bluuebunny/crossref_metadata_2025 huggingface dataset:
Deep level transient spectroscopy of metal-oxide-semiconductor capacitors fabricated on CF4 reactive-ion-etched Si
Authors: Vuillaume D. , Lakhdari H. , Gambino J. P.
Published: July 2002

Metal-oxide-semiconductor capacitors have been fabricated on CF4 reactive-ion-etched silicon in order to study defects at the Si-SiO2 interface and in the bulk of the Si substrate, produced by the combination of reactive ion etching (RIE) and oxidation. High interface state densities (in the range 1010 –1011 cm−2  eV−1 ) are observed for capacitors fabricated with either dry or wet oxidations, and are probably due to disrupted or strained bonds at the Si-SiO2 interface. It is proposed that the disrupted or strained bonds result from implanted impurities and/or lattice defects from RIE that accumulate at the interface during the oxidation process. Capacitors fabricated with a wet oxidation on CF4 -etched Si contain bulk traps in the Si, which may be partly responsible for the low generation lifetimes observed for these samples. The bulk traps are probably related to carbon contamination, in SiC form, introduced during RIE.
Investigations on resonant tunneling in III-V heterostructures: Comparison between experimental data and model calculations
Authors: Guéret P. , Rossel C. , Schlup W. , Meier H. P.
Published: July 2002

Data obtained on a set of GaAs/AlGaAs double-barrier quantum-well resonant tunneling structures are compared with model calculations of the ideal case where scattering is negligible and tunneling is coherent throughout the entire structure. The comparison points to interface roughness in the well as the most likely cause for the observed large valley currents. The currents at low biases, before resonance sets in, are also studied. Their magnitude is found to be consistent also with the sequential tunneling picture.
The effect of fluorine implantation on the interface radiation hardness of Si-gate metal-oxide-semiconductor transistors
Authors: Nishioka Yasushiro , Ohyu Kiyonori , Ohji Yuzuru , Natsuaki Nobuyoshi , Mukai Kiichiro , Ma T. P.
Published: July 2002

The radiation hardness of fluorinated SiO2/Si interface in metal-oxide-semiconductor field-effect transistors has been found to depend strongly on the amount of fluorine introduced. In this study, the fluorine was introduced by low-energy F implantation onto the surface of the polycrystalline silicon gate electrode, followed by annealing at 950 °C to diffuse F into the gate SiO2 toward the SiO2/Si interface. The improved radiation hardness is attributed to the strain relaxation near the SiO2/Si interface by fluorine incorporation.
Thermochemistry of alkylarsine compounds used as arsenic precursors in metalorganic vapor phase epitaxy
Authors: Lum R. M. , Klingert J. K.
Published: July 2002

Despite their increased safety, alkylarsine compounds have not generally replaced arsine (AsH3) in the metalorganic vapor phase epitaxy (MOVPE) of GaAs because of carbon incorporation and high background doping levels. We have studied the thermal decomposition of AsH3 and its alkyl derivatives (methyl, ethyl, and butyl compounds) to determine the impact of the thermochemistry on growth processes. The thermal stability of the As-precursor compounds was found to decrease in the order AsH3>MenAsH3−n >Et3As>t-BuAsH2. We report the first evidence for production of diarsine (As2H4) from t-BuAsH2 and for formation of lower substituted methylarsine homologs from Me3As and Me2AsH. The presence of these species is strong evidence that decomposition of the alkylarsines occurs via a free-radical mechanism. Formation of carbon-free arsenic products appears to be the key difference between t-BuAsH2 and the more highly substituted alkylarsines in attaining high quality films by MOVPE.
Theory of the microwave-frequency magnetic susceptibility of insulating ferri- and ferromagnets
Authors: Sokoloff J. B.
Published: July 2002

An expression for the ac susceptibility of a ferro or ferrimagnet, including damping resulting from various microscopic proceses, is derived microscopically. The two-magnon case can be derived from the equations of motion methods given in Lax and Button [Microwave Ferrites and Ferrimagnetics (McGraw–Hill, New York, 1962), pp. 172–180], but other processes require many-body perturbation theory.
Reflectivity of GaSb-AlSb quantum-well structures in the range 2–5 eV
Authors: Ance C. , Raisin C. , Ferraton J. P.
Published: July 2002

We report reflectance spectra of two GaSb-AlSb quantum-well structures in the range 2–5 eV at different temperatures. In the region of the E1 and E1+Δ1 peaks, our experimental study shows that electronic properties can be related to strain and confinements effects in a type-II heterostructure at the L point.
Low-temperature photoluminescence studies of mercuric-iodide photodetectors
Authors: James R. B. , Bao X. J. , Schlesinger T. E. , Markakis J. M. , Cheng A. Y. , Ortale C.
Published: July 2002

Mercuric-iodide (HgI2 ) photodetectors with sputtered indium-tin-oxide (ITO) entrance electrodes were studied using low-temperature photoluminescence spectroscopy. The photoluminescence spectrum obtained on each photodetector was found to differ for points beneath the ITO contact and points adjacent to it, indicating that the contact fabrication process introduces new carrier traps and radiative recombination centers within the ITO-HgI2 interfacial region. In particular, a new broad band was observed in the spectra taken from points beneath the ITO electrode. Photocurrent-versus-position measurements showed that the intensity of this broad band was enhanced in regions having relatively poor photoresponse.
Oxidation of tin on silicon substrate by rapid isothermal processing
Authors: Singh R. , Chou P. , Radpour F. , Nelson A. J. , Ullal H. S.
Published: July 2002

We report an oxidation study of an Sn overlayer on Si(100) carried out at 400 °C by rapid isothermal processing (RIP) and furnace processing. Single oxide phase SnO2 could be obtained only by rapid isothermal processing. Based on x-ray diffraction, x-ray photoelectron spectroscopy, high-frequency capacitance-voltage characteristics, and breakdown measurements, improved quality of dielectric films was obtained by RIP. A possible explanation based on the difference in the radiation spectrum of the two sources of energy is also given.
Temperature distributions and molten zones induced by heating with line-shaped electron beams
Authors: Timans P. J. , McMahon R. A. , Ahmed H. , Hopper G. F.
Published: July 2002

A recently developed time-resolved reflectivity technique has been used to characterize the temperature distributions and molten zones induced in silicon-on-insulator structures by heating with scanned line-shaped electron beams. Measured temperature distributions were compared to theoretical predictions from a one-dimensional heat-flow model, which assumes that the heat flow parallel to the surface can be ignored. The results from the experiments and the predictions from the numerical model were also compared to predictions from an analytical model for heating of a homogeneous material. The range of heating conditions for which the one-dimensional approximation was suitable was determined, and it was found to be satisfactory for heating with line beams of more than 200-μm width at sweep speeds greater than 5 cm/s. Conditions which produced melting of the silicon film were explored, and it was found that the numerical model did not adequately describe this phase transition. The discrepancy between the theoretical predictions and the observed results can be explained by the need to supercool the liquid silicon by approximately 155 °C before it freezes.
A theory of abrupt termination and spontaneous restart of electrical current in surface flashover arcs
Authors: Kadish A. , Robiscoe R. T. , Maier II William B.
Published: July 2002

The space-time dynamics of surface flashover discharges is studied using a nonlinear one-dimensional transmission line model. When the current I is not zero, the relation between the resistance per unit length, R̂, and I is assumed to be given by a local arc welder’s ansatz, R̂‖I‖=E*, where E* is a constant. The model predicts a threshold for discharge, and abrupt local termination and spontaneous restart of the discharge current. If at a place on the discharge path it happens that the charge gradient fails to exceed the threshold condition when the current vanishes, then the current will abruptly terminate there. However, if a discharge current flows in a region adjacent to one where the current has terminated, the edge of the current-free region can be ‘‘ignited,’’ resulting in the ‘‘active’’ region encroaching on the ‘‘quiet’’ one. A formula for the speed of encroachment is derived. Formulas are also derived for current pulse waveforms and the charge transported during the discharge.
Semiconductor electron-wave slab waveguides
Authors: Gaylord T. K. , Glytsis E. N. , Brennan K. F.
Published: July 2002

A one-dimensional semiconductor quantum well can act as a waveguide for ballistic electrons owing to the quantum mechanical wave behavior of these electrons. The allowed modes in an asymmetric quantum well slab waveguide are quantified. Electron waveguiding can occur for energies above one or both of the potential barriers. Due to dispersion, each electron waveguide mode has an upper-energy cutoff as well as a lower-energy cutoff. An example waveguide consisting of Ga0.85Al0.15As (substrate), GaAs (film), and Ga0.70Al0.30As (cover) is treated. This structure is a single-mode electron waveguide for [100] GaAs thicknesses of from 6 through 31 monolayers.
Photoablation of polymers at 193 nm: Shot-to-shot study of emission spectra, etch depths, and transmission
Authors: Deshmukh Subhash , Rothe Erhard W. , Reck Gene P.
Published: July 2002

Excimer laser pulses (193 nm) were used to photoablate graphite and polymers: polymethylmethacrylate (PMMA) and polycarbonate (PC) in a vacuum (∼10−5 Torr). The resulting emission spectra were obtained on a shot-to-shot basis in the 375–520 nm wavelength range. The relative and absolute intensities of most transitions are a function of the number of laser shots. Etch profiles were measured as a function of the number of shots. The etch depth was almost linear with number of shots for the first 30 shots. The transmittance of the polymers in the range of 350–800 nm was measured as a function of number of shots and showed a minimum for PMMA.
Oxygen distribution in silicon-on-insulator layers obtained by zone melting recrystallization
Authors: Mertens P. W. , Leclair J. , Maes H. E. , Vandervorst W.
Published: July 2002

The oxygen content in zone melting recrystallization silicon-on-insulator (ZMR SOI) layers with thicknesses ranging between 0.5 and 25 μm obtained with a movable lampheater is studied. Secondary-ion-mass spectrometry profiling as well as numerical calculations are presented. The simulations are based on oxygen redistribution during cooling down. In the model it is assumed that the interface reaction is fast enough to be not the rate-limiting step in the redistribution process. Consequently, the oxygen transport was considered to be entirely diffusion limited. Good agreement was found between the measurements and calculated values. The profiles show a maximum at the center of the layer and symmetrically depleted regions in the top and bottom of the silicon film. It has been generally accepted that ZMR SOI layers have a high oxygen concentration corresponding to the saturation level at melting point. In the present study, however, we show that in the 0.5-μm layers the oxygen concentration is as low as 1×1017(O atoms)/cm3.
Anisotropy effects on the electronic transport in photoexcited GaAs
Authors: Joshi R. P. , El-Ghazaly S. , Grondin R. O.
Published: July 2002

We investigate the effects of both carrier and phonon k-space anisotropy on the transport in bulk GaAs photoconductors. Our results show that photogeneration by laser pulses polarized perpendicular to the electric field can delay the initial velocity rise. Furthermore, anisotropic phonon amplification can degrade the turn-off characteristics. Finally, unlike n-doped semiconductors, we find that the steady-state velocity-field values in photoconductors are reduced because of the nonequilibrium phonon modes.
New formulation of the Stoner–Wohlfarth hysteresis model and the identification problem
Authors: Friedman G.
Published: July 2002

A new formulation of the Stoner–Wohlfarth hysteresis model is introduced. This formulation simplifies the analysis of the model through the use of a diagram technique similar to the one employed by the Preisach model. It is shown that using the new formulation the identification problem can be posed in terms of an integral equation relating the switching field distribution to the set of vertical chords of symmetric minor hysteresis loops. Solution of this integral equation is discussed, and some limitations of the Stoner–Wohlfarth model are revealed.
Observation of a commensurate temperature plateau induced by c-axis applied magnetic fields in holmium
Authors: Noakes D. R. , Tindall D. A. , Steinitz M. O. , Ali N.
Published: July 2002

Measurements of the magnetic structure of holmium in c-axis applied magnetic fields were made by neutron diffraction in the (h0l) plane. In applied fields of 1.7 and 2.2 T directed along the c-axis, the overall periodicity of the spiral structure locks into the commensurate superlattice value 4c0 over a finite range of temperature (approximately 2 K at 2.2 T) near 98 K, whereas no such effect is seen in the crystal in zero field. The commensurate plateau extends between two transitions bracketing 98 K reported in magnetization and dilatometry by Steinitz et al. [Phys. Rev. B 40, 763 (1989)]. No new satellites were found in this temperature range, but the intensities of the fundamental magnetic Bragg peaks exhibited precursor behavior as the commensurate state was approached in temperature both from above and below.
Phenomenological theory of the 1/4 commensurate phase of holmium
Authors: Plumer M. L.
Published: July 2002

A model derived from a nonlocal Landau-type free energy is proposed to explain the recently observed lock-in at Q=0.25c* of the helical spin density wave vector in Ho around 96 K. The analysis suggests that Umklapp terms of the form Δ4Q,G are responsible for stabilizing the commensurate phase over a narrow temperature range. An essential requirement of the model is the existence of a mechanism to distort the polarization of the spin density from helical to elliptical. This can be achieved by a component in the basal plane of uniform magnetization or of uniaxial stress. With suitable adjustment of parameters, the measured temperature dependence of Q is reproduced.
Synthesis of band and model Hamiltonian theory for strongly hybridizing uranium systems
Authors: Hu Gong-Jia , Sheng Qing G. , Cooper Bernard R.
Published: July 2002

For a specified chemical environment (e.g., isostructural compound), uranium typically shows the most delocalized correlated f-electron behavior of the light rare earths and actinides. This provides perhaps the most interesting correlated f-electron behavior for phenomena such as heavy fermion behavior, but also provides the greatest difficulty for the theory. Here we are concerned with the synthesis of band and model(Anderson lattice) Hamiltonian theory to be able to evaluate the phenomenological behavior on a materially predictive ab initio basis. In previous studies for cerium and plutonium systems, use was made of U(the correlation energy) being rather large in dealing with the f-f banding term, derived from the Schrieffer–Wolff transformation of the Anderson lattice Hamiltonian. Since the bandwidth is suppressed by a factor of 1/U, it was justified to neglect the f-f banding term. This is not justified for uranium systems which have a much smaller U. Therefore, rather than treating f electrons as core(resonant) states during the self-consistent band calculation, we first treat 5f’s as valence electrons and determine the self-consistent potential. Then the density of states, and hence the f bandwidth (Γ1) which characterizes hybridization between all the band electrons, can be calculated. Then we let the 5f’s form bands among themselves, while suppressing hybridization with other bands during the determination of the self-consistent potential. We then use that potential as the basis to calculate the density of states and the f bandwidth (Γ2), which characterizes the hybridization between f’s. We then use the value of (Γ1−Γ2), the hybridization strength so obtained, to absolutely evaluate the magnetic ordering behavior and compare with experiment.
The effect of intergranular silver on the surface resistivity of YBa2Cu3O7
Authors: Wilber W. D. , Finnegan R. D. , Tauber A. , Silber L. M.
Published: July 2002

In an effort to improve the high-frequency properties of bulk high-Tc superconductors, the surface resistivity was measured for a series of YBa2Cu3O7 samples with various levels of silver addition. The nominal weight percent of silver in the sample series ranged from 7.0% to 23.8%, and the sintering temperature varied from 860 to 930 °C. The surface resistivity was measured by cavity perturbation at frequencies of 8 and 35 GHz. While the addition of intergranular silver does improve the dc resistance for temperatures above the critical temperature Tc, the high-frequency surface resistivity for T<Tc does not improve with the addition of silver. The intergranular silver can, in fact, increase the surface resistivity. The optimum sintering temperatures were 910–930 °C. The data are examined with respect to a model for high-frequency losses in ceramic superconductors.
Electron microscopy studies of new phases in Nd-Fe alloys
Authors: Strzeszewski J. , Tsoukatos A. , Hadjipanayis G. C.
Published: July 2002

The magnetic properties, structure, microstructure, and chemical composition of new phases found in melt-spun Nd-Fe alloys are reported. High coercivities were obtained in ribbons after a heat treatment for 10–15 min at temperatures in the range of 450–550 °C. Thermomagnetic data showed the existence of two new phases with Curie temperatures at around 250 and 340 °C, respectively. Electron microscopy observations confirmed the existence of two different iron-rich phases. One of them had 70 at. % Fe and a tetragonal structure with a=8.0 Å and c=11.9 Å, similar to Nd2Fe14B. The other one had 85 at. % Fe and a hexagonal structure with a=20.5 Å and c=11.5 Å. These phases are probably ternary Nd-Fe-O stabilized by oxygen. The hexagonal phase is believed to correspond to the phase with a Curie temperature of 250 °C.
Magnetotransport studies of epitaxial Cr thin films
Authors: Mattson J. , Brumitt B. , Brodsky M. B. , Ketterson J. B.
Published: July 2002

We report the results of transport measurements on epitaxial Cr thin films. The variation of TN (The Néel transition temperature) with respect to the film thickness is discussed in terms of the stress in the film. In addition, the temperature dependence of the magnetoresistance and Hall resistance for temperatures from 4 to 150 K are measured and discussed, with particular attention to the temperature dependence of the nonlinear portion of the Hall data.
Three-dimensional transmission line model for flux conduction in thin-film recording heads
Authors: Mallary M. , Torabi A. , Batra S.
Published: July 2002

Flux spreading in thin-film recording heads has been studied using a three-dimensional transmission line model. This model uses the observed domain wall structure in a thin-film head as the map on to which a set of electrical circuit nodes in the model are placed. These nodes are connected in the transverse direction by inductive circuit elements which simulate the domain wall mobility for transverse flux conduction by wall motion. In the longitudinal direction skin-effect-limited conduction by magnetization rotation is simulated by a R/L series element. At frequencies above 8 MHz this model begins to exhibits a concentration of flux on the axis of the head.
Antiferromagnetic form factor of Sr2CuO2Cl2
Authors: Wang X. L. , Miller L. L. , Ye J. , Stassis C. , Harmon B. N. , Johnston D. C. , Schultz A. J. , Loong C.-K.
Published: July 2002

Neutron diffraction techniques have been used to study the antiferromagnetic form factor of Sr2CuO2Cl2, which has the body-centered-tetragonal (I4/mmm) K2NiF4-type structure (the same as that of tetragonal La2CuO4 but with the out-of-plane oxygens replaced by Cl and the La by Sr). The antiferromagnetic form factor was obtained at 15 K by measuring the integrated intensities of the ( (1)/(2) (1)/(2) 0), ( (1)/(2) (1)/(2) 2), ( (1)/(2) (1)/(2) 3), ( (3)/(2) (3)/(2) 0), ( (3)/(2) (3)/(2) 6), ( (3)/(2) (5)/(2) 1), ( (3)/(2) (3)/(2) 8), and ( (5)/(2) (5)/(2) 0) magnetic reflections of a single crystal of Sr2CuO2Cl2. The experimentally determined magnetic form factor is similar to that of La2CuO4. The experimental data were compared with the Cu2+ magnetic form factor and with the results of band theoretical calculations. We find that the fit to the experimental data is improved if one assumes a dipolar spin polarization on the in-plane oxygen ions.
Spin states and electronic conduction in Ni oxides
Authors: Dionne Gerald F.
Published: July 2002

Magnetic and electronic properties of the mixed-valence semiconductor LixNi2+1−2xNi3+xO are reinterpreted in terms of low-spin states for both Ni ions. Anomalous decreases in hopping electron activation energies are discussed on the basis of (i) breakdown in antiferromagnetic ordering through spin canting of the Ni sublattices through exchange isolation caused by diamagnetic Li1+ ions that group with the low-spin Ni3+ (S= (1)/(2) ) to form polarons, and (ii) enhanced disruption of magnetic superexchange that results from a combination of Li1+ dilutants and S=0 states of surrounding Ni2+ ions induced at low temperatures by static Jahn-Teller tetragonal distortions of the oxygen octahedra around the Ni3+ polarons. Reported magnetic ordering and conduction anomalies in La2−xSrxNiO4 are then compared to the behavior of Cu in LixCu1−xO, and in the high-Tc superconducting La2−xSrxCuO4 system. Spontaneous conduction through molecular-orbital states involving zero-spin Ni and Cu ions is discussed, together with the role of S=0 polarons in other oxide superconductors.
Reflection high-energy electron-diffraction study of metalorganic molecular-beam epitaxy of GaAs using trimethylgallium and arsenic
Authors: Liang B. W. , Chin T. P. , Tu C. W.
Published: July 2002

The growth behavior of metalorganic molecular-beam epitaxial (MOMBE) growth of GaAs using trimethylgallium and solid arsenic is studied by the intensity oscillation behavior of reflection high-energy electron-diffraction (RHEED). The growth process is more complicated than conventional MBE using elemental sources. In MOMBE the growth rate depends not only on the substrate temperature but also on the arsenic pressure. In addition, the RHEED behavior indicates a possibility of atomic layer epitaxy using trimethylgallium.
On the lifetime broadening of the E
v10 and E
v20 excitons in the GaAs/AlxGa1−xAs alloy system
Authors: Logothetidis S. , Cardona M. , Trallero-Giner C.
Published: July 2002

The E0 exciton splitting into Ev10 and Ev20 excitons (due to lattice mismatch), their energy shift and the lifetime broadening are obtained in the GaAs/AlxGa1−xAs alloy system grown by liquid-phase epitaxy from the analysis of spectroscopic ellipsometry measurements in the temperature range between 12 and 800 K. The lifetime broadenings of these excitons at low temperature is shown to be described well by the statistical fluctuations of the alloy composition caused by the random distribution of Al and Ga on the cation sites (Schubert’s model). The Ev10 exciton lifetime broadening was found to be larger in the Ga-rich region as compared to the corresponding one of the Ev20 exciton and smaller in the Al-rich region. The former broadening is explained qualitatively by the different effective masses (mv1Γ>mv2Γ), whereas the latter is produced in terms of the increase in the density of states of the holes in the V2 valence band by the increasing energy splitting δEs with x.
Column III vacancy- and impurity-induced layer disordering of AlxGa1−xAs-GaAs heterostructures with SiO2 or Si3N4 diffusion sources
Authors: Guido L. J. , Major J. S. , Baker J. E. , Plano W. E. , Holonyak N. , Hsieh K. C. , Burnham R. D.
Published: July 2002

Experiments are described determining the critical parameters for vacancy- and impurity-induced layer disordering of AlxGa1−xAs-GaAs quantum-well heterostructure (QWH) crystals that utilize SiO2 and Si3N4 diffusion source layers. The SiO2- or Si3N4-capped QWH crystal surface reaches equilibrium with the external annealing ambient by diffusion of Ga and As through the encapsulant layer, thus determining the crystal-surface deviation from stoichiometry and the column III vacancy concentration for layer disordering. By proper design of the QWH crystal, encapsulant layer thickness, and annealing ambient, the SiO2 (Si3N4) can be employed as a column III vacancy source (or mask) or as a Si and O (or N) diffusion source to effect impurity-induced layer disordering.
A Monte Carlo study of steady-state electron transport in uncompensated and compensated Al0.25In0.75As
Authors: Wu Ernest Yue
Published: July 2002

Monte Carlo calculation on steady-state electron transport properties in uncompensated and compensated Al0.25In0.75As at several lattice temperatures is reported. It is found that alloy scattering has a significant effect on electron drift velocities at high fields, and that the electron velocity-electric field characteristics of compensated Al0.25In0.75As exhibit less temperature dependence than uncompensated Al0.25In0.75As. The small Γ valley effective mass and the large Γ to L and Γ to X valley separations of Al0.25In0.75As result in the excellent low-field mobilities and the peak velocities in comparison to those of GaAs, InP, and In0.53Ga0.47As over the range of doping compensations considered.
On the magnetic (electric) field associated with semi-infinite slabs in front of conducting or insulating planes
Authors: Owen D.
Published: July 2002

Systems consisting of two-dimensional semi-infinite slabs in front of conducting or insulating planes are examined. The slabs which are symmetric may either be thick or thin and of rather general shape. Some of these systems may be identified with magnetic recording head systems, while others are complementary to systems examined by Sproston [IEE Proc. 129, 619 (1982)] and Gibbings [J. Electrostat. 6, 121 (1979)]. Four examples are treated giving the behavior of a dimensionless intensity over their geometrical surfaces. On the conducting plane of certain types of systems, it is seen that the intensity may be approximated quite well by that due to an ideal rectangular slab and also that it decreases along the plane faster than that due to the ideal slab.
Change in the optical-absorption coefficient induced by optical modulation of the internal electric field in doping-modulated amorphous silicon multilayers
Authors: Oheda Hidetoshi
Published: July 2002

Optical modulation of doping-modulated amorphous silicon multilayers (n-i-p-i multilayers) gives rise to an increase in optical transmission at around band-gap energy (∼1.8 eV). Results of the photoinduced transmission measurement for series of samples with different thicknesses of undoped or doped layers can be well explained by a model in which an internal electric field is screened under illumination by spatial separation of photoexcited electrons and holes, leading to a decrease in the optical-absorption coefficient as a result of photoinduced inverse electroabsorption. It can be confirmed through these optical measurements that spatial separation of photoexcited carriers takes place at room temperature in amorphous n-i-p-i multilayers based on hydrogenated amorphous silicon.
MeV Be implantation in GaAs
Authors: Rao Mulpuri V. , Thompson Phillip E. , Dietrich Harry B. , Simons David S.
Published: July 2002

High-energy Be implantation was performed at 1, 2, and 3 MeV for a dose of 1×1013 cm−2 and at 2 MeV in the dose range of 4×1012–1×1014 cm−2. Range statistics from as-implanted secondary ion mass spectrometry profiles were calculated. The implanted wafers were activated by either conventional furnace or rapid thermal annealing. For the same implant dose, 1×1013 cm−2, the dopant electrical activation decreased with increasing ion energy. For the 2-MeV implants, the dopant electrical activation increased with the implant dose, in the range used in this study. An activation as high as 98% was measured for the 2-MeV/1×1014-cm−2 Be implant.
Enhancement of nonradiative interface recombination in GaAs coupled quantum wells
Authors: Krahl M. , Bimberg D. , Bauer R. K. , Mars D. E. , Miller J. N.
Published: July 2002

The recombination dynamics of GaAs multiple quantum wells as a function of barrier widths LB are studied in a semiconductor in the range between LB=0.87 nm (superlattice) and LB=18.1 nm (uncoupled wells) by means of cathodo- and photoluminescence. With decreasing LB the nonradiative recombination rate is found to be drastically enhanced, where-as the radiative recombination probability decreases. Thus a pronounced decrease of the quantum efficiency results. The controlled variation of the barrier width is found to be decisive for an unambiguous identification of the origin of the traps which are responsible for the nonradiative processes: Comparison with a theoretical calculation shows that they are localized at the heterointerfaces and not in the barriers.
Magneto-optical properties of Co/Pd superlattice thin films
Authors: Shin Sung-Chul , Palumbo Anthony C.
Published: July 2002

We present the remnant polar Kerr rotation and ellipticity for a Co/Pd superlattice. The magneto-optical properties of Co/Pd superlattice thin films have been investigated by measuring both the polar Kerr and ellipticity hysteresis loops at a wavelength of 780 nm. It was found that the remnant Kerr rotation was strongly dependent on the thickness of Co and Pd sublayers as well as the total film thickness. In this system, the maximum polar Kerr rotation of 0.43° was observed at the film thickness of 110 Å, where each bilayer was composed of 2-Å-thick Co and 9-Å-thick Pd sublayers.
Brillouin study of spin waves in sputtered CoNiPt alloy films
Authors: Murayama A. , Miyamura M. , Ishikawa S. , Oka Y.
Published: July 2002

Sputtered CoNiPt films prepared for high-density magnetic recording media have been studied by Brillouin scattering. The spin-wave spectra in the film are remarkably broadened with width 13 GHz (full width at half maximum), which is much larger than the width of 3 GHz in a film prepared by vapor deposition. Observation by a transmission electron microscope has clarified that the sputtered film consists of Co crystallites with a diameter of 50–100 Å, which are separated from each other. The remarkable damping of the spin waves in the sputtered CoNiPt film is caused by the film structure. The film is, however, elastically homogeneous, which is known from the undamped surface acoustic wave spectra. The result shows the segregation of the nonmagnetic Pt-related alloys takes place between the Co crystallites. The exchange stiffness constant was determined as 2.4×10−9 Oe cm2 in the sputtered film, which is 1/1.7 that in the vapor-deposited films.
Evanescent wave excitation of the surface polariton
Authors: Li Guifang , Seshadri S. R.
Published: July 2002

The characteristics of the surface polariton existing on the surface of a free electron metal in the proximity of a higher permittivity prism dielectric are investigated including the effects of the finite length of the prism dielectric and the slow spatial variation of the amplitude of the surface polariton. The radiative decay characteristics of the surface polariton and the characteristics of the antiresonance in the angular response of the reflectivity of light incident on the metal surface via the air gap from the prism dielectric are treated, and the effect of a small loss in the metal on these characteristics is also presented.
Scattering of noble gas clusters with energies in the keV range
Authors: Knauer Wolfgang
Published: July 2002

Noble gas clusters with an average size of several thousand atoms and with energies in the keV range were directed at metal surfaces under small angles of incidence. The scatter products were examined with respect to size, energy, and recoil angle. All observations fit an impact model in which the tangential momentum is preserved during impact, while the normal kinetic energy is converted to cluster heat. The associated temperature rise results in the evaporation of cluster atoms. Small clusters evaporate completely; large clusters are reduced in size. The evaporated atoms continue in a forward direction (together with the residual cluster fragments) and form a well-collimated and energetic atom beam.
The effect of concentration-dependent defect recombination reactions on phosphorus diffusion in silicon
Authors: Mulvaney B. J. , Richardson W. B.
Published: July 2002

A previous model for phosphorus diffusion in silicon [J. Appl. Phys. 65, 2243 (1989)] is extended to include four additional reactions among substitutional phosphorus, silicon self-interstitials, vacancies, and phosphorus-defect pairs. All reaction rates in the model are based on physically plausible kinetic estimates. The numerical solution to the resulting system of eight coupled partial-differential equations yields profiles in good agreement with experiment.
Lattice matched and pseudomorphic In0.53Ga0.47As/InxAl1−x As resonant tunneling diodes with high current peak-to-valley ratio for millimeter-wave power generation
Authors: Mehdi Imran , Haddad George
Published: July 2002

Lattice matched and pseudomorphic In0.53 Ga0.47 As/InxAl1−x As resonant tunneling diodes, with some of the best dc performance ever reported, have been fabricated and their high-frequency power generation capabilities have been theoretically studied. For the lattice matched system a peak-to-valley ratio of 7 (300 K) and 21 (77 K) with a peak current density of approximately 10 kA/cm2 is measured. The pseudomorphic system with a In0.53 Ga0.47 As well and AlAs barriers results in a peak-to-valley ratio of 24 (300 K) and 51 (77 K) with a peak current density of approximately 15 kA/cm2. Based on a quasistatic large signal waveform analysis the power generating capability of the InGaAs device is compared with a GaAs based device with an equally high peak current density and it is found that for very high-frequency power applications the InGaAs based device is better.
Hole impact ionization enhancement in AlxGa1−xSb
Authors: Jiang Y. , Teich M. C. , Wang W. I.
Published: July 2002

The threshold energy and scattering rate for impact ionization in AlxGa1−xSb have been calculated for compositions x near the value where the spin-orbit-split gap Δ equals the band gap Eg. We have found that a minimum in the threshold energy for impact ionization near the Δ=Eg composition cannot explain the enhancement of the hole ionization coefficient, although it has been proposed as a possible mechanism. Rather, an increased scattering rate is responsible for this enhancement. It is caused by a minimum change of momentum in the hole ionization near the threshold and the mixing of an s-like state into the valence-like state induced by a composition disorder in this ternary compound. Our results indicate that the maximum hole ionization coefficient will occur at a composition x that lies between zero and the composition at which Δ=Eg.
High critical current density ultrathin YBa2Cu3Ox films made by a modified rf-magnetron sputtering technique
Authors: Gao J. , Häuser B. , Rogalla H.
Published: July 2002

High-quality ĉ-axis oriented thin films have been grown in situ on (100) surfaces of ZrO2 , SrTiO3 , and MgO. Sharp transitions to superconductivity were observed with Tc,off of 87–89.5 K for films thicker than 70 Å. The critical current density at 77.3 K was found to be strongly dependent on the film thickness. A maximum value was found for a 100-Å film with 8×106 A/cm2 at 77.3 K. On atomically flat single-crystal MgO substrates, films as thin as 15 Å revealed a full transition to superconductivity above 45.5 K. The superconducting properties of the films turned out to be quite insensitive to the deposition parameters, such as substrate temperature, oxygen partial pressure, sputter power, etc.
Magnetism of Pr2(Fe1−x−yCoxAly)17 alloys with a Th2Zn17-type structure
Authors: Weitzer F. , Klesnar H. , Hiebl K. , Rogl P.
Published: July 2002

Alloys with the composition Pr2(Fe1−xCox)17−yAly have been synthesized by the arc-melting technique followed by 125-h annealing at 900 °C in evacuated silica capsules. From room-temperature x-ray powder diffraction analysis a complete solid solution Pr2(Fe1−xCox)17−yAly has been observed for all values of 0≤x≤1 and 0≤y≤5.1. All alloys were found to crystallize with the Th2Zn17-type structure; Al atoms tend to preferentially occupy the (6c) sites. Fe/Co substitution generally leads to an increase of the Curie temperature and of the magnetocrystalline anisotropy, thereby enhancing the remanence as well as the coercivity. These effects are predominantly due to the strongly distant-dependent exchange interactions of the Fe-Fe(Co) and the Fe(Co)–rare-earth coupling mechanism. Whereas most of the alloys exhibit easy-plane magnetism, a small range exists in the Pr2(Fe1−xCox)17−yAly system (0.38<x<0.82, 300 K), in which the crystallographic c axis is the direction of easy magnetization. Small amounts of Al, however, close the easy-axis region at y=1.8 (∼300 K).
Retardation of implantation damage annealing in InP due to local nonstoichiometry
Authors: Moriya N. , Kalish R. , Bahir G.
Published: July 2002

The regrowth of P- or Si-implanted InP following thermal annealing (400–600 °C, 2–20 h) has been studied using Rutherford backscattering channeling experiments. Differences in damage annealing are consistently found between identically treated 29 Si- or 31 P-implanted regions on the same sample, the former always being retarded. This retardation is suggested to be caused by stoichiometric imbalance due to the recoil kinematics, which is less severe for the case of the phosphorus implantation.
Optical properties of GaAs/GaP strained-layer superlattices
Authors: Recio M. , Armelles G. , Meléndez J. , Briones F.
Published: July 2002

The optical properties of a novel system, the GaAs/GaP strained-layer superlattice, are studied and compared with a theoretical model. Photoluminescence and photoreflectance measurements revealed that among the set of superlattices under study type-I and type-II behaviors (similar to those found in the lattice-matched GaAs/AlAs system) are present. The evolution of the photoluminescence peaks as a function of temperature and excitation density supported the assignment of the transitions involved. This is to our knowledge the first observation of direct (type-I) and indirect (type-II) transitions in strained-layer superlattices. A comparison with a theoretical model has led to an estimation of the conduction-band offset as 0.4 eV, which is the first value obtained from experiment in a GaAs/GaP heterojunction.
The kinetics of the Au-InP interaction
Authors: Fatemi Navid S. , Weizer Victor G.
Published: July 2002

An analysis of the reaction of Au and Au-In alloys with InP has permitted the identification of the mechanisms occurring during the first two stages of the Au-InP interaction. The first stage of the interaction, during which the Au is converted to a saturated Au(In) solution, is controlled by the vacancy-generation rate at the free surface of the metallization. The activation energy for this process is the activation energy for Au self-diffusion. Evidence is presented for the existence of large localized variations in this value due to surface related effects. At the completion of stage I stage II becomes active and continues until the metallization is converted to Au3 In. This process, proceeding via an interstitial interchange mechanism, is many orders of magnitude slower than stage I. The rate-limiting step, with an activation energy of 2.8 eV, is shown to be the diffusion of In from the InP-metal interface. The P atoms that are released when In enters the metallization during stage I leave the system without reacting, whereas in stage II they form a compound (Au2 P3 ) at the InP-metal interface. The presence of the Au2 P3 severely retards the stage II interaction rate.
Diffusion phenomena due to ion implantation damage and arsenic and phosphorus codiffusion
Authors: Deaton R. , Gösele U. , Smith P.
Published: July 2002

Arsenic and phosphorus codiffusion was studied using a buried boron layer. Analysis of the dopant profiles was performed using secondary ion mass spectroscopy, spreading resistance profiles, and junction staining. Contrary to expectations, the profiles of arsenic and phosphorus diffused by themselves were enhanced over the codiffused profiles. The buried boron profile in the case of phosphorus alone was enhanced over the boron profile in the case of arsenic and phosphorus codiffusion. The residual annealing of implantation damage is thought to be responsible for these effects. In addition, the suppression of the self-interstitial supersaturation for codiffused conditions is a transient effect and is postulated to be caused by an increase in recombination of implantation-generated vacancies and self-interstitials due to the presence of a high concentration of arsenic atoms.
A theory of nonequilibrium carrier transport in multivalley semiconductors
Authors: Cheng M. , Kunhardt E. E.
Published: July 2002

The concept of a macrokinetic distribution (MKD) is used to develop a theory of nonequilibrium carrier transport in multivalley semiconductors. The MKD is a momentum-dependent function with macroscopic space-time scales, whose equation of evolution is macroscopically equivalent to the semiclassical Boltzmann transport equation for the phase-space distribution. A MKD is obtained for each valley and used to close the set of coupled moment equations that describe carrier transport in each valley. The resulting set of equations constitutes the model. A two-valley model is developed to illustrate the theoretical procedure. Results are obtained for the response of electrons to a rapidly varying (in time) electric field. These results are compared to those obtained using Monte Carlo (MC) methods and also an equivalent single-valley model. Excellent agreement is obtained between the macrokinetic model and the MC results. The single-valley model is shown to be inadequate in situations where intervalley carrier transfer is significant.
Changes in relative permeability and domain structures of Fe-C/Ni-Fe multilayered films with the insertion of nonmagnetic BN layers
Authors: Nakatani Ryoichi , Kobayashi Toshio
Published: July 2002

Fe-C/Ni-Fe multilayered films have a pattern of stripes 10 or 20 μm wide. Their magnetic properties and domain structures are examined. For certain film geometries, insertion of nonmagnetic BN layers eliminates 90° closure domains in the stripe-patterned Fe-C/Ni-Fe films. The disappearance of the closure domains increases the relative permeability of the films. The stripes, with a width of 10 or 20 μm, display a relative permeability of 1500 and 1700, respectively, when closure domains have disappeared.
Enhanced carrier diffusion lengths and photon transport in AlxGa1−x As/GaAs structures
Authors: Bradshaw J. L. , Choyke W. J. , Devaty R. P. , Messham R. L.
Published: July 2002

Several novel features are observed in the low-temperature photoluminescence spectra of AlxGa1−xAs layers grown on GaAs by metalorganic chemical vapor deposition. GaAs substrate luminescence spectra are observed through AlxGa1−xAs layers as thick as 22 μm. Both carrier diffusion to the substrate and AlxGa1−xAs luminescence are identified as the excitation mechanisms of the GaAs luminescence, and a minority-carrier diffusion length of 10 μm is estimated. The presence of photon recycling in the AlxGa1−xAs layers is demonstrated by comparison of photoluminescence (PL) spectra for layers with and without GaAs substrates, as well as PL examination of two AlxGa1−xAs heterostructures.
Local oxidation of GaP wafers heated by Nd:YAG laser beam
Authors: Kawamura Tsutomu
Published: July 2002

GaP wafer optical properties, such as absorption coefficient and reflectance, were investigated around 1.06 μm wavelength. Next the wafers were locally heated by Nd:YAG laser beam (1.06 μm) between 600 and 1470 °C (melting point). A steep temperature gradient and the consequent explosive disordering played an important role in violent exothermic reaction on oxidation for differently surface-treated GaP wafers, resulting in the formation of GaPO4 polycrystals. However, there was a marked difference in initial oxidation rates between a wafer, which had been mirror-polished on only one surface, and a wafer mirror-polished on both surfaces. The reason for this phenomena is discussed in detail.
Electrical and xerographic properties of biaxially stretched poly( p-phenylene sulfide) films annealed in oxygen
Authors: Tanaka Eiichiro , Takimoto Akio , Watanabe Masanori
Published: July 2002

Biaxially stretched poly (p-phenylene sulfide) (PPS) film showed high photosensitivity after being annealed in oxygen for 6 h at a temperature between 270 and 285 °C. The spectral dependence of xerographic photosensitivity of the film had a peak at around 365 nm, and xerographic gain under 365-nm UV irradiation was 0.1 or above. The micro-Vickers hardness of PPS reached 60 kg/mm2 after annealing at 280 °C for 6 h. The spectral photosensitivity was greatly improved by depositing a thin amorphous selenium-tellurium alloy on the annealed PPS film. The half-decay exposure of the annealed PPS with Se-Te alloy film was 2.3 lx s under white illumination. These experimental results demonstrate that the annealing of PPS film under an oxygen environment gives this film excellent photosensitivity and mechanical durability and hence, renders this material attractive for a xerographic application.
Surface reactions in the chemical vapor deposition of tungsten using WF6 and SiH4 on Al, PtSi, and TiN
Authors: Yu Ming L. , Ahn Kie Y. , Joshi Rajiv V.
Published: July 2002

The initial surface chemical reactions that lead to the chemical vapor deposition (CVD) of tungsten on aluminum, PtSi, and TiN using WF6/SiH4 mixtures have been studied in an ultrahigh vacuum system using x-ray photoemission and mass spectrometry. In all these cases, tungsten deposition can be initiated by initial deposition of a tungsten or silicon seed layer. Aluminum was found to react with WF6 at elevated temperatures to deposit a seed metallic tungsten layer with the formation of volatile aluminum subfluoride. SiH4 then reacted with the tungsten seed layer to provide silicon to sustain the CVD reaction. The silicon atoms in PtSi, similar to the case of a silicon substrate, initiated the deposition process by reacting with WF6. TiN, on the other hand, was decomposed by both WF6 and SiH4 to deposit the necessary tungsten and silicon seed layers, respectively, for the deposition reaction. Deposition reactions on an oxygen-contaminated technical TiN surface were also investigated.