bluuebunny/crossref_metadata_2025 huggingface dataset:
Be-ion implantation in AlxGa1−x As
Authors: Yamahata Shoji , Adachi Sadao , Ishibashi Tadao
Published: July 2002

The rapid thermal annealing (RTA) behavior of Be+-ion-implanted AlxGa1−xAs is investigated by means of Hall-effect and photoluminescence (PL) measurements. The electrical activation in GaAs occurs from 400 °C and saturates at about 450 °C, while in AlxGa1−xAs alloys, the activation fractions increase gradually with increase in the annealing temperature. These fractions are evidently smaller in the AlxGa1−xAs alloys than in the GaAs, and larger x alloys give smaller activation fractions at any fixed temperature. PL intensity measurements indicate that annealing at 900 °C results in the maximum optical activation and lattice recovery both for GaAs and AlxGa1−xAs alloys. Secondary ion mass spectrometry (SIMS) analysis reveals Be accumulation at the AlxGa1−xAs (0≤x≤0.3) / SiO2 encapsulant interface caused by Be out-diffusion during RTA. SIMS and differential Hall-effect measurements also suggest significant Be in-diffusion in AlxGa1−xAs alloys especially for larger x values.
Argon-ion implantation damage studies in silicon Schottky barriers using anodic oxidation/etching
Authors: Chien H.-C. , Ashok S.
Published: July 2002

The nature of ion bombardment damage on Si surface barriers has been studied with 20-keV, variable-dose Ar ion implantation and controlled removal of the damaged Si surface layers prior to Schottky metallization. The electrical properties of resultant Al/p-Si Schottky diodes are found to be insensitive to the removal of the first few tens of nm of Si, and subsequent etching of over 100 nm is needed to restore the Schottky barrier height. Low-temperature I-V characteristics of these devices further reveal the presence of ion damage-induced polycrystalline regions, confirming recent observations under high-resolution electron microscopy.
Observation of single-carrier space-charge-limited flow in nitrogen-doped α-silicon carbide. III. Computer calculations
Authors: Tehrani S. , Bosman G. , Hench L. L. , Van Vliet C. M.
Published: July 2002

We report here computer calculations of current-voltage characteristics, impedance, and noise in space-charge-limited (SCL) flow in SiC crystals composed of layered polytypes. The results are compared with previously reported experimental data [Part I of the same title, J. Appl. Phys. 58, 1562 (1985) and Part II of the same title, J. Appl. Phys. 58, 1571 (1985)], and are found to give excellent agreement. In contrast to the analytical computations reported previously, the diffusion term is not neglected. It is shown to play an important role at low and moderate bias voltage. Also, these computations show clearly that while many types of traps are present, ranging from 63 to 367 meV below the conduction band, at a given temperature only one trap determines the I-V characteristics. On the contrary, in the impedance and in the generation-recombination noise spectra, many traps show up simultaneously and must be taken into account. In general, the main features of the analytical theory developed by Van Vliet et al. are confirmed.
Anomalous expansion of tungsten-carbon multilayers used in x-ray optics
Authors: Lepêtre Y. , Ziegler E. , Schuller Ivan K. , Rivoira R.
Published: July 2002

Using microcleavage transmission electron microscopy and x-ray diffraction, we have studied the anomalous expansion observed in tungsten-carbon multilayers. Our results show that the expansion is mostly due to an agglomeration of the tungsten and the effect is larger for samples that have a thinner tungsten layer. Implications for soft x-ray optics are discussed.
Ga0.47In0.53As ultrahigh gain, high sensitivity photoconductors grown by chloride vapor-phase epitaxy
Authors: Antreasyan A. , Garbinski P. A. , Mattera V. D. , Olsson N. A. , Temkin H.
Published: July 2002

We report highly sensitive planar, interdigitated Ga0.47In0.54As photoconductive detectors prepared by trichloride vapor-phase epitaxy. The devices exhibit dc gains as high as 104 at 1.3 μm. For a bit rate of 500 Mbit/s a sensitivity of P̄=−35.4 dBm has been measured at 1.55 μm. With devices having unity gain quantum efficiencies of η=33% we obtain ηP̄=−40 dBm matching the highest sensitivity measured with a p-i-n photodetector at similar bit rates. The devices show responsivities in excess of 3000 A/W and detectivities ranging between 1012 and 1013 cm Hz1/2 W−1. These values represent the highest performance that has ever been achieved with photoconductors in this wavelength range.
Analytic Green’s dyads for an electrically conducting half-space
Authors: Beissner R. E.
Published: July 2002

Analytic expressions are presented for the components of the quasistatic electric and magnetic field dyadic Green’s functions for a conducting half-space. Numerical results illustrate the effects of the conductor–air interface on electric and magnetic dipole fields. Applications to modeling of eddy current flaw detection are discussed.
Zinc-implantation-disordered (InGa)As/GaAs strained-layer superlattice diodes
Authors: Myers D. R. , Arnold G. W. , Zipperian T. E. , Dawson L. R. , Biefeld R. M. , Fritz I. J. , Barnes C. E.
Published: July 2002

We have examined the properties of (InGa)As/GaAs strained-layer superlattices (SLSs) that have been disordered by implantation of 5×1015/cm2, 250 keV 64Zn+ followed by controlled atmosphere annealing at 680 °C for 30 min. Ion channeling techniques indicate that the Zn-disordered regions of the SLS contain extensive crystalline damage after annealing. Simulations of the disordering process using an analytic ion range code predict that the electrical junction resulting from the implantation process is located outside the disordered region of the SLS in both the vertical and the lateral directions. Junction electroluminescence intensity for given drive current densities from the Zn-disordered SLS devices is comparable to that from reference Be-implantation-doped (SLS retained) devices and greatly exceeds that from heavily dislocated grown-junction mesa diodes in the homogeneous alloy of the average SLS composition; this result is consistent with the results of the simulations. This study demonstrates that implantation disordering can be as useful for strained-layer systems as for less severely mismatched heterojunction systems.
Transport properties and persistent photoconductivity in InP/In0.53Ga0.47As modulation-doped heterojunctions
Authors: Kane M. J. , Anderson D. A. , Taylor L. L. , Bass S. J.
Published: July 2002

This paper reports a study of the electrical properties of a systematic series of InP/In0.53Ga0.47As modulation-doped heterostructures grown by metalorganic chemical vapor deposition. Both Hall-effect and Shubnikov–de Haas measurements are used to obtain consistent values for carrier densities and mobilities. The heterostructures are shown to display a persistent photoconductive effect at low temperatures (<80 K) which results in changes in both the carrier density and the mobility. The variation of mobility with carrier density is analyzed to show that alloy disorder and background charged impurity scattering are the dominant scattering mechanisms. Excitation across the InP band gap is shown to be necessary for the persistent photoconductivity. We propose a mechanism for this effect in which electron hole pairs created by illumination are separated by electric fields built into the heterojunction with the holes subsequently being trapped in the InP substrate.
Energy-loss rate and enhanced diffusion due to a low-frequency plasma oscillation
Authors: Anastassiades Alexander J. , Sideris Efstathios G.
Published: July 2002

We have studied the relation of the energy-loss rate and the enhanced diffusion with the amplitude of spontaneously excited low-frequency plasma oscillation in a current-carrying argon plasma. The experimental results (radial distributions of the electron density, electric floating potential, and electric field) and the theoretical model that is developed showed the important role of the low-frequency plasma oscillations on the additional power losses of the plasma. Also, the energy-loss rate has been studied as a function of the plasma radius.
Boundary element model of eddy current flaw detection in three dimensions
Authors: Beissner R. E.
Published: July 2002

Boundary integral equations are developed for the electromagnetic field on the surface of an arbitrary, three-dimensional flaw in a conducting medium in the presence of a known incident field. A boundary element technique for the numerical solution of these equations is then presented and applied to the computation of eddy current flow around a rectangular slot.
Determination of dynamic release curves of manganin stress gauges from their resistive hysteresis
Authors: Rosenberg Z.
Published: July 2002

We extend our previous analytical modeling of the dynamic response of shock loaded piezoresistance gauges to the unloading region. We present a new approach in which we use the measured resistive hysteresis of manganin gauges to get their release stress-strain characteristics. This procedure is especially suited for manganin gauges because their resistive response depends only on the stresses and strains which prevail in them. Other gauge materials which are sensitive to the temperature rise and/or shock generated defects would not lend themselves to this direct analysis. We present an example in which we calculate the unloading stress-strain curve for manganin from a shock level of 120 kb down to zero longitudinal stress. Various aspects of this curve are discussed and compared to data obtained by other techniques.
Disilicide solid solutions, phase diagram, and resistivities. II. TaSi2-WSi2
Authors: Gas P. , Tardy J. , LeGoues F. K. , d’Heurle F. M.
Published: July 2002

The preparation of TaSi2-WSi2 alloys from the reaction of Si with Ta-W films allows one to explore the constitution diagram of the TaSi2-WSi2 pseudobinary system. The structure of the alloys has been investigated by means of Rutherford backscattering, x-ray diffraction, and transmission electron microscopy. The ‘‘equilibrium’’ phase diagrams for the system TaSi2-WSi2 and for TiSi2-WSi2 are compared in light of simple ideas of alloy theory based on the consideration of the electron to atom ratios. The resistivity of the alloys is analyzed in terms of what has been established about the transport properties of the disilicides and of possible contributions of structural defects, mostly stacking faults, to scattering processes.
Composite-cavity waveguide complementary semiconductor lasers with low-threshold current and large-output power
Authors: Du Guotong , Xiao Jianwei , Gao Dingsan , Yang Delin
Published: July 2002

This paper demonstrates the design ideas of composite-cavity waveguide complementary semiconductor lasers for improving lateral-mode characteristics. As a first example, we fabricated sectional constricted-planar composite-cavity semiconductor lasers by connecting a gain-guided oxide-stripe laser and an index-guided constricted double-heterostructure laser. Threshold current as low as 29 mA, fundamental lateral- and single longitudinal-mode oscillation with large-output power, and wavelength locking over a temperature range of 4 °C have been achieved.
Remote measurement of in-plane diffusivity components in plates
Authors: Welch Christopher S. , Heath D. Michele , Winfree William P.
Published: July 2002

A method of determining thermal diffusivity in thin plates is presented. The method, using infrared images of evolving thermal patterns previously injected with a laser, is noncontacting, one-sided, and remote. It does not require independent estimates of either the emissivity of the sample or the sample thickness. With a line-segment pattern for thermal input, it yields the in-plane components of the diffusivity tensor in anisotropic materials and also the rate of heat loss to the environment of the plate. Two methods of data analysis are presented, one corresponding to a heating line of general cross section and the other considering a Gaussian cross section, thereby saving considerable computer time. Both methods produce a statistical evaluation of measurement quality as well as estimates of diffusivity and loss rate. Results are shown for plates of metals and graphite-epoxy composite materials. Principal components and orientation for the diffusivity tensor are obtained in the anisotropic graphite-epoxy sample.
Field effect on aging and relaxation of the thermoremanent magnetization in spin glasses (low-field regime)
Authors: Alba M. , Vincent E. , Hammann J. , Ocio M.
Published: July 2002

The time decay of the thermoremanent magnetization (TRM) was measured for the insulating spin-glass compound CdIn0.3Cr1.7S4 for different applied fields in a range where the TRM at time t=0 remains linear. The same scaling analysis of the aging effects which perfectly accounted for the very low-field results has also been successfully applied in this case. Constant age relaxation curves have been derived at 0.72 Tg and 0.84 Tg. They are fitted to a function of the form of a power law multiplied by a stretched exponential, and the field dependence of the parameters has been determined.
Characteristics of thermal SiO2 films during nitridation
Authors: Pan Paihung
Published: July 2002

Thin thermal SiO2 films were annealed in pure NH3 gas in a polycrystalline silicon (poly Si) resistance-heated reactor. The nitrogen concentration in the nitridized oxide films was found to be a function of annealing temperature, annealing time, NH3 partial pressure, initial SiO2 film thickness, and the degree of oxidant contamination in the nitridation ambient. After nitridation, an increase in hydrogen concentration with increasing annealing time was observed by nuclear reaction analysis and an increase in N–H bonds with increasing annealing time was detected by infrared analysis. A negative flatband shift was caused by the nitridation process. The amount of negative flatband shift was found to be a function of annealing time, annealing temperature, NH3 partial pressure, and initial SiO2 film thickness. Positive charges inside the nitridized films were the main cause of the negative flatband shift. The positive charge distribution was calculated for a thick SiO2 film (75 nm) annealed at 1000 °C in NH3 for 10 min. A model which included two mechanisms, the indiffusion of radicals and the formation of Si–N bonds, was proposed to explain the negative flatband shift behavior. The midgap surface-state density of SiO2/Si structures increased 3–5 times when annealed in NH3 gas. The conduction of the nitridized oxide films depended on the amount of nitrogen concentration incorporated into these films. Electron trapping was observed for nitridized oxide films during current-voltage ( I-V ) measurements. The breakdown behavior of the nitridized oxide films was found to depend on the quality of the initial SiO2 films, the amount and distribution of the generated positive charge, and the amount of nitrogen incorporated into these nitridized films.
Raman study on the variation of the silicon network of a-Si:H
Authors: Hishikawa Yoshihiro
Published: July 2002

The silicon network of the ‘‘device-quality’’ hydrogenated amorphous silicon (a-Si:H) fabricated by a glow-discharge method has been studied by means of Raman spectroscopy, infrared spectroscopy, and mechanical stress measurements. Attention has been focused on the variation of the network structure induced by the change in fabrication conditions. An increase in the substrate temperature results in a shift of the TO peak in the Raman spectra toward a high wave number, an increase in the compressive mechanical stress, and a decrease in the hydrogen content in a-Si:H. It is found that the hydrogen content of the monohydride configuration (CHm) has a positive correlation with the compressive stress in a-Si:H, and the hydrogen content of the dihydride configuration (CHd) has the opposite correlation. It is also found that the position of the TO peak (ωTO) shifts toward a low wave number as the CHm increases, and that the ωTO shifts toward a high wave number when an external compressive stress is applied to a-Si:H. The experimental results suggest that the shift of the TO peak in the Raman spectra originates from the change in the force constant of Si–Si bonds induced by hydrogen atoms of a monohydride configuration in the silicon network. Variations of the silicon network caused by the change in substrate materials are also discussed.
Atomic resolution imaging of a nonconductor by atomic force microscopy
Authors: Albrecht T. R. , Quate C. F.
Published: July 2002

We have demonstrated the capability of the atomic force microscope to image the surface of an electrically insulating solid with atomic resolution. Images of highly oriented pyrolytic boron nitride taken in air show atomic corrugations with a lateral resolution better than 3 Å. Low-noise images of graphite and molybdenum disulfide are also presented.
X-ray photoemission of Co-Sn and Co-Cu bimetallic systems
Authors: Cheung T. T. P.
Published: July 2002

Co-Sn and Co-Cu bimetallic systems produced by sequential vapor deposition have been studied using x-ray photoelectron spectroscopy. When cobalt is deposited on tin at low concentrations, the Co(3d) band becomes narrower and is shifted to higher binding energy. This leads to a reduction of Co(2p3/2) line-shape asymmetry because of a decrease in the d electron density of states at the Fermi level at the cobalt site. The Co(2p3/2) line shift is small and toward lower binding energy. When exposed to oxygen, the cobalt in Co-Sn is more resistant to oxidation than pure cobalt. At low concentrations of cobalt, cobalt atoms are not oxidized at all. On the other hand, tin shows a larger extent of oxidation as the cobalt concentration increases. When a low concentration of copper is deposited on cobalt, shifts of the Cu(3d) and Cu(L3M45M45) are observed, which may be understood in terms of the d-d repulsion between the Co(3d) and Cu(3d) states. When exposed to oxygen, copper atoms are oxidized to CuO as well as Cu2O. This is unlike the cobalt deposited on copper, where both the cobalt and copper behave like their bulk metals. There are no shifts in the copper and cobalt photoelectron spectra, and when exposed to oxygen, cobalt goes to CoO while copper is partially oxidized in Cu2O only.
Solid-phase crystal growth of molecular-beam-deposited amorphous GaAs
Authors: Yokoyama S. , Yui D. , Tanigawa H. , Takasugi H. , Kawabe M.
Published: July 2002

Solid-phase crystallization processes of molecular-beam-deposited amorphous GaAs with various As/Ga composition ratios are investigated by reflection high-energy electron diffraction, Rutherford backscattering spectroscopies, and time-resolved reflectivity measurements at various annealing temperatures. In a low-temperature region (≲300 °C), solid-phase epitaxial growth takes place, and the activation energy of the growth rate (1.6 eV) is shown to agree well with that of the ion-implanted amorphized GaAs. In a high-temperature region (≳400 °C), polycrystallization takes place, followed by a realignment of the polycrystal to a single crystal. The epitaxial growth rate is more strongly affected by the As/Ga composition ratio for the low-temperature crystallization than for the high-temperature crystallization. The interface roughnesses between crystallized and amorphous layers are evaluated to be 14–20 nm from the reflectivity measurements and the transmission electron microscopy. The atomic bonding state in the amorphous GaAs is examined by Auger electron spectroscopy, and no local precipitation of As atoms is detected in the nearly stoichiometric film.
Thermionic currents and acceptor diffusion in p+-In0.53Ga0.47As/n-InP heterojunctions
Authors: Whitney Peter S. , Vlcek James C. , Fonstad Clifton G.
Published: July 2002

p +-In0.53Ga0.47As/n-InP heterojunctions grown by liquid-phase epitaxy have been investigated through I-V and I0(T) measurements. It is shown that the injection of electrons across the heterointerface is well described by a thermionic emission model characterized by a barrier height which is strongly affected by p-type dopant diffusion. Heterojunction bipolar transistors with Schottky collectors were used as tools to measure the injection current in as-grown p+-In0.53Ga0.47As/n-InP diodes, and the results were compared to the predictions of the thermionic emission model. In this way, the relative diffusivity in InP at 600 °C of three p-type dopants, Mn, Mg, and Be, have been evaluated. The results can be summarized as follows: DBe/DMn≊20, DMg/DBe≊1. The effects of postgrowth heat treatments on the observed barrier height are also discussed.
Thermally and ion-induced reaction between Si and binary metallic alloys
Authors: Hung L. S. , Hong Q. Z. , Mayer J. W.
Published: July 2002

Thermally and ion-induced reactions, between Si and binary metallic alloys of PtV (solid solution), NiTa (amorphous phase), and PtTi (intermetallic compound) were investigated. Thermal annealing was carried out at temperatures of 500–700 °C. Separated binary silicides were formed in Pt-V and Ni-Ta systems, while the ternary compound of PtTiSi was observed in the Pt-Ti system. Ion irradiation was performed at temperatures of 200–440 °C. Uniform mixed amorphous layers were produced in all the three systems upon irradiation at relatively low temperatures. The difference in reactions between thermal annealing and ion mixing was attributed to the enhanced Si mobility. The mixtures of PtVSi2 and NiTaSi2 were transformed to separated binary silicides by post-annealing, but the PtTiSi2 underwent an amorphous-metastable phase transformation. It was also found that ion mixing and thermal annealing behaved similarly when ion irradiation was carried out at relatively high temperatures.
Defect levels in CdS/CuInSe2 thin-film solar cells
Authors: Ramanathan V. , Noufi R. , Powell R. C.
Published: July 2002

Thermally stimulated capacitance spectroscopy has been employed to study the defect levels in high-efficiency, CdS/CuInSe2 thin-film solar cells. Voltage bias changes were used to probe the majority-carrier traps and light bias was employed, for the first time, to reveal minority-carrier traps. The light bias thermally stimulated capacitance has shown the presence of a distribution of electron trapping levels in CuInSe2. The capacitance under steady illumination shows that the traps produce a large photocapacitance. The implications of these observations in terms of device performance is discussed.
GaAs surface cleaning by thermal oxidation and sublimation in molecular-beam epitaxy
Authors: Saito Junji , Nanbu Kazuo , Ishikawa Tomonori , Kondo Kazuo
Published: July 2002

GaAs surface cleaning by thermal oxidation and sublimation prior to molecular-beam-epitaxial growth has been investigated as a means of reducing the carrier depletion at the substrate and epitaxial layer interface. The carrier depletion between the substrate and epitaxial films, measured by a C-V carrier profiling technique, was shown to decrease significantly with an increase in the thickness of the thermal oxidation. The concentration of carbon contamination near the substrate-epitaxial interface was measured using secondary ion mass spectroscopy. The carbon concentration correlated very well with the carrier depletion. Therefore, the main origin of the carrier depletion is believed to be the carbon concentration of the initial growth surface. Based on these results, the thermal oxidation and sublimation of a semi-insulating GaAs substrate was successfully applied to improve the mobility and sheet concentration of the two-dimensional electron gas in selectively doped GaAs/N-Al0.3Ga0.7As heterostructures with very thin GaAs buffer layers.
Application of thin silicon films to closed-tube Si and Zn diffusion in GaAs and AlxGa1−xAs
Authors: Vawter G. Allen , Omura Etsuji , Wu X. S. , Merz James L. , Coldren Larry , Hu Evelyn
Published: July 2002

The application of thin Si films for selective area Si and Zn diffusion into GaAs and AlGaAs is described in detail. The concentration-dependent pair diffusion coefficient and the activation energy for Si diffusion into AlxGa1−xAs under As overpressure for 0≤x≤0.8 are measured using both secondary ion mass spectrometry and junction depth studies. Furthermore, Si films are seen to act as an ideal mask for Zn diffusion at temperatures below 750 °C. Ideal lateral Zn diffusion profiles are routinely observed using these films, independent of stress at the interface which provides new insight into the nature of laterally enhanced diffusion.
A new method for ion charge-state analysis
Authors: Brown I. G. , Kelly J. C.
Published: July 2002

We present results showing charge-state separation of an ion beam in a purely cylindrical geometry, using the azimuthal magnetic field of a straight conductor. This geometry, which we refer to as a current coaxial lens, has advantages for the analysis of intense ion beams where it is important to minimize space-charge blowup of the beam due to loss of space-charge neutralization.
Spin reorientation in substituted Nd2Co17 compounds
Authors: Chen H. Y. , Sankar S. G. , Wallace W. E.
Published: July 2002

Nd2Co17 alloy exhibits a saturation magnetization about 30% higher than that of Sm2Co17 at room temperature. However, the former is not a useful material for permanent magnet fabrication due to its basal plane anisotropy near room temperature. In this study, an attempt is made to investigate the effect of partial substitution of Nd2Co17 with other elements. In particular, alloys of the compositions Nd2−xSmxCo13Fe4 and Nd2Co13Fe4−xTx (where T=Zr or Mn) have been examined. The results obtained in this investigation show several interesting trends in the behavior of these alloys. Substitution of ∼20% Sm in Nd2−xSmxCo13Fe4 decreases the spin-reorientation temperatures from 613 to 224 K. Further, an increase in x up to 1.0 causes only a moderate decrease in the saturation magnetization but results in a considerable enhancement of the anisotropy field. Typical thermomagnetic curves of Nd2Co13Fe4−xTx (T=Zr,Mn) exhibit spin-reorientation temperatures. These results are discussed in terms of preferential substitution of Zr or Mn in this system.
Bipolar transistor with ion implanted, rapid thermal annealed base and semi-insulating polycrystalline silicon emitter
Authors: Ozguz V. H. , Posthill J. B. , Wortman J. J. , Littlejohn M. A.
Published: July 2002

The purpose of this work was to investigate the use of ion implantation combined with rapid thermal annealing for the base and semi-insulating polycrystalline silicon (SIPOS) for the emitter of a bipolar transistor. The microstructure of the SIPOS/Si interface after rapid thermal annealing conditions and its influence on the electrical performance of the device was studied. The SIPOS/Si interface was found to be more stable than the polysilicon/Si interface after similar processing conditions, and a thin interfacial oxide layer was observed to inhibit epitaxial alignment at the interface. Lower emitter series resistances were obtained for devices where epitaxial alignment occurred at the interface, however, no quantitative correlation was observed between the microstructure of the interface and the current gain of the transistor. Bipolar transistors with enhanced current gain/base resistance ratios were fabricated.
Growth-induced anisotropy and Faraday rotation of bismuth-substituted europium-iron-garnet films
Authors: Hansen P. , Klages C.-P. , Witter K.
Published: July 2002

The saturation magnetization Ms, the growth-induced uniaxial anisotropy constant Kgu, and the Faraday rotation θF, of [111]-oriented epitaxial iron-garnet films of composition Eu3−xBixFe5O12 with x≤1.3, have been investigated as a function of composition and temperature, and, have been compared with bismuth-free films of composition Eu3−xLuxFe5O12 and Eu3−uPbuFe5O12 with u≤0.124. The results indicate a strong dependence of Kgu on growth direction, lead and bismuth content, and growth parameters, which are associated with the noncubic occupancy of the Bi3+, Pb2+, and Eu3+ ions. A maximum Kgu value of 8×104 J m−3 occurs for x=1.3 and T=4.2 K. The temperature dependence of Kgu for bismuth-substituted films is interpreted in terms of the calculated Eu3+ and the Bi3+-Fe3+ contributions. At λ=633 nm and T=295 K, the lead- and bismuth-induced Faraday rotations ΔθF/u and ΔθF/x are −1.1×106 and −2.06×106 deg m−1, respectively, in good agreement with results reported for other rare-earth garnets. These data confirm the result that ΔθF/x is independent of the rare-earth ion.
Si-substrate preparation for GaAs/Si molecular-beam epitaxy at low temperature under a Si flux
Authors: Castagne J. , Bedel E. , Fontaine C. , Munoz-Yague A.
Published: July 2002

A technique for preparing Si substrates in molecular-beam epitaxy (MBE) systems devoted to III–V compound growth is described. A C- and O-free Si surface is obtained on previously oxidized substrates using a HF solution etch. A (2×1) reconstructed surface with steps of monoatomic height is achieved with an atomic Si flux provided by a standard effusion cell, while the substrate is maintained at 600 °C for ∼10 min. The experimental results presented were obtained using Auger electron spectrometry and reflection high-energy electron diffraction.
A Monte Carlo simulation of a photodetection scheme employing noninstantaneous multiplication
Authors: Jindal R. P.
Published: July 2002

We present here numerical simulations of photodiode performance when its response time is comparable to or larger than the measurement time. The effect of the absorption of a photon is modeled as the initiation of a steady current exhibiting full shot noise. The duration of this current is again a random variable. We thus permit randomness both in the number of carriers generated per photon and also the time at which these carriers are released into the external circuit. Computed results support our previously published analytical findings. As opposed to the conventional temporally deterministic approach (first analyzed by Shockley and Pierce), the present method provides a unique way to approach the ideal performance without requiring the carrier multiplication process to be noise free. The physical reasoning that leads to this effect is explained in detail. Signal multiplication, randomly distributed over time, therefore provides the possibility of an alternate approach to design photodiodes that can achieve the ideal performance limit.
A new metastable phase in the Nd-Fe-B system
Authors: Altounian Z. , Ryan D. H. , Tu G. H.
Published: July 2002

A new metastable compound has been obtained during the crystallization of Fe-rich Nd-Fe-B amorphous alloys. The composition range for the precipitation of this phase is Nd4.5±1Fe82.5±5B12.5±3.5. A single phase, however, is obtained in a much restricted composition range. The amorphous alloy has a Curie temperature of 466 K and crystallizes at 852 K (for a heating rate of 40 K min−1 ) into the new metastable compound which has a body-centered-cubic structure with a=1.238 nm. Its Curie temperature is 548 K. Upon heating above 975 K, this phase transforms into Nd2Fe14B, NdFe12B6, and α-Fe. It appears that it is necessary to start from a truly amorphous state in order to form the new phase, otherwise, a competing body-centered-cubic phase Nd2Fe23B3 forms. X-ray diffraction and Mössbauer spectroscopy data are also presented and compared to that of Nd2Fe23B3.
Transport properties in amorphous Ux-T1−x films (T=Fe, Ni, Gd, Tb, and Yb) (invited)
Authors: Freitas P. P. , Plaskett T. S. , Moreira J. M. , Amaral V. S.
Published: July 2002

We describe the competing magnetic, localization, and phonon effects on the transport properties of amorphous magnetic UxT1−x films, with T=Fe, Ni, Gd, Tb, and Yb. Amorphous UxFe1−x films change from collinear to random ferromagnetism as x increases, and the temperature dependence of the resistivity denotes the competing effects of spin-flip and non-spin-flip exchange scattering processes. The resistivity has a minimum at Tf rising sharply below this temperature. The sign of the magnetic resistivity and the magnetoresistance indicates 〈Si ⋅Sj 〉>0, while the anisotropic magnetoresistance indicates a local exchange gap. Amorphous UxGd1−x and a-UxTb1−x are, respectively, spin glasses and random anisotropy dominated systems. The resistivity increases smoothly through Tf and has a slight upturn at low temperatures that we associate with weak localization. The magnetoresistance is negative in both systems and the anisotropic magnetoresistance is null, although the applied field induces anisotropic behavior in the Tb containing films (asperomagnets). All samples show quadratic and positive field dependence of magnetoresistance well inside the paramagnetic regime, and a linear regime below Tf. At low temperatures and in the a-UxGd1−x films, negative (H)1/2 and H2 regimes occur and are associated with weak localization processes dominated by the inelastic mean free path.
Electrochemical effects and charge-transport phenomena in metal1-polymer-metal2 systems under vacuum and water-vapor atmosphere
Authors: Leclerc Gervais , Yelon Arthur
Published: July 2002

It has been observed that metal1-polymer-metal2 cells form electrochemical systems whose open-circuit voltages under vacuum and under atmosphere are significantly different. Having studied the influence of a number of gases, we find that water vapor is responsible for this behavior. We then propose a simple electrochemical model that relates the open-circuit voltage to the water-vapor pressure and the temperature. It is shown that water vapor is simultaneously involved in electrode reactions and in dissociation processes in the polymer. It can also be inferred that the dominant charge carrier is involved in electrode reactions.
Dispersion of elastic waves in supported CaF2 films
Authors: Karanikas J. M. , Sooryakumar R. , Phillips Julia M.
Published: July 2002

The velocities of the principal and several higher-order elastic modes localized in CaF2 films grown epitaxially on Si(111) have been measured using Brillouin scattering. The effective elastic constants of the epilayers are evaluated from a fit to the mode dispersion. With decreasing film thicknesses from about 1500 Å reductions from the bulk elastic constants are found. Thicker films are well characterized by bulk parameters.
The relation between electrical conductivity and an infrared absorption parameter of carbons derived from several polymers
Authors: Ozaki Jun-ichi , Nishiyama Yoshiyuki
Published: July 2002

A new model including the semiconducting phase for the structure of carbons heat treated at lower temperatures is proposed to explain the relation between the electrical conductivity and the infrared (IR) absorption parameter for four carbonized polymers. The latter parameter was obtained by analyzing the absorption edge in the IR region. The conductivity was semiquantitatively simulated using effective medium theory coupled with percolation theory. Alternatively, an extension of effective medium theory to a three-phase model proposed here is able to simulate the conductivity.
A new analytical model for heterostructure field-effect transistors
Authors: Grinberg A. A. , Shur M.
Published: July 2002

We describe a new analytical model for heterostructure field-effect transistors. This model is based on detailed consideration of different forces acting on carriers in a two-dimensional gas and on the analysis of the difference between the electric potential and electron quasi-Fermi level. We also propose an approximate analytical model that takes into account the velocity saturation in the channel. This model incorporates an arbitrary dependence of the carrier concentration in the channel on the gate voltage. The obtained results are in good agreement with experimental data for n-channel heterostructure insulated gate field-effect transistors. Similar analytical models can also be developed for other devices such as p-channel transistors, superlattice field-effect transistors, and quantum well field-effect transistors.
A Monte Carlo simulation of damage to the gate oxide of metal-oxide-silicon field-effect transistors from electron beam lithography
Authors: Cummings K. D.
Published: July 2002

This work uses a single-scattering Monte Carlo simulation of electron-solid interactions to predict the effects of electron beam lithography on the gate oxide of metal-oxide-silicon field-effect transistors (MOSFET). Both 20 and 50 keV electron energies are examined. Electron radiation can cause significant disorder in the gate oxide and this paper discusses possible solutions to minimize the electron damage. One solution examined in detail is the effect of a high-density material incorporated in the MOSFET. The paper also explores the generation of x rays by the electron lithography. X-ray damage to the gate oxide is calculated to be small.
The effects of dopant and impurity redistributions on WSi2 formation by rapid thermal processing
Authors: Siegal Michael P. , Santiago Jorge J.
Published: July 2002

Thin-film samples of WSi2 were formed by sputter depositing tungsten metal directly onto chemically etched, p-type, B-doped, 5 Ω cm Si(100) wafers, followed by rapid thermal processing (RTP) in high vacuum at temperatures over 1100 °C. The resulting dopant and impurity elemental redistributions are studied by secondary ion mass spectroscopy. Boron, initially present both at the W/Si(100) interface as an impurity and in low concentration in the Si substrate, diffuses into the growing WSi2 film, eventually escaping into the vacuum. It is shown that RTP can be used to form high-quality, low-resistivity (∼30 μΩ cm) WSi2 films without total dopant out-diffusion. Oxygen is the major impurity in these samples and is gettered at the metal/Si(100) interface during RTP from the vacuum ambient. Removal of this interfacial oxide is needed for the growth of uniform, low-resistivity silicide films and can be done with RTP. Trace quantities of F, Cl, Na, K, C, and Cr have also been detected. Their origin and movement through the growing silicide films are also monitored as a function of RTP conditions.
Electrical characteristic degradation of ZnO varistors subjected to partial discharges
Authors: Bui A. , Loubière A. , Hassanzadeh M.
Published: July 2002

Zinc oxide is a polycrystalline ceramic having nonlinear current-voltage characteristics. This specific property allows it to be used as varistors. When these components are set in medium- or high-voltage lightning arresters, they may be subjected to partial discharges. The objectives of this study were to determine the action of partial discharge parameters on the I(V) characteristic degradation. Varistor samples under test were made with a standard process. They were metallized on both ends and were either covered with an insulating layer or not. The results obtained from bare samples in dry and wet air and at room temperature showed an important modification of the I(V) characteristic in the ohmic region with a large increase of leakage current.
Endurance limit of reversible T
c increase with compressive stress of YBa2Cu3O7−y oxide
Authors: Nishi Yoshitake , Ninomiya Nobuyuki , Oguri Kazuya , Tokunaga Shigeki
Published: July 2002

Effect of compressive stress on Tc is studied for YBa2Cu3O7−y oxide. Tc increases with compressive stress for small strain, reversibly. Excess strain decreases Tc, irreversibly. We obtain a compressive stress between reversible Tc increasing and irreversible Tc decreasing as endurance limit (16.5 N/mm2). The maximum Tcoff is about 94.4 K at 16.5 N/mm2. We suggest that the YBa2Cu3O7−y oxide sample should be formed below the endurance limit of the compressive stress on sample preparation.
Point-of-use arsine generation for organometallic vapor-phase epitaxial growth
Authors: Salzman K. A. , Davis G. A.
Published: July 2002

A technique for the continuous generation of arsine as required for organometallic vapor-phase epitaxial growth is described. Arsine is generated through the reduction of arsenic trichloride by lithium tetrahydridoaluminate in a nonvolatile ether. Reaction conditions appropriate for steady-state operation, necessary for this application, have been established. Arsenide conversion efficiencies in excess of 95% have been consistently demonstrated with arsine flows up to 100 μmol/min. GaAs grown using generated arsine exhibits a 77-K carrier concentration of 1.29×1015 cm−3 and mobility of 33 000 cm2/V s.
Density of states and linewidths of quantum wells with applied electric field
Authors: Bloss Walter L.
Published: July 2002

We calculate the density of states and corresponding linewidths for the quasi-bound energy levels of a quantum well including both barriers of finite height and width, and an applied electric field. For a GaAs/AlxGa1−xAs quantum well with a well width of 85 Å, barrier width of 50 Å, and barrier height of 240 meV, we find a field-induced linewidth for the excited state that increases from 2.9 meV at a field of 25 kV/cm to 9.5 meV at 150 kV/cm. This corresponds to a tunneling lifetime of 228 fs at 25 kV/cm decreasing to 69 fs at 150 kV/cm. The ground eigenstate has a narrow linewidth, less than 1 meV, up to a field of 150 kV/cm. The quasi-bound approximation is shown to be applicable to the ground state, but not for the excited state.
Resonant tunneling in amorphous-silicon-barrier Josephson junctions
Authors: Bradley P. , Ruby W. , Hebert D. , Van Duzer T.
Published: July 2002

We have fabricated amorphous-silicon-barrier Josephson junctions to test the theory of resonant tunneling due to localized electron states. The position of a very thin oxide layer embedded in the silicon barrier was varied, with the barrier thickness fixed, in order to observe its effect on resonant tunneling. An expression for the conductance of this structure was derived from the resonant-tunneling equation and found to agree with our results. We calculate the density of localized states from these measurements and find it is in the range typically obtained from electron-spin-resonance measurements. It is also found, as indicated by theory, that the localized states support supercurrent in the same proportion to quasiparticle current as does direct tunneling.
Reply to ‘‘Comment on ‘Laser-induced reemission of silicon atoms implanted into quartz’ ’’ [J. Appl. Phys. 6
4, 3663 (1988)]
Authors: Shimizu Tsutomu , Itoh Noriaki , Matsunami Noriaki
Published: July 2002

We present evidence for laser-induced solid-phase migration of Si atoms implanted into SiO2; the results of measurements of annealing of the electron-spin-resonance spectrum of the E′1 centers. We interpreted the migration in terms of thermal diffusion under a catastrophic condition where Si atoms are energized by laser photons and the energy is gradually imparted to SiO2 during migration.
Spectroscopy, kinetics, and laser effects of HgBr (B-state) formation due to collisions of CO+ ions with CH3HgBr
Authors: Mahmood Mohammad F.
Published: July 2002

Dissociative excitation of the HgBr (B-X) band system and atomic mercury lines have been observed in the present studies during collisions involving CO+ ions with CH3 HgBr in the laboratory kinetic energy range of 100–1000 eV. By using integrated intensity of the most intense band (0,22) of the HgBr (B-X) transition at 502 nm, emission cross sections have been measured and found to be in the range of 0.94–2.31×10−18 cm2.
Photon emission from metal-oxide-semiconductor capacitors under fast-ramp conditions
Authors: Lou L. F. , Kitazaki K. S.
Published: July 2002

Low-intensity photon emissions from a metal-oxide-semiconductor (MOS) capacitor biased with a fast-ramp voltage have been measured with a gated photon counting technique. The number of photons detected in depletion, avalanche, electron emission, and accumulation regimes of one ramp cycle shows characteristic time dependence that manifests novel aspects of the many-electron dynamics in an MOS surface potential well. This optical signature provides direct evidence for hot-electron relaxation via intersubband transitions and electron-hole recombinations at the interface trap sites.
Trapezoidal channeled substrate inner stripe phase-locked semiconductor laser arrays
Authors: Zhao Fanghai , Du Guotong , Zhang Xiaobo , Gao Dingsan
Published: July 2002

A novel type of trapezoidal channeled substrate inner stripe diode laser array grown by single-step liquid-phase epitaxy was designed and fabricated. A six-element array with evanescent wave coupling, as well as leaky wave coupling, shows a continuous-wave threshold current of 170 mA and a pulsed peak power over 675 mW per facet without a coating. A clean single-lobe far-field pattern of beam width 2.4° is obtained.
An x-ray diffraction method for measuring thicknesses of epitaxial thin films
Authors: Chaudhuri J. , Shah S. , Harbison J. P.
Published: July 2002

An x-ray diffraction technique capable of measuring the thicknesses of epitaxial thin films with high precision is described. The advantages of this method are that it is nondestructive, straightforward, and rapidly performed. The equations, based on the kinematical theory of x-ray diffraction and the mosaic crystal model, were developed. As an example of the application of this method, thicknesses of AlxGa1−xAs thin films on GaAs were determined. The integrated reflected intensities from the film and the substrate were obtained using an x-ray double-crystal diffractometer. Excellent agreement between the results from x-ray measurements and reflection high-energy electron diffraction oscillation data was obtained.
Doping mechanism in Bi(Pb)-Sr-Ca-Cu-O superconductors
Authors: Ramesh R. , Hegde M. S. , Chang C. C. , Tarascon J. M. , Green S. M. , Luo H. L.
Published: July 2002

A model that explains the doping mechanism in Bi(Pb)-Sr-Ca-Cu-O superconductor is presented. X-ray microanalysis reveals that the excess oxygen can be accounted for by the exact stoichiometry of the n=2 and 3 phases. We show that the presence of excess oxygen associated with the structural modulation in the compound is not sufficient to explain the hole concentration required by the transition temperature observed. Using a bond valence argument, we show that the effective valence of the Bi ion in the BiO bilayers is smaller than the expected value of +3, due to the incomplete oxygen coordination around the Bi ion. The model qualitatively explains the observations of lowering of Tc with Er (or Tm) doping or oxygen annealing. The role of Pb addition is suggested to be one of altering the thermodynamics and kinetics of formation of the n=3 phase.
SiO2 and Si3N4 passivation layers on Y-Ba-Cu-O thin films
Authors: Jia Q. X. , Anderson W. A.
Published: July 2002

High-Tc Y-Ba-Cu-O superconductor thin films were passivated with thermally evaporated SiO2 or rf magnetron sputtered Si3N4. Thermal evaporation of SiO2 on the Y-Ba-Cu-O thin-film surface did not degrade the zero resistance temperature of Y-Ba-Cu-O films. A seriously lowered zero resistance temperature of Y-Ba-Cu-O films was found if Si3N4 was sputtered onto the Y-Ba-Cu-O film surface. A one month exposure of the Y-Ba-Cu-O film to the environmental air did not change the Tc onset of the superconductor thin film but gave a slight decrease of Tc zero with SiO2 as the surface passivation layer. High-frequency capacitance-voltage studies were made on metal-insulator-superconductor to investigate the interface and surface properties of Ya-Ba-Cu-O thin films. The experimental data suggested that a very thin layer semiconductor phase Y-Ba-Cu-O was produced between Y-Ba-Cu-O films and the insulator films during the deposition of the passivation film onto the Y-Ba-Cu-O surface.