bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of electric field profiles in amorphous silicon solar cells
Authors: Könenkamp R. , Muramatsu S. , Itoh H. , Matsubara S. , Shimada T.
Published: July 2002

Time-resolved photoconductivity measurements with subnanosecond time resolution are applied to study the electric field profile in amorphous silicon solar cells in the range from 0.3 V forward to 0.8 V reverse bias. The method is used for a comparison of state-of-the art devices with different junction design. Optical and electrical contributions to the device performance are discussed and the limitations in improving the performance by use of a-SiC:H window layers are pointed out.
Quantum and classical lifetimes in a Ga0.49In0.51P/GaAs heterojunction
Authors: Ben Amor S. , Dmowski L. , Portal J. C. , Martin K. P. , Higgins R. J. , Razeghi M.
Published: July 2002

We report a study of the subband structure of Ga0.49In0.51P/GaAs heterojunctions. High-field (0<B<20 T) magnetotransport measurements were performed at low temperatures (4.2 K) under hydrostatic pressure (P<12 kbar). The strong persistent photoconductivity effect in this system allowed us to tune the two-dimensional electron gas (2DEG) density (N2D) with short light bursts from a red electroluminescent diode. The pressure dependence of N2D shows that in contrast with other systems, pressure effects on the band discontinuity and the effective mass are responsible for the observed density dependence. Both single particle (quantum) and scattering (classical) lifetimes were measured. The ratio of the classical-to-quantum lifetimes was large (≊10) at ambient pressure and confirmed the dominant role of scattering by remote ionized impurities. After illumination, the ratio quickly decreases with increasing 2DEG density. However when pressure is applied, this ratio decreases with decreasing N2D, giving evidence of a pressure-induced misfit strain at the interface that modifies the dominant scattering mechanisms.
Second-harmonic generation of a new chalcone-type crystal
Authors: Zhang G. J. , Kinoshita T. , Sasaki K. , Goto Y. , Nakayama M.
Published: July 2002

A new type of chalcone crystal was prepared. Anisotropic indices with wavelength dispersion were measured by the Brewster angle method. The two largest second-harmonic generation (SHG) tensor components were determined by the wedge method and compared with d11 of 2-methyl-4-nitroaniline. Calculated collinear and noncollinear phase-matched SHG patterns reasonably fit the observed photographs.
Optical channel waveguide fabrication based on electron beam irradiation of silica
Authors: Madden S. J. , Green Mino , Barbier D.
Published: July 2002

The bombardment of silica by low-energy electrons induces compaction and an increase in refractive index. We have used this phenomenon, combined with photolithographic processing, to make channel waveguides in silica, most of which are monomode, with a depth of 2–7 μm, and peak index variation between 10−3 and 10−2. Channel waveguide widths down to 2 μm have been fabricated on fused silica plates and on silica layers grown on silicon by plasma-enhanced chemical vapor deposition (PECVD) methods. The lowest measured linear losses at 633 nm were 0.3 db/cm in PECVD silica and 1.9 db/cm in the fused silica plates, although much lower losses are anticipated in the latter material. Using this method we have fabricated 3 dB directional couplers in both materials.
Permanent grating induced by nonlinear absorption in polysilane films
Authors: Nakano H. , Ishida Y. , Yanagawa T. , Matsumoto N.
Published: July 2002

The optical grating memory effect in polysilane film is investigated. A refractive index grating is formed within a few minutes by using visible light near room temperature. The grating formation time is dominated by the peak intensity of the pumping beams, and its dependence on the wavelength of the pumping beams corresponds to the two-photon absorption spectrum. The grating formation mechanism is explained as the result of the chain scission induced by two-photon absorption.
Effects of different processes with hydrogen on the photoluminescence of GaAlAs:Si grown by molecular beam epitaxy
Authors: Grilli E. , Guzzi M. , Zamboni R. , Bosacchi A. , Franchi S. , Vanzetti L. , Allegri P. , Pavesi L.
Published: July 2002

We present a study on low-temperature photoluminescence (PL) of Si-doped Ga1−xAlxAs (n ∼ 1×1017 cm−3, 0.2≤x≤ 0.5) grown by molecular beam epitaxy (MBE) either in the presence and in the absence of a hydrogen backpressure and/or post-growth hydrogenated by exposure to a hydrogen plasma; we show that GaAlAs grown with hydrogen has a PL efficiency higher than that of material grown without hydrogen by a factor of up to 20; even more interestingly, the relative enhancement of transitions related to excitons and to shallow donors and acceptors is so large that the two kinds of PL spectra are qualitatively different. On the contrary, independently on whether material grown without hydrogen is post-growth hydrogenated, the spectral features of PL spectra are dominated by transitions involving relatively deep donors and/or acceptors. Our results suggest that the two treatments with hydrogen act on deep levels of different origin.
Monte Carlo simulation of hot electrons in silicon p-i-n cold cathodes
Authors: Boots H. M. J. , Schuurmans M. F. H. , Arnold D. , Higman J. M. , Hess K.
Published: July 2002

Monte Carlo simulation of electron transport in p-i-n cold cathodes yields an exponential dependence of the efficiency on the work function similar to the relation found in the experiment. The effective temperature characterizing the exponential dependence is higher in the model than in the experiment and is not equal to the calculated electron temperature. The efficiency at breakdown decreases with the intrinsic layer width and is very sensitive to the X-X intervalley scattering rates.
Liquid phase epitaxy regrowth of two-dimensional electron gas on GaAs patterned by in situ meltback
Authors: Zaslavsky A. , Frei M. R. , Tsui D. C.
Published: July 2002

Selective in situ meltback of V-groove channels followed by liquid phase epitaxial regrowth of a modulation-doping AlGaAs layer is used to produce a two-dimensional electron gas on a patterned GaAs substrate. The in situ meltback patterning of the substrate forms channels made up of definite crystallographic planes. Characterization of the two-dimensional electron gas by magnetotransport measurements in a tilted magnetic field at 4.2 K confirms that the electron gas exists on all the planes that comprise the channels. Since the regrowth surface is exposed neither to air nor chemical etchants, this technique holds promise of producing high quality interfaces on patterned GaAs.
Observation of Lomer–Cottrell locks in SiGe strained layers
Authors: Ferret P. , Robinson B. J. , Thompson D. A. , Baribeau J.-M.
Published: July 2002

Misfit dislocations in the SiGe system are usually not dissociated. We present the first observation of a Lomer–Cottrell lock array in a Si/Si1−xGex/Si heterostructure (0.4<x<0.6). We describe the character of the stacking faults and the partial dislocations which form the locks.
High average power edge emitting laser diode arrays on silicon microchannel coolers
Authors: Mundinger D. , Beach R. , Benett W. , Solarz R. , Sperry V. , Ciarlo D.
Published: July 2002

We have demonstrated high average power output devices in both one-dimensional (1-D) and two-dimensional (2-D) arrays of laser diodes using efficient edge emitting cleaved bars and silicon microchannel coolers. These packages are based on the rack and stack architecture. For the 1-D array a cw optical power output of 22.2 W was obtained with 20% electrical to optical conversion efficiency. For the 2-D array an average optical power density of greater than 100 W/cm2 was obtained at an efficiency of 25%.
Improvement of electrical characteristics of polycrystalline silicon-contacted diodes after forward bias stressing
Authors: Wu S. L. , Lee C. L. , Lei T. F.
Published: July 2002

Improvement of the electrical characteristics of polycrystalline silicon (polysilicon) contacted n+-p diodes after application of a forward bias stressing is reported. The improvement existed for diodes whose emitter-implanted doses of arsenic were larger than 6×1015 cm−2 for HF-dipped devices, and 1×1016 cm−2 for H2SO4 heat-treated devices. The improvement is believed to be due to the neutralization by arsenic of dangling bonds at polysilicon grain boundaries and at the poly/mono silicon interfaces during the stressing process.
In situ x-ray photoelectron spectroscopy and reflection high-energy electron diffraction study of diethylgalliumchloride adsorption on Si (100) and Si (111) surfaces
Authors: Sasaoka C. , Kato Y. , Usui A. , Hirayama H. , Tatsumi T.
Published: July 2002

Diethylgalliumchloride (DEGaCl) adsorption on Si(100) 2×1 and Si(111) 7×7 surfaces is studied by reflection high-energy electron diffraction and x-ray photoelectron spectroscopy. DEGaCl adsorbs molecularly on the (100) surface at room temperature, while the Ga—Cl bond dissociates on Si(111). The Si(111) 7×7 structure is greatly disturbed after DEGaCl exposure, indicating a strong interaction between the surface and the adsorbate. The spatial distribution of dangling bonds is thought to be responsible for the differences in the reactivity between the two surfaces. The Ga—ethyl bond dissociates on both Si(100) and (111) surfaces after annealing at 210 °C, and at the same time Cl desorbs from the surfaces. The Cl desorption process is also discussed.
Influence of high-dose γ irradiation on electron mobility in a silicon inversion layer
Authors: Majkusiak B. , Jakubowski A. , Grigorov K. , Balasiński A.
Published: July 2002

An influence of high-dose γ irradiation on the dependence of electron mobility on transverse electric field in the silicon surface inversion layer is experimentally determined and considered.
Femtosecond erbium-doped optical fiber amplifier
Authors: Nakazawa Masataka , Kurokawa Kenji , Kubota Hirokazu , Suzuki Kazunori , Kimura Yasuo
Published: July 2002

A gain of 9 dB has been obtained in an erbium-doped optical fiber amplifier for input pulses with a peak power of 30 W, an average power of 30 μW (−15.2 dBm), and a pulse width of 260 fs. When the input peak power is increased in the soliton power regime, an adiabatic soliton narrowing occurs due to the optical gain. By increasing the pump power further, an optical gain enhanced soliton self-frequency shift dominates, which is due to the excitation of high-order soliton. Thus, soliton narrowing from 250 to 60 fs is observed.
Evaluation of device quality germanium-germanium oxynitride interfaces by high-resolution transmission electron microscopy
Authors: Paine D. C. , Rosenberg J. J. , Martin S. C. , Luo D. , Kawasaki M.
Published: July 2002

Previous work has shown that germanium oxynitride films grown on Ge substrates by thermal oxidation followed by nitridation provide a passivating dielectric which can be used to fabricate metal-oxynitride-semiconductor field-effect transistors. We have investigated the interfacial microstructure of this semiconductor-dielectric system with high-resolution transmission electron microscopy (TEM) and show that 21-nm-thick germanium oxynitride films grown using this technique are uniform in thickness and interfacially smooth on a scale of ±0.5 nm over lateral peak-to-peak distances on the order of 100’s of nm. The germanium oxynitride was seen to be electron beam sensitive with significant damage to both the oxynitride and the semiconductor-insulator interface being observed after exposure for 15 s to 200 keV electrons at a current density of 2.250 A/cm2 at the specimen.
Radiation damage in ReSi2 by a MeV 4He beam
Authors: Bai G. , Nicolet M-A. , Mahan John E. , Geib Kent M. , Robinson Gary Y.
Published: July 2002

Epitaxial ReSi2 thin films grown on Si (100) substrates were analyzed at room temperature by MeV 4He backscattering and channeling spectrometry. The minimum yield of [100] axial channeling increases with increasing exposure of the ReSi2 sample to the analyzing He beam. This means that ReSi2 suffers irradiation damage induced by a MeV 4He beam. The damage in the film induced by a beam incident along a random direction is about one order of magnitude larger than that induced by a beam with an aligned incidence, indicating that the damage is mainly generated by elastic collisions of nuclei. The experimentally measured defect concentration produced at 300 K by a beam of random incidence is compared with the theoretically estimated one produced at 0 K in an amorphous target. The agreement is fairly good, suggesting that the defects are stable at room temperature.
High critical current density in grain-oriented bulk YBa2Cu3Ox processed by partial melt growth
Authors: Shi Donglu , Fang M. M. , Akujieze Justin , Xu Ming , Chen J. G. , Segre Carlo
Published: July 2002

A uniform grain-oriented microstructure was developed in 50-mm-long bar samples of bulk YBa2Cu3Ox prepared by a partial melt growth process. In sharp contrast to previous reports, the textured products contained only small amounts of second phases. The samples were dense and nearly free of porosity. Transport measurements showed that the textured samples could carry a critical current density greater than 4.4×104 A/cm2 at 77 K and 1.8 T. The possible effects of processing parameters on the superconducting properties of the tested materials are discussed.
Phase alignment in Ag-clad Bi-Sr-Ca-Cu-O (2:2:1:2) wires
Authors: Ray R. D. , Hellstrom E. E.
Published: July 2002

Powder-in-tube wires that contained Bi, Sr, Ca, and Cu in a 2:2:1:2 mole ratio were drawn then rolled flat before processing. The superconducting phase was aligned with its c axis perpendicular to the wide plane of the wire by sintering the wires just below the melting point and by melt processing. Melt processing with slow cooling of the melt yielded the most alignment. Gravity did not influence alignment during melt processing.
Properties and thermal stability of the SiO2/GaAs interface with different surface treatments
Authors: Paccagnella A. , Callegari A. , Batey J. , Lacey D.
Published: July 2002

High quality SiO2 films were deposited by plasma-enhanced chemical vapor deposition on GaAs wafers which received different surface treatments. It was found that metal-oxide-semiconductor (MOS) capacitors which received surface nitridation were unstable under high-temperature anneal (600 °C). These instabilities are interpreted in terms of free As precipitates at the interface. When, instead, a thin Si layer was deposited on the GaAs surface, stable interfaces were obtained at 600 °C. These MOS capacitors appear to show both deep depletion and inversion.
Molecular beam epitaxy deposited thin films of bismuth compound superconductors
Authors: Bernhoff H. , Flodström A. S.
Published: July 2002

Thin films of superconducting BiCaSrCuO have been grown by molecular beam epitaxy depositions of Bi, Cu, and CaF2/SrF2 on MgO and SrTiO3 followed by a high-temperature oxygen anneal. The films showed a fairly wide transition of 20 K at a Tc of 80 K. Residual amounts of fluorine, detected with secondary-ion mass spectrometry, are believed to cause the broad superconducting transition. X-ray diffraction analysis of the superconducting films revealed strongly c-axis oriented films consisting of Bi2CaSr2Cu2O8 and Bi2Sr2Cu1O6 phase. Surface structure studies, with scanning electron microscopy and scanning tunneling microscopy, show oriented 1 μm sized very smooth flat grains of superconducting phase in the plane of the film with islands of CuOx scattered on top of these.
Search for a proximity effect induced gap in gold/high T
c junctions
Authors: Dessau D. S. , Wells B. O. , Shen Z.-X. , Spicer W. E. , Arko A. J. , List R. S. , Olson C. G. , Eom C. B. , Mitzi D. B. , Kapitulnik A. , Geballe T. H.
Published: July 2002

We have used high-resolution photoemission spectroscopy to search for a proximity effect induced superconducting gap in gold overlayers on c-axis single crystals of Bi2Sr2CaCu2O8 and a-axis thin films of YBa2Cu3O7. These two junction types give us a representative sampling of very well characterized near-ideal interfaces (gold/c-axis Bi2Sr2CaCu2O8) and junctions in which the geometry more strongly favors the existence of the proximity effect but the interfacial quality may not be as ideal (gold/a-axis YBa2Cu3O7). In neither of these junction types did we observe any evidence for a proximity effect induced gap, and we place an upper limit of approximately 5 meV on its existence in the junctions that we have studied.
Independent and ambipolar tunneling in asymmetric-coupled quantum well structures
Authors: Tanguy C. , Deveaud B. , Regreny A. , Hulin D. , Antonetti A.
Published: July 2002

We report femtosecond pump-probe transmission spectroscopy experiments on GaAs/AlGaAs asymmetric-coupled quantum wells, using a spectrally narrow optical excitation at 740 nm. The time-resolved evolution of the bleaching demonstrates the tunneling of both carriers through the barrier. At high densities a single tunneling time is observed in opposition to the low density regime, where the electron and hole contributions are well separated.
Formation of highly n-doped gallium arsenide layers by rapid thermal oxidation followed by rapid thermal annealing of silicon-capped gallium arsenide
Authors: Sadana D. K. , de Souza J. P. , Cardone F.
Published: July 2002

Carrier concentrations at a level of ≳1×1019 cm−3 were achieved when Si-capped GaAs underwent rapid thermal oxidation (RTO) in Ar+0.1% O2 ambient at 850–1000 °C for 10–60 s followed by rapid thermal annealing (RTA) in Ar ambient at 850–950 °C. Carrier concentrations in the RTO only samples were in the range of 2–5×1018 cm−3. Kinetic data on the diffusion of Si under RTO and RTO+RTA conditions are presented. The enhancement in the electrical activation of the diffused Si during RTA appears to be partly due to its local atomic rearrangement and partly due to redistribution in the GaAs. Ohmic contacts to the doped layer were made using Au-Ge-Ni alloy and contact resistances of ≲0.1 Ω mm were obtained.
Phase conjugation in amorphous germanium diselenide thin films
Authors: Guasti M. Fernández , Poniatowski E. Haro , López S. Camacho
Published: July 2002

We report a phase conjugate mirror (PCM) using germanium diselenide amorphous thin films with a 25 mW He Ne laser. The size of the PCM area can be made very large as opposed to the size limitations of crystal PCMs. The induced hologram may be recorded temporarily or permanently depending on the incident light parameters. The main drawback of this system is the long exposure time, of the order of minutes, required to generate the phase conjugate signal. The modulation of the refractive index is suggested to be due to a photostructural reorientation.
Calculations of a Ta soft x-ray laser (44.8 Å) using a sub-Kilojoule pump
Authors: Maxon S.
Published: July 2002

A design is presented for a Ni-like Ta x-ray laser which uses less than 1 kJ pump energy. This is in contrast with previous experiments carried out at the Nova two-beam chamber which have used several kJ pump energy. The main features of the new system are the use of a thin target (30 μg/cm2 Ta), a much lower intensity, and a shorter pulse.
Inverted pseudomorphic high electron mobility heterostructures by atmospheric pressure metalorganic chemical vapor deposition
Authors: Pan N. , Carter J. , Zheng X. L. , Hendriks H. , Wu C. H. , Hsieh K. C.
Published: July 2002

Inverted pseudomorphic high electron mobility transistor (HEMT) and inverted HEMT heterostructures are demonstrated by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) for the first time and characterized by transmission electron microscopy (TEM), variable temperature Hall effect, and Shubnikov–de Haas measurements. TEM micrographs of both structures show distinct and sharp heterojunction interfaces without indications of interface roughness at the AlGaAs/channel layer interface. Variable temperature Hall effect measurements reveal a monotonic increase in mobility as the temperature is lowered. For the inverted HEMT, the mobility at 15 K is 90 000 cm2/V s with a sheet density of 8.2×1011 cm−2. The mobility of the inverted pseudomorphic HEMT at 15 K is 73 000 cm2/V s with a sheet density of 1.5×1012 cm−2. Shubnikov–de Haas measurements at 4.2 K in magnetic fields up to 18.5 T show clear magnetoresistance oscillations and plateaus in the quantum Hall effect confirming the existence of a two-dimensional electron gas. Fast Fourier power transform of the magnetoresistance versus magnetic field shows two subband levels with a total sheet density of 8.7×1011 cm−2 for the inverted HEMT and a total sheet density of 1.55×1012 cm−2 for the inverted pseudomorphic HEMT in close agreement to the variable temperature Hall effect measurement results.
Performance of a high T
c superconducting ultralow-loss microwave stripline filter
Authors: Zahopoulos C. , Sridhar S. , Bautista J. J. , Ortiz G. , Lanagan M.
Published: July 2002

We report the successful fabrication of a five-pole interdigital stripline filter made of the 93 K superconductor Y1Ba2Cu3Oy coated on a silver substrate, with a center frequency of 8.5 GHz and an extremely high rejection ratio of 80 dB. The lowest insertion loss measured was 0.1 dB at 12 K, with a return loss better than 16 dB, representing significant improvements over a similar Cu filter, and comparable to low Tc filters. The insertion loss appears to be limited by extrinsic factors such as tuning mismatch and joint losses, and not by the superconducting material losses.
Double-heterostructure Pb1−x−yCdxSryS/PbS/Pb1−x−yCdxSryS lasers grown by molecular beam epitaxy
Authors: Koguchi N. , Takahashi S.
Published: July 2002

Pb1−x−yCdxSry S/PbS/Pb1−x−yCdxSryS double-heterostructure lasers emitting at a midinfrared wavelength region were fabricated for the first time using molecular beam epitaxy. Effects of the lattice mismatches between active and confinement layers and also between substrate and confinement layers using a tilted substrate on the laser properties were investigated. The maximum pulsed operating temperature increases as the lattice mismatch decreased using a tilted substrate.
Contour photoetching of n-type semiconductors
Authors: van de Ven J. , Nabben H. J. P.
Published: July 2002

In wet photoetching of semiconductors with a projected beam on a large surface the kinetics are limited by the dissolution of reaction products at high light intensities. The structures obtained after prolonged etching are of no practical use. For short etching times, however, it is shown that in specific etchants the contour of the projected beam can be etched, whereas the central part remains comparatively passive with an etch rate which is at least ten times lower. With this maskless method, narrow grooves can be produced which are interesting for isolation of specific areas of a wafer. The method is discussed and the mechanism explained in detail for n-GaAs in H2O2/H2SO4 solutions. It is shown that the principle can be extended to other solutions and semiconductors.
Enhanced critical current density in Ca-doped Y1Ba2Cu4O8
Authors: Narwankar P. K. , Chandrachood M. R. , Morris D. E. , Sinha A. P. B.
Published: July 2002

The Jc of Ca0.1Y0.9Ba2Cu4O8 (Ca-1:2:4) synthesized in elevated oxygen pressure is found to be ≳106 A/cm2 at low temperatures and fields, two orders of magnitude greater than the Jc of undoped Y1Ba2Cu4O8 (1:2:4). The Jc (determined by magnetic hysteresis measurements) remains high (5×105 A/cm2) up to B=4 T at 5 K, and is still ≳104 A/cm2 at 40 K and 4 T indicating strong flux pinning. At 77 K, Jc drops to 103 A/cm2 at B=1 T. Ca-1:2:4 was partially converted to 1:2:3+CuO by brief thermal treatment to generate additional flux pinning centers, but Jc did not improve further.
Raman microprobe characterization of photorefractive nonlinearity in Ti:LiNbO3 channel waveguides
Authors: Ramabadran Uma B. , Jackson Howard E. , Boyd Joseph T.
Published: July 2002

We report on the use of a Raman microprobe to investigate the nonlinear optical process of polarization rotation in Ti:LiNbO3 optical channel waveguides. Selection rules allow the Raman scattered signal collected in a direction orthogonal to the plane of the waveguide to provide information regarding the polarization state of the light propagating in the waveguide. From this data a threshold value of power necessary to initiate the polarization rotation is obtained and used to calculate a value of β15, an asymmetric component of the photovoltaic tensor. The value of β15 for an X-cut, Y-propagating channel waveguide was found to be 8×10−13 A/W and that for a rapid thermally annealed Z-cut, Y-propagating sample 4×10−14 A/W.
Compact hybrid resonant optical reflector lasers with very narrow linewidths
Authors: Ackerman D. A. , Dahbura M. I. , Shani Y. , Henry C. H. , Kistler R. C. , Kazarinov R. F. , Kuo C. Y.
Published: July 2002

Hybrid resonant optical reflector lasers of less than 1 cm length are described. These external cavity devices operate with very narrow linewidth approaching the resonator-loss-limited minimum. Best linewidth results are 7.1 kHz at 1.3 μm and 24 kHz at 1.55 μm.
Measurement of very low-loss silica on silicon waveguides with a ring resonator
Authors: Adar R. , Shani Y. , Henry C. H. , Kistler R. C. , Blonder G. E. , Olsson N. A.
Published: July 2002

The loss in phosphorus-doped silica on silicon waveguides was accurately measured using a 6-cm-diam ring resonator, by recording the transmission of a narrow linewidth external-cavity laser through the resonator as a function of temperature. A finesse of 45 and resonance width of 24.2 MHz were obtained, indicating guide loss of 2.6 dB per meter, which is the best result thus far measured for these waveguides. The shift in the modes with temperature was measured in the temperature range 30–120 °C and found to be close to 1/8 Å/deg.
Metallizations of AuGeNi/GaAs(001) and Au/GaAs(001) contacts at 4×10−3 Pa and 7×108 Pa pressure
Authors: Zhao Y. C. , Wu Z. Q.
Published: July 2002

The metallizations of AuGeNi/GaAs(001) and Au/GaAs(001) contacts at 4×10−3 Pa and 7×108 Pa pressure have been analyzed by using x-ray diffraction, transmission electron microscopy, and scanning electron microscopy. Our observations show that the high-pressure ambient inhibits the As sublimation loss and that only interdiffusion takes place without any formation of compounds in those contacts annealed in argon at 7×108 Pa. The experimental results are also discussed on the basis of phase diagrams.
Guiding-center-drift resonance of two-dimensional electrons in a grid-gate superlattice potential
Authors: Liu C. T. , Tsui D. C. , Shayegan M. , Ismail K. , Antoniadis D. A. , Smith Henry I.
Published: July 2002

We have studied the low-field magnetoresistance of the two-dimensional electron gas in GaAs/AlxGa1−xAs in the presence of a two-dimensional lateral surface superlattice (2D LSSL) potential, and observed, for the first time, the guiding-center drift resonance, previously reported for one-dimensional LSSL structures. The 2D LSSL potential is created by applying a voltage Vg to a 200 nm period grid-gate structure fabricated on top of the sample and can be tuned continuously from being repulsive to attractive by tuning Vg.
Magneto-optical recording by short pulses
Authors: Ohtsuki T. , Owa S. , Yamada F.
Published: July 2002

It was experimentally demonstrated that a laser pulse with a duration of less than 10 ns gives a steep temperature distribution in the film plane with little thermal diffusion out of the irradiated area. This results in the writing of domains whose sizes closely fit the cross sections of the laser power profile, and a reduction in the amount of laser energy needed for writing. The experimental results agree well with thermal analysis in which the thermal conductivity adopted for the film is one order of magnitude smaller than that of the bulk material. The advantages of short pulse writing in high-density recording are described.
Universal elastic scattering cross sections for electrons in the range 1–100 keV
Authors: Browning R.
Published: July 2002

For high atomic numbers the total cross section for electron-atom elastic scattering calculated using the partial-wave method is found to fall into two regimes over the range 1–100 keV. The cross section in the higher energy regime scales as E−1, and in the lower energy regime as E−0.5. An empirical equation has been drawn up that describes these trends, and can give a universal expression for the cross sections over the Periodic Table to allow economical Monte Carlo simulation of electron scattering over a wide range of energies and materials.
Role of amphoteric defects in the formation of metal/GaAs Schottky barriers
Authors: Zhang T. , Sigmon T. W.
Published: July 2002

The effect of near interface bulk defects on metal/GaAs Schottky barriers, calculated using a modified amphoteric native defect (MAND) model, is shown to explain the measured experimental data. The simulation results successfully predict the trend in barrier heights for interfaces which undergo thermal processing for both n- and p-type substrates. It also correctly gives the surface Fermi level positions for pulsed laser melted GaAs which contain a large quantity of As vacancies. The MAND model provides an alternative approach to the understanding of the Schottky barrier formation mechanism on GaAs.
GexSi1−x optical directional coupler
Authors: Mayer Robert A. , Jung K. H. , Hsieh T. Y. , Kwong Dim-Lee , Campbell Joe C.
Published: July 2002

We have fabricated and characterized the first GexSi1−x optical directional couplers. These structures were fabricated from GexSi1−x grown by rapid thermal processing chemical vapor deposition. The average attenuation of single, straight waveguide sections was 3.3 dB/cm at a wavelength of 1.52 μm. For the directional couplers, the coupling coefficient was 3.9 cm−1 for a waveguide separation of 1.5 μm.
Ultrathin silicon membranes to study supercurrent transport in crystalline semiconductors
Authors: van Huffelen W. M. , de Boer M. J. , Klapwijk T. M.
Published: July 2002

We have developed a two-step anisotropic etching process to fabricate thin silicon membranes, used to study supercurrent transport in semiconductor coupled weak links. The process uses a shallow BF+2 implantation, and permits easy control of membrane thickness ≤100 nm. Preliminary measurements on membrane-based Nb-Si-Nb junctions reveal the simultaneous occurrence of tunnel behavior and Josephson coupling.
Fabrication of photodiode arrays by molecular assembly technique
Authors: Yoneyama Mitsuru , Fujii Akiteru , Maeda Shuichi , Murayama Tetsuo
Published: July 2002

Mixed monolayers of 5-(4-N-decylpyridinium)-10,15,20-tri-p-tolyl porphyrin (PyP) and arachidic acid (AA) were prepared on a water surface as a precursor for organized arrays of photodiodes. By compression and expansion of the films, PyP self-assembled to form nearly circular domains with their size dependent on the molar ratio of PyP and AA. These structures were successfully incorporated into Schottky-type cells, and their photoelectric properties were studied on the domain level by illumination of a focused light with a diameter of 20 μm. The short-circuit photocurrents showed large fluctuations depending on the position of illumination, which reveals that the PyP domains function as photodiode arrays.
Reduction of real-space transfer in depletion-mode dipole heterostructure field-effect transistors
Authors: Zou J. , Abid Z. , Dong H. , Gopinath A.
Published: July 2002

The real space transfer in depletion-mode dipole heterostructure field-effect transistors (HFETs) has been investigated both theoretically and experimentally. Theoretically, we demonstrate that parallel conduction will be substantially reduced in the dipole HFET and to a smaller extent in the planar-doped HFET when compared to the conventional HFET due to the increased carrier confinement. By measuring the cutoff frequency at various dc biases, the experimental results indicate that a reduced real space transfer effect occurs in the depletion-mode dipole HFETs.
Anomalous change of extinction spectra of CuCl microcrystals
Authors: Masumoto Yasuaki , Wamura Tetsuro , Kawamura Tomohiro
Published: July 2002

Optical transmission spectra of CuCl microcrystals embedded in NaCl crystals were studied around the Z3 exciton resonance by varying the annealing time. With the increase in the annealing time, extinction spectra of the Z3 exciton change anomalously from the absorption-type spectrum to the emission-type spectrum via the dispersion-type spectrum. The Mie theory [Ann. Phys. 25, 377 (1908)] successfully explains the spectral change due to the growth of microcrystals. We report here for the first time an anomalous change of the exciton spectra due to the growth of semiconductor microcrystals.
Threshold shifting in pseudomorphic semiconductor-insulator-semiconductor heterostructure field-effect transistors
Authors: Wright S. L. , Solomon P. M. , Baratte H. , LaTulipe D. C. , Jackson T. N.
Published: July 2002

Pseudomorphic (In,Ga)As layers are used in GaAs-based semiconductor-insulator- semiconductor (SIS) structures to shift the threshold voltage from the natural, near-zero value. The threshold voltage is shifted positively for (In,Ga)As gate layers, and negatively for (In,Ga)As channel layers, by the (In,Ga)As/GaAs conduction-band offset. The thermionic and field emission barrier heights agree with shifts obtained in capacitance-voltage characteristics. The structures withstand implant activation anneals, establishing a simple technology to create either enhancement or depletion-mode devices.
Pulse shortening of a copper bromide laser by quenching of resonator transients
Authors: Lei Zhu , Fucheng Lin
Published: July 2002

Generation of single pulses from a copper bromide laser with 2 ns pulse width is described here. At 11 kHz the pulse repetition rate, the stability of the amplitude, and the pulse width of these pulses are excellent. Theoretical considerations of the pulse shortening are also shown to agree well with the experiment.
AlInGaAs/AlGaAs separate-confinement heterostructure strained single quantum well diode lasers grown by organometallic vapor phase epitaxy
Authors: Wang C. A. , Walpole J. N. , Missaggia L. J. , Donnelly J. P. , Choi H. K.
Published: July 2002

Separate-confinement heterostructure diode lasers containing a strained Al0.18In0.20Ga0.62 As single quantum well active layer and Al0.25Ga0.75As confining layers have been fabricated from structures grown on GaAs substrates by low-pressure organometallic vapor phase epitaxy. The emission wavelength of these devices is 814 nm. Threshold current density is as low as 103 A cm−2 for cavity length L=1500 μm, and differential quantum efficiency as high as 90% for L=280 μm. The characteristic temperature T0 is 214 K between 10 and 40 °C, and 159 K between 40 and 80 °C. Preliminary tests of cw operation suggest that these lasers are more reliable than AlGaAs/AlGaAs lasers.
A cantilever shadow mask technique for reduced area molecular beam epitaxial growth
Authors: Beam III E. A. , Kao Y. C. , Yang J. Y.
Published: July 2002

A type of shadow mask growth technique (cantilever shadow masking) for reduced area molecular beam epitaxial growth has been developed and applied to the growth of GaAs and InxGa1−xAs on selective areas of Si and GaAs substrates, respectively. This technique eliminates detrimental sidewall growth interactions, results in precisely positioned growth areas, and can be more readily planarized than other reduced area growth structures. This technique is particularly useful for defect density reduction during latticed-mismatched heteroepitaxy using reduced growth areas.
Impulse compression using soliton effects in a monolithic GaAs circuit
Authors: Case Michael , Kamegawa Masayuki , Yu Ruai , Rodwell M. J. W. , Franklin Jeff
Published: July 2002

A monolithic GaAs impulse compressor circuit which utilizes soliton wave propagation effects in nonlinear transmission lines has been fabricated. The circuits compress a 20 dBm, 8 GHz sinusoid to a train of 3.9 V peak to peak, 5.5 ps full width at half maximum impulses.
Coherent emission from two-dimensional Josephson junction arrays
Authors: Benz S. P. , Burroughs C. J.
Published: July 2002

Coherent emission has been generated by two-dimensional arrays of SIS Josephson junctions and detected in a junction coupled to the array through a dc-blocking capacitor. The detector junction exhibits Shapiro steps at frequencies corresponding to the voltage across single array junctions and ranging from 60 to 210 GHz. The maximum power coupled to the detector junction occurs at 150 GHz and is estimated to be 0.9 μW, based on simulations of the detector circuit. Possible mechanisms for coherent emission from two-dimensional arrays are discussed.
Tandem active layer superluminescent diode with a very wide spectrum
Authors: Noguchi Yoshio , Yasaka Hiroshi , Mikami Osamu
Published: July 2002

Broader spectral width superluminescent diodes having a new structure of tandem active layers are proposed and fabricated at a 1.3 μm wavelength. The emission spectral widths were successfully broadened over 100 nm, thus achieving a very short coherence length of less than 10 μm. Applying this new active layer structure to a Fabry–Perot cavity, a unique function of superluminescent/laser mode switching is also demonstrated.
Organometallic vapor phase epitaxy of AlGaAs/GaAs heterojunction bipolar transistors using tertiarybutylarsine
Authors: Kim T. S. , Bayraktaroglu B. , Henderson T. S. , Plumton D. L.
Published: July 2002

We have studied the use of tertiarybutylarsine (t-BuAsH2) for organometallic vapor phase epitaxy (OMVPE) growth of AlGaAs/GaAs heterojunction bipolar transistors (HBTs). Good dc characteristics were achieved with t-BuAsH2-grown HBT structures, including common-emitter current gains higher than 200 and 1000 for n-p-n and p-n-p structures, respectively. Near-ideal current gain dependence on the collector current density was observed, indicating that the quality of AlGaAs was suitable for high-performance HBTs. The microwave characteristics were also comparable to those of arsine-grown HBTs. These results demonstrate that t-BuAsH2 can successfully replace arsine for OMVPE growth of AlGaAs/GaAs HBT structures.
Surface reactions in the atomic layer epitaxy of GaAs using monoethylarsine
Authors: Maa B. Y. , Dapkus P. D.
Published: July 2002

The use of monoethylarsine (MEAs) as an arsine alternative source in GaAs atomic layer epitaxy (ALE) is studied. We use x-ray photoelectron spectroscopy and reflection high- energy electron diffraction (RHEED) to characterize the surface reactions of MEAs on GaAs(001) Ga-rich surfaces. At substrate temperatures between 320 and 540 °C, no carbon-related species are observed. At Ts=320 °C and an exposure of 100 L of MEAs, AsHx (x=1 or 2) is thought to be the adsorbed arsenic species. However, arsenic atoms are formed if a longer exposure time or a larger injection level is applied. As the substrate temperature increases As-rich surfaces are readily obtained with an improved RHEED 2×4 pattern. Two reaction steps are proposed. It is suggested that the reaction leading to AsHx species is the rate-limiting step. AsHx pairs react to form arsenic atoms by H2 release. Judging from the existence of intermediate AsHx species and the easier cleavage of As-ethyl bond, MEAs is believed to be a promising candidate as an arsenic source in GaAs ALE. 
Coupling of interdigital transducer to ultrasonic Lamb waves
Authors: Jin Yu , Joshi Shrinivas G.
Published: July 2002

The coupling of an interdigital transducer to ultrasonic Lamb waves propagating in a piezoelectric plate has been calculated using Green’s function method. It is found that when the plate thickness is more than a few acoustic wavelengths, the lowest order symmetric (S0) and antisymmetric (A0) modes are almost equally generated. The slight difference in the velocities of these modes gives rise to the beating effect whereby wave energy transfers periodically between the upper and lower plate surfaces. Experimental measurements performed on a Y-cut, Z-propagating lithium niobate plate are found to be in good agreement with theoretical predictions. The coupling coefficients have also been calculated using the simpler definition K2 = 2(v0−vm)/v0, where v0 and vm are Lamb wave velocities on a free and metallized surface, respectively. It is found that this definition gives erroneous results if the ratio of plate thickness to acoustic wavelength is greater than 1.
Magneto-optical characterization of YBa2Cu3O7 film uniformity
Authors: Raider S. I. , Gupta A. , Hussey B. W. , Oh B. , Batalla E. , Zwartz E. G. , Wright L. S.
Published: July 2002

Using a magneto-optical technique, we have nondestructively imaged macroscopic variations in magnetic flux that penetrate laser-ablated, c-axis oriented, epitaxial YBa2Cu3O7 superconducting films deposited on crystalline (100)SrTiO3 substrates. Flux penetration into YBa2Cu3O7 films in an externally applied magnetic field is enhanced at crystalline substrate defect sites. A relationship between flux penetration and substrate defects is experimentally demonstrated with a YBa2Cu3O7 film deposited on an intentionally degraded crystalline SrTiO3 surface.
Flexural resonant samples for submonolayer measurements of oxygen on Si surfaces
Authors: Dreyfus Russell W.
Published: July 2002

Photothermal deformation measures optical energy absorption by thermal expansion of a solid. This work describes how deflection amplitude is increased by a factor of 104 by mechanically resonating thin bars in a flexural mode of vibration. Small (∼10−5–5×10−3 fractional) infrared optical absorptions from Si:O surfaces are reported in various reactive gases using a tunable CO2 drive laser. Alternately, conventional low-power light sources can be used to provide sufficient excitations for submonolayer infrared absorption measurements.
Transmission of 1 kW-class CO2 laser light through circular hollow waveguides for material processing
Authors: Hongo Akihito , Morosawa Ken’ichi , Shiota Tsuneo , Suzuki Kenji , Iwasaki Souta , Miyagi Mitsunobu
Published: July 2002

For the purpose of material processing, we have studied transmission characteristics of germanium-coated silver hollow waveguides with 1.5 mm φ×80 cm. The maximum input power was 1 kW and the transmission was 90% under straight condition. Steel plates 1.6 mm thick were cut by CO2 laser light through the hollow waveguide and the authors confirmed that this type of waveguide could deliver sufficient laser energy for material processing.
Varistors based on mixed-phase ceramics containing ZnO and negative temperature coefficient spinels
Authors: Raghu N. , Kutty T. R. N.
Published: July 2002

High nonlinearity coefficients of 60–150 are observed in the current-voltage (I-V) curves of the mixed phase ceramics formed by cosintering ZnO with spinel phases having large negative temperature coefficients (NTCs) in resistivity. The region of negative slope in the I-V curves of the NTC ceramics is progressively made positive with ZnO phase content, wherein ZnO grains function as a built-in resistor in series to the resistance of the NTC phase. High α depends on the optimum phase content of ZnO as much as its intrinsic conductivity. The studies indicate that the predominent contribution to power dissipation is by way of joule heating from the resistive component of the current.
Atomic layer epitaxy of device quality GaAs with a 0.6 μm/h growth rate
Authors: Colter P. C. , Hussien S. A. , Dip A. , Erdoǧan M. U. , Duncan W. M. , Bedair S. M.
Published: July 2002

The two main problems, carbon contamination and a low growth rate, facing atomic layer epitaxy (ALE) of GaAs are addressed. A reactor was designed to process 2 in. wafers with a growth rate as high as 0.6 μm/h. Background carbon concentration less than 1015 cm−3 and a 77 K mobility of 30 000 cm2/V s were measured. The new reactor is based on the concept of rotating the substrate between streams of reactant gases with provisions to shear off and sweep away the thermal boundary layer. Self-limited growth was observed for a growth temperature as high as 600 °C.
Acoustic graded-index lenses
Authors: Jen C. K. , Wang Z. , Nicolle A. , Neron C. , Adler E. L. , Kushibiki J.
Published: July 2002

Experimental investigations of the focusing behavior of rods having acoustically graded-index profile across the rod diameter are presented for the first time. The ray acoustics approach is used for the theoretical interpretation. Acoustic velocity profiles have been measured using a 225 MHz line focus beam scanning acoustic microscope. The focusing behavior is visualized with a Schlieren system.
Cumulative nature of two-wave mixing and its dependence on crystal orientation
Authors: Joseph Joby , Singh K. , Pillai P. K. C.
Published: July 2002

Experimental investigation into the cumulative nature of two-wave mixing in photorefractive BaTiO3 crystal has been carried out. Signal beam amplification via two-beam coupling has been studied with continuous wave exposure and periodic pulse exposure. A comparison of the two shows the presence of a noncumulative component in the signal beam gain. Dependence of this component on crystal c-axis orientation has been measured.  
Oxidation studies of fluorine containing diamond films
Authors: Grannen K. J. , Tsu D. V. , Meilunas R. J. , Chang R. P. H.
Published: July 2002

The thermogravimetric method is used to study the oxidation properties of plasma grown diamond films both with and without fluorine. The oxidation experiments occur over a temperature range of 600–800 °C in pure oxygen at atmospheric pressure. Diamond films with fluorine are found more resistant (by a factor of 4 at 700 °C) to oxidation. The activation energy for oxidation, however, is a factor of at least 2.3 lower for fluorinated diamond films. Consequently, it is postulated that oxidation mechanisms for diamond films are quite different depending upon the fluorine content. Oxidation on nonfluorinated diamond films seem to proceed as a rate-limited reaction while the oxidation of fluorinated films seems to be a diffusion limited reaction. Oxidation rates are also found to depend weakly on film density, crystal texture, and phase composition of the diamond films.
Ultraviolet absorption studies on photosensitive germanosilicate preforms and fibers
Authors: Williams D. L. , Davey S. T. , Kashyap R. , Armitage J. R. , Ainslie B. J.
Published: July 2002

Detailed measurements of the ultraviolet absorption spectra of germanosilicate preforms, multimode and single-mode fibers are presented. Significant differences between the spectra of preforms and fibers are revealed and these differences are thought to be caused by the stresses induced during fiber pulling. Measurements are also presented of the changes in the absorption spectra in single-mode fibers into which reflection gratings have been written using an ultraviolet laser. These results suggest that changes in the absorption between 200 and 600 nm are not responsible for the inferred changes in the refractive index.
Generation of steerable submillimeter waves from semiconductor surfaces by spatial light modulators
Authors: Zhang X.-C. , Auston D. H.
Published: July 2002

We propose a novel optoelectronic technique for optical submillimeter-wave interaction. By illuminating a spatially periodic pattern of a femtosecond laser beam on a semiconductor surface, optically induced THz electromagnetic beams can be steered by controlling the pattern structure with two degrees of freedom. We also demonstrated the temporal encoding of the radiated electromagnetic wave by the optical intensity spatial distribution.