bluuebunny/crossref_metadata_2025 huggingface dataset:
Native oxide removal during chlorine reactive ion etching of silicon in an rf diode reactor
Authors: Thomas III J. H. , Hammer L. H.
Published: July 2002

Chlorine reactive ion etching of silicon requires the initial removal of the native oxide prior to rapid etching of silicon. The threshold energy for sputter removal of the native oxide on silicon was measured from the apparent oxide thickness on the silicon surface as determined by x-ray photoemission spectroscopy of the Si 2p core level. Using model computations, the threshold energy to sputter the modified native oxide was determined to be 72±5 eV. The surface film chemistry during etching is different above and below the sputter threshold energy. Above the threshold, the silicon surface is contaminated with 1–2 monolayers of SiClx (x=1,2,3) and residual SiClOy. Below the threshold, the oxide is not etched and SiClOy forms on the native oxide surface. The film thickness is observed to increase with ion energy to the threshold energy indicating that ion induced chemisorption phenomena control the film thickness.
Formation and structure of epitaxial ruthenium silicides on (111)Si
Authors: Chang Y. S. , Chou M. L.
Published: July 2002

Epitaxial ruthenium silicides have been successfully grown on silicon for the first time. Chemical electroless plating of a Ru thin film on silicon with subsequent annealing is a new approach and also the first demonstration of epitaxial growth of these silicides. Transmission electron microscopy was applied to characterize phases of silicides, microstructure, and orientation relationships. Three different epitaxial phases were found and identified to be Ru2Si3, RuSi, and Ru2Si. RuSi and Ru2Si are two new phases discovered in comparison with those previously reported in thin film reactions. Furthermore, Ru2Si3 was found to be a stable phase at elevated temperatures since it can be transformed from Ru2Si and RuSi by sufficiently long annealing. Various diffraction patterns were analyzed and orientation relationships were determined. Moire’s fringes of RuSi and interfacial dislocations of Ru2Si3 and Ru2Si were found. The average spacings were measured to be from 1000 to 4000 Å for Ru2Si3/Si. The composition of the silicides was measured by scanning Auger electron spectroscopy and 2% phosphorus was found.
Platinum metal etching in a microwave oxygen plasma
Authors: Chou C. H. , Phillips J.
Published: July 2002

As part of a general effort to understand the etching of metals in both plasma and chemical systems the etching of platinum foils in an oxygen plasma generated in a flow-type microwave system was studied. It was found that very rapid etching (∼ 6 Å/s) took place even at low power inputs (200 W). The principal plasma parameters, including oxygen atom concentration, ion concentration, and electron temperature, were measured as a function of distance below the microwave coupler. These were correlated to the rate of foil etching, which decreased with increasing distance from the coupler. On the basis of these correlations a simple mechanistic model was formulated. Etching of platinum in an oxygen plasma jet results from the concomitant action of oxygen atoms and high energy electrons.
Time-of-flight mass spectroscopy of ionized cluster beam in film deposition conditions
Authors: Franghiadakis Y. , Tzanetakis P.
Published: July 2002

A time-of-flight mass spectroscopy technique was developed that enables continuous monitoring of ion mass distribution in the output of a typical ionized cluster beam (ICB) source with minimum modification of the setup and negligible disturbance of film growth. The low mass resolution of this spectrometer is sufficient for cluster size determination and is counterbalanced by a number of advantages promising a more general applicability of the technique. This spectrometer has been used to study germanium cluster formation in a commercially available ICB source. No clusters larger than a few atoms were observed during several deposition runs, under conditions relevant to practical applications. It is difficult to reconcile these findings with the original hypothesis of homogeneous nucleation and growth of large clusters by free jet expansion of metal vapor. Since the precise temperature gradient in the crucible could not be controlled in this type of source, it cannot be excluded that large clusters may be formed under very particular conditions. If this is the case, vapor condensation on the nozzle’s walls must play the key role in the formation of clusters, of germanium at least, making ICB less attractive as a semiconductor thin film growth technique.
GaInAsP/InP integrated ridge laser with a butt-jointed transparent optical waveguide fabricated by single-step metalorganic vapor-phase epitaxy
Authors: Remiens D. , Rose B. , Carre M. , Hornung V.
Published: July 2002

A monolithic integration between an active and an external passive waveguide in such a way they are directly butt-jointed in a single epitaxial step is demonstrated in the InP system. The growth behavior during nonplanar metalorganic vapor-phase epitaxy on a patterned InP substrate was investigated by using a periodic structure on GaInAs or InGaAsP/InP layers. A 1.5-mm-long ridge laser consisting of an active guide butt-jointed to a transparent waveguide has exhibited lasing oscillation at 1.5 μm with a threshold current of 82 mA. A coupling coefficient of 60% has been experimentally measured.
Physics modeling of a substrate-backed annular fuse
Authors: Parks P. B. , Tsunoda S. I.
Published: July 2002

The dynamic behavior of a novel fast fuse opening switch has been analyzed theoretically. The outer cylinder of a resistive substrate, e.g., SiC, is uniformly coated with a thin film (∼10 μm) of aluminum fuse. The substrate provides mechanical stability and guards against voltage breakdown. The key aspects of the modeling are as follows: (1) time-dependent ordinary differential equations for the fuse-intensive variables which include coupling to circuit waveforms; (2) spatial dependence within the fuse is suppressed by assuming uniform expansion (linear velocity profile). Intimate contact between the fuse and substrate layer induces an additional inductive load voltage which the fuse must support due to the skin effect inside the substrate. The resulting overvoltage is not severe enough to cause fuse restrike before switching has completed. The fuse opening times are quite short (∼20–50 ns) and the voltage multiplication factors are high (∼10–30). These results raise the hope that a single-stage fuse could ultimately be used in an inductive storage device intended for high-current, high-power pulsed diode applications.
Delayed optical detection of magnetic resonance for defects in Si and GaAs
Authors: Chen W. M. , Monemar B.
Published: July 2002

We report on a modified optically detected magnetic resonance (ODMR) technique, here called delayed ODMR (D-ODMR), for studies of geometric (atomic) and electronic structure of defects in semiconductors. This D-ODMR technique is shown to be very successful in overcoming the dominating optically detected cyclotron resonance background signal in ODMR studies of defects in Si and GaAs.
Trapping parameters in CdTe single crystals determined by thermally stimulated conductivity
Authors: Lewandowski A. C. , McKeever S. W. S. , Cantwell E. , Aldridge J.
Published: July 2002

Thermally stimulated conductivity (TSC) data on high-resistivity, p-type CdTe single crystals are presented. The CdTe samples under study were either nominally undoped or doped with Mn or Fe. Deconvolution and peak fitting analysis of the TSC curves consistently revealed the presence of traps at approximately Ev+0.16, Ec−0.24, Ev+0.23, Ev+0.32, Ev+0.39, Ev+0.40, and Ev+0.47 eV in etched samples corresponding to TSC maxima at approximately 95, 110, 120, 145, 165, 170, and 190 K, respectively. An additional TSC peak, believed to be related to surface damage caused by mechanical polishing, is observed at approximately 105 K corresponding to electron traps at Ec−0.21 eV. The evidence indicates that the TSC curve from 80 to 200 K may be best described as a superposition of first-order (slow-retrapping) processes. Frequency factors and capture cross sections are calculated as temperature-dependent power-law functions. Some of the traps have been associated with particular defect structures, however, no clear correlation with the presence of Mn or Fe is observed.
Effect of hydrogen content on the light induced defect generation in direct current magnetron reactively sputtered hydrogenated amorphous silicon thin films
Authors: Pinarbasi Mustafa , Kushner Mark J. , Abelson John R.
Published: July 2002

The kinetics of light induced defect generation or the Staebler–Wronski effect have been investigated on device quality hydrogenated amorphous silicon films which were deposited by dc magnetron reactive sputtering. The total hydrogen content (CH) of the films, which varied from ∼10 to 28 at. %, had a strong influence on the defect generation. Low CH (10%–15%) films had a high initial density of defect states (∼7 to 10×1015 cm−3 ) compared to the high CH (≥17 at. %) films with a density of ∼3×1015 cm−3. However, light exposure increased the defect density more slowly on the low CH films, such that after about 1 h of light exposure their defect density was lower. A high-quality glow discharge produced film was also measured, and behaved similarly to the high CH sputtered films. The greater stability of the low CH films was also reflected in a slower decrease of the electron photoconductivity relative to the other samples. For exposure times (t) up to 1000 h, the total density of defect states of the films increases as a power law: the high CH and glow discharge deposited films follow t0.3 and t0.32, respectively, whereas the low CH film shows t0.23 at long times. The latter behavior is in sharp contrast with previous reports, and indicates that the degradation does not follow the Stutzmann theory or obeys it with a 100× smaller susceptibility to degradation.
Electrical properties of polycrystalline silicon under optical illumination
Authors: Bhatt D. P. , Joshi D. P.
Published: July 2002

A new theoretical model for electrical conduction in polycrystalline silicon under optical illumination is introduced to investigate the effect of grain size, illumination level, temperature, and grain-boundary scattering effect on the carrier mobility and resistivity of polycrystalline silicon by considering the variation of grain-boundary space-charge potential barrier height (Vg) with these parameters. This theory is based on the assumption that the grain-boundary scattering effect on carrier transport is represented by a rectangular potential barrier with a constant width of 20 Å and height φ. It is found that this barrier cannot be completely eliminated by lowering the temperature, while the barrier Vg can be removed in some cases, especially when the illumination level is very high and the grain size is large. Our theory predicts that the carrier mobility is approximately proportional to the temperature in the temperature range 100–125 K and approximately proportional to T−2/5 between 125 and 200 K. Computations show that the dependence of resistivity and carrier mobility of illuminated polysilicon on grain size is large at small grain sizes and at low temperatures and illumination levels.
Study of ErAs/GaAs strained-layer structures using optical absorption and ion channeling
Authors: Ralston J. D. , Fuchs F. , Schneider J. , Schmälzlin J.
Published: July 2002

The crystal-field splittings recently observed in the Er-related optical absorption spectra of ErAs films grown on GaAs by molecular-beam epitaxy are further investigated with respect to their applicability in characterizing strain accommodation in ErAs/GaAs multilayer structures. Rutherford backscattering axial channeling measurements are used to directly assess strain accommodation in the epitaxial films. The crystal-field splittings observed in room-temperature absorption spectra of samples containing thick strain-relieved ErAs layers are consistent with the cubic (Oh) symmetry expected for the Er lattice site in unstrained ErAs. In sharp contrast, a multilayer structure containing two-monolayer-thick, coherently strained ErAs layers shows pronounced changes in the energies, linewidths, and relative intensities of the crystal-field-split spectral lines, as well as the appearance of additional weak absorption lines. This behavior is attributed to strain-induced distortion of the crystal field in which the rare-earth ions reside. The relative influence of hydrostatic and uniaxial strain components on the optical spectra is discussed.
Removal of the process-induced fluorine associated to chemical vapor deposition of tungsten onto a polycrystalline silicon gate structure by heat treatment in a hydrogen-containing atmosphere
Authors: Eriksson Th. , Carlsson J.-O. , Mohadjeri B. , Östling M. , d’Heurle F. M. , Petersson C. S. , Keinonen J.
Published: July 2002

Tungsten was deposited from a gas mixture of hydrogen and tungsten hexafluoride onto a polycrystalline silicon gate structure in a chemical vapor deposition system. During the deposition process fluorine was also deposited as an undesired impurity. In order to remove the fluorine, heat treatments in the temperature range 550–1050 °C were performed in a hydrogen atmosphere. By this treatment it is possible to form volatile hydrofluoric acid and hence remove fluorine from the structure. Nuclear-resonance-broadening technique and secondary ion mass spectrometry were used for the analysis of fluorine. Fluorine was detected in all the samples except for the sample heat treated at 1050 °C. Moreover, etching of the polycrystalline silicon was observed. The gettering of fluorine, the etching of silicon and the observed formation of tungsten disilicide at 650 °C are discussed with respect to conceivable mechanisms. A thermodynamic study supporting the interpretations is also included.
Nondestructive evaluation of Fe-doped InP using surface acoustic wave technique
Authors: Abedin M. N. , Das P.
Published: July 2002

Surface acoustic wave (SAW) technique is used to investigate the electrical and optical properties of Fe-doped InP. Transverse acoustoelectric voltages (TAV) versus incident photon energy and applied bias voltage are measured to change the surface conductivity induced by impurity level trapping of the carriers. After the sample is etched, an impurity level is detected around 1.405 eV which considerably changes the shape of the experimental TAV versus incident photon energy and TAV versus bias voltage measurements. SAW semiconductor interaction models that tentatively explain the observed data are discussed.
A new ultrasonic method for measuring elastic moduli in unsupported thin films: Application to Cu-Pd superlattices
Authors: Moreau A. , Ketterson J. B. , Davis B.
Published: July 2002

We have developed a new ultrasonic method for measuring the phase velocity of longitudinal and shear waves in self-supporting thin films. The film is bonded at one end to an interdigital transducer (IDT) which emits a continuous wave signal. The film is supported at the other end and maintained flat under a weak tension. A receiving IDT detects the in-phase and quadrature components of the sound waves as they propagate. A liquid bond is used between the receiving IDT and the film to allow a continuous variation of the path length. From the longitudinal and shear wave velocities, we can deduce the flexural and shear moduli of the film. For films of uniaxial or higher symmetry, the Young’s and biaxial moduli can be expressed as combinations of the flexural and shear moduli. We applied this technique to Cu-Pd composition modulated thin films. Contrary to previous reports, we have not observed the supermodulus effect in either the flexural, shear, Young’s or biaxial moduli for modulation wavelengths between 13 and 36 Å.
D
X centers in Si-doped AlxGa1−xAs grown by metalorganic chemical vapor deposition
Authors: Okamoto K. , Koizumi H. , Yamaguchi K.
Published: July 2002

Three levels corresponding to photo energies E0(=1.7 eV), E1(=1.43 eV), and E2 (=energy gap) were observed in differential photocapacitance measurements of Si-doped AlxGa1−xAs grown by metalorganic chemical vapor deposition (0.23<x<0.4). On the other hand, E1 and E2 were observed but E0 was not observed in the differential photoconductance measurements. Both photon energies E1 and E2 cause persistent photoconductance (PPC) and the electron concentration coincides with the concentration of Si atoms. Our results support the broken-bond model proposed by D. J. Chadi and K. J. Chang [Phys. Rev. B 39, 10063 (1989)].
X-ray near total external fluorescence method: Experiment and analysis
Authors: Yun W. B. , Bloch J. M.
Published: July 2002

The synchrotron x-ray near total external fluorescence technique is used to measure the concentration profiles of elements near a sample surface along its surface normal. This novel nondestructive technique is capable of providing information about the concentration profiles on a length scale of tens to hundreds of angstroms from the sample surface. It does not require vacuum and can be applied at ambient pressures. Concentration profiles of virtually all the elements in the periodic table can be investigated using this technique. The lower limit of detection is approximately equivalent to (1)/(10) of a monolayer coverage. The technique is particularly useful in applications where the fluorescence signal originating from a thin surface layer can be normalized against that originating from the same element in the bulk of the sample. The experimental procedure and the data analysis are demonstrated using experimental results of metal-ion segregation from a liquid solution to a liquid/air interface.
Effects of viscosity on capillary wave instabilities of a planar liquid-metal surface in an electric field
Authors: He J. , Miskovsky N. M. , Cutler P. H. , Chung M.
Published: July 2002

An electrohydrodynamic surface capillary wave theory has previously been developed for ion and droplet formation in electrically stressed conducting viscous fluids. In this paper the formalism has been used to derive the dispersion relation for the simplest model, a planar liquid-metal ion source, which includes both gravitational and viscous effects. The calculation required the simultaneous solution of the linearized Navier–Stokes equation, the Maxwell equation, and the time-dependent Laplace–Young stress condition. The critical field necessary for the onset of instability of the fluid surface is obtained, as well as its dependence on surface tension, viscosity, and gravity. In addition, the effects of viscosity and gravity on the growth and decay rates of particle emission are investigated. It is found that, as a function of applied field, the effects of viscosity and gravity on the dominant capillary wave mode and growth rate range from a few percent for liquid Li to about 20%–40% for liquid Ga and Au, respectively. However, for the liquid metals Li, Al, Ga, Sn, and Au viscosity dominates gravity: a factor of 3 larger for Li to more than an order of magnitude greater for the heavier liquid metals. Finally, it is found that the field above a model protrusion on the perturbed surface is significantly larger than the average field over the liquid surface.
Growth of as-deposited superconducting thin films of Y1Ba2Cu3O7−δ using Nd:YAG laser
Authors: Misra D. S. , Palmer S. B.
Published: July 2002

As-deposited superconducting thin films of Y1Ba2Cu3O7−δ are grown using, for the first time, a Nd:YAG laser (λ=1.06 μm) at substrate temperatures ≂450–500 °C in the presence of dc plasma of O2 on SrTiO3 substrates (100 orientation). We find that the conventional ring electrode geometry used by others does not have the desired effect with Nd:YAG lasers. We use a simple disc electrode to generate O2 plasma.
Superconducting Y-Ba-Cu-O thin films by spray pyrolysis
Authors: Derraa A. , Sayer M.
Published: July 2002

Crystallographically textured superconducting YBa2Cu3O7−δ thin films 2–10 μm in thickness have been grown on (100) MgO substrates by a spray pyrolysis method. The structure, morphology, and composition of the films have been demonstrated by x-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy, respectively, to show strong texturing and a composition close to that expected for the bulk ceramic. The onset of the superconducting transition is at 82 K and zero resistance is achieved at 76 K with a critical current density of 3700 A/cm2 at 30 K.
Helium-ion damage and nanowire fabrication in GaAs/AlGaAs heterostructures
Authors: Knoedler C. M.
Published: July 2002

Nanometer scale features (75–1000 nm) were defined on GaAs/AlGaAs heterostructure surfaces by electron beam patterning. The use of low-voltage, helium-ion damage laterally confined the two dimensional electron gas to these patterned areas. Electrical characterization of the conducting channels as well as the ion-damaged material outside the patterned areas included measurements of the Hall mobility, the carrier concentration and the sheet resistance at various temperatures. The major problem encountered with the nanowires was an increase in the wire sheet resistance over the as-grown value at 4.2 K. Process-related factors contributed to this increase, but the most probable cause is boundary scattering at the lateral edges of the nanowires.
Superconducting Bi1.5Pb0.5Sr2Ca2Cu3Ox ceramics by rapid melt quenching and glass crystallization
Authors: Bansal Narottam P.
Published: July 2002

A glass of nominal Bi1.5Pb0.5Sr2Ca2Cu3Ox composition, prepared by rapid quenching of the melt, showed a glass transition temperature of 383 °C, crystallization temperature of 446 °C, melting temperature of 855 °C, and bulk density of 5.69 g/cm3 in air. The activation energy for crystallization of the glass has been estimated to be 292 kJ/mol from nonisothermal differential scanning calorimetry. On heating in oxygen, the glass showed a slow and continuous weight gain starting at 530 °C which reached a plateau at 820 °C. The weight gained during heating was retained on cooling to ambient conditions indicating an irreversible oxidation step. The influence of annealing conditions on the formation of various phases in the glass has been investigated. The Bi2Sr2Ca0Cu1O6 phase crystallized out first followed by formation of other phases at higher temperatures. The high-Tc phase, isostructural with Bi2Sr2Ca2Cu3O10, was not detected below 840 °C, but its fraction increased with the annealing time at 840 °C. A sample annealed at 840 °C for 243 h in air and furnace cooled showed the highest Tc(R=0) of 107.2 K and a narrow transition width, ΔTc (10%–90%), of 2 K. The high-Tc phase does not seem to crystallize out directly from the glass but is rather produced at high temperature by reaction between the phases formed at lower temperatures. The kinetics of 110-K phase formation was sluggish. It appears that the presence of lead helps in the formation and/or stabilization of the 110-K phase.
Quantum-confinement effects in CdTe-glass composite thin films produced using rf magnetron sputtering
Authors: Potter B. G. , Simmons J. H.
Published: July 2002

Quantum-confinement-induced shifts in the fundamental absorption edge of isolated CdTe crystallites are reported in CdTe-glass composite thin films produced using a sequential rf magnetron sputtering process employing two separate sputtering sources. Films ranging in thickness from 0.5 to 4.5 μm and containing as much as 30 vol % CdTe have been produced, illustrating the versatility of this technique over a more conventional melting approach. Post-deposition heat treatments were used to produce average crystallite sizes in the range 46–158 Å. An improved fit to theory at larger crystal sizes is found if a cylindrical crystal morphology is assumed. The effective mass of the confined specie, which governs the shift of the absorption edge with crystal size, is found to be 0.20m0 (spherical morphology) and 0.12m0 (cylindrical morphology), both of which are greater than the exciton-reduced mass in bulk CdTe. The data suggests, therefore, that a non-negligible Coulomb interaction may still exist in crystals even as small as 0.31 times the size of the bulk Wannier exciton diameter. Planar waveguiding has also been demonstrated in these samples as a preliminary step to the production of waveguide-based nonlinear device structures.
Strain relaxation of GaAs layers grown on heavily In-doped substrates by organometallic vapor phase epitaxy
Authors: Fuke Shunro , Mori Katsumi , Kuwahara Kazuhiro , Imai Tetsuji
Published: July 2002

Heavily Zn-doped epitaxial layers have been grown on In-doped GaAs substrates by organometallic vapor phase epitaxy in order to investigate the strain relaxation mechanism and hence the nucleation and propagation of misfit dislocations. Samples doped with Zn higher than 3×1020 cm−3 still show a perfectly strained state beyond the coherent length obtained for undoped GaAs epilayers. Hence, epilayers having a higher Zn concentration seem to have a higher activation barrier for nucleation and propagation of misfit dislocations. Furthermore, for the Zn-doped/undoped/substrate(In-doped) double-epilayer structure, the elastic strain in the heavily Zn-doped layer is found to be unrelaxed, regardless of the increase in the thickness of the Zn-doped upper layer. This result suggests dislocation generation at the growing surface and glide along the {111} slip planes into the heterointerface.
A photoluminescence study of hydrogenated GaAs grown on an InP substrate by metalorganic chemical vapor deposition
Authors: Swaminathan V. , Chakrabarti U. K. , Hobson W. S. , Caruso R. , Lopata J. , Pearton S. J. , Luftman H. S.
Published: July 2002

The effects of hydrogenation on the low-temperature (5 K) photoluminescence properties of GaAs grown on InP substrate by metalorganic chemical vapor deposition are investigated. An emission band at ∼1.4 eV originating from the GaAs/InP interfacial region shows a 30-fold increase in intensity relative to the GaAs band-edge emission after exposure to hydrogen plasma for 30 min at 250 °C. This improvement in intensity is attributed to hydrogen passivation of defects at the heterointerface caused by the large (≊4%) lattice mismatch between GaAs and InP. Annealing the hydrogenated sample at 350 °C nullifies the passivation effect. Further, the 1.4-eV band shifts to higher energy on annealing the sample in the temperature range 150–450 °C with the hydrogenated sample exhibiting a larger shift than the untreated sample. It is suggested that the annealing-induced peak shift arises due to modification of the interface and that it is greater in the hydrogenated sample compared to the untreated sample.
Experimental verification of temperature calculations in multilayers used for CO2 laser recrystallization of silicon-on-insulator films
Authors: Theunissen M. J. J. , van de Nieuwenhoff R. P. M. L. C. , Kuiken H. K.
Published: July 2002

Temperature profiles were calculated numerically for a three-layer stack of SiO2-Si-SiO2 on top of a monocrystalline Si substrate. The stack was locally heated by a CO2 laser whereas the wafer background temperature was controlled by a heat chuck. The calculation method makes it possible to simulate temperatures as functions of laser power, spot radius, scan speed, substrate bias temperature, and layer thickness. These parameters play a major role in CO2 laser recrystallization of polycrystalline silicon for making single crystalline silicon films on insulator films. It is shown that under conditions of maximum absorption experimental verification of the calculations is possible by measuring the recrystallized track width. A good agreement was found between the calculated and measured results.
Effect of annealing on the ac leakage components of the ZnO varistor. II. Capacitive current
Authors: Gupta T. K. , Straub W. D.
Published: July 2002

Following an earlier study on the temperature dependence of the resistive component of the leakage current of a ZnO varistor, a detailed study has been undertaken in this paper to compare the temperature dependence of the resistive (IR), capacitive (IC), and total (IT) leakage currents between unannealed and 600 °C annealed samples. It is shown that, as before, an Arrhenius plot of IC and IR versus temperature can best be represented by a break in the plot comprising a high-temperature regime (125–165°C) with a high activation energy and a low-temperature regime (30–100 °C with a low activation energy. The activation energies of IR-T curves are generally higher than those of IC-T curves in both temperatures regimes. Upon annealing at the critical temperature of 600 °C, the activation energy changes for both current components, accompanied by increased stability of the varistor. For IR, the activation energy becomes higher in the low-temperature regime in agreement with previous observation, and for IC, it becomes lower in the higher-temperature regime. The relative contributions of these two current components on total current are also different in the two temperature regimes. In the low-temperature regime, the total current is mostly capacitive, and in the high-temperature regime, it is mostly resistive. The varistor is thus prone to more Joule heating in the high-temperature regime than in the low-temperature regime.
Characteristics of high-temperature superconducting wires on the basis of YBa2Cu3Ox
Authors: Löhle J. , Mattenberger K. , Vogt O. , Wachter P.
Published: July 2002

Using the powder-in-tube technique, superconducting monocore and multicore wires have been produced with several outer diameters (the thinnest one was (1)/(10) mm) and a length of more than 1000 m. The procedure was optimized for achieving high-transport current density. Three parameters were varied, namely, wire diameter, sinter duration, and sinter temperature. The most powerful wire prepared had a critical transport current density of 750 A/cm2.
Effects of copper precipitation in Σ=25 silicon bicrystals by deep-level transient spectroscopy
Authors: Hamet J. F. , Abdelaoui R. , Nouet G.
Published: July 2002

The electrical properties of grain boundaries have been investigated by means of capacitance measurements such as deep-level transient spectroscopy and thermally stimulated capacitance. This paper describes the evolution of the electrical properties of n-type Σ=25 silicon bicrystals as a function of heat treatments. It results from this work, that after annealing and quenching, the Σ=25 bicrystal presents an electrical activity and that metallic impurities are responsible for the grain boundary electrostatic potential barrier. The investigations by transmission electron microscopy have shown that the grain boundary activity is in relationship with the presence of colonies of precipitates at the interface, these precipitates being silicides. The results of microanalysis experiments made elsewhere on other similar bicrystals indicate the presence of copper and nickel in the precipitates forming the colonies. The importance of the heating and cooling rates of the samples about the energy distribution of the interface states display the kinetic aspect of the mechanisms involved (segregation-precipitation).
The effect of annealing temperature on electrical properties of Pd/n-GaSb Schottky contacts
Authors: Su Y. K. , Li N. Y. , Juang F. S. , Wu S. C.
Published: July 2002

Thermal stability for Pd/n-GaSb Schottky contacts is analyzed and studied. At room temperature, Pd/n-GaSb Schottky diodes have better performance, but when the annealing temperature is increased to 300 and 450 °C for 30 min, Schottky contacts gradually become ohmic contacts. From the measurement of Rutherford backscattering spectroscopy and x-ray diffraction analysis, the result indicates that the interdiffusion between palladium and gallium forming Ga5Pd is the dominant factor for degrading properties of Schottky diodes.
Elastic distortion field in single layer heterostructures in the presence of misfit dislocations
Authors: Mazzer M. , Carnera A. , Drigo A. V. , Ferrari C.
Published: July 2002

The elastic distortion field in (001)-grown lattice mismatched heterostructures of diamond or zinc-blende structure having misfit dislocations at the interface is calculated within the linear elasticity theory. Not only the misfit dislocation densities in the two 〈110〉 directions but also the distribution of the possible Burgers vectors are taken into consideration. A transition layer where the elastic field is appreciably laterally nonuniform extends from the interface up to a distance of the same order of the mean dislocation spacing. It is shown that this transition layer affects x-ray diffraction measurements. Beyond this region, the elastic distortion field is uniform and is found to depend only on the mean values of the Burgers vectors associated with the two dislocation distributions. In particular it is shown that in general the strain field, i.e., the symmetric part of the elastic distortion field, is not biaxial. The three independent parameters describing the lattice deformations in the epilayer depend not only on the projections on the interface of the edge components but also on the screw components of the Burgers vectors. The predictions of this model are tested on InxGa1−xAs/GaAs samples analyzed by means of channeling and double crystal x-ray diffractometry. The unbalance of the dislocation densities in the two 〈110〉 directions measured by the dechanneling behavior of the samples agrees rather well with the prediction of the model on the basis of the measured asymmetries of the strain field.
Temperature dependence of boron neutralization in silicon by atomic hydrogen
Authors: Pankove J. I.
Published: July 2002

The dependence of boron neutralization on the hydrogenation temperature was studied systematically in 2-Ω-cm, B-doped crystalline silicon. The maximum penetration depth of H increases with temperature. The migration of H has an activation energy of 0.39 eV. The B neutralization, measured as surface resistivity, reaches a maximum at 100 °C. The surface resistivity reverts to the bulk value above 160 °C. The bond breaking that reactivates the acceptors has an activation energy of 0.76 eV.
A thyristor model of switching in metal-thin insulator-semiconductor-semiconductor devices: The influence of insulating layer and illumination
Authors: Choi W. K. , Owen A. E.
Published: July 2002

The influence of the insulating layer and illumination on the threshold switching voltage (Vs) of metal-thin insulator-semiconductor-semiconductor (MISS) devices has been modeled using the phenomenological approach we developed previously. [J. Appl. Phys. 65, 2102 (1989)]. The influence of the thin insulating layer on Vs has been examined by investigating the influence of the effective barrier heights of the insulating layer on the current amplification factor of the metal-thin insulator-semiconductor part of the model. The influence of illumination is modeled in a similar way to the effect of base current injection in three-terminal devices; the base current is replaced by the photocurrent generated as a result of illumination. Our model provides good agreement for MISS devices with silicon oxide insulating layers and illumination of fixed wavelength.
Design and construction of 1064-nm liquid-crystal laser cavity end mirrors
Authors: Lee Jae-Cheul , Jacobs Stephen D.
Published: July 2002

We describe the design and construction of cholesteric liquid-crystal elements for laser cavity end mirror applications and we give the Jones matrix [J. Opt. Soc. Am. 31, 488 (1941)] representation of these devices.
Ion-assisted doping of p-CdTe films
Authors: Sharps Paul , Fahrenbruch Alan L. , Lopez-Otero Adolfo , Bube Richard H.
Published: July 2002

Ion-assisted doping has been used to control the phosphorus incorporation and p-type doping of CdTe epitaxial films. Ion dose, ion energy, growth temperature, and growth rate were all varied. A saturated carrier density of 2×1017 cm−3 was observed, although secondary ion mass spectroscopy analyses of several films indicated a continuous increase in phosphorus concentration in the films with increasing ion dose. Hole mobilities, majority-carrier lifetimes, and minority-carrier lifetimes were measured as a function of carrier density. n-CdS/p-CdTe heterojunction solar cells were prepared to further characterize the CdTe films for solar cell applications. Spectral response measurements indicated that both the minority-carrier lifetime and the interface collection function decreased with increases in carrier density. Such reduced values were not seen for CdS/CdTe heterojunctions prepared on P-doped single-crystal CdTe with high carrier densities.
Silicon epitaxy by hot wall plasma enhanced chemical vapor deposition
Authors: Williams L. M. , O’Hara P. A. , Bohrer M. P.
Published: July 2002

Hot wall plasma enhanced chemical vapor deposition is examined for epitaxial silicon growth for advanced devices. The reactor has a load lock and can provide an in situ plasma clean of the wafers before deposition. At 800 °C, layers of good quality are obtainable at growth rates of 1.4 μm/h. Defect densities for the layers are low. Concentrations of carbon and oxygen at the epilayer-substrate interface are comparable to those for more elaborate cleaning processes. Although the wafers are directly exposed to the plasma during the cleaning and the deposition, no additional defects caused by the plasma were detected.
Fluctuating deep-level trap occupancy model for 1/f noise in semiconductor resistors
Authors: Folkes P. A.
Published: July 2002

A quantitative theoretical model for 1/f and low-frequency noise due to bulk traps in semiconductor resistors has been developed. The model is based on the fact that random fluctuations of the steady-state deep-level-trapped electron density, at some point in a depletion layer, decay exponentially with a relaxation time which depends on the local free electron density, the intrinsic properties of the semiconductor and the trap energy. The model, which is valid for relaxation times which are much longer than the free electron transit time, was applied to the case of a Schottky-barrier field effect resistor. Our results show that the low-frequency noise spectrum generated by deep-level traps with a broad spatial distribution throughout the depletion layer, is very sensitive to Fermi-Dirac trap statistics. The discrete distribution of flatband trap energy levels is the crucial parameter which determines the spectral density and range of the low-frequency noise. Monoenergetic traps generate a considerably broadened Lorentzianlike low-frequency noise spectrum which is highly sensitive to temperature. Traps with an arbitrary distribution over a set of discrete energy levels may exhibit 1/f  noise or generic low-frequency noise. We deduce the condition that has to be satisfied in order for an arbitrary discrete distribution of bulk traps over energy to exhibit 1/f noise and derive an exact integral and approximate analytical expressions for the spectral density and range of bulk 1/f  noise in semiconductors. The temperature dependence of the 1/f noise spectrum is discussed while in the process elucidating the subtle temperature-dependent relationship between 1/f and low-frequency noise arising from bulk traps. Experimentally observed low-frequency and 1/f  noise characteristics are explicitly accounted for by the model. A qualitative argument for the application of the model to 1/f noise generated by surface traps is given.
Electric microwave absorption for the study of GaAs/AlGaAs heterostructure systems
Authors: Zappe Hans P. , Jantz Wolfgang
Published: July 2002

The use of magnetic-field-dependent microwave absorption as a nondestructive and contact-free means to study transport behavior in GaAs/AlGaAs devices is explored. This technique allows quick measurement of resistance, mobility, and carrier concentration in bulk substrates as well as in the two-dimensional electron gas of heterostructure quantum wells. The two- and three-dimensional conductivities may be separably evaluated, allowing detailed study of conduction in the active layer of high-electron-mobility devices. A brief theoretical foundation is provided, followed by application of the approach to examination of device structural dependencies, carrier-density conduction behavior, and the effects of etch processing on quantum-well integrity.
Radiation effects in superconducting NbN/AlN multilayer films
Authors: Herzog R. , Weber H. W. , Gray K. E. , Kampwirth R. T. , Miller D. J. , Murduck J. M.
Published: July 2002

The results of neutron irradiation up to a fluence of 1023 m−2 (E>0.1 MeV) are reported for sputtered NbN/AlN multilayer films. The superconducting properties change only slightly with neutron fluence. For the best multilayers, which exhibit critical current densities Jc of >108 A/m2 at 4.2 K and 20 T, the high-field data show virtually no change in Jc. It is therefore proved experimentally that NbN/AlN multilayers, which exhibit higher Jc than single NbN thin films, exhibit the same extremely radiation-hard, high-field behavior which was reported previously for such NbN films.
Low-temperature reaction of thin-film platinum (≤300 Å) with (100) silicon
Authors: Tsui Bing-Yue , Chen Mao-Chieh
Published: July 2002

Thin platinum films of 164 and 303 Å thickness are deposited on (100) silicon and annealed at temperatures ranging from 180 to 300 °C in a nitrogen furnace for various times ranging from 1 min to 200 h. Sheet resistance (Rs ) measurement shows a four-stage silicide formation sequence: (1) the Rs increases to a maximum value; (2) the Rs then decreases to a minimum value; (3) the Rs increases once again and reaches a second maximum value; and (4) the Rs decreases to a final stable value. X-ray diffraction analysis indicates that the initial phase grown is Pt12Si5 which corresponds to the sheet-resistance increase in the first stage. This phase is also identified by the transmission electron diffraction analysis. This is the first time that the Pt12Si5 phase formed by the Pt/Si direct reaction is observed. The second stage corresponds to the growth of Pt2Si as confirmed by the x-ray diffraction and Auger spectroscopy analyses. The third stage corresponds to the growth of PtSi and the final stage corresponds to the increase of PtSi grain size. Samples with initial Pt films of 500, 800, and 2000 Å thickness were also prepared and analyzed by x-ray diffraction. The increase of film thickness suppresses the growth of Pt12Si5, and for Pt films thicker than 800 Å the initial phase grown becomes Pt2Si. The film thickness dependence is explained by the partial lattice-match-induced preferred phase growth effect. The effective absorption coefficient (Kse ) of the Pt/Si structure after annealing is determined by ellipsometry measurement, and the activation energy of the Pt12Si5 phase formation derived from the Rs -time plot or the Kse -time plot is determined to be 1.5–1.6 eV.
Experimental study of the effect of the ion-implanted dose on the resistance-area product of Hg0.8Cd0.2Te n+p photodiodes
Authors: Centeno J. M. , Gonzalez C. , Sangrador J. , Rodriguez T.
Published: July 2002

The temperature dependence of the differential resistance by area product at zero bias (R0 A) of boron-implanted n-on-p infrared photodiodes made in x≊0.20 Hg1−xCdxTe has been measured and characterized as a function of the implanted dose assuming a simple model of the junction. The R0 A product and its functional dependence in the different temperature ranges are found to be dependent on the implanted dose in n+p as-implanted abrupt junctions. The best performance diodes are found at the lowest implanted dose. The results indicate that there is an upper limit of the R0 A, in the range where the current is controlled by a minority-carrier diffusion mechanism, that is determined in n+p junctions by the p-side contribution. However, the indicated behavior of R0 A and its functional dependence at low temperatures supports the hypothesis defended by some workers in the literature indicating that the n-side contribution to the current-voltage characteristics may be important under some conditions, such as is the case when the current is controlled by conduction mechanisms through traps in the depletion region which are related to the heavily damaged n+ layer caused by the implantation process in this material.
Oxidation and formation mechanisms in disilicides: VSi2 and CrSi2, inert marker experiments and interpretation
Authors: Thomas O. , Stolt L. , Buaud P. , Poler J. C. , d’Heurle F. M.
Published: July 2002

The process of atomic transport in the silicide during oxidation of silicide layers formed on Si substrates has been analyzed by means of implanted inert markers. The results confirm that CrSi2 oxidizes via the diffusion of Cr atoms towards the Si substrate, and reveal that the same type of transport occurs in VSi2, which is in opposition to the growth of these disilicides that proceeds via Si motion. Moreover during the oxidation of both VSi2 and CrSi2, the diffusing metal atoms are accompanied by a large proportion of the Si atoms from the silicide which also diffuse towards the substrate. Thus, the experimental evidence now available reveals that all the silicon-rich silicides, in increasing atomic numbers from TiSi2 to NiSi2, oxidize with the formation of metal-free SiO2 in a process that involves the diffusion of both metal and Si regardless of the predominant moving species during silicide formation. In CrSi2, VSi2, as well as TiSi2, with similar structures, examination of the structure shows that diffusion should occur via a vacancy mechanism. The thermodynamic conditions that prevail during oxidation lead indifferently to metal diffusion in one direction or Si diffusion in the other. Any selection between one mechanism or the other has to be dictated by kinetic conditions relating to the relative mobilities of the two atomic species. What is known about this is discussed in detail. Finally it is proposed that the observed dual, parallel diffusion of metal and Si, results from the very nature of the oxidation process which modifies the chemical potential of the atoms at the surface being oxidized. Thus is created a force that drives some of the atoms away from the surface, into the inside of the samples. The best known example of this behavior is the often observed ‘‘injection’’ of interstitials during Si oxidation, but a similar process is at work in silicide oxidation, with somewhat similar results. Volume effects, thought to play an important role in solid state chemical reactions, are remarkably well illustrated by the oxidation of silicides.
Interimpurity transitions in heavily doped semiconductors
Authors: Park S. H. , Choe B. D.
Published: July 2002

We report on the first observation of theoretical predictions that, even in the case of a single acceptor level, the luminescence spectrum can have more than one peak depending on the temperature and pumping rate. Two peaks are observed: One peak (peak A) is related to the tail-impurity transition, and the other (peak B) to the band-impurity transition. The intensity of peak A is quenched at low and high temperatures, reaching its maximum value at about 30 K. At a high current and high temperature, peak B dominates and its energy increases with temperature.
Probe beam heating of AlGaAs single-quantum-well laser facets in Raman microprobe spectroscopy
Authors: Tang W. C. , Rosen H. J. , Buchmann P. , Vettiger P. , Webb D.
Published: July 2002

The facet temperature of AlGaAs single-quantum-well laser diodes were examined via Raman microprobe spectroscopy. The facets were fabricated either by cleaving in air or by chemically assisted ion-beam etching. The ridge width was 5 μm. Large sample-dependent variations in the heating induced by the argon probe beam are observed. These variations correlate with the appearance of disorder-induced modes in the Raman spectrum and the bias current-induced heating of the laser facet.