bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct observation of magnetization dynamics in spinning magneto-optic discs (invited)
Authors: Schultz Mark D. , Xue Tsing , Kryder Mark H.
Published: July 2002

The development of a system capable of direct observation of magnetization and thermal dynamic behavior of magneto-optic recording materials at various relative media-to-laser spot velocities is described along with demonstrations of its value in furthering the understanding of such behavior. A 10-ns-wide observation laser pulse is utilized to produce ‘‘stop-action’’ images of magnetization states in an environment almost identical to that of an actual magneto-optical disc drive operating at linear velocities of 0–40 m/s (7200 rpm, 53 mm radius). Thermal modeling is correlated with images of the instantaneous temperature distributions at various velocities to demonstrate that the thermal conductivity in the materials is approximately 7 W/m/K rather than the bulk 40–50 W/m/K. Techniques for isolating signal due to moving magnetization reversal regions from that due to moving areas of elevated temperature are used to analyze the writing behavior of single layer direct-overwrite recording films.
Delta-M, vertical component, and media noise of NiP- and Cr-underlayer media for longitudinal recording
Authors: Ranjan R. , Chang J. , Yamashita T. , Chen T.
Published: July 2002

Media having Cr-underlayer and NiP-underlayer were compared using transmission electron microscopy (TEM), delta-M, torque (vertical component), and media noise measurements. TEM micrographs show that NiP-underlayer media were more isolated than Cr-underlayer media. Of the Cr-underlayer media, CoCrTa media seem to exhibit grain isolation. The grain size of NiP-underlayer media was smaller (30 nm) than that of Cr-underlayer media (60 nm). Results indicate that media with isolated grains seem to have higher vertical component than media with more continuous grains. The NiP-underlayer media exhibits lower media noise than the Cr-underlayer media. This is attributed to smaller and more isolated grains in the NiP-underlayer media.
Substrate bias effects on composition and coercivity of CoCrTa/Cr thin films on canasite and glass
Authors: Deng Y. , Lambeth D. N. , Sui X. , Lee L.-L. , Laughlin D. E.
Published: July 2002

CoCrTa/Cr thin films were prepared by rf diode sputtering onto canasite and glass substrates at various bias voltages from two targets of different compositions (Co82.8Cr14.6Ta2.6 and Co86Cr12Ta2). While Auger depth profile analysis indicates that there is some broadening at the CoCrTa-Cr interface, x-ray fluorescence spectroscopy reveals that changes in alloy composition due to the resputtering processes are even more prominent. For both targets, as the substrate bias increases the Co content in the films declines, and the magnetization decreases. The maximum film coercivity appears to correlate to the final film composition. By investigating the results from both targets, it is concluded that the coercivity reaches a maximum when the film composition is in the neighborhood of Co84Cr13Ta3. Thus, to optimize the coercivity different bias voltages are required for each target. Excessive substrate bias, however, leads to films with low magnetization and coercivity.
Monte Carlo study of critical behavior in the three-dimensional classical Heisenberg ferromagnet
Authors: Chen Kun , Ferrenberg Alan M. , Landau D. P.
Published: July 2002

The static critical properties of classical, isotropic Heisenberg ferromagnets have been studied numerically. Using an improved cluster algorithm we performed extensive Monte Carlo simulations on L×L×L simple cubic and body-centered cubic systems with L≤40 over a temperature range covering the critical region. Temperature dependences of thermodynamic quantities were determined with an optimized multiple-histogram method, and both critical temperatures and critical exponents were extracted from finite-size scaling of several different thermodynamic quantities. It was found that within their respective error bars the critical exponents for both ferromagnets agree with each other and with field theoretical predictions.
The yield point of In-doped GaAs between 500 and 900 °C
Authors: Siethoff Hans , Brion Hans Georg , Völkl Johannes
Published: July 2002

In-doped (5×1019/cm3) GaAs single crystals with 〈123〉 orientation are compressed at different strain rates and temperatures between 500 and 900 °C. Two different regimes are observed. At high strain rates and temperatures below 700 °C, the strain-rate dependence of the lower yield stress is characterized by a power law with a stress exponent of 3.7, while its temperature dependence obeys an Arrhenius law with an activation energy of 0.93 eV. The latter value is smaller than that found for undoped GaAs, but the stress exponent is practically unchanged. This regime is interpreted in terms of a kink mechanism; the rate-controlling process is assumed to be governed by a strong interaction of In atoms with α dislocations. The regime occurring at low strain rates and temperatures above 700 °C is characterized by strong hardening and a weak temperature and strain-rate dependence of the lower yield stress. This behavior is ascribed to a direct alloying effect. Different types of interaction between dislocations and impurities are discussed. The knowledge of the strain-rate dependence of the lower yield stress, besides its temperature dependence, is a prerequisite for the interpretation of the measurements.
Electrical characterization of atomic layer epitaxy ZnS:Mn alternating-current thin-film electroluminescent devices subject to various waveforms
Authors: Abu-Dayah A. , Wager J. F. , Kobayashi S.
Published: July 2002

The electrical response of ZnS:Mn alternating-current thin-film electroluminescent devices grown by atomic layer epitaxy (ALE) is studied by systematically varying the characteristics of the standard driving waveform. Charge-voltage, capacitance-voltage, and internal charge-phosphor field analysis are used to accomplish electrical analysis. The turn-on voltage, polarization charge, conduction charge, leakage charge, relaxation charge, preclamping interface state density, and steady-state phosphor field are all monitored as a function of the driving waveform for both polarities. The electrical response is found to be asymmetric with respect to the polarity of the applied voltage pulse; this asymmetry is attributed to an asymmetry of the interface state density and to the existence of space charge within the ALE-grown phosphor layer.
Codiffusion of arsenic and phosphorus implanted in silicon
Authors: Solmi S. , Maccagnani P. , Canteri R.
Published: July 2002

The codiffusion of arsenic and phosphorus implanted in silicon has been investigated after annealing at 900 and 1000 °C for different concentrations of the dopants. Analysis of the profiles was performed using secondary-ion-mass spectroscopy, junction staining, and incremental resistivity and Hall measurements. The results do not evidence any direct interaction between the dopants. All the observed anomalous effects of the codiffusion, compared with the diffusion of the single elements by themselves, seem to be justifiable on the basis of the interactions between the dopants and the defects produced by ion implantation. In addition, it has been observed that the presence of a high concentration of As atoms makes the annealing of the implantation damage faster and strongly reduces the P transient-enhanced diffusion. This effect favors the fabrication of graded shallow junctions with a high-surface-carrier concentration.
Anomalous electroreflectance spectrum of spontaneously ordered Ga0.5In0.5P
Authors: Kurtz Sarah R.
Published: July 2002

The electroreflectance spectrum of spontaneously ordered Ga0.5In0.5P contains two extra features at energies near 2.2 and 2.35 eV. The energies and intensities of these transitions are shown to be dependent on growth temperature and substrate misorientation. The possible origins of the two transitions are explored. The analysis shows that the transition at about 2.35 eV exhibits shifts consistent with those expected for Ga0.5In0.5P with ordered {111} planes. The second transition is shown to be unexpected and is not conclusively assigned. However, a possible assignment is identified, implying that a complete understanding of spontaneously ordered Ga0.5In0.5P may require simultaneous consideration of two different types of order.
Angular distributions of current density in liquid Ga-ion sources
Authors: Cho Guang-Sup , Choi Eun H. , Seo Yoonho , Kim Tae-Whan , Kang Seung-Oun
Published: July 2002

Current-voltage (I-V) characteristics and angular distribution of the current density of a liquid gallium ion source were investigated under various emitting tip temperatures and surface flow impedances. It is shown that the I-V slope is significantly influenced by the flow impedance of the liquid gallium on the emitting tip. The slopes of the I-V curve are shown to be steep for an emitting tip with a rough surface, and gentle for a smooth surface. The angular distribution of Ga ions was determined by measuring the current on metal rings concentric with the emission axis and located so as to form a portion of a hemisphere. The current density was found to be depressed near the center compared to the surrounding region. This density distribution persists for various axial locations of the rings. Moreover, the angular profile of current density at fixed axial locations is found to be identical for the same amount of emission current, irrespective of the tip-surface condition or the applied voltage. It shows that the amount of emission current has a strong correlation with the surface shape of the ion emitting Ga-liquid.
Electrical and microstructural characteristics of Ti contacts on (001)Si
Authors: Liauh H. R. , Chen M. C. , Chen J. F. , Chen L. J.
Published: July 2002

An investigation of the electrical and microstructural characteristics of the Ti contact on silicon has been carried out. The presence of As in Ti/n+-Si samples was found to retard the formation of polycrystalline silicide (p-silicide) compared with that in Ti/p+-Si samples with BF2+ implantation. Amorphous interlayers (a-interlayers) were found to be present in both Ti/n-Si and Ti/p-Si samples annealed at temperatures of and lower than 450 °C. Although the Schottky barrier heights (SBH’s) vary for about 0.05–0.08 eV for samples annealed over a temperature range from room temperature to 900 °C, SBH’s at the a-interlayer/n-Si and a-interlayer/p-Si were measured to be about 0.52–0.54 and 0.59–0.57 eV, respectively. The specific contact resistance (ρc) in the Ti/n+-Si system was measured to be the lowest with a value of 1.4×10−7 Ω cm2 when the a interlayer is present. In Ti/p+-Si system, the minimum ρc is about 3×10−7 Ω cm2. The variation in contact resistance with annealing temperature for both Ti/n+-Si and Ti/p+-Si samples is correlated to the change in dopant concentration beneath the contacts as well as microstructures. In the temperature regime where the a interlayer is in contact with the silicon substrate, the junction diode leakage current densities (Jleak’s) are considerably lower than those in samples annealed at higher temperatures. The Jleak at −6 V reverse bias is lower than 1 nA/cm2. The breakdown voltage is about 14 V (16 V) for the n+/p (p+/n) junction. The thickness of consumed Si is less in samples annealed at low temperature, and the a-interlayer/Si or p-silicide/Si interface is accordingly farther away from the junction as well as the end-of-range defects. The interface of p-silicide/Si is rougher than that of a-interlayer/Si. In addition, the roughness of the p-silicide/Si interface increases with annealing temperature. For both p+/n and n+/p junctions annealed at 900 °C, rough p-silicide/Si interfaces are thought to lead to spiking and increase the leakage currents.
Application of blazed gratings to millimeter-submillimeter wave gyrotrons
Authors: Hong K. D. , Brand G. F. , Idehara T.
Published: July 2002

A novel combination of a quasioptical antenna and a blazed grating which has been applied to gyrotron investigations at millimeter and submillimeter wavelengths is described. In this system the quasioptical antenna converts the conical beam from the gyrotron into a well-collimated, linear-polarized beam and the blazed grating acts as a frequency-selective demultiplexer. The system is very effective in separating the submillimeter wavelength output from GYROTRON V at the second harmonic of the electron cyclotron frequency from the nearby strong fundamental. This has enabled the study of mode competition between the second harmonic and the fundamental processes.
Optical study of an n-type modulation-doped GaAs/AlAs multiple quantum well structure
Authors: Schmiedel T. , Fu L. P. , Lee S. T. , Yu W. Y. , Petrou A. , Dutta M. , Pamulapati J. , Newman P. G. , Boviatsis J.
Published: July 2002

We present an optical study (photoluminescence and Raman scattering) of a GaAs/AlAs multiple quantum well structure doped n-type in the AlAs barriers. The photoluminescence shows that the Si donors of the barriers release their electrons in the GaAs wells, creating a dense quasi-two-dimensional electron gas. The Raman spectra contain a feature associated with the e1→e2 intersubband transition.
Surface reactivity of luminescent porous silicon
Authors: Coffer Jeffery L. , Lilley Sean C. , Martin Rebecca A. , Files-Sesler Leigh Ann
Published: July 2002

The effects of addition of a series of organoamine molecules on the luminescence of porous silicon has been examined by steady-state photoluminescence (PL) and Fourier transform infrared spectroscopies. These samples, prepared nonanodically via stain etching techniques and characterized by atomic force microscopy, show dramatic quenching of visible PL upon addition of dilute solutions of the above Lewis base adsorbates. The fractional changes in integrated PL intensity as a function of quencher concentration obey a simple equilibrium model, demonstrating Langmuir-type behavior from which equilibrium constants can be calculated. An observation concomitant with this loss of PL is a diminution of the silicon hydride stretching frequencies near 2100 cm−1.
Many-body effect in the static yield stress of electrorheological fluid
Authors: Ota Montonori , Miyamoto Tetsuo
Published: July 2002

We have calculated the static yield stress of electrorheological fluid directly introducing cubic particle chains arranged in a triangular lattice to elucidate the influence of the many-body effect. The shape of the stress-strain curve at a high concentration of particles is much different from that at a low concentration, and the static yield stress saturates at a high concentration (φ=0.4), the same as is the case of spherical particle chains arranged in a rectangular lattice. In both cases of low and high volume fractions, the yield stress increases in proportion to the permittivity ratio of particles and dispersion fluid.
Evidence of donor center involvement in ac thin film electroluminescent devices exhibiting memory
Authors: McClean I. P. , Thomas C. B.
Published: July 2002

Alternating current thin film electroluminescent (EL) devices exhibiting memory with low Mn concentrations have a temperature independent threshold, but a temperature dependent saturation brightness and memory margin. Based upon these observations we argue that EL emission is initiated via the usual tunneling process from interface states, but subsequent characteristics are determined via a second carrier generation process. Shallow donor sites are calculated to exist at a depth of 0.12 eV below the conduction band. These are believed to be involved in the second carrier generation process since brightness-voltage characteristics are associated with Poole–Frenkel emission.
Photoresponses of granular (Pb)BiSrCaCuO films to millimeter wavelength radiation
Authors: Ngo Phong L. , Shih I.
Published: July 2002

The photoresponses of Pb doped 2223 phase BiSrCaCuO films to low power 5 mm cw radiation were measured at temperatures near Tc. To identify the involved detection mechanisms, dependence of responsivity on temperature, supplied current, radiation power, and film granularity were investigated. At temperatures in the vicinity of the transition to the normal state, good agreement was obtained with the responses derived from a bolometric model. At temperatures below the transition, a nonbolometric response mode was found to occur when the film was biased into a partially resistive regime. Transient measurements were carried out showing a response time for this mode of at least 5 orders of magnitude smaller than that of the bolometric response. Further characteristics inherent to the nonbolometric mode include square law detection, nonlinear current dependence, and short wavelength cutoff. In addition, a correlation between responsivity and film granularity was established. For strongly granular films with an active area of 300×1800 μm2, a detectivity D* of about 1.1×108 cm Hz1/2/W was typically achieved at a modulation frequency of 5 kHz. Consistency of the experimental results with the sub-gap responses of Josephson arrays is discussed.
A Monte Carlo study of hot electron injection and interface state generation model for silicon metal-oxide-semiconductor field-effect transistors
Authors: Ellis-Monaghan John J. , Kim K. W. , Littlejohn Michael A.
Published: July 2002

This paper describes a model which can predict the quantity and lateral distribution of hot-electron-induced interface states in Si metal-oxide-semiconductor field-effect transistors (MOSFETs). The results are obtained using an advanced Monte Carlo method, which incorporates two lowest conduction energy bands from pseudopotential calculations, coupled with an interface state generation model. The coupled model simulates transport-induced hot electron emission from Si into SiO2 and the subsequent generation of interface states in MOSFETs operating under realistic high-voltage stress conditions. The calculations explore the sensitivity of the channel electron energy distribution to various Monte Carlo parameters, such as impact ionization coefficients, self-consistent electron-electron interactions, and surface scattering. Within the validity of our treatments of these physical phenomena, it is shown that while the effects of Monte Carlo parameters on the energy distribution can result in uncertainties in the net interface state generation, quantitative studies may be allowed by using scaling principles. The interface state distribution obtained from the model agrees with experimental data from charge pumping measurements. The model also predicts that the interface state generation extends spatially beyond the range which is accessible by the charge pumping measurements.
Site selectivity in Fe doped β phase NiAl
Authors: Chartier Patrick , Balasubramanian Mahalingam , Brewe Dale , Manzur Tariq , Pease Douglas , Budnick Joseph , Huang Li , Law Chi , Russell Scott , Kimball Clyde
Published: July 2002

We have investigated site selectivity in iron doped β phase ternary alloys of the composition NixFeyAl(100−x−y), where the Ni concentration is within a few at. % of stoichiometry. Experimental techniques used include extended x-ray absorption edge fine structure and Mössbauer measurements. The transition metal atoms in excess of 50 at. %, which occupy sites with transition metal nearest neighbors, are not chosen randomly among Ni and Fe, but are exclusively Fe, to within the accuracy of the measurements. This result requires a re-analysis of previous magnetic susceptibility measurements on this system, which as re-analyzed here imply more reasonable moment values for the Fe dopants. Our findings regarding Fe site selectivity are of significance in regards to recent studies showing a ductilization effect of Fe dopants microalloyed into Ni50Al50.
Planar to columnar transformation of PtSi in the epitaxial growth process of Si/PtSi/Si(111) double heterostructures
Authors: Kumagai Y. , Hasegawa F. , Park K.
Published: July 2002

Epitaxial growth of Si on PtSi(010)/Si(111) structure, which was fabricated by coevaporation of Pt and Si with the stoichiometric ratio (Pt/Si=1/1), was carried out in a molecular beam epitaxy system. At the substrate temperature of 400 °C, Si grew epitaxially on the PtSi layer and Si(111)/PtSi(010)/Si(111) double heterostructure was obtained. On the other hand, at the substrate temperature of 600 °C, the PtSi layer transformed into epitaxial columns and/or walls in the process of Si deposition and evaporated Si filled the space among the PtSi columns and/or walls epitaxially.
Optical excitation of Hall current in a GaAs crystal
Authors: Sochava S. L. , Stepanov S. I.
Published: July 2002

Nonsteady-state photocurrent induced by a vibrating interference pattern was used to excite the orthogonal Hall current in GaAs in an external magnetic field. Application of this technique for measuring relevant parameters of the material (charge carrier mobilities, electron/hole conductivity ratio, electron and hole diffusion lengths) is demonstrated.
Structural model of sulfur on GaAs(100)
Authors: Wang Xue-sen , Weinberg W. Henry
Published: July 2002

Based both on previous experimental results and new low-energy electron diffraction measurements, we propose a structural model for the sulfur passivating layer on GaAs(100). The model consists of S-Ga dimers that form a (2×1) superstructure on top of a complete Ga layer. This structure possesses stable electrostatic and electronic properties which lead to excellent surface passivation.
Surface modification of CaF2 on Si(111) by low-energy electron beam for over growth of GaAs films
Authors: Izumi Akira , Tsutsui Kazuo , Furukawa Seijiro
Published: July 2002

Surface modifications of epitaxial CaF2 on Si(111) by low-energy electron beam, in order to get modified surfaces with reduced damage on which high quality GaAs films could be grown, were studied. By using x-ray photoelectron spectroscopy measurements, it was found that it is possible to modify the surface of CaF2(111) even though the energy of the electron beam was as low as ∼10 eV. The generation of defects in bulk CaF2 and the diffusion of As were found at an energy of 305 eV, whereas no such evidence of defect, but rather, a stable adsorption of As on the surface of CaF2, was observed at an energy of 40 eV.
Intergranular exchange coupling
Authors: Muller M. W. , Indeck R. S.
Published: July 2002

We evaluate the exchange interaction between neighboring grains of a polycrystalline magnetic material with uniaxial magnetocrystalline anisotropy, based on the energy of the domain wall formed at the portion of the interface in atomic contact. The analysis suggests that previous work [J.-G. Zhu and H. N. Bertram, in Solid State Physics Vol. 46, edited by H. Ehrenreich and T. Turnbull (Academic, San Diego, 1992)] may underestimate the interaction, and it predicts a different dependence on grain size.
Band-to-band recombination in Ga0.5In0.5P
Authors: Strauss U. , Rühle W. W. , Queisser H. J. , Nakano K. , Ishibashi A.
Published: July 2002

The recombination kinetics of the electron-hole plasma in strongly excited, undoped Ga0.5In0.5P are investigated at 300 and 150 K by time-resolved photoluminescence measurements using line-shape analysis of transient spectra. Radiative recombination dominates, and no influence of the Auger effect is observed up to our highest carrier concentration of 1.5×1019 cm−3. Random alloy and ordered samples have the same recombination rate. The radiative recombination coefficients are found to be (1.0±0.3)×10−10 and (4±1)×10−10 cm3 s−1 at 300 and 150 K, respectively. An upper limit for the Auger coefficient is 3×10−30 cm6 s−1 at 300 K.
Correlation of x-ray diffraction and Mössbauer effect measurements with magnetic properties of heat-treated Cu80Co15Fe5 ribbons
Authors: Harris V. G. , Rubinstein M. , Das B. N. , Koon N. C.
Published: July 2002

X-ray diffraction (XRD) and Mössbauer Effect (ME) measurements were performed on heat-treated Cu80Co15Fe5 melt-spun ribbons in an attempt to understand the trends in magnetic properties with heat treatment. ME measurements indicate that the majority of Fe atoms (86%) occupy sites in ferromagnetic FCC CoFe clusters after the initial quench. A heat treatment at 900 °C acts to complete the chemical separation of Fe from the Cu matrix. The presence of Co in the Cu matrix, even after high temperature anneals, provides a paramagnetic component that prohibits saturation even at high fields.
Exchange coupling through ferromagnetic bridges in magnetic multilayers (abstract)
Authors: Slonczewski J. C.
Published: July 2002

It has been known for 27 years1 that ferromagnetic bridges joining two ferromagnetic films can result in a cos θ dependence of the exchange-coupling energy Wb only under very restricted circumstances. In more natural circumstances, considered here, one expects Wb=Cθ2≥0 to hold in the full angular range 0≤θ≤π. The principal condition for this relation to hold is that local spontaneous spin polarization actually exists at the given temperature for all sites composing complete chains of exchange-coupled local spins extending between the ferromagnetic films. One easily finds estimation formulas in special limits; e.g., for a set of thin uniform filamentary bridges, C=Aφ/w, where A is the exchange stiffness, φ is the fractional cross section of filaments, and w is the spacer thickness. Because of this peculiar angular dependence of Wb, ferromagnetic bridges are conducive to noncolinear arrangements of the sublayer moments. In particular, nearly 90°-domain arrangements are favored in epitaxial (100) multilayers which have sufficiently strong positive cubic anisotropy Wk. Observed 90° arrangements were previously attributed to biquadratic coupling.2 One condition for 90° arrangements due to bridges is that the additional coupling Wa=−J cos θ through the normal-metal spacer medium is antiferromagnetic and its strength is in the appropriate range. Let the total energy be W=Wk+Wa+Wb. Then, if W(0) is thus made nearly equal to W(π), the θ2 dependence of the bridge term insures that W is minimized near θ=π/2.
Kinetic analysis of silicon oxidations in the thin regime by incremental growth
Authors: Ajuria Sergio A. , Kenkare Prashant U. , Nghiem Anh , Mele Thomas C.
Published: July 2002

The scaling of dry thermal oxides into the thin (<400 Å) range continues to motivate studies of the rapid initial oxidation rate of silicon unaccounted for by a linear-parabolic model. In this paper, silicon oxidation kinetics in this unresolved regime are studied by the incremental reoxidation of thin thermally grown and deposited silicon oxide layers on silicon. It is found that the reoxidation rates of thermally grown oxides in the thin regime rapidly decrease with increasing oxide thickness. In contrast, the reoxidation rates of deposited oxides are faster, and nearly thickness independent. It is also found that the reoxidation rates of thin thermal oxides can be significantly increased by inert thermal annealing. Existing thin-regime oxidation models are evaluated in light of these experimental findings, and it is concluded that only models invoking stress suppression of early oxidation kinetics can reconcile all experimental observations. In further support of a stress argument, the time and temperature effects of inert annealing are shown to be quantitatively consistent with a Maxwellian model for stress relaxation. Kinetic parameters extracted from experimental data are utilized to isolate specific mechanisms for the suppression of oxidation rate during the initial stages of silicon oxidation.
Spatially localized energy shifts in the photoemission spectroscopy of insulators
Authors: Coluzza C. , Almeida J. , dell’Orto Tiziana , Gozzo F. , Alméras P. , Berger H. , Bouvet D. , Dutoit M. , Contarini S. , Margaritondo G.
Published: July 2002

Core-level photoemission peaks taken on several insulators with spatial resolution of 30–300 μm rigidly shift in energy from place to place, most likely because of local charging effects. Such phenomena can affect the linewidth and the general lineshape of conventional, spatially integrated spectra even when a flood gun is used, which is one of the standard remedies against charging. This may require a critical revision of photoemission linewidths and lineshapes for many past experiments on insulators.
Structural investigation of Fe silicide films grown by pulsed laser deposition
Authors: Karpenko O. P. , Olk C. H. , Yalisove S. M. , Mansfield J. F. , Doll G. L.
Published: July 2002

Pulsed laser deposition was used to grow epitaxial β-FeSi2 films on Si(111) (1×1) and Si(111) (7×7) with the following epitaxial orientations: β-FeSi2(001)//Si(111) with β-FeSi2[010]//Si〈110〉 and three rotational variants. Silicide growth was influenced by substrate temperature and deposition rate, but not by the structure of the starting surface. Films containing both β-FeSi2 and FeSi were formed at low substrate temperatures and high deposition rates, while films containing only β-FeSi2 were formed at higher substrate temperatures and lower deposition rates. FeSi grains had the following epitaxial relationship to the Si substrate, FeSi(111)//Si(111) with FeSi(1̄10)//Si(112̄). The microstructure of the silicide films varied with film thickness, as did the roughness at the silicide/Si interface. These results suggest that an Fe-rich environment was created during the growth of the silicide films.
Mechanical stress in gallium-arsenide on silicon substrates
Authors: Budnick B. , Wilke K. , Heymann G.
Published: July 2002

Mechanical stress of thin GaAs layers on Si(100) was investigated by photo- and cathodoluminescence at 77 K and by x-ray diffraction. The thickness of the GaAs layers was varied between 1.3 and 3.3 μm. The mechanical stress was measured before and after a treatment by rapid thermal annealing (RTA) at a temperature of 930 °C. The results of these measurements show a significant increasing of stress on the 1.3 μm layer samples (30%) after RTA. A considerable improvement (50%) of the full width at half maximum of rocking curves on the 3.3 μm layer samples was observed. We have also observed a splitting of stress into two different values.
Atomic layer epitaxy of Si on Ge(100): Direct recoiling studies of film morphology
Authors: Koleske D. D. , Gates S. M.
Published: July 2002

Two Si atomic layer epitaxy schemes based on Cl/H exchange chemistry are compared by deposition of Si on Ge(100). Time-of-flight direct recoiling and reflection high-energy electron diffraction are used to characterize the very thin Si layers. It is shown that alternating exposure to SiCl2H2 and atomic hydrogen deposits Si in a process that is self-limiting. Growth of Si by this method results in either alloy formation or Si island growth as low as 465 °C on Ge(100), which prohibits a simple measurement of Si thickness/cycle. In contrast, alternating exposure to Si2Cl6 and Si2H6 below 500 °C results in Si deposition with uniform thickness. Plots of direct recoil intensity versus incident angle (with respect to the surface plane) are a sensitive probe of the thin layer morphology.
Reciprocity theorem for charge collection by a surface with finite collection velocity: Application to grain boundaries
Authors: Donolato C.
Published: July 2002

A proof is given of a reciprocity theorem which applies to charge collection by a semiconductor surface with finite collection velocity. The theorem leads to a boundary-value problem for the charge collection probability φ. This problem is solved by the eigenfunctions expansion method for the normal collector geometry, where the collecting surface corresponds to the edge of a nonideal junction or to a charge-collecting grain boundary. The solution thus obtained is equivalent to that found earlier by the method of images but has a much simpler form. This solution, its asymptotic approximations and low-order moments, as well as the boundary conditions for φ can find use in the determination of the surface collection/recombination velocity and minority-carrier diffusion length in a semiconductor from experimental induced current scans. The new expression for φ is used to calculate the collection efficiency profile of a charge-collecting grain boundary for a generation with finite lateral extent.
Photorefractive properties of a thiapyrylium-dye-sensitized polymer composite
Authors: Zhang Yue , Spencer Christopher A. , Ghosal Saswati , Casstevens Martin K. , Burzynski Ryszard
Published: July 2002

The detailed photorefractive properties of a thiapyrylium-dye-sensitized photorefractive polymeric composite are presented. The composite contains an ionic thiapyrylium dye, 4-(4-dimethylaminophenyl)-2,6-diphenylthiapyrylium perchlorate, as a photocharge generation sensitizer, 4-(N,N-diethylamino)-(β)-nitrostyrene as a second-order nonlinear optical chromophore, and poly(9-vinylcarbazole) as a host polymer as well as a charge transporting agent. The electrooptic and photoconductive properties of the composite have been studied and an apparent sublinear dependence of the photoconductivity on the illumination power density has been observed. Both degenerate and nondegenerate four-wave-mixing experiments have been carried out and a holographic diffraction efficiency of 1.1% has been achieved in a 160-μm-thick film at an external field of 62.5 V/μm. A nonlocal character of the photorefractivity has been established through the asymmetric energy transfer with a gain of 7 cm−1 in a two-beam coupling experiment. The dynamics of the formation and erasure of the holographic gratings has been studied. The rise time and erasure time for the space-charge field have been measured as a function of the writing and erasure beam intensities, respectively. The sublinear character of these dependencies can be explained by the apparent sublinear photoconductivity of the composite. The dependence of the grating rise time on the applied electric field is attributed to the field dependence of both the photocharge generation quantum efficiency and the charge mobility in the polymer matrix. The application of this material to information storage and image processing has been explored with demonstrations of holographic image recording and retrieval.
Inductance dependence of noise properties of a high-T
c dc superconducting quantum interference device
Authors: Enpuku K. , Tokita G. , Maruo T.
Published: July 2002

Properties of white noise of a high-Tc dc superconducting quantum interference device (SQUID) have been studied using numerical simulation. It is shown that thermal noise at T=77 K significantly affects the noise properties of the SQUID. As a result, dependencies of noise properties on inductance become quite different from conventional results at T=4.2 K. In contrast to the case T=4.2 K, the voltage noise of the SQUID at T=77 K depends very weakly on the inductance, while the transfer function degrades rapidly with inductance. Consequently, rapid degradation of flux noise with inductance, as compared with the case T=4.2 K, is caused mainly by that of the transfer function. These simulation results explain reasonably experimental results reported recently. Therefore, it is necessary to improve the transfer function for the improvement of noise properties in the case of large inductances. Numerical simulation shows that a method for improving the transfer function using resistively shunted inductance or three Josephson junctions, which was proposed by the authors, is also useful for improving noise properties in the case of large inductances.
Surface-sensitive x-ray fluorescence analysis at glancing incident and takeoff angles
Authors: Tsuji Kouichi , Sato Shigeo , Hirokawa Kichinosuke
Published: July 2002

The possibility of the glancing incidence and takeoff x-ray fluorescence (GIT-XRF) method for surface analysis has been investigated. In this method the observation depth can be restricted by both the incident angle of primary x rays and the takeoff angle of observed fluorescent x rays. As a result, it has been found that the surface-sensitive analysis is achieved when the incident angle is small below the critical angle for total reflection of the primary x rays and the takeoff angle is set slightly below the critical angle for total reflection of the fluorescent x rays from the element on the substrate.
Interface processing in multilayer films
Authors: Pollard R. J. , Wilson M. J. , Grundy P. J.
Published: July 2002

We have investigated the effect of ion modification of multilayer growth and ion etching of multilayer interfaces on perpendicular anisotropy and giant magnetoresistance in sputter deposited Co/Pt and Co/Cu multilayers. These two properties are thought to be particularly sensitive to the form of the interface profile in multilayers. We find that the ion-assisted deposition conditions used degrade both perpendicular anisotropy and GMR through interface smoothing and mixing. In contrast, thermal annealing and first experiments in ion etching show that GMR can be increased by smoothing of the Co/Cu interfaces.
Microstructure characterization of Cu3Ge/n-type GaAs ohmic contacts
Authors: Aboelfotoh M. O. , Oktyabrsky S. , Narayan J. , Woodall J. M.
Published: July 2002

We have systematically investigated the microstructure and interface structure of ε1-Cu3Ge films on n-type (001)GaAs substrates using high-resolution transmission electron microscopy (HRTEM). The copper-germanium alloy forms ohmic contacts on n-type GaAs over a wide range of Ge concentrations from 5 to 40 at. % with a minimum contact resistivity of 6.5×10−7 Ω cm2 on (001) GaAs (doping concentration ∼1.0×1017 cm−3 in the Ge concentration range 25–30 at. %). The cross-sectional HRTEM results show that a low-resistivity ε1-Cu3Ge phase is formed at 25 at. % Ge concentration, and above this concentration excess Ge precipitates out between the ε1-Cu3Ge grains and the GaAs substrate. Ge grows epitaxially with the GaAs substrate, but it is not present as a continuous interfacial layer. The interface between ε1-Cu3Ge and GaAs is quite sharp, with no secondary phases. The secondary ion mass spectrometry results indicate interdiffusion between Ge and Ga, which results in highly doped regions by the incorporation of Ge atoms into the GaAs on the Ga sites. The current transport by the tunneling of the carriers through this doped region provides the low-resistance ohmic behavior of the contact. From correlations between the microstructure and the properties of the heterostructure we deduce the optimum concentration of Ge to be 30 at. % for formation of low-resistance ohmic contacts.
Electric-field induced excitons in an AlInAs/InP type-II superlattice
Authors: Kobayashi Hideki , Kawamura Yuichi , Mogi Kazuo , Iwamura Hidetoshi
Published: July 2002

The optical properties of an AlInAs/InP type-II superlattice are studied at room temperature. The photocurrent spectra have peaks that are attributable to excitons. An electroabsorption experiment confirms that the peaks are enhanced by applying an electric field. The change in absorption coefficient occurs at wavelengths of around 1 μm, where the linear absorption coefficient is small. Time-resolved photoluminescence shows the relaxation time is close to those in type-I superlattices.
Optical properties in fractional-layer-superlattice quantum wires calculated by multi-band effective mass theory
Authors: Ando Hiroaki , Chavez-Pirson Arturo , Saito Hisao , Kanbe Hiroshi
Published: July 2002

We present the results of theoretical studies numerically analyzing the optical absorption and gain properties in AlGaAs fractional-layer-superlattice (FLS) quantum wires. With our calculation method we can treat any asymmetrical FLS wire with arbitrary dimensionality from 2D to 1D and to calculate not only absorption spectra but also gain properties. Our theory accurately reproduces the optical absorption anisotropy, experimentally evaluated for an AlGaAs FLS quantum wire. It is numerically shown how optical features evolve as the quantum confinement changes from 2D to 1D by varying the FLS lateral modulation. The small modulation of Al content in the AlGaAs FLS layer is found to change the optical properties markedly and improve the gain characteristics largely.
Hydrogen incorporation in silicon nitride films deposited by remote electron-cyclotron-resonance chemical vapor deposition
Authors: Kotecki David E. , Chapple-Sokol Jonathan D.
Published: July 2002

We have studied the incorporation of hydrogen in films of silicon nitride deposited by remote electron-cyclotron-resonance chemical vapor deposition using silane (SiH4) as the silicon precursor and both ammonia (NH3) and deuteroammonia (ND3) as nitrogen precursors. Nearly stoichiometric films of silicon nitride, with a refractive index ranging from 1.84 to 2.08, were obtained at substrate temperatures from 50 to 550 °C, microwave powers from 0.5 to 2.5 kW, and NH3 (ND3) to SiH4 flow ratios from 2.5 to 10. The total hydrogen incorporation decreased linearly with increasing temperature from a maximum value of 2×1022 to 6×1021 cm−3. The amount of hydrogen incorporated in the film was independent of the microwave power and the NH3/SiH4 flow ratio, though both variables strongly influenced the hydrogen bonding configuration. The majority of the hydrogen ends up bound to the excess species in the film. Films deposited from deuteroammonia show that 70%–80% of the incorporated hydrogen originates from the ammonia precursor. Optical emission spectroscopy shows the formation of both SiD and NH in the gas phase indicating that an isotopic exchange takes place during the downstream excitation of SiH4. The relative number of N—H and Si—H bonds measured in the gas phase and in the film, as a function of the NH3 to SiH4 flow ratio, are similar. These results suggest that the hydrogen configuration in the film may be determined primarily by gas phase chemistry. Temperature programmed desorption analysis on deposited films shows that hydrogen starts to evolve from the film at a temperature of 620 °C. Films deposited at temperatures ≳350 °C were found to be stable after a 920 °C anneal.
Influence of defects on electron–hole plasma recombination and transport in a nipi-doped InxGa1−xAs/GaAs multiple-quantum well structure
Authors: Rich D. H. , Lin H. T. , Larsson A.
Published: July 2002

The nonlinear optical and transport properties of a nipi-doped InxGa1−xAs/GaAs multiple-quantum well sample (x=0.23) has been studied using a novel approach called electron-beam-induced absorption modulation (EBIA). The absorption in the sample is modulated as a result of screening of the built-in electric field in the nipi structure due to excess carrier generation. The change in field causes a Stark shift of the first quantized optical transitions in QWs which are situated in the intrinsic layers. In EBIA, a scanning electron probe is used to locally generate an electron–hole plasma that is used to study the spatial distribution of defects that impede excess carrier transport and reduce the lifetime of spatially separated carriers. The Stark shift in the MQW structure is imaged with micrometer-scale resolution and is compared with cathodoluminescence imaging results which show dark line defects resulting from strain-induced misfit dislocations. Theoretical calculations using Airy functions in the transfer-matrix method with a self-consistent field approximation were used to determine the energy states, wave functions, and carrier recombination lifetimes of the MQW as a function of the built-in field. A quantitative phenomenological analysis is employed to determine the built-in field, excess carrier lifetime, and ambipolar diffusion coefficient as a function of the excitation density. The defects are found to create potential barriers and recombination centers which impede transport and markedly reduce the excess carrier lifetime.
Plasma-enhanced growth, composition, and refractive index of silicon oxy-nitride films
Authors: Mattsson Kent Erik
Published: July 2002

Secondary ion mass spectrometry and refractive index measurements have been carried out on silicon oxy-nitride produced by plasma-enhanced chemical vapor deposition (PECVD). Nitrous oxide and ammonia were added to a constant flow of 2% silane in nitrogen, to produce oxy-nitride films with atomic nitrogen concentrations between 2 and 10 at. %. A simple atomic valence model is found to describe both the measured atomic concentrations and published material compositions for silicon oxy-nitride produced by PECVD. A relation between the Si–N bond concentration and the refractive index is found. This relation suggest that the refractive index of oxy-nitride with a low nitrogen concentration is determined by the material density. It is suggested that the relative oxygen concentration in the gas flow is the major deposition characterization parameter, and that water vapor is the predominant reaction by-product. A model, that combine the chemical net reaction and the stoichiometric rules, is found to agree with measured deposition rates for given material compositions. Effects of annealing in a nitrogen atmosphere has been investigated for the 400 °C– 1100 °C temperature range. It is observed that PECVD oxy-nitrides release nitrogen and hydrogen in the form of NH for annealing temperatures in the 500 °C–700 °C range. The relaxation process during annealing is found to be governed by a viscoelastic relaxation process similar to the relaxation process observed for thermally grown SiO2. Upon nitrogen release, the PECVD material is in a state of internal tension. The viscoelastic relaxation process for temperatures above 700 °C is dominated by the relaxation of this internal tension. A linear relation between the refractive index and material density is determined for silicon oxy-nitride with a nitrogen concentration below 30 at. %.
Effect of Ni substitution on the magnetic and electrical properties of Dy0.73Tb0.27Fe2
Authors: Senthil Kumar M. , Reddy K. V. , Rama Rao K. V. S.
Published: July 2002

Alloys of Dy0.73Tb0.27Fe2−xNix [0≤x≤2] were prepared and the lattice parameters obtained at room temperature showed a deviation from Vegard’s law owing to the presence of magnetovolume effect. Magnetization studies were carried out up to an applied field of 10 kOe in the temperature range 4.2–750 K. Magnetization data at 4.2 K indicate the effect of domain wall pinning. Temperature dependence of magnetization curves showed maxima at low temperatures as a consequence of this pinning effect. Electrical resistivity studies were carried out in the temperature range 16–750 K. A minimum observed for x=2 in the vicinity of its Curie temperature is attributed to the presence of critical fluctuations due to short-range spin ordering of the rare earths. All the samples, except x=2, showed a T2 dependence at low temperatures and this has been attributed to electron-spin wave scattering mechanism.
Optical epilayers on silicon substrate: Electronic and optical properties of ZnS/Si superlattice
Authors: Wang E. G. , Ting C. S.
Published: July 2002

The optimal epilayers on a silicon substrate are suggested to integrate the superior properties of ZnS semiconductor with the mature technology of Si. In a semiempirical tight-binding scheme, the band structures and optical transitions are studied for the (ZnS)n/(Si2)m (110) superlattices with a wide range of n,m≤20. Because of the quantum confinement effect caused by the large band-gap ZnS layers, the band-edge states are confined two dimensionally in the Si quantum wells. A single empty interface band is found lying below the conduction band. Furthermore, the influence of valence-band discontinuity has been checked over all possible energy ranges. The optical matrix elements of the superlattices are calculated and compared with those of bulk ZnS and Si.