bluuebunny/crossref_metadata_2025 huggingface dataset:
Ferromagnetic resonance of single-crystal YIG/GGG/YIG layers (abstract)
Authors: Sun Kunquan , Vittoria Carmine , Glass H. L. , De Gasperis P. , Marcelli R.
Published: July 2002

We report on the microwave properties of single crystal of YIG/GGG/YIG grown in (11̄0) layers. The YIG layers were sufficiently thin so that single-domain ferromagnetic resonance (FMR) was observed. FMR fields were measured as a function of field direction, magnitude, and frequency. Bulk magnetic parameters were deduced from FMR and VSM measurements. For the YIG layer next to the GGG substrate, we measured 4πM(1)eff =1750 G, 2K(1)l/M =−82 Oe, K(1)u =0, and for the other layer 4πM(2)eff =1256 G, 2K(2)1/M=−82 Oe, 2K(2)u/M =50 Oe, g=2.025, where 4πM(i)eff (i=1,2) is the sum of the saturation magnetization and uniaxial magnetic anisotropy field normal to the film plane, and K(i)l and K(i)u (i=1,2) are cubic and in-plane uniaxial anistropy energies, respectively. FMR measurements at low fields show typical ‘‘butterfly’’ variations1 of FMR fields versus frequency for H, the magnetic field parallel to either 〈110〉 or 〈100〉 axis. However, a new butterfly pattern was also observed for the magnetic field parallel to the 〈111〉 axis. This new result is intrinsic to layered structure and not to single-layer excitations. We explain this data in terms of nonuniform distribution of strain in the two YIG layers and misalignment between the magnetization direction in the two YIG layers in zero field. For a reverse field of −2 Oe the misalignment is total and equal to 180°
Structure and magnetic properties of compositionally modulated Tb-Fe thin films (abstract)
Authors: Choe G. , Walser R. M.
Published: July 2002

Artificially layered structures have attracted attention because of their unique structural and magnetic characteristics. It has been reported that in these structures the anisotropic distribution of atomic pairs can play an important role in determining their magnetic anisotropy.1 Our previous work showed that the application of substrate bias in a rf diode sputtering system was effective in producing dense and stable amorphous compositionally modulated films (CMFs).2 In this work, we studied the interrelationships of the structural and magnetic properties of amorphous Tb-Fe CMFs deposited under various substrate bias conditions (0, −70, −90 V) in a multitarget rf diode sputtering system. Although considerable research has been conducted on the effect of ion bombardment during deposition on the film structure, it has been difficult to independently control the film structure and the composition in such experiments because of the preferential backsputtering of atoms.

Accordingly, in this research we systematically prepared Tb-Fe CMFs by independently controlling the rf voltage ratio of both the Tb and Fe targets, thereby allowing the composition of the film to be held constant as the substrate bias was changed. In contrast to alloy films, atomic clustering was observed in ultrathin layered films and produced anomalous structural and magnetic property changes, e.g., a shift in the room-temperature compensation composition (25 at. % Tb for −70 V biased films and 23 at. % Tb for −90 V biased films), higher Curie temperatures, and an increased compositional range over which amorphous phase was stable. The atomic arrangements in layered films were modified by a variation of deposition parameters such as layer periodicity, substrate bias, and composition. Although all the bias-sputtered CMF films, except those with small Tb content (<18 at. % Tb), had a dense and featureless amorphous structure, electron diffraction revealed significant differences in atomic short-range ordering for different Tb compositions. The results indicated that the magnetic moments of the Fe atoms in the CMF were increased by an enhanced pair ordering of like atoms produced by the alternate deposition of ultrathin layers. This result was consistent with the observed anomalies in magnetic properties.
Dissociation of O2−2 defects into paramagnetic O− in wide band-gap insulators: A magnetic susceptibility study of magnesium oxide
Authors: Batllo F. , LeRoy R. C. , Parvin K. , Freund F.
Published: July 2002

The magnetic susceptibility of single-crystal MgO has been measured in the temperature range 300–1000 K, using a Faraday balance. The high-purity crystal (<100 ppm transition metals), grown from the melt in a H2O-containing atmosphere, was found to be paramagnetic due to the presence of defects on the O2− sublattice. The defects derive from OH− introduced into the MgO matrix by the dissolution of traces of H2O during crystal growth. The OH− converts into O2−2 and H2. Each O2−2 represents two coupled, spin-paired O− states. The observed strongly temperature-dependent paramagnetism can be described by three contributions that overlay the intrinsic diamagnetism of MgO and arise from (i) the low level of transition-metal impurities, (ii) O− generated by O2−2 dissociation, and (iii) O− states trapped by quenching from high temperatures from previous experiments.
Magnetization measurements by magneto-optical methods on films with Fe particles in an Al2O3 amorphous matrix
Authors: Dormann J. L. , Fiorani D. , Giammaria F. , Lucari F.
Published: July 2002

We made magneto-optical measurements (Faraday Rotation) on four different films with an approximate thickness of 0.5 μm obtained by cosputtering. The films are composed by Fe particles, with different average diameter in the range 50<Φ<100 Å, dispersed in amorphous Al2O3. At the surface of each particle the presence of Fe2+ and a smaller quantity of Fe3+ ions were previously detected. Fe3+ ions were also found in large quantities at the surface of the whole sample. Our measurements are able to distinguish signals coming from the two different ions. We followed these signals by varying the temperature down to 4 K. We observed that the magneto-optical response of Fe3+ ions remains constant, while that of Fe2+ increases with decreasing temperature (T) for T above a characteristic temperature Tc. Below Tc the Fe2+ response remains constant. Measured Tc values were 23, 29, 36, and 250 K for the four samples containing 45, 55, 60, and 70–85 wt. % iron, respectively. These results are comparable with those obtained by other techniques (Mössbauer and susceptibility). We conclude that the blocking process concerns only the magnetic moments of the particles located in the bulk of the film.
dc-erased edge-noise simulations in thin-film media
Authors: Beardsley Irene A. , Zhu Jian-Gang
Published: July 2002

Edge noise in thin-film magnetic recording media is modeled using a planar array of hexagonal grains with long-range magnetostatic interactions as well as possible nearest-neighbor exchange interactions. The Landau–Lifschitz equations of motion with infinite damping are used to find the magnetization configurations. dc-erased track edges were simulated in a standstill manner using a gap centerline approximation to a realistic three-dimensional head field. The intergranular exchange coupling was varied keeping the medium parameter Mr/Hc constant. Magnetization patterns and modeled Fresnel images demonstrate the effects of exchange coupling on the ripple and vortex structures in the presence of the edge-field gradient. The fluctuation of the downtrack magnetization is a maximum at the edge of the track, where the local average of the magnetization itself is near zero.
Effects of convection and electric field on thermofluid transport in horizontal high-pressure mercury arcs
Authors: Shyy Wei , Chang Peggy Y.
Published: July 2002

A three-dimensional theoretical model based on first principles has been developed to predict the characteristics of mass, momentum, energy, and electrostatic potential transport in high-pressure mercury arcs confined in a quartz arctube. The model is utilized to systematically investigate the impact of convection on the transport process by including and excluding the gravity effect. Strong three-dimensional convection flows with multiple contrarotating vortices have been identified. These vortices substantially change the energy balance within the arc, causing highly nonuniform gas temperature distribution and lowering the maximum gas temperature. Geometrical modifications of the arctube such as wall contour curvature and electrode offsets do not change the strength of convection but can produce better overall temperature uniformity within the arctube by accommodating the upward-moving tendency of temperature contours caused by convection. In agreement with the experimental measurement, the model predicts that the arctube curvature can cause large differences of wall temperature profiles, including shape, level, and locations of peak values.
Type conversion by high-energy particles in Hg1−xCdxTe compounds
Authors: Blanchard C. , Favre J. , Barbot J. F. , Desoyer J. C. , Toulemonde M. , Konczykowski M. , Le Scoul D. , Dessus J. L.
Published: July 2002

p-type crystals of the ternary compounds Hg1−xCdxTe have been irradiated with high-energy ions and electrons. Electron-beam-induced current signals on xenon- and krypton-irradiated Hg1−xCdxTe show that n-type conversion, occurring all along the ion path, is related to the presence of mercury atoms. Resistivity and Hall measurements on carbon-, oxygen-, xenon- and electron-irradiated Hg0.8Cd0.2Te crystals allow us to determine the effective cross section for atomic displacement. We observe, for electron-irradiated samples, a saturation in carrier concentration interpreted as the pinning of the Fermi level at a resonant donor state 370 meV above the bottom of the conduction band. Comparison between ion and electron irradiations shows that electrically active produced defects are mainly due to atomic collisions. Additional reduction of defect production efficiency for xenon ions may be the onset of some energy transfer from electronic loss to target atoms.
Selenium and silicon delta-doping properties of GaAs by atmospheric pressure metalorganic chemical vapor deposition
Authors: Kim Yong , Kim Moo Sung , Min Suk-Ki , Lee Choochon , Yoo Kyung-Hwa
Published: July 2002

We investigate selenium and silicon delta-doping characteristics for GaAs layers grown by atmospheric pressure metalorganic chemical vapor deposition. Broadened capacitance-voltage (C-V) profiles and low doping activities are found in case of Se delta doping. In contrast, excellent delta-doping characteristics result for silicon. The obtained C-V full width at half maximum are in the range of 44–49 Å for samples even with substrate temperatures of 700–750 °C, which are relatively high compared with the molecular-beam epitaxy (MBE) substrate temperature. Hall mobility measurements show the mobility enhancement due to a screening of impurity charges. Also, Shubnikov–de Haas oscillations demonstrate the two-dimensional nature of electrons confined in the delta-doped layers. Therefore, our delta-doped layers show no substantial differences in quality with MBE-grown delta-doped layers. In addition, preliminary delta field-effect transistors having a gate length of 1.5 μm and a gate width of 300 μm are fabricated.
Epitaxial YBa2Cu3Ox thin films with x=6–7 by oxygen in-diffusion following laser deposition
Authors: Ohkubo M. , Kachi T. , Hioki T.
Published: July 2002

We have synthesized (001)-epitaxially grown YBa2Cu3Ox thin films with x=6–7 by laser deposition without post-annealing. A key point in the control of x is oxygen pressure during rapid cooling following the deposition. The relation between x and oxygen pressure almost agrees with a thermal equilibrium curve at 500 °C. This can be explained by the incorporation of oxygen during the cooling, considering that the oxygen in-diffusion is enhanced by the fast ab-plane diffusion in misoriented regions.
Gold implantation in n-type silicon: Entropy factor and diffusion studies
Authors: Coffa S. , Calcagno L. , Ferla G. , Campisano S. U.
Published: July 2002

Rutherford backscattering spectrometry and spreading resistance techniques have been used to determine the concentration profiles of gold implanted and diffused in n-type silicon. Diffusion has been performed at 1243 K for times ranging between 1 and 20 h in a dry-nitrogen flux. Resistivity profiles were transformed into concentration profiles by solving the charge balance equation. The entropy factor for the ionization of gold acceptor level was determined to be 50±5. By using this value and solving the charge balance equation we have calculated the silicon resistivity versus gold concentration (and therefore minority-carrier lifetime) curves as a function of the resistivity of starting material. Experimental gold concentration profiles were compared to the profiles obtained by numerical solution of the diffusion equation for gold in silicon. The measured diffusion coefficients coincide with the values determined for p-type material.
Ambipolar diffusion coefficient in molecular-beam-epitaxy-grown silicon layers
Authors: Grivickas V. , Netiksis V. , Noreika D. , Petrauskas M. , Willander M. , Hasan M.-A. , Ni W.-X.
Published: July 2002

The noncontact transient grating technique under constant electron-hole pumping to the density 4×1019 cm−3 was used to characterize the ambipolar diffusion coefficient Da in Si:Al, Si:In, and Si:Sb molecular-beam-epitaxy-grown layers. Da was found to be almost constant at a value of ≊8 cm2/s up to an equilibrium carrier density of 2×1019 cm−3 in the layer and was independent of the doping type. At higher doping density, evidence for a sharp increase in Da was observed. For example, Da increased to a value of 20 cm2/s at a doping density of about 1020 cm−3. The Da behavior is in reasonable agreement with results of the high-density ambipolar diffusion theory of Young and van Driel and is incompatible with majority-carriers diffusion coefficients according to the formula Da = 2DnDp/(Dn + Dp). An explanation for this behavior is given.
Formation of aluminum nitride films on GaAs(110) at room temperature by reactive molecular-beam epitaxy: X-ray and soft x-ray photoemission spectroscopy
Authors: Baier H.-U. , Mönch W.
Published: July 2002

AlxN1−x films were prepared on GaAs(110) surfaces at room temperature by simultaneous evaporation of aluminum and exposure to a beam of ammonia molecules (reactive molecular-beam epitaxy). The formation of aluminum nitride was followed by using photoemission spectroscopy excited with ZrMζ radiation (hν=151.2 eV). The composition of the deposited films was monitored by recording the N(1s) and Al(2p) core lines excited with MgKα radiation (hν=1253.6 eV). The intensity ratio of these core levels as a function of impinging rate ratio z=ν(NH3)/ν(Al) was compared with the intensity ratio determined with an AlN standard under the same experimental conditions. Aluminum nitride was found to form at room temperature for z values larger than some 104.
Quasistatic magnetic field penetration through a circular aperture of a spherical shield enclosing a spherical conductor
Authors: Boridy Elie
Published: July 2002

The quasistatic magnetic field penetration through a circular aperture of a spherical shield enclosing a spherical conductor is considered in the framework of the dual series equations theory. Both cases of an applied magnetic field parallel and perpendicular to the system’s symmetry axis are analyzed. Induced currents on the cavity and internal sphere surfaces are calculated, as well as the aperture effective dipole moment and polarizability. Convergence of the different series involved is discussed. The magnetic field behavior at the aperture edge is also investigated, and the discontinuity occurring in this region is treated analytically. The theoretical analysis is finally complemented and illustrated by several numerical results.
Simultaneous dysprosium- and lead-substituted high-T
c superconductor bismuth cuprates
Authors: Schieber M. , Friedman M. , Levinsky M. , Zhou B. L. , Gasga J. Reyes , Van Tendeloo G. , Amelinckx S.
Published: July 2002

The introduction of small amounts of Dy in ceramic BiSrCaCuO (BSCCO) with nominal composition of Bi2Sr2Ca1−xDyxCu2O8+z, Bi2Sr2Ca2−xDyxCu3O10+z, and Bi1.6Pb0.4Sr2Ca2−xDyxCu3O10+z with 0.1<x<0.3 was studied in both stoichiometric and nonstoichiometric compositions where the nonstoichiometric composition was used to aid the sintering process in order to obtain a maximum Tc and contained excesses of CaO and CuO. It was found that regardless of the sintering conditions and starting compositions only the Bi:Sr:Ca:Cu=2:2:1:2 (2212) phase was produced. The highest Tc (R=0) in the Dy-substituted sample obtained was 84 K and this was obtained only for the nonstoichiometric composition Bi1.6Pb0.4Sr2Ca2.5Dy0.3Cu3.5Ox which contained mostly the 2212 phase together with tiny amounts of Bi2Sr2Ca2Cu3Ox (2223) phase. High-resolution electron microscopy data performed on Bi1.6Pb0.4Sr2Ca2.5Dy0.3Cu3.5010+z show that the introduction of Dy in the original 2223 Pb-containing phase caused only the formation of the 2212 phase without changing the modulated structure known to occur in the substituted Bi and Sr BSCCO compounds confirming also earlier suggestions made by Tarrascon et al. [Phys. Rev. B 2, 4316 (1989)] that the rare-earth cations stabilize the 2212 phase and substitute only for Ca and not for the Sr or Bi sites in the 2212 phase.
On the saturation of Tb phosphors under cathode-ray excitation. II. Upconversion processes in the excited-activator bath
Authors: Nieuwesteeg K. J. B. M. , Raue R.
Published: July 2002

A physical model based on resonant electric dipole interaction between excited activators is presented that may be used for gaining insight into the second-order energy-loss process in cathode-ray-irradiated Tb phosphors. It is shown that resonant up-conversion of the 5DJ excitons (J=3,4) to highly excited 4f and 5d states may be of equal importance. The derivation of the rate constants for this second-order energy-loss process is given and experimental values for the 5D4 -5D4 and 5D3 -5D4 interaction are presented for Tb-doped YAG, YAGaG, LaOBr, and Y2SiO5. The values depend on previously determined optical cross sections for excited-state absorption. Based on this model we explain well-known differences in saturation behavior between these Tb-doped phosphors under cathode-ray excitation.
Phonon-drag thermopower in semiconducting quantum well structures in a quantizing magnetic field
Authors: Sankeshwar N. S. , Kubakaddi S. S. , Mulimani B. G. , Butcher P. N.
Published: July 2002

A theory of phonon-drag thermopower (PDTP) of a quasi-two-dimensional electron gas in quantum well semiconductor heterostructures in the presence of a quantizing magnetic field is presented. At liquid-helium temperatures PDTP is found to be of the order of a few mV/K which is two to three orders of magnitude larger than diffusion thermopower. The effect of screening is to suppress PDTP and to modify its variation with temperature.
Preparation of high-density YBa2Cu3Ox ceramics with improved superconducting properties by hot pressing under controlled atmosphere
Authors: Kuwabara M. , Shimooka H.
Published: July 2002

High-density YBa2Cu3Ox (relative sintered density ≥97%, as hot pressed) ceramics with an improved superconducting temperature (Tc) of 95 K and a critical current density (Jc) of 700 A/cm2 at 77 K, 0 T have successfully been produced by using hot pressing under a carefully controlled ambient gas system, followed by an appropriate oxygenation process. The obtained results indicate that in the oxygenation process of an YBa2Cu3Ox crystal the phase transition from the tetragonal phase (nonsuperconducting) to orthorhombic I phase (Tc≥90 K) occurs much easier than from orthorhombic II phase (Tc≊60 K) to orthorhombic I phase. This may also demonstrate a possible solution to the oxygenation problem in high-density YBa2Cu3Ox ceramics usually with degraded superconducting properties.
Determination of spin-polarized secondary-electron escape depth through oxidation of iron
Authors: VanZandt T. , Browning R.
Published: July 2002

The decay of the spin polarization of low-energy secondary electrons from Fe+ oxygen is measured as a function of oxygen exposure. We conclude that the spin polarization data can be explained through a simple model in which the spin polarization of secondary electrons generated from the oxide is small. From this, we determine, that the escape depth for spin-polarized electrons is approximately 29±3 Å at 2 eV kinetic energy, decreasing to approximately 22±2 Å at 7 and 12 eV. These results indicate that spin-polarization measurements on Fe and its oxide are less surface sensitive than previously thought.
Multiple scattering of electrons in the reflex triode
Authors: Creedon John M.
Published: July 2002

Analytical theories and Monte Carlo calculations are used to treat the scattering and energy loss of electrons in the anode of a reflex triode. The solution of this scattering problem is combined with the equations for particle flow in vacuum to give a quantitative theory of triode operation. It is now possible to calculate several important properties of this device. These include the operating voltage in the constant voltage mode, the ratio of ion-to-electron current and the ion transit time.
Resonance Raman scattering from epitaxial InSb films grown by metalorganic magnetron sputtering
Authors: Feng Z. C. , Perkowitz S. , Rao T. S. , Webb J. B.
Published: July 2002

We have examined epitaxial InSb films by Raman scattering for the first time. The films, 0.17–2.67 μm thick, were grown on (100) GaAs substrates by the new technique of metalorganic magnetron sputtering. We observe the first and second order longitudinal optical phonon peaks, the latter enhanced by outgoing resonance with the E1+Δ1 gap of InSb, and an upshift of this gap due to compressive biaxial stress. We also observe an anomalous dependence of stress on film thickness. The Raman data indicate good sample quality despite the large lattice mismatch between InSb and GaAs.
Lithium niobate stress gauge current diagnostic for noninductive measurement of fast-rise-time multimegampere currents
Authors: Hanson D. L. , Williams R. R. , Porter J. L. , Spielman R. B. , Matzen M. K.
Published: July 2002

Accurate modeling of load behavior in Z-pinch plasma radiation sources driven by high-current generators requires the measurement of fast-rise-time multimegampere currents close to the load. Conventional current diagnostics mounted in inductive cavities (such as B-dot loops and Rogowski coils) fail at small radius because of electrical breakdown produced by high dI/dt. In this paper, we describe the use of large-signal, nanosecond-time-resolution lithium niobate piezoelectric stress gauges to directly measure the magnetic pressure B2/2μ0=μ0I2/8π2r2 generated at radius r by a current I flowing in a radial transmission line. Current measurements have been performed at radius r=2.54×10−2 m on Sandia National Laboratories’ Proto-II (10 TW) and SATURN (30 TW) gas puff Z-pinch experiments with maximum currents of 10.1 MA and dI/dt to 2.1×1014 A/s. Comparisons with Faraday rotation and B-dot current diagnostic measurements at large radius are presented. Bremsstrahlung noise problems unique to the SATURN gas puff source are discussed. For a Y-cut lithium niobate stress gauge on a pure tungsten electrode, current densities up to I/2πr=78 MA/m can be measured before the electrode yield strength and the piezoelectric operating stress limit are exceeded. Above the Hugoniot elastic limit of the electrode material, the dynamic range and accuracy of the diagnostic are greatly reduced, but it appears that the technique can be extended to higher current densities using an X-cut quartz piezoelectric element and a tungsten-sapphire electrode impedance stack.
Subband structures of semiconductor quantum wires from the effective bond-orbital model
Authors: Citrin D. S. , Chang Yia-Chung
Published: July 2002

The effective bond-orbital model is used to calculate the subband structures of GaAs/AlGaAs and InGaAs/InP quantum wires of various geometries. The advantages of the effective bond-orbital model over standard effective-mass theory are its flexibility to accommodate otherwise awkward geometries, the straightforward manner in which boundaries between materials are treated, and the inclusion in the Hamiltonian of terms in k higher than quadratic. We focus our attention on the subband structures of epitaxially buried Ga0.47In0.53As/InP quantum wires of triangular cross section with axis in the [011] direction and (111), (11̄1̄), and (100) faces.
Fabrication of textured Bi-Sr-Ca-Cu-O thick film by electrophoretic deposition
Authors: Sarkar Partho , Mathur Sharad , Nicholson Patrick S. , Stager Carl V.
Published: July 2002

Bi-Sr-Ca-Cu-O thick films (≊5–40 μm) were electrophoretically deposited on silver foil using ethyl alcohol as the suspending liquid. The deposition voltage was ≊70 V/cm and the current ≊550 μA/cm2. X-ray diffraction of the as-deposited sample shows texturing. This texturing was enhanced by pressing the film uniaxially at ≊82 MPa. Samples were sintered at 810 °C in a 10% oxygen-in-argon atmosphere. Liquid at the sintering temperature promotes textured grain growth. The critical current density (Jc) of the film determined by magnetic measurement at 5 K in a 2 kOe field is ≊1.3×104 A/cm2.
Investigation of electric field effect in PrBa2Cu3O7−x thin films by capacitance-voltage measurement
Authors: Tarutani Yoshinobu , Saitoh Shin’ichiro , Fukazawa Tokuumi , Kawabe Ushio
Published: July 2002

Electric field effect in PrBa2Cu3O7−x thin films is investigated by capacitance-voltage (C-V) measurement. An SrTiO3 thin film with a dielectric constant of 250 is used for the insulating layer in the C-V measurement to compensate for the high carrier density of PrBa2Cu3O7−x thin films. A PrBa2Cu3O7−x -SrTiO3 -Au capacitor reveals capacitance decrease at positive voltage of the Au electrode in the C-V curve which agrees with the calculated one derived from the metal-insulator-semiconductor model. This result indicates the existence of a kind of electric field effect at the PrBa2Cu3O7−x film surface layer.
Effect of intermediate vibration in ceramic superconductor YBa2Cu3Ox
Authors: Zheng X. G. , Kuriyaki H. , Hirakawa K.
Published: July 2002

The transport critical current density Jc in the ceramic superconductor YBa2Cu3Ox was improved by an intermediate vibration introduced during the preparation process. A dependence of Jc on the vibrational parameters, frequency and amplitude, was found. The improved Jc was shown to be accompanied by the enhancement in the orientation degree. Furthermore, a theoretical discussion was tried to explain the Jc dependence.
Photoluminescence in GaAs/AlGaAs heterojunction bipolar transistors: Dependence of signal strength on excitation density
Authors: Humer-Hager T. , Asenov A.
Published: July 2002

In this paper we present 300 and 77 K photoluminescence (PL) investigations of GaAs/AlGaAs heterojunction bipolar transistor (HBT) structures grown by low-pressure metalorganic vapor phase epitaxy. Special attention is paid to the dependence of the PL signal intensity on the excitation power. We find a strongly nonlinear behavior which we attribute to the modification of the internal p-n junctions in the HBT layer structure by the above band-gap excitation. Model calculations performed in the framework of a drift-diffusion mechanism are shown to agree well with the experimental results if generation and recombination of electron-hole pairs are correctly included in the simulation procedure. The photoluminescence of HBT layer sequences with variations in collector doping and thickness, in base thickness and composition is examined. It is shown that these layer parameters have a unique influence on the relation between PL intensity and excitation density. A thorough analysis of the PL data provides additional information about electrical properties of the base-collector junction within the HBT structure. This information can be obtained without employing any process technology. For this reason PL is a very comfortable and efficient characterization method even for complicated multilayer structures designed for device applications.
A new kinetic model for vapor phase epitaxy of GaAs1−xPx from the Ga-As-P-H-Cl system
Authors: Mani V. N. , Dhanasekaran R. , Ramasamy P.
Published: July 2002

In this paper, we have made an attempt to describe a model based on thermodynamics, nucleation, and chemical kinetics for the GaAs1−xPx vapor phase epitaxial growth. Nucleation behavior has been examined as a function of supercooling and substrate orientation using the classical heterogeneous nucleation theory. The model, which includes an eleven-step reaction mechanism for the deposition of GaAs1−xPx from the Ga-As-P-H-Cl system, predicts surface coverage factors of the individual adsorbed species and general trends of growth kinetics. Assuming that the formation of complex molecules at the substrate surface are the rate determining steps, an expression for the deposition rate has been developed. The growth rate expression also predicts the effects of deposition temperature and pressure of the gases on the growth rate of the layer. Numerical analysis of our theoretical predictions indicates that gas phase chemical kinetic processes are important in describing GaAs1−xPx vapor phase epitaxy. The validity of our model has been tested by comparing our results with reported experimental results.
Investigation of interfacial roughness of InxGa1−xAs epitaxial layers on GaAs and InP substrates by soft x-ray reflectivity
Authors: Krol A. , Resat H. , Sher C. J. , Woronick S. C. , Ng W. , Kao Y. H. , Cole T. L. , Green A. K. , Lowe-Ma C. K. , Nee T.-W. , Rehn Victor
Published: July 2002

The grazing incidence x-ray reflectivity is a nondestructive and sensitive technique for probing the depth profile of electron density in layered structures. This method has been utilized in the soft x-ray regime to determine the roughness of interfaces, and the epilayer thickness in InxGa1−xAs/InP and InxGa1−xAs/GaAs heterostructures, for x=0.57 and x=0.60, grown by molecular beam epitaxy. By fitting the experimental results to our model, assuming uncorrelated interfacial roughness, we conclude that the top surface roughness does not depend on the type of the substrate or presence of stress in the epilayer, and is always smaller than interfacial roughness. The main factors which control the interfacial roughness are the quality of substrate and/or growth conditions rather than strain or lattice mismatch.
Influence of the potential spike on heterostructure-emitter bipolar transistor
Authors: Liu Wen-Chau , Lour Wen-Shiung
Published: July 2002

The influence of potential spike on the transport properties of heterostructure-emitter bipolar transistor (HEBT) has been demonstrated. The potential spike is attributed primarily to the extended depletion region adjacent the p+ GaAs base layer. Due to the existence of potential spike, the electrical properties including conducting current, current gain, and offset voltage, etc., are degraded seriously. The knee-shaped characteristics and strong reachthrough effect are observed. Consequently, the design of the structural parameters, such as GaAs emitter (collector) width adjacent p+ base, plays an important role of high-performance HEBT devices.
Effect of junction and band-gap grading on the electrical performance of molecular beam epitaxial grown AlGaAs/GaAs/AlGaAs double-heterojunction bipolar transistors
Authors: Mohammad S. Noor , Chen J. , Chyi J.-I. , Morkoç H.
Published: July 2002

Current-voltage characteristics of AlGaAs/GaAs/AlGaAs double-heterojunction bipolar transistors (DHBTs) grown by molecular beam epitaxy have been studied. DHBTs with both abrupt and graded heterojunctions at the emitter-base and base-collector heterojunctions have been employed for the study. It is noted that DHBTs with abrupt heterojunctions are better than those with graded heterojunctions. These abrupt heterojunctions, along with a nonuniform doping in the base, lead to significantly improved results in current gain and offset voltage. Physical reasons underlying the improvement in the current gain and offset voltage have been analyzed.
Photocathodic hydrogenation of p-type silicon
Authors: de Mierry P. , Etcheberry A. , Aucouturier M.
Published: July 2002

An electrolytic technique is shown to introduce hydrogen into p-type silicon at room temperature. The penetration depths investigated by secondary ion mass spectroscopy are found to be strongly dependent on the doping level. These differences are explained in terms of a donor hydrogen-related level close to the midgap.
Temperature dependence of the transient photoconductive response in stretched trans-polyacetylene films with below-gap excitation
Authors: Walser A. D. , Dorsinville R. , Alfano R. R. , Tubino R.
Published: July 2002

The temperature dependence of the picosecond photocurrent with below-gap excitation (1.06 μm) has been measured for a highly oriented form of trans-polyacetylene. The 1-d picosecond photocurrent is independent of temperature. The 3-d picosecond photocurrent is temperature dependent with an activation energy of 63 meV. These results demonstrate the photoproduction of nonlinear charged carriers (solitons and polarons) at energies that are below the principal interband absorption edge.
Directional asymmetries due to write-laser mode hopping during optical recording
Authors: Gage Edward C. , Bartholomeusz Brian J.
Published: July 2002

The wavelength of semiconductor lasers generally increases with increased output power due to changes in laser gain with current and temperature. Time-resolved studies of the optical spectrum during the write-pulse train clearly depicted the quasirandom mode hopping that occurred. In optically dispersive systems, the wavelength shifts caused significant write-spot displacements down at the recording surface and affected mark lengths. Thermal modeling studies successfully duplicated the salient features of this effect and provided explanations for some of the experimental observations.
Diffraction by a half-plane in a lossy mediuma)
Authors: Hill David A.
Published: July 2002

The classical problem of plane-wave diffraction by half-plane is extended to allow for loss in the surrounding medium. The loss causes the arguments of the integral functions to become complex. Numerical results show that the relative importance of the edge-diffracted field decreases as the loss is increased. This effect is important in interpreting the effects of off-path scatterers in remote sensing of lossy media. The results for both electric and magnetic polarizations are in qualitative agreement with previous results based on the Kirchhoff approximation [D. A. Hill, J. Appl. Phys. 69, 1772 (1991)].
Zn drops at a Si surface measured by the refracted x-ray fluorescence method
Authors: Sasaki Y. C. , Kisimoto M. , Nagata S. , Yamaguchi S. , Hirokawa K.
Published: July 2002

Si and Zn are essentially mutually insoluble. We were able to detect Zn drops at a Si surface by using the refracted x-ray fluorescence method when the Si wafer was implanted with Zn ions at 50 keV up to doses of 1 × 1016 cm−2. The presence of the Zn drops at the Si surface was confirmed both by measuring surface roughness and Rutherford-backscattering spectroscopy spectra.
Reply to ‘‘Comment on ‘Nonlinear piezoelectricity and electrostriction of alpha quartz’ ’’ [J. Appl. Phys. 6
9, 7907 (1991)]
Authors: Kittinger E. , Tichý J.
Published: July 2002

We appreciate the formal analysis presented in the comment while putting some interpretative aspects into perspective.
Ohmic contacts to p-GaAs with p+/p regrown structures formed by metalorganic molecular beam epitaxy
Authors: Shimawaki Hidenori , Furuhata Naoki , Honjo Kazuhiko
Published: July 2002

Excellent ohmic contacts to p-GaAs are fabricated using selective growth by metalorganic molecular beam epitaxy. Specific contact resistance of about 5×10−8 Ω cm2 is achieved, without any heat treatment, at AuMn/Au and Ti/Pt/Au metal contacts, formed on p+-GaAs layers heavily carbon-doped to 4.4×1020 cm−3. Regrown contacts with planar and lateral p+/p structures are fabricated to clarify interface contact resistivities. A fairly low value of 7.1×10−8 Ω cm2 is established, using an equivalent circuit model, for the lateral contacts to thin p-GaAs layers, reasonably independent of its thicknesses in the range of 9.5–95 nm. These results, in addition to excellent growth selectivity, have confirmed prospects for practical use.
Spectrally selective surfaces of etched eutectoid steel
Authors: Saint-Jacques R. G. , Arnoux C. , Rheault F.
Published: July 2002

A study is made of the mechanisms affecting the spectral absorptance of a gratinglike surface obtained by etching of an eutectoid steel. This microstructure is made of alternating lamellae of iron and iron carbide. The spacing of lamellae is a function of their nucleation temperature and their relative height can be modified by chemical etching. Reduction of the interlamellar spacing from 0.8 to 0.1 μm increases the absorptivity of the visible light but has no effect on thermal emissivity. The height of the lamellae increases not only the absorptivity of the visible light but also the thermal emissivity. These observations agree with the theoretical predictions of Wirgin.
On the switching characteristics of Co and CoPtCr thin films
Authors: Heidmann J. , Nguyen T. A. , Yogi T. , Lambert S. E. , Speriosu V. S.
Published: July 2002

We have studied the influence of intergranular magnetic coupling on switching characteristics in Co and CoPtCr thin films. The strength of the intergranular interactions was varied by changing the sputtering pressure and film or underlayer thickness. For each sample we have measured the deviation δM from the behavior expected for noninteracting single-domain particles and correlated the results to the magnetic layer and under layer thickness and to the microstructure of the recording film. We show a correlation between δM and the strength of magnetic coupling. Where similar magnetic parameters allow a comparison, we find a correlation between media noise and the trend in δM.
The stability of stretching and accelerating plastic sheets. II
Authors: Romero Louis A.
Published: July 2002

The equations governing the linearized stability of a perfectly plastic sheet that is isotropically stretching in the horizontal direction and accelerating in the vertical direction are analyzed. The stability of the sheet depends on two dimensionless parameters. The parameter Γ measures the ratio of the inertial forces to the plastic forces, and the parameter Π measures the importance of the pressure gradient induced by the stretching to the pressure gradient induced by the vertical acceleration. Both of these parameters decrease as the sheet stretches. When Π is small and Γ/Π is not, the sheet breaks up because of Rayleigh–Taylor instability. When both Π and Γ/Π are small, the sheet breaks up to the necking instability. The case where Π is large has already been covered in part I of this paper.
A thin film CdS-self-electro-optic effect device with identically contrasted (0.95/1) optical and electro-optical loops at 210 K
Authors: Ullrich B. , Bouchenaki C. , Zielinger J. P. , Cong H. Nguyen , Chartier P.
Published: July 2002

We report an investigation of the improved photothermal bistable features of a thin (6 μm) CdS Self-Electro-optic Effect Device prepared by spray deposition on pyrex. For the excitation, the 514.5 nm laser line was used. Optical, optoelectronic, electrical, and electrooptical bistabilities were observed at 210 K. It is shown that it is possible to reach with thin CdS films comparable contrasted ratios in the optical and optoelectronic bistabilities. The function of the device is explained by the measured transmission dependence of the temperature. A generalized model basing on Urbach’s rule for calculating the temperature dependence of the absorption coefficient is presented, leading to a fairly good agreement with the measured curve. Furthermore, the switch-off time of the optical bistability is observed to be unusually small (5 ms) for the used laser focus diameter (400 μm).
Room-temperature stability of the electrical properties of metalorganic vapor phase epitaxial Hg1−xCdxTe on GaAs
Authors: Young M. L. , Giess J.
Published: July 2002

Significant changes have been observed in the electrical properties after prolonged storage at room temperature of undoped metalorganic vapor phase epitaxial layers of Hg1−xCdxTe grown on (100) GaAs. These changes occur in uniform n-type and nonuniform n-p layer structures and are due to the out-diffusion of donors from the bulk of the layers. In situ growth of a surface passivation layer of CdTe prevents these effects and produces stable electrical properties. Uniform n-type layers grown simultaneously on (111) GaAs do not show changes in electrical properties even when not in situ passivated with CdTe. The time dependent properties do not appear to be associated with impurities and are attributed to the diffusion of a combination of native donor defects and Hg acceptor vacancies, which are estimated to have diffusion coefficients, respectively, of 7×10−14 and 2–3 ×10−16 cm2 s−1 at room temperature.
Numerical simulation of electromagnetic acoustic transducer in the time domain
Authors: Ludwig R. , Dai X.-W.
Published: July 2002

A novel multistage numerical modeling approach to simulate acoustic-wave generation and propagation of an electromagnetic acoustic transducer (EMAT) is presented. The model assumes a uniform static magnetic field in a conducting half-space. A meander coil winding situated above the half-space is driven by a transient high-frequency current pulse. The numerically computed eddy currents in the conducting specimen are combined with the static magnetic field to yield spatially and temporally diffusive Lorentz forces which in turn are coupled into the elastic-wave equation. This hyperbolic elastodynamic system is solved for the displacement field vector which gives rise to propagating elastic waves. Numerical transduction results are discussed for a generic two-wire transient EMAT configuration and for an isotropic half-space with electric and acoustic material parameters equivalent to those of aluminum.
Energy deposition in direct nuclear pumped optical cavities
Authors: Montierth L. M. , Neuman W. A. , Nigg D. W. , Merrill B. J.
Published: July 2002

A two-dimensional, time-dependent model has been developed to determine the coupled fluid dynamic and charged particle transport behavior of a flowing gas, nuclear pumped laser cavity. Stationary results are presented for a typical cavity that uses a flowing He buffer gas pumped with charged particles produced by the 10B(n,α)7Li reaction. The boron is coated on fuel plates mounted parallel to the flow direction. The effects of changing the buffer gas inlet flow velocity and outlet pressure are investigated. For a fixed inlet velocity, the results presented show that the gradients of the charged particle energy deposition and density increase in magnitude primarily in the direction perpendicular to the gas flow, i.e., normal to the fuel plates, as the outlet pressure is increased. With increasing inlet velocity and a fixed outlet pressure, the density variations decrease, whereas the variations in energy deposition increase in the direction perpendicular to the flow and decrease in the direction parallel to the gas flow. For higher inlet velocity cases, the deposition is nearly one-dimensional, varying primarily in the direction perpendicular to the flow. Qualitatively similar results can be found with an argon buffer gas and fission fragment pumping for similar charged particle ranges. In general, for a fixed cavity geometry similar charged particle energy deposition behavior can be obtained for different laser gases by adjusting the outlet pressure and charged particle source.
Time-dependent changes of parasitic effects induced by high-field electron injection in metal-oxide-semiconductor transistors
Authors: Nishioka Yasushiro , Kato Masataka , Ohji Yuzuru , Ma T. P.
Published: July 2002

The subthreshold characteristics of n-channel metal-oxide-semiconductor field effect transistors after high-field, high current density (100 mA/cm2) Fowler–Nordheim electron injection are investigated. Rapid changes are observed and recorded within 1000 s after injection. A ‘‘bump’’ in the subthreshold I-V characteristic appears if electron trapping in the gate oxide dominates. This bump can be made to disappear and reappear by controlling the amount of trapped electrons in the oxide. This may be readily explained by the parasitic channel leakage current along the isolation field oxide edges.
Optical capture cross sections of palladium in silicon
Authors: Rubio E. , Vicente J. , Jaraiz M. , Arias J. , Bailón L. , Barbolla J.
Published: July 2002

Optical electron and hole capture cross sections for the deep levels Ec−0.22 eV and Ev+0.33 eV associated to Pd in Si have been measured using constant-capacitance deep level optical spectroscopy and optical admittance spectroscopy. The experimental results fit well to the model of Lucovsky. The threshold energies obtained for the electron and hole emission from the Ec−0.22 eV level are 250 and 890 meV, respectively. The threshold energies obtained for the electron and hole emission from the Ev+0.33 eV level are 820 and 330 meV, respectively.
Electromigration-induced abrupt changes in electrical resistance associated with void dynamics in aluminum interconnections
Authors: Shingubara Shoso , Kaneko Hisashi , Saitoh Makoto
Published: July 2002

Electromigration-induced failure mechanisms were investigated by means of extremely sensitive resistance change measurements and simultaneous observations using scanning electron microscopy. Abrupt changes in resistance (ACRs), classified into three types: downward steps, upward steps, and oscillations, were found to occur frequently during the dc current stressing test. It was conspicuously observed that there was a rapid void annihilation associated with an abrupt increase in resistance, and a rapid void formation with a decrease in resistance. ACRs are considered to be caused by a rapid change in the number of excess vacancies concomitant with void annihilations or formations. The thermodynamical analysis on the stability of a void strongly suggests that the change of a local stress from tensile to compressive causes a rapid annihilation of voids, and the opposite one causes a rapid formation. Temperature dependence of the intensity of ACRs exhibited an activation energy of 0.43 eV, which implied that grain boundary electromigration was the driving force of ACRs.
The evolution of sputtered iron nitride thin films under thermal treatment
Authors: Mosca D. H. , Teixeira S. R. , Dionisio P. H. , Baumvol I. J. R. , Schreiner W. H. , Monteiro W. A.
Published: July 2002

The thermal evolution of reactively sputtered iron nitride thin films has been investigated by x-ray diffraction, Mössbauer conversion electron spectroscopy, transmission electron microscopy, and magnetic measurements. The results show that, independently of the original nitrogen content of the films, a similar composition of the end products after the 500 °C annealings is reached, being all composed of α-Fe plus γ′-Fe4N in a wide range of relative proportions. The magnetic characteristics, however, are different depending on the nitrogen content of the as-deposited films.
Spin arrangements in (Nd1−xYx)2Co14B studied by NMR
Authors: Jedryka E. , Wojcik M. , Panissod P. , Pedziwiatr A. T. , Slepowronski M.
Published: July 2002

5 9Co NMR has been studied at 4.2 K and as a function of temperature in the mixed (Nd1−xYx)2Co14B compounds throughout the full substitution range. It was found that the anisotropy of the Nd sublattice determines the canted magnetic structure of the system at 4.2 K up to the threshold Y content of 92%. Above 92% Y, the system switches rapidly to a planar structure which is enforced by the 3d sublattices. Below the threshold Y content, the system undergoes two spin reorientations with increasing temperature: a second-order phase transition from canted to uniaxial state and a first-order phase transition from uniaxial to planar structure.