bluuebunny/crossref_metadata_2025 huggingface dataset:
Calorimetric absorption spectroscopy of free and bound excitons in CdS at millikelvin temperatures
Authors: Podlowski L. , Gutowski J. , Broser I.
Published: July 2002

It is shown for the first time that the recently developed calorimetric absorption spectroscopy (CAS) is most fruitfully applicable as a direct measure of nonradiative decay of excitonic systems even concerning their fine structure properties if experiments are performed in the mK range achieved in a 3He/4He-dilution refrigerator. CAS gives hints on different scattering and relaxation processes of longitudinal AL and triplet AF excitons in CdS, and directly evidences nonradiative decay ratios of different bound-exciton complexes. Even TA-phonon-assisted recombination of such systems leads to well measurable CAS signal enhancement.
Gain and gain saturation spectra in 1.5 μm multiple quantum well optical amplifiers
Authors: Eisenstein G. , Koren U. , Raybon G. , Wiesenfeld J. M. , Wegener M.
Published: July 2002

We describe the wavelength dependence of small-signal picosecond pulse energy gain and cw power gain, as well as saturation energy and saturation output power spectra, in 1.5 μm multiple quantum well optical amplifiers of different lengths and under various drive conditions. The present devices have gain spectra with bandwidths (3 dB) that can exceed 1000 Å. Saturation output energies and powers increase with wavelength and are as large as 5 pJ and ∼40 mW, respectively.
Asymmetric conductance peaks observed in silicon metal-oxide-semiconductor capacitors
Authors: Collins S. , Kirton M. J. , Uren M. J.
Published: July 2002

We report the observation of highly asymmetric peaks in conductance data from silicon metal-oxide-semiconductor capacitors. By extending the standard surface-potential fluctuation model to incorporate a range of capture cross sections at a given surface potential, we obtain excellent fits to the experimental data. Our results are consistent with capture into the ‘‘fast’’ Si:SiO2 interface states taking place either by direct tunneling or via an activated capture process.
Hydrogen passivation of Si δ-doped GaAs grown by molecular beam epitaxy
Authors: Swaminathan V. , Asom M. T. , Livescu G. , Geva M. , Stevie F. A. , Pearton S. J. , Lopata J.
Published: July 2002

Hydrogen passivation of Si δ-doped GaAs grown by molecular beam epitaxy is studied. Just as in uniformily Si-doped GaAs, exposure of the δ-doped material to a low frequency (30 kHz) hydrogen plasma at 250 °C for 30 min deactivates the Si donors in the δ spikes. For samples with Si doping of (1–6)×1018 cm−3, carrier concentration in the spikes decreased by nearly three orders of magnitude following hydrogenation. Secondary-ion mass spectrometric analysis of deuterated samples confirmed trapping of deuterium in the Si-doped spikes. Consistent with the deactivation of Si donors following hydrogenation, changes were observed in the near-band edge luminescence spectrum at 4.2 K, which showed in the hydrogenated sample the absence of Burstein–Moss shift that was observed in the as-grown sample. This hydrogen-induced passivation of Si donors in the δ spikes can be of benefit in selectively deactivating donor atoms in device applications, and also provide a method for tailoring the hydrogen distribution in an epitaxial structure.
Visible mechanism of liquid crystals on graphite under scanning tunneling microscopy
Authors: Nejoh H.
Published: July 2002

Liquid crystals on graphite have been observed by scanning tunneling microscopy. Although an isolated 4-n-octyl-4′-cyanobiphenyl (8CB) molecule shows a wide 11 eV energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), its image could be obtained by tunneling bias around 800 mV far below this energy gap. The fact that 8CB with a large energy gap could be imaged was confirmed by a spectroscopic measurement. This LC molecule visualizing mechanism is interpreted from one viewpoint as the result of energy level shift possibly caused by molecule-substrate interaction and from another viewpoint as the result of periodic molecules forming an energy band.
ZnSe/ZnSe0.92S0.08/GaAs single-crystal waveguides as visible modulators
Authors: Jupina M. H. , Garmire E. M. , Shibata N. , Zembutsu S.
Published: July 2002

Electro-optic and electroabsorptive modulations have been demonstrated in Schottky barriers in epitaxial ZnSe waveguides with cladding layers of ZnSeS grown single crystal on GaAs substrates. Using an argon laser we demonstrate guided-wave electro-optic modulation with voltages which are predicted by bulk ZnSe electro-optic coefficients. With a 3 mm sample, half-wave modulation was observed at 4 V per micron electrode separation. Electroabsorption with 9.2 dB modulation in a 0.6-mm-long sample was observed at 488 nm. With surface electrodes, rectification within the Schottky barrier made possible a unique rectified optical modulation.
Ultra-efficient erbium-doped fiber amplifier
Authors: Kimura Yasuo , Nakazawa Masataka , Suzuki Kazunori
Published: July 2002

The gain and saturation characteristics of 0.98 μm and 1.48 μm pumping are investigated for an erbium-doped fiber amplifier with a mode field diameter of 4.8 μm, and a relative refractive index difference of 1.67%. Gain coefficients of 10.2 dB/mW at 0.98 μm pumping and 5.1 dB/mW at 1.48 μm pumping are obtained. The saturation output power is +12 dBm with a launched pump power of 50 mW for 1.48 μm pumping. The energy conversion efficiency at 1.48 μm pumping reaches as high as 71%.
Efficient InGaAsP/InP multiple quantum well waveguide optical phase modulator
Authors: Tsang H. K. , Soole J. B. D. , LeBlanc H. P. , Bhat R. , Koza M. A. , White I. H.
Published: July 2002

We report an InGaAsP/InP multiple quantum well optical phase modulator which has a high phase modulation efficiency and low loss modulation over the entire 1.5–1.56 μm fiber band. For a 4-mm-long device, π phase modulation requires a modulation voltage of only 0.6 V at 1.49 μm and 1.1 V at 1.55 μm wavelength. The absorption modulation for a 0–5 V bias change is negligible at 1.55 μm, rising to 0.7 cm−1 at 1.49 μm. The spectral dependence of the electrorefraction from the quantum-confined Stark effect has also been measured for the first time over a wide continuous wavelength range. Far from the absorption edge the electrorefraction decreases approximately as the square of the energy detuning.
Quantitative electron channeling measurements for high sensitivity surface analysis
Authors: Ophir-Arad E. , Fastow R. , Kalish R.
Published: July 2002

Very high sensitivity to low dose implantation damage has been achieved by a novel quantitative analysis of electron channeling patterns (ECPs). An algorithm, based on the statistical analysis of the two-dimensional ECP pictures obtained from a scanning electron microscope, has been developed. The analysis yields a single number (the variance), analogous to the quantity χmin deduced from ion channeling measurements, which characterizes the surface crystallinity. Measurements performed on implanted silicon (point defects) and CdTe (extended defects) crystals show that electron channeling is approximately two orders of magnitude more sensitive to implantation damage than ion channeling. Changes in the ECP of Si and CdTe were observed after implantations with 200 keV Ar and 320 keV In ions at doses as low as 1×1012 cm−2 and 1×1013 cm−2, respectively. Moreover, electron channeling is capable of probing areas about four orders of magnitude smaller than commonly used ion channeling.
Electron concentration and mobility loss in GaAs/GaAlAs heterostructures caused by reactive ion etching
Authors: Beinstingl W. , Christanell R. , Smoliner J. , Wirner C. , Gornik E. , Weimann G. , Schlapp W.
Published: July 2002

We have investigated the influence of reactive ion etching on the properties of a two-dimensional electron gas in GaAs/GaAlAs heterostructures at 4.2 K. After removing the GaAs cap layer and overetching on the surface of the n-GaAlAs with CCl2F2 under various etching conditions we observe both a reduction of the electron concentration and a low-field mobility loss which are correlated with ion energy. We ascribe this mobility loss to a capture of electrons into traps created by the etching process. Ion energies around 25 eV were found to meet best the requirements for low damaging as well as anisotropic etching, whereas energies exceeding 35 eV result in a complete depletion of the two-dimensional electron gas.
Insulated-gate multiple quantum well optical modulator on InP
Authors: Chen C. W. , Iyer R. , Lee H. Y. , Hafich M. , Robinson G. Y. , Lile D. L.
Published: July 2002

Insulated-gate metal-insulator-semiconductor (MIS) diodes have been fabricated on multiple quantum well stacks of InP/InGaAs grown by gas-source molecular beam epitaxy. These devices have shown excitonic resonances and optical modulation spectra in pass-through operation similar in shape, but smaller in magnitude, to what has been previously reported with p-i-n and Schottky diode structures. Compared to these other devices the MIS modulator has the advantage of being totally planar with excellent interdevice electrical isolation suggesting its suitability for high complexity array applications.
Side plane domain observation of Fe-C/Ni-Fe/BN multilayers with a spin-polarized scanning electron microscope
Authors: Matsuyama H. , Koike K. , Kobayashi T. , Nakatani R. , Yamamoto K.
Published: July 2002

Magnetization distributions of four-magnetic-layer (0.5 μm/layer) strips (300×50 μm2) are observed on the top and side planes using a spin-polarized scanning electron microscope. From the domain images of the side planes, the magnetization direction of each magnetic layer is studied. The strips do not always show the predicted energy minimum magnetic structure, in which the magnetization direction alternates layer by layer.
Hole trap level in Pt-Ti/p-InGaAs/n-InP heterostructures due to rapid thermal processing
Authors: Jiao K. L. , Soltyka A. J. , Anderson W. A. , Katz A.
Published: July 2002

Low-resistance ohmic contacts of Pt/Ti to p-InGaAs/n-InP heterostructures were formed by rapid thermal processing (RTP). Deep level transient spectroscopy and current-voltage temperature (I-V-T) measurements were used to characterize this system in order to evaluate the stability of the Pt/Ti ohmic contact and the effects of different RTP temperatures on the device performance. A new hole trap level with activation energy of 0.89 eV was found in samples treated at temperatures above 500 °C but not in those treated at lower temperatures. This trap, featured by a higher density when closer to the junction, was thought to be caused by Ti interdiffusion at high RTP temperature, in agreement with the analysis from Auger depth profiling. Four electron trap levels with activation energies of 0.61, 0.45, 0.35, and 0.30 eV were observed for all samples and believed to be native defects in InP. I-V-T measurements revealed current mechanisms independent of the RTP temperatures indicating that the new hole trap does not influence current conduction mechanisms.
Mirrorless all-optical bistability in polymer dispersed liquid crystals
Authors: Simoni F. , Cipparrone G. , Umeton C.
Published: July 2002

We report the observation of a bistable behavior from dye-doped polymer dispersed liquid crystals. The interpretation of the phenomenon is given in the theoretical framework of an absorption which increases with the excitation of the material.
Polarization characteristics of AlGaAs/GaAs double-heterostructure lasers grown on Si substrates
Authors: Liu Xiaoming , Lee Henry P. , Wang Shyh
Published: July 2002

The polarization of laser radiations from AlGaAs/GaAs double-heterostructure lasers grown on planar, trenched, and SiN-patterned Si substrates are examined. It was found that TM modes lase first in most of these lasers. Competition between TE and TM modes also occurs in some devices. A qualitative explanation is given on the basis of stress-induced changes in the optical gains between TE and TM modes. The difference in the polarization behavior among these lasers indicates that the residual tensile stress is influenced by substrate patterning.
Wide area disk-shaped vacuum ultraviolet lamp
Authors: Yu Z. , Sheng T. Y. , Luo Z. , Collins G. J.
Published: July 2002

A wide area vacuum ultraviolet (VUV) lamp employs a ring-shaped cold cathode to produce an electron beam excited plasma of disk geometry. When excited by the soft vacuum electron beam, molecular hydrogen, nitrogen, and atomic helium emit strong atomic resonance radiation at 121.6, 120, and 58 nm, respectively. The VUV optical power emitted on the atomic resonance line is typically 6–10% of the total applied discharge power. The spatial uniformity of the VUV emission intensity at a discharge input power level of 30 W approaches 6% across the entire disk diameter, up to a maximum of 20 cm.
Influence of indium doping on AlGaAs layers grown by molecular beam epitaxy
Authors: Chang K. H. , Lee C. P. , Wu J. S. , Liu D. G. , Liou D. C.
Published: July 2002

Influence of indium doping on the qualities of AlGaAs layers grown by molecular beam epitaxy has been studied. It was found that a proper amount of In doping can increase the photoluminescence intensity drastically by a factor greater than 10 indicating an improvement in the optical quality of AlGaAs epilayers. The improvement in the material quality is attributed to a higher surface migration rate of In atoms than those of Ga and Al atoms leading to a reduction of group III vacancies. However, too great a concentration of In atoms leads to effects that may degrade the film quality.
N
+ doping of gallium arsenide by rapid thermal oxidation of a silicon cap
Authors: Sadana D. K. , de Souza J. P. , Cardone F.
Published: July 2002

Shallow (<200 nm) Si profiles with doping levels in excess of 2×1018 cm−3 were reproducively obtained in GaAs by rapid thermal oxidation (RTO) of Si caps (50 or 160 nm) in 0.1% O2/Ar ambient at 850–1050 °C. The doping level as well as distribution of the diffused Si can be controlled by the thickness of the Si cap, RTO temperature, RTO time, and oxygen level in the annealing ambient. It appears that the generation of Si interstitials at the oxidizing surface of the Si cap during RTO is responsible for the Si diffusion into the underlying GaAs substrate.
Optical detection of biatomic sheets of silicon in Si/Ge superlattices
Authors: White J. D. , Fasol G. , Ghanbari R. A. , Gell M. A. , Gibbings C. J. , Tuppen C. G.
Published: July 2002

A distinctive Raman spectrum associated with biatomic sheets of silicon in Si/Ge superlattices has been found in the energy range 370–410 cm−1. This double-peaked structure was obtained over an order of magnitude of germanium layer thickness, but was not found in the alloy control layers or structures with thicker Si layers. It is proposed that the signal is due to modes that are normally forbidden in this scattering configuration. Strong direct optical transitions have been predicted for certain Si/Ge superlattices incorporating biatomic sheets of Si and this distinctive Raman signal could be used to characterize the biatomic sheets of silicon in these structures.
Importance of adsorption in ion beam induced deposition of carbon
Authors: Kirch S. J. , Seeger D. E.
Published: July 2002

Ion beam induced deposition of carbon films has been studied as a function of temperature and pressure for both 2-bromo vinyl benzene and 2-bromo ethyl benzene. In contrast to recently published results involving vinyl and ethyl benzene, deposition is possible for both materials at and below room temperature for a wide range of pressures. Further, deposition yield for each material scales directly with its vapor pressure at the deposition temperature. This behavior shows that physical adsorption plays the dominant role in determining deposition properties. In addition, the yield of 2-bromo vinyl benzene is consistently higher than 2-bromo ethyl benzene at a given normalized pressure. The importance of the double bond on the vinyl substituent observed in previous work is simply a manifestation of enhanced physical adsorption due to the presence of this double bond.
High-energy argon-ion implantation for waveguide formation in (AlGa)As/GaAs multilayers
Authors: Myers D. R. , Lee Kyu , Hausken T. , Simes R. J. , Ribot H. , Laruelle F. , Coldren L. A.
Published: July 2002

We have intermixed GaAs/(AlGa)As multiquantum structures for waveguides and lasers by 3 MeV Ar implantation and 850 °C, 30 min closed-tube annealing. Buried-heterostructure lasers defined by Ar mixing had threshold currents of 100 mA for 370-μm-long devices. As waveguides for 1.15 μm light, the devices exhibited losses of 25 cm−1 in the annealed, implanted regions, and 15 cm−1 in unimplanted regions defined by adjacent implants. Analysis of the results illustrates important considerations for implant mixing for waveguide formation.
Formation process of high T
c superconducting Bi-Pb-Ca-Sr-Cu-O thick films via melt solidification
Authors: Tatsumisago Masahiro , Tadanaga Kiyoharu , Tsuboi Shinzo , Tohge Noboru , Minami Tsutomu
Published: July 2002

High Tc superconducting thick films Bi1.6Pb0.4Ca2Sr2Cu3Ox were prepared by the melt solidification process. The preparation conditions were optimized to obtain films with higher Tc. Rapid cooling of the molten samples to the heat treatment temperature of 855 °C produced superconducting films with a maximum Tc (zero) of 104 K. Slow cooling of the melt declined the superconducting properties of the films because of the formation of Ca2CuO3, which may prevent the formation of the 110 K phase, during cooling through the temperature range around 900 °C.
Magnetic shielding properties of YBa2Cu3O7−x superconductors
Authors: Chen Q. Y. , McArdle J. L. , Werner T. R. , Lenz J. E.
Published: July 2002

We have developed a highly sensitive ac magnetic method, using a modified two-coil technique, for measuring magnetic shielding effectiveness (S) of high-temperature superconductors in planar form. Incorporated in the measurement was a pair of iron E pieces, which significantly reduce flux leakage around the sample edge. Below a threshold field, the S values measured at 77 K for bulk superconducting YBa2Cu3O7−x compounds were typically 110 dB. This method is particularly useful for determining threshold field and observing trapped-flux behaviors in high-temperature superconductors.
Critical current density of Bi-Pb-Ca-Sr-Cu-O high T
c superconductors via rapidly quenched glass precursors
Authors: Tatsumisago Masahiro , Tsuboi Shinzo , Tohge Noboru , Minami Tsutomu
Published: July 2002

Two- and three-step heat treatment processes of Bi1.6Pb0.4Ca2Sr2Cu3Ox rapidly quenched precursor glasses were examined to produce dense high Tc superconducting glass ceramics with a high critical current density Jc. The heat treatment at around the glass transition, which was expected to accelerate the nucleation rate, contributed to enhance the Jc values. The maximum Jc value of 1800 A cm−2 was obtained through the three-step heat treatment performed firstly at 350 °C, for 1 h, then at 700 °C for 1 h, and finally at 855 °C for 20 h.
Studies of picosecond carrier dynamics in polysilane alloys: Evidence for geminate recombination in small hydrogenated amorphous silicon clusters
Authors: Han S. G. , Hess B. C. , Kanner G. S. , Vardeny Z. V. , Nitta S.
Published: July 2002

The ultrafast photocarrier dynamics in polysilane alloys, amorphous (SiH2)n, has been studied using the picosecond photoinduced absorption (PA) technique. For excitation below the optical gap, the PA response decays exponentially and is faster at low temperatures. This is interpreted in terms of e-h geminate recombination in the small clusters (∼10 Å) of a-Si:H embedded in the polysilane matrix. The PA response with above-gap excitation is similar to that of conventional a-Si:H; it decays much slower in the form of a power law t −β (β<1), independent of spectral range between 1.4 and 2.2 eV. This shows that the e-h distance after above-gap photogeneration is larger than the size of the a-Si:H clusters.
Lanthanum-substituted Y-Ba-Cu-O superconductors synthesized at elevated oxygen pressures
Authors: Morris D. E. , Narwankar P. K. , Sinha A. P. B. , Takano K. , Shum V. T.
Published: July 2002

Lanthanum substitution in the Y-Ba-Cu-O system at elevated P(O2) results in superconducting compositions which throw interesting light on the effects of nonisovalent substitution in a Y-Ba-Cu-O system. Like Ca substitution, La substitution also shifts the phase formation boundary between 123, 247, and 124 phases to higher P(O2), and stabilizes a tetragonal 123 structure at moderately elevated P(O2). However, in contrast with Ca substitution, Tc decreases continuously and rapidly with increasing La content. This can be only partly explained by a decrease of the hole concentration.
Anisotropic transport in a modulation-doped GaAs quantum well microstructured by growth on a submicron grating
Authors: Helm M. , Colas E. , Hayes J. R. , Van der Gaag B. , Schiavone L. M. , Hwang D. M.
Published: July 2002

We report on the transport properties of quantum wire-like GaAs/AlGaAs heterostructures, obtained by organometallic chemical vapor deposition of a modulation-doped quantum well structure on a submicron grating, etched in the substrate prior to growth. Shubnikov–deHaas and mobility measurements show that the electron gas is preserved in the grating areas and that transport parallel to the grating is not severely degraded as compared to an unpatterned control sample. Perpendicular to the grating the mobility strongly decreases at low temperatures, leading to an anisotropy ratio of 1:200. The temperature dependence of the perpendicular mobility indicates strong boundary scattering at the GaAs/AlGaAs interfaces.
Thickness-dependent kinetics of laser-induced oxidation of thin copper films
Authors: Wautelet M. , Hanus F.
Published: July 2002

Thin copper films are deposited onto glass and irradiated, in air, by means of a scanned Ar+ laser beam. The kinetics of oxidation is measured by an interferometric method. It is shown that the kinetics of oxidation depends on the laser beam power density and on the initial thickness of the deposited copper films.
Fiber fragmentation in a single-filament composite
Authors: Curtin W. A.
Published: July 2002

The fiber fragment distribution obtained from tensile testing of a single-filament composite contains vital information on the in situ strength of the fiber at short gauge lengths and on the shear stress across the fiber/matrix interface. Here, this fragmentation problem is mapped onto the problem of hard rods distributed randomly along a one-dimensional line, but with a stress-dependent rod length, and is then solved exactly. The solution utilizes the ‘‘car-parking’’ problem of equal sized cars parked along a line and the theory predictions agree well with existing simulation results. The theory also applies to multiple cracking of brittle films on pliable substrates, film coatings on fibers, and matrix cracking in ceramic matrix composites, and now allows the in situ fiber or film statistical strength and interfacial shear strength to be derived from experimental fragment distributions.
Surface localization of the photochemical vapor deposition of SiO2 on InP at low pressure and room temperature
Authors: Houzay F. , Moison J. M. , Sébenne C. A.
Published: July 2002

The first stages of the chemical vapor deposition of SiO2 on chemically polished InP substrates, promoted by UV illumination at room temperature and low (≊0.01 Torr) precursor pressure, have been studied in an ultrahigh vacuum environment. Chemical species deposited are found to be quite similar to those deposited by the thermally promoted process. Both Si and O atom depositions need UV illumination. The reaction rates observed in separate or mixed gas exposures indicate that surface-located mechanisms play a major part in the buildup of the SiO2/InP interface at low precursor pressure, thus opening perspectives for localized insulator growth under the UV beam.
Anisotropy of the reflectivity spectra of a BiSrCaCuO single crystal within the (001) plane
Authors: Huang Dajin , Zhu Bing , Ming Hai , Gu Genda , Cai Weili , Ruan Yaozhong
Published: July 2002

A BiSrCaCuO 2212 phase single crystal was grown by a directional solidification method. The ac susceptibility versus temperature curve is given. Some structural analyses were carried out. The measurements of reflectivity spectra by polarized light have been performed on the (001) plane in the wavelength range from 0.6 to 1.7 μm at room temperature. The spectra of both a and b-axis directions are characterized by a strongly damped plasma edge of similar shape. By fitting the Lorentz–Drude model we get some quantitative results, which may be related to the structural features of the BiSrCaCuO 2212 phase single crystal.
Comparison between the magnetic and transport critical current densities in high critical current density melt-textured yttrium barium copper-oxide
Authors: Gao L. , Meng R. L. , Xue Y. Y. , Hor P. H. , Chu C. W.
Published: July 2002

Using our recently developed pulsed critical current density (Jc) measuring system, the Jc of the high Jc melt-textured YBa2Cu3O7−δ (Y123) bulk samples has been determined. I-V curves with a voltage resolution of 0.5 μV were obtained, and transport Jc’s along the a-b plane (Jc∥ a-b) as high as 7.2×1 04 A/cm2 were extracted. These results are comparable to the values obtained magnetically. On the other hand, transport Jc along the c axis (Jc∥c) were found to be two orders of magnitude smaller, even though the magnetic Jc∥c is only about five times smaller than Jc∥a-b. We suggest that for the high-temperature superconducting materials which are highly anisotropic, caution should be taken when using the nontransport magnetic methods to determine Jc.
Emission kinetic of the slow interface states in Si3N4/In0.53Ga0.47As structures
Authors: López-Villegas J. M. , Morante J. R. , Samitier J. , Cornet A. , Renaud M. , Boher P.
Published: July 2002

In this work we have studied the emission kinetics related to the slow interface states of metal Si3N4/In0.53Ga0.47As structures, by means of the analysis of isothermal transients measurements performed at constant capacitance. The transients show the presence of two kinds of slow interface states. One of them presents a kinetics which can be explained by means of a direct exchange of carriers with the semiconductor conduction-band states. The other one shows a more complex emission kinetics. In this last case, the slow states emission is controlled by the occupancy factor of the fast interface states, and this suggests the existence of a connection mechanism between them.
Domain boundary control of edge roughness in vicinal Si(001)
Authors: Swartzentruber B. S. , Mo Y. W. , Lagally M. G.
Published: July 2002

Steps on vicinal Si(001) miscut toward 〈110〉 directions are known to be alternately rough and smooth. It is shown that a significant contribution to the local meandering of the rough edge, so-called ‘‘kissing sites,’’ are nonthermodynamic. They are caused by surface antiphase domains that are created during surface cleaning.
Electric field-induced optical waveguide intensity modulators using GaAs/AlxGa1−xAs quantum wells
Authors: Wickman R. W. , Moretti A. L. , Stair K. A. , Bird T. E.
Published: July 2002

We demonstrate a new waveguide intensity modulator that uses the field-dependent refractive index change associated with quantum wells to control the lateral confinement of light in a slab waveguide. By operating at photon energies ∼40 meV below the zero field electron–heavy hole transition energy, we show, conclusively, that the field-induced refractive index change is primarily due to the quantum-confined Stark effect. Intensity modulators are demonstrated with on/off ratios better than 3:1. Devices based on this electrically controllable lateral confinement will play an important role in integrated optics.
Ferroelectric layers for the stabilization of poled polymer films
Authors: Knabke G. , Franke H.
Published: July 2002

A method for measuring the in situ poling and relaxation of an electro-optic polymer lightguide is presented. The poling/relaxation of a single film is compared with the behavior of the same film in the vicinity of a ferroelectric composite sublayer. The stability of the dye orientation obtained by poling is controlled by the ferroelectric substrate. Thus the stability of dye orientation in an electro-optic polymer may be enhanced.
Nature of the infrared spectrum in band-edge region of KTiOPO4
Authors: Jacco J. C. , Loiacono G. M.
Published: July 2002

The infrared transmission spectra of KTiOPO4 (KTP) have been closely inspected in the region between 4000 and 1000 cm−1 (2.5–10 μm) using single-crystal samples of various thicknesses. The spectral information obtained reveals that the band edge at 4.5 μm is due to the first overtone of the ν3 tetrahedral phosphate fundamental vibration. A heretofore questionable absorption centered at 3.3 μm has been shown to be the second overtone of this same fundamental vibration.
Ejection angle dependence of electrical properties of ion beam sputtered tantalum oxide films
Authors: Ishiyama Kengo , Taga Yasunori
Published: July 2002

Ion beam sputtering was used to deposit tantalum oxide films on silicon substrates at different positions surrounding a Ta2O5 target. dc conductance of the films shows dependence on the ejection angle of sputtered particles and primary ion energy. Capacitance-voltage characteristics also vary by changing the primary ion energy. These variations of electrical properties are discussed by considering the effect of anisotropic ejection of the sputtered energetic particles.
Excitation transfer in donor-acceptor pair luminescence
Authors: Yi G.-J. , Tuchman J. A. , Neumark G. F.
Published: July 2002

In the analysis of spectral and time dependencies of donor-acceptor pair (DAP) spectra, it has usually been assumed that the primary factors are the distribution of pair separations together with the dependence of the decay and of the emitted energies on these separations. We have measured the time decay of the DAP luminescence in ZnSe as a function of excitation wavelength and show that, instead, excitation transfer via localized states cannot be neglected. We also point out that such transfer appears very reasonable, based on transfer versus luminescence decay rates.
Chlorine reactive ion beam etching of InSb and InAs0.15Sb0.85/InSb strained-layer superlattices
Authors: Vawter G. Allen , Wendt Joel R.
Published: July 2002

We report the first successful application of Cl2 reactive ion beam etching (RIBE) to the dry etching of bulk InSb and InAs0.15Sb0.85/InSb strained-layer superlattices (SLSs). Etching was performed in a load-locked ultrahigh vacuum chamber using an electron cyclotron resonance ion source. Etching rates for InSb and InAs0.15Sb0.85/InSb SLS with a 500 eV Cl2 beam at 0.6 mA/cm2 are 280 and 240 nm/min, respectively, compared to 310 nm/min for GaAs. The sputter yield for Cl2 RIBE in this antimonide system is double that obtained by Ar ion milling under identical conditions.
Mechanical strength of silicon crystals with oxygen and boron impurities
Authors: Fukuda Tetsuo , Ohsawa Akira
Published: July 2002

The mechanical strength of epitaxial and Czochralski (CZ) silicon single crystals having boron concentrations of 1015–1020 cm−3 is investigated by varying the concentration of oxygen atoms. Crystal strength is measured by the indentation technique in a temperature range from 800 to 1100 °C. The strength of both epitaxial and CZ silicon crystals is insensitive to boron concentrations up to 1018 cm−3. As boron concentration increases above 1018 cm−3, the strength of both the crystals improves dramatically. The strengthening is caused by dislocation locking of boron atoms in epitaxial crystals and of both oxygen and boron atoms in CZ crystals.
Defect characterization in amorphous silicon based solar cells by subband-gap spectroscopy with constant photocurrent measurements
Authors: Frammelsberger W. , Rübel H. , Lechner P. , Geyer R. , Kniffler N.
Published: July 2002

We used the constant photocurrent method to characterize a-Si:H based pin cells in order to discuss the correlation between the device characterizing quantity, the fill factor (FF), and the number of defects which is related to the quantity αD (subbandgap optical absorption constant). We show that the changes in the i layer due to the creation of metastable defects after light soaking or current injection−characterized by αD−directly correlate with the changes in solar cell performance (FF). We are able to show that other reasons than an increased defect density can lead to a reduction of the fill factor. Further we try to quantify αD in terms of a defect density of states.
Normal incidence parallel intraband photoconductivity in GaAs/AlGaAs multiquantum wells
Authors: Rosencher E. , Martinet E. , Böckenhoff E. , Bois Ph. , Delaitre S. , Hirtz J. P.
Published: July 2002

For the first time, resonant parallel photoconductivity due to intraband optical transitions is observed in GaAs/AlGaAs multiquantum wells. The angle of incidence dependence of the detected signals indicates that the photoconductivity process is not directly related to intersubband transitions. Indeed, contrary to usual detectors based on intersubband transitions, infrared radiations are detected at normal incidence with responsivity as high as (0.05 A/W). Photoconductivity spectra reproduce roughly the absorption spectra with, however, significant differences in peak positions, indicating that the intersubband transitions are indirectly involved in the detection process. Elements of an explanatory model based on hot-electron bolometric effects are discussed.
Preparation of high-purity Tl-based ‘‘1223’’ superconductor phase by modified Pechini process in water solution
Authors: Chiang Cyril , Shei C. Y. , Wu S. F. , Huang Y. T.
Published: July 2002

Because of the mixed metal valance state of thallium in a Tl-based superconductor, a nearly single ‘‘1223’’ phase can be readily prepared by a modified Pechini method (US Patent 3 330 697). Tl2O3 and other metal nitrates are dissolved in an aqueous solution plus a certain amount of oxalic acid for chelating the metal cations. The desired phase shows zero resistance at 114 K and the phase purity is identified by x-ray diffraction. Characteristics of superconductivity also are evidenced by the Meissner effect. The preparation technique is considered valuable to purify multiphase superconductors for mass production.
Controlling H atom production in the 193 nm laser photolysis of triethylarsenic
Authors: Xu Xiaodong , Deshmukh Subhash , Brum Jeffrey L. , Koplitz Brent
Published: July 2002

We report on the production of atomic hydrogen subsequent to the 193 nm photolysis of triethylarsenic (TEAs) using an excimer laser. The H atoms are probed via two-photon (121.6+364.7 nm) ionization, and the resulting H atom Doppler profile at Lyman-α is presented. Photolysis power dependence studies demonstrate that substantial H atom formation occurs at relatively low laser powers. However, the H atom signal actually begins to diminish as the photolysis laser power is increased beyond ∼70 MW/cm2. Correlations with time-of-fight mass spectral data suggest that ion channels are being accessed. The possible mechanisms for TEAs excitation that lead to H atom formation/depletion are presented, and the implications of these observations on controlling carbon incorporation in the laser-enhanced growth of films of GaAs, AlGaAs, etc. are discussed.
Reduction in linewidth enhancement factor for In0.2Ga0.8As/ GaAs/Al0.5Ga0.5As strained quantum well lasers
Authors: Banerjee S. , Srivastava A. K. , Chand Naresh
Published: July 2002

The linewidth enhancement factor α as low as 0.54 in In0.2Ga0.8As/GaAs/AlGaAs strained single quantum well lasers emitting at 0.97 μm has been measured from spontaneous emission spectra below threshold. On reducing the current further, α goes down to 0.34. These low values of α have been attributed to strain in the In0.2Ga0.8As active layer.
Enhancement of boron diffusion through gate oxides in metal-oxide-semiconductor devices under rapid thermal silicidation
Authors: Lin J. , Park K. , Batra S. , Banerjee S. , Lee J. , Lux G.
Published: July 2002

It has recently been reported that there is anomalous enhanced diffusion of B through the gate oxide in metal-oxide-semiconductor (MOS) structures from B-implanted, p+-polycrystalline silicon gates upon annealing in the presence of H or F. This letter discusses the effects of TiSi2 formation on B penetration through the gate oxide in p+ polycrystalline silicon gate MOS devices. From secondary-ion mass spectrometry analyses, it is found that B penetration effect is enhanced by TiSi2 formation, for 950 and 1100 °C rapid thermal annealing, in spite of the fact that the F concentration in the gate oxide for samples with silicide is lower than that for samples without silicide. Furthermore, samples with a one-step TiSi2 formation process exhibit more serious B penetration effects than those with a two-step process. This indicates that the effect of silicide on B penetration is more complicated than simply acting as a sink for F. Pileup of B at the silicide/polycrystalline silicon interface, the generation of point defects such as Si vacancies and interstitials during silicide formation, and B-defect interactions must be taken into account to explain the results.
Growth processes in molecular beam expitaxy of single-crystal Al layers on AlAs
Authors: Nakahara Hiroaki , Matuhata Hirofumi , Okada Yasumasa , Kurosu Tateki , Iida Masamori , Yao Takafumi
Published: July 2002

The molecular beam epitaxial growth processes of Al single-crystal layers deposited at room temperature on As-stabilized and on Al-stabilized AlAs surfaces are investigated in situ using reflection high-energy electron diffraction (RHEED). The epitaxy relationship of Al with the underlying AlAs is (011)[100]Al//(001)[110]AlAs irrespective of the surface stoichiometry of AlAs. Detailed RHEED investigation suggests that the initially deposited two one-monolayer-thick Al layers form a sphalerite lattice on As-(Al-)stabilized AlAs with the same lattice spacing as AlAs, while the deposition of additional Al layers induces the structural phase transition from the sphalerite lattice to an fcc lattice with bulk Al lattice constant. Thick epitaxial Al layers show (4×1) surface reconstruction.
Parametric superfluorescence in KTiOPO4 crystals pumped by 1 ps pulses
Authors: Nishikawa Tadashi , Uesugi Naoshi , Yumoto Junji
Published: July 2002

Parametric superfluorescence in KTiOPO4 crystals pumped by 1 ps pulses is demonstrated using an amplified synchronous mode-locked dye laser. The tuning range of the output pulses is from 0.93 to 1.59 μm. The maximum output power at the degenerate wavelength of 1.2 μm is 0.85 μJ, and a conversion efficiency of 9.9% is obtained. Height gain under phase mismatching broadens the spectral bandwidths of the output pulses.
Effect of etch treatment prior to Schottky contact fabrication on In0.05Ga0.95As
Authors: Johnson Marilyn J. , Kuhn Kelin J. , Darling Robert B.
Published: July 2002

The Schottky barrier characteristics of aluminum contacts to In0.05Ga0.95As/GaAs strain-relieved material were investigated. Acidic and alkaline wet chemical etching experiments were performed to determine the importance of semiconductor surface preparation prior to the deposition of the contact metal. Acidic etch treatments utilizing HCl and HF resulted in a range of ideality factors significantly greater than 1 (1.90–2.91 for HCl, 1.35–2.46 for HF), variable reverse bias leakage currents (0.038–0.440 μA/cm2 for HCl, 23.0–110 μA/cm2 for HF), and a range of barrier heights (0.88–0.93 eV for HCl, 0.63–0.77 eV for HF). In addition, the HCl treated devices exhibit time-dependent I-V behavior with continuous measurements, as well as changes in characteristics with both annealing and room-temperature storage. The 10 s NH4OH:H2O (1:1) alkaline etch surface preparation produced stable Schottky contacts with a 0.79 eV barrier height, a 1.15±0.02 ideality factor, and ≊10 μA/cm2 leakage current at −1 V bias.
Densification of high T
c superconductor YBa2Cu3O7−x by hot isostatic pressing: A novel approach
Authors: Dijken D. K. , DeHosson J. Th. M.
Published: July 2002

In this letter a relation is derived between hot isostatic pressing (HIP) temperature, the initial oxygen concentration of sintered Y-Ba-Cu-O powder, the relative density, the oxygen pressure, and the oxygen concentration during HIP densification. The maximum attainable relative density is calculated as a function of HIP pressure. It turns out that degassing oxygen during HIP densification processing has considerable effects on densification maps. Using corrected and modified densification maps a recipe for manufacturing highly dense YBa2Cu3O7−x is presented.
Ion-induced formation of stable and metastable phases in the Y-Si system
Authors: Alford T. L. , Bo/rgesen P. , Mayer J. W. , Lilienfeld D. A.
Published: July 2002

Bilayers of yttrium and amorphous silicon have been irradiated with 60 keV inert ions. Between liquid-nitrogen temperature and 100 °C, ion mixing resulted in an amorphous alloy of Y and Si. For temperatures of 125–190 °C, we observed formation of the YSi phase. YSi is not formed during thermal anneals of bilayers. Ion mixing at higher temperatures (≥205 °C) results in the formation of the stable YSi1.7 phase. Such sequential silicide formation has not been observed for comparable rare-earth silicides. The minimum temperatures for ion-induced YSi1.7 formation agrees with the prediction by a simple model which correlates vacancy mobility to phase transformation. The YSi formation temperature is associated with the onset of radiation-enhanced diffusion. This temperature does not correlate well with the prediction of the model, but agrees with a scaling based on the average cohesive energy.
Measurement of the temperature and the pumping uniformity inside a Nd:YAG rod by an interferometric method
Authors: Kim Kwang Suk , Kong Hong Jin , Kim Cheol Jung
Published: July 2002

The thermal behavior of a Nd:YAG laser rod under flashlamp pumping has been investigated experimentally using a very simple interferometric technique. The degree of pumping uniformity and the heat generation rate inside the rod was evaluated for single pulse pumping. The temperature increase at the center of the rod under a high repetition rate pulsed operation was also measured, and this result is used to deduce the surface heat transfer coefficient.
Internal light-coupled optical device array
Authors: Nakano Yoshinori , Ikeda Masahiro , Kawakami Wataru , Kitayama Ken-ichi
Published: July 2002

A novel internal light-coupled optical device (ILCOD) array is proposed, where the element consists of a pnpn digital optoelectronic switch and an npn phototransistor. The ILCOD with seven point-symmetric elements was fabricated. Quenching the light emission of the center element due to light coupling between the peripheral elements is observed. This quenching is achieved with an input optical power of 2.5 μW.
Transverse junction vertical-cavity surface-emitting laser
Authors: Schaus C. F. , Torres A. J. , Cheng Julian , Sun S. , Hains C. , Malloy K. J. , Schaus H. E. , Armour E. A. , Zheng K.
Published: July 2002

An all-epitaxial, transverse-junction GaAs/AlGaAs vertical-cavity surface-emitting laser (TJ-VCSEL) incorporating wavelength-resonant periodic gain is reported. Metalorganic chemical vapor deposition is used for epitaxial growth of a structure containing five GaAs quantum wells. The simple p+-p-n+ transverse junction is fabricated using reactive ion etching and diffusion techniques. Contacts are situated on the wafer surface resulting in a nearly planar structure. The device exhibits a room-temperature threshold of 48 mA (pulsed) and a resolution-limited spectral width of 0.11 nm at a 855.8 nm lasing wavelength.
Effect of structural parameters on transport characteristics of GaInAs/AlInAs two-dimensional electron gases grown by molecular beam epitaxy
Authors: Tischler M. A. , Parker B. D.
Published: July 2002

The effect of structural parameters on the transport characteristics from 15 to 300 K of molecular beam epitaxy grown GaInAs/AlInAs two-dimensional electron gas structures lattice matched to InP is determined. The AlInAs buffer layer thickness was varied from 1000 to 10 000 Å. One sample also incorporated a GaInAs/AlInAs superlattice. The AlInAs spacer layer was varied from 25 to 200 Å. The buffer layer thickness and structure has almost no effect on the mobility or sheet density. Increases in the AlInAs spacer thickness resulted in a monotonically decreasing sheet density and a peak in the mobility at 100 Å. The highest 77 K mobility was 66 700 cm2/V s with ND=1.20×1012 cm−2 in the structure with the 100 Å spacer. The effect of illumination and temperature on the sheet concentration in these structures as well as on ‘‘bulk’’ AlInAs:Si is much smaller than in AlGaAs/GaAs structures or ‘‘bulk’’ AlGaAs, indicating that devices based on this material system will not be characterized by freeze-out and persistent photoconductivity.
One monolayer of Sb or Bi used as a buffer layer preventing oxidation of InP
Authors: Yamada Masao , Wahi Anita K. , Meissner Paul L. , Herrera Alberto , Kendelewicz Tom , Spicer William E.
Published: July 2002

One monolayer of Sb or Bi has been used as a buffer layer to protect InP surfaces against the oxidation. We have used photoemission spectroscopy to estimate the oxide fraction of In and the surface Fermi level position. We find that one monolayer of Sb or Bi reduces the oxidation of underlying InP at least by more than two orders of magnitude. For passivated surfaces with one monolayer of Sb or Bi, the surface Fermi level remains pinned at the conventional pinning level 0.45 eV below the conduction-band minimum (CBM) even for oxygen exposures above 1×107 L, whereas without the Sb or Bi overlayers, the surface Fermi level is near the CBM for the same O2 exposure. Core-level studies indicate that the Sb or Bi overlayer must be itself oxidized before there is strong oxidation of the InP.
Elastoresistance tensor components for thick-film resistors
Authors: Amin Ahmed
Published: July 2002

The longitudinal M11, transverse M12, and hydrostatic Mh elastoresistance tensor components have been measured for thick-film resistors as a function of temperature. The results are analyzed in terms of the spherical ∞/∞mm and conical ∞mm symmetry groups.
Active-passive mode-locked Nd:YAG laser with a saturable absorber centered in a Fabry–Perot cavity
Authors: Lee Jung Hwan , Kong Hong Jin
Published: July 2002

We have found that the use of a saturable dye cell, placed at the center of a Fabry–Perot cavity, produced more stable mode-locked pulses without satellite pulses than a contacted dye cell configuration in active-passive mode locking of a pulsed Nd:YAG laser. The mode-locked pulse width was measured to be 23 ps and the energy stability of its frequency-doubled output was within ±3%. The displacement of the dye cell position from the exact center of the cavity was found not to be critical.
Cavity-enhanced detection of surface photovaporization
Authors: Benck E. C. , Rong Z. , Chen S. H. , Tang Z. C. , Schuessler H. A.
Published: July 2002

Cavity-enhanced detection is used to monitor minute vapor plumes produced by focusing a pulsed laser beam onto a surface placed inside a resonant optical cavity. The photovaporization signals from a variety of different materials are examined, with emphasis being placed on their amplitude and temporal structure.
Semiconducting properties of sol-gel derived vanadium silicate glasses
Authors: Ghosh A. , Chakravorty D.
Published: July 2002

Preparation of semiconducting vanadium silicate glasses by the sol-gel route and the results of electrical measurements are reported for the first time. The temperature dependence of the electrical conductivity has been analyzed in terms of small polaron as well as percolation models.