bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic properties of FeCu (3d transition metals) SiB alloys with fine grain structure
Authors: Sawa T. , Takahashi Y.
Published: July 2002

Soft magnetic properties were investigated together with crystallization process and grain size for FeCu (3d transition metals) SiB alloys with fine grains. They were rapidly quenched from the melt to achieve amorphous states and then annealed above their crystallization temperatures. In the group of 3d transition metals studied, low magnetic core loss at high frequency was obtained for V-substituted Fe-based alloys, because only a bcc Fe solid solution with diameter of about 20 nm precipitated. On the other hand, Cr- or Mn-substituted alloys could not be attained with good soft magnetic properties because of the existence of Fe-metalloid compounds besides the bcc phase by annealing above their crystallization temperatures. The effect of grain size on the soft magnetic properties is more prominent at lower frequency. Diffraction peaks which are characteristics of an ordered phase (DO3) are observed, which is the origin of excellent soft magnetic properties in FeAlSi alloys.
Neutron scattering studies of the spin dynamics in nonlinear and Haldane systems (invited)
Authors: Steiner M.
Published: July 2002

In 1D magnets contributions to the spin dynamics which are outside the scope of spin-wave theory can be studied theoretically as well as experimentally. Two prominent examples of such effects are discussed here: solitons and the Haldane gap. We discuss inelastic polarized neutron scattering results on the stability of solitons in CsNiF3 and on the existence of the Haldane gap in CsNiCl3. In both cases, the separate determination of the different correlation functions 〈SαSα〉 with α=x,y,z is essential for definite conclusions: Solitons in CsNiF3 appear to be much more stable than expected from classical theories, and the Haldane gap is the only explanation for the observed gaps in CsNiCl3.
Magnetization processes in amorphous R-Co/R′-Co/R-Co sandwiches (R, R′=Y, Nd, Gd, Er)
Authors: Dieny B. , Givord D. , Ndjaka J. M. B. , Alameda J. M.
Published: July 2002

Sandwiches consisting of three amorphous layers (R0.33,Co0.67)1000 Å/ R′0.33,Co0.67)1000 Å/ (R0.33Co0.67)1000 Å, have been prepared by dc triode sputtering (R, R′ are rare-earth elements). The systems chosen are such that the bulk magnetization alternates from one layer to the next or the coercivity of each layer is significantly different. Magnetic transitions are observed under field. They have been quantitatively analyzed in terms of successive reversals of magnetization in the different layers. The creation or annihilation of planar Bloch walls parallel to the surface are associated with the magnetic transitions. The wall energy and wall width depend essentially on the competition between exchange energy and Zeeman energy. It is suggested that the existence of such Bloch walls may favor magnetization reversal in thin films by coherent processes.
Magnetic properties of random-mixture graphite intercalation compounds
Authors: Suzuki Masatsugu , Tien Li-Fen , Suzuki Itsuko S. , Burr Charles R.
Published: July 2002

The magnetic properties of a quasi-two-dimensional mixed ferromagnetic and antiferromagnetic system, stage-2 CocMn1−cCl2 -graphite intercalation compounds (GICs), have been studied by dc magnetic susceptibility measurements. The Curie–Weiss temperature determined as a function of Co concentration indicates that the intraplanar exchange interaction between Co2+ and Mn2+ is ferromagnetic and that J(Co-Mn)=1.3 [J(Co-Co)‖J(Mn-Mn)‖]1/2. With decreasing Co concentration c, the transition temperature tends to decrease to zero as c approaches 0.5 (the percolation concentration for the triangular lattice sites), but is not reduced to zero even below c=0.5. There may be a possibility of a spin-glass phase for 0≤c<0.4 arising from the competition between J(Mn-Mn), J(Co-Mn), and J(Mn-Mn).
The passivation of InP by arsenic surface stabilization and Al2O3 deposition: Correlations between interface chemistry and capacitance measurements
Authors: Hollinger G. , Blanchet R. , Gendry M. , Santinelli C. , Skheyta R. , Viktorovitch P.
Published: July 2002

A new approach is presented for the development of a metal-insulator–semiconductor field-effect transistor technology. It is applied to the optimization of Al2O3/InP structures prepared by the deposition of evaporated Al2O3 on arsenic-stabilized InP surfaces. Molecular beam epitaxy and surface-science techniques (reflected high-energy electron diffraction and x-ray photoelectron spectroscopy are used to control step by step the fabrication of the structures and to describe the microscopic properties of the interfaces. The optimization of the fabrication process is based on correlations between interfacial physicochemical properties and metal–insulator-semiconductor capacitor electrical properties. It is shown that an interfacial oxide buffer layer can favor crystallochemical matching between Al2O3 and InP.
First principles approach to magnetostrictive hysteresis (abstract)
Authors: Sablik M. J. , Jiles D. C. , Barghout L.
Published: July 2002

A theoretical result for the magnetostriction λ in a ferromagnet is obtained via minimization of the energy with respect to the strains. This result contains terms which produce three experimentally observed hysteretic phenomena which hitherto have not been explained by existing models.1 The first of these phenomena is liftoff. Although the magnetostriction starts at zero in the unmagnetized sample, it never returns to zero as the external magnetic field H is cycled around the magnetostrictive hysteresis loop. This liftoff phenomenon is seen experimentally in iron.1 Second, the butterfly-shaped hysteretic variation of magnetostriction against magnetic flux density B now exhibits a negative derivative ∂λ/∂B just as the flux density decreases from its maximum in agreement with experiment. Thirdly, the λ-vs-H loops are in general wider loops than the λ-vs-B loops, which is quite noticeable experimentally in iron.1 Thus, our new result exhibits all the characteristics of experimentally observed magnetostriction hysteresis.
Signal generation mechanisms in scanning-electron acoustic microscopy of ionic crystals
Authors: Urchulutegui M. , Piqueras J.
Published: July 2002

MgO crystals have been studied by scanning-electron acoustic microscopy under different experimental conditions. Contrast mechanisms in imaging are discussed and compared. The experimental results obtained by earthing or nonearthing the specimen-transducer interface suggest the existence of a signal generation mechanism that is related to the ionic nature of these kind of crystals. Electron-acoustic microscopy appears then to be a useful tool for the characterization of ionic materials.
Optical monitoring of ion beam Y-Ba-Cu-O sputtering
Authors: Klein J. D. , Yen A.
Published: July 2002

The emission spectra resulting from ion beam sputtering a Y-Ba-Cu-O target were observed as a function of beam voltage and beam current. The spectra were relatively clean with several peaks readily attributed to each of Y, Ba, and Ar. Monitoring of copper and oxygen was more difficult with a single CuO peak and one O peak evident. The intensities of the cation peaks were linear with respect to beam voltage above 400 V. Since target current was found not to be directly proportional to beam current, target power was defined as the product of beam voltage and target current. The response of cation peak height to changes in target power was linear and similar for variations of either beam voltage or target current.
Electronic mode absorption at multi-acceptor levels of copper-doped GaAs
Authors: Kang Nam Soo , Zirkle Thomas E. , Schroder Dieter K.
Published: July 2002

We have observed a very interesting feature in the mid-infrared region of copper-doped semi-insulating liquid encapsulated Czochralski grown GaAs at liquid helium temperature. After gettering copper using backside mechanical damage, the transmittance of this particular feature became much weaker. The first absorption feature occurs at 1182 cm−1 (0.147 eV), the second at 1460 cm−1 (0.181 eV), and the third at 1750 cm−1 (0.217 eV), which is a transition of an electron from the valence of three copper levels. This electronic mode absorption allows us to obtain information about the activation energies of deep-level impurities like Cu and their relative concentration after each process. This electronic mode absorption at multilevels of Cu in GaAs is proposed for the first time using the Fourier transform infrared technique to detect deep-level metal impurities in GaAs.
Pressure-assisted reaction bonding between a W sheet and a Si80Ge20 alloy
Authors: Xu Y. , Beaudry B. J. , Gschneidner K. A. , Laabs F. C.
Published: July 2002

The conditions and mechanism of bonding a tungsten sheet directly onto a Si80Ge20 alloy by hot pressing have been studied. It was found that W/Si80Ge20 bonds are formed only at relatively high temperatures. The pressure and time required for bonding decrease with increasing temperature. In the initial stage, the W/Si80Ge20 reaction follows a parabolic kinetics, suggesting it is a diffusion-controlled process. The activation energy is 4.9 eV, and the parabolic rate constant is given by Kp=(4.2±0.1)×1018 exp[−(5.7±0.1)×104/T] (μm2/ min) A bonding mechanism is proposed based on scanning electron microscopic observations and chemical analyses of the interface. Selective reaction between silicon and tungsten leaves a Ge-rich layer at the W/Si80Ge20 interface, thus reducing the melting temperature. When the silicon content in the interfacial layer becomes sufficiently low, the layer melts at the hot-press temperature. Molten materials fill in voids and microcracks by the capillary effect, resulting in an intimate contact and a strong bond. A mathematical model of Si diffusion is proposed. Solving the equation by the finite-difference method, silicon composition profiles were obtained and the silicon diffusion coefficient was estimated.
CdTe (111)B growth on oriented and misoriented GaAs (100) grown by hot-wall epitaxy
Authors: Tatsuoka H. , Kuwabara H. , Nakanishi Y. , Fujiyasu H.
Published: July 2002

CdTe (111)B layers were grown on oriented and misoriented GaAs (100) substrates by hot-wall epitaxy. The crystallinity of the layers was examined by x-ray diffraction. The strain relaxation was investigated by x-ray diffraction and optical reflectance spectra. (1) For the layers on oriented substrates, it is found that the strain of the layer is relaxed as the layer thickness increases, but additional strain, which is probably due to the formation of twinned domains, remains and is hardly relaxed. (2) Layers on misoriented substrates are twin free with good crystalline quality. Strain is relaxed as the layer thickness increases. The residual strain of layers thicker than 10 μm is for the most part due to the difference of thermal expansion coefficients between CdTe and GaAs.
Resonant tunneling diodes and transistors with a one-, two-, or three-dimensional electron emitter
Authors: Bagwell Philip F. , Broekaert Tom P. E. , Orlando T. P. , Fonstad Clifton G.
Published: July 2002

We calculate the current versus emitter to collector voltage, current versus emitter Fermi energy, and current versus potential energy in the quantum well for double-barrier resonant tunneling devices having a one-, two-, or three-dimensional electron emitter. We consider both transistor and diode operation of the devices. For each device, the current is obtained using a method which describes the effects of finite temperature, finite voltage, and free-electron motion perpendicular to the tunneling direction as independent convolutions.
Characteristics of p-type PtSi Schottky diodes under reverse bias
Authors: Chin Vincent W. L. , Storey John W. V. , Green Martin A.
Published: July 2002

The characteristics of p-type PtSi Schottky diodes are determined under reverse bias at cryogenic temperatures. Zero-bias and flat-band barrier heights of 0.242 and 0.263 eV, respectively, are evaluated from the data. In addition, the observed lack of excess barrier lowering (other than the image force lowering) is discussed. This excess barrier lowering has previously been postulated to arise from the penetration of the tail end of the metal wave function into the midgap of the semiconductor. Reverse activation analysis is reported for 30 Schottky diodes and an average experimental effective Richardson constant of 45 A/cm2  K2 is determined. The difference from the theoretical value (32 A/cm2 K2) is attributed to the temperature coefficient of the barrier height. A value of 2.7×10−5 eV/K for this coefficient is obtained, which is at least one order of magnitude smaller than the variation of the bandgap of silicon. This provides further evidence that the barrier of the p-type PtSi Schottky diode is pinned at the valence-band edge, in agreement with previous results and the expectation inferred from the n-type measurements.
Temperature dependence of the resistance in the Pt/Ti nonalloyed ohmic contacts to p-InAs induced by rapid thermal processing
Authors: Katz A. , Chu S. N. G. , Weir B. E. , Dautremont-Smith W. C. , Logan R. A. , Tabun-Ek T. , Savin W. , Harris D. W.
Published: July 2002

The temperature dependence of the resistance in the Pt(60 nm)/Ti(50 nm) nonalloyed ohmic contacts to p-InAs (Zn doped 1×1018 to 1×1019 cm−3 ) induced by rapid thermal processing in the temperature range of 300–600 °C was studied. The ohmic nature of these contacts was attributed to both the low metal-semiconductor interfacial barriers and to the heavily doped semiconductor contacting layers. A phenomenological model was used to fit the measured temperature dependence contact resistance. The results indicated conversion from thermionic emission as the dominant carriers transport mechanism across the interfacial barrier for the as-deposited sample to a combination of thermionic and field emission mechanism for the heat-treated samples.
Ion bombardment in rf plasmas
Authors: Liu J. , Huppert G. L. , Sawin H. H.
Published: July 2002

Ion bombardment energy and angle distributions have been measured in an argon plasma. The measured ion angle distribution at 10 mTorr shows that 30% of the ions have incident angles greater than 10° from the surface normal. However, ions with large incident angles have much lower energies than those incident perpendicular to the surface. At 500 mTorr a very large fraction of the ions have large incident angles, and the average energies of these ions are relatively independent of incident angle. Monte Carlo simulations of the sheath kinetics predict the trends shown in the experimental data for ion energy and angle distributions. Fine structure in the ion energy distribution was observed below 50 mTorr and is shown to be caused by charge-exchange collisions in the sheath. The average ion energy in a symmetric parallel plate system is linearly related to the voltage applied across the electrodes for measured plasma pressures up to 500 mTorr.
Negative differential resistance due to resonant interband tunneling of holes
Authors: Chow D. H. , Yu E. T. , Söderström J. R. , Ting D. Z.-Y. , McGill T. C.
Published: July 2002

The current-voltage (I-V) behavior of a GaSb(p)/AlSb/InAs/AlSb/GaSb(p) resonant interband tunneling (RIT) heterostructure is analyzed experimentally and theoretically. The structure has been successfully grown on a (100)-oriented GaAs substrate by molecular-beam epitaxy, demonstrating that more exotic lattice-matched substrates (such as InAs or GaSb) are not required for RIT devices. Theoretical simulations of I-V behavior are developed, employing a two-band tight-binding model. Experimental I-V curves show pronounced negative differential resistance, with a peak-to-valley current ratio of 8.3 at 300 K. Good agreement is observed between measured and calculated peak current densities, consistent with light-hole tunneling through the confined InAs conduction-band state.
Comment on ‘‘Lateral restoring force on a magnet levitated above a superconductor’’ [J. Appl. Phys. 6
7, 2631 (1990)]
Authors: Yang Z. J. , Johansen T. H. , Bratsberg H. , Helgesen G. , Skjeltorp A. T.
Published: July 2002

Based on Davis’ model for the lateral restoring force on a magnet levitated above a superconductor [J. Appl. Phys. 67, 2631 (1990)], we calculate the restoring force as a function of lateral displacement for a more realistic magnetic field profile.
Thermal expansion coefficients of high-T
c superconductor substrate NdGaO3 single crystal
Authors: Sasaura Masahiro , Miyazawa Shintaro , Mukaida Masashi
Published: July 2002

We report the temperature dependence of lattice constants for a NdGaO3 single crystal grown by the Czochralski method and thermal expansion coefficients which were obtained for the first time. Lattice mismatch between the NdGaO3 substrate and YBa2Cu3Ox superconducting film is 0.27% at elevated temperatures and the appropriate expansivities are similar. The crystalline quality of deposited YBa2Cu3Ox films on NdGaO3 by the laser ablation method was extremely good. NdGaO3 is, therefore, an excellent candidate for epitaxial high-Tc superconducting films.
Formation of buried oxynitride layers in silica glass by ion implantation
Authors: Oyoshi Keiji , Tagami Takashi , Tanaka Shubei
Published: July 2002

Buried oxynitride layers were formed in silica glass by N+ only or both N+- and Si+-ion implantation. These samples were characterized by secondary-ion mass spectroscopy, Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, and scanning electron microscope. The depth profile of implanted N without Si implantation is a trapezoidal shape at a high-dose condition (more than about 3 × 1016 ions/cm2). In the N+ implantation only, a part of implanted N reacts with Si, and forms a SiON layer which is thermally unstable. In both Si+ (100 keV, 1 × 1017 ions/cm2) and N+ (50 keV, 11× 1017 cm2) implantation, the depth profile of N is a Gaussian distribution, and the thermal stability of a SiON layer is dramatically improved. However, bubbles were generated near the projected range of Si and N at a high-dose condition (the total dose was 4 × 1017 ion/cm2 and the dose ratio Si/N=3/4). The generation of bubbles was suppressed by two-step N+ implantation (40 and 60 keV).
Synthesis and properties of high-T
c YBa2Cu3O7−y oriented thin films
Authors: Zhao B. R. , Yuan C. W. , Zhang Y. Z. , Gao J. , Zhao Y. Y. , Xu P. , Yang Y. M. , Li L.
Published: July 2002

The a- and c-axis-oriented YBa2Cu3O7−y thin films were prepared by rf magnetron sputtering technique. The characterization of the thin films was carried out by inductively coupled plasma atomic emission spectroscopy, x-ray diffraction, and scanning Auger profile techniques. The Tc, Tc(H), Jc(H), and Hc2 -T(near Tc) were measured by the standard dc four-probe method. It was found that very strong anisotropy of this material was manifested in its superconducting properties, especially for c-axis-oriented thin films. It was also found that Jc depends very strongly upon stoichiometric composition 123, preferential orientation of the film, and the characteristic of the film-substrate interface.
Kinetics of cw laser-assisted synthesis of thin CuxTey films
Authors: Hanus F. , Wautelet M.
Published: July 2002

Thin films of Cu and Te on glass are irradiated by means of a CW Ar+ laser beam. CuxTey compounds are synthesized. The variation of the temperature of the irradiated zone with time is measured by an interferometric method. It turns out that the different compounds of the Cu-Te system (CuTe, Cu7Te5, Cu2Te) begin to form at fixed threshold temperatures, independent on the laser beam power. Reactions take place in the solid phase. These results suggest that the reactions are controlled by nucleation.
Intrinsic Cu gettering at a thermally grown SiO2/Si interface
Authors: Bai P. , Yang G.-R. , Lu T.-M.
Published: July 2002

SiO2 film of 1500-Å thickness has been grown by a conventional thermal dry oxidation process on commercial Si(111) and Si(100) wafers. A secondary-ion mass spectrometry study of the SiO2/Si structure showed that a gettering of Cu atoms, which were present in the Si wafers as residual impurities, has occurred at the SiO2/Si interface due to the thermal dry oxidation process. The areal concentration of the Cu atoms at the interface has been found to depend on the Cu concentration in the Si wafers. Areal concentrations in order of 1×1012/cm2 were measured at the interfaces. Facilitated by the high diffusivity of Cu in SiO2 and Si, the gettering is thermodynamically driven by the low solid solubility of Cu, either in SiO2 at the temperature range up to the oxidation temperature, or in Si at low temperatures as the wafers cool down. The defects generated at the SiO2/Si interface provide the nucleation sites for the Cu gettering.
Spectral properties of rf emission from high T
c films
Authors: Jung G. , Konopka J. , Vitale S.
Published: July 2002

Spectral properties of rf radiation from intrinsic Josephson junctions in high Tc Y-Ba-Cu-O thin film have been measured in the frequency range up to 1.5 GHz. Narrow emission lines with the 3 dB bandwidth of the order of 20 MHz were detected indicating that Josephson clusters radiate coherently. Synchronization conditions are determined by dc current and external magnetic field bias. Frequency locking of radiation to external resonant circuit was also observed. Spectral line narrowing due to resonant lock was distinguished from the coherence-induced narrowing by different tuning properties of the emission line. Noncoherent Josephson radiation manifests itself as a broadband background noise increase. A pronounced 1/f-like tail sensitive to dc bias and magnetic field was observed in a low frequency part of the spectrum.
Stress reduction resulting in reduced degradation in GaAs lasers grown on Si substrates by post growth patterning and SiO2 layers
Authors: van der Ziel J. P. , Chand Naresh
Published: July 2002

The thermally induced biaxial stress in GaAs lasers grown on Si substrates is reduced by patterning the active region to an effective width of 10 μm and by introducing a compensating stress from a thermally deposited SiO2 layer. The largest stress compensation is obtained for oxide stripe lasers and results in a significant reduction in the degradation rate of the lasers.
Microwave surface resistance of YBa2Cu3O7 thin films on LaAlO3 substrates
Authors: Cooke D. W. , Gray E. R. , Arendt P. N. , Elliott N. E. , Rollett A. D. , Schofield T. G. , Mogro-Campero A. , Turner L. G.
Published: July 2002

The surface resistance Rs of YBa2Cu3O7 (YBCO) thin films (0.6±0.1 μm) deposited onto 2.5-cm diam (100) LaAlO3 substrates has been measured at 22 GHz using both Cu and Nb cavities. The surface resistance falls precipitously at the superconducting transition (Tc =90 K) from a normal state value of approximately 2 Ω to a 77 K value of 13.7±1 mΩ, which is 1.6 times lower than Cu. At 4 K the surface resistance is 1±0.1 mΩ, as measured in a Nb superconducting cavity, which is an order of magnitude lower than Cu. The critical current density at 77 K is 4.5×104 A/cm2. Pole figure analyses show the ratio of c-axis to a-axis-oriented material in the film is 2.4:1. YBCO films deposited onto either LaGaO3 or LaAlO3 substrates with varying c/a ratios yield surface resistance values at 77 K that are crudely correlated with Rs. Therefore, the principal effect of orienting the material is to improve the sharpness of the high-frequency superconducting transition, consistent with the notion that the sharpness is associated with intergranular rather than intragranular properties.
A new type of epitaxial growth in lithium phthalocyanine film on KBr(100) prepared by the molecular-beam epitaxy
Authors: Hoshi Hajime , Maruyama Yusei , Masuda Hideki , Inabe Tamotsu
Published: July 2002

A new type epitaxial growth was found in lithium phthalocyanine (LiPc) film on KBr(100) prepared by the molecular-beam epitaxy. The structure was directly observed by transmission electron microscopy and two epitaxial phases were observed. One is bidirectional tetragonal phase KBr(100)(√10×√10)R±27°−LiPc. The other is a new type of tetradirectional monoclinic phase (√10×√12.5), in which LiPc lattices match with both K+ and Br− ions, which form unusual unit meshes.
Fabrication and chemical composition of rf magnetron sputtered Tl-Ca-Ba-Cu-O high T
c superconducting thin films
Authors: Subramanyam G. , Radpour F. , Kapoor V. J. , Lemon G. H.
Published: July 2002

High-temperature superconducing Tl-Ca-Ba-Cu-O (TlCaBaCuO) thin films were fabricated by rf magnetron sputtering on strontium titanate (SrTiO3) substrates. Thin films of 0.5–0.7-μm thickness were deposited by pure argon sputtering from a single composite powder target of Tl2Ca2Ba2Cu3Ox at an rf power of 250 W and a pressure of 5 mTorr. As-deposited thin films were sintered and annealed in a thallium-rich ambient to obtain superconductivity with a zero resistance temperature (Tc0) at 107 K. X-ray diffraction results showed highly c-axis oriented films with Tl2Ca2Ba2Cu3Ox (2223) and Tl2Ca1Ba2Cu2Ox (2122) phases present. Auger electron spectroscopy survey and depth profiles were performed to determine the compositional uniformity and impurity contents of the thin films. X ray photoelectron spectroscopy high-resolution spectra were obtained at the surface, in the bulk, and near the interface with the substrate. Our XPS results support two possible mechanisms for the creation of holes in the TlCaBaCuO compound: (1) partial substitution of Ca2+ for Tl3+ and (2) charge transfer from Tl3+ to the CuO layers resulting in a valence of Tl between +3 and +1 states and the creation of holes in the CuO layers. In addition, a wet chemical etching process was developed for patterning the as-deposited TlCaBaCuO thin films. A 125-μm-wide line was formed using standard photolithography and wet chemical etching which, after heat treatments, showed superconductivity with a Tc0 of 80 K.
Magnetostrictive influence on the bistability of amorphous wires
Authors: Madurga V. , Costa J. L. , Inoue A. , Rao K. V.
Published: July 2002

We have studied the effect of tension and external field on the magnetization process in amorphous positive magnetostrictive Fe-Si-B wires. The radial stress created during the in-rotating water quenching technique of producing these wires causes a radial anisotropy. Using a simple phenomenological model which assumes a continuous distribution for the values of these radial stresses, we fit the observed values of the remanence as a function of the applied longitudinal stress and obtain information about the stress distribution. We also explain in a consistent manner the dependence of the magnetization process on the applied longitudinal stress. On doing so, a value of the saturation magnetostriction constant λs=28×10−6 is obtained for a Fe77.5Si7.5B15 amorphous wire. In the stress dependence of the nucleation field for the Barkhausen jump we observe a minimum. A quantitative explanation for this minimum is given.
Compensation in Ge-doped InP
Authors: Sun S. W. , Wessels B. W.
Published: July 2002

The electronic and optical properties of Ge-doped vapor epitaxial indium phosphide were studied. From Hall-effect measurements, it was determined that the Ge-doped material was heavily compensated even for highly doped material. The defects responsible for compensating the InP were investigated by low-temperature photoluminescence measurements at 10 K. Strong acceptor-related transitions at 1.379 and 1.395 eV were observed in the doped material. Deep-level emission at 1.17 eV was also observed in the heavily doped material. The relationship between these bands and compensation is discussed. The observed doping dependence of Ge in InP suggests that self-compensation by native defects may be important in determining the electronic properties of group IV doped III-V compounds in support of recent theoretical predictions.
Molecular dynamics study of deformation and fracture for pure and bismuth-segregated tilt copper bicrystals
Authors: Zhou Fu-xin , Peng Ba-yi , Wu Xi-jun
Published: July 2002

The microprocess of deformation and fracture for pure and Bi-segregated Σ3(1̄1̄1)/[101] 70.53° and Σ33(5̄4̄5)/[101] 58.99° tilt bicrystals of metal copper has been studied by the molecular dynamics method. It has been found that deformation and fracture are dependent on the grain boundary (GB) structure and bismuth segregation. For pure Σ33 bicrystal, the deformation is mainly due to the glide of partial dislocations generated from the GB structural units where the GB dislocations exist. The ductile fracture is attributed to the dislocation emission, which leads to vacancy generation and void coalescence. The bismuth segregation weakens the atomic bonds between copper atoms in the vicinity of GB. Under the action of the external load, the weakened bonds break and lead to formation of microcracks. Finally, the brittle fracture takes place along the binding weakening region. For Σ3 bicrystal, the ductile fracture is related to the void coalescence generated not by dislocation emission but by lattice distortion, and the brittle fracture induced by bismuth segregation is also caused by the breaking of weakened Cu—Cu bonds.
Polarized memory effect in the device including the organic charge-transfer complex, copper-tetracyanoquinodimethane
Authors: Sato Chiaki , Wakamatsu Seiichi , Tadokoro Kaoru , Ishii Kikujiro
Published: July 2002

The polarized memory effect, in which the switching between the on and off states depends on the polarity of the bias voltage, was found in the device including the film of the organic charge-transfer complex, copper-tetracyanoquinodimethane (Cu-TCNQ). The device consists of three layers, Al/Cu-TCNQ/Cu. The dc I-V characteristics and the dielectric behavior up to 106 Hz were studied. The number of the charge carriers which make the dielectric response below 103 Hz increases in the on state. The mechanism of the switching is briefly discussed.
Defect clustering in silicon emitter junctions
Authors: Andersson Gert I. , Engström Olof
Published: July 2002

Process induced defect centers in highly doped n++-p+ junctions with phosphorus and gallium or boron diffusion profiles have been investigated. The emission properties of the generation centers in these types of emitter junctions have been studied for the first time by using a specially designed method based on Deep Level Transient Spectroscopy. The emission of charge carriers from defect electron states and hole states in the space charge region of the p-n junctions is shown to consist of thermal and tunneling processes. The latter component is more pronounced for higher concentrations of shallow dopants in the p-n junction and can be explained only by assuming the presence of local electric fields to be much higher than the average fields in the space-charge regions. The emission of charge carriers is localized to the n++ region and has the same properties for p-type profiles of gallium and boron. We conclude that the creation of defects, giving rise to increased local electric fields in the emitter junctions, is determined by a clustering process related to the concentration of phosphorus.
Grazing x-ray reflection analysis of nanometric scale structures
Authors: Boher Pierre , Houdy Philippe , Schiller Claude
Published: July 2002

Grazing x-ray reflection (GXR) has been performed on thick WN layers and on C/W multilayer mirrors deposited in a diode rf-sputtering system. In the first case, we show that GXR can provide not only the layer thickness but also precise information on the occurrence of intermediate layers (native oxide superlayer, reactionlike sublayer). The relative thickness of each layer is determined very precisely. The GXR analysis of C/W multilayers can be perfectly interpreted using a physical model which includes a thickness drift during the deposit, an interface layer between W and C layers due to the interdiffusion, and interface roughness. In each case, the GXR simulation models are confirmed by in situ kinetic ellipsometry and ex situ transmission electron microscopy. Moreover, in the W/C multilayer case the soft x-ray reflectivity calculated at the CKα line assuming the same model agree very well with the experimental value.
Si impurity-induced layer disordering of Alx Ga1−x -GaAs quantum-well heterostructures by As-free open-tube rapid thermal annealing
Authors: Major J. S. , Kish F. A. , Richard T. A. , Sugg A. R. , Baker J. E. , Holonyak N.
Published: July 2002

Data are presented describing Si impurity-induced layer disordering (IILD) and Al-Ga interdiffusion in AlxGa1−x As-GaAs quantum-well heterostructures (QWHs) using open-tube rapid thermal annealing (900–1000 °C) in a flowing N2/H2 ambient. The data show that Al-Ga interdiffusion is enhanced by n-type crystal doping and suppressed by p-type doping. By surrounding the active layers of the heterostructure with layers of opposite doping, we show that the surrounding layers modify the interdiffusion by controlling the diffusion of point defects to the active layers of the heterostructure. Data are presented showing the effects of dielectric encapsulation (SiO2, Si3N4 ) on Al-Ga interdiffusion. The data show that regardless of doping SiO2 enhances interdiffusion as compared to Si3N4. To achieve more thorough layer intermixing of AlxGa1−x As-GaAs QWHs, Si IILD is also investigated in the high-temperature As-poor regime. The experimental data show that in a high-temperature As-poor annealing ambient, little or no Si diffusion occurs from an elemental Si source in contact with a p-type GaAs QWH cap layer. To achieve Si diffusion under these conditions requires removal of the GaAs cap and the use of Al-reduced SiO2 or Si3N4 as a Si diffusion source. Based on secondary-ion mass spectroscopic measurements, direct comparison of Si diffusion from closed-tube (825 °C, 48 h) and open tube (1000 °C, 10 min) anneals shows increased Si incorporation and layer disordering at higher temperatures.
Tabulation of the theoretical band-to-band luminescence spectra of heavily doped GaAs and application to experimental n-type GaAs spectra
Authors: Visser R. , Lochs H. G. M. , Giling L. J.
Published: July 2002

We have calculated the expressions for band-to-band luminescence given by Lasher and Stern for heavily doped GaAs. The resulting values in the case of no k selection rule are tabulated. A comparison between theory and experiment is made, which shows that good agreement can be obtained. From this comparison can be concluded that the band-to-band luminescence in heavily doped n-type GaAs is governed by transitions without k selection, whereas in moderately doped GaAs the transitions are without k selection at low temperatures but with k selection at room temperature.
Hydrogenation-defined stripe-geometry In0.5(AlxGa1−x)0.5P quantum-well lasers
Authors: Dallesasse J. M. , El-Zein N. , Holonyak N. , Fletcher R. M. , Kuo C. P. , Osentowski T. D. , Craford M. G.
Published: July 2002

Data are presented on the continuous-wave (cw), room-temperature (300 K) operation of stripe-geometry In0.5(AlxGa1−x)0.5P quantum-well heterostructure lasers defined via hydrogenation. Passivation of the Zn acceptors in the cap and upper confining layer provides gain guiding, and elimination of the current-blocking oxide reduces the thermal impedance. The resultant device is capable of better performance than conventional oxide-stripe diodes fabricated on the same material.
Influence of growth interruption on inverted interface quality in single AlAs-GaAs quantum wells grown by molecular beam epitaxy
Authors: Zhang J. , Dawson P. , Neave J. H. , Hugill K. J. , Galbraith I. , Fawcett P. N. , Joyce B. A.
Published: July 2002

Three techniques have been combined to correlate interface morphology and optical properties of single AlAs-GaAs quantum wells grown by molecular beam epitaxy (MBE) with and without growth interruption at the inverted (GaAs on AlAs) interface. Surface recovery and interface formation were monitored in situ by reflection high energy electron diffraction, optical properties were assessed by photoluminescence excitation (PLE) spectroscopy and the results compared with a Monte Carlo simulation of MBE growth, extended to evaluate PLE linewidths. Criteria for linewidth reduction have been established and interface morphology described.
Suppression of the dominant recombination center in n-type GaAs by proximity annealing of wafers
Authors: Wong D. , Schlesinger T. E. , Milnes A. G.
Published: July 2002

n-type GaAs specimens have been annealed in sealed quartz ampoules and characterized with electron-beam-induced current and photoresponse measurements, deep-level transient spectroscopy, and photoluminescence spectroscopy. By correlating changes in the concentrations of defects with minority-carrier diffusion length (Lp) it is shown that the dominant recombination center in this material is a hole trap termed HCX (Ev+0.29 eV). Increases in Lp of up to a factor of 3, which can be achieved by proximity annealing at 950 °C for 16 h, are related to the loss of As from the specimen surfaces during the early stages of annealing. The beneficial effect of the annealing is associated with a limited source diffusion process since the total amount of As loss is determined by the ratio of the ampoule volume to the GaAs surface area. Proximity protection of the surfaces is necessary to prevent the generation of a Ga vacancy-related hole trap HCZ (Ev+0.57 eV).
A detailed Hall-effect analysis of sulfur-doped gallium antimonide grown by molecular-beam epitaxy
Authors: Lee M. E. , Poole I. , Truscott W. S. , Cleverley I. R. , Singer K. E. , Rohlfing D. M.
Published: July 2002

Experimental data are presented for the Hall coefficient and the apparent Hall mobility over the temperature range 160–500 K for five samples of molecular-beam epitaxially grown sulfur-doped GaSb. The donor concentration of the different samples varied between 3.3×1017 and 7.5×1016 cm−3, and the native acceptor concentration between 8×1016 and 1.2×1016 cm−3. The samples show a large spread in the apparent carrier activation energy. A two valley compensated conduction model is presented that shows that the variation in apparent carrier activation energy results from different compensation ratios in the samples. This model also shows that the constant value of the Hall coefficient observed at high temperatures is not due to donor exhaustion but carrier promotion to the lower mobility L1 band. Using constraints provided by secondary ion mass spectrometry and capacitance-voltage measurements on the samples, as well as growth data, it is shown that a narrow spread of values for the donor binding energy around 60 meV is required to account for the data. It is suggested that this spread is due to the formation of a donor band and to the strongly attractive central cores of the sulphur donors.
Scanning tunneling microscopy assisted oxide surface etching
Authors: Saulys D. , Rudd G. , Garfunkel E.
Published: July 2002

A scanning tunneling microscope (STM) is used to image the surface of and to etch defects on a quasi-two-dimensional conducting oxide, Na0.9Mo6O17. The surface defects (pits) are produced by briefly increasing the bias voltage or current between the tip and sample. The pits expand and change with time into either faceted or rounded shapes. These changes are strongly accentuated by the STM imaging process. We discuss explanations to account for the defect creation and STM-assisted surface etching processes.
Comment on ‘‘The pinning force between a Bloch wall and a planar pinning site in MnAlC’’
Authors: Bishop J. E. L.
Published: July 2002

Pinning of a domain wall in uniaxial material by a thin layer defect is discussed. A coercivity Hc≂(2/3(3)1/2) (‖ακ−1‖/α) WfGM(K/M)((K/A)1/2) is found, where A, K, and M represent the exchange, anisotropy, and saturation magnetization of the bulk, and αA, and κK are those for the layer of thickness W≪((A/K))1/2. The Gaunt-Mylvaganam thermal excitation factor fGM≂1–0.40 K1/2A−3/2kT. This model is shown to be capable of explaining both the magnitude and temperature dependence of Hc in MnAlC for plausible values of α and κ for the layer, identified as grain boundary. Objections to the more complex treatment by Chen and Gaunt are discussed, in particular violation of exchange torque continuity.
Electro-optic switching in a p-i-n doped multiple quantum well directional coupler
Authors: Cada M. , Keyworth B. P. , Glinski J. M. , SpringThorpe A. J. , Rolland C. , Hill K. O.
Published: July 2002

The quantum-confined Stark effect observed in multiple quantum well (MQW) materials has been employed recently in a variety of electro-optic devices. This communication reports on some encouraging results achieved with a MQW-based, nonlinear vertical directional coupler. The device may be operated as an electrooptic switch through changes in the coupling length in response to large Stark shifts.
Ferroelectric and pyroelectric properties of strontium barium niobate films prepared by the sol-gel method
Authors: Chen Ching Jih , Xu Yuhuan , Xu Ren , Mackenzie John D.
Published: July 2002

Thin films of Sr0.6Ba0.4Nb2O6 on silicon and fused silica substrates have been prepared by the sol-gel method. The dense, transparent, and crack-free films were fabricated by the dipping and then firing at a temperature of 700 °C. Ferroelectric properties were confirmed by P-E hysteresis loops. The refractive index and optical transmission were measured. The temperature variation of the dielectric constant was obtained. The pyroelectric coefficient at room temperature was found to be 2×10−8 C/cm2 K.
A generalization of the Cornu spiral for lossy media
Authors: Hill David A.
Published: July 2002

The classical problem of Fresnel diffraction by a straightedge is extended to allow for loss in the medium. The loss modifies the usual Cornu spiral solution because the argument of the Fresnel integral becomes complex. For high loss the contributions of the outer Fresnel zones are highly attenuated.
Nonequilibrium phonon detectors
Authors: Peterreins Th. , Jochum J. , Pröbst F. , Feilitzsch F. V. , Kraus H. , Mössbauer R. L.
Published: July 2002

Many experiments in nuclear and particle physics would benefit from a device capable of detecting nonionizing events with a low energy threshold. We report on experimental tests of a low-temperature detector based on the registration of nonequilibrium phonons. The device is composed of a silicon single crystal with superconducting tunnel junctions (Al/Al2O3/Al) evaporated onto its surface. In first experiments a 20×10×3 mm3 crystal at an operating temperature of T = 0.37 K was tested with 5.5-MeV α particles. Pulse-height analysis and the timing of pulses in different junctions is shown to yield position and energy resolution. An energy threshold of 250 keV was estimated for absorption anywhere in the crystal. A position resolution of 0.6 mm was determined over a sensitive length of 10 mm. Though phonon focusing effects were registered in the vicinity of the [001] direction, scattered and reflected phonons dominate the signals in the general case. The experimental results are discussed in terms of ballistic and quasidiffuse phonon propagation. To improve the energy threshold, the operating temperature was lowered to 60 mK in order to increase junction sensitivity and a weak thermal coupling of the absorber to the heat bath was introduced to force phonons to leave the crystal via the detecting junctions. Si crystals of up to 20×20×10 mm3 size were used in these second experiments. With a 4 cm3 crystal a threshold of 270 keV was obtained. The performance in these experiments at 60 mK, however, was limited by exceptionally high values of the normal conducting junction resistances. With a reasonable value of this parameter it should be possible to realize an energy threshold of 1 keV with absorbers of a volume of several cm3.
Photoconductivity studies in Cd1−xFexSe
Authors: Stankiewicz Jolanta , Lorenzo Mauricio Di
Published: July 2002

The photoconductivity of the diluted magnetic semiconductors Cd1−xFexSe (0.01≤x≤0.07) has been measured at temperatures between 1.6 and 4.2 K in a magnetic field up to 5 T. Below the band-gap energy, the photoionization of Fe+2 (3d6) centers is responsible for the observed photocurrent. Near the band-gap energy the photocurrent spectra are interpreted in terms of free-exciton (exciton A and B) dissociation. As the magnetic field intensity is increased the photocurrent peaks shift towards lower energies. The observed red shift is larger for samples with higher Fe content. The large exchange interaction in the materials studied is responsible for the shift; their measured values allow us to estimate the exchange integrals for the Cd1−xFexSe valence band.
Electrical characterization of reoxidized nitrided silicon films on silicon
Authors: Faigón Adrián , Shappir J.
Published: July 2002

Thin oxynitride layers in the range of 50–100 Å thickness were grown by the oxidation of a thermally nitrided silicon surface. The interface electrical properties were investigated and related to the film composition. Similar values to those observed in standard oxides were obtained for the density of interface states, the surface generation velocity, and surface mobility for those layers having the highest oxidation resistance.
Fabrication and properties of indium oxide/n-GaAs junctions
Authors: Golan A. , Bregman J. , Shapira Y. , Eizenberg M.
Published: July 2002

Indium oxide/n-GaAs junctions have been prepared by deposition of indium oxide layers onto n-type GaAs by means of reactive evaporation of In in the presence of oxygen. The electrical and structural properties and the chemical composition of the resulting junctions have been investigated as a function of the oxygen pressure and substrate temperature during deposition. The analytical tools employed were Auger electron spectroscopy, x-ray diffraction, capacitance-voltage measurements, and current-voltage measurements in the dark at room temperature and elevated temperatures. The results show that the substrate temperature during deposition dominated the interface composition, especially the degree of In oxidation. The oxygen pressure mainly affected the oxide stoichiometry and the In oxidation state in the bulk of the oxide. The resulting changes in the oxide and interface properties had direct implications on the barrier height and the ideality factor of the junctions. The best diodes yielded barrier heights of 0.85 eV and ideality factors of 1.04. The role of the deposition parameters in determining the diodes characteristics is discussed.
Influence of the implantation of C+ ions on photoluminescence and electrical properties of GaAs
Authors: Shigetomi Shigeru , Makita Yunosuke , Beye Aboubaker C. , Yamada Akimasa , Ohnishi Nobukazu , Matsumori Tokue
Published: July 2002

Ion implantation of carbon (C) into extremely pure GaAs grown by molecular- beam epitaxy is carried out over a wide range of C atomic concentrations [C], from 1×1016 to 5×1019 cm−3. The impurity levels in the implanted layer are investigated by using photoluminescence (PL) and Hall-effect measurements. Below the well-defined exciton luminescence lines, one broad emission band, namely [g-g], is found to be exclusively attributable to acceptor impurities and is dominant for [C] lower than 3×1017 cm−3. However, a decrease of its intensity and a ‘‘locking’’ of its emission energy shift is observed for [C] higher than this value. A carrier transport mechanism is found to be relevant to the C acceptor level for C atoms at As sites, and deep acceptors caused by residual radiation defects. The concentration of substitutional C atoms is nearly coincident with [C] up to 1×1017 cm−3, but the activation efficiency for [C]=1×1018 cm−3 decreases by about 13%. The decrease of overall PL intensity and the locking of the emission energy shift of [g-g] are the peculiar features in highly C+- implanted GaAs. Moreover, the location of a moderately deep acceptor level and its related-emission properties as a function of [C] strongly suggest the formation of complexes involving arsenic vacancies (VAs) and C impurities, or residual radiation defects.