bluuebunny/crossref_metadata_2025 huggingface dataset:
Pd/Ti bilayer contacts to heavily doped polycrystalline silicon
Authors: Tang Y. S. , Wilkinson C. D. W. , Jeynes C.
Published: July 2002

Ohmic contact properties of Pd/Ti bilayer to heavily doped n+-polycrystalline silicon, prepared by electron beam evaporation, were studied by using both electrical measurements and Rutherford backscattering spectroscopy. The electrical behavior of the contacts at different sintering conditions is explained by the corresponding chemical composition changes at the metal/silicon interface during the sintering process.
Microstructural degradation during Zn diffusion in a GaInAsP/InP heterostructure: Layer mixing, misfit dislocation generation, and Zn3P2 precipitation
Authors: Park Hyo-Hoon , Lee Kyung Ho , Lee Jung Kee , Lee Yong Tak , Lee El-Hang , Lee Jeong Yong , Hong Soon-Ku , Kwon O’Dae
Published: July 2002

The microstructural degradation of a lattice-matched Ga0.28In0.72As0.61P0.39/InP heterointerface during Zn diffusion has been investigated using high resolution transmission electron microscopy and Auger electron spectroscopy. The diffusion-induced intermixing of In and Ga across the GaInAsP/InP interface causes tensile stress in the Ga-mixed InP side and compressive stress in the In-mixed GaInAsP side. The effect of the localized interfacial stress on the nucleation of misfit dislocations and on the strain accommodation behaviors thereof are clearly revealed throughout the intermixed region, reaching several thousand angstroms on each side of the interface. The interfacial strain is relaxed by generation of paired dislocations with antiparallel Burgers vectors initiating from the intermixed GaInAsP/GaInP interface. The dislocation morphologies reveal striking contrasts across the intermixed interface: stacking faults in the tensile layer and perfect dislocation tangles in the compressive layer. The dislocation lines are concentrated at the GaInAsP/GaInP interface and along the misfit boundaries in the forefront areas of the intermixed region. A model is proposed to explain the strain relaxation behavior in the intermixed region using the mechanism of homogeneous nucleation and splitting of the paired dislocations from the intermixed interface. Also observed in a limited region on the GaInP side is the precipitation of a Zn3P2 phase. The Zn3P2 precipitates grow to form epitaxial layers to a certain depth of the intermixed GaxIn1−xP layer, where the Zn3P2 crystal lattice coherently matches with the matrix crystal lattice. The precipitation reaction of Zn3P2 is explained using the kickout mechanism.
Generation phenomena of localized interface states induced by irradiation and post-irradiation annealing at the Si/SiO2 interface
Authors: Kimura Mikihiro
Published: July 2002

The generation phenomena and mechanisms of localized interface states at the Si/SiO2 interface, induced by irradiation and post-irradiation annealing, are investigated by using 60Co γ rays. In a low dose irradiation of less than 1×106 rad, localized interface states having a peak at about 0.2–0.25 eV above the Si midgap are generated. At a higher irradiation dose, a peak of localized interface states generated by a low dose irradiation is eliminated, and is confirmed to be replaced by a peak of localized interface states that bulge near the Si midgap. This phenomenon is difficult to explain by the water related breakage bond model, but can be explained by the Si—O weak bond stable state and the trivalent Si dangling bond caused by the breakage of the Si—O weak bond. In addition, post-irradiation annealing generates localized interface states, having a steep peak in the Si band gap near the conduction band, which caused the peak of the localized interface states to move toward the conduction band. In order to elucidate the generation mechanism of such localized interface states, we have proposed an acceptor-like trap center model that is generated in the oxide near the Si/SiO2 after hole detrapping and recombined with the interface electrons by means of direct tunneling. To investigate its features, we have also investigated the influence on the local oxidation of silicon isolation structure and the effect of Fowler–Nordheim hot-electron injection after post-irradiation annealing.
Optical emission spectroscopy of ArF-laser-irradiated disilane-acetylene mixtures for 3C-SiC epitaxial growth
Authors: Mizunami Toru , Toyama Naotake , Uemura Takayuki
Published: July 2002

A mixture of Si2H6 and C2H2 was used for deposition of SiC by ArF-excimer-laser chemical vapor deposition. Optical emission spectroscopy was employed to study the radicals CH, C2, SiH, and Si atoms in the photolyzed gas. The line intensities were measured changing the disilane/acetylene flow ratio. The concentrations of excited CH and C2 were very low without disilane, however they rapidly increased with the addition of disilane. This is attributed to the reactions of silicon-based radicals with C2H2 or C2H to form CH and C2. A measurement on the deposition rates of the films agreed well with the result.
Electric-field effect on intersubband optical absorption in a Si/Si1−xGex superlattice
Authors: Cho Sung M. , Lee Hong H.
Published: July 2002

Electronic band structure and absorption coefficient for intersubband transitions in a Si/Si1−xGex superlattice under external electric fields are reported using a full Brillouin-zone energy-band description. Full spectra of the absorption coefficient are calculated from zero to high electric fields. The effect of Wannier–Stark localization on intersubband transitions is theoretically studied for the superlattice and the charge densities are given for various electric fields. A finite-length superlattice instead of an infinite superlattice is considered to show the effects of electric fields on the optical absorption. The Stark shift is observed toward the shorter photon wavelength for an intersubband transition in a quantum well.
Enhanced flux-line pinning in Bi2Sr2CaCu2Ox by neutron irradiation and Li(n,3T)α reaction-induced charged-particle defects
Authors: Schwartz Justin , Wu Shiming
Published: July 2002

Large enhancements in the width of the magnetization hysteresis were obtained by neutron irradiating Bi2Sr2CaCu2Ox and Bi2Sr2Ca(Cu1−yLiy)2Oz. By inducing Li(n,3T)α reactions, high-energy ions are produced, allowing a direct comparison of the effects of neutron damage and ion damage in polycrystalline powders. It is shown that the ion damage leads to significantly greater magnetization enhancements, particularly at intermediate temperatures (5, 30, and 77 K results are compared). Significant differences in the magnetic field and temperature dependencies of the induced pinning are quantified.
Buried SiO2 layer formation in Si with an MeV O ion beam
Authors: Ellingboe S. , Ridgway M. C. , Schultz P. J.
Published: July 2002

A systematic study of O implantation into Si at MeV energies and stoichiometric doses is reported. Si substrates were implanted with 1 MeV O ions to doses of 0.73, 1.45, and 2.18×1018 cm−2 at implant temperatures of 150, 300, and 450 °C. The samples were then subjected to a high temperature anneal (1250 °C for 2 h). Cross-sectional transmission electron microscopy and Rutherford backscattering combined with channeling were used to study the resultant defect structures. The microstructure after annealing was found to be highly implant temperature dependent while very little dose dependence was observed. In the Si overlayer, twinning and polycrystalline Si were observed at the lowest implant temperature while SiO2 precipitation was apparent at all temperatures with precipitate size increasing with implant temperature. In the SiO2 layer, Si islands were observed at the high implant temperatures. A comparison is made between MeV and conventional implant energies. At MeV implant energies and stoichiometric doses, crystallinity in the Si overlayer is retained even at implant temperatures as low as 150 °C. Such temperatures are shown to be advantageous for inhibiting SiO2 precipitation in the Si overlayer.
Laser-induced surface heating
Authors: Bartholomeusz Brian J.
Published: July 2002

Simple expressions were derived for the temperature rise at the surface of a thick medium under sustained laser irradiation. These were employed to estimate the thermal contributions to property measurements in a few simple representative scenarios.
Evidence for Pd bonding with Si intermediate oxidation states
Authors: Faraci G. , La Rosa S. , Pennisi A. R. , Hwu Y. , Lozzi L. , Margaritondo G.
Published: July 2002

The bonding of Pd atoms evaporated on a thin layer of silicon intermediate oxidation states has been studied by core level and valence band photoemission spectroscopy. The particular substrate was obtained by controlled exposure of a cleaved Si surface to oxygen in order to have few angstroms of silicon oxidation states with a small percentage of SiO2. The deposition of Pd on this substrate was investigated studying the Pd 3d and Si 2p core level spectra as well as the valence band as a function of the metal coverage. Our results indicate evidence that the pristine Si intermediate oxidation states modify their configuration and bind metal atoms. In fact in the Si 2p spectrum changes in the chemical shift are observed for these states, and new peaks arise whose areas increase with metal coverage. The three-dimensional growth characteristics of the metal are deduced from the behavior of the relative intensity for the different components of the Si 2p core spectrum. Furthermore, the shifts of the Pd 3d core level and of the Fermi edge towards higher binding energies at low coverage confirm the formation of metal islands on a nonconducting substrate.
Studies of turbulent oxyacetylene flames used for diamond growth
Authors: Marks C. M. , Burris H. R. , Grun J. , Snail K. A.
Published: July 2002

Turbulence in the flame of an oxyacetylene torch used for diamond growth was studied with mass spectrometry and dark-field shadowgraphy. H2, CO, N2, and C2H2 were observed in both laminar and turbulent diamond growing flames, while O2, CO2, and H2O were detected in only the turbulent flame. Dark-field shadowgraphs showed a broken, changing flame front in the turbulent flame, although the boundary layer remained laminar under all flow conditions. The broken flame front suggests that unburned gases are passing through the turbulent flame front to form the detected oxidation products. A model is proposed in which the gas phase environment above the surface in turbulent flame diamond growth oscillates between oxidizing and reducing conditions.
Transmission electron microscopy study of heavily delta-doped GaAs grown by molecular beam epitaxy
Authors: Liu D. G. , Fan J. C. , Lee C. P. , Chang K. H. , Liou D. C.
Published: July 2002

N-type and p-type delta-doped GaAs grown by molecular beam epitaxy with rather significantly high doses of Si and Be have been investigated by transmission electron microscopy (TEM). The amount of doses ranged from half a monolayer to two monolayers. The microscopic structures of the delta-doped regions and the adjacent epilayers were directly observed by TEM. The effect of impurity spreading on the heterointerfaces and superlattices was also studied. Si atoms present in Si delta-doped samples were confined to within a few atomic layers. The Be atoms present in Be delta-doped samples, however, spread over a quite wide region and caused rough heterointerfaces and wavy superlattices to form. Spreading of Be was attributed to segregation and diffusion which occurred during growth. Stacking faults were found in the delta-doped samples when they were grown at low temperatures. They could be attributed to local strain caused by heavy doping.
Multicarrier characterization method for extracting mobilities and carrier densities of semiconductors from variable magnetic field measurements
Authors: Kim J. S. , Seiler D. G. , Tseng W. F.
Published: July 2002

A simple, practical method is described to extract the carrier concentration and mobility of each component of a multicarrier semiconductor system (which may be either a homogeneous or multilayered structure) from variable magnetic field measurements. Advantages of the present method are mainly due to the inclusion of both the longitudinal and transverse components of the conductivity tensor and normalization of these quantities with respect to the zero-field longitudinal component of the conductivity tensor. This method also provides a simple, direct criterion by which one can easily determine whether the material under test is associated with a one-carrier or multicarrier conduction. The method is demonstrated for a simple one-carrier system [GaAs single-channel high-electron-mobility-transistor (HEMT) structure] and two multicarrier systems (an InGaAs-GaAs double-channel HEMT structure and two types of carriers present in an InGaAs single-channel HEMT structure). The analysis of the experimental data obtained on these samples demonstrates the utility of the method presented here for extracting carrier concentrations and mobilities in advanced semiconductor structures.
Effects of crystallization on structural and dielectric properties of thin amorphous films of (1−x)BaTiO3-xSrTiO3 (x=0–0.5, 1.0)
Authors: Kawano H. , Morii K. , Nakayama Y.
Published: July 2002

The possibilities for fabricating solid solutions of (Ba1−x,Srx)TiO3 (x≤0.5,1.0) by crystallization of amorphous films and for improving their dielectric properties by adjusting the Sr content were investigated. Thin amorphous films were prepared from powder targets consisting of mixtures of BaTiO3 and SrTiO3 by sputtering with a neutralized Ar-ion beam. The amorphous films crystallized into (Ba1−x, Srx)TiO3 solid solutions with a cubic perovskite-type structure after annealing in air at 923 K for more than 1 h. The Debye-type dielectric relaxation was observed for the amorphous films, whereas the crystallized films showed paraelectric behavior. The relative dielectric constants were of the order of 20 for the amorphous samples, but increased greatly after crystallization to about 60–200, depending on the composition; a larger increase in the dielectric constant was observed in the higher Sr content films, in the range x≤0.5, which could be correlated with an increase in the grain size of the crystallites. The crystallization processes responsible for the difference in the grain size are discussed based on the microstructural observations.
ac magnetic-flux penetration in a sample disk-type sintered Bi2Sr2CaCu2Ox under low magnetic fields applied by a planar coil
Authors: Ara K. , Katagiri M. , Itoh H. , Sakasai K.
Published: July 2002

Characteristics of the ac magnetic-flux penetration in a sample disk-type sintered Bi2Sr2CaCu2Ox were examined under relatively low magnetic fields at a temperature of 72 K and an ac-excitation frequency of 10 kHz. The results indicated an interesting nonlinear magnetic-flux-penetration phenomena. Increases and decreases of the ac excitation field yielded a hysteresis ac magnetic-flux penetration characteristic. The superposition of a dc bias field on the ac excitation field enhanced the ac magnetic-flux penetration. Once the ac magnetic-flux penetration was completed by the dc bias field, the ac magnetic-flux penetration was sustained, even though the dc bias field was decreased to zero, presenting evidence of a dc magnetic-flux remanence.
The effect of silicon doping on lattice parameter and silicon related defects in gallium arsenide grown by the gradient freeze method
Authors: Fujii Katsushi , Okada Yasumasa , Orito Fumio
Published: July 2002

We investigated the effect of Si doping on the lattice parameter of gallium arsenide single crystals grown by the gradient freeze method. We also studied the carrier concentration and photoluminescence spectra of these crystals. We concluded that the lattice parameters of these crystals depend not only on the silicon concentration, but also on heat treatment and on melt composition. These changes in lattice parameter are assumed to relate to native defects and silicon clusters.
Hydrothermal BaTiO3 films on silicon: Morphological and chemical characterization
Authors: Pilleux M. E. , Fuenzalida V. M.
Published: July 2002

Insulating barium titanate films were successfully grown on Ti-deposited silicon substrates using the hydrothermal method. The film thickness was 35 and 49 nm for films treated at 200 and 250 °C, respectively, in a 0.25 M Ba(OH)2 solution for 8 h. The BaTiO3 films did not reach the Ti/Si interface. X-ray photoelectron spectroscopy revealed OH-free and nearly carbon-free films, which was corroborated using Auger electron spectroscopy (AES) depth analysis. AES revealed that the oxygen and barium concentrations are correlated throughout the film, and the existence of a diffuse BaTiO3/Ti interface. A discussion on the film growth mechanism is made using existing information on the subject.
Ultrathin delta doped GaAs and AlAs tunnel junctions as interdevice ohmic contacts
Authors: DeSalvo Gregory C.
Published: July 2002

Ultrathin (200 Å), highly conductive GaAs and AlAs p/n junction tunnel diodes were fabricated using delta doping. The current carrying capacity of these tunnel diodes is the highest reported to date. The GaAs tunnel junction is capable of handling over 30 A/cm2 at a voltage drop of only 0.02 V, and the AlAs tunnel diode is capable of handling 27 A/cm2 at 0.10 V. These tunnel junctions are useful for interconnecting three-dimensional integrated circuits, integrated optoelectronic devices, and monolithic multijunction solar cells. The delta doping of tunnel junctions to form interdevice ohmic contacts can also be applied to other material systems as well as any devices requiring vertical interconnection.
Superconducting Sr0.875Nd0.125CuO2−δ thin films
Authors: Sugii Nobuyuki , Matsuura Kiyotaka , Kubo Koichi , Yamamoto Kiyoshi , Ichikawa Michiharu , Yamauchi H.
Published: July 2002

Single-phase Sr0.875Nd0.125CuO2−δ (SNCO) thin films of the ‘‘infinite-layer’’ structure were fabricated by a pulsed-laser deposition technique. The films directly grown on SrTiO3 (100) substrates had superconductivity onset temperatures around 20 K, but zero resistances were not observed down to 4.2 K. The a-axis length of the film samples did not exceed the values reported for bulk SNCO samples. It was demonstrated that, when deposited onto a Pr2CuO4 buffer layer formed on a SrTiO3 substrate, the a-axis length of the thin film SNCO increased up to 0.395 nm which was comparable to that for bulk SNCO. The film sample exhibited a zero resistance state below 7 K. Thermoelectric-power measurements indicated that the carrier density for the film deposited on a Pr2CuO4 buffer layer was higher than that for the film fabricated without a buffer layer.
Magnetic reversal processes in exchange-coupled double layers
Authors: Mergel Dieter
Published: July 2002

The classical theory to determine the interface wall energy from magnetization reversal experiments in exchange-coupled double layers is reviewed and extended. From the energy balance three elementary reversal processes of one of the layers together with transition diagrams and corresponding reversal curves of ferrimagnetic A and P double layers are systematically derived. The wall energy can be determined from the minor loops of double layers without requiring parameters obtained on the individual layers. A novel type of partial magnetic reversal experiments is applied to amorphous rare-earth transition-metal bilayers. The results can be interpreted by assuming that the interface wall can move vertically through one layer and that common domains in both layers as well as separate domains may be nucleated. This can lead to asymmetric reversal loops, which make the evaluation of the wall energy density and the coercive force incorrect by the classical theory. Other asymmetries originate from the magnetic-field dependence of the wall energy and from pinning effects at the interface. Such effects can explain some of the inconsistent values of coercive fields and interface wall energy that have been reported in the literature.
Stress, strain, and microstructure in thin tungsten films deposited by dc magnetron sputtering
Authors: Vink T. J. , Walrave W. , Daams J. L. C. , Dirks A. G. , Somers M. A. J. , van den Aker K. J. A.
Published: July 2002

Tungsten thin films were deposited on glass substrates by direct-current planar magnetron sputtering. The induced thickness-averaged film stress within the plane of the film was determined with the bending-beam technique and changed from compressive to tensile on increasing working-gas pressure. The microstructure of these films was investigated by cross-sectional transmission electron microscopy. Compressively stressed films consisted of tightly packed columnar grains, whereas in films with a maximum value for the tensile stress the onset of a void network surrounding the columnar grains was observed. High-pressure conditions resulted in dendritic-like film growth, which brought about complete relaxation of internal stresses. The α phase was predominantly found in films under compression, while an increasing amount of β-W coincided with the transition to the tensile stress regime. Special attention was focused on stress-depth dependence and the development of two overlapping line profiles in x-ray diffraction (XRD) diagrams with film thickness as observed in compressively stressed films. Both findings constitute a remarkable result in respect of stress-depth distributions in thin films: the presence of two sublayers in a monophase film, one experiencing tensile and the other compressive stress. The occurrence of a modest tensile stress maximum present in the substrate-adjacent part of the film was explained by an elastically accommodated volume reduction, associated with a phase transformation (β into α) of initially formed β-W. Furthermore, a comparison of bending-beam stresses and XRD lattice strains (utilizing the sin2 ψ method) provided a consistent view of the mechanical behavior of the differently strained sublayers in this monophase (α-W) film.
Enhancement of the shear elastic constant in periodic and quasiperiodic Ta/Al superlattices
Authors: Carlotti G. , Socino G. , Hu An , Xia Hua , Jiang S. S.
Published: July 2002

The Brillouin light-scattering technique has been exploited in order to reveal surface acoustic phonons in both periodic and Fibonacci quasiperiodic Ta/Al superlattices. In periodic specimens, about 0.5 μm thick, it is found that, as the superlattice period is reduced from 10 to 4 nm, the phase velocity of the Rayleigh acoustic mode exhibits an anomalous increase, corresponding to a 20% enhancement of the effective shear elastic constant c44. In 2k-component and 3k-component Fibonacci quasiperiodic superlattices, with total thickness of about 1.5 μm, an enhancement of c44 similar to that of periodic specimens has been evidenced, which is connected to the average density of the interfaces, rather than to the quasiperiodicity. This enhancement can be attributed to the presence of interfaces extended over a number of atomic planes, due to the mutual interdiffusion between Ta and Al, as inferred by x-ray and electron microscopy experiments.
Distribution of radial energy deposition around the track of energetic charged particles in silicon
Authors: Fageeha O. , Howard J. , Block R. C.
Published: July 2002

The distribution of radial energy deposition around the track of carbon, aluminum, and iron ions with energy range from 10 MeV to 10 GeV inside silicon was calculated. A simple and direct approach was developed utilizing a corrected semianalytical model. The results of the present work agree very well with Monte Carlo calculations as well as stopping power tables.
Oscillatory exchange coupling in Fe/Au/Fe(100)
Authors: Unguris J. , Celotta R. J. , Pierce D. T.
Published: July 2002

Scanning electron microscopy with polarization analysis was used to investigate the interlayer exchange coupling in Fe/Au/Fe(100) sandwich structures. The films were epitaxially grown on single-crystal Fe(100) substrates. Electron diffraction measurements revealed that the Au spacer film grew with a surface reconstruction consistent with that observed for bulk Au crystals. The exchange coupling oscillates between primarily ferromagnetic and antiferromagnetic coupling for Au spacer layers up to 65 layers (13 nm) thick, but a significant biquadratic coupling component was also observed. The oscillatory coupling exhibited two components with periods of 2.48±0.05 layers (0.506±0.010 nm) and 8.6±0.3 layers (1.75±0.06 nm). The measured periods are in excellent agreement with those calculated from spanning vectors of the Au Fermi surface.
Atomic configuration of the Er-O luminescence center in Er-doped GaAs with oxygen codoping
Authors: Takahei K. , Taguchi A. , Horikoshi Y. , Nakata J.
Published: July 2002

This article investigates the structure of an Er luminescence center in GaAs by using its intra-4f-shell luminescence spectrum as an atomic probe to identify the atomic configuration. This Er center is formed in GaAs by metalorganic chemical vapor deposition with O codoping and the center shows a high efficiency and a sharp luminescence spectrum under above-band-gap photoexcitation. A single luminescence line in the spectrum of a GaAs:Er,O splits into more than eight lines in the spectrum of Al0.01Ga0.99As:Er,O. This drastic change due to the addition of 1% Al can be explained by assuming that, because of the high tendency of Al atoms to react with O atoms, the Al atoms preferentially occupy the nearest-neighbor Ga sites of two O atoms, both of which are coupled with the Er atom. Based on the luminescence spectra and additional experiments of Rutherford backscattering and secondary ion mass spectroscopy, we propose that the structure of the Er luminescence center under study is Er occupying the Ga sublattice with two O atoms most likely located at the nearest-neighbor As sites. An Er-related spectrum of GaAs0.97P0.03:Er,O can also be understood based on this model if the chemical difference of Al and P is taken into account.
Linewidth of phonon modes in infrared transmission spectra of GaAs/AlAs superlattices
Authors: Giehler M. , Jahne E. , Ploog K.
Published: July 2002

The infrared transmission spectra of (GaAs)n(AlAs)n superlattices (1≤n≤5) grown on (001) GaAs have been studied in the region of the AlAs-like phonons using polarized light and oblique incidence. The longitudinal optical (LO) phonon frequency decreases with increasing confinement. For n<3 the width of the LO phonon band increases due to disordering at the interfaces. The width of the transverse optical (TO) phonon band is substantially larger than that of the LO one. The LO phonon linewidth is mainly attributed to intrinsic damping, whereas that of the TO one is ascribed to radiative damping of polaritons.
Extensions of thermal grooving for arbitrary grain-boundary flux
Authors: Klinger L. M. , Glickman E. E. , Fradkov V. E. , Mullins W. W. , Bauer C. L.
Published: July 2002

Groove profiles are computed under isotropic conditions for the intersection of a periodic array of grain boundaries with an external surface, assuming that grain boundary flux I is directed to (I≳0) or away from (I<0) the surface. When I=0, the surface assumes an equilibrium (time-independent) profile. For I≠0, in a range bounded by upper and lower limits that depend on geometry and material parameters, a global steady-state develops in which the entire surface advances (I≳0) or recedes (I<0) from its original position at constant velocity. Beyond these limits, the surface near the groove roots becomes diffusively detached from the remaining surface. A rapidly growing ridge (I≳0) or slit (I<0) then develops along each grain boundary, whose tip ultimately translates at constant velocity in a local steady state, leaving the remaining surface behind. These velocity regimes govern the ultimate stability of polycrystalline materials subjected to large electric (electromigration) or stress (creep) fields, especially in thin films where grain size approximates film thickness.
Properties of silicon-tin alloys prepared by pulsed laser deposition
Authors: Siebentritt Susanne , Treece Randolph E. , Williams R. Stanley
Published: July 2002

Metastable thin-film alloys of tin and silicon have been grown on room temperature substrates by pulsed laser deposition. The composition of the targets, made by pressing pellets of a mixture of tin and silicon powders, was maintained in the deposited films. The granular films consisted of tin nano-crystallites surrounded by an amorphous matrix. Deposited films with tin concentration greater than 15% showed metallic behavior, optically as well as electrically, while films with tin contents less than 15% displayed optical bandgaps ranging from 100 to 300 meV. Charge transport in the semiconducting films can be modeled by a combination of conduction in extended states and hopping at the Fermi level.
Temperature dependence and dispersion of electro-optic and elasto-optic effect in perovskite crystals
Authors: Bernasconi Pietro , Zgonik Marko , Günter Peter
Published: July 2002

We relate the linear electro-optic coefficients to the quadratic polarization-optic and the elasto-optic tensors by analyzing the dielectric phenomena driven by the spontaneous and induced polarization as well as the mechanical effects given by the deformation of the crystals. We determine the temperature dependence and the wavelength dispersion of the electro-optic tensor in all the ferroelectric phases from a smaller set of data: the quadratic polarization-optic tensor of the cubic phase, the dielectric permittivity, and the spontaneous polarization. Under the assumption that the elasto-optic tensor at constant polarization is constant, the elasto-optic coefficients at constant electric field in the ferroelectric phases are derived. Numerical evaluations of these coefficients for two perovskite crystals KNbO3 and BaTiO3 are presented. Modifications of the electro-optic properties in doped crystals, mainly due to a change of the dielectric permittivity, are discussed as well.
Low-temperature transport properties of the filled and unfilled IrSb3 skutterudite system
Authors: Tritt Terry M. , Nolas G. S. , Slack G. A. , Ehrlich A. C. , Gillespie D. J. , Cohn Josh L.
Published: July 2002

We have measured the electrical resistivity, ρ, thermoelectric power, α, and thermal conductivity, κ, of the skutterudite material IrSb3 in a temperature range from 300 down to 4 K. It is found that the electrical resistivity and thermopower decrease monotonically as the temperature is reduced to 50–60 K. Below approximately 60 K the resistivity rises in a semiconducting manner. It appears the thermopower exhibits a large phonon drag peak at around 20 K and then falls towards zero. The thermal conductivity increases rapidly as the temperature is decreased with a maximum at around 20 K, corresponding to the peak in the thermopower. We will discuss these results and compare them to higher temperature data from G. A. Slack and V. G. Tsoukala [(IrSb3) J. Appl. Phys. 76, 1635 (1994)]. We have also measured some of the so-called ‘‘filled skutterudites,’’ Ir4LaGe3Sb9, Ir4NdGe3Sb9 and Ir4SaGe3Sb9. The thermoelectric properties of these materials are considerably different than those of the unfilled sample. The thermopower is considerably lower and the resistivity is a factor of 2–4 times higher than the unfilled sample at room temperature. The thermal conductivity is markedly reduced by the filling, as much as a factor of 20 reduction for some of the systems.
Characterization of lattice spacing and inclination around cells in liquid-encapsulated Czochralski GaAs crystals using a 100×100 μm2 incident x-ray beam
Authors: Usuda K. , Ando M.
Published: July 2002

Lattice spacing and inclination around cells were investigated precisely for both undoped high etch-pit-densities (EPD) liquid-encapsulated Czochralski (LEC) GaAs crystal of the order of 104 cm−2 and undoped As-ambient LEC (As-LEC) crystal of low EPD of the order of 103 cm−2. Measurement of the lattice spacing and the inclination was carried out by the triple crystal method using a 100×100 μm2 size incident beam of high-intensity synchrotron radiation. It was revealed that the lattice spacing varied by almost Δd, on the order of 10−4 Å, due to the cellular structure of the high EPD crystal. In addition, the low EPD GaAs crystal grown by the As-LEC method showed considerably less variation in lattice spacing and inclination than the high EPD LEC GaAs crystal.
Effective dielectric constant of periodic composite materials
Authors: Sareni B. , Krähenbühl L. , Beroual A. , Brosseau C.
Published: July 2002

We present computer simulation data for the effective permittivity (in the quasistatic limit) of a system composed of discrete inhomogeneities of permittivity ε1, embedded in a three-dimensional homogeneous matrix of permittivity ε2. The primary purpose of this paper is to study the related issue of the effect of the geometric shape of the components on the dielectric properties of the medium. The secondary purpose is to analyse how the spatial arrangement in these two-phase materials affects the effective permittivity. The structures considered are periodic lattices of inhomogeneities. The numerical method proceeds by an algorithm based upon the resolution of boundary integral equations. Finally, we compare the prediction of our numerical simulation with the effective medium approach and with results of previous analytical works and numerical experiments.
Substrate dependence of initial growth of microcrystalline silicon in plasma-enhanced chemical vapor deposition
Authors: Kondo Michio , Toyoshima Yasutake , Matsuda Akihisa , Ikuta Kazuyuki
Published: July 2002

Very thin microcrystalline silicon films have been deposited by plasma-enhanced chemical vapor deposition (CVD) from hydrogen diluted SiH4 gas in order to study its initial growth mechanism. The dependence of the crystallinity and the Si-H bonding configuration on electrical and chemical properties of substrates have been studied using a high sensitivity Raman spectrometer. It is found that conductive and oxygen free substrates provide good crystallinity in the initial stage. The origin of the substrate dependence is explained in terms of the ion bombardment from the plasma and the chemical nature of the substrate surface.
Biaxial strain dependence of exciton resonance energies in wurtzite GaN
Authors: Shikanai Amane , Azuhata Takashi , Sota Takayuki , Chichibu Shigefusa , Kuramata Akito , Horino Kazuhiko , Nakamura Shuji
Published: July 2002

We have systematically studied the strain dependence of the free-exciton resonance energies in wurtzite GaN by photoreflectance measurements using well-characterized samples. The experimental data have been analyzed using the appropriate Hamiltonian for the valence bands in wurtzite GaN and determined the values of the crystal field splitting, the spin–orbit splitting, the shear deformation potential constants, and the energy gap in the unstrained crystal. Discussions are given on the strain dependence of the energy gaps, of the effective masses, and of the binding energies for the free-exciton ground states as well as on the valence-band parameters.
Structural and dielectric characterization of Sm2Bi2Ti3O12 ferroelectric ceramics
Authors: Alvarez-Fregoso Octavio
Published: July 2002

X-ray diffraction, scanning electron microscopy, and ac impedance techniques have been used to characterize Sm2Bi2Ti3O12 (SmBTO) whose structural and dielectric properties were compared with those of the Bi4Ti3O12 parent ceramic. Impedance response, activation energies, bulk dielectric constant and ferroelectric Curie temperature transition are presented. Results of these ferroelectric materials are analyzed as a function of the crystallite morphology for crystalline-layered Bi4Ti3O12 and polycrystalline plate-like and needle-like Sm2Bi2Ti3O12 ceramics. When samarium substitutes bismuth in BTO, a 100 °C decrease of the ferroelectric Curie temperature was observed.
Electric field effect on the transport properties of ultrathin Y0.9Pr0.1Ba2Cu3Oy channels in the insulating phase of superconductor-insulator transition
Authors: Kabasawa U. , Hasegawa H. , Fukazawa T. , Tarutani Y. , Takagi K.
Published: July 2002

The electric field effect on the transport properties of ultrathin Y0.9Pr0.1Ba2Cu3Oy channels was examined as a function of channel thickness and channel length. Samples having a planar YBa2Cu3Ox ultrathin Y0.9Pr0.1Ba2Cu3Oy- YBa2Cu3Ox structure with a gate electrode on the backside of their SrTiO3 substrate were used. The channel layer exhibited superconducting properties when its thickness was more than 9 nm, whereas channels less than 7.5 nm thick were in the insulating phase of the superconductor-insulator transition. The modulation ratio of the conductance of the insulating (I)-phase channels was a few orders of magnitude higher than the modulation ratio of the carrier density. The field-effect mobility increased with increasing channel thickness when the film was in the insulating phase. The sheet conductance of channels shorter than 10 μm was higher than that of a 100-μm-long channel of the same thickness due to a size effect on the transport of the I-phase Y0.9Pr0.1Ba2Cu3Oy channel. The field-effect mobility was also enhanced by the size effect. These results imply that the performance of possible field-effect transistors with high-temperature superconductors may be much improved by utilizing an I-phase channel whose length is short enough for the size effect to be evident.
Differences in the densities of charged defect states and kinetics of Staebler–Wronski effect in undoped (nonintrinsic) hydrogenated amorphous silicon thin films
Authors: Güneş Mehmet , Wronski Christopher R.
Published: July 2002

A variety of undoped (nonintrinsic) hydrogenated amorphous silicon (a-Si:H) thin films was studied in greater detail using steady-state photoconductivity, σph, subband-gap absorption, α(hν), steady-state photocarrier grating (SSPG), and electron-spin-resonance (ESR) techniques both in the annealed and stabilized light soaked states. The experimental results were self-consistently modeled using a detailed numerical analysis. It was found that large differences in the optoelectronic properties of device quality a-Si:H thin films can only be explained using a gap state distribution which consists of positively charged D+ defect states above the Fermi level, the neutral D0 defect states, and the negatively charged D− defect states below the Fermi level. There are large differences both in the densities of neutral and charged defect states and R ratios in different a-Si:H films in the annealed state. The densities of both neutral and charged defect states increased, however, R ratios decreased in the stabilized light soaked state. Very good agreement was obtained between the densities of neutral defect states measured by ESR and those derived from the numerical analysis in the stabilized light soaked state. The kinetics of the Staebler–Wronski effect was also investigated. There was no direct correlation between the decrease of steady-state photoconductivity and increase of subband-gap absorption. The self-consistent fits to wide range of experimental results obtained with the three Gaussian distributions of charged defect states imply that this model is much better representation of the bulk defect states in undoped hydrogenated amorphous silicon thin films.
Electro-optic phase modulation by polymer dispersed liquid crystals
Authors: Vicari L.
Published: July 2002

We present a mathematical model to describe the optical phase shift induced by polymer dispersed liquid crystals (PDLCs) on light impinging transversely on the sample. PDLCs are dispersions of liquid crystal microdroplets in a polymeric binder. Droplets appear as optically uniaxial spheres randomly oriented so that the material is optically isotropic. The application of an external electric field results in a reorientation of the liquid crystal and therefore in an electrically controllable optical uniaxicity of the material. The model is discussed by comparison with experimental data and with previous theory [F. Basile, F. Bloisi, L. Vicari, and F. Simoni, Phys. Rev. E 48, 432 (1993)].
Partial density of states in the CuInSe2 valence bands
Authors: Löher T. , Klein A. , Pettenkofer C. , Jaegermann W.
Published: July 2002

The valence band spectra of a vacuum cleaved CuInSe2(011) surface were measured with synchrotron radiation at photon energies between 16 and 95 eV. The strong dependence of the photoionization cross section of atomic levels between 28 and 60 eV is used to divide the valence band emissions into contributions from Se 4p and Cu 3d states in order to map the respective partial density of states. The derived partial density of Cu 3d states to the total valence band density of states is around 50% in the upper part of the valence band and about 75% at its maximum corresponding to non-bonding Cu d states.
Lattice parameter changes and point defect reactions in low temperature electron irradiated AlAs
Authors: Gaber A. , Zillgen H. , Ehrhart P. , Partyka P. , Averback R. S.
Published: July 2002

X-ray diffraction was employed to investigate damage accumulation and the subsequent thermally activated annealing reactions in AlAs layers on GaAs substrates. Irradiations were performed at 4.6 K with 2.5 MeV electrons up to a total dose of 2×1019 electrons/cm2. The irradiation-induced increase of the lattice parameter amounts to about half of the changes observed in the GaAs substrates. There is a major annealing step near room temperature, a rather continuous annealing up to 500 K, and a final recovery stage between 700 and 900 K. The observations are discussed in relation to the resistance of AlAs against amorphization under ion irradiation.
Basal-plane stacking faults and polymorphism in AlN, GaN, and InN
Authors: Wright A. F.
Published: July 2002

Energies of basal-plane stacking faults in wurtzite AlN, GaN, and InN are determined using a one-dimensional Ising-type model incorporating effective layer–layer interactions obtained from density-functional-theory calculations. Stacking-fault energies are found to be largest for AlN and smallest for GaN consistent with density-functional results for the wurtzite/zinc-blende energy differences. Estimates are also given for stacking-fault energies in the zinc-blende structure. The values are negative, consistent with observations that nominal zinc-blende films typically contain large numbers of stacking faults. A related result is that hexagonal structures with stacking sequences repeating after four and six bilayers have lower energies than zinc-blende for all three compounds.
Effect of the heterointerface on the spin splitting in modulation doped InxGa1−xAs/InP quantum wells for B→0
Authors: Schäpers Th. , Engels G. , Lange J. , Klocke Th. , Hollfelder M. , Lüth H.
Published: July 2002

Spin splitting of conduction band electrons in In0.53Ga0.47As/In0.77Ga0.23As/InP heterostructures due to spin-orbit coupling is studied by performing Shubnikov–de Haas measurements on nongated and gated Hall bars. From an analysis of the beating pattern in the Shubnikov–de Haas oscillations, the spin-orbit coupling constant is determined. For a symmetric sample no beating pattern and thus no spin splitting is observed. This demonstrates that the k3 contribution to the spin-orbit coupling constant can be neglected. By applying an envelope function theory it is shown that the major contribution to the Rashba spin-orbit coupling originates from the band offset at the interface of the quantum well. Using gated Hall bar structures it is possible to alter the spin-orbit coupling by application of an appropriate gate voltage. A more negative gate voltage leads to a more pronounced asymmetry of the quantum well, which gives rise to a stronger spin-orbit coupling.
Electrical properties of Co-doped and Ni-doped β-FeSi2
Authors: Tani Jun-ichi , Kido Hiroyasu
Published: July 2002

The Hall effect and electrical resistivity of iron disilicide, Fe1−xCoxSi2(0.01≦x≦0.03) and Fe1−yNiySi2 (0.01≦y≦0.03) have been measured in the temperature range between 80 and 300 K. The solid solution Fe1−xCoxSi2 is n type over the measured temperature range, while the solid solution Fe1−yNiySi2 is p type below 160 K and n type above 160 K. The carrier concentration of Fe1−xCoxSi2 at 300 K, which is in good agreement with the Co atom concentration, is one order of magnitude higher than that of Fe1−yNiySi2. The electron conduction at high temperatures for these solid solutions is explained by the small polaron mechanism.
Lattice compression of Si crystals and crystallographic position of As impurities measured with x-ray standing wave spectroscopy
Authors: Herrera-Gómez A. , Rousseau P. M. , Woicik J. C. , Kendelewicz T. , Plummer J. , Spicer W. E.
Published: July 2002

In an earlier letter [Appl. Phys. Lett. 68, 3090 (1996)] we reported results about heavily arsenic doped silicon crystals, where we unambiguously showed, based on x-ray standing wave spectroscopy (XSW) and other techniques, that electrically deactivated As remains essentially substitutional. In this article we present the analysis methodology that led us to said conclusion, and show how from further analysis it is possible to extract the compression or expansion of thin epitaxial layers. We report the evolution of the compression of highly As doped Si epitaxial layers as deactivation takes place. The XSW measurements required a very small thickness of the doped layer and a perfect registry between the substrate and the surface layer. We found larger values for compression than previously reported, which may be explained by the absence of structural defects on our samples that relax the interface stress. Our results show a saturation on the compression as the electron concentration increases. We also report an estimation of the small displacement from perfect substitutional positions suffered by deactivated As.
The dependence of the antiferromagnet/ferromagnet blocking temperature on antiferromagnet thickness and deposition conditions
Authors: Devasahayam A. J. , Kryder M. H.
Published: July 2002

The blocking temperature was measured for several exchange biasing materials as a function of the antiferromagnet thickness and deposition conditions. For the oxide materials Co0.5Ni0.5O and NiO and for IrMn, the blocking temperature was found to decrease from the bulk values of 150, 190, and 250 °C, respectively, with decreasing thickness of the antiferromagnet. The minimum thickness needed in order to maintain a blocking temperature within 25% of the bulk value was 125, 145, and 140 Å for Co0.5Ni0.5O, NiO, and IrMn, respectively. The functional dependence with thickness was found to follow a power law relationship, which is consistent with the finite size scaling phenomenon. The shift exponent for scaling obtained by curve fitting the experimental data was 1.65, 1.40, and 1.52 for the three materials, respectively. These values were in good agreement with the theoretical values of 1.4–1.6, as calculated for idealized antiferromagnets. The corresponding values for the correlation length at 0 K were 22, 19, and 30 Å, respectively. For Co0.5Ni0.5O, the blocking temperature was also found to vary with deposition conditions, with high negative substrate biases and low pressures yielding the largest blocking temperatures. These trends were also found to follow a power-law relation.