to O− and Fe4+ ions, respectively. The temperature dependence of the Fe4+ peak indicates that the localization energy is about 50 K. The temperature dependence of the photoabsorption peaks indicates that the O− ion is less stable than the Fe4+ ion. The strong photoinduced transmission near the band edge is consistent with the formation of a band tail in the density of states of the highly doped Ca:YIG.
A representation of magnetization characteristics and its application to the ferroresonance circuits
Authors: Saito Y. , Namiki M. , Hayano S.
Published: July 2002

Previously, a Chua-type model representing the magnetization characteristics of ferromagnetic materials was presented for computational analysis and design of magnetic devices. Typical magnetization characteristics, such as saturation, hysteresis, and aftereffect, have been reproduced by the model. In this paper, our Chua-type model is derived by means of the barlike domain walls model. As a concrete example, this model is applied to the computations of ferroresonance circuits and is compared with those of the experimental results. Agreement to a considerable extent confirms the validity of this model.
Magnetic properties of ultrafine Fe-Ni-B particles
Authors: Nafis S. , Hadjipanayis G. C. , Sorensen C. M. , Klabunde K. J.
Published: July 2002

Ultrafine Fe-Ni-B particles were synthesized by reducing iron and nickel salts with NaBH4 in aqueous solutions. The particles had diameters in the range of 100–300 Å. X-ray diffraction patterns showed that particles with boron concentration 18 at. % or more were amorphous; otherwise they were crystalline. It was also found that the amorphous particles contain less than 50 at. % of Fe. The coercivity of Fe-B particles was increased by an addition of a small amount of Ni to the system. The room-temperature coercivity and saturation magnetization for particles of composition Fe63Ni24B13 and of diameter 100 Å were 1275 Oe and 70 emu/g, respectively.
The effect of oxygen on phase formation in Al/Nb diffusion couples
Authors: Barmak K. , Coffey K. R. , Rudman D. A. , Foner S.
Published: July 2002

The effect of an aluminum oxide layer at the interface of Al/Nb on phase formation in thin-film binary diffusion couples was studied. Al/Nb bilayers with or without aluminum oxide at the interface were prepared by electron-beam evaporation. The samples were annealed at a constant heating rate of 50 °C/min to temperatures in the range 800–950 °C, and the progress of the reaction was monitored by x-ray diffraction and measurement of the superconducting transition temperature. The presence of an aluminum oxide layer at the interface was found to significantly retard the formation of the superconducting A15 Nb3Al phase.
Relief of compressive biaxial strains in thin films via microtwins
Authors: Twigg M. E. , Richmond E. D. , Pellegrino J. G.
Published: July 2002

For heteroepitaxial systems, such as silicon on sapphire, microtwins can usually be observed in the epitaxial layer. It has also been suggested that microtwins play a significant role in strain relief in these systems. From a knowledge of the differential volume fraction of microtwins occurring in a heteroepitaxial systems, it is possible to estimate the greatest possible strain relief due to microtwins. Measurements of the differential volume fraction of microtwins in silicon-on-sapphire, however, indicate that the strain relief due to microtwins cannot be greater than 0.7%, even though the lattice mismatch between silicon and sapphire is an order of magnitude larger. Therefore, if the silicon/sapphire interface is coherent, the misfit strain must be relieved by another mechanism.
Cryogenic cathodoluminescence of plasma-deposited polycrystalline diamond coatings
Authors: Partlow William D. , Ruan Juai , Witkowski Robert E. , Choyke W. J. , Knight Diane S.
Published: July 2002

The cathodoluminescence spectra of microwave plasma-deposited polycrystalline diamond films have been measured at liquid-nitrogen temperatures over the spectral region of 230–800 nm. The diamond coatings had been deposited under several different deposition temperatures and reactant compositions. Measurements on natural type-IIB diamond crystals were made for comparison. The intrinsic exciton emission bands which fall in the UV just below the band edge were observed, as well as several defect and impurity bands which extend throughout the visible part of the spectrum. SEM micrographs and Raman spectra were obtained for the same set of samples used for the cathodoluminescence measurements. It was found that the diamond-related cathodoluminescence features were most intense in samples whose Raman spectra exhibited the most intense cubic diamond line at 1332 cm−1 and the least intense graphitic band at about 1500 cm−1.
Transport properties of InAsxSb1−x (0≤x≤0.55) on InP grown by molecular-beam epitaxy
Authors: Tsukamoto S. , Bhattacharya P. , Chen Y. C. , Kim J. H.
Published: July 2002

Molecular-beam epitaxy has been successfully used to grow InAsxSb1−x on InP substrates with good electrical characteristics. The samples are all n type with electron concentrations varying in the range (3–9)×1015 cm−3. The mobilities are high (70 000 and 110 000 cm2/V s at 300 and 77 K, respectively) in InSb and the alloys. More importantly, the mobilities remain high at the low temperatures in the alloys also, without any type conversion. The mobility data have been analyzed taking into account the appropriate scattering mechanisms. The alloy scattering potential in InAs0.24 Sb0.76 is estimated to be 0.3 V.
Fractal-like Si crystallization during interfacial reactions in thin Al/amorphous SiC layers
Authors: Nathan M. , Ahearn J. S.
Published: July 2002

Interfacial reactions between thin films of Al and amorphous (a-) SiC annealed with tungsten-halogen lamps lead to the formation of Si fractal-like structures at temperatures as low as 275 °C in less than 100 s. By using a-SiC/Al/a-SiC sandwiches with different SiC/Al thickness ratios, it is shown that the nucleation of Si crystals is faster on smaller-grained Al. This is attributed to the higher Al surface energy and the increased density of high-energy multiple grain junctions in thinner (smaller grained) Al layers. When the Al layer is very thin (≤50 Å) a solid-state amorphization reaction occurs between Al and a-SiC without subsequent Si crystallization. Formation of Al4C3 follows Si crystallization, or in the very thin Al layer, the amorphization reaction.
Measurements of the nonlinear refractive index of a GaInAs/InP multiple quantum well
Authors: Fisher M. A.
Published: July 2002

Measurements of the nonlinear refractive index of a GaInAs/InP multiple quantum well structure are reported. Optical absorption data obtained by a pump and probe technique were analyzed using the Kramers–Krönig relations to give index change as a function of wavelength for various pump intensities. The results indicate that optical devices should be realizable in this material system. The importance of saturation of the nonlinearity is demonstrated and the behavior shown to be well described by a simple band filling model.
Simultaneous extraction of minority-carrier transport parameters in crystalline semiconductors by lateral photocurrent
Authors: Misiakos K. , Wang C. H. , Neugroschel A. , Lindholm F. A.
Published: July 2002

The mathematical analysis and parameter-extraction process for a new characterization method are presented. This method allows simultaneous measurement of the minority-carrier lifetime, diffusion coefficient, and diffusion lengths as well as surface recombination velocity. The technique employs semi-infinite two-dimensional photodiodes and uniform, instead of focused, illumination. The paper deals with the derivation of exact closed-form solutions associated with two-dimensional devices and discusses the simultaneous extraction of minority-carrier transport parameters.
Isotopic exchange in hard amorphous carbonized layers
Authors: Boutard D. , Möller W. , Scherzer B. M. U.
Published: July 2002

Hard amorphous films of a-C:H and a-C:D were deposited by a rf glow discharge in either CH4 or CD4 . By ion bombardment with protons and deuterons, the H/D exchange process was studied as function of the bombardment fluence by means of depth profile measurements. The local hydrogen and deuterium contents are not adding up to a constant ‘‘saturation’’ value: the local mixing model is not valid. Instead of that an initial depletion appears, which depends on the incident energy of the ions. At higher fluences, the total (H+D):C ratio tends to increase again, due to an increasing influence of the deposition process. This demonstrates a structural difference between a-C:H films and hydrogen-saturated layers of implanted carbon.
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u fabrication of epitaxial YBa2Cu3O7 films on lattice-mismatched (100) YS-ZrO2 substrates by the pulsed laser evaporation method
Authors: Singh R. K. , Narayan J. , Singh A. K.
Published: July 2002

The formation of good quality epitaxial c-axis-perpendicular YBa2 Cu3 O7 superconducting thin films on (100) yttria-stabilized-zirconia (YSZ) substrates in the temperature range of 550–650 °C by a biased laser deposition method is reported. However, below 550 °C, the epitaxial quality of the films decreased appreciably with corresponding changes in the superconducting properties. For temperatures much below the critical temperature, the critical current density showed a linear variation with temperature, with a value of 1.0×106 A/cm2 at 77 K and zero magnetic field. Because of the lattice mismatch between the substrate and the film, the interface was found to be highly strained in the presence of a large number of defects. The epitaxial nature and the crystalline quality of the films were determined by a number of techniques including Rutherford backscattering/channeling, electron channeling, cross-section transmission electron microscopy (TEM), and x-ray diffraction techniques. Rutherford backscattering channeling showed a minimum channeling yield of about 18%–25% for films deposited at and above 550 °C. Cross-section TEM and x-ray diffraction revealed the following thin film and substrate relationships: [001]film ∥[001]YSZ and [110]film ∥[100]YSZ. The electron channeling pattern taken from a large area confirmed the epitaxial relationship. The lattice parameters mismatch in this orientation has been found to gives rise to stresses near the interface.
On the in-plane acceleration sensitivity of ST-cut quartz surface-wave resonators with interior rectangular supports
Authors: Tiersten H. F. , Shick D. V.
Published: July 2002

An analysis of the in-plane acceleration sensitivity of ST-cut quartz surface-wave resonators with the substrate extending beyond interior rectangular supports is performed. In the treatment the variational principle with all natural conditions is extended in such a way as to permit interior surfaces of discontinuity with spring supports at which the approximating solution functions need not satisfy the constraint-type conditions. This extension is required for the approximation procedure used in the calculation of the biasing state. The resulting extensional biasing state is employed in an existing perturbation integral along with the proper continuous representation of the acoustic-surface-wave mode shape to calculate the in-plane acceleration sensitivity. The calculated results indicate how to select the distances between the supports so as to minimize the in-plane acceleration sensitivity for a given surface-wave resonator.
Effect of piezoelectricity on the excitation and radiation of acoustic waves in rotated Y-cut quartz
Authors: Zhang Y. , Planat M.
Published: July 2002

Recently we reported a far field theory of transverse acoustic waves radiated from an interdigital transducer deposited on a singly rotated quartz crystal. This was done by an approximation called the local decoupling approach, allowing us to consider electrical effects as forcing fields for the mechanical motion. The present analysis demonstrates that this approximation is not valid in predicting the complete spectrum of acoustic waves. It is shown that near the cutoff frequency the bulk wave may be converted into a surface wave of Bleustein–Gulyaev type in the free surface case, and that a surface metallization reinforces the strength of this conversion. Velocity of surface waves are determined by means of the effective permittivity function and correct radiation diagrams are plotted in the far field.
Anisotropy and kinetics of the etching of tungsten in SF6 multipolar microwave plasma
Authors: Durandet A. , Arnal Y. , Pelletier J. , Pomot C.
Published: July 2002

An experimental study of the etching of tungsten with SF6 has been performed in a microwave multipolar plasma using an electron cyclotron resonance excitation with an independent low dc biasing. The anisotropy and etch rate of tungsten have been measured as a function of atomic fluorine concentration in the plasma and compared with silicon characteristics. The etching mechanisms of tungsten are analyzed in light of published data on the fluorine-tungsten interaction, and the results are explained in terms of the diffusion model for plasma etching developed for the Si-F system. Atomic fluorine adsorption on tungsten appears to be monolayerlike, whereas it is of multilayer type on silicon, and associative desorption of WF6 occurs from WF3 and/or WF4 adspecies in nearest-neighbor positions.
Isotope separation and growth mechanisms of intermetallic phases: An investigation of nickel silicides by secondary ion mass spectrometry
Authors: Gas P. , Zaring C. , Svensson B. G. , Östling M. , Petersson C. S. , d’Heurle F. M.
Published: July 2002

Isotope separation resulting from the diffusion-controlled growth of reacted films has been proposed as a tool to elucidate the diffusion mechanism which controls the growth. A ‘‘reverse’’ isotope separation would be indicative of a grain boundary diffusion mechanism. Such an isotope separation has been studied by secondary ion mass spectrometry (SIMS) during the growth of nickel silicides (Ni2Si and NiSi) for different experimental growth conditions: silicon substrate orientation, temperature of reaction, and silicide thickness. In every case, the isotope separation resulting from the diffusion-controlled growth is below the accuracy of the SIMS measurements. This is consistent with the fact that isotope effects are usually very small. The difficulties of such studies and the multiple SIMS artifacts encountered at interfaces—matrix effects, variations in the sputtering yield, mass interferences, and sequential acquisition of data—are analyzed in detail. They are found to be quite important in the case of nickel silicides and may lead to erroneous conclusions. A model for isotope separation during layer growth, which had been previously proposed, is shown to provide overoptimistic estimates of the magnitude of the anticipated effect.
Low-temperature ion mixing of yttrium and silicon
Authors: Alford T. L. , Bo/rgesen P. , Mayer J. W. , Lilienfeld D. A.
Published: July 2002

Ion mixing of yttrium and amorphous silicon bilayers was measured as a function of fluence and temperature using 600-keV Xe++ ions between 80 and 498 K. At 80 K the mixing rate was in excellent agreement with a theoretical model based on thermal spike mixing. For temperatures up to ≊372 K, the temperature-dependent contributions accounted for less than 50% of the overall mixing rate. For mixing at or above 400 K, our results revealed the formation of an ion-beam-induced orthorhombic Y-Si phase, which is not normally formed during thermal anneals of such bilayers.
Effect of an SiO2 layer on the superconductive properties of the high-T
c Bi-Sr-Ca-Cu-O films
Authors: Kalkur T. S. , Kwor R. Y. , Byrne D.
Published: July 2002

High-Tc Bi-Sr-Ca-Cu-O thin films were coated with electron-beam-evaporated SiO2. The room-temperature resistivity of the coated films and their superconductivity onset and zero-resistance temperatures were not affected by the dielectric film. High-frequency capacitance-voltage studies did not show any modulation of space charge in the surface layer of the superconducting film. It is observed that the high-frequency (1 MHz) capacitance of the metal-insulator-superconductor structure has an appreciable temperature dependence.
Anisotropic strain relaxation in buried CoSi2 layers formed by mesotaxy
Authors: Vandenberg J. M. , White A. E. , Hull R. , Short K. T. , Yalisove S. M.
Published: July 2002

The lattice mismatch in and out of the orientation direction was measured in layers of CoSi2 grown by high dose implantation and annealing. A comparison of (111), (100), and (110) orientations showed that the lateral mismatches were similar but the perpendicular mismatch increased monotonically through the series. The differences in the degree of relaxation of the three orientations provide a possible explanation for the observed anisotropy in the electrical properties.
Magnetic studies of Fe-Y compositionally modulated thin films
Authors: Badia F. , Ferrater C. , Lousa A. , Martinez B. , Labarta A. , Tejada J.
Published: July 2002

Compositionally modulated thin films of Y/Fe have been studied by using SQUID magnetometry. Samples were grown by electron-beam evaporation onto Kapton substrates. In the low applied field regime, the samples show irreversible behavior when they are submitted to ZFC-FC magnetization processes, increasing the irreversibility zone as the thickness of the Fe layers increases. In the high applied magnetic field regime (H≥10 000 Oe), samples show ferromagnetic behavior. The temperature dependence of the saturation magnetization has been studied, and it was found that both spin-wave excitations and Stoner excitations occur at temperatures higher than 40 K, and a marked deviation from the T3/2 law was noted below 30 K.
Effects of Fe on the ferromagnetic properties of Al-Mn-based quasicrystals
Authors: Srinivas V. , Dunlap R. A. , McHenry M. E. , O’Handley R. C.
Published: July 2002

Magnetization and Mössbauer-effect studies of ferromagnetic Al-Mn-Si and Al-Mn-Cu-Ge quasicrystals are presented. All alloys show paramagnetic or spin-glass behavior in addition to ferromagnetism at low temperatures. The effects of Fe substitution on the magnetic properties were investigated. Possible models for ferromagnetic order in quasicrystals are discussed.
High-temperatures magnetism in icosahedral Al52.5Ge22.5Mn25 and Al52.5Ge22.5Mn24.85Fe0.15
Authors: Stadnik Z. M. , Stroink G.
Published: July 2002

Magnetization and 57Fe Mössbauer-effect measurements are reported for the magnetically ordered icosahedral alloys Al52.5Ge22.5Mn25 and Al52.5Ge22.5Mn24.85Fe0.15. The lack of saturation of magnetization suggests a noncollinear magnetic structure. It is shown that transition-metal atoms are distributed among a multiplicity of sites, which is interpreted as evidence for atomic disorder characteristic of icosahedral alloys. The reported and literature data show that the two-site model leads to unphysical Mössbauer parameters. It is shown that 57Fe Mössbauer spectra are due to the simultaneous presence of the electric-quadrupole interaction and the magnetic-dipole interaction, and that the former is significantly stronger than the latter.
Properties of magnetic curtain produced by magnetic fields
Authors: Ueno S. , Iwasaka M.
Published: July 2002

This study focuses on the mechanism of magnetic curtain. Gas flow experiments in nitrogen atmosphere and oxygen atmosphere are carried out first. Flows of carbon dioxide are not blocked by magnetic fields in nitrogen atmosphere. The results show that oxygen as a paramagnetic molecule acts an important role in formation of the magnetic curtain. Second, pressure of gas flow near the magnetic curtain is measured. Flows of gases such as nitrogen and oxygen are supplied to an air gap between magnetic poles, and the differential pressure is measured by a manometer. It is found that the blocking properties of magnetic curtain against gas flow are classified into three regions with respect to flow velocity. When the flow velocity is slow, gas flow leaks out of the magnetic curtain (region I). When the flow velocity is medium, gas flow is blocked (region II). When the flow velocity is fast, gas flow is pinched to pass through the magnetic curtain (region III). Based upon the experimental results, a model of magnetic curtain is introduced, and the magnetic curtain is simulated.
Very-low-pressure deposition by electron cyclotron resonance plasma chemical vapor deposition method
Authors: Shirai Koun , Gonda Shun-ichi
Published: July 2002

This paper presents the deposition characteristics of the electron cyclotron resonance plasma chemical vapor deposition from the viewpoint of very-low-pressure operation, taking an instance of the deposition of amorphous boron films from diborane and hydrogen mixtures. The films were deposited at very low pressures, e.g., 0.1 Pa, and at low substrate temperatures below 600 °C. This very-low-pressure deposition is made possible by virtue of radicals produced by the discharge. Deposition characteristics have been studied by observing the dependence of the deposition rate on various parameters of the preparation. As a result, this deposition is characterized by a heterogeneous reaction with respect to predominant collisions of radicals and characterized by a mass-transfer controlled reaction with respect to rate-controlling factors. The feature of very-low-pressure deposition, however, modifies the mass-transfer controlled reaction with respect to the pressure range at which the reaction holds and with respect to the pressure dependence of the deposition rate. This modification can be explained in terms of lowering the efficiency of the mass transport onto the substrate at very low pressures.
Metal-oxide-semiconductor structures on germanium/boron doped silicon
Authors: Hashemipour O. , Ang S. S. , Brown W. D. , Yeargan J. R.
Published: July 2002

Metal-oxide-semiconductor (MOS) capacitors were fabricated on germanium/boron (Ge/B) doped silicon substrates. Typical fixed charge and interface state densities were found to be 5×1010 cm−2 and 5×1010 eV−1 cm−2, respectively. Germanium counterdoping in the boron-doped silicon does not appear to degrade the interfacial properties of MOS structures. Avalanche electron injection produces a slight increase in interface state density, a reduction in inversion capacitance due to deactivation of boron, and a shift in flatband voltage. However, turnaround in flatband voltage shift is not observed due either to enhanced electron trapping or a reduction in donorlike interface state generation. Three different methods used to determine the electron barrier energy height at the silicon dioxide-Ge/B silicon interface yielded a value of 2.2 eV. This smaller barrier height is attributed to the smaller electron affinity of Ge/B-doped silicon.
The in-plane effective mass in strained-layer quantum wells
Authors: Ridley B. K.
Published: July 2002

The problem of calculating the valence-band structure of strained-layer quantum wells in the effective-mass approximation is reviewed. Using the spherical approximation and exploiting the simplicity of the infinitely deep well model we show that the in-plane effective mass is determined by two factors—a splitting contribution which is dominant at large strains, and a quantum confinement contribution. A model for finite-depth wells is presented which gives analytic expressions for the zone-center in-plane mass and associated nonparabolicity factor, and it is applied to the system InxGa1−xAs/GaAs. The model allows the computation of valence-band structure using no more than a pocket calculator. It is shown to give results in reasonable agreement with experiment.
Interface state densities for metal-nitride-oxide-silicon devices
Authors: Xu Dan , Kapoor Vik J.
Published: July 2002

The interface state density of metal-nitride-oxide-silicon (MNOS) devices was investigated as a function of silicon nitride (Si3N4) deposition temperature and postdeposition annealing conditions. The interface state density around the midgap of the oxide-silicon interface of the MNOS structures as a function of deposition temperature between 650 to 850 °C increased from 1.1 to 8.2×1011 cm−2 eV−1, for as-deposited silicon nitride films,; but decreased from 5.0 to 3.5×1011 cm−2 eV−1, for films annealed in nitrogen at 900 °C for 60 min; and further decreased and remained constant at 1.5×1011 cm−2 eV−1, for films which were further annealed in hydrogen at 900 °C for an additional 60 min. The interface state density increase is due to an increase in the loss of hydrogen at the interfacial region and also due to an increase in the thermal stress caused by differences in thermal expansion coefficients of silicon nitride and silicon dioxide films at higher deposition temperatures. The interface state density is subject to two opposing influences; an increase by thermal stress, and a reduction by hydrogen compensation of these states. Thus either low-temperature processing or subsequent hydrogen annealing after high processing temperatures is warranted.
Tin diffusion and segregation in GaAs processed with a pulsed ruby laser
Authors: Garcia B. J. , Martinez J. , Piqueras J. , Muñoz-Yagüe A. , Fontaine Ch.
Published: July 2002

Tin-diffused GaAs layer samples, with mean concentrations larger than 1019 cm−3, were obtained by irradiating with a ruby laser GaAs substrates covered with thin tin layers. Mobilities between 100 and 200 cm2/V s were obtained. Both carrier concentration and mobility decrease with increasing energy density. Strong segregation effects were observed in the samples processed with large energy densities.
Electron dynamics in magnetized CO2 laser and He discharges
Authors: Labun A. H. , Capjack C. E. , Seguin H. J. J.
Published: July 2002

The energy density of the electron flux in magnetized 30-Torr He and He:N2:CO2 dc glow discharges was obtained by Monte Carlo simulation of the cathode region. The application of transverse magnetic fields to the cathode region caused an increase in collisions. This effect became increasingly important in the second half of the cathode region, where magnetic trapping of high-energy electrons occurred. Ionization was enhanced in the cathode region as well as the negative glow, with maximal electron multiplication observed for magnetic field strengths of approximately 0.1 T. This suggests both that a lower cathode fall may be possible in a magnetized discharge and that the electric field reversal in the negative glow will be accentuated. Thus, magnetization of the cathode region may improve the electrical efficiency of CO2 lasers.
On the quantum theory of electron transport in the Wigner formalism
Authors: Buot F. A.
Published: July 2002

The use of a lattice-space Weyl–Wigner formalism of quantum dynamics of particles in solids, coupled with the nonequilibrium Green’s function technique, provides a rigorous and straightforward derivation of an exact integral form of the equation for a quantum-distribution function in many-body quantum transport theory. This formulation leads to a straightforward and fully gauge-invariant derivation of the exact quantum transport equation of a uniform electron-phonon scattering system in high electric fields which do not involve any gradient expansion. The resulting expressions serve to generalize previous results.
Reproducible group-V partial pressure rapid thermal annealing of InP and GaAs
Authors: Pearton S. J. , Katz A. , Geva M.
Published: July 2002

We compare the effectiveness of two types of SiC-coated graphite susceptors in providing degradation-free rapid thermal annealing of InP and GaAs. The first type of susceptor must be charged with the group-V species prior to any annealing cycles. Under the optimum charging conditions, effective surface protection is provided for up to five sequential high-temperature (900 °C, 10 s) anneals of GaAs, or only one anneal (750 °C, 10 s) of InP before recharging is necessary. The incorporation of small reservoirs into the susceptor allows for the provision of a constant group-V partial pressure over the wafer, and it appears that for this type of susceptor many dozens of InP or GaAs wafers can be annealed without any apparent surface degradation. The relative merits of using InAs, GaAs, or InP as the group-V source in the reservoirs have been compared, and it is found that the best protection is achieved when one uses the same semiconductor in the reservoirs as is being annealed.
Scanning electron microscopy investigations of the initial degradation mechanism of GaAs quantum well lasers grown on silicon substrates
Authors: Martins R. B. , Henoc P. , Akamatsu B. , Bartenlian G. , Charasse M. N.
Published: July 2002

Cathodoluminescence and electron beam induced current are used to investigate the degradation of the graded-index separate-confining heterostructure laser devices grown on silicon substrates. By examining the evolution of the microscopic electronic properties of these devices during operation or under electron beam bombardment, a better understanding of the initial mechanism of degradation in a laser device results: it is concluded from this study that the degradation starts in the vicinity of the p-n junction before attaining the active layer or the formation of dark line defects. This starting of degradation is attributed to the point-defect migration or coupling in the space-charge region. The built-in electrical field plus the nonradiative recombination of excesses carriers seems to be related to these phenomena. It is also pointed out that the technological processes for device fabrication have a strong influence on the degradation mechanism.