bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of PtSi-contacted p+n shallow junctions by BF+2 implantation and low-temperature furnace annealing
Authors: Tsui Bing-Yue , Tsai Jiunn-Yann , Chen Mao-Chieh
Published: July 2002

This work investigates the characteristics of PtSi-silicided p+n shallow junctions fabricated by implanting BF+2 ions into either the Pt/Si (ITM scheme) or the PtSi/Si (ITS scheme) structure followed by annealing in N2 furnace at temperatures from 650 to 800 °C. For a structure with Pt film of 30 nm thickness or PtSi film of 60 nm thickness, the implantation energy ranges from 40 to 80 keV with a dose ranging from 1×1015 to 1×1016 cm−2. For the ITS samples with BF+2 implantation at 40 keV, all ions are confined in the PtSi layer; therefore, only a modified Schottky junction is formed by the diffusion of boron atoms from the PtSi film during the annealing. The junction depth may be as shallow as 30 nm from the PtSi/Si interface. A complete p+n junction is formed for the ITM samples with implantation at 40 keV as well as all the samples implanted at 80 keV. The junction thus obtained has a forward ideality factor lower than 1.02 and a reverse current density less than 0.2 nA/cm2 at −5 V. Activation energy measurement indicates that most of the implantation damages have been recovered after annealing at a temperature as low as 700 °C. The reverse area and peripheral leakage current density are separated by measuring diodes of different perimeter/area ratio. For good samples, the reverse peripheral current comes from the surface generation current within the depletion region underneath the field oxide. All of the experimental results reveal that either Pt or PtSi film can be employed as an efficient barrier film in the ITM/ITS technique to form excellent and ultrashallow junctions with a low thermal budget.
Discharge tube breakdown voltages for alternating polarity pulses
Authors: Curzon F. L. , Mikoshiba S.
Published: July 2002

The breakdown voltage (VKB) of a cold cathode glass discharge tube, driven by negative voltage pulses, is greatly increased by charges which the pulses deposit on the inside walls of the tube. It is shown that VKB can be almost halved by neutralizing these negative wall charges with positive pulses of amplitude V+, applied to the tube electrodes. Explanations are given of the dependence of VKB on V+ and the implications for gas discharge display systems are also considered.
Synthesis and properties of superconducting Bi2Sr2CaCu2Oy films prepared by chemical diffusion
Authors: Ummat P. K. , Krause Thomas W. , Datars W. R.
Published: July 2002

Films of Bi2Sr2CaCu2Oy have been prepared by diffusing Bi2CaCu2O5 into Sr2CaCu2O5. Examination by x-ray diffraction and scanning electron microscopy showed a highly preferred orientation of columnar grains with the [100] axis normal to the surface. The maximum oriented texture was for a film thickness of 76 μm for thicknesses between 51 and 150 μm. The preferred orientation existed up to the surface of the sample, and there was no evidence of an unreacted region at the surface when the diffusion was done for at least 3 days. The films had the usual superconducting transition of the 2212 phase.
Photoluminescence excitation by band-gap optical absorption in chemical vapor deposition diamond films
Authors: Robins Lawrence H. , Tjossem Paul J. H. , Smyth Kermit C. , Barnes P. Yvonne , Farabaugh Edward N. , Feldman Albert
Published: July 2002

Photoluminescence excitation (PLE) spectra at photon energies near the indirect band gap of diamond have been obtained for diamond films grown by the filament-assisted chemical vapor deposition (CVD) method. The PLE intensity was observed to increase abruptly with photon energy above 5.5 eV. This increase coincides with the onset of phonon-emission-assisted interband absorption, which was observed independently by diffuse transmittance measurements. A lower-energy PLE threshold at ∼5.25 eV, which coincides approximately with the onset of phonon-absorption-assisted interband absorption, was observed in the spectrum of a gem-quality natural diamond, but not in the spectra of the CVD-grown films. Emission spectra of the luminescence excited by above-band-gap photons have features similar to luminescence spectra of the same specimens excited by 20-keV electrons. The spectrally integrated intensities of the luminescence excited by above-band-gap photons and by electrons were found to vary from specimen to specimen in a linearly related manner, suggesting that similar recombination processes occur in both cases.
Nonstationary laser-sustained plasma
Authors: Szymanski Z. , Filipkowski S.
Published: July 2002

Decay and recovery of laser-sustained argon plasma have been studied both experimentally and theoretically. Temperature distributions at various phases of the discharge were determined experimentally from the continuum emission coefficient. A quasi-two-dimensional cylindrical model has been employed to describe the observed plasma evolution. It was found that the model well described plasma evolution that was observed in the experiment.
Temperature dependence of scanning electron acoustic microscopy signal in MgO and SiC
Authors: Urchulutegui M. , Piqueras J.
Published: July 2002

The variation of the electron acoustic signal as a function of temperature in ceramic materials has been studied. Scanning electron acoustic microscopy (SEAM) contrast in MgO single crystals and in reaction bonded SiC, between 100 and 273 K, is discussed and compared. SEAM signal and contrast have been found to be temperature dependent in both materials as a consequence of the temperature dependence of several material parameters.
Anomalous misfit strain relaxation in ultrathin YBa2Cu3O7−δ epitaxial films
Authors: Kamigaki K. , Terauchi H. , Terashima T. , Bando Y. , Iijima K. , Yamamoto K. , Hirata K. , Hayashi K. , Nakagawa I. , Tomii Y.
Published: July 2002

Ultrathin YBa2Cu3O7−δ epitaxial films were successfully grown in situ on (001) SrTiO3 and MgO substrates by means of ozone-incorporating activated reactive evaporation. The x-ray-diffraction study was carefully examined to determine the structural properties of the grown films. Excellent crystallinity with no interfacial disorders was revealed by the appearance of the Laue oscillations. It was found that in a well lattice-matched YBa2Cu3O7−δ/SrTiO3 system, the crystallinity was deteriorated due to defect introduction at the critical layer thickness hc ( ∼ 130 Å). Interestingly, also in a poorly lattice-matched YBa2Cu3O7−δ/MgO system, excellent crystallinity was revealed even at above hc ( < 24 Å). This implies that an anomalous misfit relaxation process exists in the YBa2Cu3O7−δ/MgO system. In such a system, no crystal imperfection of the MgO substrate caused by defect introduction was elucidated by the grazing incidence x-ray scattering, which indicated that the MgO substrate did not contribute to the anomalous misfit relaxation. The anomalous growth manner was also found in YBa2Cu3O7−δ/MgO according to surface morphology investigations. Below 40 Å( ≳ hc), island nucleation growth was found. Above 40 Å, it was observed that an atomically smooth surface was obtained and the crystallinity was simultaneously improved. It is suggested that YBa2Cu3O7−δ possesses an anomalous misfit relaxation mechanism, and that especially in the growth on MgO, it couples with the characteristic growth behavior at the initial stage.
Relativistic electron-beam generation in a plasma-filled diode and its interaction with plasma
Authors: Rao G. Venugopala , Paithankar A. S. , Iyyengar S. K.
Published: July 2002

A relativistic electron beam of 150–300 keV, 1–2 kA, and 40–80 ns generated in a plasma-filled diode is injected into a magnetized hydrogen plasma of density 1011–1014 cm−3. Beam-plasma interaction was observed to be strong when the plasma density in the diode and interaction region was ≂1012 cm−3. The effective collision frequency was estimated to be around 10−2 times the ion plasma frequency. The plasma heating levels of ≂1016 eV cm−3 μs−1 were inferred. The observed net current multiplication was explained by two-stream instability.
Nonresonant third-order optical response of polyphenyl acetylene
Authors: Vijaya R. , Murti Y. V. G. S. , Prasada Rao T. A. , Sundararajan G.
Published: July 2002

Optical phase conjugation by degenerate four-wave mixing in samples of pristine and iodine-doped polyphenylacetylene at ruby laser wavelength (694.3 nm) is reported here. The nonresonant values of the third-order optical susceptibility χ(3) are determined from the measurements of reflectivity of phase conjugate signals.
Surface states and buried interface states studies in semiconductors by photothermal deflection spectroscopy
Authors: Zammit U. , Marinelli M. , Pizzoferrato R.
Published: July 2002

A method is presented which, through the simultaneous analysis of the photothermal deflection spectroscopy (PDS) signal amplitude and phase spectra, enables to detect surface states and buried interface states and to measure their absorption. A theoretical model for the PDS signal suitable for the present approach has been developed and the measurements were performed on single crystalline GaAs wafers with ion-implanted layers on the front surface or buried beneath the front surface.
Kinetic study of metalorganic molecular beam epitaxy of GaP, InP, and GaxIn1−xP
Authors: Garcia J. Ch. , Maurel Ph. , Bove Ph. , Hirtz J. P.
Published: July 2002

The growth rates of GaP and InP deposited by metalorganic molecular beam epitaxy using triethylgallium, trimethylindium, and precracked phosphine have been studied by reflection high energy electron diffraction and related to composition variations of the ternary alloy GaxIn1−xP. The influence of the substrate temperature and phosphine flow rate have been investigated for each material. The GaP growth rate dependence with temperature exhibits qualitatively the same behavior as already reported for the growth of GaAs by metalorganic molecular beam epitaxy. In the case of InP, a constant growth rate is observed in the temperature range of 450–500 °C. At higher temperatures, a strong decrease of the growth rate, attributed to the desorption of dimethylindium species, is measured. Meanwhile, the GaxIn1−xP composition is found to become Ga rich while increasing temperature. Furthermore, it is found to significantly depend on the phosphine flow rate at a fixed temperature. In the low phosphine flow regime, the composition is associated with the preferential formation of GaP bonds, and in the high phosphine flow regime, the composition is closely correlated with the sharp decrease observed for the binary InP growth rate.
Photoreflectance studies of silicon films on sapphire
Authors: Giordana Adriana , Glosser R.
Published: July 2002

We present the results from the photoreflectance (PR) analysis of a set of molecular-beam epitaxially grown silicon on sapphire films whose thicknesses ranged from 6 to 4000 nm. The strain undergone by the silicon films due to lattice mismatch at the silicon sapphire interface and to the difference in the thermal expansion coefficient of the two materials was investigated. To this purpose the position of the 3.4-eV PR structure was monitored with bulk silicon as a standard. A shift of this structure toward lower energies was observed in the thinnest films. A drastic increase in elasticity is observed as the film thickness varies from 550 to 700 nm. This fact can be correlated with transmission electron microscope observations of the predominant defects in the films. Special attention was also devoted to the effects of native oxide on the films, that appeared to cause a shift of the 3.4 eV structure toward higher energies. This shift suggests that the native oxide layer is exerting a compressive strain on the silicon films.
Organoarsine pyrolysis mechanisms and their influence on GaAs epilayer purity
Authors: Speckman D. M. , Wendt J. P.
Published: July 2002

Thermal decomposition mechanisms have been inferred for a series of organoarsine chemical vapor deposition precursors, and this data has been correlated with the quality of GaAs films grown from these reagents. Tri-, di-, and mono-ethylarsine, as well as a mixture of triethylarsenic and arsine, were pyrolyzed under pseudogrowth conditions, and their decomposition mechanisms were inferred from a qualitative and quantitative analysis of the reaction mixture components. The primary decomposition step for the ethylarsines appears to be a thermally induced, arsenic-carbon bond homolysis to produce both an ethyl radical and an alkyl and/or hydride substituted arsenic radical species. For a mixture consisting of arsine and triethylarsenic, it appears that the triethylarsenic reagent undergoes arsenic-carbon bond homolysis, and the radicals thus produced enhance the decomposition of the arsine coreagent. The more highly substituted ethylarsine reagents were found to generate the greatest number of alkyl-substituted arsenic radicals upon decomposition, and also produced the least pure GaAs films. Since alkylarsenic radicals can react with a growing GaAs epilayer to cause severe carbon contamination, this decomposition data is consistent with the observed growth results. In the coreagent mixture, the free-radical activation of arsine results in a large production of dihydridoarsenic radicals, which is consistent with the high-purity, low-carbon films produced from this reagent mixture. These results indicate that any viable organoarsenic precursor must decompose preferentially to produce hydrido-arsenic radical intermediates, in order to produce high-purity GaAs epilayers.
Synthesis of superconducting La2−xSrxCaCu2O6 using O2-hot-isostatic-pressing techniques
Authors: Sakurai Takeshi , Yamashita Toru , Yamauchi H. , Tanaka Shoji
Published: July 2002

Superconducting 326 samples, La2−xSrxCaCu2Oz with x=0.2 and 0.4, which exhibited superconducting onsets at temperatures (Tonc’s) higher than 40 K were successfully synthesized using hot-isostatic-pressing (HIP) techniques. As starting materials, powders of conventional carbonates (SrCO3 and CaCO3) and oxides (La2O3 and CuO) were employed. Sintering of the samples was made at a variety of temperatures (Ts) for 72 h in flowing O2 gas (of 1 atm). The sintered samples were post-annealed at various temperatures (Ta) for 6 h in a mixture of 80% Ar gas and 20% O2 gas of the total pressure of 1000 atm by means of HIP techniques. Optimum combinations of Ts and Ta were determined for obtaining superconducting samples. Single-phase samples were obtained only for the composition La1.8Sr0.2CaCu2Oz for which the oxygen content, z, was determined to be 6.01±0.01 by coulometric titration. It was concluded that Ta was a crucially important factor for obtaining superconducting 326 phase with Tonc ≳ 40 K, that is, Ta ≳ 970 °C was required (for 6-h HIP annealing). It was demonstrated that a long HIP annealing was necessary to obtain a significant volume fraction for the superconducting 326 phase.
Elimination of DX centerlike behavior of donors in heavily doped GaAs
Authors: Suski T. , Wisniewski P. , Skierbiszewski C. , Dmowski L. H. , van der Wel P. J. , Singleton J. , Giling L. J. , Harris J. J.
Published: July 2002

The pressure dependencies of the electrical conductivity, Hall coefficient, and Shubnikov-de-Haas effect have been studied for n-GaAs heavily doped with Sn and Te. The results demonstrate that the energy level related to the DX centers formed by these donors is resonant and degenerate with the conduction band of GaAs. The energy separation of the GaAs conduction-band minimum and the DX center (EDX) for the Sn donor has been found to be similar to those of the Si- and S-related DX centers (around 0.3 eV at T≊100 K), whereas EDX(Te) is much greater, at around 0.55 eV. An analysis of the sample recovery after pressure-induced freezeout of electrons onto the DX centers has enabled the energy barrier for electron emission from the Sn-related DX center to the conduction band and the barrier for electron capture by the DX center, the inverse process, to be determined. Both energy barriers are very small compared to those associated with Si- and S-donor-induced DX centers. The values for EDX (for Sn and Te) and the barrier sizes (for Sn) measured in this work for donors in GaAs are found to be rather different than the equivalent energies in (Ga,Al)As, and this difference is interpreted as evidence that the local vicinity of the DX center (Ga only or Al/Ga) strongly influences its properties. Finally, these results have led to the proposal of Te as the most effective dopant from the point of view of elimination of the DX centerlike properties of donors in heavily doped GaAs.
Effects of oxygen on diamond growth using platinum substrates
Authors: Belton David N. , Schmieg Steven J.
Published: July 2002

The effect of gas phase oxygen on chemical vapor deposition diamond growth on Pt substrates was studied using x-ray photoelectron spectroscopy (XPS). Samples were transferred between the diamond growth chamber and an attached ultrahigh vacuum analysis chamber without exposure to air. The time-dependent evolution of surface carbon species was monitored by interrupting growth at specific times and analyzing the surface with XPS. In this paper we compare samples prepared from four different mixtures of H2/CH4/O2. With low gas phase O/C ratios (≤0.5) diamond growth on Pt proceeds by a three-step mechanism: (1) decomposition of surface contaminants to form graphitic carbon, (2) conversion of these graphitic species to stable hydrocarbon species, (3) replacement of hydrocarbons with diamond. At higher gas phase O/C ratios (≥0.75) we observed that the Pt surface had less than 1 ML of carbon. In other words, the surface was very clean, and diamond growth did not occur at a measurable rate. However, once diamond is nucleated on the surface under conditions of low oxygen concentration, diamond growth proceeds readily using a high oxygen feed with O/C=1. We conclude that the addition of oxygen affects diamond formation primarily by decreasing the nucleation rate on metals like Pt. Growth rates of existing diamond films are not strongly affected by oxygen.
Chamber material effects on actinometric measurements in rf glow discharges
Authors: Cotler Tina J. , Passow Michael L. , Fournier Jeffrey P. , Brake Mary L. , Elta Michael E.
Published: July 2002

The relative concentration of atomic fluroine was measured in a CF4 rf glow discharge using the actinometric technique. The dependence of fluorine concentration on power, pressure and flow are presented and shown to be dependent upon reactor wall material and electrode material.
Dilute tritides of Nb and Ta: A resistivity study of the aging behavior
Authors: Schober T. , Condon J. B. , Trinkaus H.
Published: July 2002

The changes in resistivity for niobium and tantalum wires, which had been loaded with 5.37% (atom ratio) and 6.24% tritium respectively, was measured over a 1-year period. After an initial rapid increase corresponding to roughly 5 μΩ m for He interstitials, the resistivity reached a local maximum. It then continued to increase at a rate expected for the development of insulating He bubbles and material swelling. The local maximum corresponds to the point at which active acoustic emission is taking place and is indicative of dislocation loop punching at the bubbles. The stabilization of the resistivity after this local maximum is thought to be due to the general lattice relaxation and the formation of a complex and well-developed dislocation network.
Conditions for oriented growth of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O films by pulsed laser ablation
Authors: Krebs H. -U. , Kehlenbeck M. , Steins M. , Kupcik V.
Published: July 2002

Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O films have been grown in situ on amorphous SiO2 by excimer laser ablation in order to study the growth and orientation of the perovskite structures and to compare it with the epitaxial growth on single-crystalline SrTiO3. Under fixed experimental conditions optimum combinations of the oxygen partial pressure and substrate temperature for the deposition of c-axis oriented films were determined. The results on the morphology and orientation of the grains, which influence the superconducting properties, are discussed with respect to thermodynamic data available for the 123 phase and kinetic constraints. While superconducting transitions Tc of 90 K and critical current densities of about 3×106 A/cm2 at 77 K are obtained on SrTiO3, the values are reduced to about 84 K and 104 A/cm2 on SiO2, respectively, due to the diffusion of Si into the film and the different microstructure.
Hall effect in Bi-Sr-Ca-Cu-O thin films
Authors: Viret M. , Donnelly K. , Lunney J. G. , Coey J. M. D.
Published: July 2002

Resistivity and Hall effect are measured in the a-b plane for thin films of Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10 superconductors prepared by laser ablation deposition. The Hall coefficient shows a maximum at 150 K for both compounds which could be associated with bipolaron formation.
Preparation and grain boundary chemistry of dense polycrystalline YBa2Cu4O∼8
Authors: Williams R. K. , Brynestad J. , Henson T. J. , Kroeger D. M. , Marsh G. C. , Padgett R. A. , Scarbrough J. O.
Published: July 2002

Dense polycrystalline samples of the compound YBa2Cu4O∼8, Y124, were prepared by a three-step procedure. In the first step a mixture of Y2O3, CuO and BaO2 was reacted at 960 °C under an oxygen pressure of 55 bar. The compound did not sinter under these conditions but electrical resistivity and susceptibility measurements showed that the oxide mixture converted to Y124. In the second step densification was produced by hot isostatic pressing at 875 °C. This degraded the superconducting properties severely and a final high-temperature anneal in pressurized oxygen was required to restore optimum properties. This anneal consisted of a one hour hold at 1010 °C in 40-bar O2 followed by a 24-h anneal at 950 °C in 55-bar O2. After this treatment the samples were ∼90% dense, phase pure Y124. The maximum grain dimensions were about 10 μm, and Auger spectroscopy data were obtained on a fracture surface. These data showed that the grain boundary composition does not differ significantly from the bulk values.
Superconducting YBaCuO thin films by Cu-ion implantation
Authors: Hubbard Kevin M. , Bordes Nicole , Nastasi Michael , Tesmer Joseph R.
Published: July 2002

We have investigated the fabrication of thin-film superconductors by Cu-ion implantation into initially Cu-deficient Y(BaF2)Cu thin films. The precursor films were co-evaporated on SrTiO3 substrates, and subsequently implanted to various doses with 400 keV 63Cu2+. Implantations were performed at both LN2 temperature, and at 380 °C. The films were post-annealed in oxygen, and characterized as a function of dose by four-point probe analysis, x-ray diffraction, ion-beam backscattering and channeling, and scanning electron microscopy. It was found that a significant improvement in film quality could be achieved by heating the films to 380 °C during the implantation. The best films made became fully superconducting at 60–70 K, and exhibited good metallic R vs T behavior in the normal state.
Electric dipole effects in magnetic crystals
Authors: Graham E. B. , Raab R. E.
Published: July 2002

A consistent multipole theory which is able to describe optical phenomena to any selected multipole order is applied to nonabsorbing magnetic crystals in the electric dipole approximation. Magnetic effects are shown to depend on an antisymmetric polar tensor of rank 2, and the magnetic point groups for which such a tensor may exist are listed. In addition to yielding certain known results the theory also predicts a new effect, namely that when a monochromatic plane light wave propagates along a crystallographic axis perpendicular to the magnetization in a ferromagnet, the Poynting vector of the so-called extraordinary ray does not coincide with the wave normal. An estimate of the angular deviation in EuSe suggests that the effect should be observable.
Thermostimulated impurity conduction in characterization of electrodeposited Cu2O films
Authors: Rakhshani A. E.
Published: July 2002

Electrodeposited films of cuprous oxide show high resistivities in the range of 109–1012 Ω cm. The p-type conductivity, its temperature dependence, and its thermostimulated characteristics can be explained by assuming that a pair of deep levels (acceptor and donor type) control the electrical properties of these films. A novel thermostimulated conductivity model is introduced to include the effect of impurity conduction. Impurity conduction through the acceptor-type level is the dominant transport mechanism at temperatures below approximately 200 K. The experimental results on thermostimulated conductivity measurements reveal the effect of Poole–Frenkel lowering of the ionization energy of the acceptor-type deep level. For a typical sample the zero-field ionization energy of this level is 0.792 eV. Having a concentration of 5×1013 cm−3 and a hole capture cross section of 3.12×10−9 cm2, this level is compensated with a donor-type level of unknown ionization energy having a concentration of 1.89×1013 cm−3. Impurity conduction in this sample shows an activation energy of 0.03 eV before and 0.08 eV after a sample is illuminated at 77 K. From the measurement of the Poole–Frenkel constant the electron affinity of the film is obtained to be 2.9 eV.
Phase formation in ion-irradiated and annealed Ni-rich Ni-Al thin films
Authors: Alexander Dale E. , Was Gary S. , Rehn L. E.
Published: July 2002

Phase formation was studied in ion-irradiated multilayer and coevaporated Ni-20 at. % Al films supported by Cu, Mo, and Ni transmission electron microscopy (TEM) grids. Irradiation with either 700-keV Xe or 1.7-MeV Xe, to doses sufficient to homogenize the multilayers (≥7.5×1015 cm−2), resulted in the formation of metastable supersaturated γ and HCP phases in both film types. Post-irradiation annealing of multilayers at 450 °C for 1 h transformed the metastable phases to a two-phase γ+γ′ microstructure. In the absence of Cu, the formation of γ′ appeared to proceed by a traditional diffusional growth mechanism, resulting in small (<50 Å) γ′ precipitates in γ matrix grains. The presence of Cu caused the formation of a dual-phase γ+γ′ structure (i.e., distinct, equal-sized grains of γ and γ′) during post-irradiation annealing. It is suggested that copper affected the nucleation of γ′ precipitates and increased the kinetics of growth resulting in the dual-phase morphology. Strong irradiation-induced textures were observed in the multilayers that were less pronounced in the coevaporated films. The texture in the multilayers was attributed to the presence of a slight as-evaporated texture combined with the enhanced atomic mobility due to the heat-of-mixing released during irradiation. The irradiation-induced texture appeared to be necessary for the formation of the dual-phase structure since it likely provided high-diffusivity paths for Cu to diffuse into the film from the TEM grid.
Photovolatilization of thin polysilane films detected by surface-plasmon spectroscopy
Authors: Sawodny Michael , Stumpe Joachim , Knoll Wolfgang
Published: July 2002

Surface-plasmon optical techniques (attenuated total internal reflection and surface plasmon microscopy, in particular) are employed to characterize the optical and structural properties of thin films of poly(methyl-phenyl-silane) in the thickness range d0=40–400 nm. Irradiation with deep UV light (90% at λ=253.7 nm) is shown to cause photovolatilization which results in a self-development of illuminated areas. The time dependence of this etching process is investigated, and substantial differences between irradiation in air or in an Ar atmosphere of 10−3 MPa partial pressure are found: For 40-nm-thick films in the presence of oxygen an ablation rate of 1.3 nm/min is derived for the first 5–10 min which drops rather abruptly to zero (irradiation power density ∼0.4 mW/cm2 ). In Ar atmosphere the etching rate is ∼0.1 nm/min but constant for more than 1 h. UV-absorption spectra and gel permeation chromatography are performed to gain some insight into the molecular mechanisms of these photochemical and photophysical differences which are of great importance for the photolithographic application of these materials.
Epitaxial growth of graphite layer on {111} surface of vapor-deposited diamond
Authors: Kurihara Noriko Iwasaki , Hirabayashi Keiji , Suzuki Kunio , Ichihara Masaki , Takeuchi Shin
Published: July 2002

The epitaxial growth of graphite layer on {111} surface of vapor-deposited diamond has been found by observations of diffraction patterns and high resolution lattice images. While the lattice spacing in the ab plane of the epitaxial graphite is the same as that of bulk graphite, the lattice spacing in the c direction is in the range of 0.33–0.42 nm depending on the thickness of the graphite layer. This is the first experimental evidence for the generation of graphite on the {111} surface of vapor-deposited diamond proposed by Frenklach and Spear [J. Mater. Res. 3, 133 (1988)].
Bulk and surface components of recombination lifetime based on a two-laser microwave reflection technique
Authors: Buczkowski A. , Radzimski Z. J. , Rozgonyi G. A. , Shimura F.
Published: July 2002

An algorithm for separating the bulk and surface components of recombination lifetime, tailored for contactless measurement techniques with laser excitation, is presented in the paper. In order to analyze the carrier decays and subtract the surface recombination term, two lasers operating at 910 and 830 nm are applied. A separation of carrier decay resulting from the different contribution of surface and bulk components due to difference in the light absorption is observed for such a case. This separation is a function of surface recombination velocity S. An experimental verification of the analysis is presented using microwave absorption/reflection measurements.
Characterization of Y-Ba-Cu-O thin films using their nonlinear magnetic response
Authors: Shaulov A. , Bhargava R. , Shatz S.
Published: July 2002

Measurement of the third harmonic component in the ac magnetic response was used to investigate the multiphase nature of Y-Ba-Cu-O thin films grown epitaxially on single-crystal wafers of SrTiO3. Films prepared by electron beam evaporation and by activated reactive evaporation techniques exhibit several peaks in the harmonic amplitude versus temperature, indicating multiple phase transitions. The film prepared by laser ablation technique exhibits a sharp single peak, indicating a single phase transition. These results, corroborated by x-ray diffraction and x-ray photoelectron spectroscopy, demonstrate the usefulness of third harmonic measurements in characterizing thin-film samples.
Conduction and scattering mechanisms in potential modulated inversion layers
Authors: Almaggoussi A. , Sicart J. , Robert J. L. , Vincent G.
Published: July 2002

A quantitative approach to the polycrystalline semiconductor model using an original e-beam irradiation method is proposed. The e-beam was scanned along lines parallel and perpendicular to the drain-source direction in a metal-oxide-semiconductor field-effect transistor (MOSFET) structure. Consequently, the electrostatic surface potential ψs was periodically modulated and appeared similar to that of a polycrystalline semiconductor. The threshold voltage shift, effective and field-effect mobilities were measured as a function of both the irradiation period and dose. Conductivity and Hall effect measurements were performed between 4 and 400 K and a two-mobility conduction model is proposed to interpret the dependence of the carrier concentration and Hall mobility on temperature. Potential modulation scattering and screening mechanisms were studied by varying the gate voltage. The results are compared with those obtained in polysilicon thin layers and polysilicon MOSFETs.
Influence of the sample geometry on critical current density of high T
c granular superconductors
Authors: D’Ovidio Claudio A. , Fiscina Jorge E. , Esparza Daniel A.
Published: July 2002

I-V characteristics of a polycrystalline Y-Ba-Cu-O sample of rectangular cross section were measured while varying the specimen thickness by successive polishings. The critical current density (Jc) was found to increase with the reduction of the sample thickness (e). A model based on junctions decoupling due to the self-magnetic field generated by the transport current is proposed to explain our results. For this particular geometry and assuming a uniform current distribution along the sample, the magnetic field distribution inside the sample was calculated. From this, an expression for Jc as a function of e was derived which is in good agreement with the experimental results. From the measured values, the value of the decoupling field obtained was of 4.47 Oe.
The use of triisopropylantimony for the growth of InSb and GaSb
Authors: Chen C. H. , Fang Z. M. , Stringfellow G. B. , Gedridge R. W.
Published: July 2002

A newly developed Sb source, triisopropylantimony (TIPSb), has been successfully used to grow InSb and GaSb epilayers by atmospheric pressure organometallic vapor phase epitaxy (OMVPE). Both GaSb and InSb have been grown with excellent morphologies. Growth efficiencies indicate that there are no parasitic reactions between TIPSb and trimethylgallium (TMGa) or trimethylindium. For GaSb growth, the temperatures have been varied between 500 and 600 °C. V/III ratios close to unity are necessary to obtain the best morphologies at 600 °C. As the growth temperature is decreased, lower V/III ratios are required. This is because TMGa decomposition is incomplete and TIPSb decomposes completely at these temperatures. The GaSb layers grown at 500 °C have background hole concentrations of 2×1016 cm−3. Low-temperature photoluminescence (PL) measurements indicate that the acceptor is due to Sb vacancies rather than carbon acceptors. A major advantage of TIPSb is that it decomposes at temperatures much lower than that for trimethylantimony (TMSb). InSb with good morphologies can be grown using V/III ratios close to unity at temperatures as low as 430 °C. On the other hand, growth temperatures higher than 500 °C are necessary for the growth of InSb using TMSb with V/III ratios of close to 1. For temperatures lower than 430 °C, InSb can be grown using TIPSb, but higher V/III ratios are required due to incomplete TIPSb pyrolysis. The InSb epilayers have electron concentrations of about 5×1016 cm−3 at 77 K and low-temperature PL shows well-resolved exciton and acceptor-related peaks. These results indicate that TIPSb is a viable source for the OMVPE growth of Sb-containing III-V semiconductors.
Hyperfine field distributions and transverse spin freezing in iron-rich amorphous Fe-Zr alloys
Authors: Ryan D. H. , Ren Hong
Published: July 2002

In order to settle the question of homogeneous versus inhomogeneous ordering in amorphous Fe-Zr alloys, we have obtained Mössbauer spectra with well-defined magnetic texture and without line overlap by subtracting spectra measured with and without a small polarizing field. These spectra allow us to show that P(Bhf) has no bimodal structure at any temperature, and there is no paramagnetic component in the spectra above Txy. We therefore rule out the possibility that magnetically isolated clusters or precipitates play a role in the ordering. We also present high-field spectra which show homogeneous transverse-spin freezing at ∼28 K in a-Fe90Zr10.
An analysis of charge states for local vibrational modes by oxygen defects in semi-insulating GaAs
Authors: Zhong Xue-Fu , Jiang De-Sheng , Song Chun-Ying
Published: July 2002

The high-resolution spectral measurements for new local vibrational modes near 714 cm−1 due to the oxygen defect in semi-insulating GaAs are analyzed on the basis of a model calculation by self-consistent bond orbital approach. Two charge states of oxygen atom with 1 and 2 extra electrons are assigned to be responsible for these local modes. The observed frequencies are explained by the properties of Ga—O−1 and Ga—O−2 bonds and the calculated cohesive energy indicates that the O−2 state is stable. The results are in good agreement with the kinetic analysis
X-ray-diffraction characterization of silicon-on-insulator films
Authors: Thompson L. R. , Collins G. J. , Doyle B. L. , Knapp J. A.
Published: July 2002

Silicon-on-insulator layers produced by the processes of oxygen implantation into single-crystal silicon substrates, zone melt recrystallization of deposited polysilicon films, and silicon epitaxy on sapphire substrates have been examined by an improved x-ray-diffraction technique. The technique incorporates a position-sensitive x-ray detector placed on the 2θ arm of a conventional double-crystal diffractometer, thus allowing the measurement of scattered x-ray intensity in both the incident and diffracted x-ray beam angles simultaneously. X-ray scattering intensity maps plotted in k space reveal the relative strain and mosaic spread of the silicon overlayers with respect to the (001) silicon substrates. Oxygen-implanted films and graphite strip recrystallized films exhibit mosaic spreads (<±0.08° and ±0.05°, respectively) approaching that of bulk single-crystal Si. The electron-beam-recrystallized films exhibit significantly larger mosaic spreads (≊±0.52°). These silicon overlayer films all exhibit similar perpendicular strain values with an average of approximately 0.08%. Silicon layers produced by both zone melt recrystallization techniques contain a preferential tilt of the diffraction planes along the recrystallization scan direction with respect to the underlying (001)-oriented silicon substrate. Silicon-on-sapphire samples exhibit both a large mosaic spread (±0.18°) and a large perpendicular strain (0.13%). These x-ray results are consistent with crystalline data taken by backscattered electron images and Rutherford ion backscattering.
Effect of Nd3+ concentration on the emission spectra of CaF2:Nd layers grown by molecular-beam epitaxy
Authors: Bausá L. E. , Legros R. , Muñoz-Yagüe A.
Published: July 2002

Nd3+-doped CaF2 monocrystalline films have been grown by molecular-beam epitaxy using CaF2 and NdF3 evaporation on CaF2 (100) substrates. Auger electron spectrometry and high-energy electron diffraction have been used as in situ techniques to characterize the grown layers. No degradation of crystallinity was observed even for the highest levels of doping considered. The effect of Nd3+ concentration is studied by means of the photoluminescence signal of Nd3+ ions. The results can be compared favorably with those of bulk CaF2:Nd crystals. For a given Nd3+ concentration a lower quantity of Nd3+ aggregate centers is observed. Nd3+ ions can, therefore, be efficiently incorporated in isolated Nd3+-F− centers up to concentrations of 3.7 wt % Nd3+ without emission quenching of the associated line at 1.0457 μm. The results are related to the thermodynamic conditions imposed by the molecular-beam epitaxy technique.
An investigation of the effects of doping profile variations on AlGaAs/GaAs high electron mobility transistor performance
Authors: Tian H. , Kim K. W. , Littlejohn M. A.
Published: July 2002

We present results from a theoretical study of the influence of doping profile variations on the performance of delta-doped AlGaAs/GaAs high electron mobility transistors (HEMTs). An ensemble Monte Carlo simulation coupled with a self-consistent solution of the two-dimensional Poisson equation is used to investigate HEMTs which employ both single and double delta-doped profiles with varying doping configurations. The calculated results reveal that single delta-doped HEMTs designed with identical threshold voltages exhibit improved device behavior when thinner delta-doped layers with more heavily doped concentrations are utilized. For double delta-doped HEMTs with an identical total doping in the AlGaAs layer, improved threshold voltage control is obtained as the spacing between two delta-doped layers increases. However, this increase in spacing also causes a degradation in transconductance, cut-off frequency, and switching time. As gate bias increases, the dependence of device performance (or degradation) on the spacing between doping planes becomes less pronounced due to the upward shift in threshold or ‘‘onset’’ of parallel conduction in the AlGaAs layer.
Interactions between superconducting YBa2Cu3O7−x and silicon using different buffer layers
Authors: Jia Q. X. , Jiao K. L. , Anderson W. A.
Published: July 2002

Superconducting YBa2Cu3O7−x (YBCO) thin films were deposited on Si substrates using rf magnetron sputtering from a stoichiometric YBa2Cu3O7−x target. Either metallic RuO2 or insulating yttria-stabilized zirconia (YSZ) was used as a buffer layer to nucleate the superconducting film, and also to prevent interactions between Si and YBCO. The electrical properties of the Si were studied using deep level transient spectroscopy on a structure of metal/SiO2 (∼15 Å)/Si diode after removing YBCO and the buffer layer. The introduction of a new deep level in the Si at EA = Ev + 0.244 eV after YBCO deposition, where YSZ (∼100 nm) was used as a buffer layer, was attributed to Cu after interaction between YBCO and Si. However, this energy level was not found in the Si if RuO2 was used as a buffer. The degradation of electrical properties of the Si after YBCO deposition places limitations on the choice of buffer layers in order to realize the integration between superconductor and semiconductor as used in passive or hybrid electronic devices.
Effects of grain size, Cu addition, and Nd substitution for Pr on intrinsic coercivity in cast–hot-pressed Pr-Fe-B magnets
Authors: Chen Zhongmin , Xie Faqin , Shi Zhengxing , Wang Leyi , Fu Hengzhi
Published: July 2002

The coercivity of anisotropic cast–hot-pressed Pr19Fe74.5B5Cu1.5 magnets is investigated. The microstructure features and virgin magnetization curve reveal a nucleation-controlled coercivity mechanism. Regression analysis shows that the intrinsic coercivity varies inversely as the logarithm of the average grain size: iHc(kOe) = 21.7550 − 6.0517 ln d (μm), which is in good agreement with the nucleation statistical model. Investigation of Cu addition and Nd substitution shows that Cu mainly plays a role of suppressing grain growth during the final annealing. Higher coercivity is thus obtained with Cu addition. Nd19Fe74.5B5Cu1.5 magnets exhibit a much lower coercivity due to their coarse-grained cast structure.
Optical band gap of the ternary semiconductor Si1−x−yGexCy
Authors: Soref Richard A.
Published: July 2002

Single-crystal alloys of diamond with Si and Ge are investigated theoretically. An indirect band gap Γv25′ → Δc1 is found for the new semiconductor Si1−x−yGexCy over most compositions x and y, with an indirect Γv25′ → Lc1 gap found for the remaining compositions. The estimated band gaps span the 0.62–5.5-eV-range. Predictions are made for band gap versus lattice parameter in the new alloy semiconductors Si1−xCx and Ge1−xCx.
Metalorganic chemical vapor deposition on mesoscopic-structured substrates with closed topologies
Authors: Ishibashi Akira , Ogawa Masamichi , Funato Kenji , Ugajin Ryuichi , Mori Yoshifumi
Published: July 2002

We have performed metalorganic chemical vapor deposition (MOCVD) on substrates of closed topologies, i.e., on a single cylindrical surface and on multiple cylindrical surfaces of ∼1000-Å-diam rods. The side geometry of epitaxial growth can be controlled by rod direction, growth temperature, and ratio of the amount of group-V material to that of group-III materials. We have succeeded in growing mesoscopic multiply connected AlAs with multiplicity up to 6. The MOCVD growth on substrates with closed topology is of potential interest for fabrication of sophisticated mesoscopic structures.
Characteristics of periodically domain-inverted LiNbO3 and LiTaO3 waveguides for second harmonic generation
Authors: Yamamoto Kazuhisa , Mizuuchi Kiminori , Takeshige Kunihiko , Sasai Yoichi , Taniuchi Tetsuo
Published: July 2002

Characteristics of waveguides with periodically domain-inverted regions in LiNbO3 and LiTaO3 for quasi-phase-matched (QPM) second harmonic generation are investigated. The domain-inverted regions in LiNbO3 are formed by heat treatment using selective SiO2 mask and those in LiTaO3 are formed by heat treatment using selective proton exchange. The domain-inverted region in LiTaO3 is fabricated up to 2.7 μm depth, which is twice as deep as that in LiNbO3. The channel waveguides incorporating the regions are fabricated using proton exchange by pyrophosphoric acid. The propagation loss (0.9 dB/cm) of LiTaO3 waveguide is much lower than that of LiNbO3 waveguide (2.9 dB/cm). The second harmonic power generated in LiTaO3 waveguide by third-order QPM consequently has three time higher conversion efficiency, compared to that in LiNbO3 waveguide. In domain-inverted LiNbO3 waveguide, we have observed optical damage. On the other hand, in domain-inverted LiTaO3 waveguide, stable blue light (421 nm) has been obtained without optical damage.
Electric field and conduction current in ac thin-film electroluminescent display devices
Authors: Singh Vijay P. , Krishna Srinivas , Morton David C.
Published: July 2002

Current flow through the phosphor layer of ac thin film electroluminescent display devices has been analyzed. It is shown that the traditional capacitive bridge technique for measuring the time dependence of phosphor conduction current [iLP(t)] can yield inaccurate results, especially when the multiplication factor of [(CI + Cp)/CI] is not used, and the phosphor layer has bulk space charge; CI and Cp are insulator and phosphor layer capacitances, respectively. A new method for the measurement of iLP(t) has been developed. It is more accurate and is applicable even when the bulk charge in the phosphor layer is not negligible. The new method was applied to the study of ZnS:Mn ac thin-film electroluminescent (ACTFEL) devices excited by voltage pulses of three different slew rates. iLP(t) measured by the new method was compared against the bridge current (ibridge). Electric field and displacement current in the phosphor were calculated. Transferred charge computed by integrating iLP and ibridge over half cycle was compared against the polarization charge obtained from the Q–V curve of the device.
Transmission electron microscopy study of N+-implanted silicon on insulator by energy-filtered imaging
Authors: Duan X. F. , Du A. Y. , Chu Y. M.
Published: July 2002

We report on the first study of N+-implanted silicon on insulator by energy-filtered imaging using an Opton electron microscope CEM 902 equipped Castaing–Henry electron optical system as a spectrometer. The inelastic images, energy window set at ΔE=16 eV and ΔE=25 eV according to plasmon energy loss of crystal Si and of silicon nitride respectively, give much structure information. The interface between the top silicon layer and the upper silicon nitride layer can be separated into two sublayers.
Analysis of ion-implanted amorphous and polycrystalline silicon films as diffusion sources for ultrashallow junctions
Authors: Park Keunhyung , Batra Shubneesh , Banerjee Sanjay , Lux Gayle , Smith T. C.
Published: July 2002

This paper discusses the diffusion of As, P, and B in amorphous and polycrystalline silicon-on-single-crystal silicon systems during rapid thermal annealing and furnace annealing. It is found that the changes of microstructure during annealing play a major role in determining the diffusion profiles in the substrate as well as in the polycrystalline silicon layer. For As or P doping, a drive-in diffusion results in a much larger grain microstructure for as-deposited amorphous silicon than for as-deposited polycrystalline silicon, which leads to the formation of shallower junctions in the substrate for the first case. For B doping, there is little difference in the final microstructure and junction depth between the two cases. At high anneal temperatures, the native interfacial oxide breaks up, causing epitaxial realignment of the polycrystalline silicon film and subsequent enhanced diffusion in the substrate.