bluuebunny/crossref_metadata_2025 huggingface dataset:
Single heterostructures for optical transport experiments
Authors: Höpfel R. A. , Shah J. , Chang T. Y. , Sauer N. J.
Published: July 2002

We introduce a new GaAs/AlxGa1−xAs single heterostructure, which allows local optical injection of a one-component confined plasma. The heterojunction is placed in the undoped region of a p-i-n structure, which provides a high built-in electric field for the separation of injected electrons and holes, as well as for the two-dimensional confinement of electrons. A time-of-flight measurement of the majority-electron drift velocity at room temperature is demonstrated.
Efficient degenerate four-wave mixing in an ion-exchanged semiconductor-doped glass waveguide
Authors: Gabel A. , DeLong K. W. , Seaton C. T. , Stegeman G. I.
Published: July 2002

We report the first observation of efficient degenerate four-wave mixing in a planar waveguide. Four-wave mixing reflectivities near one percent were seen inside a single mode waveguide fabricated by ion exchange in a sample of semiconductor-doped glass.
Detection and characterization of individual Ge layers in Si(100) using Raman spectroscopy
Authors: Tsang J. C. , Iyer S. S. , Delage S. L.
Published: July 2002

The Raman active vibrational modes of single, 1 to 6 layer thick Ge films grown epitaxially on Si(100) and covered by thin layers of Si(100) have been measured. Both the Ge-Ge vibrations from the interior of the Ge films and the Ge-Si vibrations at the Ge-Si interfaces have been observed. These modes and the weak defect activated scattering are used to characterize the Ge layers. These results show that Raman spectroscopy can now be used to directly characterize the properties of buried interfaces at the level of single atomic layers.
Realization of both p- and n-type conduction for ZnSe-ZnTe strained-layer superlattices
Authors: Kobayashi Masakazu , Dosho Shiro , Imai Akira , Kimura Ryuhei , Konagai Makoto , Takahashi Kiyoshi
Published: July 2002

The conduction types of ZnSe-ZnTe strained-layer superlattices (SLS’s) have been controlled by using the modulation doping technique. Two kinds of modulation-doped SLS’s were prepared. One of them consisted of gallium (Ga) doped ZnSe layers and undoped ZnTe layers. The other consisted of undoped ZnSe layers and antimony (Sb) doped ZnTe layers. The conduction types of the samples modulation doped with Ga and Sb were shown to be n and p type, respectively whereas the undoped samples exhibited n-type conduction. The electrical properties of the undoped and modulation-doped samples were evaluated by the van der Pauw method. The carrier concentrations of all types of samples were about 5×1013/cm3 at room temperature. The temperature dependence of the electrical properties was measured for an undoped sample and a sample modulation doped with Sb. The carrier concentrations increased with temperature and reached about 1×1017/cm3 at 500 K.
Lateral optical confinement of the heterostructure semiconductor Raman laser
Authors: Suto K. , Kimura T. , Nishizawa J.
Published: July 2002

This letter describes the first lasing experiment of the heterostructure semiconductor Raman laser with lateral confinement of both the Stokes and pump fields. It has a GaP Raman active layer with thickness of 10 μm and Al0.1Ga0.9P cladding layers. The stripe of the active layer has been fabricated by a plasma etching technique. Steps should be taken to realize the semiconductor Raman laser pumped by an injection laser, applicable to wideband optical communication.
Evidence by Raman spectroscopy and x-ray diffraction of a strong influence of H2O traces on the metalorganic vapor phase epitaxy of GaAs on Si
Authors: Freundlich A. , Leycuras A. , Grenet J. C. , Vèrié C. , Huong Pham V.
Published: July 2002

The metalorganic vapor phase epitaxy of GaAs on Si is shown to be strongly sensitive to the residual water vapor content in the growth reactor atmosphere. This finding is evidenced both by Raman spectroscopy and double-crystal x-ray diffraction. For the growth of good crystalline quality GaAs on Si, the upper hygrometric level limit is found around 0.5 ppm by volume.
Photon-controlled oxidation of silicon
Authors: Micheli F. , Boyd Ian W.
Published: July 2002

A cw argon laser was used to oxidize crystalline silicon in dry oxygen. Under otherwise identical conditions, two visible wavelengths were used to identify possible nonthermal contributions to the reaction. With a simple technique to amplify small differences in the growth rate we have confirmed that the reaction is primarily thermally controlled and that there is a photonic enhancement to Si oxidation. A simulation has also provided some initial quantitative evaluation of the process.
Incorporation of boron during thermal chemical vapor deposition of doped hydrogenated amorphous silicon
Authors: Branz Howard M. , Flint John H. , Harris Christopher J. , Haggerty John S. , Adler David
Published: July 2002

We report investigations of B incorporation during the growth of B-doped hydrogenated amorphous silicon (a-Si:H) thin films by laser-induced chemical vapor deposition (CVD) from mixtures of SiH4 and B2H6. Because B2H6 decomposition is very rapid, nearly all the B admitted into the reaction cell is incorporated in the growing film and the B concentration in the solid is B2H6 flow rate limited rather than controlled by the gas phase dopant concentration. Widely varying B-incorporation efficiencies reported for B-doped a-Si:H grown by a variety of thermal CVD techniques are summarized and explained.
CdTe metal-semiconductor field-effect transistors
Authors: Dreifus D. L. , Kolbas R. M. , Harris K. A. , Bicknell R. N. , Harper R. L. , Schetzina J. F.
Published: July 2002

We report the first demonstration of CdTe metal-semiconductor field-effect transistors. These transistors were fabricated using n-type CdTe films grown by photoassisted molecular beam epitaxy. Using this new film deposition technique, it is possible to obtain highly activated n-type or p-type films suitable for device applications. In the present work, transistor structures with 5 or 100 μm gate lengths having channel dopings in the range from 2×1016 to 2×1017 cm−3 were fabricated and tested. The 5 μm gate devices have transconductances as large as 10 mS/mm and pinch-off voltages of 4.0 V.
Microstructure and properties of YBa2Cu3O9−δ superconductors with transitions at 90 and near 290 K
Authors: Narayan J. , Shukla V. N. , Lukasiewicz S. J. , Biunno N. , Singh R. , Schreiner A. F. , Pennycook S. J.
Published: July 2002

We have investigated the microstructure and properties of YBa2Cu3O9−δ that contain resistive transitions at 90 and near 290 K using high-resolution and analytical transmission electron microscopy and Raman scattering techniques. The specimens contain normal orthorhombic (Pmmm space group) phase associated with Tc=90 K, and another phase which we tentatively assign it to be associated with the resistive transitions near 290 K. The new phase has a c axis larger by about 16% and it grows epitaxially on the {100} planes of the orthorhombic (tripled perovskite unit cell) phase having Tc=90 K.
Tunneling and transverse wave vector conservation in GaAs/AlGaAs heterostructures
Authors: Lebens John A. , Silsbee Robert H. , Wright Steven L.
Published: July 2002

We have studied transverse wave vector conservation in the tunneling of electrons between a quantum well and an n+ electrode while varying the density of electrons in the well. The sample is a ‘‘tunnel capacitor’’ structure in which a GaAs well is separated by an AlGaAs tunnel barrier from the bottom n+ electrode and by a much thicker AlGaAs barrier from the top n+ electrode. In a regime where the transverse wave vector cannot be conserved in the absence of scattering, we present a model that includes scattering effects and show that it agrees with our experimental data and can be used to draw some conclusions about the efficacy of spacer layers to reduce these scattering effects.
Characterization of a thin Si-implanted and rapid thermal annealed n-GaAs layer
Authors: Sugitani Suehiro , Yamasaki Kimiyoshi , Yamazaki Hajime
Published: July 2002

Very thin, high carrier concentration layers for high performance GaAs field-effect transistors are realized by lamp annealing, combined with low-energy (<30 keV) ion implantation. The characteristics of these thin layers are investigated by the Hall effect, capacitance-voltage, photoluminescence, and secondary ion mass spectrometry (SIMS). The optimum temperature giving the maximum sheet carrier concentration is the result of a balance between damage recovery and acceptor generation. The optimum temperature decreases as the implantation energy is reduced. The effective implanted layer thicknesses obtained by SIMS are larger than the Lindhard–Scharff–Schiott calculated values. The minimum effective active layer thickness of 0.045 μm is obtained with a 10-keV implanted sample. This value is about one-half that obtained for the 30-keV implanted furnace annealed sample.
Stable continuous room-temperature laser operation of AlxGa1−xAs-GaAs quantum well heterostructures grown on Si
Authors: Nam D. W. , Holonyak N. , Hsieh K. C. , Kaliski R. W. , Lee J. W. , Shichijo H. , Epler J. E. , Burnham R. D. , Paoli T. L.
Published: July 2002

Data are presented demonstrating stable room-temperature continuous (cw) photopumped laser operation of an AlxGa1−xAs-GaAs quantum well heterostructure (QWH) grown on Si by a combination of molecular beam epitaxy and metalorganic chemical vapor deposition. The cw 300 K laser operation of the single well AlxGa1−xAs-GaAs QWH occurs at an excitation threshold of 6.7×103 W/cm2 (Jeq=2.8×103 A/cm2), or a factor of 10 lower than similar multiple well QWH’s. The laser operation is stable for four (or more) hours, the length of the ‘‘test.’’
Capless rapid thermal annealing of Si+-implanted InP
Authors: Woodhouse J. D. , Gaidis M. C. , Donnelly J. P. , Armiento C. A.
Published: July 2002

An enhanced-overpressure capless annealing technique suitable for annealing ion-implanted InP at temperatures of 900 °C is described. The technique utilizes a Sn-coated InP wafer and is based on the same principle as the In-Sn-P liquid-solution method for eliminating InP surface degradation prior to epitaxial growth. InP samples implanted with 140 keV, 1014 cm−2 Si+ and annealed at 900 °C for 10 s exhibited improved electrical characteristics over samples annealed at 750 °C for 5 min using conventional encapsulation techniques.
Large third-order optical nonlinearity of the organic metal α-[bis(ethylenedithio) tetrathiofulvalene] triiodide
Authors: Huggard P. G. , Blau W. , Schweitzer D.
Published: July 2002

The organic metal α-[bis(ethylenedithio) tetrathiofulvalene]2I3 shows a large third-order optical nonlinearity around 650 nm, as observed by forward degenerate four-wave mixing. Nonlinear susceptibilities of ‖χ(3)‖ ∼5×10−8 esu are observed along the direction of maximum conductivity. The frequency dispersion of the nonlinearity points to a plasma effect due to the conduction electrons.
Gamma radiation resistance of the high T
c superconductor YBa2Cu3O7−δ
Authors: Bohandy J. , Suter J. , Kim B. F. , Moorjani K. , Adrian F. J.
Published: July 2002

Exposure of the high Tc superconductor YBa2Cu3O7−δ to 60Co γ irradiation up to 1.3 Mrad is found to have virtually no effect on its superconductive properties as measured by a novel variant of the microwave absorption method.
Formation of thin-film high T
c superconductors by metalorganic deposition
Authors: Hamdi A. H. , Mantese J. V. , Micheli A. L. , Laugal R. C. O. , Dungan D. F. , Zhang Z. H. , Padmanabhan K. R.
Published: July 2002

Metalorganic deposition (MOD) is a nonvacuum method of thin-film deposition which allows easy alteration of chemical components and is compatible with thin-film processing. We report the preparation of thin-film superconductors by MOD. Rutherford backscattering spectrometry was used to determine film compositions and thicknesses. Films, approximately 500 nm thick, of YBa2Cu4Oz (z undetermined) were deposited on 〈100〉 single-crystal SrTiO3. A superconducting onset temperature of 90 K was measured with 37 K the zero resistance temperature. Scanning electron microscopy revealed grain sizes approximately 250 nm in diameter.
Transient electrical conductivity of nonequilibrium carriers excited by subpicosecond optical pulses in GaAs
Authors: Vengurlekar A. S. , Jha Sudhanshu S.
Published: July 2002

We calculate the time-dependent electrical conductivity σ(t) for the nonequilibrium carriers excited by a subpicosecond laser pulse in a polar semiconductor like GaAs. The photoexcited carriers are assumed to relax towards equilibrium by emitting longitudinal optical (LO) phonons in a cascade via the strong Fröhlich interaction. We show that σ(t), obtained in the picosecond time domain, has a highly nonlinear time evolution. It develops a pronounced dip, with its value becoming negative, whenever the generated low density carrier distribution is sharply peaked initially at energy ε≂mℏωLO, m=integer, ℏωLO being the long wavelength LO phonon energy.
Nearly degenerate four-wave mixing in a traveling-wave semiconductor laser amplifier
Authors: Inoue Kyo , Mukai Takaaki , Saitoh Tadashi
Published: July 2002

Nearly degenerate four-wave mixing (NDFWM) in a traveling-wave semiconductor laser amplifier is demonstrated by simultaneously injecting two lights of slightly different frequencies in the same direction. A new frequency light at an expected frequency for NDFWM is observed with the same order of output as that of the injected light. The output power ratio of the three beams is strongly dependent on the sign of the frequency detuning. Theoretical analysis, in which the carrier rate equation is coupled with nonlinear Maxwell’s equations, explains the experimental results well. The observed behaviors are attributed to a unique third-order nonlinearity stemming from saturation-induced refractive index change in the semiconductor gain medium.
Dependence of elastic strain on thickness for ZnSe films grown on lattice-mismatched materials
Authors: Yokogawa Toshiya , Sato Hisanao , Ogura Mototsugu
Published: July 2002

We present a new approach for calculation of the dependence of elastic strain on layer thickness concerning ZnSe films grown on GaAs and on ZnS. The basic concept involved in our model is that the interfacial misfit dislocations are generated only when the areal strain energy density exceeds an energy barrier. It is found that the elastic strain calculated by this model is quite in agreement with experimental results for the ZnSe/GaAs system with the energy barrier of 79 erg/cm2. To compare the theory with experiments, the difference of thermal expansion coefficient between the epitaxial layer and the substrate must be taken into consideration. Applications of the model to other systems are also discussed.
Reduced carbon acceptor incorporation in GaAs grown by molecular beam epitaxy using dimer arsenic
Authors: Garcia J. C. , Beye A. C. , Contour J. P. , Neu G. , Massies J. , Barski A.
Published: July 2002

Doubly doped (C,Be) GaAs layers grown by molecular beam epitaxy under dimer or tetramer arsenic flux are studied by selectively excited photoluminescence. Acceptor spectroscopy gives the first experimental evidence of the decrease of carbon shallow acceptor concentration when using dimer rather than tetramer arsenic.
Band gap and activation energy in amorphous silicon doping-modulated superlattices
Authors: Zhang D. H. , Haneman D.
Published: July 2002

It has been found that both the activation energy and optical energy gap of amorphous silicon doping-modulated nipi... superlattices vary consistently with i layer thickness. There is a pronounced maximum at an i layer thickness of approximately 14 nm. The occurrence of this maximum, and the general variation, correspond exactly with the behavior of the persistent photoconductivity for the structures. The results are explained in terms of the development of deep trap boron-phosphorus complexes which are rendered shallow by hydrogen accretion.
Elimination of secondary defects in As-implanted Si by high concentration oxygen atoms
Authors: Tamura M. , Horiuchi M. , Ito T. , Abe T.
Published: July 2002

Arsenic precipitate-induced dislocation loops generated at the projected range Rp of As in high-dose As-implanted, annealed (100) Si are eliminated, if oxygen-atom concentrations at the Rp region are high, i.e., above about 1×1020 atoms/cm3 . This is confirmed by the following two experiments: 80 keV, 2×1016 As+/cm2, 18-nm-thick through-oxide implantation together with subsequent annealing and a double implantation of 80 keV, 2×1016 As+ /cm2 and 22 keV, 5×1015 O+ /cm2 , followed by an annealing sequence. Experimental results suggest that the bonding of several As atoms with one oxygen atom suppresses As clustering.
Effect of copper related defects on the electron transport properties of semi-insulating CdSe
Authors: Roth M. , Burger A.
Published: July 2002

Semi-insulating CdSe crystals with a reduced concentration of electron trapping centers have been grown and characterized. The existence of complex electron traps is attributed to the presence of trace copper impurity. The trap density, trap level depth, trapping time, cross section for trapping of electrons, and the electron mobility have been determined for the first time on one single CdSe crystal using the combination of space-charge-limited currents (SCLC’s) method, standard nuclear measurements, and the transient charge technique (TCT). The advantages for applications of semi-insulating CdSe as a novel material for spectrometer grade nuclear radiation detectors are emphasized.
High-rate growth at low temperatures by free-jet molecular flow: Surface-reaction film-formation technology
Authors: Ohmi T. , Morita M. , Kochi T. , Kosugi M. , Kumagai H. , Itoh M.
Published: July 2002

Surface-reaction film-formation technology of epitaxial Si and polcrystalline silicon using free-jet molecular flow is proposed. High-rate (∼0.5 μm/min or higher) growth of homoepitaxial Si films with high crystallographic perfection has been achieved at temperatures as low as 600 °C without the chemical by-product deposition on the inner surface of the reaction chamber. This result also implies that this system has the cleaning-free function. The film-formation mechanism appears to be dominated by the chemical reaction on the substrate surface without the vapor phase reaction.
Crystallography of phase transition of YBa2Cu3O7−δ
Authors: Dravid Vinayak P. , Lyman C. E. , Notis M. R.
Published: July 2002

A space-group theoretical approach has been applied to the high Tc superconducting oxide YBa2Cu3O7−δ (δ∼0.3) to explain the occurrence of coherent domain boundaries. This method quantitatively accounts for the transmission electron microscopy (TEM) observations of {110} twin boundaries in the room-temperature orthorhombic phase. The possible nature of the relaxation of these twin boundaries and the atomic arrangement at these boundaries are briefly discussed.
Vanishing contact resistance on polycrystalline YBa2Cu3O7−x
Authors: Wieck A. D.
Published: July 2002

The preparation and characterization of gold contacts on polycrystalline YBa2Cu3O7−x ceramics that carry high currents and exhibit contact resistances of only 50 mΩ at room temperature are reported. By cooling the sample this resistance remains essentially constant until the superconducting transition temperature, Tc≂89 K, is reached. At Tc the contact resistance decreases like the resistivity of YBa2Cu3O7−x, reaching at T<Tc about 10 μΩ. This value is comparable to the intrinsic resistance of the contact material. Thus, below Tc, the contacts exhibit vanishing contact resistance at the metal–high-Tc-superconductor interface. Such low contact resistances may be extremely important for the technical application of the novel superconductors.
Growth of RhGa on GaAs (001) in a molecular beam epitaxy system
Authors: Guivarc’h A. , Secoué M. , Guenais B.
Published: July 2002

Thin films of RhGa were grown on GaAs(001) in a molecular beam epitaxy system, by codeposition of rhodium and gallium from separated sources. The RhGa/GaAs contact is stable at least up to 550 °C and the film resistivity is low enough ( ρ≂36 μΩ cm) to allow applications in microelectronics. In spite of high linear misfits, the as-deposited RhGa films exhibit the two following epitaxial arrangements related by a 90° rotation: [100](011)RhGa//[110](001)GaAs and [100](011)RhGa//[11̄0](001)GaAs. After annealing at 550 °C, only one arrangement is observed.
InAs strained-layer quantum wells with band gaps in the 1.2–1.6 μm wavelength range
Authors: de Miguel J. L. , Tamargo M. C. , Meynadier M.-H. , Nahory R. E. , Hwang D. M.
Published: July 2002

Strained In0.52Al0.48As/InAs single quantum wells have been grown by molecular beam epitaxy on InP substrates and their structural quality and commensurability demonstrated by transmission electron microscopy. Intense photoluminescence in the wavelength range of 1.2–1.6 μm for well widths between 10 and 30 Å was obtained, indicating a very efficient carrier collection into the highly (3.4%) biaxially compressed InAs wells.
GaAs-Si heterojunction bipolar transistor
Authors: Chen J. , Won T. , Ünlü M. S. , Morkoç H. , Verret D.
Published: July 2002

A GaAs/Si heterojunction bipolar transistor (HBT) structure is proposed having application for high-frequency operation. The structure combines the high-frequency capability of the GaAs/AlGaAs system with the advanced processing technology of Si. The proposed device consists of an n-AlGaAs/p-GaAs emitter and base layers on an n-Si collector with improved junction characteristics at the GaAs/Si heterointerface afforded by thermal annealing. This novel device structure combines the advantages associated with a wide band-gap AlGaAs emitter, the high electron mobility of GaAs, and the substantial reduction in device parasitics accorded the self-aligned structure. Additionally, the proposed device offers the possibility of planar GaAs processing. With the use of a compact transistor model, calculations of the high-speed capability of this transistor are presented. For an emitter-base junction area of 1 μm×5 μm, optimized fmax=108 GHz and fmax=ft=89 GHz were computed for the GaAs/Si HBT, compared to 76 and 62 GHz, respectively, for equivalent GaAs/AlGaAs HBT’s.
Influence of oxygen implantation on the carrier concentration profile in p-GaAs
Authors: Humer-Hager T. , Zwicknagl P.
Published: July 2002

The effect of oxygen implantation in p-type GaAs is discussed. Be and O ions are co-implanted into semi-insulating GaAs. Rapid thermal annealing with peak temperatures up to 900 °C is employed to activate the free carriers. The Be/O implanted layers exhibit a distinct narrowing of the carrier profile as compared to the pure Be implantation. This is ascribed to the formation of deep donor complexes associated with oxygen which can compensate the shallow Be acceptors.
Dislocation-free GaAs epitaxial growth with the use of modulation-doped AlAs-GaAs superlattice buffer layers
Authors: Shinohara Masanori
Published: July 2002

Suppression of dislocation threading from the substrate into GaAs epitaxial layers is investigated by using AlAs-GaAs superlattice buffer layers grown by molecular beam epitaxial technique. The efficiency of suppression is compared among several types of AlAs-GaAs superlattices with different electrically active impurity-doping distributions. With the use of modulation-doped AlAs(Si)-GaAs superlattice, dislocation threading is almost perfectly suppressed, and consequently, a dislocation-free epilayer can be grown. Dislocation bending at the AlAs/GaAs interface is thought to be due to the interaction between dislocations and electric charges.
Degradation phenomenology in (Al)GaAs quantum well lasers
Authors: Waters R. G. , Bertaska R. K.
Published: July 2002

The degradation rates for continuously operated quantum well lasers with natural facets have been investigated. For most devices, a simple functional relationship exists between degradation rate and operating current density and the data suggest that the role of optical flux is secondary. For device configurations with high excess nonradiative current densities, however, exceptionally high degradation rates are observed and a correlation is proposed.
Langmuir–Blodgett film passivation of unpinned n-type gallium arsenide surfaces
Authors: Tabib-Azar M. , Dewa A. S. , Ko W. H.
Published: July 2002

This letter reports the results of the passivation of photochemically unpinned GaAs surfaces using Langmuir–Blodgett (LB) films. Metal-insulator-semiconductor structures are fabricated with LB films as the insulator. The high-frequency capacitance versus voltage measurements show an order of magnitude decrease in the interface trap density (1011 cm−2 eV−1) as compared to the GaAs/anodic oxide interface. The hysteresis in the capacitance versus voltage curves was reduced from a 3-V shift in the flatband voltage, to about a 1-V shift, a level which has been seen in Si/LB film metal-insulator-semiconductor structures. Passivation with LB films is of interest because of their interesting electrical, chemical, and optical properties that can be used in GaAs-based devices.
Light emission from CH and H sputtered from hydrogen-implanted graphite
Authors: Klekamp A. , Möller W. , Snowdon K. J.
Published: July 2002

Characteristic spectra of light emission from CH molecules and hydrogen atoms sputtered from hydrogen-implanted graphite are observed. The relative intensities from both species vary with the implanted fluence. The CH yield remains constant while the Hα yield increases. This is consistent with two binding states of implanted hydrogen in graphite.
Thermal donor formation and the loss of oxygen from solution in silicon heated at 450 °C
Authors: Claybourn M. , Newman R. C.
Published: July 2002

A calibration is established which allows the thermal donor (TD) concentration in heat-treated Czochralski (CZ) silicon to be determined taking account of the fact that TD centers are double donors. It is then shown that for CZ samples heated at 450 °C, 13 oxygen atoms are lost from solution during the time taken to produce one TD center. It appears that TD production is a minority process in relation to oxygen precipitation.
Production of a low-pressure processing plasma with ion beam injection for thin-film preparation
Authors: Fujita Hiroharu , Yagura Shinya
Published: July 2002

A low-pressure processing plasma production with an ion beam injection is presented by applying microwave and rf discharges in a low-pressure gas for thin-film preparation. Electrostatic ion energy analyzer and emissive probe techniques are used in the plasma of a nonreactive gas to get plasma characteristics. The measurement reveals that an energy of ion beam injected into a reactor is controllable by adjusting a bias potential applied between the two plasmas, and electric fields at the steady state are affected by a configuration of a magnetic field applied for an enhancement of a microwave plasma production.
Time-resolved x-ray study of Ge during pulsed laser melting
Authors: Tischler J. Z. , Larson B. C. , Mills D. M.
Published: July 2002

Nanosecond resolution time-resolved x-ray diffraction has been used to make the first measurements of the liquid-solid interface overheating and undercooling in germanium. The results show an orientation-dependent undercooling for growth on (111) and (001) faces. For both the (111) and (001) faces the velocity versus temperature interface response function has a slope of ∼5 K/(m/s), except for undercooling on the (111) face where the slope is 20 K/(m/s).
Sputter deposition of YBa2Cu3O7−x films using a hemispherical target in a Hg vapor triode plasma
Authors: Wehner G. K. , Kim Y. H. , Kim D. H. , Goldman A. M.
Published: July 2002

High-quality stoichiometric films of YBa2 Cu3 O7−x have been grown epitaxially on SrTiO3 substrates by sputtering from a stoichiometric target of hemispherical shape using a Hg vapor triode plasma. Films exhibited superconducting transitions of a width ΔT∼2.5 K, with zero resistance being achieved at 89 K. From both the x rays and the temperature dependence of the normal-state electrical resistance it can be inferred that the films contain an admixture of domains with either the c or a axes normal to the plane.
Determination of crystallographic orientation of YBa2Cu3Ox grains from their optical twin patterns
Authors: Verhoeven J. D. , Gibson E. D.
Published: July 2002

Polycrystalline arrays of YBa2Cu3Ox grains display optical twin patterns and flat sides. The long sides of elongated grains are basal planes, {001}, and the twin planes are {110} planes. A technique is presented here for evaluating the crystallographic orientation of an elongated grain from the angles formed on the polish surface by its (110) and (1̄10) twin traces with the long grain boundary. Comparison with selected area channeling patterns from individual grains confirms the validity of the technique. The technique may be of some use in evaluating the texture of polycrystalline samples.
Micropatterning of high T
c films with an excimer laser
Authors: Mannhart J. , Scheuermann M. , Tsuei C. C. , Oprysko M. M. , Chi C. C. , Umbach C. P. , Koch R. H. , Miller C.
Published: July 2002

Micron-wide lines of high Tc Y-Ba-Cu-O have been successfully patterned by ablating the films with a pulsed excimer laser. The high Tc films are mounted onto a computer-controlled stepping stage and irradiated with a demagnified image of a variable-size rectangular aperture. This technique has been used for fabricating features ranging from several centimeters in length to submicron in width without any degradation in Tc. For example, a superconducting microstructure of Y-Ba-Cu-O, nominally 1 μm wide and 2.5 μm long, with a Tc (R=0) of 88 K and a Jc of 5×104 A/cm2 at 4.2 K was fabricated.
Infrared absorption study of N–H bonds in plasma-deposited silicon oxynitride films
Authors: Denisse C. M. M. , Janssen J. F. M. , Habraken F. H. P. M. , van der Weg W. F.
Published: July 2002

A study of the infrared (IR) absorption by N–H bonds in plasma-deposited silicon oxynitride films is presented. Emphasis in this study is placed on the absorption strength for the N–H stretching mode per bond, i.e., the absorptivity. It is found that the absorptivity strongly peaks at an oxygen-to-nitrogen ratio of O/(O+N)=0.2. A tentative explanation for the unusually high IR absorption strength in relation to the structure of the material is given.
Ion beam analysis of oxygen distribution in superconducting YBa2Cu3Ox
Authors: Rauhala E. , Keinonen J. , Järvinen R.
Published: July 2002

It has been shown that by combining the elastic scattering of protons and Rutherford scattering of α particles, the total composition and oxygen distribution of superconducting YBa2Cu3Ox films and bulk samples can be analyzed. The non-Rutherford scattering due to the 16O(p,p0)16O reaction enhances at the bombarding energy of 2.3 MeV the elastic scattering cross section by a factor of 5 over the cross section of the Rutherford scattering and makes it possible to determine the oxygen distribution in the matrix of heavy elements Y, Ba, and Cu.
Role of added fluorine to enhance the electromagnetic properties of superconducting Y-Ba-Cu-O compounds
Authors: Hakuraku Y. , Sumiyoshi F. , Ogushi T.
Published: July 2002

An experimental study was carried out on the role of a small quantity of fluorine which leads to an increment of the critical current density at 77 K of an Y-Ba-Cu-O compound. Such a small quantity of fluorine did not change its crystal structure according to x-ray diffraction analysis. From the comparison of the magnetization curves of both a bulk and a powder sample, we recognized that the added fluorine plays the role of strengthening superconductive connections among the grains. To clarify the growth mechanism of those grains, we also observed the feature of the grown grains in the fluorine-diffused sample which had an interface between Y1Ba2Cu3Oy and Y1Ba2Cu3F4Oy compounds before sintering.
Self-aligned diffusion barrier by nitridation of TiSi2
Authors: Wittmer Marc
Published: July 2002

Nitridation of TiSi2 has been shown to provide a self-aligned diffusion barrier layer on top of the silicide. A detailed analysis of the nitridation mechanism shows that the compound formed is TiN as commonly expected. The reaction TiSi2→TiN starts at the surface and progresses through the silicide film with a laterally uniform interface. The Si atoms that are dissociated from the TiSi2 grow epitaxially onto the Si substrate material. Implications for contact applications are mentioned.
Thickness dependence of superconductivity in rf-sputtered Y-Ba-Cu-O thin films
Authors: Akoh H. , Shinoki F. , Takahashi M. , Takada S.
Published: July 2002

Y-Ba-Cu-O thin films (100–730 nm) with small grains and a smooth surface have been fabricated by rf diode sputtering. The values of transition temperature Tc and critical current density Jc for the film (730 nm thickness) on SrTiO3 are 65 K and 1.2×105 A/cm2 at 4.2 K, respectively. The thickness dependence of Tc and Jc for the patterned films shows that Tc and Jc are almost constant for films with a thickness d≥200 nm.
Use of ion beams to decompose metalorganics into patterned thin-film superconductors
Authors: Mantese J. V. , Catalan A. B. , Hamdi A. H. , Micheli A. L.
Published: July 2002

Ion implantation of 400 keV O+2 ions, at a dose of 5×1014 ions/cm2, was used to selectively decompose a high Tc superconductor-forming metalorganic (MO). Implantation rendered the metal carboxylates insoluble in their solvent, xylene, permitting patterning of the MO prior to pyrolysis and annealing. Fine line superconductors were formed having 90 K onset temperatures and zero resistance at 68 K.
Spin-on Bi4Sr3Ca3Cu4O16+x superconducting thin films from citrate precursors
Authors: Furcone S. L. , Chiang Y.-M.
Published: July 2002

Thin films in the Bi-Sr-Ca-Cu-O system have been synthesized from homogeneous liquid citrate precursors by a spin-coating and pyrolysis method. Films prepared on SrTiO3 substrates of [100] orientation show strongly textured orientations with the c axis of the predominant Bi4 Sr3 Ca3 Cu4 O16+x phase normal to the film plane. In a single coating and firing, crack-free films of 0.2–0.5 μm thickness are obtained. For films fired to peak temperatures of 850–875 °C, linearly decreasing resistance with temperature is observed, with ρ (300 K)∼460 μΩ cm and ρ (300 K)/ρ (100 K)∼2.4. Clear onsets of superconductivity are observed at 90–100 K, with occasional films showing smaller resistant drops at 110–120 K. For all films, Tc (R=0) occurs in the range 70–75 K. High critical current densities at 4.2 K of 5–8×105 A/cm2 are measured by direct transport.
Observation of iron pileup and reduction of SiO2 at the Si-SiO2 interface
Authors: Kamiura Yoichi , Hashimoto Fumio , Iwami Motohiro
Published: July 2002

It was found by secondary-ion mass spectrometry in-depth profiling technique that approximately 1×1020 iron atoms/cm3 accumulated at the Si-SiO2 interface of oxidized silicon crystals where iron was introduced by the indiffusion prior to the oxidation at 1000 °C and above. The origin of iron accumulation is ascribed to the iron precipitation from the bulk silicon. It was also found that iron atoms that diffuse in through the bulk from the lapped backside of a preoxidized sample were trapped and aggregated at the front Si-SiO2 interface. An interesting observation is shown that the above indiffusing iron also entered into the oxide region near the interface possibly to reduce SiO2.
Effect of heat treatment on the properties of gallium-implanted polycrystalline silicon
Authors: Harrison H. B. , Komen Y. , Cao D. X. , Pogany A. P.
Published: July 2002

Polycrystalline silicon films deposited on silicon dioxide were partially amorphized by implantation with 100 keV gallium ions to a dose of 6×1015 cm−2. These films were then subjected to various heat treatments at 580 and 900 °C using conventional furnace or rapid thermal heating techniques. Sudden drops in sheet resistance occurred at lower temperatures with little change upon further heating. However, the high-temperature annealed specimen shows only an increase in sheet resistance with time. An explanation of these changes is proposed in terms of a liquid phase melting mechanism taking place during the crystallization of the amorphized near-surface layer. Transmission electron microscopy and Rutherford backscattering observations support this explanation.
Very low pressure chemical vapor deposition process for selective titanium silicide films
Authors: Ilderem V. , Reif R.
Published: July 2002

We report for the first time the selective deposition of titanium silicide using a very low pressure chemical vapor deposition technique with silane and titanium tetrachloride as the silicon and titanium sources, respectively. A method is described for the blanket and selective deposition of titanium silicide. A thin polycrystalline silicon (polysilicon) layer is deposited prior to the silicide deposition to promote the nucleation of titanium silicide. It is shown that selective deposition is possible by controlling the polysilicon and the titanium silicide deposition times. The resulting titanium silicide films have resistivities in the range of 15–25 μΩ cm.
Photoluminescence from the two-dimensional electron gas at GaAs/AlGaAs single heterojunctions
Authors: Yang C. H. , Lyon S. A. , Tu C. W.
Published: July 2002

We have studied photoluminescence from GaAs/Al0.3Ga0.7 As modulation-doped single heterojunctions, using excitation sources from infrared to ultraviolet near-liquid-helium temperature. The spectra have a strong interface component, accompanied by bulk GaAs and AlGaAs band-gap luminescence. Using ultraviolet instead of infrared as the excitation, the interface signal is greatly enhanced relative to the bulk GaAs luminescence. The interface signal can be shifted to the higher energies when a semitransparent front gate is positively biased. Our observations indicate that the interface luminescence comes from the recombination of the two-dimensional electrons with holes trapped at or near the interface. The peaks and the shoulders in the interface spectra appear to correspond to subbands of the two-dimensional electron gas at the interface. Our results demonstrate the feasibility of doing spectroscopic studies on high-mobility electrons at single heterojunctions.
Observation of a short optical pulse (<1.3 ps) from a gain-switched quantum well laser
Authors: Sogawa T. , Arakawa Y. , Tanaka M. , Sakaki H.
Published: July 2002

Short light pulse generation from an optically pumped GaAs/AlGaAs quantum well laser is measured. The shortest pulse width achieved so far is less than 1.3 ps. In addition, it is found that the pulse from varies randomly even when the same excitation condition, which results from stochastic behavior of the spontaneous emission coupling to the lasing mode. In order to discuss these results in more detail, spatial dependent rate equations are analyzed in which the stochastic process of the spontaneous emission and the traveling effect of spontaneously generated optical wave packets are included.
Photoluminescence measurements on open-tube heat-treated and Cd-diffused InP
Authors: Banerjee S. , Srivastava A. K. , Arora B. M. , Sulhoff J. W. , Zyskind J. L.
Published: July 2002

Cadmium incorporation in nominally undoped n-InP using open-tube diffusion has been investigated by photoluminescence (PL) measurements. A Sn-InP solution has been used to provide P vapor overpressure during the diffusion. This results in a 2–3 times larger incorporation of Cd acceptors in InP as compared to a low P vapor overpressure condition. In addition, the overall degradation in the PL intensity is considerably reduced by this technique. The degradation in InP during diffusion is further investigated by PL measurements on heat-treated InP under the diffusion conditions.
Universal relation between electron channeling line intensity and thickness of disordered layers on single crystals
Authors: Suzuki Tadashi , Kido Yoshiaki
Published: July 2002

Electron channeling patterns (ECP’s) were measured for Si and GaAs single crystals with thin polycrystal films or ion-damaged layers on the top surfaces. The intensity scans along channeling lines provide quantitative information on the above disordered layer thickness. We have derived a universal relation between the channeling line intensity and disordered layer thickness. This scaling law is independent of channeling planes and species of the single crystals and disordered layers.
I
n s
i
t
u observation of photochemical prenucleation and patterned metalorganic chemical vapor deposition
Authors: Mantell D. A.
Published: July 2002

Photochemical activation of a silicon native oxide surface with triisobutylaluminum (TIBA) and subsequent patterned metalorganic chemical vapor deposition (MOCVD) is observed in situ with x-ray photoelectron spectroscopy. At room temperature and in the presence of a low vapor pressure (10−7 Torr) of TIBA, an ArF excimer laser is used to photodissociate the metalorganic adsorbed on the surface. The deposit forms islands consisting of oxygen, carbon, and aluminum. The oxygen is included by the reduction of the native oxide surface and the aluminum by the photodissociation of the TIBA. When the surface is heated to 300 °C (with the laser off), this deposit nucleates MOCVD film growth. The unprocessed native oxide surface does not nucleate growth so the deposit grows in the pattern initially written with the laser. The source of the prenucleation barrier that inhibits growth on the native oxide is discussed.
Local structure around Zn atoms diffused into the GaAs crystal
Authors: Kitano T. , Matsumoto Y. , Matsui J.
Published: July 2002

We have studied the local structure around Zn atoms diffused into the GaAs crystal using the extended x-ray absorption fine structure method. Although Zn atoms are associated with vacancies at the first nearest neighbor (NN) sites, the first NN distance remains constant even where vacancies occur. Extra second NN atoms are located at a distance of 3.35 Å which is a bit less than the distance to position on a hexagonal site, and the third NN atoms are observed at a distance of 3.97 Å. From the above results, almost all Zn atoms occupy the substitutional site.
Systematic assembly of the double molecular boxes: {Cs⊂[CpCo(CN)3]4[Cp*Ru]3} as a tridentate ligand
Authors: Contakes Stephen M. , Kuhlman Matthew L. , Ramesh Maya , Wilson Scott R. , Rauchfuss Thomas B.
Published: July 2002

Cubic cage compounds composed of Co-CN-Ru linkages have been prepared which illustrate the following features: (i) new motifs for alkali metal ion complexation (i.e., cationic receptors for cations), (ii) a new family of triaza-metalloligands, and (iii) a double box-like cage. The cages are synthesized by the condensation of [CpCo(CN)3]−and [Cp*Ru(NCMe)3]+(cyclopentadienyl, Cp; pentamethylcyclopentadienyl, Cp*) the presence of Cs+. The species {Cs⊂{[CpCo(CN)3]4[Cp*Ru]4}+and {Cs⊂{[CpCo(CN)3]4[Cp*Ru]3[Cp*Rh]}2+illustrate the box-completion reaction Cs ⊂ Co4Ru3+ M (M = Cp*Rh2+, Cp*Ru+). With the naked ion precursors [Na(NCMe)6]+and [Fe(NCMe)6]2+, the box-completion reactions afforded {Na{Cs⊂[CpCo(CN)3]4[Cp*Ru]3]}2}+and {Fe{Cs⊂ [CpCo(CN)3]4[Cp*Ru]3]}2}2+. These cages provide the first examples, to our knowledge, of the double-box motif.
Communication between noncontacting macromolecules
Authors: Völker Jens , Klump Horst H. , Breslauer Kenneth J.
Published: July 2002

We present a quantitative experimental demonstration of solvent-mediated communication between noncontacting biopolymers. We show that changes in the activity of a solvent component brought about by a conformational change in one biopolymer can result in changes in the physical properties of a second noncontacting biopolymer present in solution. Specifically, we show that the release of protons on denaturation of a donor polymer (in this case, a four-stranded DNA tetraplex, iDNA) modulates the melting temperature of a noncontacting, acceptor polymer [in this case poly(A)]. In addition to such proton-mediated cross talk, we also demonstrate counterion-mediated cross talk between noncontacting biopolymers. Specifically, we show that counterion association/release on denaturation of native salmon sperm DNA (the donor polymer) can modulate the melting temperature of poly(dA)⋅poly(dT) (the acceptor polymer). Taken together, these two examples demonstrate how poly(A) and poly(dA)⋅poly(dT) can serve as molecular probes that report the pH and free salt concentrations in solution, respectively. Further, we demonstrate how such through-solvent dialogue between biopolymers that do not directly interact can be used to evaluate (in a model-free manner) association/dissociation reactions of solvent components (e.g., protons, sodium cations) with one of the two biopolymers. We propose that such through-solution dialogue is a general property of all biopolymers. As a result, such solvent-mediated cross talk should be considered when assessing reactions of multicomponent systems such as those that exist in essentially all biological processes.
Germinal center-associated nuclear protein (GANP) has a phosphorylation-dependent DNA-primase activity that is up-regulated in germinal center regions
Authors: Kuwahara Kazuhiko , Tomiyasu Shinjirou , Fujimura Satoru , Nomura Kazumi , Xing Yan , Nishiyama Noriko , Ogawa Michio , Imajoh-Ohmi Shinobu , Izuta Shunji , Sakaguchi Nobuo
Published: July 2002

Antigen stimulation induces a rapid proliferation of B cells for expansion of specific B cell clones and their further differentiation into antibody-producing cells in germinal centers of T-dependent antigen-immunized mice. Previously, we identified a 210-kDa germinal center-associated nuclear protein (GANP) that is up-regulated selectively in germinal centers and carries an MCM-binding domain in the carboxyl-terminal side. In addition, here, we found a region (from 414 to 550 aa) in GANP molecule that is slightly similar to the known DNA-primase component p49. The recombinant GANP fragment covering this region synthesizes RNA primers for extension by DNA polymerase I with single-stranded DNA templatesin vitro. GANP DNA-primase activity is controlled by phosphorylation at Ser502that is induced by CD40-mediated signalingin vitroand in the germinal center B cells stimulated with antigenin vivo. Overexpression ofganpcDNA in Daudi B cells caused the increased DNA synthesis more than the levels of themock-transfectants. These evidences suggested that the novel DNA-primase GANP is involved in regulation of cell proliferation of antigen-driven B cells in germinal centers.
A tumor host range selection procedure identifies p150
sal2
as a target of polyoma virus large T antigen
Authors: Li Dawei , Dower Ken , Ma Yupo , Tian Yu , Benjamin Thomas L.
Published: July 2002

Cancer cells may undergo loss or alterations in functions that
certain viruses normally target to promote virus replication.
Virus mutants that have lost the targeting function(s) should be able
to grow in such cancer cells but not in normal cells. A “tumor host
range” (
t-hr
) selection procedure has been devised
and applied to polyoma virus based on this rationale. Studies of one
t-hr
mutant have led to the identification of the mSal2
gene product (p150
sal2
) as a binding partner of the large T
antigen. mSal2 encodes a multizinc finger protein and putative
transcription factor homologous to the
Drosophila
homeotic gene
Spalt
. The
t-hr
mutant
encodes an altered large T protein that fails to interact with
p150
sal2
and is defective in replication and tumor
induction in newborn mice
.