bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of fluorine in chemical-vapor-deposited tungsten silicide film on electrical breakdown of SiO2 film
Authors: Shioya Yoshimi , Kawamura Seiichiro , Kobayashi Ikuro , Maeda Mamoru , Yanagida Kimio
Published: July 2002

The effect of fluorine in chemical-vapor-deposited tungsten silicide film on electrical breakdown of SiO2 film was investigated. Fluorine diffuses into the SiO2 film through the upper layer of poly Si above 800 °C. At 1000 °C, fluorine diffuses into the SiO2 film to a concentration on the order of 1020 cm−3. Electrical breakdown field of the SiO2 film degrades remarkably at 1000 °C. However, it was clear that the diffusion of fluorine was blocked by a thin chemical-vapor-deposited Si3N4 layer on the SiO2 film. In this case, the degradation of SiO2 film was not observed. From the above results, it is concluded that the diffusion of fluorine included in the chemical-vapor-deposited tungsten silicide film is one of the causes in degradation of electrical breakdown of the SiO2 film when the chemical-vapor-deposited tungsten silicide film was used as a gate electrode in metal oxide semiconductor integrated circuits.
Dopant redistribution at Si surfaces during vacuum anneal
Authors: Liehr M. , Renier M. , Wachnik R. A. , Scilla G. S.
Published: July 2002

We have measured dopant distribution profiles by spreading resistance and secondary ion mass spectroscopy (SIMS) profiling at silicon surfaces annealed to high temperature in vacuum. Accumulation of electrically active p-type dopants is found to occur. The p-type dopant is identified by SIMS and by its diffusion characteristics as being boron. The measured doping profiles can be interpreted as indicating that the chemically cleaned surface contains boron impurities in the 1012/cm2 range that become electrically activated and diffuse into the substrate during high-temperature anneals. It is concluded that the boron exists initially in an oxidized state at the surface. Borosilicate parts present in any standard ultrahigh vacuum system are identified as a source of the pollution.
Elementary excitations and phase transition in uniformly frustrated Heisenberg spin systems
Authors: Azaria P. , Diep H. T.
Published: July 2002

A Green’s-function method is used to study spin-wave excitations and phase transition in a three-dimensional uniformly frustrated Heisenberg spin system of simple cubic structure. The frustration is made to vary by changing the antiferromagnetic bond strength. We take into account different sublattices that result in gaps at the Brillouin zone boundaries in the spin-wave spectrum. The sublattice order parameters as a function of temperature and the critical temperature are calculated self-consistently. Comparison with Monte Carlo simulations performed by us is shown and discussed.
Study of rapidly quenched Fe100−xMx crystalline alloys by Mössbauer effect spectroscopy (M=B, C, Al, Si, P)
Authors: Sánchez F. H. , Budnick J. I. , Zhang Y. D. , Hasegawa R.
Published: July 2002

The rapidly quenched, crystalline, Fe-rich Fe100−xMx system has been studied by 57Fe Mössbauer effect spectrometry. Boron and carbon alloys were found to have regions with cementite local structure. Small amounts of fcc γ-Fe were also observed in some of the cases. Furthermore, almost half of the carbon was concluded to be in interstitial solution. Upon annealing the carbon alloy, the fcc phase disappears to benefit formation of the cementite. In contrast, the alloys with aluminum, silicon, and phosphorous are substitutional solid solutions. After being annealed at 1073 K, they do not show changes in their hyperfine interactions nor in their crystalline structure. However, the lattice parameter of the alloy with phosphorous unexpectedly increased from a value below that corresponding to pure iron to another above it. These results are discussed on the basis of the metalloid solubilities in iron and their atomic sizes.
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9Sn Mössbauer study of the evolution of the magnetic state in U(Sn,Pb)3
Authors: Bykovetz N. , Herman Warren N. , Yuen T. , Jee C. S. , Lin C. L. , Crow J. E.
Published: July 2002

USn3 is a highly enhanced paramagnet that is very near a magnetic instability, and UPb3 has an antiferromagnetic transition at 31.3 K. As Sn is substituted for Pb in U(Sn1−xPbx)3, the Néel temperature, TN, initially increases to 38 K at x=0.7, then decreases, and appears to go to zero for x≲0.1. The temperature dependence of the magnetic susceptibility for 0≤x≤1.0 and 119Sn Mössbauer spectra for 0≤x≤0.98 have been measured. The Mössbauer spectra indicate that the antiferromagnetic structure for the Pb-rich pseudobinary alloys is not type I as previously reported. As x decreases, at least two, and possibly four, distinct Sn hyperfine field sites are found. The saturation hyperfine fields at the Sn sites do not show as pronounced a variation with concentration as is seen in TN. For larger x the saturation hyperfine fields are independent of x, which suggests that the U magnetic moments are nearly constant for the Pb-rich pseudobinary alloys, and then drop rapidly to zero at the magnetic instability. The fraction of Sn sites seeing a particular hyperfine field is observed to vary monotonically across the series.
Torque anisotropy and magnetization in Mo/Ni superlattices
Authors: Strouse Gregory F. , Pechan Michael J.
Published: July 2002

Angular and field varying torque measurements have been made on Mo/Ni superlattices. The angular results show good agreement with FMR measurements, indicating no frequency-dependent aspects of the anisotropy at room temperature. It is observed that field varying measurements provide an accurate, inexpensive method of determining the magnetization, but the magnetic anisotropy obtained by this technique differs significantly from FMR and angular results.
Structures and magnetic properties of Fe/Cu multilayered films fabricated by a magnetron sputtering method
Authors: Kozono Y. , Komuro M. , Narishige S. , Hanazono M. , Sugita Y.
Published: July 2002

Fe and Cu single-layered films and Fe/Cu multilayered films were prepared by an rf-magnetron sputtering method, and the film structures and magnetic properties were investigated. Fe and Cu single-layered films become continuous when their thickness is more than 4 nm for Fe and 10 nm for Cu. The crystal structure of Fe/Cu multilayered films depends on the thickness or continuity of Fe and Cu layers. A Fe 1.6 nm/Cu 2 nm multilayered film has a periodic structure. As the thickness of the Fe layer decreases, the magnetic flux density and coercivity decrease and the magnetostriction constant changes from negative to positive. Uniaxial magnetic anisotropy in the plane of the multilayered Fe/Cu films is observed when the Fe layer is discontinuous, but it is not clearly observed for a continuous Fe film.
Magnetization and its temperature dependence in compositionally modulated amorphous Fe70B30-Ag films
Authors: Xiao Gang , Chien C. L. , Natan M.
Published: July 2002

Compositionally modulated amorphous Fe70B30-Ag films have been prepared by dc magnetron sputtering. The thickness of the magnetic layer (d) ranged from 3 to 90 Å, while the Ag layer thickness was always kept at four times as large. The multilayer structure is well established by the cross-sectional transmission electron micrograph. The magnetic properties of the system were investigated with a SQUID magnetometer. The spontaneous magnetization (Ms) at T=8 K remains constant over the thickness range studied, indicating the absence of magnetically dead layers at the interfaces. The temperature dependence of Ms follows Bloch’s law for d≥6 Å, with the spin-wave constant inversely proportional to d. This is explained by an interface effect on spin-wave excitation. As the thickness is reduced to 4 Å, a linear temperature dependence of Ms is observed, indicating a magnetic 3D-to-2D transition.
Properties of electrodeposited Co-Cu multilayer structures
Authors: Dariel M. , Bennett L. H. , Lashmore D. S. , Lubitz P. , Rubinstein M. , Lechter W. L. , Harford M. Z.
Published: July 2002

Alternate layers of Co and Cu of individual layer thicknesses from 1.5 to 8.0 nm and total thickness of about 100 layers and of Co bilayers separated by Cu have been electroplated from an electrolyte having a low concentration of Cu and a high concentration of Co atoms. The properties of the resulting structures have been analyzed using SEM, x-ray diffraction, VSM, and FMR methods. Comparable structures have also been fabricated by e-beam evaporation in high vacuum for comparison purposes. X-ray diffraction patterns indicate only the fcc structure. Assuming the Co thickness to be that deduced from the plating charge, we infer 4πM values in the range 6.0–14.5 kG from VSM and FMR. Some uniaxial anisotropy is apparent in this system. These results are similar to those of earlier work on thin fcc Co layers in the same range of thicknesses, where the room-temperature moment was reduced but depended only slightly on layer thickness, and where the uniaxial anisotropy was observed to be small.
Magnetic susceptibility and magnetic resonance of a composition-modulated spin glass
Authors: Cowen J. A. , Kenning Gregory G. , Slaughter Jon M.
Published: July 2002

Composition-modulated multilayer spin glasses of the form CuMn-Cu and CuMn-SiO2 have been produced by sputtering. Magnetic susceptibility and electron spin resonance measurements on these carefully prepared but not very well characterized systems have provided the following results. We have observed no obvious dimensional effects on the spin-glass temperature with varying layer thickness. The layers exhibit no new macroscopic anisotropy. Mean-free-path effects, if present, produce no difference in Tg from what one calculates using the concentration of Mn averaged over the whole sample.
Noncollinear rotation of Gd+3 and Tb+3 magnetic moments in Gd1−xTbxAl2 intermetallic compounds
Authors: Ibarra M. R. , del Moral A. , Arnaudas J. I.
Published: July 2002

We have developed a new method to explain the magnetic and magnetoelastic properties of pseudobinary intermetallic compounds Gd1−xTbxAl2 (0.05≤x≤1) when the magnetic field is applied along the hard magnetization direction. This method uses a single ion crystal electric field model and considers a noncollinear rotation for the magnetic moments in order to give a determination of the irreducible cubic equilibrium strain associated with the tetragonal mode of the magnetostrictive distortion.
Continuous-symmetry ferromagnets with random anisotropy
Authors: Serota R. A. , Lee P. A.
Published: July 2002

We report the results of zero-temperature Monte Carlo simulations on the one-dimensional XY model with weak random magnetic anisotropy. Emphasis is made on metastable properties of the system. Some experimental implications are briefly discussed.
Magnetization-vector measurements on a Ni-Mn spin-glass alloy
Authors: Ziq Kh. , Kouvel J. S.
Published: July 2002

Measurements were made simultaneously of both the longitudinal and transverse magnetization components (ML,MT) of a field-cooled thin-disk sample of disordered Ni75Mn25 as it was rotated quasistatically in various fixed fields (Ha) up to 4 kOe. For Ha<1 kOe, the observed behavior at sample-rotation angles (θ) up to 90° is consistent with a purely unidirectional anisotropy field (HK=0.6 kOe), but at higher θ both ML and MT are anomalously low, signifying that the size of the rotating magnetization vector (MS) becomes substantially smaller than the thermoremanence. The normal demagnetizing fields are too weak to account for this effect. At higher Ha, MS rises slightly above the thermoremanence near θ=90°. This derives from the fact that while ML(θ) is normally behaved, the peak in MT(θ) is anomalously high, indicating that the effective unidirectional anisotropy grows with increasing Ha. Moreover, the shape of MT(θ) shows the additional presence of higher-order (e.g., uniaxial) anisotropy components.
Mn-Mn exchange constants in zinc-manganese chalcogenides
Authors: Giebultowicz T. M. , Rhyne J. J. , Furdyna J. K.
Published: July 2002

Excited levels of isolated nearest-neighbor Mn-Mn pairs of Zn1−xMnxS, Zn1−xMnxSe, and Zn1−xMnxTe have been studied by inelastic neutron scattering. The measurements have been carried out on several single-crystal and polycrystalline samples with x≤0.05 at various temperatures. Values obtained for the exchange constants 2JNN are −2.78, −2.12, and −1.64 meV for the three studied systems, respectively.
Neutron diffraction study of the wurtzite-structure dilute magnetic semiconductor Zn0.45Mn0.55Se
Authors: Giebultowicz T. M. , Rhyne J. J. , Furdyna J. K. , Debska U.
Published: July 2002

We report the first results of neutron diffraction studies of magnetic ordering phenomena in a wurtzite-structured diluted magnetic (semimagnetic) semiconductor Zn0.45Mn0.55Te. At low temperatures the system exhibits a short-range antiferromagnetic ordering, closely related to the antiferromagnetic structure seen in the wurtzite form of β-MnS. This type of ordering indicates short-range and antiferromagnetic only interactions between the Mn spins, in agreement with present theories of exchange mechanism in DMS materials. Similarly as in cubic DMS systems, the magnetic correlation range in Zn0.45Mn0.55Te exhibits a pronounced anisotropy.
Moment canting in the erbium-iron-manganese-boron system: Magnetization effects
Authors: Pinkerton F. E. , Fuerst C. D. , Meisner G. P.
Published: July 2002

We report that Er2Fe14−x MnxB compounds at 4 K have a component of the magnetization which is linear in the applied field. We attribute this to a noncollinear Er moment structure in which the Er moments rotate under application of an external field. The slope becomes very large (dM/dH=0.51μB/f.u./T) at x=2, near the composition where the net Er and transition metal sublattice magnetizations are equal at zero temperature. This enhanced field dependence suggests an additional moment rotation mechanism near compensation. In the compositions x=2.5 and 2.75, just above zero temperature compensation, the slope of the linear field dependence abruptly increases when the field reaches 5 and 7.2 T, respectively. High Mn concentrations have rare-earth-dominated magnetization curves with substantial curvature at low fields and a linear nonsaturating field dependence at high fields. Anomalies are also observed in the initial magnetization behavior above x=2.5.
The production of laminar fields with permanent magnets
Authors: Potenziani E. , Clarke J. P. , Leupold H. A.
Published: July 2002

With the increasing demands upon millimeter/microwave devices with regard to miniaturization, power, frequency range, etc., there have arisen requirements for strong (kOe) magnetic fields of unusual shape, confined to small regions by permanent magnetic configurations of minimal bulk. The present work describes several novel permanent magnet structures that produce uniform fields of up to several kOe confined to spaces with thicknesses an order of magnitude smaller than the other two dimensions. Such structures are potentially useful for focusing ribbonlike electron beams in devices such as orotrons. The structural principles used to accomplish this can also be used to shorten long, but efficient, (permanent magnet) transverse field sources, without loss of field strength or incurrence of flux leakage. Examples of proposed structures are discussed and analyzed.
Influence of preparation conditions on magnetic properties and aging behavior of rf diode sputtered GdTbCo films
Authors: Heitmann H. , Hartmann M. , Klahn S. , Rosenkranz M. , Tolle H. J. , Willich P.
Published: July 2002

GdTbCo films were rf diode sputtered from a composite target varying the argon pressure PAr and the substrate bias voltage Vb. Both the uniaxial magnetic anisotropy constant Ku and the aging behavior of the films depend strongly on the preparation parameters. The absolute maximum of Ku was obtained at Vb=−150 V. However, at this bias voltage nearly the highest oxidation rate of unprotected 100-nm-thick films was observed. Films of highest stability are obtained without any bias voltage. The oxidation rate is correlated with the Ar concentration in the films. It was argued recently that the anisotropy of sputtered films could depend on argon incorporation. Our results seem to rule out this mechanism since GdTbCo films prepared at zero bias show a relative Ku maximum in dependence on PAr where the argon concentration is near its absolute minimum. The magneto-optic Kerr rotation θK of the films can only be correlated with the Co concentration for zero bias films. Some additional variation depending on the bias voltage has been observed.
Theory of optical beam induced current images of defects in semiconductors
Authors: Wilson T. , McCabe E. M.
Published: July 2002

We present a model of image formation in scanning optical microscopes operating in the optical beam induced current mode. A perturbation analysis is used, a point spread function is introduced, and specific images of point defects obtained. It is found that the resolution is not limited by the diffusion length.
Glassy metal alloys with perminvar characteristics
Authors: Hasegawa Ryusuke
Published: July 2002

A number of glassy metal alloys with near-zero magnetostriction have been found to exhibit perminvarlike properties of relatively constant permeability at low magnetic fields and constricted B-H loops. A wide variety of perminvar properties can be obtained by varying heat-treatment conditions and the compositions of the materials. The low field permeability and dc coercivity of the glassy alloy perminvars can range between about 600 and 90 000 and between about 0.2 and 12 A/m, respectively. The magnetic shock problem associated with the crystalline perminvars is absent in these materials.
Magnetic and galvanomagnetic properties of amorphous CoZr thin films
Authors: Jagielinski T.
Published: July 2002

Magnetic and galvanomagnetic properties of Co94Zr6 amorhous films were studied over a thickness range from ∼100 Å to 3 μm. The values of magnetization and magnetostriction were 14.5 kG and <10−6, respectively, independent of thickness. The coercivity Hc, however, was a strong function of thickness and follows the Néel predictions for wall motion coercivity mechanism. The induced anisotropy was uniaxial and decreased with film thickness. This change is not understood, since the anisotropy is believed to be due to pair ordering, which should be independent of thickness. The anisotropy dispersion angle α90 and, therefore, the ripple parameter S, were found to be very small for samples thicker than 5000 Å. The resistivity of the films increased as the thickness decreased and could be described over the entire thickness range by a ‘‘bulk resistivity’’ of ρ0=80 μΩ cm and a mean free path of the conductive electrons of l0=33 Å.
High-sensitivity ultrasonic interferometer for the detection of magnetic phase transitions
Authors: Huan C. H. A. , Gregg J. F. , Wells M. R. , Briggs G. A. D. , Wolf W. P.
Published: July 2002

An improved technique is described for the detection of magnetic phase transitions using acoustic waves with electrical interferometry. The method employs zinc oxide transducers sputtered directly onto the sample. These transducers operate efficiently at frequencies up to 3 GHz, corresponding to acoustic wavelengths of the order of 2 μm. By measuring the phase of high-order multiple echoes, changes in sample thickness and/or velocity of parts in 109 can be detected. The method has been used to determine the phase diagram of the metamagnet dysprosium aluminum garnet for magnetic fields parallel to [001]. General agreement with earlier determinations based on thermodynamic measurements is obtained.
Effect of Ar+ ion bombardment on the electrical characteristics of Al/n-Si contacts
Authors: Carr B. A. , Friedland E. , Malherbe J. B.
Published: July 2002

Ion bombardment of aluminum contacts on n-type silicon has been investigated by measuring the I-V characteristics before and after implantation of Ar+. These characteristics have been quantified in terms of the saturation current, the ideality factor, and the diode series resistance. Before implantation, large variations in these parameters were found. After implantation, much more uniform characteristics were obtained but they were still far from ideality. Auger electron spectroscopy showed that very little mixing took place, but that the concentration of oxygen at the interface decreased. From α-particle channeling analysis it was ascertained that the implantation caused severe damage to the silicon. This damage was probably responsible for the observed increase in the series resistance.
A Mössbauer effect study of the structural and magnetic properties of Y2(Fe1−xAlx) 14B
Authors: Yang Ying-chang , Tharp Dwayne E. , Long Gary J. , Pringle O. A. , James W. J.
Published: July 2002

The crystallographic and magnetic properties of Y2(Fe1−xAlx) 14B, where x equals 0.00, 0.02, 0.04, 0.06, and 0.08, have been investigated by Mössbauer spectroscopy and magnetic measurements at room temperature and 85 K. Magnetic anisotropy and magnetization changes with aluminum substitution indicate that, because of size, the aluminum preferentially occupies the j2 site over the remaining five crystallographically nonequivalent iron sites. This preferential occupation has been confirmed by Mössbauer spectral studies, which indicate that the compositional variation of the hyperfine field for each site is related to the number of near-neighbor aluminum atoms for the site. This compositional variation is helpful in assigning the different spectral components in these alloys as well as in the related Nd2(Fe1−xCox)14B and Y2(Fe1−xCox)14B alloys. In all cases these assignments are consistent with the local symmetry and coordination environment for each site.
Ferromagnetic phase transition of the film and surface
Authors: Shi Long-pei
Published: July 2002

A ferromagnetic phase transition of the film and surface is studied by the Green’s function method based upon the Heisenberg model with surface magnetic anisotropy. It is proved that the order parameter (spontaneous magnetization) changes with the position in the ferromagnetic film which loses translational invariance in one direction. Expressions for the Curie temperature and spontaneous magnetization of each atomic plane in the film have been derived. The properties of magnetic order of the surface atomic plane are very different from those of the other atomic planes in the film. One expects that the extraordinary phenomena will exist in ultrathin films, since for strong surface magnetic anisotropy, as the thickness of film is decreased, the Curie temperature rises, etc.
Magnetothermal properties of UIrGe and systematic trends in magnetic heavy fermion compounds
Authors: Ramirez A. P. , Batlogg B. , Bucher E.
Published: July 2002

We have measured the low-temperature susceptibility and specific heat of the compound UIrGe and find both an antiferromagnetic phase transition at 16 K and a high-temperature electronic specific heat coefficient of 145 mJ/mole K2. Comparison of this behavior is made with other heavy fermion magnetic systems and a monotonic relationship is found between TN and the difference in the electronic specific heat coefficient γ above and below the transition.
Effect of interface states on the electrical properties of W, WSix, and WAlx Schottky contacts on GaAs
Authors: Callegari A. , Ralph D. , Braslau N. , Latta E. , Spiers G. D.
Published: July 2002

Barrier heights of refractory W, WSix, and WAlx Schottky contacts deposited on n-GaAs with different surface treatments have been electrically characterized by current-voltage, capacitance-voltage, and internal photoemission measurements. Internal photoemission measurements indicate that the Fermi level pins approximately at midgap (Φn ≂0.7–0.8 eV). The current-voltage barrier heights were consistent with internal photoemission for diodes with little oxide at the GaAs/metal interface. For an oxide layer of about 2.5 nm, current-voltage barrier heights as high as 0.9 eV were observed. Capacitance-voltage barrier heights were found to be 0.9–1 eV with a weak dependence on interface oxide. A theoretical model was developed to explain these results. A large density of states (5×1013–1014/cm2) at the GaAs/metal interface which exchanges charge mainly with the metal appears to explain well our experimental capacitance-voltage and current-voltage data.
Recrystallization by rapid thermal annealing of implanted low-pressure chemical-vapor-deposited amorphous Si films
Authors: Alvi N. S. , Tang S. M. , Kwor R. , Fulcher M. R.
Published: July 2002

Amorphous Si films of 4000 Å were deposited using low-pressure chemical-vapor deposition and implanted with arsenic or boron at doses of 5×1013, 5×1014, and 5×1015 cm−2. These films were then rapid thermally annealed (RTA) using an Eaton Nova ROA-400 system at temperatures ranging from 900 to 1200 °C and dwell times ranging from 1 to 30 s. It was found that grain growth initiated very rapidly (less than 2 s at 1100 °C). Grain growth saturation (when grain size equals the film thickness) was reached in 5×1015 dose samples after a 1200 °C, 10-s RTA. The sheet resistance decreased with increasing RTA temperature and dwell time. Hall mobility increased with both RTA temperature and time. The temperature coefficient of resistance (TCR) was negative at low dose implants and became positive at higher dose implants. The lowest TCR was found in films implanted with medium dose. In general, 1200 °C/10-s RTA is an optimal condition for crystallization and annealing of the 5×1015 and 5×1014 cm−2 dose films while longer times are necessary for the 5×1013 cm−2 dose films.
Magnetomechanical sensing of laser-generated ultrasound to assess structural change in metallic amorphous ribbons
Authors: Greenough R. D. , Dewhurst R. J. , Edwards C.
Published: July 2002

A new noncontacting technique is described for monitoring the structural changes in metallic amorphous ribbons. Laser-generated ultrasound is propagated from a line source, and a magnetomechanical sensing coil is used to monitor the waveform at some distance away from the source. The quality of the ribbon is assessed by either changes in velocity or amplitude of the magnetomechanical signals from the coil, which itself depends on the strength of the applied magnetic field. Metglas 2605 SC has been studied in this way, showing that velocities change from 4940 to 5830 ms−1 as the material becomes progressively less amorphous, while corresponding maximum amplitudes of the sensing coil signal reduce some 18-fold.
Electrolyte electroreflectance in the characterization of HgCdTe heterostructures
Authors: Berlouis L. E. A. , Peter L. M. , Astles M. G. , Gough J. , Humphreys R. G. , Irvine S. J. C. , Steward V.
Published: July 2002

We have used the technique of electrolyte electroreflectance (EER) coupled with electrochemical etching to profile through epitaxial layers and heterostructures of Hg1−xCdxTe. The need for proper electrochemical control during EER measurements is discussed. The resolution achieved in both composition, Δx=±0.002, and etch depth, ±30 Å, has made possible the observation of the variations in composition at the ambient/epilayer, epilayer/substrate, and high-x/low-x interfaces. Good correlations of the profiles observed have been obtained with secondary ion mass spectroscopy, electron dispersive x-ray diffraction, and Rutherford backscattering measurements. The variation of the broadening parameter Γ at these interfaces is also discussed.
Raman-gain estimates for high-gain optical fibers
Authors: Lines M. E.
Published: July 2002

The amplification of light signals by the mechanism of stimulated Raman scattering is discussed, with specific reference to certain heavy-metal germanate and arsenate glasses with Raman-gain-coefficients G of up to 20 times that of fused silica. Calculations are presented of the intrinsic scattering losses from Rayleigh, Brillouin, and spontaneous Raman sources for these compositions which, when combined with the measured G values, determine the potential signal-amplification capabilities as a function of pump power and fiber length L. Direct comparisons are made with an equivalent calculation for an ideally pure germania fiber. The results hinge sensitively upon the degree to which concentration fluctuations (leading to concentration-scattering Rayleigh loss) are intrinsic in the multicomponent high-G glass compositions. In spite of this, some compositions are located which can outperform pure germania fibers even in the presence of signficant concentration-scattering loss. This is particularly so for high pump powers and short fiber lengths L<2 km.
Electron energy distribution function in He-CO radio-frequency plasmas: The role of vibrational and electronic superelastic collisions
Authors: Capitelli M. , Celiberto R. , Gorse C. , Winkler R. , Wilhelm J.
Published: July 2002

The role of vibrational and electronic superelastic collisions in collision-dominated He-CO rf bulk plasmas has been studied by solving the time-dependent Boltzmann equation in the presence of different concentrations of vibrational [CO(v=1)] and electronic [CO(a3Π),He(3S)] states. The results, which have been obtained for a field frequency ω of π 107 s−1 Torr−1, show that the presence of excited states is such to markedly enlarge at medium electron energies and to strongly enhance at high energies the electron energy distribution function with large consequences on the related macroscopic quantities of the electrons, particularly on the mean collision frequencies of high threshold inelastic collision processes.
TiSi2/polycrystalline silicon: Arsenic distribution and Si grain growth
Authors: Zheng L. R. , Hung L. S. , Phillips J. R. , Mayer J. W.
Published: July 2002

The diffusion behavior of arsenic in polycrystalline silicon (poly-Si) and the grain growth of arsenic-doped poly-Si with a TiSi2 overlying layer were investigated by MeV 4He2+ backscattering techniques and transmission electron microscopy. Fine-grain (30–40 nm) poly-Si was implanted with 1 or 3×1016 arsenic ions/cm2 and annealed in two stages: (1) at 885 or 985 °C in an oxygen atmosphere to distribute (homogenize) the arsenic throughout the poly-Si layer and (2) at 750 °C in a vacuum ambient with deposited Ti or TiSi2 overlay to determine the out-diffusion of arsenic. After a 750 °C anneal for 8 h, there was essentially no arsenic redistribution in the sample homogenized at 985 °C, but a loss of 40% arsenic was observed in the sample homogenized at 885 °C. The Si grains in the 280-nm-thick poly-Si layer grew in size during homogenization, up to 400 nm at 985 °C and 150 nm at 885 °C. No grain growth was observed after a 750 °C, 8-h anneal of doped poly-Si films in contact with Ti.
Growth of Si1−xGex on silicon by liquid-phase epitaxy
Authors: Alonso M. I. , Bauser E.
Published: July 2002

We demonstrate heteroepitaxial growth of smooth homogeneous Si1−xGex layers on crystalline silicon substrates by means of liquid-phase epitaxy. For a given saturation temperature Tsat, different alloy compositions x can be grown by varying the composition of the solutions. However, smooth epitaxial layers are obtained only up to a critical germanium content xc which increases as Tsat decreases and depends upon the choice of solvent.
Electrical conduction in a polyblend of poly(methyl methacrylate) and poly(vinyl acetate)
Authors: Sekar R. , Tripathi A. K. , Goel T. C. , Pillai P. K. C.
Published: July 2002

Electrical conduction in a polyblend of poly (methyl methacrylate) and poly (vinyl acetate) is studied as a function of voltage and temperature with three different electrodes: aluminum, copper, and silver. The results show that the Schottky–Richardson emission is dominant in the present case. The values of Schottky field-lowering constant β, the effective metal-insulator potential barrier, and the activation energy involved in the conduction are reported.
Annealing behavior of Ga+ implanted GaAs/AlGaAs observed by transmission electron microscopy
Authors: Werder D. J. , Pearton S. J.
Published: July 2002

The structural aspects and annealing behavior of induced damage by Ga+ ion implantation of a GaAs single quantum well as investigated by transmission electron microscopy are presented. After rapid thermal annealing, vacancy and interstitial perfect dislocation loops are found on 〈110〉 and 〈111〉 type planes. In contrast to previous results from superlattices of AlGaAs/GaAs, we find dislocation loops in the AlGaAs as well as in the GaAs layer. The cathodoluminescence intensity of the implanted quantum well recovers completely after annealing.
Surface conductance of a copper wire in a fluid at high pressure
Authors: Decker D. L.
Published: July 2002

The three-dimensional flow of heat in a wire carrying a current and immersed in a liquid is solved in detail. Using this exact result the surface conductance of copper in petroleum ether has been measured as a function of pressure to 40 kbars. The measured surface conductance for copper in a fluid is very small, justifying approximations which yield results that are in agreement with a simplified one-dimensional heat-flow problem. Surprisingly, even at 40 kbars pressure a very large fraction of the joule heating within a wire with a length-to-diameter ratio of ∼100 is dissipated through the ends of the wire rather than to the surrounding liquid.
Design of n-p-n AlGaAs double-heterojunction bipolar transistors
Authors: Chen Chung-Zen , Lee Si-Chen , Lin Hao-Hsiung
Published: July 2002

Two device structures are presented for the solution of two problems that result when an AlGaAs heterojunction bipolar transistor is used in GaAs integrated circuits. The first is the 2-kT surface recombination current problem, which seriously reduces the current gain, especially at low current level. It is found that by sandwiching a high band-gap p-type AlGaAs in the emitter-base junction interface, the 2-kT current could be substantially reduced, and the current gain displays flattened characteristics at low collector current (<1 μA). The second problem is how to reliably smooth out the potential spike at the base-collector interface which results in a serious voltage-dependent collector current in the common emitter I-V characteristics of the transistors. It is found that by adding a thin spacer layer with the same composition but the opposite type as the base layer in the base-collector junction interface, the potential spike can be easily and reproducibly suppressed.
Majority-carrier diffusion coefficients in degenerately doped silicon
Authors: Silard Andrei P. , Duţă Miron J.
Published: July 2002

A detailed analysis of the majority carrier diffusion coefficients (Dn and Dp) behavior in degenerately doped silicon is performed. Simple analytical expressions showing that for carrier concentrations equal to or larger than the corresponding density of states in the conduction and valence bands, respectively (i.e., n≥NC and p≥NV), the ratio of majority-carrier diffusion coefficient to drift mobility increases with the power of (2/3) of the corresponding majority-carrier concentrations are derived. Based upon the available experimental dependencies of the drift mobilities μ on doping concentration N, it is shown explicitly that the majority-carrier diffusion coefficients D in strongly doped silicon increase sharply with the dopant level N in the 5×1019–5×1020 cm−3 range of the latter, regardless of the ambient temperature T. The peculiar behavioral details and the main consequences of the reported results are discussed in this work as well.
Electrical activation of silicon implanted in semi-insulating GaAs: Role of boron and the midgap electron trap (EL2)
Authors: Morrow Richard A.
Published: July 2002

A model based on the constraint of stoichiometry is developed to account for some existing data on the donor activation of silicon ions implanted in semi-insulating, boron-doped GaAs grown by the liquid encapsulated Czochralski method. As a function of increasing implant dose (up to 1013 ions/cm2), three stages of activation are pictured: facilitation by EL2, inhibition by boron, and finally, 100% differential activation when boron is depleted. Possible atomic structures are suggested for the boron-related defects and silicon-related donors. A proposal for using implant measurements to help establish the atomic structure of EL2 is advanced.
Effects of ion-beam mixing on the epitaxial growth of MoSi2 on (111)Si
Authors: Cheng J. Y. , Cheng H. C. , Chen L. J.
Published: July 2002

Both plan-view and cross-sectional transmission electron microscopy as well as sheet resistance measurement have been applied to study the effects of As+ ion-beam mixing on the epitaxial growth of MoSi2 on (111)Si. Significant improvement in the epitaxial growth of MoSi2 on (111)Si and lower electrical resistivity of the MoSi2 overlayer were found as a result of ion-beam mixing. Island formation was almost completely alleviated in samples implanted under suitable conditions and subsequently annealed up to 1100 °C. The dispersion of impurities near the Mo/Si interface and/or the generation of defects as a result of the ion-beam mixing are thought to be particularly beneficial to the growth of MoSi2 epitaxy on silicon. The ineffectiveness of the ion-beam mixing for the improvement of the silicon surface coverage in some instances is attributed to the more pronounced accumulation of As atoms at the MoSi2/Si interface to increase the interface energy so that island formation becomes energetically more favorable.
Characteristics of GaAs with inverted thermal conversion
Authors: Kang C. H. , Lagowski J. , Gatos H. C.
Published: July 2002

GaAs crystals exhibiting inverted thermal conversion (ITC) of resistivity were investigated in conjunction with standard semi-insulating (SI) GaAs regarding characteristics important in device processing. It was established that dislocation density and Si implant activation are unaffected by transformation to the ITC state. However, in ITC GaAs the controlled increase of the EL2 (native midgap donor) concentration during annealing makes it possible to attain resistivities one order of magnitude greater (e.g., about 109 Ω cm of 300 K) than those attained in standard SI GaAs (e.g., 107–108 Ω cm).
A generalized thermal model for stripe-geometry injection lasers
Authors: Papannareddy R. , Ferguson W. , Butler J. K.
Published: July 2002

We present a generalized thermal model based on a finite-element code for estimating the temperature rise, associated thermal resistance, and cw optical power in a stripe-geometry double-heterostructure laser. In particular, we report the first thermal analysis of a zinc-diffused, oxide-insulated AlGaAs laser structure below and above threshold taking into account the lateral current spreading, the temperature dependence of the threshold current, and external differential quantum efficiency. The results show that the thermal resistance of the device increases approximately by 18% with the effects of zinc diffusion and oxide insulation.
Thermally stable ohmic contacts to n-type GaAs. II. MoGeInW contact metal
Authors: Murakami Masanori , Price W. H. , Shih Yih-Cheng , Braslau N. , Childs K. D. , Parks C. C.
Published: July 2002

It was previously found that a small amount of In impurity was able to convert MoGeW contacts from Schottky to ohmic behavior yielding thermally stable, low-resistance ohmic contacts n-type GaAs. In the present experiment transport measurements and materials studies were carried out for MoGeInW contacts in which a thin layer of In was directly added to the MoGeW contacts during deposition. The transition from Schottky to ohmic behavior was observed by adding an In layer as thin as ∼1 nm to the MoGeW. Contact resistances were found to be very sensitive to the deposition sequence, the annealing method, the annealing temperature, and the In layer thickness. Low resistances of ∼0.5 Ω mm were obtained in the MoGeInW contacts with 2-nm-thick In layers, annealed by the heat-pulse method at temperatures in the range of 880–960 °C for 2 s. Contact resistances were stable during subsequent annealing at 400 °C for 100 h. Evidence of formation of the parallel diode areas with various barrier heights was obtained for these contacts after annealing at elevated temperatures. These low-barrier-height areas are believed to be the interfaces between the contact metals and InGaAs phases. The composition within the ternary phases was uniform, and no composition gradient was observed. The composition was determined by small-probe x-ray energy dispersive spectrum to be close to In0.2Ga0.8As. The distribution of these ternary phases, influenced by the contact fabrication process parameters, strongly affected the contact resistance.
Experiments concerning the connective nature of superconductivity in YBa2Cu3O7
Authors: Larbalestier D. C. , Daeumling M. , Cai X. , Seuntjens J. , McKinnell J. , Hampshire D. , Lee P. , Meingast C. , Willis T. , Muller H. , Ray R. D. , Dillenburg R. G. , Hellstrom E. E. , Joynt R.
Published: July 2002

Samples of YBa2Cu3O7 have been prepared with rather sharp inductive transitions having in the best cases breadths of 7 K and midpoint Tc values of 88 K. The resistive Tc midpoints are 92–95 K with transition widths of ±1–2 K. Flux shielding at 4.2 K is normally 100% and flux expulsion at 4.2 K reaches 95%. However, even small fields of order 1 mT decouple some 15%–20% of the volume, allowing flux to enter the samples. Resistive Hc2 measurements suggest that Hc2(0) varies from <1 to >300 T, depending on the criterion chosen. ac susceptibility measurements suggest that Hc2(0) is ∼60 T. Magnetization current densities are relatively high (150–200 A/mm2 at 1–10 T at 4.2 K) but measured transport current densities are small (≤1 A/mm2). Magnetization current densities at 77 K are about two orders of magnitude lower. The samples were seen to be heavily twinned by light microscopy (scale of 1–5 μm) and by transmission electron microscopy (scale of ∼250 nm). It is concluded that these measurements are consistent with a model of superconducting regions of reduced dimensionality coupled by tunneling.
Unified analysis of solute diffusion with reversible reaction
Authors: Mikhailov M. D. , Özişik M. N.
Published: July 2002

Generalized three-dimensional time-dependent formal analytic solutions are developed for the problem of solute diffusion with reversible reaction in finite regions, including the important case when zero is also an eigenvalue for the problem.
Characterization of the intrinsic double acceptor in undoped p-type gallium arsenide
Authors: Mitchel W. C. , Brown Gail J. , Fischer David W. , Yu P. W. , Lang Joseph E.
Published: July 2002

A detailed study of the dominant double acceptor found in p-type, undoped GaAs grown by the liquid-encapsulated Czochralski technique has been performed using temperature-dependent Hall effect, infrared absorption, spectral photoconductivity, and photoluminescence. Improved fitting techniques are presented for analyzing the temperature-dependent Hall-effect data. A dependence of the activation energy of the neutral state of the double acceptor as determined by Hall effect on the concentration of the defect has been observed and is discussed in terms of prevalent theories. The ionization energy of this level as determined by all three optical techniques is constant and independent of any concentration. Additional data on the correlation between the concentration of the double acceptor and the boron concentration in the material is presented. A model for this correlation is presented that is consistent with the isolated gallium antisite model for the double acceptor. Aluminum and indium alloyed samples were studied and no additional acceptors that could be attributed to these isovalent dopants were discovered.
Hall effect of nonparabolicity in a nondegenerate indium antimonide
Authors: Wu Chhi-Chong , Tsai Jensan , Lin Chau-Jy
Published: July 2002

The Hall effect and transverse magnetoresistance in an intrinsic nondegenerate InSb have been investigated when the acoustic phonon scattering is the dominant scattering process. The energy-band structure is assumed to be nonparabolic. Results show that Hall angle, Hall coefficient, and transverse magnetoresistance depend strongly on the dc magnetic field because of the energy-dependent relaxation time. We have also studied the temperature dependence of the Hall effect and transverse magnetoresistance in an intrinsic nondegenerate InSb. The results show that the Hall coefficient is greatly enhanced in low temperatures, whereas the Hall angle changes very slowly with temperature.
Dual phase formation in multilayered Ni-Al by ion beam mixing
Authors: Eridon J. , Was G. , Rehn L.
Published: July 2002

Ion beam mixing is used to homogenize multilayered thin films of nickel and aluminum, vapor deposited onto pure nickel substrates. Doses of 500-keV Kr+ at fluences of 2×1016 ions/cm2 produced a supersaturated solid solution of between 16 and 23 at. % aluminum in nickel at room temperature. Subsequent thermal treatment at 425 °C for 1 h resulted in the formation of a dual phase structure of γ and γ′ with grain sizes in the range 640 to 710 Å. Although the dual phase structure was obtained either by ion beam mixing followed by thermal annealing or by thermal annealing alone, only the former process resulted in a surface film with a texture. The films are stable against thermally induced grain growth at temperatures up to 700 °C for 10 h.
Influence of hydrostatic pressure on O2(1Δg) yield in a bubbler-type chemical generator
Authors: S̆palek Otomar , Kodymová Jarmila , Hirs̆l Ales̆
Published: July 2002

The yield of O2(1Δg) in the reactor of a bubbled chemical generator increases markedly on lowering the height of the liquid column. This finding offers a way of improving the efficiency of O2(1Δg) bubbled generators and, hence, enhancing the power of oxygen-iodine lasers. The process responsible for major losses of O2(1Δg) is a dimolar reaction of singlet oxygen, whose rate in gas bubbles within the two-phase gas-liquid system is strongly accelerated as a result of the hydrostatic pressure of the liquid. Consistent with this finding are calculations based on a model which takes into account the various processes leading to loss of O2(1Δg).
Resonant Raman scattering in ZnTe-ZnSe strained layer superlattices
Authors: Nakashima S. , Wada A. , Fujiyasu H. , Aoki M. , Yang H.
Published: July 2002

Resonant Raman scattering and photoluminescence spectra have been measured in ZnTe-ZnSe superlattice. Strong out-going and in-coming resonant enhancements have been observed for multilongitudinal optic phonon bands of the ZnTe-like mode close to the photoluminescence band, which is assigned to direct recombination of excitons. The calculated exciton energies taking into account the effects of quantum well and strain field agree well with photoluminescence energies in superlattices with different thicknesses of the ZnTe layer.
Interfacial interactions of evaporated iridium thin films with (100) GaAs
Authors: Yu Kin Man , Sands T. , Jaklevic J. M. , Haller E. E.
Published: July 2002

We report a systematic study of thermally activated solid phase reactions between (100) GaAs and evaporated iridium thin films (100 and 550 Å thick). The investigation is carried out with Rutherford backscattering spectrometry, x-ray diffraction, and transmission electron microscopy. Interfacial interactions are observed after annealing the system at temperatures higher than 500 °C. Complete reaction at 700 °C results in the formation of Ir3Ga5 and IrAs2 phases. Intermediate phase IrGa is formed in the annealing temperature range of 500–650 °C. Vertical phase segregation is also observed with the IrAs2 phase at the interface and the Ir-Ga phases on the surface layer. Specific information on the reaction kinetics, transformation, and structures of different phases and phase distributions are also discussed. Comparisons with interfacial reactions of other near noble metal/GaAs systems are presented. Based on the metallurgical information obtained, the potential applications of this contact system are suggested.