bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential scanning calorimetric study of hydrogen–induced amorphization in C15 Laves phase GdCo2
Authors: Aoki K. , Li X-G. , Hirata T. , Masumoto T.
Published: July 2002

Differential scanning calorimetry and x-ray diffractometry have been used to monitor reactions of the C15 Laves phase GdCo2 during constant-rate heating in a hydrogen atmosphere and to determine the enthalpy change of each reaction. The values of the enthalpy change ΔH of hydrogen absorption, hydrogen-induced amorphization and crystallization are evaluated to be −67.2, −10.2, and −9.8 kJ/mol Gd, respectively. On the other hand, ΔH of hydrogen desorption is +31.4 kJ/mol Gd. The amorphous a-GdCo2Hx alloy crystallizes to GdH2 and Co. Therefore, the total value of ΔH of the above reactions along with the formation of GdCo2, −103 kJ/mol Gd, becomes nearly equal to that of formation of GdH2, −101 kJ/mol Gd.
Optical probing of pulsed, focused ultrasonic fields using a heterodyne interferometer
Authors: Royer D. , Dubois N. , Fink M.
Published: July 2002

The pulsed acoustic field of a piezoelectric focused transducer transmitted in water has been investigated by using an optical heterodyne interferometer. The probe beam is reflected by a thin membrane that follows the motion of the fluid particle. Absolute measurements of the mechanical displacement have been performed in the frequency range 5–15 MHz with a spatial resolution better than 0.1 mm and a sensitivity of 0.1 nm with a 20 MHz detection bandwidth that corresponds to a minimum detectable acoustic energy density of 2 μJ/m2. The experimental results all agree quantitatively with diffraction theory predictions of impulse response at the focus of the transducer.
Al/Si/AlGaAs/GaAs Schottky barriers by molecular beam epitaxy
Authors: Miller T. J. , Nathan M. I.
Published: July 2002

We have grown Al/Si/AlGaAs/GaAs Schottky diode structures by molecular beam epitaxy utilizing thin Si (6 Å) and AlxGa1−xAs (1500 Å) interfacial layers with Al mole fractions of x=0, 0.15, and 0.30. The compositional dependence of the Schottky barrier height, as determined by I-V measurement, is equal to that of the conduction band discontinuity between AlGaAs and GaAs. The barrier heights as determined by C-V, however, show no compositional dependence. Since the C-V characteristics depend only on the difference in the conduction band discontinuities for the Si-AlGaAs and GaAs-AlGaAs heterojunctions, this suggests that the change in conduction band discontinuity due to Al mole fraction is the same for both heterojunctions for the range of x studied.
Mg2TiO4 as a novel substrate for high-temperature superconducting thin films
Authors: Haefke H. , Lang H. P. , Sum R. , Güntherodt H.-J. , Berthold L. , Hesse D.
Published: July 2002

Single-crystalline Mg2TiO4 layers have been employed as a novel substrate material for superconducting YBa2Cu3O7−δ (YBCO) thin films. The Mg2TiO4 substrate layers have been grown on MgO cleavage faces by a solid-state reaction between the MgO crystal and TiO2 vapor. The structure and morphology of laser-deposited YBCO thin films have been studied by x-ray diffraction, transmission electron microscopy, electron diffraction, and scanning tunneling microscopy. YBCO has been grown on Mg2TiO4(001) with the epitaxial relationship [100](001) YBCO ∥[100](001)Mg2TiO4 and (considering twins)∥[010](001)Mg2TiO4. The film morphology is characterized by growth spirals originating from screw dislocations.
On the theory of frequency chirped pulse coherent amplification in inhomogeneously broadened gain medium
Authors: Belenov E. M. , Kryukov P. G. , Nazarkin A. V.
Published: July 2002

Frequency chirped pulse interaction with inhomogeneously broadened two-level active medium when the pulse width is shorter than the homogeneous relaxation time T2 (coherent interaction) is studied theoretically. It is shown that, unlike the case of incoherent interaction when only half an energy stored can be converted into field, in the nonlinear coherent regime full extraction of active medium energy is possible. The analogy of the effect with Landau–Zener transition between crossing molecular curves is pointed out. Giving high-energy output at relatively low peak intensities, this nonlinear mechanism of energy extraction can be useful for excimer lasers.
All-optical picosecond switch using organic single-mode fiber waveguide
Authors: Kanbara Hirohisa , Asobe Masaki , Kubodera Ken’ichi , Kaino Toshikuni , Kurihara Takashi
Published: July 2002

A highly efficient optical Kerr shutter switch is demonstrated, using a 1 m long and 4 μm core diameter waveguide consisting of a capillary glass fiber. An organic solution of 4-(N, N-diethylamino)-β-nitrostyrene is used as a large nonlinear optical material and contained in the capillary glass fiber. A deuterated solvent is used to achieve a high transmittance, and a solution concentration is adjusted to attain a single-mode waveguide. The very low driving power of less than 1 W is obtained with this organic solution fiber switch. A group-delay analysis shows that a picosecond response time is feasible.
In situ emissivity measurements to probe the phase transformations during rapid thermal processing Co silicidation
Authors: Schreutelkamp R. J. , Vandenabeele P. , Deweerdt B. , Coppye W. , Vermeiren C. , Lauwers A. , Maex K.
Published: July 2002

Phase transformations during RTP Co silicidation on both crystalline and polycrystalline silicon have been monitored for the first time by in situ emissivity measurements at a wavelength of 2.4 μm. The method can be used to accurately control the silicidation process and the final silicide phase. It is demonstrated that factors influencing silicidation, such as background doping level and the degree of crystallinity of the substrate can be determined. Ex situ emissivity measurements as a function of wavelength show that an analyzing wavelength of 10 μm can be applied to further improve the probing sensitivity for all silicide phase transformations.
Interactions between beryllia and high-lead glasses
Authors: Moro L. , Lazzeri P. , Prudenziati M. , Morten B. , Savigni P.
Published: July 2002

Interactions between BeO substrates and high-lead glasses of typical composition for hybrid thick films have been studied by means of secondary neutral mass spectrometry. The Be atomic concentration on top of glass layers, 2–40 μm thick, prepared at various temperatures Tf, ranging from 750 to 1000 °C have been measured. The results give insight of Be solubility values from 0.5 to about 6 at. %, according to the glass type and firing temperature, and diffusion coefficients higher than 10−10 cm2/s. Moreover, the diffusion mechanism appears quite different from that involved in interactions between the same glasses and alumina substrates, since no correlated diffusion process has been observed in the present case.
Electron mobility measured in undoped InGaAs epitaxial layer grown on n-InP substrate
Authors: Somogyi K. , Pfeifer J.
Published: July 2002

Electron mobility in an epitaxial layer grown on a highly conductive substrate can be determined by angle dependent magnetoresistance measurements. In this letter electron mobility has been measured first in the literature in undoped InGaAs epitaxial layers (n∼1×1015 cm−3) on n-InP substrate (n∼1018 cm−3). Because of the low resistance of the InGaAs layer compared to the series resistance of the structure, mainly that of the contacts, the acceptable range of contact resistances is indicated.
High-resolution transmission electron microscopy study of the radiation damage defects in high temperature superconductors
Authors: Zhao Y. J. , Chu W. K. , Liu J. R. , Kulik J. , Zandbergen H. , Tao Y. K.
Published: July 2002

High resolution transmission electron microscopy (HREM) reveals that MeV heavy ions like Au generate radiation damage defects, a few nanometers in size, in surface regions (about 100 Å) of the superconductors. Much larger defects have been found in the deeper regions of the superconductor sample, which is believed to be due to the larger damage cascade created by the slower ions after their electronic energy loss along the track. Monte Carlo simulation (trim) shows the same result in damage size as the HREM study. Light ions, like protons, generate mostly point defects, which are not visible to current electron microscopy. These point defects, although they can pin the flux, are not ideal for flux pinning, due to their small sizes.
Far-infrared Fabry–Perot resonator with high T
c YBa2Cu3O7−δ films on silicon plates
Authors: Pechen E. V. , Vent S. , Brunner B. , Prückl A. , Lipp S. , Lindner G. , Alexandrov O. , Schützmann J. , Renk K. F.
Published: July 2002

We report on a far-infrared Fabry–Perot resonator consisting of two high Tc YBa2Cu3O7−δ films on silicon plates. By pulsed laser deposition we prepared on the (100) silicon plates c-axis oriented epitaxial films (thickness ∼30 nm) with zero resistance at 88.5 K. We demonstrate operation of the resonator in the terahertz frequency range, up to ∼20 THz. At low temperature a high peak transmissivity (between 0.2 and 0.6) and a finesse of the order of 10 have been reached.
DX center electron occupancy under hydrostatic pressure in Si-doped Iny(Ga1−xAlx)1−yAs alloys
Authors: Romero A. L. , Calleja E. , García F. , Muñoz E. , Powell A. L. , Rockett P. I. , Grey R. , Claxton P. A.
Published: July 2002

DX centers in In-mixed AlGaAs alloys are analyzed by deep level transient spectroscopy and capacitance vs temperature measurements. The addition of In to Si-doped AlGaAs, with x=0.21 and 0.30, shifts the Si-DX center to a shallower position. Under hydrostatic pressure, DX centers deepen again into the band gap. The DX center shift, and consequently, the reduction of the DX center electron occupancy, when In is added, is due to an increase of the Γ to L energy difference. In terms of band-gap energy and DX center depth, adding 1% In is equivalent to a 1% Al reduction. Then, In mixing does not offer any new benefit to minimize DX center effects in AlGaAs-based heterojunction devices.
Observation of deep-level-free band edge luminescence and quantum confinement in strained Si1−xGex/Si single quantum well structures grown by solid source Si molecular beam epitaxy
Authors: Usami N. , Fukatsu S. , Shiraki Y.
Published: July 2002

Well-resolved band edge luminescence with no deep level emissions is reported for Si0.8Ge0.2/Si single quantum well (SQW) structures grown at high substrate temperatures (Ts≊620 °C) by solid source Si molecular beam epitaxy (MBE). No-phonon (NP) transitions due to symmetry-breaking alloy disordering in SiGe layers and transverse optical (TO) phonon replicas were clearly identified. With decreasing well width, NP and TO emissions were found to show systematic blue shift due to quantum confinement effect. Excellent crystal quality was evidenced by total absence of defect-related deep level emissions characteristic of photoluminescence spectra of samples grown at lower temperatures, Ts<600 °C. This result indicates that high growth temperature environment is essential to efficient radiative recombination in SiGe/Si QW structures.
The Born approximation in the problem of elastic wave scattering by a spherical inhomogeneity in a fluid-saturated porous medium
Authors: Gurevich Boris , Sadovnichaja Ada P. , Lopatnikov Serge L. , Shapiro Serge A.
Published: July 2002

The Born approximation is applied to the problem of scattering of elastic waves by a small (compared to the wavelength of the fast compressional wave) spherical porous inclusion placed in another porous medium described by the low-frequency version of Biot’s theory. The results depend significantly on the ratio of the wavelength of slow compressional wave to the inhomogeneity size. For small values of this ratio results are in accordance with exact results of Berryman [J. Math. Phys. 26, 1408 (1985)]. In the opposite case new results are obtained and used to calculate compressional wave attenuation in a porous medium containing randomly distributed inclusions. The frequency dependence of attenuation is found to be in agreement with the results for randomly layered porous materials.
Quantitative element analysis in high resolution electron microscopy in both phases of nanocrystalline Fe75.5Cu1Nb3Si12.5B8
Authors: van Bouwelen Frank , Sietsma Jilt , de Haan C. D. , van den Beukel A.
Published: July 2002

Element analysis is performed in both the crystalline and the amorphous phase of partially crystallized Fe75.5Cu1Nb3Si12.5B8, having a nanocrystalline structure. The crystallites are shown to contain significantly less Nb than the amorphous phase, which is important for understanding the nanocrystallization process. The amount of Si in the crystalline phase is found to be about 13%.
Use of triethylindium and bisphosphinoethane for the growth on InP by chemical beam epitaxy
Authors: Chin Albert , Martin Paul , Das Utpal , Mazurowski John , Ballingall Jim
Published: July 2002

We have demonstrated the first CBE growth of InP using bisphosphinoethane as a group V source. Mirrorlike surface morphology and excellent reflection high-energy electron diffraction patterns were observed. Room temperature and 77 K Hall mobilities for a 2.0 μm thick InP epitaxial layer were 4200 and 22 000 cm2/V s, with carrier densities of 5.7×1015 and 4.0×1015 cm−3, respectively. Although a high n-type impurity concentration is observed at the epitaxial layer-substrate interface, the epitaxial layer background impurity concentration is low enough for device fabrication. The full width at half maximum linewidth of the dominant donor bound exciton is 0.84 meV.
Evidence for preferential formation of the (Bi,Pb)2Sr2Ca2Cu3Ox phase at the Ag interface in Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox tapes
Authors: Feng Yi , High Y. E. , Larbalestier D. C. , Sung Y. S. , Hellstrom E. E.
Published: July 2002

Studies of the phase evolution in Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes processed with fine aerosol spray pyrolysis powder show that the 2223 phase always forms preferentially at the Ag interface at temperatures lower than those needed to form 2223 away from the Ag. The 2223 basal planes align themselves with the Ag surface and 2223 can penetrate into the Ag where the interface undulates. In the interior of the Bi-Sr-Ca-Cu-O core, away from the Ag, reaction to alkaline earth cuprate is favored over reaction to 2223. These results provide direct evidence of the beneficial role that Ag plays in developing the 2223 phase and emphasize the need to produce smooth Ag interfaces to attain highly aligned 2223.
Ion deflection due to sheath field curvature
Authors: Horwitz C. M.
Published: July 2002

Plasma sheath electric fields, hence ion motions, deviate near patterned substrate features. This results in a basic directionality limit to ion-assisted processes. Ion deviation is here derived analytically for dc sheaths, and expressed as an ‘‘ion isotropy ratio,’’ the fraction of ions bombarding a trench sidewall instead of its bottom. This ratio is equal to (trench depth/ion acceleration distance) multiplied by a factor of about 0.5. Thus, ion deviation is especially significant for discharges with small sheath heights and yields a fundamental tradeoff between ion directionality, ion energy, and permissible ion current.
Transport characteristics of Tl2Ba2CaCu2O8 bicrystal grain boundary junctions at 77 K
Authors: Cardona A. H. , Suzuki H. , Yamashita T. , Young K. H.
Published: July 2002

We report the fabrication and characterization of thin-film grain boundary junctions in Tl-based superconductors on bicrystal substrates. Post-deposition processed Tl2Ba2CaCu2O8 films were grown on bicrystal SrTiO3 substrates, with varying degrees of misorientation angle θ. Critical current densities and current-voltage curves had a strong dependence on θ. For θ≥10°, there was a two-to-three order of magnitude reduction in critical current density, and for θ≥20°, the current-voltage curves displayed resistively shunted junction behavior. These high angle grain boundary junctions have features at 77 K that are attractive for device applications, including sharp voltage onsets, well-behaved dc magnetic and rf field dependence, IcRn products as large as 300 μV, and low 1/f noise. Simple dc superconducting quantum interference devices fabricated with these junctions exhibited transfer functions of up to 30 μV/Φ0 at 77 K.
Spatial subharmonics in photorefractive Bi12SiO20 crystal with a square wave applied field
Authors: Kwak C. H. , Shamonin M. , Takacs J. , Solymar L.
Published: July 2002

The instability leading to the appearance of subharmonics in the presence of a square wave applied field is investigated both theoretically and experimentally. The threshold conditions are found for a range of parameters and the temporal variation of the subharmonic amplitude is measured. It is shown that a relatively simple theory, based on a set of material equations, gives good agreement with some of the experimental results but other experiments indicate that the materials equations alone cannot describe all the observations.
Difference Raman spectra of PbTiO3 thin films grown by metalorganic chemical vapor deposition
Authors: Feng Z. C. , Kwak B. S. , Erbil A. , Boatner L. A.
Published: July 2002

The technique of Raman scattering has been used to investigate the properties of ferroelectric PbTiO3 thin films grown on both single-crystal KTaO3 and fused quartz substrates by means of metalorganic chemical vapor deposition. The ‘‘difference Raman’’ technique was employed in which substrate contributions were subtracted in order to obtain Raman spectra for the PbTiO3 films. A comparison of the Raman spectra taken at 300 and 80 K for PbTiO3 and KTaO3 reveals two different types of temperature behavior and these effects are accounted for by the soft-mode theory.
Transport in submicrometer buried mesotaxial cobalt silicide wires
Authors: Zimmerman Neil M. , Liddle J. Alex , White Alice E. , Short Ken T.
Published: July 2002

We describe the formation of narrow (down to 130 nm) buried CoSi2 wires by implantation of Co ions through an oxide mask into a Si wafer followed by annealing. Fabrication of free-standing wires is also demonstrated. The temperature dependence of the four-terminal resistance from 4 to 600 K shows that these wires are good metals, very similar to wider layers. Measurements at high current density and temperature suggest that the wires may be robust with respect to electromigration damage.
Reduction of interface-trap density in metal-oxide-semiconductor devices by irradiation
Authors: Balasiński Artur , Ma T. P.
Published: July 2002

Annealing of interface defects in metal-oxide-semiconductor (MOS) devices by x-ray irradiation has been observed. The effect occurs in rad-hard devices which had been previously damaged severely by high-field Fowler–Nordheim electron injection, but has not been observed in standard MOS devices which are not radiation-hardened. A mechanism based on the recombination-enhanced-defect-reactions process is proposed to explain the results.
Submicrometer lithographic patterning of thin gold films with a scanning tunneling microscope
Authors: Stockman L. , Neuttiens G. , Van Haesendonck C. , Bruynseraede Y.
Published: July 2002

A scanning tunneling microscope (STM) has been used to locally expose Langmuir–Blodgett layers of a negative electron beam resist (ω-tricosenoic acid) on top of a thin gold film. The STM operates in a dry nitrogen atmosphere at a voltage difference of about −10 V between the electrochemically etched Pt-Ir tip and the gold surface. After development in ethanol, the unexposed areas of the gold film are removed by argon ion milling. Gold wires with a linewidth down to 15 nm have been prepared. Electrical transport measurements confirm the homogeneity and the one-dimensional metallic character at low temperatures of the gold structures.
Multilayer structure for epitaxial growth of oxide films on Si with an underlying electrode
Authors: Hung L. S. , Bosworth L. A.
Published: July 2002

Multilayers of CaF2 , Pd, and Pt were epitaxially grown on HF treated (100)Si by sequential deposition of the desired materials in ultrahigh vacuum. This structure is suitable for epitaxial growth of oxide films on Si with an underlying electrode. The epitaxial layer CaF2 effectively acts as a barrier to impede metal-substrate reaction, and the metal bilayer Pd/Pt forms an epitaxial electrode with good adhesion to the underlying substrate and high resistance to oxidation. KNbO3 deposited on this multilayer structure showed epitaxial growth in a mixed (001)/(110) orientation.
Optical gas detection using metal film enhanced leaky mode spectroscopy
Authors: Osterfeld M. , Franke H. , Feger C.
Published: July 2002

Sensors based on fiber optics or optical waveguides are finding increasing interest for applications in aggressive environments, in the vicinity of high electric fields, or in areas where miniaturization is a necessity. Many of these optical sensors utilize interaction of evanescent fields with the environment. If the optical component is made of a polymer, the ability of polymers to ad- or absorb vapors can be utilized for the sensing of such vapors. This is based on changes in refractive indices or anisotropy upon interaction with the vapor.
Integration of low-temperature GaAs on Si substrates
Authors: Frankel Michael Y. , Tadayon Bijan , Carruthers Thomas F.
Published: July 2002

GaAs was grown on Si substrates by molecular-beam epitaxy at low substrate temperatures. Femtosecond time-resolved reflectivity investigations revealed a significant reduction of carrier lifetime in GaAs epilayers from 14 ps to <0.5 ps as the growth temperature was reduced from 400 to 150 °C. Photoconductors were fabricated on the epilayers, and electro-optic sampling was used to confirm the electrical response times of <1 ps. The responsivity is comparable to that for low-substrate-temperature GaAs grown on GaAs substrates, with a photogenerated carrier mobility of ∼100–300 cm2/V s. The low growth temperatures allow ultrafast GaAs-based photodetector incorporation into Si-based integrated circuits for novel optoelectronic applications.
New Pb-free solder alloy with superior mechanical properties
Authors: McCormack M. , Jin S. , Kammlott G. W. , Chen H. S.
Published: July 2002

New high-strength Pb-free solder alloys, based on the Sn-Ag-Zn system, have been developed. A relatively small addition of Zn significantly improves the mechanical strength of Sn-3.5% Ag eutectic solders while maintaining the same level of ductility. The observed increase in strength is as much as 48% over that of the Zn-free alloy. This strengthening from the Zn additions is attributed to a substantial refinement of the precipitates in the solidification microstructure. The problems of nonuniformity in solidification dendrite structure and solder surface roughness often observed in the Sn-Ag binary alloys are also alleviated by the Zn addition. It is found that essentially all of the added Zn resides in the more corrosion-resistant, Ag-based, intermetallic precipitates, leaving the Sn-rich matrix primarily free of Zn in solid solution. High-temperature creep tests indicate that the new Zn-containing alloys exhibit a remarkably improved creep resistance of more than an order of magnitude.
Electro-optic properties of single crystalline ferroelectric thin films
Authors: Reitze D. H. , Haton E. , Ramesh R. , Etemad S. , Leaird D. E. , Sands T. , Karim Z. , Tanguay A. R.
Published: July 2002

We have investigated the transverse and longitudinal electro-optic properties of epitaxial single crystalline lead lanthanum zirconate titanate ferroelectric thin films grown by pulsed laser deposition on [100] silicon and MgAl2O4 substrates. With the electric field applied in a longitudinal geometry, we measure birefringence shifts of up to 1×10−3. These films exhibit a large optical hysteresis, and may provide a basis for electrically written, optically and nondestructively read nonvolatile memories.
Silicon dioxide thin films prepared by chemical vapor deposition from tetrakis (dimethylamino)silane and ozone
Authors: Maruyama Toshiro , Shirai Toshimasa
Published: July 2002

Silicon dioxide thin films were prepared by a low-temperature atmospheric-pressure chemical vapor deposition method. The raw materials were tetrakis(dimethylamino)silane and ozone in oxygen gas. At a substrate temperature above 40 °C, the thin films were obtained with a high deposition rate.
Minority-carrier mobility enhancement in p+ InGaAs lattice matched to InP
Authors: Harmon E. S. , Lovejoy M. L. , Melloch M. R. , Lundstrom M. S. , Ritter D. , Hamm R. A.
Published: July 2002

Minority electron mobilities in p+-In0.53Ga0.47As have been measured with the zero field time-of-flight technique. The room-temperature (297 K) minority electron mobilities for p+-In0.53Ga0.47As doped 0.9 and 3.1×1019 cm−3 are found to be 2900 and 3300 cm2 V−1 s−1, respectively. These are the first measurements to demonstrate enhancement in minority-carrier mobility as doping is increased for heavily doped In0.53Ga0.47As. This enhancement in mobility as doping is increased is similar to that observed in p+-GaAs, which has been attributed to reductions in plasmon and carrier–carrier scattering between minority electrons and majority holes.
Multiple dislocation loops in linearly graded InxGa1−xAs (0≤x≤0.53) on GaAs and InxGa1−xP (0≤x≤0.32) on GaP
Authors: Chang J. C. P. , Chin T. P. , Tu C. W. , Kavanagh K. L.
Published: July 2002

We report transmission electron microscopy studies of dislocation structures in two lattice-mismatched III-V systems, InxGa1−xAs (0≤x≤0.53)/GaAs and InxGa1−xP (0≤x≤0.32)/GaP, grown by gas-source molecular beam epitaxy. Multiple dislocation-loops, extending from within a linearly graded buffer layer to deep inside the substrate, were observed in both systems. All dislocations in each set of loops consisted of 60° dislocations with the same Burgers vector on a similar {111} glide plane. The density in the graded buffer and the substrate was estimated to be 2×109/cm2, and their appearance was associated with low threading dislocation densities and good optical quality in material grown on top of the buffer layer, InP/In0.53Ga0.47As on GaAs or In0.32Ga0.68P on GaP.
Possible origin of the anomalous magnetization behavior in melt-textured Y1Ba2Cu3O7−δ crystallites
Authors: Ullrich M. , Müller D. , Heinemann K. , Niel L. , Freyhardt H. C.
Published: July 2002

Magnetization measurements of the hysteresis loop, M(B), of melt-textured Y1Ba2Cu3O7−δ (YBCO) crystallites were performed in external magnetic fields up to 10 T. The M(B) curves exhibit, between the superconducting transition temperature Tc and almost 39 K, a peak at a finite field B* which increases with decreasing temperature. The crystallites possess a high density of dislocations which could have been introduced during the high temperature treatment and/or by stresses created due to differences in the lattice parameter of small inclusions and the YBCO matrix. The large dislocation density together with the high sensitivity of the superconducting order parameter on deviations from the regular crystal structure and the small coherence length are suggested to be responsible for the observed fishtail shape of the magnetization curves.
High-frequency polarization self-modulation in vertical-cavity surface-emitting lasers
Authors: Jiang Shijun , Pan Zeqi , Dagenais M. , Morgan R. A. , Kojima K.
Published: July 2002

Polarization self-modulation at frequencies up to 6 GHz is observed in a vertical-cavity surface-emitting laser. This self-oscillation is observed when a portion of the laser output power is injected back into the laser after having rotated its polarization by 90° with respect to the initial laser polarization state. Our experiment demonstrates a simple technique for generating an ultrahigh frequency optical clock. New applications in optical storage are also envisioned.
High contrast, high reflectivity, optical modulator using the Franz-Keldysh effect in a thin film of GaAs
Authors: Tayebati Parviz
Published: July 2002

The bulk Franz-Keldysh effect in a thin film of GaAs is used to demonstrate high contrast ‘‘normally on’’ and ‘‘normally off’’ optical modulation at 885.2 and 877.5 nm, respectively. The device, a Ag/GaAs/ITO asymmetric Fabry–Perot structure, exhibits a contrast ratio of ∼75:1 and reflectivity of 32.5% in the normally on mode. This is a demonstration of an asymmetric Fabry–Perot device using the bulk Franz–Keldysh effect. Using the Franz–Keldysh effect makes a larger number of materials and wider wavelength range available for optical modulation than quantum confined effects.
Control of porous silicon luminescent pattern formation by ion implantation
Authors: Bao Xi-Mao , Yang Hai-Qiang
Published: July 2002

We present a method to generate luminescent patterns of porous silicon. The crystal Si samples were selectively amorphized by self-implantation through a deposited Al mask. After anodization, the porous Si formed on the crystal regions exhibits visible luminescence, while that on the preamorphized regions does not. The limit of resolution of the light-emitting patterns is about 2 μm.
Buried heterostructure 0.98 μm InGaAs/InGaAsP/InGaP lasers
Authors: Vail E. C. , Lim S. F. , Wu Y. A. , Francis D. A. , Chang-Hasnain C. J. , Bhat R. , Caneau C.
Published: July 2002

We report the fabrication and comparison of buried heterostructure and ridge waveguide 0.98 μm lasers with strained InGaAs quantum wells, stepped InGaAsP confinement layers, and InGaP claddings. The buried heterostructure (BH) lasers exhibit superior performance with lower threshold and higher power. We demonstrate a BH laser with 4.4 mA threshold current, 77% differential quantum efficiency, 196 mW of output power, and 150 K characteristic temperature. No catastrophic optical damage is observed on the laser facets, although the facets were not coated or treated.
Ultrafast photodetection with an AlInAs/GaInAs heterojunction bipolar transistor
Authors: Carruthers T. F. , Frankel M. Y. , Kyono C. S.
Published: July 2002

Femtosecond visible-wavelength optical pulses were injected into unmodified AlInAs/GaInAs single-heterojunction bipolar transistors with current unity-gain frequencies of ∼20 GHz. Emitter photocurrent transients as fast as 2.4 ps, corresponding to a photodetection bandwidth in excess of 200 GHz, were measured electro-optically. The responsivity was as high as 0.078 A/W at 620 nm. Slow photocurrent components due to photogenerated holes could be canceled with appropriate base biasing; measurements of the slow photocurrents provided information about the dynamics of carrier recombination in the base.
Ultrafast transient absorption measurement of the electron-LO phonon scattering time in GaAs-Al0.33Ga0.67As multiple quantum wells
Authors: Collings D. , Schumacher K. L. , Raksi F. , Hughes H. P. , Phillips R. T.
Published: July 2002

The electron-LO phonon scattering time in GaAs-Al0.33Ga0.67As quantum wells is determined to be 200±50 fs using transient absorption with low excitation density, a more direct method than previous measurement techniques.
Doped microcrystalline silicon growth by high frequency plasmas
Authors: Hollingsworth R. E. , Bhat P. K.
Published: July 2002

The growth of boron- and phosphorus-doped microcrystalline silicon films on glass using plasma enhanced chemical vapor deposition at high rf frequencies was examined for substrate temperatures from room temperature to 400 °C. Microcrystalline growth was obtained by heavy hydrogen dilution of silane with phosphine or trimethylboron as the doping gas. A maximum conductivity of 8 (Ω cm)−1 was obtained at a substrate temperature of 180 °C for p-type films and 74 (Ω cm)−1 at 210 °C for n-type films.
Effect of using pure ozone on in situ molecular beam epitaxy of YBa2Cu3O7−x thin films at low pressure
Authors: Sawa Akihito , Obara Haruhiko , Kosaka Shin
Published: July 2002

We studied the effect of ozone on molecular beam epitaxy (MBE) of YBa2Cu3O7−x (YBCO) films. The minimal ozone flux required for in situ synthesis of YBCO films was discussed taking into account the influences of kinetics and thermodynamics. Films were deposited at various growth rates and with various ozone fluxes on MgO(100) substrates at 650 °C. The minimal ozone flux required for in situ growth of YBCO films increased linearly with increasing growth rate. We suggest that in situ MBE growth of YBCO thin films with ozone is kinetically limited by the ozone-to-metal reaction ratio.
Fabrication of in-plane-gate transistor structures by focused laser beam-induced Zn doping of modulation-doped GaAs/AlGaAs quantum wells
Authors: Baumgartner P. , Brunner K. , Abstreiter G. , Böhm G. , Tränkle G. , Weimann G.
Published: July 2002

Local Zn doping of n-modulation-doped GaAs/AlGaAs quantum well samples induced by absorption of a focused laser beam has been used to fabricate in-plane-gate transistor structures. Laser-induced thermal Zn diffusion from a highly doped SiO2 emulsion into the sample surface layers allows direct writing of lateral npn structures with sub-μm resolution. The p-doped lines form lateral potential barriers which are efficiently isolating the gate electrodes for large applied voltages at room temperature. Transistor structures with a 3-μm-wide electron channel in between V-shaped gates yield a transconductance of about 50 μS and are pinched-off at gate voltages UG≤−2.0 V.
Shallow oxygen-related donors in bonded and etchback silicon on insulator structures
Authors: Warren W. L. , Fleetwood D. M. , Schwank J. R. , Shaneyfelt M. R. , Winokur P. S. , Devine R. A. B. , Maszara W. P.
Published: July 2002

Using electron paramagnetic resonance we have been able to identify a new oxygen-related donor defect in the Si substrate of bonded and etchback silicon-on-insulator structures. This axially symmetric donor is preferentially aligned along the [100] direction, and resides close to the Si/SiO2 interface. It is tentatively suggested that the donors result from the nonoxidizing anneal received by the wafers during the bonding process.
Franz–Keldysh effect in a two-dimensional system
Authors: Schmeller A. , Hansen W. , Kotthaus J. P. , Tränkle G. , Weimann G.
Published: July 2002

We report luminescence and photocurrent experiments on an InGaAs/GaAs quantum well in strong lateral electric fields. The fields are imposed with an interdigitated gate on the crystal surface that consists of an array of metal stripes with a 250 nm period. The small period allows generation of electric fields of about 105 V/cm by application of only 1.5 V at the gate electrodes. Strong subgap absorption and oscillations of the interband absorption as function of radiation energy are observed and discussed in view of the Franz–Keldysh effect. The resulting photo-I-V characteristic shows high potential for electro-optic applications.
Effect of bulk microdefects induced in heat-treated Czochralski silicon on dielectric breakdown of thermal SiO2 films
Authors: Satoh Y. , Murakami Y. , Furuya H. , Shingyouji T.
Published: July 2002

We examine the effect of bulk microdefects (BMD) intentionally introduced in Czochralski silicon substrates by heat treatment on the dielectric breakdown of thermally grown SiO2 films. Transmission electron microscope observations reveal that the BMD consist of oxygen precipitates, perfect dislocation loops, and faulted dislocation loops. When the BMD are incorporated into the SiO2 film during thermal oxidation, an apparent decrease in the breakdown field is observed. The size of the oxygen precipitates has a clear relationship with the breakdown field: larger oxygen precipitate causes greater degradation. The dislocation loops are unrelated to the breakdown field.
Thermally stable polyester polymers for second-order nonlinear optics
Authors: Nahata Ajay , Wu Chengjiu , Knapp Charles , Lu Victor , Shan J. , Yardley James T.
Published: July 2002

We report electro-optic and thermal stability properties of a novel thermostable fluorene-based polyester polymer. The electro-optic coefficient, r33, at 810 nm is 2.6 pm/V for a poling field of 0.5 MV/cm. This value is comparable to that obtained from many reported side-chain polymers. Isothermal decay measurements of the charge transfer absorption band and electro-optic effect demonstrate that the chemical stability of the fluorene molecule appears to dominate over orientational relaxation in the decline of the electro-optic response at elevated temperatures.
Improvement of the lasing performance of the CuCl-He laser by adding Ag atoms as energy donors and Cs atoms as energy acceptors
Authors: Masumura Yuuki , Ishikawa Toshiaki , Saitoh Hiroshi , Ishibashi Masamichi , Fujii Kan-ichi
Published: July 2002

The lasing performance of the CuCl-He system has been largely improved with increases in the pulse widths and pulse peak values by adding Ag atoms as energy donors and Cs atoms as energy acceptors. As typical results, we simultaneously obtained a range from 20 to 40 ns of the pulse widths and an average increase in the peak power of the laser pulses from 103 to 288 W. Our experimental equipment was a homemade small size simple laser device.
Modulation of one-dimensional electron density in n-AlGaAs/GaAs edge quantum wire transistor
Authors: Nakamura Y. , Tsuchiya M. , Koshiba S. , Noge H. , Sakaki H.
Published: July 2002

An array of AlGaAs/GaAs edge quantum wires (EQWIs) with an effective width of 80 nm was successfully prepared on a (111)B microfacet structure on a patterned substrate by molecular beam epitaxy. By forming a gate electrode on the wires, field effect transistor action has been successfully demonstrated. The conductance of the wire measured in magnetic fields has exhibited a clear Shubnikov–de Haas (SdH) oscillation, and its Landau plot shows a characteristic nonlinearity caused by the magnetic depopulation of one-dimensional (1D) subbands. It has been found that as the gate voltage decreases, the SdH peaks shift systematically toward lower magnetic fields, indicating a successful modulation of 1D electron density in the EQWI.
Dependence of the off-state current in polycrystalline silicon thin film on electric field in the channel
Authors: Lifshitz N. , Luryi S.
Published: July 2002

We correlated the off-state current in polycrystalline silicon (polysilicon) thin film transistor (TFT) with the peak electric field in the channel of the device. We investigated p-channel TFTs with different gate oxide thicknesses, at varying gate and drain biases. The electric fields in the channel of the devices under these experimental conditions were calculated using both process and device simulators, and the experimental off-state current was plotted against simulated fields. We found that in a wide range of electric fields the current exhibits a nearly exponential behavior. Different combinations of the drain and gate biases produce nearly the same off-state current, provided the calculated peak field is the same; moreover, curves corresponding to different gate oxide thicknesses overlay each other. Our results are compatible with the model of the off-state current as being due to the field emission at grain boundaries.
Controllable narrow band and broadband second-harmonic generation by tailored quasiphase matching with domain gratings
Authors: Fischer Baruch , Horowitz Moshe
Published: July 2002

We demonstrate second-harmonic generation for various discrete input wavelengths by a controllable quasiphase matching method. This is done by forming ferroelectric domain gratings in SrxBa1−xNb2O6 crystals. The method allows flexible preparation of tailored quasiphase matching for prespecified wavelengths over prespecified bandwidths. Conversion efficiencies of 5% were achieved.
Scaling of ferroelectric properties in La-Sr-Co-O/Pb-La-Zr-Ti-O/La-Sr-Co-O capacitors
Authors: Ramesh R. , Dutta B. , Ravi T. S. , Lee J. , Sands T. , Keramidas V. G.
Published: July 2002

The scaling of ferroelectric properties with the capacitor size has been studied using epitaxial La-Sr-Co-O/Pb-La-Zr-Ti-O/La-Sr-Co-O heterostructures grown on Si. Discrete, large area capacitors were fabricated using a shadow mask or lift-off process. Capacitors with areas smaller than 10−5 cm2 were fabricated by a full-wafer process involving argon ion milling. The fatigue, aging, and retention characteristics of the capacitors fabricated by ion milling are commensurate with those of the discrete capacitors fabricated by the shadow mask technique. These results are very relevant with respect to the ultimate application of the capacitors in high density nonvolatile memories.
Reversible pyroelectric and photogalvanic current in epitaxial Pb(Zr0.52Ti0.48)O3 thin films
Authors: Lee J. , Esayan S. , Prohaska J. , Safari A.
Published: July 2002

The pyroelectric and photogalvanic effects have been studied in epitaxial Pb(Zr0.52Ti0.48)O3 (PZT) thin films. Photoinduced currents, which were completely reversible by electrical voltage, were observed. The photoinduced currents exhibited transient and steady state components. The transient component, in turn, consisted of two components with fast (<1 s) and slow (∼hours) relaxation times. The mechanisms of the photoinduced currents in PZT films and their possible applications in nondestructive readout ferroelectric memory are discussed.
Far-infrared photocurrent of quantum wires
Authors: Drexler H. , Hansen W. , Kotthaus J. P. , Holland M. , Beaumont S. P.
Published: July 2002

We study the photocurrent of quantum capacitor devices consisting of an electron wire array induced in an undoped AlAs/GaAs heterojunction with an interdigitated gate electrode. The photocurrent measures the collective one-dimensional intersubband resonance in the electron wires. The new technique to measure fundamental excitations of nanostructured electron systems yields strong signals even at very low electron densities so that only a single one-dimensional subband is occupied. Compared to previous far-infrared transmission studies the length and the number of the wires averaged in our technique is substantially smaller. The intersubband resonance in our devices is tunable in a wide range of energies up to 10.5 meV.
Improving the mobility of an In0.52Al0.48As/In0.53Ga0.47As inverted modulation-doped structure by inserting a strained InAs quantum well
Authors: Akazaki Tatsushi , Nitta Junsaku , Takayanagi Hideaki , Enoki Takatomo , Arai Kunihiro
Published: July 2002

The mobility of two-dimensional electrons in an In0.52Al0.48As/In0.53Ga0.47As inverted modulation-doped structure improved by inserting an InAs quantum well into the InGaAs channel. This letter addresses the main cause of this mobility improvement. By optimizing the thickness of the InAs quantum well, its distance from the underlying InAlAs spacer layer, and the InAlAs spacer-layer thickness, maximum mobilities of 16 500 cm2/V s at 300 K and 155 000 cm2/V s at 10 K are attained. The improvement in mobility is attributed to a decrease in scattering caused by ionized impurities, interface-roughness, and trap impurities. This decrease is a result of the superior confinement of two-dimensional electron gas in the InAs quantum well.
Surface cleaning effect on dielectric integrity for ultrathin oxynitrides grown in N2O
Authors: Hao Ming-yin , Lai Kafai , Chen Wei-Ming , Lee Jack C.
Published: July 2002

In this study, we developed a wafer-cleaning procedure for ultrathin dielectric growth. This involves a modified RCA clean, a dilute-HF dip and a subsequent immersion in methanol/HF solution. Ultrathin (≊42 Å) oxynitride films were grown in pure N2O using this new cleaning procedure and some other schemes to investigate the effects of surface preparation on dielectric integrity. Devices fabricated by this new cleaning procedure were found to exhibit the lowest leakage current level and the best breakdown performance among all samples. The variation in the current-voltage characteristics across a 4-in. wafer was also minimized by this two-step dipping process. The results suggest that the new cleaning procedure is desirable to yield high-quality ultrathin dielectrics.
Quantum transport in polycrystalline silicon ‘‘slit nano wire’’
Authors: Wada Yasuo , Suga Mitsuo , Kure Tokuo , Yoshimura Toshiyuki , Sudo Yoshimi , Kobayashi Takashi , Goto Yasushi , Kondo Seiichi
Published: July 2002

Electrical conduction characteristics of polycrystalline silicon (poly-Si) ‘‘slit nano wire’’ between room temperature and 2 K are reported. The slit nano wire is fabricated by the self-aligned confinement of a 100-nm-wide and 100-nm-deep trench formed in silicon substrate; the wire is 5–8 nm wide, 10–20 nm high and has grain length of around 100 nm. The resistance increases with the reduction of temperature, which might be due to the quasi-one-dimensional structure of the slit nano wire. The conductance exhibits a dip of about 30 mV below 10 K, which is attributed to a barrier height of about 1 meV at the grain boundary of the poly-Si layer.
Strained InAs/InP quantum well heterostructure lasers grown by low-pressure metalorganic chemical vapor deposition
Authors: Xing Q. J. , Brebner J. L. , Masut R. A. , Ahmad G. , Zhao G. , Tran C. A. , Isnard L.
Published: July 2002

This letter reports the successful operation at room temperature of a separate confinement heterostructure InAs/InGaAs/InP strained-layer multiple quantum well laser grown by low-pressure metalorganic chemical vapor deposition. The threshold current density was as low as 250 A/cm2 for a 600×200 μm broad area laser device. The characteristic temperature T0 was found to be 190 K between 100 and 130 K, and 147 K between 130 and 300 K. The lasing wavelength was 1.7 μm at room temperature.
High-temperature superconductor Josephson junctions with a gradient Pr-doped Y1−xPrxBa2Cu3O7−δ (x=0.1, 0.3, 0.5) as barriers
Authors: Jia Q. X. , Wu X. D. , Reager D. , Foltyn S. R. , Mombourquette C. , Tiwari P. , Campbell I. H. , Houlton R. J. , Peterson D. E.
Published: July 2002

High-temperature superconductor YBa2Cu3O7−δ based superconducting-normal-superconducting (SNS) Josephson junctions were fabricated using a unique device design. The normal material included a gradient Pr-doped Y1−xPrxBa2Cu3O7−δ layer which was composed of a light doping (x=0.1) next to both YBa2Cu3O7−δ electrodes, a slightly higher doping (x=0.3) towards the center, and a doping concentration of x=0.5 in the middle of the N layer. This design graded the lattice mismatch between YBa2Cu3O7−δ and the N layer, thus avoiding the accumulation of all the lattice strain at one interface. It also results in good chemical, thermal, and structural compatibility between adjacent layers for the desired multilayer structures. The SNS junctions fabricated in this way showed resistively shunted junction current-voltage characteristics under dc bias and Shapiro steps under microwave irradiation at a temperature in the range of 75–87 K. Direct current superconducting quantum interference devices showed a voltage modulation about 5 μV by a magnetic field at liquid nitrogen temperature.
Novel laser induced interaction profiles in clusters of mesoscopic particles
Authors: Claro F. , Rojas R.
Published: July 2002

We show that clusters of polarizable particles can form one or more equilibrium configurations in the presence of a laser field, with an equilibrium distance that depends sensitively on the frequency. The binding energy of these laser induced states scales with the particle volume and laser power making it possible to control by illumination the speed of agglomeration of weakly interacting particles in gas suspension or colloids. Purely repulsive regimes are also accesible at certain frequencies, a property potentially useful to break-up agglomerates and clean surfaces.
Carrier heating dynamics in semiconductor waveguide saturable absorbers
Authors: Karin J. R. , Uskov A. V. , Nagarajan R. , Bowers J. E. , Mo/rk J.
Published: July 2002

Pump-probe measurements in GaAs/GaAlAs waveguide saturable absorbers reveal an ultrafast transient in the absorption recovery dynamics, and a second slower signal before the final recovery. We present a model of the differential transmission measurements which includes high field and space charge effects in addition to the spectral hole burning and carrier heating typically found in semiconductor amplifiers. The results of the model indicate that field-induced carrier heating strongly influences the absorption dynamics in saturable absorbers used for mode-locked diode lasers.