bluuebunny/crossref_metadata_2025 huggingface dataset:
Origins of reverse bias leakage currents in hydrogenated amorphous silicon p-i-n detector structures
Authors: Arch J. K. , Fonash S. J.
Published: July 2002

The transport-simulation computer program amps has been used to explore the origin and behavior of dark leakage currents in hydrogenated amorphous silicon p-i-n detector structures. A comparison of simulated and experimental data reveals that the experimentally observed voltage dependence of the reverse bias current-voltage characteristics can be explained by a varying defect density through the i layer, due either to dopant permeation or to Fermi-level-driven defect densities, as well as by the previously suggested field-enhanced generation. amps simulations indicate that the dependence of these reverse leakage currents on i-layer thickness would be useful in determining the relative importance of each possible mechanism.
Selective Si epitaxial growth by plasma-enhanced chemical vapor deposition at very low temperature
Authors: Baert K. , Deschepper P. , Poortmans J. , Nijs J. , Mertens R.
Published: July 2002

A rf-plasma chemical vapor deposition process for selective epitaxial Si growth from SiH4 and SiF4 at a deposition temperature of 300–400 °C is described. Selective epitaxial growth is obtained as a balance of deposition precursors versus etching by F species. Also, the results indicate that a high H-surface coverage is not essential to deposit crystalline Si films by very low temperature rf-plasma chemical vapor deposition. P-doped films with a mobility of 80 cm2/V s and a carrier concentration of 3×1018 cm−3 are reported.
Single-step implant isolation of p+-InP with 5-MeV O ions
Authors: Ridgway M. C. , Jagadish C. , Elliman R. G. , Hauser N.
Published: July 2002

The applicability of a single, 5-MeV O implant for electrical isolation of epitaxial p+-InP layers on semi-insulating InP substrates has been investigated. For such an implant, the ion range is several times that of the epitaxial layer and, consequently, end-of-range disorder is buried deep within the substrate. Though sheet resistances of ∼5×106 Ω/sq were achieved, irradiation-induced conduction in the substrate limits the maximum sheet resistance attainable. The single, high-energy implant scheme has been compared with a multiple, low-energy implant sequence. For a given level of disorder in the epitaxial layer, the latter yields higher sheet-resistance values though the former offers significant process simplification.
Gunn oscillations up to 20 GHz optically induced in GaAs/AlAs superlattice
Authors: Le Person H. , Minot C. , Boni L. , Palmier J. F. , Mollot F.
Published: July 2002

Direct observation of Gunn oscillations up to 20 GHz, induced by picosecond light pulses in an undoped GaAs/AlAs superlattice, is reported. They are obtained in the superlattice growth direction and from 7 K up to room temperature. The frequency is strongly dependent on the applied bias voltage and on the photoexcited carrier density. The oscillation frequency and the mode of operation are modeled by a classical numerical simulation.
Excess tunnel currents in AlGaAs/GaAs multiple quantum well infrared detectors
Authors: Williams G. M. , DeWames R. E. , Farley C. W. , Anderson R. J.
Published: July 2002

We present experimental evidence of excess tunnel current at low temperatures in AlGaAs/GaAs multiple quantum well infrared detectors that is not accounted for by existing theory. Prior discussions of current mechanisms in these detectors only take into account ideal device properties. For quantum well detectors with thick barrier layers, which are useful for infrared detection, the excess tunnel current component possesses the features of sequential resonant tunneling, i.e., temperature independence of the current, and saturation of the current at intermediate bias voltages with negative conductance oscillations. However, the current is orders of magnitude larger than theory predicts. Comparison with data reported by other groups shows the magnitude of the discrepancy is sample dependent. These results suggest that defects play an important role in determining the tunnel current magnitude. This current component is significant because it limits attainable detector performance at low temperatures for applications requiring operation in reduced infrared backgrounds.
Size and packing of fullerenes on C60/C70 crystal surfaces studied by atomic force microscopy
Authors: Dietz Peter , Fostiropoulos Kosta , Krätschmer Wolfgang , Hansma Paul K.
Published: July 2002

Atomic force microscopy was used to image C60/C70 crystal surfaces under ethanol with resolution of single molecules. Spherical and elongated elliptical fullerenes were observed which most likely correspond with C60 respectively C70. Measurements of the maximum diameter for a large number of molecules confirm the presence of two species of fullerenes, one with 9.4 Å, the other with 11.2 Å. The observed ratio C60:C70 is 81:19, in good agreement with spectroscopical data. The molecules are arranged either in hexagonal or cubic packing; in some areas the two arrangements alternate within a few nm. Elongated fullerenes appear to prefer the hexagonal packing.
Improved stability of thin cobalt disilicide films using BF2 implantation
Authors: Wang Q. F. , Tsai J. Y. , Osburn C. M. , Chapman R. , McGuire G. E.
Published: July 2002

The thermal stability of ∼50 nm CoSi2 and TiSi2 thin films after BF2+ implantation was investigated. The electrical characteristics of silicide films were evaluated after high temperature annealing as a function of implanted BF2+ energy. It was observed that implantation with a projected range near the silicide/silicon interface produced the most stable films. The silicide/silicon interface morphology was investigated using scanning tunneling microscopy, where with appropriate BF2 implantation conditions, smoother interfaces were seen after high temperature annealing. The stabilizing effect is attributed to fluorine segregation into the silicide grain boundaries and at the silicide/silicon interface.
Long-pulse electron-beam generation from the back-lighted thyratron
Authors: Liou Rong Lin , Hsu Tseng-Yang , Gundersen Martin A.
Published: July 2002

A variable pulse-length electron-beam source capable of 100’s μs pulse is reported. Long-pulse electron-beam generation was based on the hollow cathode discharge mode of operation of the back-lighted thyratron and achieved by the modification of circuit parameters that control the discharge. With 75 mTorr Ar and 20 kV applied voltage, the electron beam went through a transient phase before reaching a steady-state long-pulse generation. During the transient phase, a fast-decaying voltage (20–2 kV) and a pulse of 2.5 A and 130 ns FWHM electron beam were observed. The self-extracted long-pulse electron beam has a duration ∼100 μs, energy ∼2 keV, and current density ∼10 A/cm2. The results demonstrate the feasibility of controlling the electron-beam pulse length. The device is simple, robust, and compatible with a plasma environment.
Preparation of SrTiO3 thin films on Si(100) substrates by laser ablation: Application as buffer layer for YBa2Cu3O7 films
Authors: Sánchez F. , Varela M. , Queralt X. , Aguiar R. , Morenza J. L.
Published: July 2002

SrTiO3 thin films have been deposited on Si(100) by pulsed laser ablation. The films were characterized by x-ray diffractometry, field emission scanning electron microscopy, and secondary ion mass spectrometry. The films show the (h00) or (hh0) preferential orientations depending on the substrate temperature and oxygen partial pressure during the deposition. Depth profiles indicate that films grow without an important reaction with the substrate. Superconducting YBa2Cu3O7−x thin films were successfully deposited by laser ablation on Si(100) substrates coated with SrTiO3 buffer layer. This indicates that SrTiO3 is a good material as a buffer layer for deposition of YBa2Cu3O7−x on silicon.
Influence of dose rate and temperature on the accumulation of Si-implantation damage in indium phosphide
Authors: Akano U. G. , Mitchell I. V. , Shepherd F. R.
Published: July 2002

The influence of dose rate and temperature on the implantation damage accumulation in InP has been investigated. InP crystals were implanted at 80–323 K with 600 keV Si+ ions at a beam flux of 0.005–1.0 μA cm−2, and to total fluences of between 5×1012 and 2×1014 Si cm−2. The residual damage following implantation was analysed by the Rutherford backscattering/channeling technique. The results show that at 80 K, the influence of the beam flux on the accumulated displacement damage is small. However, at T≥295 K the displaced atom density, Nd, exhibits a power law dependence on J:Nd=αJn, with the value of n dependent on both the total ion dose and implant temperature. At 295 K and Si doses of 1–4×1013 cm−2, the value of n varies from 0.23 to 0.15.
Model for dielectric growth on silicon in a nitrous oxide environment
Authors: Dimitrijev Sima , Sweatman Denis , Harrison H. Barry
Published: July 2002

In this letter, a model for growth kinetics of ultrathin dielectrics obtained by oxidation of silicon in a nitrous oxide environment is proposed. The model assumes that the oxide growth is limited by time-dependent interface reaction, which is slowed down and eventually completely blocked as oxide growth sites are neutralized by nitrogen atoms. The model fits experimental data extremely well, both with time and temperature.
Bistable saturation in coupled quantum dots for quantum cellular automata
Authors: Lent Craig S. , Tougaw P. Douglas , Porod Wolfgang
Published: July 2002

A simple model quantum dot cell containing two electrons is analyzed as a candidate for quantum cellular automata implementations. The cell has eigenstates whose charge density is strongly aligned along one of two directions. In the presence of the electrostatic perturbation due to a neighboring cell, the ground state is nearly completely aligned (polarized) in one direction only. The polarization is a highly nonlinear function of the perturbing electrostatic fields and shows the strong bistable saturation important for cellular automation function.
Depth profiling of proton exchanged LiNbO3 waveguides by micro-Raman spectroscopy
Authors: Paz-Pujalt Gustavo R. , Tuschel David D.
Published: July 2002

Z-cut LiNbO3 wafers were proton exchanged (PE) with pyrophosphoric acid. The polished edges provided a side view of the exchanged region. The region was probed by micro-Raman spectroscopy by stepping a 488.0 nm laser at intervals as small as 0.2 μm across the edge face starting below the exchanged region and moving towards the wafer surface, thereby traversing the PE region. Profiling revealed significant changes, in the 125–800 cm−1 and 3200–3600 cm−1 frequency ranges. The PE region expanded after annealing at 300 °C indicating proton penetration into the wafer. Continued annealing resulted in the progressive recovery of spectral characteristics resembling unexchanged lithium niobate. Micro-Raman profiles provide spectroscopic information regarding which vibrational modes are affected by the exchange and the annealing processes as a function of depth.
Light emission in thermally oxidized porous silicon: Evidence for oxide-related luminescence
Authors: Prokes S. M.
Published: July 2002

The luminescence behavior of thermally oxidized porous silicon has been examined at various temperatures and times. No blue shifting of the photoluminescence has been noted with extended oxidation time (3–120 min), in a range where a 30% oxide thickness increase has been reported. This result does not easily fit the quantum confinement model, since the luminescence does not appear to depend on particle sizes. An oxide related luminescence, which is broad, in the red, and stable at high temperatures will be discussed as a possible source of this light emission.
Extremely high quantum efficiency (86%) operation of AlGaInP visible laser diode with lateral leaky waveguide structure
Authors: Kidoguchi Isao , Kamiyama Satoshi , Mannoh Masaya , Ban Yuzaburoh , Ohnaka Kiyoshi
Published: July 2002

AlGaInP visible laser diode with lateral leaky waveguide structure has been demonstrated for the first time. The laser has differential quantum efficiency as high as 43% from one facet without coating in addition to stable fundamental transverse-mode oscillation. The high differential quantum efficiency is due to the propagation loss as low as 4.2 cm−1 of this laser, which is the lowest value for AlGaInP visible diode to the best of our knowledge. This laser can be successfully fabricated by selective growth of AlGaInP quarternary alloy.
Control of electric field domain formation in multiquantum well structures
Authors: Shakouri A. , Gravé I. , Xu Y. , Ghaffari A. , Yariv A.
Published: July 2002

The formation, expansion, and readjustment of electric field domains in multiquantum well stacks is described and explained in terms of sequential resonant tunneling. These effects are used to control the multiband spectral response in IR detector applications of these structures.
Enhancement of electrical activation of ion-implanted phosphorus in Si(100) through two-step thermal annealing
Authors: Yu N. , Ma K. B. , Kirschbaum C. , Varahramyan K. , Chu W. K.
Published: July 2002

We report an improvement of the electrical activation of 50 and 100 keV ion-implanted P in Si(100) by a two-step anneal process. The two-step process, which combines annealing for 30 min at 550 °C with annealing for 10 s at 1050 °C, activates nearly 75%–100% of the implanted P. A parallel study shows that one-step annealing for 10 s at 1050 °C only activates 40%–60% of the doped P. In the two-step process, the low-temperature anneal is for solid state regrowth of implantation-damaged Si, while the high-temperature anneal is for P activation. Our study demonstrates that, to enhance the electrical activation, it is important to separate the regrowth process from the activation process.
Analysis of SiH vibrational absorption in amorphous SiOx:H (0≤x≤2.0) alloys in terms of a charge-transfer model
Authors: He L. , Kurata Y. , Inokuma T. , Hasegawa S.
Published: July 2002

Amorphous SiOx:H films were deposited at 300 °C by rf glow discharge of SiH4-O2 mixtures, and the SiH stretching vibrational absorption was investigated as a function of the oxygen content x. The absorption profiles were examined on the basis of the random-bonding model (RBM). The length dSiH of SiH bonds in four H-Si (Si3−nOn) bonding units was examined in terms of a charge-transfer model, using the Sanderson’s electronegativity. Using these dSiH values, the peak wave numbers for the four components were found to be 2000, 2108, 2195, and 2260 cm−1, in agreement with the experimental ones determined on the basis of the RBM.
Observation of deep levels in undoped GaSb grown by molecular beam epitaxy
Authors: Kuramochi Eiichi , Kondo Naoto , Takanashi Yoshifumi , Fujimoto Masatomo
Published: July 2002

Deep levels in undoped GaSb grown by molecular beam epitaxy are investigated with the deep level transient spectroscopy method. The measurements are performed on diodes consisting of undoped and Te-doped GaSb layers. Three hole traps are detected in the undoped GaSb, the activation energies of shallowest and deepest traps being 0.25 and 0.63 eV, respectively. The depth profile of trap concentration suggests that the origin of these two traps is related to native defects or interdiffusion of Te from n+ layer. The capture cross sections of these traps are also measured by using the filling pulse technique.
Finite element analysis of stress relaxation in thin foil plan-view transmission electron microscopy specimens
Authors: Hull R.
Published: July 2002

Finite element analysis has been used to model stress relaxation in thin foil plan-view transmission electron microscope specimens of strained epitaxial layers. Relaxation of the orders of 2%–20%, relative to the unthinned specimen, are determined for lattice strains of the order 1%, epitaxial layer thicknesses in the hundreds of angstrom regime and sample thicknesses of the order 1 μm. These calculations show that under carefully controlled experimental conditions, the stresses in thinned samples used for in situ electron microscope observations of dislocation dynamics in strained epitaxial layers are not substantially different from those in unthinned structures.
Elimination of pinholes in epitaxial thin film YBa2Cu3O7−x/SrTiO3/PrGaO3 multilayers
Authors: Olsson E. , Brorsson G. , Nilsson P. Å. , Claeson T.
Published: July 2002

Pinholes have been eliminated in trilayers of YBa2Cu3O7−x(YBCO)/PrGaO3(PGO)/YBCO by introducing 13-nm-thick SrTiO3(STO) films in the intermediate PGO film. The STO continuously covers the bottom YBCO layer and promotes a uniform growth of the subsequent PGO films. The individual PGO films are of high quality up to a thickness of about 40 nm where voids start to appear in the films. The voids disrupt the continuity of the subsequent STO and PGO layers. The technique of introducing thin layers that establish the growth of pinhole-free films can be used for other similar multilayer systems that suffer from pinholes between individual films.
Nanostructure of mechanically alloyed zinc-bonded Sm2Fe17Nx magnets
Authors: Kuhrt C. , Cerva H. , Schultz L.
Published: July 2002

The nanostructure of mechanically alloyed Sm2Fe17Nx-based magnets, which were Zn-bonded by pressure-assisted sintering at elevated temperature, was characterized by means of high-resolution and analytical transmission electron microscopy. The hard magnetic Sm2Fe17Nx grains were found to be about 100 nm in average size separated by a nonmagnetic Zn-rich phase of 5–10 nm in thickness. High-resolution imaging revealed various lattice planes in the grain boundary region which may be attributed to the presence of Γ-Fe-Zn. Obviously, this nonmagnetic phase at the grain boundaries provides additionally magnetic decoupling of the individual Sm2Fe17Nx grains, which is responsible for the coercivity increase of up to 50% induced by the pressure-assisted Zn bonding process.
Ordered vacancy compound CuIn3Se5 on GaAs (100): Epitaxial growth and characterization
Authors: Nelson A. J. , Horner G. S. , Sinha K. , Bode M. H.
Published: July 2002

Epitaxial growth of the ordered vacancy compound CuIn3Se5 has been achieved on GaAs (100) by molecular beam epitaxy from Cu2Se and In2Se3 sources. Electron probe microanalysis and x-ray diffraction have confirmed the composition for the 1-3-5 phase and that the films are single-crystal CuIn3Se5 (100). Transmission electron microscopy characterization of the material also showed it to be single crystalline. Structural defects in the layer consisted mainly of stacking faults. Photoluminescence measurements performed at 7.5 K indicate that the band gap is 1.28 eV. Raman spectra reveal a strong polarized peak at 152 cm−1, which is believed to arise from the totally symmetric vibration of the Se atoms in the lattice.
Each dopant can absorb more than ten photons: Transient absorbance measurement at excitation laser wavelength in polymer ablation
Authors: Fujiwara H. , Hayashi T. , Fukumura H. , Masuhara H.
Published: July 2002

Transient absorbance of two doped polymers, poly(methyl methacrylate) with pyrene or biphenyl, at the excitation wavelength was measured under laser ablation conditions. The fluence dependence of the etch depth was explained in terms of absorbance changes due to transient species and scattering by ablated fragments. The total energy absorbed at the threshold was confirmed to be almost identical, independent of the dopant. The number of photons absorbed per dopant was about 12 at the threshold, which will be discussed on the proposed model.
Neutron transmutation doping of isotopically engineered Ge
Authors: Itoh K. M. , Haller E. E. , Hansen W. L. , Beeman J. W. , Farmer J. W. , Rudnev A. , Tikhomirov A. , Ozhogin V. I.
Published: July 2002

We report a novel approach for obtaining precise control of both p- and n-type dopant concentrations in bulk Ge single crystals. High-purity Ge single crystals of controlled 74Ge/70Ge isotope composition ratios were grown and subsequently doped by the neutron transmutation doping (NTD) technique. The resulting net-impurity concentrations and the compensation ratios were precisely determined by the thermal neutron fluence and the [74Ge]/[70Ge] ratios of the starting Ge materials, respectively. Application of NTD to seven crystals with 0≤[74Ge]/[70Ge]≤4.34 lead to p-type Ge:Ga,As with compensation ratios in the range 0–0.76. The ability to grow crystals with accurately controlled Ge isotope mixtures allows us to obtain ratios anywhere between 0 and 1 for both p- and n-type doping.
InGaAs/InP and InAsP/InP quantum well structures on GaAs (100) with a linearly graded InGaP buffer layer grown by gas-source molecular beam epitaxy
Authors: Chin T. P. , Hou H. Q. , Tu C. W. , Chang J. C. P. , Otsuka N.
Published: July 2002

A linearly graded InxGa1−xP (x=0.48–1) buffer layer is used for growing a high-quality InP layer on a GaAs substrate. We show that an InxGa1−xP buffer layer is superior to an InyGa1−yAs buffer layer because it is transparent to long wavelengths and allows a less stringent composition control. InGaAs/InP single quantum wells and InAsP/InP multiple quantum wells grown on the InP/InxGa1−xP/GaAs substrate show comparable quality to similar structures grown on InP (100) substrates. Photocurrent spectra for the latter exhibit quantum-confined Stark effect near 1.3 μm.
Mylar-film-compensated π and parallel-aligned liquid crystal cells for direct-view and projection displays
Authors: Wu Shin-Tson , Lackner Anna M.
Published: July 2002

Optical properties of stretched Mylar films [poly(ethylene terephthalate)] were evaluated. Similar birefringence dispersion to liquid crystals over a wide spectral range makes Mylar an attractive phase retardation plate for display applications. Two display modes employing an antiparallel (or π) and a parallel-aligned cell with a Mylar phase compensator were demonstrated. The film-compensated π cell shows an 80:1 black-to-white contrast ratio, 60 Hz frame rate and ±45° viewing angle, and is attractive for direct view display. The film-compensated parallel cell shows an 85:1 black-to-white contrast ratio, 180 Hz frame rate, and ±10° viewing angle, and is suitable for projection display.
Deposition of metal nanostructures onto Si(111) surfaces by field evaporation in the scanning tunneling microscope
Authors: Hsiao Gregor S. , Penner Reginald M. , Kingsley Jeff
Published: July 2002

Islands of gold or copper having dimensions as small as 200 Å in diameter and 10 Å in height were prepared by field evaporation from a tip of the appropriate metal in a scanning tunneling microscope (STM). The field emission of metal is induced by the application of tip-negative bias pulses having amplitudes of 6–20 V, and durations of 2 μs to 2 ms. The metallic composition of the protrusions observed by STM are confirmed by ex situ elemental analysis using the field emission scanning Auger microprobe (FE-SAM). Tip-positive bias pulses also produce protrusions, however these are unstable either to STM imaging or to exposure to high-energy electron beams, as in the FE-SAM instrument. It is therefore probable that nonostructures formed via tip-positive bias pulses are not metallic. These data provide the first direct experimental evidence for metal transfer between an STM tip and a surface.
Photothermoelastic transfer matrix
Authors: Bozóki Zoltán , Miklós András , Bicanic Dane
Published: July 2002

The photothermoelastic transfer matrix method introduced here was demonstrated to be generally applicable for the calculation of the thermoelastic response of multilayered samples exposed to modulated laser heating. The method enables the modelization of photothermal measurements of samples having arbitrary number of layers and values of optical, thermal, and elastic parameters. To demonstrate its feasibility, a general expression for photopyroelectric signals is being presented.
Photoluminescence of oxidized silicon nanoclusters deposited on the basal plane of graphite
Authors: Dinh L. N. , Chase L. L. , Balooch M. , Terminello L. J. , Wooten F.
Published: July 2002

Silicon (Si) nanoclusters, with an average size of 3–5 nm in diameter, have been deposited on the basal plane of highly oriented pyrolytic graphite in an ultrahigh vacuum chamber, and investigated by scanning tunneling microscopy. Clusters passivated in situ with hydrogen or oxygen showed no detectable visible photoluminescence (PL). Prolonged exposure of the clusters to ambient air, however, resulted in strong stable red to green-blue PL spectra. Further study of these clusters by x-ray photoelectron spectroscopy and Auger electron spectroscopy revealed the existence of only SiO2 for the prolonged air-exposed samples, and the existence of SiOx (x ranged from 0 to 2) for the in situ oxidized samples which did not exhibit any detectable visible PL. We believe that the observed visible PL originated from defects in SiO2.
Sol-gel method for synthesizing visible photoluminescent nanosized Ge-crystal-doped silica glasses
Authors: Nogami Masayuki , Abe Yoshihiro
Published: July 2002

Ge-nanocrystal-embedded SiO2 glasses were prepared by a sol-gel process. The glasses synthesized through hydrolysis of Si(OC2H5)4 and GeCl4 were heated in the presence of hydrogen at 400–700 °C, in which Ge4+ ions were reduced to precipitate nanosized Ge crystals. Glasses doped with Ge nanocrystals of diameter of ∼5 nm showed a strong room-temperature photoluminescence with peaks at 2.32, 2.17, and 2.0 eV. Large Ge crystals precipitated by heating at 800 °C showed no photoluminescence.
Influence of oxygen impurity in the intrinsic layer of amorphous silicon solar cells
Authors: Isomura Masao , Kinoshita Toshihiro , Hishikawa Yoshihiro , Tsuda Shinya
Published: July 2002

The influence of oxygen impurity in the i layer of hydrogenated amorphous silicon (a-Si:H) solar cells is studied. At the initial state, the dark conductivity, and photoconductivity of a-Si:H films increase and the conversion efficiency of the solar cells drops as the oxygen concentration increases. After the light soaking, these film properties become independent of the oxygen concentration, but the conversion efficiency of a-Si:H solar cells is still influenced by the oxygen impurity. The dominant effect of the oxygen impurity in a-Si:H solar cells is a modification of the electric field distribution in the i layer, due to the donorlike states created by oxygen.
Influence of fluorine preamorphization on the diffusion and activation of low-energy implanted boron during rapid thermal annealing
Authors: Huang T. H. , Kinoshita H. , Kwong D. L.
Published: July 2002

The diffusion and activation of low-energy implanted B in F preamorphized Si during rapid thermal annealing has been studied. Compared with low-energy B or BF2 implant into crystalline Si, low-energy B ion implantation into F preamorphized Si allows the formation of shallow junctions with reduced junction depth and increased B activation. F preamorphization suppresses the B transient enhanced diffusion in the low B concentration region resulting in a steep dopant profile which is necessary for shallow junction formation. Secondary ion mass spectroscopy and cross-sectional transmission electron micrograph results show F accumulation near the surface and at end-of-range defects. The interaction of F with defects is believed to reduce B diffusion in the low B concentration region. Low-energy B implant into F preamorphized Si followed by rapid thermal annealing has been demonstrated as a promising process for shallow junction formation.
Upconversion luminescence of Er3+ in chloride glasses based on ZnCl2 or CdCl2
Authors: Shojiya Masanori , Takahashi Masahide , Kanno Ryoji , Kawamoto Yoji , Kadono Kohei
Published: July 2002

Upconversion luminescence of Er3+ in the chloride glass system has been investigated in ZnCl2-BaCl2-KCl-ErCl3 and CdCl2-BaCl2-KCl-ErCl3 glasses. Under 800 nm excitation, the glasses gave upconversion luminescence with barely detectable red (around 660 nm), very intense green (around 525–560 nm), and considerably intense blue (around 410 nm) emissions. The intensity of blue emissions was far stronger than that observed for any of other Er3+-doped glass systems, revealing that Er3+-doped chloride glasses can efficiently convert the infrared light into much shorter wavelengths. The green emission is attributed not only to the thermally coupled 2H11/2 and 4S3/2→4I15/2 transition but also to the 2H9/2→4I13/2 transition. The blue emission is due to the 2H9/2→4I15/2 transition. The blue and green upconversion luminescence results from a two-photon process.
Alloy composition and temperature dependence of the fundamental absorption edge in CuGaxIn1−xSe2
Authors: Lárez C. , Bellabarba C. , Rincón C.
Published: July 2002

We have proposed a semi-empirical expression for the alloy composition and temperature dependence of the fundamental energy gap in the CuGaxIn1−xSe2 alloy system. A good agreement between theoretical predictions and available experimental data is found. It seems that such semi-empirical expressions are of considerable importance for the analysis of results on new ternary and quaternary compounds and its alloys for which detailed studies based on a more fundamental analysis are not available.
Misorientation angle distributions for large-angle grain boundaries in Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10 composite tapes
Authors: Zhu Yimei , Suenaga M. , Sabatini R. L.
Published: July 2002

The angular distributions of large-angle grain boundaries were studied by electron microscopy for Bi(2:2:1:2) and Bi(2:2:2:3) composite tapes. For Bi(2:2:2:3) the distributions are random, while for Bi(2:2:1:2), there was a high incidence of special boundary misorientations. The preferred orientations in Bi(2:2:1:2), which were analyzed for [001] and [100] rotations, agreed well with the calculated lattice coincidences based on the constraint Coincidence Site Lattice model, and were attributed to the reorientation of the neighboring grains during its partial melt process.
Absorption edge of silicon from solar cell spectral response measurements
Authors: Keevers M. J. , Green M. A.
Published: July 2002

The optical absorption coefficient of crystalline silicon near the band edge is determined to values as low as 10−7 cm−1 by sensitive photocurrent measurements on high efficiency silicon solar cells. Structure due to three- and four-phonon assisted absorption processes is observed. Discrepancies between absorption coefficient values around 10−2 cm−1 reported in the literature are resolved. The role of disorder theory in understanding the absorption edge of crystalline semiconductors such as silicon is discussed.
Self-organization of strained GaInAs microstructures on InP (311) substrates grown by metalorganic vapor-phase epitaxy
Authors: Nötzel Richard , Temmyo Jiro , Kozen Atsuo , Tamamura Toshiaki , Fukui Takashi , Hasegawa Hideki
Published: July 2002

The evolution of low-dimensional microstructures in the growth of strained GaInAs/AlInAs and GaInAs/InP heterostructures on planar InP (311)B and (311)A substrates by metalorganic vapor-phase epitaxy is investigated by atomic force microscopy. The surface structures are found to be similar to those previously reported for GaAs (311)B and (311)A substrates. In particular, the appearance of zero-dimensional microstructures in the GaInAs/AlInAs system on InP (311)B substrates is analogous to the self-organizing formation of buried InGaAs quantum disks in the case of GaAs (311)B substrates.
Magneto-optical imaging of flux patterns in multifilamentary (BiPb)2Sr2Ca2Cu3Ox composite conductors
Authors: Welp U. , Gunter D. O. , Crabtree G. W. , Luo J. S. , Maroni V. A. , Carter W. L. , Vlasko-Vlasov V. K. , Nikitenko V. I.
Published: July 2002

We present a study of the superconducting morphology of the transport current carrying cross section of a 19-filament (BiPb)2Ca2Cu3Ox (Bi-2223) composite conductor using magneto-optical imaging of magnetic flux patterns. In conjunction with electron microscopy on the same sample this technique allows a unique correlation of superconducting and microstructural properties. Direct evidence for enhanced superconducting properties in platelike regions along the silver/Bi-2223 interface and for weak properties near the core of the filaments is obtained. Misaligned grain colonies are found to cause an interruption of the superconducting continuity in the filaments.
Ballistic electronic stub tuner for potential use in analog-to-digital conversion
Authors: Debray P. , Akis R. , Vasilopoulos P. , Blanchet J.
Published: July 2002

Electron transmission in the fundamental transverse mode of an asymmetric double-stub electronic stub tuner (ADEST) in the ballistic regime is theoretically shown to be a symmetric, almost sine wavelike, periodic function of an offset parameter d, where d is a measure of the stub asymmetry and is the distance between the lines that bisect the stub and the main wire. The periodic pattern remains quite robust at finite temperatures (≊5 K). This unique multiple folding output characteristic of a single ADEST may conceivably be used for fast, high binary bits analog-to-digital conversion.
Registration, storage, and processing of Fabry–Perot ring spectra by a diode matrix combined with a microcomputer
Authors: Hörl M. , Boes R. , Döbele H. F. , Röwekamp M.
Published: July 2002

A combination of a 32×32-element silicon-diode matrix and an Apple II computer is used to record and analyze Fabry–Perot interference ring patterns. The main advantage over conventional methods consists in the possibility of selecting the spectral resolution after registration and in the absence of alignment problems. Application of an image converter tube with VUV transmitting window in front of the matrix extends the applicability of the device to UV and VUV spectra.
The energy dispersive x-ray detector: A quantitative model
Authors: Joy David C.
Published: July 2002

When a Si(Li) solid-state energy dispersive detector is used to collect x-ray photons with energies below 2 keV the characteristic peaks in the spectrum show significant deviations from the ideal Gaussian shape observed for higher energy photons. This effect is due to incomplete collection of the charge deposited by the incident photon in the diode. The magnitude of this effect, and the resultant distortion of the spectrum, can be computed by means of a Monte Carlo simulation which models the detector in terms of the three parameters which characterize it, junction depth, diffusion length, and surface recombination velocity. For values of these parameters typical of commercial detectors it is found that the incomplete charge correction can be as high as 30% for a line such as N Kα at 400 eV. By matching simulated and experimental spectral shapes, quantitative corrections for each x-ray line of interest can be computed. The results suggest that alternative design strategies for detectors might permit a higher quality of performance to be achieved at low energies.
Subnanosecond protection circuits for oscilloscope inputs
Authors: Mitchel G. R. , Melançon C.
Published: July 2002

Overvoltage protection circuits have been developed to protect oscilloscope inputs or other 50-Ω recording systems from fast (τr∼1 ns) rise-time pulses. These circuits are voltage dividers with linear output up to a specified level, typically 1.4 V, beyond which fast switching diodes limit the output to ≲5 V for inputs as high as 5 kV. The clipping circuits are frequency compensated for flat response to several hundred megahertz.
Fast turbulent correlations from phase coherence velocimetry
Authors: Johnson J. A. , Chen S.-C. , Johnson L. E.
Published: July 2002

Flows with coherent structures allow see-free measurements of local velocity and velocity fluctuations. Continuous turbulent velocity histories in ionizing shock waves are obtained at a 10-MHz sampling rate. From this, correlation profiles and frequency spectra are determined which reveal the presence of prominent high-frequency components.
Reduction of excess low-frequency noise in rf-biased SQUID’s
Authors: Taber M. , Cabrera B.
Published: July 2002

We have observed an excess low-frequency noise associated with the operation of a commercial rf-biased SQUID (superconducting quantum interference device) sensor in freely convecting liquid helium. A simple technique for reducing convection and suppressing this low-frequency noise is described.
Improved dc current supply for high-vacuum straight through solenoid valves
Authors: Boulé Bernard , Herman Jan A.
Published: July 2002

An inexpensive improved dc voltage supply for high-vacuum straight through valves is described. The electronic circuit is composed of two parts: (1) the current generating section which withdraws the valve gate and maintains it in the open position and (2) the section which monitors whether the valve gate is open or closed.
An alpha particle diagnostic based on damping of lower hybrid waves
Authors: Wong King-Lap
Published: July 2002

The feasibility of using lower-hybrid wave damping measurement as a diagnostic for energetic (above 200 keV) alpha particles has been investigated for large tokamaks like TFTR and FED devices. Detailed ray tracing calculations show that slow lower-hybrid waves can be used for TFTR, but the fast lower-hybrid wave is necessary for wave penetration into the dense plasma core of FED. It is possible to launch waves mainly damped on the energetic alpha particles whose velocity distribution function f∝(r,v,t) is related to the wave damping rate. A 1% energetic alpha-particle concentration would cause substantial wave damping measurable by FIR laser scattering systems. Preliminary estimates show that this technique should yield good temporal resolution (∼1 ms) and some spatial resolution for the alpha-particle distribution function. However, extensive computation is necessary to unfold the velocity dependence if it is at all possible.
Evaluation of Josephson junction yield
Authors: Yoshida A. , Tamura H. , Hasuo S.
Published: July 2002

This paper describes a system which evaluates Josephson junction yields. This computer-aided system has been designed and tested and confirmed to be able to evaluate yields with an error less than 0.003% for series-connected junctions with less than 256 junctions at a time. This system frees a person from the conventional troublesome evaluation method. This system was adapted for the evaluation of initial yields of all-lead-alloy junctions and niobium/lead-alloy junctions. It has been made clear that the all-lead-alloy junctions exhibit a relatively low yield, but that the yield of the niobium/lead-alloy junctions is as high as 99.98%.
Compensator for the time dispersion in a monochromator
Authors: Bebelaar Dick
Published: July 2002

The time dispersion in a monochromator and its influence in temporal measurements has been analyzed. A special compensator as a practical solution for a limited wavelength range is presented.
High-power high-reliability pulse generator for supplying a CO2 laser
Authors: Covello A. , Gippetto C.
Published: July 2002

A description is given of a pulse generator capable of supplying a CO2 power laser at a pulse frequency rate of 16 Hz. An interesting feature of this device is that the frequency can be increased beyond 100 Hz without impairing the device’s proper functioning in any way. The main characteristic of this generator is high reliability for long-life, steady-state applications.
Life problems of dc and rf-excited low-power cw CO2 waveguide lasers
Authors: Hochuli U. E. , Haldemann P. R.
Published: July 2002

A number of different, rf-excited 3-W cw CO2 waveguide lasers have been built. Four of these lasers, after continuously working for 15 000–30 000 h, still yield about 70% of their original power output. The design variations cover N2- and CO-bearing gas mixtures, as well as internal- and external-capacitively coupled excitaton electrodes. A similar laser survived 50 000 5-min-ON/5-min-OFF cycles without significant mirror damage. We have not been able to find suitable cold cathodes that allow the building of longitudinally dc-excited cw CO2 waveguide lasers that work for such extended periods of time.
Diagnostic applications of the TFTR XIS system
Authors: McGuire K. , Colchin R. J. , Fredrickson E. , Hill K. , Johnson L. C. , Morris W. , Paré V. , Sauthoff N. , von Goeler S.
Published: July 2002

The horizontal x-ray imaging system (XIS) on the tokamak fusion test reactor (TFTR) tokamak is an array of 64 silicon surface-barrier x-ray diodes, with a 2.5-cm spatial resolution. The XIS system is primarily used to study magnetohydrodynamic (MHD) instabilities, but has also been used to measure electron thermal diffusivity, electron temperature, the radius of the q=1 surface, plasma vertical position, and toroidal rotation of the plasma. Movable absorber-foil arrays provide energy selection. Bandpass analog filters and digital techniques have been used on the x-ray signals in an attempt to infer turbulence levels in the plasmas. Details of the above techniques will be presented.
Photoconductor x/γ-ray detectors and x-ray bolometers
Authors: Wang C. L. , Eckels J. D. , Morgan W. V. , Pocha M. D. , Slaughter D. R. , Davis B. A. , Kania D. R. , Wagner R. S.
Published: July 2002

Photoconductors are very promising x/γ-ray detectors and x-ray bolometers for pulsed x/γ-ray measurements. They are fast, sensitive, and theoretically flat in spectral response for low energy x rays. We report our tests of InP:Fe, GaAs, and GaAs:Cr, both neutron damaged and undamaged, at Nova laser, Febetrons, and electron linear accelerators. The temporal and spectral responses are discussed.
Spectroscopic and interferometric measurements of laser–plasma produced blast waves
Authors: McLean E. A. , Stamper J. A. , Manka C. K. , Griem H. R. , Ali A. W. , Ripin B. H.
Published: July 2002

A laser-produced plasma generates blast waves as it expands supersonically into a stationary photoionized background gas (N2) at a pressure of 1–5 Torr.1 Using a combination of spectroscopic and interferometric measurements, time- and space-resolved values of the temperature and density are obtained. This study was performed on targets in the NRL Pharos III laser facility with laser energies of 20–120 J and pulse durations of ∼5 ns. A 1-m spectrograph equipped with three photomultiplier channels, which are calibrated on an absolute scale, is used for the spectroscopic measurements. The interferometry is done with a folded-wavefront interferometer. It uses an optical probe pulse at 5270 Å that is split off of the main laser pulse, reduced in pulse duration (∼300 ps), and time delayed. Interferometric measurements can be made simultaneously with the spectroscopic measurements. Experimental data and the technique of analysis will be shown. This work was supported by the Defense Nuclear Agency.
Time-resolved spectra in the 80–330-Å wavelength region from PLT tokamak plasmas
Authors: Dave J. H. , Feldman U. , Seely J. F. , Wouters A. , Hinnov E. , Suckewer S.
Published: July 2002

Time-resolved spectra from the PLT plasma have been recorded by the 2-m Schwob–Fraenkel spectrometer. The recording device was a 50-mm flat multichannel plate mounted with its center tangent to the Rowland circle. In order to record the 80–330-Å wavelength range, the multichannel plate was moved several times. Spectra were recorded every 50 ms for the duration of the discharge. The data obtained were corrected so that distortions introduced by the flat rather than curved surface of the multichannel plate were accounted for. Examples of typical PLT spectra with wavelength accuracy of 0.02 Å will be shown. The spectra contain primarily ground transitions in ions of C, O, Cr, Fe, and Ni. The observed lines are emitted typically from plasmas of 100–2000 eV. Examples of spectra of trace elements injected into the plasma during the discharge will also be shown. These spectra are the result of subtraction of the signals after and before the injections.
Perpendicular bremsstrahlung emission of suprathermal electrons
Authors: von Goeler S. , Stevens J. , Bernabei S. , Bitter M. , Chu T. K. , Jobes F. , Hill K. , Hooke W. , Hosea J. C. , Hsuan H. , Mazzucato E. , Meservey E. , Motley R. W. , Sesnic S.
Published: July 2002

An interpretation of the x-ray bremsstrahlung emission by suprathermal electrons perpendicular to a magnetic field is given in terms of the parallel and perpendicular temperature of a three-temperature distribution function. The slope (i.e., the temperature) of the distribution can be determined relatively well. Factor-of-two uncertainties remain for the number of electrons.
Study of the detached plasma regime in TFTR using the MIRI far-infrared interferometer
Authors: Mansfield D. K. , Park H. K. , Strachan J. D. , Bush C. E. , Grek B. , Johnson D. W. , Johnson L. C. , Stauffer F. J. , Schivell J.
Published: July 2002

Plasmas have been formed in the tokamak fusion test reactor (TFTR) which separate completely from the limiter and are called detached plasmas. The physical evidence for the separation from the limiter is that all the ohmic input power is radiated away at the plasma boundary which can be 10→30 cm inside the limiter. The 10-chord multichannel MIRI interferometer system has been used to diagnose this region and follows the formation of the detached state through a MARFE. MIRI indicates that a plasma ∼0.5→1×1013 cm−3 occurs in the region between the luminous boundary and the limiter. This work was supported by U.S. DOE Contract No. DE-AC02-76-CHO-3073.
Multichannel detector for the VUV
Authors: Hawkes N. C. , Peacock N. J.
Published: July 2002

A 2000-channel intensified diode array detector has been developed for use with a 1-m normal incidence spectrometer. The detector has been operated over the wavelength region 300–1700 Å with a readout interval of 20 ms to survey the spectrum of the DITE Tokamak. With this spectral coverage the resolution is sufficient (∼0.1 Å in first order) to monitor rotational shear from simultaneous observation of a range of ion species. Additionally, by restricting the number of channels recorded, the detector has been used to examine details of individual line profiles more frequently allowing the observation of rapid (2 ms) evolution of plasma’s mass motion effects. We also report on the intensity calibration of the spectrometer and detector combination using a deuterium lamp over the range 1700–1100 Å.
Integrated acousto-optic mode locker
Authors: Myslinski Piotr
Published: July 2002

A new type of the acousto-optic modulator is presented. The novel design reduces the number of optical elements inside the laser cavity resulting in higher quality of the mode-locked pulses. An application of the modulator to an argon-ion laser is described.
Triple monochromator for Raman scattering with electronic coupling
Authors: Ohana I. , Yacoby Y. , Bezalel M.
Published: July 2002

An electronic coupled triple monochromator is presented. The system is composed of double and single monochromators coupled together electronically and controlled by a microcomputer. The tracking is obtained via a feedback loop between the motor’s velocities and two shaft encoders which are connected to the lead screws. The resolution of the system was measured as a function of the slits width and the wavelength and is as good as the resolution of a double monochromator. The additional loss in light intensity results only from the reflection loss in the grating and in the mirrors of the third stage.
Heavy ion beam probe diagnostic systems for stellarators
Authors: Carnevali A. , Misium J. R. , Lewis J. F. , Connor K. A.
Published: July 2002

A heavy ion beam probe diagnostic is planned for ATF. The most significant device characteristics affecting the implementation of such a system on this complex magnetic geometry not encountered on tokamaks are the large toroidal separation (15°) of vertical and horizontal ports and substantial magnetic return fields in the region of the ion optics and energy analyzer electric fields. Procedures have been developed to make the application of beam probing possible in this environment.