bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystallography of Co/Cr bilayer magnetic thin films
Authors: Hono K. , Wong B. , Laughlin D. E.
Published: July 2002

Various crystallographic textures of Co-alloy/Cr bilayer thin films are discussed based on microdiffraction and selected-area diffraction (SAD) results. In order to understand the origin of the crystallographic texture of the Co thin films, the orientation relationships between the Co and Cr grains were determined by the electron microdiffraction technique. From this information, we suggest that the {110} Cr underlayer texture may not necessarily be required to obtain the highest in-plane coercivity in Co films. In order to evaluate the crystallographic texture of the film by SAD patterns, normalized intensity of SAD patterns for various thin-film textures have been calculated. Using these calculations, we interpret the SAD patterns taken from various Co and Cr thin films.
InGaAsP compositional determination from reflectance spectroscopy of InGaAsP/InP heterostructures
Authors: Tarof L. E. , Miner C. J. , Blaauw C.
Published: July 2002

Reflectance spectroscopy has been applied to the study of lattice-matched InGaAs(P)/InP single epitaxial layers and InP/InGaAs(P) double-heterostructure systems on InP substrates. In the spectral regime where the materials are transparent, the reflectance spectra exhibit periodic oscillations. The amplitude of the oscillations is related to the magnitude of the refractive index discontinuity. An analytical expression has been derived which relates the modulation amplitude of these oscillations to the thickness and refractive index (composition) of the epitaxial layers. This allows for refractive index (composition) determination from reflectance alone without prior knowledge of the thickness of the epitaxial layers. Experimental Fourier transform infrared measurements have been used to verify this relationship for InGaAs(P) layers ranging from As mole fraction 0.18 to 1. Values of the composition of the layers obtained by this method are in good agreement with values obtained using photoluminescence measurements.
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u spectroellipsometric study of the nucleation and growth of amorphous silicon
Authors: Canillas A. , Bertran E. , Andújar J. L. , Drévillon B.
Published: July 2002

A detailed in situ spectroellipsometric analysis of the nucleation and growth of hydrogenated amorphous silicon (a:Si:H) is presented. Photoelectronic quality a-Si:H films are deposited by plasma-enhanced chemical vapor deposition on smooth metal (NiCr alloy) and crystalline silicon (c-Si) substrates. The deposition of a-Si:H is analyzed from the first monolayer up to a final thickness of 1.2 μm. In order to perform an improved analysis, real time ellipsometric trajectories are recorded, using fixed preparation conditions, at various photon energies ranging from 2.2 to 3.6 eV. The advantage of using such a spectroscopic experimental procedure is underlined. New insights into the nucleation and growth mechanisms of a-Si:H are obtained. The nucleation mechanism on metal and c-Si substrates is very accurately described assuming a columnar microstructural development during the early stage of the growth. Then, as a consequence of the incomplete coalescence of the initial nuclei, a surface roughness at the 10–15 Å scale is identified during the further growth of a-Si:H on both substrates. The bulk a-Si:H grows homogeneously beneath the surface roughness. Finally, an increase of the surface roughness is evidenced during the long term growth of a-Si:H. However, the nature of the substrate influenced the film growth. In particular, the film thickness involved in the nucleation-coalescence phase is found lower in the case of c-Si (67±8 Å) as compared to NiCr (118±22 Å). Likewise films deposited on c-Si present a smaller surface roughness even if thick samples are considered (>1 μm). More generally, the present study illustrates the capability of in situ spectroellipsometry to precisely analyze fundamental processes in thin-film growth, but also to monitor the preparation of complex structures on a few monolayers scale.
Direct measurement of the electron density in electron beam irradiated Ar/HCl gas mixtures by time-resolved interferometry
Authors: Lando M. , Rozenberg Z. , Rokni M.
Published: July 2002

The electron density in electron-beam irradiated Ar/HCl gas mixtures has been measured by time-resolved infrared interferometry at 9.6 μm, using a Mach-Zehnder interferometer. Measurements were performed for e-beam irradiated gas mixtures with various HCl concentrations between 0.05% and 5.0%, and total gas pressures between 0.5 and 4.0 atm. The e-beam pulse was 350 ns long and at an energy of 150 keV. The e-beam current density was varied between 25 and 14 mA/cm2. The measured electron-density pulse had a characteristic shape with a maximum at the first 100 ns, followed by a drop toward the end of the e-beam pulse. The values of the electron density at the maximum and at the end of the e-beam pulse varied slowly as a function of HCl concentration. The experimental results were modeled by incorporating a simplified kinetic code into the elendif Boltzmann code, which calculated the electron energy-distribution function. The code calculations took into account the effect of the large cross sections for vibrational and rotational excitation of HCl molecules by electron impact. The main conclusion of the analysis is that these cross sections reduce the electron average energy below 0.5 eV for HCl concentrations higher than 0.1%. This conclusion and the results of the code calculations are qualitatively consistent with the experimental observations. But no quantitative agreement was obtained between the code predictions and the experimental results. Possible reasons for this disagreement are discussed.
Ohmic and radiation losses in superconducting films
Authors: Drabeck L. , Holczer K. , Grüner G. , Scalapino D. J.
Published: July 2002

The losses associated with leakage through thin-film superconductors with film thickness comparable to the skin depth in the normal state, and to the penetration depth in the superconducting state, are described. The method is used to describe the surface resistance of YBa2Cu3O7 films deposited on various substrates.
Dielectric properties of rf-sputtered Y2O3 thin films
Authors: Onisawa Ken-ichi , Fuyama Moriaki , Tamura Katsumi , Taguchi Kazuo , Nakayama Takahiro , Ono Yoshimasa A.
Published: July 2002

Yttrium oxide (Y2O3) thin films were deposited on indium-tin-oxide(ITO)-coated glass substrates by the radio-frequency-sputtering method using an Y2O3-sintered target. The relative dielectric constant εr and the dielectric strength EBD of the Y2O3 films were studied. It was found that εr and EBD have a maximum value and a minimum value, respectively, at 1.3 Pa when the pressure of the sputtering gas, Ar+10% O2, is varied from 0.67 to 9.3 Pa. The x-ray diffraction study showed that the Y2O3 films deposited at 1.3 Pa are predominantly oriented along the 〈332〉 direction and their grain size is the smallest. Ion mass analysis showed impurity diffusion from ITO in the films deposited at 1.3 Pa. Furthermore, the dielectric properties of the Y2O3 films deposited at 1.3 Pa are related to the structural properties, such as the 〈332〉 orientation, grain size, and impurity diffusion.
Selective interdiffusion of GaInAs/AlInAs quantum wells by SiO2 encapsulation and rapid thermal annealing
Authors: O’Brien S. , Shealy J. R. , Chia V. K. F. , Chi J. Y.
Published: July 2002

Substantial blue shifts in the photoluminescence (PL) transition energies of GaInAs/AlInAs single quantum wells were observed due to localized SiO2 capping and rapid thermal annealing at temperatures between 750 and 900 °C. Secondary-ion mass spectroscopy analyses show that the blue shifts are caused by the impurity-induced interdiffusion of the quantum well interfaces due to the simultaneous diffusion of silicon and oxygen into the crystal. The selective intermixing occurred in regions capped with SiO2 and exhibited blue shifts up to 74 meV while regions with no SiO2 showed only minimal shifting. With this band gap change, a lateral index change of approximately 0.6% is anticipated, making this process suitable for index-guided structures. Samples also exhibited up to 26-fold increases in PL efficiencies due to the annealing process. The dependence of energy shifts and PL efficiencies are studied by measuring room-temperature and low-temperature (≊80 K) photoluminescence. Interdiffusion coefficients have also been calculated as a function of temperature.
Self-field limited currents in ceramic YBaCuO
Authors: Kliem H. , Weyers A. , Lützner J.
Published: July 2002

A model is developed which relates critical current densities Jc in YBaCuO ceramics to the geometrical size of the sample via the motion of flux lines. Flux lines move with velocity v when the Lorentz force FL acting on them exceeds their pinning force Fp. The model further explains the temperature dependence of Jc and the voltage-current characteristic U(J,T) with temperature T as parameter.
A continuum model for low-pressure radio-frequency discharges
Authors: Meyyappan M.
Published: July 2002

A computational model for low-pressure (<0.3–0.5 Torr) radio-frequency glow discharges is presented. The governing equations are the first three moments of the Boltzmann transport equations. In order to describe the weakly collisional sheaths, the nonlinear inertia terms in the momentum equations are retained. The model is demonstrated for a 13.56-MHz argon discharge. A parametric study involving variations in pressure, electrode spacing, and driving voltage is presented.
Ionic assignment in Xe pulsed discharges by time-resolved spectral analysis
Authors: Bertuccelli G. , Di Rocco H. O. , Ranea-Sandoval H. F. , Sherar A.
Published: July 2002

Time-resolved spectroscopy has been used in a Xe pulsed discharge. The analysis reveals a delay in the onset of emission which is characteristic of the ion, suggesting that this can be related to the time for exciting each ionization stage, for given discharge conditions. This lag is longer for higher ions. The delay determination was done characterizing it for several lines of each ion; only some are listed below. The results enable a characterization of all the nonclassified Xe lines which are known to lase in the visible and the near UV, as belonging to three different groups of ions. One has temporal lags which coincides with those of Xe iv well-classified lines; the other two, each having longer time delays, are assigned as transitions in higher ions.
ac impedance analysis on crystalline layered and polycrystalline bismuth titanate
Authors: Huanosta A. , Alvarez-Fregoso O. , Amano E. , Tabares-Muñoz C. , Mendoza-Alvarez M. E. , Mendoza-Alvarez J. G.
Published: July 2002

A comparison is made on the dielectric properties of the ferroelectric perovskite bismuth titanate for both crystalline (along different directions) and polycrystalline (with and without flux) samples, using the complex ac impedance technique. Results for the impedance, conductivity activation energies, bulk dielectric constant, and temperature behavior of the low-frequency dielectric constant are presented. We discuss these results in terms of the conduction mechanisms depending on the nature of the sample, and compare results for crystalline and polycrystalline samples. Also, we show the important influence of the flux on the dielectric properties of the different samples, which must be taken into account in the use of these materials as substrates for the growth of superconducting thin-film ceramic oxides.
Synchrotron-radiation-induced deposition of boron and boron carbide films from boranes and carboranes: Decaborane
Authors: Perkins F. Keith , Rosenberg R. A. , Lee Sunwoo , Dowben P. A.
Published: July 2002

Boron has been deposited successfully on Si(111) from the synchrotron-radiation-induced decomposition of decaborane (14), i.e., B10H14. The rate of deposition is limited by the adsorption rate of decaborane (14) on the surface. In addition there is some indication that there is an activation barrier to dissociative adsorption. The synchrotron-radiation- induced growth rate of boron thin films from decaborane (14) is linear with coverage for a large range of thickness, suggesting a constant sticking coefficient for decaborane adsorption at room temperature.
Measurement of kappa in high T
c superconductors
Authors: Karim R. , How H. , Vittoria C. , Widom A.
Published: July 2002

The experimental magnetic-field derivative of the microwave absorption signal, obtained using electron paramagnetic resonance techniques, has a line shape that depends on the Ginzburg–Landau model parameter κ of the superconducting sample at a given temperature. The type-II superconducting equation of state can be utilized to describe the drop in the output microwave power derivative, from its maximum at H ≂ Hc1 to its much lower values when H ≫ Hc1, in order to estimate the values of κ. The technique also allows for the experimental determination of hysteretic behavior in B as a function of H.
Measurements of spatial and temporal sheath evolution for spherical and cylindrical geometries in plasma source ion implantation
Authors: Shamim M. , Scheuer J. T. , Conrad John R.
Published: July 2002

A comparison of experimental measurements and numerical calculations of temporal and spatial sheath evolution is presented. Spherical targets of copper and stainless steel (radius=2 cm) and a cylindrical target (radius=0.95 cm, height=18 cm) were immersed in an argon plasma with plasma densities of 2×108–8×109 cm−3 and biased negatively (20–50 kV). A Langmuir probe was used to detect the propagating sheath edge. Experimental measurements of sheath edge position were in good agreement with those determined by numerical calculations.
Chemical generation of optical gain at 471 nm
Authors: Benard D. J. , Winker B. K.
Published: July 2002

Stimulated emission on the P(43) and R(70) transitions of the BiF (A-X, v′=1 to v″=4) band was demonstrated, using the reaction of premixed FN3 and Bi(CH3)3. The transient chemistry was thermally initiated by a pulsed CO2 laser, using SF6 as a sensitizer, while amplification was detected using an étalon-tuned pulsed dye laser probe and a sensitive cavity ringdown technique. The magnitude of the peak gain, estimated at 3.6×10−4/cm, was consistent with a negligible concentration of the terminal BiF(X, v″=4) state, based on the calculated optical cross section and the peak concentration of the BiF (A, v′=1) state, as measured by absolute photometry.
A theoretical model for the x-ray luminescence of granular phosphor screens
Authors: Giakoumakis G. E. , Katsarioti M. C. , Lagaris I. E. , Panayiotakis G. S.
Published: July 2002

A theoretical model for the x-ray luminescence of a phosphor screen is presented. The model takes into account the granular structure of the screen and the random deposition of the phosphor grains on the screen substrate. Results based on this model are in very good agreement with the experimental data already known for the x-ray luminescence of the various phosphor screens.
Field-driven domain-wall jumps in thin-film heads
Authors: Klaassen K. B. , van Peppen J. C. L.
Published: July 2002

Modeling voltage transients in thin-film heads produced by irreversible wall motion allows calculation of wall displacement versus time. Velocity modulation of large wall jumps traversing shallow interaction sites allows calculation of the distribution of these sites. In multiple wall jumps, sympathetic secondary jumps producing flux changes of the same polarity as the primary jump involve walls situated along the flux path. Antisympathetic secondary jumps producing flux changes opposite that of the primary jump involve walls situated parallel to the flux path. Finally, thermal agitation is shown to be able to release a wall below its critical field.
Evidence for spatially indirect recombination in Ga0.52In0.48P
Authors: DeLong M. C. , Ohlsen W. D. , Viohl I. , Taylor P. C. , Olson J. M.
Published: July 2002

In previous work we have identified a near-gap photoluminescence in Ga0.52In0.48P which exhibits a strong dependence of emission energy on excitation intensity (‘‘moving emission’’) and correlated its presence and strength to conditions of growth. In this work we extend our investigations to the rise and decay lifetimes associated with the moving and nonmoving components of the emission. The two processes proceed simultaneously at the same energy. For the moving emission, the time constants scale approximately linearly with excitation intensity. Decaying luminescence can, in most cases, be well fitted with one or two exponentials with time constants as long as milliseconds. The rising luminescence is typically slower and in some cases has a nonmonotonic first time derivative. These results are discussed in terms of existing models of the microstructure of ordered Ga0.52In0.48P.
Quantitative photoacoustic depth profilometry of magnetic field-induced thermal diffusivity inhomogeneity in the liquid crystal octylcyanobiphenyl
Authors: Mandelis Andreas , Schoubs Els , Paralta Samuel B. , Thoen Jan
Published: July 2002

An observed change in the photoacoustic signal frequency response upon the application of a transverse magnetic field across octylcyanobiphenyl samples in the nematic phase at 37 °C and 37.5 °C is reported. The application of a recent thermal-wave theory developed for depth profiling of continuously inhomogeneous condensed phases has given quantitative profiles of thermal diffusivity decreases extending to 20–30 μm below the liquid crystal surface. These decaying depth profiles are qualitatively consistent with earlier photoacoustic temperature scans of liquid crystals and are a measure of the extent of bulk reorientational effects due to the magnetic field, as well as the extent of the influence of the surface as a domain reorientation inhibitor in the kG range.
Pulse-modulated microwave plasma etching
Authors: Grabowski C. , Gahl J. M.
Published: July 2002

Studies have been conducted on the etching characteristics of Si in a microwave plasma etching system having a pulse-modulated source. The experiments were performed at several pulse widths and duty cycles, as well as at cw, to determine how etch rate varied. Results indicate that the etch rate of Si increases and approaches that in a cw discharge as pulse width decreases even though total microwave energy is markedly reduced. Langmuir probe measurements suggest that these effects may be due to increased ionization early in the plasma pulse.
Deposition of amorphous silicon using a tubular reactor with concentric-electrode confinement
Authors: Conde J. P. , Chan K. K. , Blum J. M. , Arienzo M. , Cuomo J. J.
Published: July 2002

High-quality, hydrogenated amorphous silicon (a-Si:H) is deposited at room temperature by rf glow discharge at a high deposition rate using a tubular reactor with cylindrical symmetry (concentric-electrode plasma-enhanced chemical vapor deposition, CE-PECVD). Using the novel CE-PECVD design, room-temperature deposition of a-Si:H with growth rates up to 14 Å s−1, low hydrogen concentration (≲10%), and the bonded hydrogen in the Si-H monohydride configuration, is achieved for the first time using an rf glow-discharge technique. The influence of the deposition parameters (silane flow rate, pressure, and power density) on the growth rate, optical band gap, and silicon-hydrogen bonding configuration, is quantitatively predicted using a deposition mechanism based on the additive contribution of three growth precursors, SiH2, SiH3, and Si2H6, with decreasing sticking coefficients of 0.7, 0.1, and 0.001, respectively. The low hydrogen concentration is due to the enhanced ion bombardment resulting from the concentric electrode design.
The influence of ammonia on rapid-thermal low-pressure metalorganic chemical vapor deposited TiNx films from tetrakis (dimethylamido) titanium precursor onto InP
Authors: Katz A. , Feingold A. , Nakahara S. , Pearton S. J. , Lane E. , Geva M. , Stevie F. A. , Jones K.
Published: July 2002

The process kinetics, chemical composition, morphology, microstructures, and stress of rapid-thermal low pressure metalorganic chemical vapor deposited (RT-LPMOCVD) TiNx films on InP, using a combined reactive chemistry of ammonia (NH3) gas and tetrakis (dimethylamido) titanium (DMATi) liquid precursors, were studied. Enhanced deposition rates of 1–3 nm s−1 at total chamber pressures in the range of 3–10 Torr and temperatures of 300 °C–350 °C at a NH3:DMATi flow rate ratio of 1:8 to 1:15 were achieved. Stoichiometric film compositions were obtained, with carbon and oxygen impurity concentrations as low as 5%. Transmission electron microscopy analysis identified the deposited films as TiN with some epitaxial relationship to the underlying (001) InP substrate. This process provides a superior film to the preview RT-LPMOCVD TiNx film deposited using only the DMATi precursor.
Infrared laser diagnostics in methane chemical-vapor-deposition plasmas
Authors: Davies P. B. , Martineau P. M.
Published: July 2002

Tunable diode laser absorption spectroscopy has been used to measure the concentrations of reactive species in an rf (20 kHz) chemical-vapor-deposition reactor as a function of methane flow rate, pressure, current, and added inert gas. The IR measurements have been supplemented by mass spectrometry and optical emission spectroscopy. The reactive hydrocarbon species detected by IR were CH4, C2H2, C2H4, and C2H6, and the free radical CH3. No significant spatial variation in methyl radical concentration was measured between the parallel-plate electrodes under our conditions. The growth rate of amorphous carbon films on the lower (ground) electrode was found to vary linearly with the concentration of CH3 measured close to this electrode, and these results are compatible with a CH3 sticking coefficient of ≤0.02. One-dimensional modeling calculations using the facsimile program were carried out to simulate the variation of the concentration of the principle species with current (electron number density). Satisfactory agreement with the measurements of CH4, CH3, and C2H6 concentrations was obtained when ionization and ion molecule reactions, as well as reactions of neutral species, were included in the chemical model.
Fabrication of nanostructures in strained InGaAs/GaAs quantum wells by focused-ion-beam implantation
Authors: Allard L. B. , Aers G. C. , Charbonneau S. , Jackman T. E. , Williams R. L. , Templeton I. M. , Buchanan M. , Stevanovic D. , Almeida F. J. D.
Published: July 2002

Low-temperature photoluminescence (PL) spectroscopy was used to estimate the compositional disordering induced by Ga focused-ion-beam implantation in a series of strained InGaAs/GaAs quantum wells (QW). A simple formalism was derived to estimate the indium concentration and the degree of interdiffusion of the QWs from the observed shifts in PL transition energies. A study of nanostructures indicated that the lateral extent of compositional disordering was significantly larger than predicted from the lateral spreading of the ion beam.
Photoluminescence of heavily Zn-doped Ga0.85In0.15As grown by low-pressure metalorganic vapor phase epitaxy
Authors: Benzaquen R. , Roth A. P.
Published: July 2002

Zn-doped, p-type, Ga0.85In0.15As samples grown by low-pressure metalorganic vapor phase epitaxy, with free carrier concentrations in the range of 3.22×1015–1.95×1020 cm−3, have been studied by photoluminescence as a function of temperature. At low doping levels, recombinations involving discrete impurity states and free excitons provided a measurement of both the 0 K reference band gap, Eg(0)=(1.296±0.003) eV, and of the Zn acceptor binding energy, E(Zn0)=(25±3) meV in the Ga0.85In0.15As alloy. High doping concentrations cause a band gap shrinkage ‖ΔEg‖ which has been observed with photoluminescence experiments. A model taking into account Kane band tails and assuming a constant matrix element for the relevant optical transitions has been fitted to the photoluminescence spectra of layers with doping levels in the range of 1.6×1019–1.95×1020 cm−3. This provided a good description of the experimental results. The 0 K band gap shrinkage, which appeared to be smaller than in GaAs, follows the relation ‖ΔEg‖=1.4×10−8p1/3 for Ga0.85In0.15As, with ‖ΔEg‖ in eV and p in cm−3.
Near-field subwavelength micropattern generation: Pipette guided argon fluoride excimer laser microfabrication
Authors: Rudman M. , Lewis A. , Mallul A. , Haviv V. , Turovets I. , Shchemelinin A. , Nebenzahl I.
Published: July 2002

Near-field optical methods are used, together with the ability of an argon fluoride excimer laser to remove a wide variety of materials without the deposition of detectable heat, to produce structures with nanometer dimensionalities. In this new method of lithography, a hollow glass micropipette is used to guide the 193 nm light of the excimer laser to the surface to be ablated. With such micropipettes, patterns have been produced on photoresists with linewidths that are as small as 70 nm. By investigating the dimensionality of the structures drawn on the photoresist and on the substrate on which the photoresist was deposited, it appears that nonlinear characteristics of the ablation process may allow the near-field dimensionalities to be maintained at distances that are relatively remote from the tip of the pipette aperture.
In situ scanning electron microscopy observation of the dynamic behavior of electromigration voids in passivated aluminum lines
Authors: Besser Paul R. , Madden Michael C. , Flinn Paul A.
Published: July 2002

The dynamic behavior of electromigration (EM) voids has been studied in situ using a field-emission scanning electron microscope fitted with a Robinson backscatter detector. A high-temperature stage has been used to minimize the temperature gradients associated with Joule heating and to allow independent control of temperature and current density. No evidence of pre-existing voids was found. The formation, growth, and motion of electromigration voids were observed and recorded photographically. The voids moved dynamically against the electron wind. No correlation between void size and void velocity was found. The static growth of EM voids was observed in some instances; however, this did not precede void motion nor did it lead to failure. Moving voids formed late in the test dominated final failure. Comparison of experimental results with void motion models reveals that the models for dynamic void motion are not consistent with experimental observations.
Thermal stability of InGaAs/InGaAsP quantum wells
Authors: Peyre H. , Alsina F. , Camassel J. , Pascual J. , Glew R. W.
Published: July 2002

We report a cross investigation of the effect of interdiffusion on the photoluminescence and Raman spectra of a single quantum well of InGaAs (80 Å wide) sandwiched between two large InGaAsP barriers. First, we investigate the blue shift of the recombination line (2 K) after annealing at 650 and 750 °C from 15 min to 2 h. We assume one single diffusivity coefficient for all atomic species (i.e., conservation of the lattice matching after annealing) and deduce the amount of intermixing through a model calculation. We find average diffusivity coefficients D=9.5×10−3 Å2 s−1 and D=2×10−1 Å2 s−1 at 650 and 750 °C, respectively. This agrees well with previous measurements reported for the parent system InGaAs/InP and supports an activation energy EA=2.54 eV. Next we investigate, on the same series of samples, the change in phonon frequency associated with the GaAs longitudinal-optical-like mode in the active InGaAs layer. To connect quantitatively the change in wave number with the change in arsenic composition, versus annealing sequence, one must use a carefully checked calibration curve. We show that the linear relationship Δy/Δω=4×10−2(cm) provides a satisfactory agreement with the results of our photoluminescence investigation. This gives for the amount of arsenic leaving the well Δy≊−5% per h1/2 at 650 °C and −20% per h1/2 at 750 °C, respectively.
Infrared spectroscopy of chemically bonded hydrogen at voids and defects in silicon
Authors: Stein H. J. , Myers S. M. , Follstaedt D. M.
Published: July 2002

Chemical bonding of H to displacement defects and internal surfaces in Si has been investigated by infrared-absorption and nuclear reaction analysis techniques. A He implantation/anneal sequence was used to produce faceted voids which are retained to at least 800 °C in a buried layer as revealed by transmission electron microscopy. Hydrogen was injected into void layers by three different methods: ion implantation, plasma exposure, and H2 gas exposure. Infrared absorption by Si-H stretch modes with frequencies characteristic of monohydrides on (100) and (111) surfaces are observed for all methods of H injection, consistent with bonding on faceted void surfaces. Thermal stability of Si-H is higher on void surfaces than on other trapping sites. Displacement defects produced by H-ion implantation trap H but release it upon annealing for retrapping on voids. The Si-H absorption bands with frequencies characteristic of monohydrides on (100) and (111) surfaces anneal in parallel between 600 and 800 °C and in coincidence with the loss of total H measured by nuclear reaction analysis. Moreover, densities comparable to the total H density are estimated for void surface states and for Si—H bonds on void surfaces. It is inferred from these results that bonding of H on the void surfaces is energetically favored over H2 formation in the voids, and it is concluded that the 2.5±0.2 eV determined in a separate study of H release from buried voids is the Si—H bond energy descriptive of both (111) and (100) surfaces.
Double parallel-aligned cells for high speed liquid crystal displays
Authors: Wu Shin-Tson
Published: July 2002

Double parallel-aligned nematic liquid crystal cells with crossed directors: one serves as a tunable phase compensator and another as a master cell, exhibits a fast response time, improved viewing angle, reasonably high white-to-black contrast ratio, and low operation voltage. The flexibility in choosing an appropriate operation voltage enables the device to be operated at its optimal condition. This operational mode can be used for both color-sequential projection and direct view displays.
Monte Carlo simulations of electron distributions in the sheath region of reactive-ion-etching plasmas
Authors: May P. W. , Klemperer D. F. , Field D.
Published: July 2002

The results of a Monte Carlo model for calculating the trajectories of electrons in the plasma sheath region in reactive-ion-etching plasmas are described. The calculations illustrate how the oscillating movement of the sheath imparts energy to electrons and alters the electron energy distribution (EED) within the bulk of a 13.56 MHz Ar discharge. The study is limited to low-pressure discharges of less than about 10 mTorr, where the effects of electron-molecule collisions can be ignored. Under these conditions it is found that the sheath imparts energy preferentially to low-energy electrons. Calculated EEDs for electrons striking the electrodes in a radio-frequency reactor are also presented. Most electrons strike the electrodes with energies of a few eV, but some electrons strike the substrate surface with impact energies as high as 20 eV. This may be an important consideration when modeling etch mechanisms. Secondary electron emission caused by ion bombardment of the electrodes is also modeled. Simulated EEDs for secondary electrons that are produced at the electrodes and accelerated by the action of the sheath potential into the plasma region are presented. These electrons have energies of up to several hundred eV and are therefore important in plasma-sustaining mechanisms.
Hydrogen enhanced out-diffusion of oxygen in Czochralski silicon
Authors: Zhong L. , Shimura F.
Published: July 2002

Out-diffusion of oxygen in Czochralski silicon wafers annealed at 1000 and 1200 °C under a hydrogen ambient is studied with secondary ion mass spectroscopy (SIMS). The oxygen diffusivity, 1.41×102 exp(−3.1 eV/kT) cm2 s−1, obtained from fitting the oxygen SIMS profile is significantly larger than normally expected. This hydrogen enhancement effect is found at temperatures much higher than those reported (<500 °C) in literature, and is attributed to the direct interaction between in-diffused hydrogen and interstitial oxygen atoms. Estimation of the oxygen diffusivity made from hydrogen solubility and diffusivity data is in reasonable agreement with the experimental result. It is suggested that the intrinsic/internal gettering may benefit from the enhancement effect as well as a very low surface oxygen concentration, which is also observed in this work, due to hydrogen treatment.
Effect of annealing on magnetic and structural properties of Co/Re superlattices
Authors: Huai Y. , Cochrane R. W. , Sutton M.
Published: July 2002

We have studied the effect of annealing on the magnetic and structural properties of sputtered Si/Re50 Å [Co20 Å/RexÅ]40 superlattices with xRe=3,5,7,10 Å. Annealing the samples for 1 h at 300 °C causes a slight increase in interfacial mixing and a contraction of lattice spacing d(002) owing to interdiffusion and structural relaxation, as indicated by the x-ray diffraction data. In addition, the subsequent room-temperature magnetoresistance (MR) increases for samples with antiferromagnetic (AF) coupling, by up to 20% for xRe=5 Å, providing strong experimental evidence for the spin-dependent scattering mechanism which predicts an increasing MR with increasing diffuse interface scattering. A further 1 h anneal at 525 °C provokes dramatic interdiffusion between the Co and Re layers, which is accompanied by a considerable decrease of the MR, indicating a disappearance of the interlayer AF coupling.
Use of type II (end of range) damage as ‘‘detectors’’ for quantifying interstitial fluxes in ion-implanted silicon
Authors: Listebarger J. K. , Jones K. S. , Slinkman J. A.
Published: July 2002

Type-II (end of range) defects, produced by Ge+ implantation, were investigated as possible ‘‘detectors’’ for quantifying nonequilibrium interstitial concentrations following B+ implantation into silicon. The type-II damage was created with a 100 keV (1×1015/cm2) Ge+ implant into silicon followed by either a low-temperature (550 °C) or a high-temperature (800 °C) anneal. This resulted in the formation of either a layer of point-defect clusters and small (≤50 Å in diameter) dislocation loops or a layer of larger (∼160–400 Å in diameter) fully formed dislocations loops. This material was subsequently implanted with 30 keV B+ at doses between 7×1013/cm2 and 2×1014/cm2. After a final 800 °C anneal, the concentration of atoms bound by the type-II dislocation loops was measured. Results show that the concentration of interstitials bound by the type-II dislocation loops increases with increasing B+ dose. Relative to control sample values, the net concentration of interstitials trapped as a result of B+ implantation varied from 7.0×1013/cm2 to 1.8×1014/cm2 over the dose range studied. Fully formed loops were also found to be ≥20% more efficient than clusters in trapping the interstitials generated under identical B+ implant conditions. The difference is ascribed to the increase in equilibrium point-defect concentration necessary to stabilize the smaller loops prior to coarsening.
Effects of interdiffusion on the sub-band-edge structure of In0.53Ga0.47As/InP single quantum wells
Authors: Micallef Joseph , Li E. Herbert , Weiss Bernard L.
Published: July 2002

The disordering of In0.53Ga0.47As/InP single quantum wells has been studied using an error function distribution to model the compositional profile after interdiffusion. When considering interdiffusion on the group-III sublattice only, a large strain buildup results during the early stages of disordering. Details are presented showing how this interdiffusion and the effects of strain lead to an interesting carrier confinement profile which differs from that of disordered AlGaAs/GaAs and InGaAs/GaAs quantum-well structures. An abrupt confinement profile is maintained even after significant interdiffusion, with a well width equal to that of the as-grown quantum well. The combined effects of strain with the unstrained band-gap profile results in a potential buildup in the barrier near the interface, while it gives rise to two ‘‘miniwells’’ inside the potential wells. The sub-band-edge structure shows that the potential buildup can result in quasibound subband states, while the heavy-hole well can support the ground state within the miniwells. In contrast, when identical interdiffusion on both group-III and group-V sublattices is considered, the structure remains lattice matched, the confinement profile changes to that of a graded profile, and the ground-state transition energy shifts to shorter wavelengths.
A model for the Barkhausen noise power as a function of applied magnetic field and stress
Authors: Sablik M. J.
Published: July 2002

The model of Alessandro, Beatrice, Bertotti, and Montorsi [J. Appl. Phys. 68, 2901 (1990)] is used to derive the Barkhausen noise power integrated over all frequencies. Using the magnetomechanical hysteresis model of Sablik and Jiles [IEEE Trans. Magn. 29, 2113 (1993)], it is then shown how the Barkhausen noise power peaks at a magnetic field H larger than the H value at which the magnetic permeability peaks. Variation with respect to applied stress and with respect to field ramp rate Ḣ is also investigated. The almost linear increase of Barkhausen amplitude with applied stress seen experimentally is confirmed by the model.
Extension of the Kronig–Penney model for Γ-X mixing in superlattices
Authors: Erdoğan M. U. , Kim K. W. , Stroscio M. A. , Dutta M.
Published: July 2002

An extension of the Kronig–Penney model to treat mixings of different valleys in superlattices is presented. The value of the mixing parameter α used in the model is deduced by comparison with more sophisticated theory and various experiments for the GaAs/AlAs material system. It is shown that with the use of a single value for the mixing parameter, this simple and efficient model can reasonably reproduce the important aspects of valley mixing effects in GaAs/AlAs superlattices over a wide range of layer thicknesses.
Optimal long term imaging of a charged microparticle at the center of a Paul trap in an atmosphere near standard temperature and pressure: Experiment and stochastic model
Authors: Arnold S. , Folan L. M. , Korn A.
Published: July 2002

The thermal rms fluctuation in position of a levitated microparticle in a Paul trap in N2 near standard temperature and pressure is calculated numerically from a stochastic equation of motion and is measured experimentally by long term imaging. The calculations reveal loci of minima within the lowest stability region and enhanced fluctuations as the first instability is approached. Pseudopotential results deviate below our calculations progressively with increased drive potential. This disparity grows by more than an order of magnitude near instabilities, although the pseudopotential approach provides a good asymptotic approximation for small drive potentials. Long term imaging experiments are performed in a trap modified to eliminate stray static fields at its ac ‘‘null’’ point. These experiments are well-described by the stochastic model and suggest the use of such a trap as a stage for long term fluorescence and Raman microphotography experiments on individual microparticles in a gaseous environment.
Observation of nuclear diffraction from multilayers with a Fe/57Fe superstructure
Authors: Röhlsberger R. , Witthoff E. , Gerdau E. , Lüken E.
Published: July 2002

Nuclear diffraction from a 57Fe5B4C/Fe5B4C multilayer has been observed. The reflectivity was measured by Mössbauer spectroscopy in grazing incidence geometry. A pure nuclear Bragg peak showed up at the expected position in the rocking curve. The energy dependence of the reflectivity was measured at different angles near the Bragg peak. The measurements are in good agreement with the theory. The use of nuclear resonant multilayers as monochromators for synchrotron radiation is discussed.
Annealing of boron-implanted corrosion resistant copper films
Authors: Ding P. J. , Lanford W. A. , Hymes S. , Murarka S. P.
Published: July 2002

Ion implantation can be used effectively to passivate copper. The effect of B ion implantation on the oxidization rate of copper is studied as a function of B energy and dose. The increase of sheet resistance associated with ion implantation damage and with the incorporation of B is studied. It is found that a post-implantation inert gas annealing (at 400 °C for 20 min) removes the increase in sheet resistance caused by implant damage while preserving the passivation effects of the B implant.
Photoluminescence from heteroepitaxial (211)B CdTe grown on (211)B GaAs by molecular beam epitaxy
Authors: Gold Jeffrey S. , Myers T. H. , Giles N. C. , Harris K. A. , Mohnkern L. M. , Yanka R. W.
Published: July 2002

Low temperature (∼5 K) photoluminescence spectroscopy was performed on undoped CdTe epilayers grown by molecular beam epitaxy on (211)B oriented bulk GaAs substrates at substrate temperatures ranging from 230 to 275 °C. The emission spectra from all samples studied contained evidence of the diffusion of gallium and arsenic atoms from the substrate. A broad, low amplitude emission band observed at 1.594 eV was related to the GaCd donor level in CdTe. Donor-acceptor pair recombination observed at 1.51 eV was due to the substitutional GaCd donor and AsTe acceptor. The level of compensation in the CdTe layers was determined from the energy shift of the donor-acceptor emission peak with excitation power, with the lowest degree of compensation observed in a sample grown at 230 °C. In addition, a bright emission peak was observed at 1.47 eV. This peak, which had been observed previously in homoepitaxial and heteroepitaxial growth of CdTe, was related to electron-hole recombination of a structural defect in the CdTe/GaAs epilayers with an electronic binding energy of ∼130 meV.
Compositional and electronic properties of chemical-vapor-deposited Y2O3 thin film-Si(100) interfaces
Authors: Sharma R. N. , Rastogi A. C.
Published: July 2002

Thin Y2O3 dielectric films on p-Si(100) structures prepared by low-pressure chemical-vapor deposition show an interfacial growth of a thin SiO2 layer (≊2 nm). Oxygen annealing at 580 °C for 45 min causes a further growth of this oxide layer to ≊8 nm. The interfacial silicon oxide has a bilayer structure consisting of crystalline SiO2 at the Y2O3 side and suboxide SiOx at the Si side of the interface as revealed by line shapes of Auger Si transition and Fourier-transformed infrared spectroscopy studies. The as-deposited Y2O3 film/Si-based metal-insulator- semiconductor MIS structures show a single-step breakdown with a sharp breakdown field distribution, whereas the O2-annealed structures show a two-step selective breakdown with a dispersive breakdown distribution. O2-annealed Y2O3 film/Si-based MIS structures do not show the expected reduction in leakage currents. This is attributed to growth of a crystalline SiO2 layer and generation of defect and charge trapping at the Y2O3/SiO2/Si interface. The hysteresis effect observed in the C-V curves at varied ramping rates shows that the nature of traps in the as-deposited Y2O3 film/Si interface is such that the electron capture process is slower than emission, while in O2-annealed structures the reverse is true.
On the Richardson constant of intimate metal-GaAs (111)B Schottky diodes grown by molecular beam epitaxy
Authors: Pilkington S. J. , Missous M. , Woolf D. A.
Published: July 2002

Careful measurements have been made of the temperature dependence of the barrier height (φb) and the Richardson constant (A**c) for several metal/GaAs (111)B Schottky diodes using current-voltage and capacitance-voltage techniques. The metals used, aluminium, copper, and gold, were evaporated at a base pressure of 10−10 Torr, to ensure no native oxide at the interface. The values obtained for the temperature dependence of the barrier height were −(4.3±0.1)×10−4 eV K−1 for all diodes except for the Cu/GaAs (111)B diode where it was −(4.7±0.1)×10−4 eV K−1. The calculated Richardson constants were 0.51×104, 0.88×104, and 1.37×104 A m−2 K−2 for the Al, Au, and Cu GaAs (111)B diodes respectively, and 0.50×104 A m−2 K−2 for the Al/GaAs (100) comparison diode. The exactness of results between the Al/GaAs (111)B and the Al/GaAs (100) Schottky diodes is believed to indicate the formation of a thin interfacial layer of AlAs, probably formed during the metal evaporation. It was found that the semiconductor orientation had a subtle effect upon the Richardson constant compared to similar Schottky diodes fabricated on (100) GaAs. The variation in A**c indicates that the band structure of the metal plays a part in the formation of a Schottky barrier, and the similarity in the value of α indicates that the barriers are pinned relative to the same position. In comparison to the GaAs band gap variation with temperature, this appears to be pinned relative to the valence band of the semiconductor.
Influence of oxide thickness nonuniformities on the tunnel current-voltage and capacitance-voltage characteristics of the metal-oxide-semiconductor system
Authors: Majkusiak Bogdan , Strojwas Andrzej
Published: July 2002

A model is presented for the tunnel current–gate-voltage and high-frequency-capacitance–gate-voltage characteristics of a metal-oxide-semiconductor system with a very thin and nonuniform oxide layer. Assuming the Gaussian distribution of the oxide thickness nonuniformities, their influence on the electrical characteristics of the Al-SiO2-Si(n) system is analyzed theoretically.
Low-temperature deposition of hexagonal ferrite films by sputtering
Authors: Morisako Akimitsu , Nakanishi Hiroaki , Matsumoto Mitsunori , Naoe Masahiko
Published: July 2002

Pb-substituted Ba-ferrite films were prepared at various substrate temperature Ts by dc magnetron sputtering and their crystallographic characteristics and magnetic properties were investigated. The substitution of Pb facilitates the crystallization and improves the crystallinity for hexagonal M phase. All of the films prepared at Ts above 460 °C exhibit a good c-axis orientation and the c-axis dispersion angle (Δθ50) for Pb-substituted Ba-ferrite films is as small as 1°. The coercivities (Hc⊥) and Hc∥) and saturation magnetization Ms of Pb-substituted Ba-ferrite films are 0.7–1.0 kOe, 0.2 kOe and 250–300 emu/cm3, respectively.
Relaxed, low threading defect density Si0.7Ge0.3 epitaxial layers grown on Si by rapid thermal chemical vapor deposition
Authors: Watson G. Patrick , Fitzgerald Eugene A. , Xie Ya-Hong , Monroe Don
Published: July 2002

Relaxed Si0.7Ge0.3 epitaxial layers that possess threading defect densities as low as 5×105 cm−2 have been grown on Si substrates by rapid thermal chemical vapor deposition. The layers were formed in a series of steps of constant Ge content, each step with either 6% or 3% more Ge than the previous one. At the low average grading rates investigated, the number of steps used to reach 30% Ge only slightly affected the density of individual threading dislocations, imaged by electron beam induced current (EBIC). However, the density of dark-line defects seen in EBIC, which are formed from pile-ups of threading dislocations, was strongly influenced only by the average grading rate. Both the dark line density and the dark spot density must be considered when assessing the surface of these relaxed layers.