bluuebunny/crossref_metadata_2025 huggingface dataset:
High-resolution electroless deposits on alumina from ultraviolet exposure of a Pt metalorganic
Authors: Mance Andrew M.
Published: July 2002

Photochemical and electroless metallization techniques have been combined to create metal patterns on alumina (Al2O3). In this positive imaging process, small amounts of an ultraviolet (uv) sensitive metalorganic (MO) Pt compound are first applied to the surface of the alumina by spin coating. A quartz photomask is then used to selectively expose the Pt MO to uv light in the areas that are to be metallized. After a xylene rinse removes the Pt MO from the unexposed areas, the substrate and xylene insoluble Pt MO are fired in air at 450 °C for 5 min, followed by electroless deposition of Ni on the uv exposed surface. Total Pt consumption is to about 0.01–0.02 g/m2 of metallized surface−no Pt or Ni was detected in nonmetallized regions. The uv exposure time is brief, ≤0.75 s, and 0.3-μm-thick Ni/B deposits can be patterned on 96% pure alumina with resolution of nearly 28 μm line/spaces.
Lateral straggle of focused-ion-beam implanted Be in GaAs
Authors: Vignaud D. , Etchin S. , Liao K. S. , Musil C. R. , Antoniadis D. A. , Melngailis J.
Published: July 2002

The lateral distribution of focused-ion-beam implanted Be atoms in GaAs has been studied by measuring the electrical resistivity in grating structures. The gratings were implanted at 230 and 260 keV with periods from 0.04 to 3 μm oriented both parallel and perpendicular to the direction of current flow. In the parallel case an initially n-type conducting layer was converted to an insulating layer as the period of the unannealed implants was decreased. The resistivity was found to be modulated for grating periods even below 0.1 μm. In the perpendicular case the gratings were implanted into both on-axis and off-axis, semi-insulating GaAs between two p-type regions and rapid thermal annealed. The minimum half-width of an implanted line was found to be 140 nm in on-axis material. In off-axis material the width was 50 to 90 nm larger depending on dose. In all cases the width is smaller than the 450 nm straggle predicted by Monte Carlo simulations.
Modulation of photoluminescent intensity by applying high electric field in doubly insulated CaS:Eu phosphor thin films
Authors: Ando M.
Published: July 2002

Emission modulation effect produced by applying electric fields in a CaS:Eu phosphor thin film was studied. The CaS:Eu polycrystalline thin film was sandwiched between the insulating layers so that high electric fields up to 106 V/cm could be applied to the film. As a result, the photoluminescent intensity decreased with increasing applied electric field and the maximum modulation degree of 97% was obtained. The photoluminescent modulation effect was found to be caused by field-induced ionization (a kind of tunneling effect) of the excited state of Eu2+ localized-luminescent centers. These results indicated that the photoluminescent intensity of the phosphor thin films can be modulated by the electric field as well as by excitation intensity. These new features should offer the phosphor thin films new applications such as a spatial light modulator.
Electroabsorption in the type II superlattices
Authors: Li Shaozhong , Khurgin Jacob B.
Published: July 2002

Electric field dependence of the optical absorption in the ZnSe0.35Te0.65-ZnSe type II superlattice has been studied. An extremely large blue shift of the absorption edge found for the structure makes it an attractive choice for the waveguide visible light modulators.
Evidence for facets with 〈210〉 azimuth in molecular beam epitaxial growth on patterned GaAs(001) substrates
Authors: Benisty H. , Böckenhoff E. , Talneau A.
Published: July 2002

We present clear experimental evidence that using axes different from the 〈110〉 mirror axes of the (001) GaAs surface generally used for lateral patterning and regrowth of nanostructures yield much better faceted morphologies in molecular-beam epitaxy (MBE) at such scales. Growth on [210] and [12̄0] oriented gratings is shown to yield almost perfect (21n) facets (n≊6). A novel directed one-dimensional growth instability is clearly revealed. The microscopic structure of these facets is discussed as well as implications for the growth of quantum wires and dots in the (In,Ga,Al)As system.
Dominant pinning mechanisms in YBa2Cu3O7−x films on single and polycrystalline yttria stabilized zirconia substrates
Authors: Harshavardhan K. S. , Rajeswari M. , Hwang D. M. , Chen C. Y. , Sands T. , Venkatesan T. , Tkaczyk J. E. , Lay K. W. , Safari A.
Published: July 2002

Critical-current densities have been measured in YBa2Cu3O7−x films deposited on (100) yttria stabilized zirconia (YSZ) and polycrystalline YSZ substrates as a function of temperature (4.5–88 K), magnetic field (0–1 T) and orientation relative to the applied field. The results indicate that in films on polycrystalline substrates, surface and interface pinning play a dominant role at high temperatures. In films on (100) YSZ, pinning is mainly due to intrinsic layer pinning as well as extrinsic pinning associated with the interaction of the fluxoids with point defects and low energy planar (2D) boundaries. The differences are attributed to the intrinsic rigidity of single fluxoids which is reduced in films on polycrystalline substrates thereby weakening the intrinsic layer pinning.
Photoluminescence topography of shallow impurities in GaAs epilayers grown by metalorganic vapor phase epitaxy
Authors: Wang Z. M. , As D. J. , Windscheif J. , Bachem K. H. , Jantz W.
Published: July 2002

Spectrally and spatially resolved low-temperature photoluminescence topography has been applied to investigate the lateral variation of impurities in nominally undoped epitaxial GaAs layers. The concentrations of both shallow donors and acceptors exhibit lateral variations. The donor variation pattern appears to be arbitrary, but the fluctuation of shallow acceptor carbon clearly reproduces the well-known cellular structure of the liquid encapsulated Czochralski GaAs substrate dislocation density distribution, suggesting that the carbon incorporation into the epitaxial layer is influenced by the substrate during the growth of metalorganic vapor phase epitaxy.
Electro-optic polymer waveguide fabricated using electric-field-assisted chemical vapor deposition
Authors: Tatsuura Satoshi , Sotoyama Wataru , Yoshimura Tetsuzo
Published: July 2002

We describe the fabrication of an electro-optic (EO) polymer channel waveguide using a new technique, electric-field-assisted chemical vapor deposition. A polymer film is deposited from epoxy and nonlinear optical (NLO) aliphatic amine using chemical vapor deposition under an electric field applied by slit electrodes on a thermally oxidized Si wafer, at room temperature. A clear propagating He-Ne laser beam is observed along the electrode gap. The propagated beam’s near field pattern is bright for the TE mode, but very weak for the TM mode. This indicates the NLO side groups’ in-plane alignment and the fabrication of a channel waveguide. The EO coefficient of this waveguide, measured in a Mach–Zehnder interferometer, is r11∼0.1 pm/V. The polymer channel waveguide, which is poled at room temperature after film deposition, shows no EO response. This means NLO molecules are actually aligned during polymerizing, not after.
Planarization in multiple polyimide layers
Authors: Chakravorty K. K. , Tanielian M. H.
Published: July 2002

A novel phenomenon, leading to the planarization of topologically prominent features, in partially cured BTDA-alkylated diamine based preimidized photosensitive polyimide films is reported. This phenomenon appears to be related to solvent interdiffusion between two polyimide layers in intimate contact leading to uniform shrinkage of the two layers. A novel approach for the fabrication of high-density copper/polyimide multichip interconnect structures has been developed based on the observed planarization phenomenon.
Pulsed amplification of continuous-wave signal fields in photorefractive BaTiO3
Authors: Vainos N. A. , Mailis S. , Gower M. C.
Published: July 2002

High-gain pulsed amplification of low intensity continuous-wave optical signals via two-wave mixing in a photorefractive barium titanate (BaTiO3) crystal is demonstrated. The technique relies on the nonlinear mixing between a signal field and a pump field produced via pulsed amplification of a continuous-wave field in excimer-pumped dye amplifiers.
Gate tunneling current in In0.53Ga0.47As junction field-effect transistors
Authors: Lo D. C. W. , Chung Y. K. , Forrest S. R.
Published: July 2002

Band-to-band tunneling leakage current is identified as the dominant source of dark current leakage at the gates of In0.53Ga0.47As/InP junction field-effect transistors (FETs) optimized for use in linear, optoelectronic integrated circuit applications. Both the temperature and voltage dependencies of the gate leakage in such devices is studied, and the results are in agreement with calculations based on the FET two-region model modified to include the effects of tunneling. Due to the fundamental nature of this leakage mechanism, and due to the fact that gate leakage induces shot noise, these results suggest that both low noise and high gain can be achieved by limiting the channel doping to ∼9×1016 cm−3 for FETs operated at a frequency of 1 GHz.
Magneto-optical absorption in a two-dimensional electron grid
Authors: Zhao Y. , Tsui D. C. , Santos M. , Shayegan M. , Ghanbari R. A. , Antoniadis D. A. , Smith Henry I.
Published: July 2002

We have fabricated a two-dimensional (2D) electron grid in the high mobility GaAs/Al0.35Ga0.65As heterostructure and observed, in the magneto-optical absorption, new resonances and an anomalous dispersion, similar to that recently reported by Kern et al.1 in antidots in a high density InGaAs/AlInAs heterostructure. We have studied their dependencies on the 2D electron density and demonstrate their plasma origin. The anomaly in magnetic field dependence is explained by the mixing of cyclotron resonance and edge magnetoplasma modes in this 2D electron microstructure.
Microstructure of the emitter polycrystalline silicon/silicon interface in bipolar transistors after rapid thermal annealing
Authors: Kim Y. , Liu T. M. , Lee K. F. , Jeon D. Y. , Rentschler J. A. , Ourmazd A.
Published: July 2002

We use high-resolution transmission electron microscopy to determine the microstructure of the emitter polycrystalline (poly) Si/Si interface of real bipolar transistor devices after rapid thermal annealing. Our results quantify the size and density of interfacial oxide voids (pinholes), the areal fraction of the interface covered with voids, and the amount of epitaxial regrowth after annealing in the range 1000–1150 °C. Correlation of these results with the characteristics of the devices shows that the most dramatic electrical changes occur before 2% of the poly-Si/Si interfacial area is covered with oxide voids.
Realization of a field-effect resonant tunneling transistor at room temperature: Observation of negative transconductance due to quantum tunneling
Authors: Yang C. H.
Published: July 2002

Room-temperature operation of a quantum transistor demonstrating negative transconductance and power gain is reported. The operating principle is based on resonant tunneling: the resonant tunneling probability between two terminals is strongly modulated by a third terminal. Criteria for this observation are discussed.
Mesa stripe transverse injection laser in HgCdTe
Authors: Bouchut P. , Destefanis G. , Bablet J. , Million A. , Colin T. , Ravetto M.
Published: July 2002

In this letter, we report the fabrication and operation of narrow stripe, transverse injection, HgCdTe lasers. The double heterostructure of the laser was grown by molecular beam epitaxy on (111) CdZnTe substrate. The n-type base was extrinsically indium doped but the upper p-type confining layer was only doped by deviation from stoichiometry. Laser emissions at 3.40 and 3.56 μm were obtained at 78 K under pulsed current conditions. Threshold current as low as 48 mA and differential quantum efficiency as high as 4.2% were achieved. Over 60 K threshold current has an exponential increase with temperature and a T0 parameter of 8 K.
Defect-assisted resonant tunneling: A theoretical model
Authors: Stievenard D. , Letartre X. , Lannoo M.
Published: July 2002

Defects are often taken as the cause of deviations in the current-voltage characteristics of heterostructures such as barrier or double barrier, and the so-called defect-assisted tunneling effect has been assumed to occur in certain cases. We present an analytical analysis of the tunneling effect which occurs through a barrier and which is assisted by an energy level associated with a defect. Moreover, we show that a negative differential resistance can occur using a single barrier in which a defect is located.
Pump-probe interferometric measurement of nonlinear phase modulation in a GaAs/AlGaAs multiple-quantum-well waveguide
Authors: Laughton F. R. , Marsh J. H. , Button C.
Published: July 2002

Nonlinear refractive index measurements have been made at 1.06 μm using a time-division interferometer, and n2 measured to be about −3×10−17 m2 W−1 for a TM pump and TE probe. The refractive index change was also seen to contain a positive component at small pump-probe delay times, corresponding to an intensity-dependent nonlinear refractive index of n2≊2×10−17 m2 W−1.
Silicon epitaxy grown by electron-beam evaporation in ultrahigh vacuum at 200 °C
Authors: Lin Yung-Jen , Yew Tri-Rung
Published: July 2002

Silicon epitaxial growth at 200 °C is reported in this letter. The epitaxy was grown by electron-beam evaporation in an ultrahigh vacuum system. Wafers were in situ cleaned in the growth chamber by thermal desorption at 840 °C for 30 min. The wafer surface was examined by reflection high energy electron diffraction (RHEED). The epitaxial growth rate was at or higher than 0.020 nm/s. Epitaxial films were characterized by cross-sectional transmission electron microscopy (XTEM) and secondary ion mass spectroscopy (SIMS).
Nonlinear optical absorption and dynamics in quantum wells
Authors: Jiang Min , Wang Hailin , Steel Duncan G.
Published: July 2002

We present measurements of differential transmission and four-wave mixing in GaAs quantum well structures at 1.8 K near the inhomogeneously broadened lowest heavy-hole (hh1) exciton resonance using narrow band cw excitation. The data show an increase in absorption and an excitation lifetime of order 1–10 μs outside the spectral hole produced by the pump. The long lifetime and the experimentally determined absence of excitation spatial diffusion in this region suggests that optical absorption produces electron-hole pairs that are correlated but separately localized due to disorder. A phenomenological model is proposed to explain the nonlinear response based on two-photon absorption.
Shifted x-ray photoelectron peak in molecular beam epitaxial GaAs grown at 200 °C
Authors: Look D. C. , Grant J. T. , Sizelove J. R.
Published: July 2002

X-ray photoelectron spectroscopic results show that molecular beam epitaxial GaAs grown at 200 °C has a reduced effective surface potential energy, about 0.5 eV, compared with the usual 0.7 eV. A Poisson analysis of the data, using parameters from Hall effect and absorption measurements, requires that the Fermi-level-controlling defect in this material must have a significantly lower activation energy than that of EL2, an unexpected result.
Observation of sol-gel solid phase epitaxial growth of ferroelectric Pb(Nb,Zr,Ti)O3 thin films on sapphire
Authors: Barlingay C. K. , Dey S. K.
Published: July 2002

This letter reports and discusses the observation of sol-gel solid phase epitaxy (SPE) of (110) Pb0.99Nb0.02(Zr0.52Ti0.48)0.98O3 or PNZT(2/52/48) on 3 in. diam (011̄2) sapphire. The epitaxial nature (with at least single crystal-like texture) of these films was ascertained by HRTEM and x-ray diffraction studies, including pole figure analysis. Such PNZT thin films (0.6 μm) were transparent to wavelengths between 0.4 and 5.6 μm, and exhibited an optical band gap and a refractive index (at 0.6328 μm), of 3.6 eV and 2.5–2.6, respectively.
Influence of silicon on the properties of reactively sputtered hydrogenated amorphous germanium
Authors: Drüsedau T. , Schröder B.
Published: July 2002

Hydrogenated amorphous germanium-silicon films (a-Ge1−xSix:H, 10−3<x<10−1) were prepared by reactive dc-magnetron sputtering from a germanium target in an Ar/H2/SiH4 atmosphere. Silicon incorporation leads to a decrease of the dark conductivity σD (mainly independent of the hydrogen pressure) and a weaker decrease of the photoconductivity σph (strongly dependent on the hydrogen pressure) and has no influence on the gap state density detected by photothermal deflection spectroscopy. The best photoconductivity corresponding to μτ=10−5 cm2/V was obtained under the highest hydrogen pressure and is not influenced by silicon up to x=0.01. The ratio of σph/σD under monochromatic excitation (632 nm, 9 mW/cm2) increases from 0.25 in a-Ge:H to more than 1 in a-Ge0.99Si0.01:H.
Effect of oxygen on the nucleation and growth of diamond thin films
Authors: Shah S. I. , Waite M. M.
Published: July 2002

We have used x-ray photoelectron spectroscopy to study the effects of oxygen on the nucleation and growth of diamond films during microwave plasma assisted chemical vapor deposition. The high film growth rate in the presence of oxygen in the feed gas mixture was found to be related to the accelerated saturation of carbon onto the Si substrate surface. This reduces the incubation period and promotes a much faster diamond nucleation and growth than with oxygen-less plasmas. In the presence of oxygen, diamond has been detected as early as 1 min into the deposition, whereas without oxygen it was not observed until after 40–50 min.
Anomalous multiplication in Hg0.56Cd0.44Te avalanche photodiodes
Authors: Liu Y. , Forrest S. R. , Loo R. , Tangonan G. , Yen H.
Published: July 2002

We quantitatively study the electric field distributions in Hg0.56Cd0.44Te avalanche photodiodes recently reported for use in the 1.6–2.5 μm wavelength region using a two-dimensional solution of Poisson’s equation. It is found that, contrary to previous reports, there is no evidence for large uniform avalanche gain in these diodes. Furthermore, to first order, it is shown that the ionization rate ratio of electrons to holes in the diodes demonstrated to date is on the order of unity. Hence, it is not expected that the present diodes will lead to low noise operation superior to Ge or In0.53Ga0.47As/InP avalanche photodetectors.
Collimated sputtering of TiN/Ti liners into sub-half-micrometer high aspect ratio contacts/lines
Authors: Joshi R. V. , Brodsky S.
Published: July 2002

In situ sputtering of TiN/Ti liners into high aspect ratio (six to eight) sub-half-micrometer contacts with step coverages more than 40% on the side as well as on the bottom is demonstrated for the first time. The process utilizes a collimator, honeycomb-like structure through which atoms are directed into contact holes. A study of step coverages, deposition rates, contact resistances, and junction leakages for Ti and TiN layers as a function of the aspect ratio of the collimator is carried out. The extendibility of collimation beyond 0.25 μm contact geometries is demonstrated. The optimum deposition rate is achieved based on the aspect ratio of the collimator. The structures formed with chemical vapor deposition (CVD) of W on TiN/Ti liners exhibit an order of magnitude improvement in contact resistance over the structures formed without collimated liners, especially for geometries below a critical geometry. The reverse leakages using the shallow junctions (0.12–0.14 μm) remain unchanged.
Evaluation of surface roughness of technological InP substrates by in situ scanning tunneling microscopy imaging in H2SO4 solution
Authors: Robach Y. , Phaner M. , de Villeneuve C. , Porte L.
Published: July 2002

The topography of different technological InP substrates has been studied by scanning tunneling microscopy in 0.25M H2SO4, under potentiostatic control. For the best surface preparation corresponding to an ‘‘epiready’’ InP surface, a rms roughness of ∼15–20 Å was measured, approximately ten times higher as for Si surfaces. Finally, it was shown that the growth of a chemical native oxide in HNO3 and its subsequent removal in a dilute HF solution led to a significant improvement of the InP surface topography.
Luminescence of strained Si1−xGex alloy layers grown by molecular beam epitaxy
Authors: Arbet-Engels V. , Tijero J. M. G. , Manissadjian A. , Wang K. L. , Higgs V.
Published: July 2002

Thick Si1−xGex strained layers grown by molecular beam epitaxy on Si(100) oriented substrates are investigated by photoluminescence spectroscopy. Well resolved near-band-gap luminescence is clearly observed in samples with a Ge concentration ranging from 10% to 20% for both as-grown and thermal annealed samples. The phonon assisted transitions are clearly identified and the phonon structure of the spectrum is resolved. The effects of deuterium passivation and rapid thermal annealing are studied and an enhancement of the intrinsic excitonic luminescence by more than a factor of three is observed upon deuteration. These results indicate that atomic deuterium is efficient in passivating nonradiative recombination centers responsible for the quenching of the band edge luminescence. The exciton energy band gap is shown to have a quasilinear dependence with Ge fraction between 9% and 26%.
Characteristics of phase-controlled superconducting device based on Andreev reflection and superconducting proximity effect at Nb-Si boundary
Authors: Hatano Mutsuko , Saito Kazuo , Nishino Toshikazu , Takagi Kazumasa
Published: July 2002

A phase-controlled superconducting device, employing an interferometer in solids analogous to the Michelson interferometer, is proposed and its operation is confirmed experimentally. In the device, a Nb-Si boundary is used as a mirror for electron waves in Si, and path-length difference between electron waves is artificially controlled by shifting the actual boundary position due to the superconducting proximity effect. Interference peaks are observed in the differential resistance curves and the energies of these peaks are controlled by gate voltage.
Vibration detection using dynamic photorefractive gratings in KTN/KLTN crystals
Authors: Hofmeister Rudolf , Yariv Amnon
Published: July 2002

We demonstrate a sensitive, all-optical, self-aligning holographic microphone/vibration sensor utilizing the zero external electric field photorefractive (Zefpr) effect. The device relies on the unique phase relationship, φ=0, between a spatially periodic intensity standing wave and the resultant index grating created with the Zefpr effect. Under this zero phase condition, the transmitted intensity of interfering beams in a two beam coupling geometry varies linearly with displacement of either the index grating or one of the interfering beams. In this way, vibrations are sensed remotely without any electrical signals in the vicinity of the sensor. The sensitivity of the microphone was determined as a noise equivalent power of 15 dB sound pressure level relative to 0.0002 μbar across the range 1.6–15.5 kHz.
Thermal stress distributions in GaAs on sawtooth-patterned Si substrates: A finite element approach
Authors: Lingunis E. H. , Haegel N. M. , Karam N. H.
Published: July 2002

Thermal stresses in GaAs on sawtooth-patterned Si substrates are studied by elastic finite element analysis under the assumption of plane strain. A comprehensive description of the highly nonuniform stress distribution is given and the possibility of band gap engineering by adjusting the geometrical characteristics of the structure is demonstrated. Results are presented in a form appropriate for interpretation of spectroscopic data and device engineering, and can be easily extended to other materials systems.
Observation of the photorefractive effect in single-domain BaTiO3 crystal fibera)
Authors: Ito Fumihiko , Kitayama Ken-ich , Tomomatsu Kazuhiko
Published: July 2002

Photorefractive effects are, for the first time to our knowledge, observed in single-domain tetragonal BaTiO3 fibers fabricated by the laser pedestal method. The diameter and length of the fiber are 250 μm and 2 mm, respectively. The photorefractivity is confirmed both by beam amplification through two-wave mixing and holographic image storage.
Exact results in linear thermomechanics of fluid-saturated porous media
Authors: Berryman James G. , Milton Graeme W.
Published: July 2002

Exact results are derived relating the various bulk moduli (frame, unjacketed, and pore) and heat capacity of inhomogeneous fluid-saturated porous media to the pertinent thermal expansion coefficients and component moduli when only two porous solid constituents are present. The porous solids need not be space filling or in perfect welded contact, so these results apply to materials containing some voids or cracks interspersed between the two constituents in addition to the interior voids associated with their pores. The key ratio of fluid pressure to temperature change producing uniform expansion or contraction is shown to be independent of porosity.
Reduction of the intensity noise from an erbium-doped fiber laser to the standard quantum limit by intracavity spectral filtering
Authors: Sanders Steve , Park Namkyoo , Dawson Jay W. , Vahala Kerry J.
Published: July 2002

The high frequency intensity noise of a tandem fiber Fabry–Perot erbium-doped fiber ring laser is reduced to the standard quantum limit, with a 0.5 dB experimental uncertainty. Noise reduction of ≳14 dB is achieved by intracavity spectral filtering of weak side modes using a narrow-band fiber Fabry–Perot etalon.
Electron tunneling into epitaxial films of Nd2−xCexCuO4−y
Authors: Homma M. , Tanda S. , Nakayama T.
Published: July 2002

We have performed tunneling experiments on planar junctions Al/AlOx/Nd2−xCexCuO4−y. This is the first experiment using epitaxial films with the planar junction for electron-doped high Tc Nd2−xCexCuO4−y. The temperature dependencies of the gap features were measured, in which the phonon structures were clearly observed in the normalized conductance curve. These results show accord with the phonon peaks in the phonon density of states obtained recently by neutron inelastic scattering experiments.
Enhanced electro-optic effect in amorphous hydrogenated silicon based waveguides
Authors: Zelikson M. , Salzman J. , Weiser K. , Kanicki J.
Published: July 2002

We report on a direct measurement of the electro-optic effect in amorphous hydrogenated silicon based waveguides. The observed phase modulation with an applied voltage shows evidence of a threshold voltage below which the electro-optic effect is weak. At high voltages the electro-optic phase modulation is nonquadratic and significantly enhanced with respect to the bulk effect in amorphous silicon. These results are explained in terms of a model which considers inhomogeneous electric fields within the silicon layer due to voltage dependent space charges.
Higher order zone-folded modes in ZnSe-ZnS strained-layer superlattices
Authors: Yamamoto Aishi , Kanemitsu Yoshihiko , Masumoto Yasuaki , Yamaga Shigeki , Yoshikawa Akihiko
Published: July 2002

Higher order (up to the 5th order) zone-folded acoustic modes in ZnSe-ZnS strained-layer superlattices (SLSs) were observed by means of Raman scattering. Structural characterization of both periodicity of superlattices and roughness of the interface was done by means of transmission electron microscopy (TEM). The Raman spectrum of zone-folded modes was well explained by the theoretical calculation which takes account of two observed structural characteristics of the sample, the periodicity of the superlattices, and the roughness of the interface. This clearly shows the strain does not matter to the observation of the zone-folded modes.
AlxGa1−xAs/AlyGa1−yAs and GaAs pseudo-heterojunction bipolar transistors with lateral emitter resistor
Authors: Gao G. B. , Fan Z. F. , Teraguchi N. , Shen T. C. , Morkoç H.
Published: July 2002

Both AlxGa1−xAs/AlyGa1−yAs and GaAs pseudo-heterojunction bipolar transistors (HBTs) with lateral emitter resistors (laterally extended emitter ledge) are shown to exhibit base current ideality factors of 1.3 and 1.1, and uniform current gains of 10 and 5, respectively, even at current densities as low as 5×10−11 A/μm2. With this test structure, it is possible to separate the surface effects from the bulk effects. The structures investigated also allowed the confirmation that the emitter edge-thinning reported recently is very effective for reducing the surface recombination. The structures under investigation also show that GaAs HBTs can operate at collector currents in the microampere range or below.
High-power index-guided distributed out-coupled grating surface emitting laser-amplifiers with narrow spectra and high-quality beams
Authors: Abeles J. H. , York P. K. , Andrews J. T. , Reichert W. F. , Kirk J. B. , Hughes N. A. , Dupuy C. G. , McGinn J. T. , Thomas J. H. , Zamerowski T. J. , Liew S. K. , Connolly J. C. , Carlson N. W. , Evans G. A. , Butler J. K.
Published: July 2002

Emission of a 100 mW cw beam into a nearly diffraction limited near-circular spot by a grating surface emitting (GSE) semiconductor laser, with radiance of 5.3×106 W/sr cm2, is described. The distributed out-coupled master oscillator power amplifier (DOC-MOPA) devices comprise active grating outcoupled power amplifiers and monolithic distributed feedback laser oscillators. With single wavelength (930 nm) operation demonstrated to 260 mW, they produce narrow linewidth (10 MHz) beams and near-ideal far-field patterns. The DOC-MOPA promises to become an efficient, compact source of high-quality ≥1 W cw light. Such fully collimated high power cw beams demonstrate the potential of GSE lasers to serve in systems requiring higher power than available from conventional edge-emitting technology.
Very thin CoSi2 films by Co sputtering
Authors: Maszara W. P.
Published: July 2002

The structure, resistivity, and thermal stability of CoSi2 films ranging in thickness from ∼11 to 52 nm were investigated. Both the bulk and the surface components of the resistivity were extracted. The films exhibited good thermal stability. The thermal stability and the silicidation temperature which gave the minimum film sheet resistance were found to increase with the sputtered film thickness. The sheet resistance was independent of the ramp-up rate (3–20 °C/s), prolonged exposure of the Co film to air, and the presence of native oxides on the Si surface prior to Co deposition.
Critical dislocation density separating different regimes of diffusion transport in metal-semiconductor systems
Authors: Vaisleib A. V.
Published: July 2002

The diffusion transport of metal impurities in semiconductors is considered. Critical magnitudes of dislocation density are obtained at which the diffusion kinetics change from the interstitial impurity regime of diffusion transport to the self-interstitial regime or the vacancy regime. It is predicted that the critical density of dislocations decreases with increasing temperature.
Preparation of Bi-Pb-Sr-Ca-Cu-O oxide superconductors by coprecipitation of nanosize oxalate precursor powders in the aqueous core of water-in-oil microemulsions
Authors: Kumar P. , Pillai V. , Shah D. O.
Published: July 2002

We describe a new technique for the synthesis of ultrahomogeneous nanoparticles of precursor oxalate powder by coprecipitation in the aqueous core of a water-in-oil microemulsion for the preparation of Bi-Pb-Sr-Ca-Cu-O (2223) oxide superconductor. This process ensures a uniform mixing of metal cations down to a scale of at least 10 nm. This finely dispersed precursor powder results in phase pure (2223) oxide superconductor after proper heat treatment.
Influence of water vapor on the susceptibility to electric-field damage of KTiOPO4
Authors: Morris P. A. , Crawford M. K.
Published: July 2002

We demonstrate that the susceptibilities of hydrothermal and flux grown KTiOPO4 (KTP) crystals to electric-field induced darkening increase with increasing water vapor content of the atmosphere surrounding the crystals. Infrared spectroscopy shows that hydrogen ions from the atmosphere migrate into the crystals in the presence of the applied electric field and charge compensate the formation of Ti3+ defects which are responsible for damage. These observations suggest that KTP-based electro-optic devices should be operated in a dry environment to reduce their susceptibility to damage.
Observation of solid phase epitaxy processes of Ar ion bombarded Si(001) surfaces by scanning tunneling microscopy
Authors: Uesugi Katsuhiro , Yao Takafumi , Sato Tomoshige , Sueyoshi Takashi , Iwatsuki Masashi
Published: July 2002

Scanning tunneling microscopy (STM) is used to investigate the surface morphology of Ar+-ion bombarded Si(001) surfaces and to elucidate the very beginning stages of solid phase epitaxy (SPE) processes of the Ar+-ion bombarded Si surfaces. The Ar+-ion bombarded Si surface consists of hillocks of 1–2 nm in diameter and 0.35–0.75 nm in height. The onset of SPE initiates at around 590 °C, at which a temperature (2×2) structure surrounded by amorphous regions is partially observed on terraces of the surface. During annealing at 590–620 °C, the areas of the (2×2) and c(4×4) reconstruction surrounded by amorphous regions develop. New defect models for the (2×2) and c(4×4) structures are proposed where alternating arrangements of the buckled dimers together with missing dimer defects are considered.
Existence of extinction temperature in WSix film growth from WF6 and SiH4: An indication of the role played by radical chain reactions
Authors: Saito T. , Shimogaki Y. , Egashira Y. , Komiyama H. , Yuyama Y. , Sugawara K. , Nagata S. , Takahiro K. , Yamaguchi S.
Published: July 2002

Low pressure chemical vapor deposition (LPCVD) was carried out to deposit tungsten silicide films (WSix) from WF6 and SiH4 in a low temperature range from 80 to 390 °C, using a tubular reactor system. Drastic decrease of the deposition rate occurred at an extinction temperature Tex. Increase of the reactor size in the range from 4 to 22 mmφ decreased Tex from 140 to 80 °C. Above Tex, the sticking probability of the film forming species (η) and the film composition, x of WSix , did not depend on the reactor diameter. Dependence of Tex on the reactor diameter and independence of η and x above Tex from the reactor diameter indicates that a radical chain process dominates CVD-WSix process to form film forming species.
Isotropic Jc-B properties of YBa2Cu3O7−x thin films containing fine precipitates by metalorganic chemical vapor deposition
Authors: Matsuno S. , Kinouchi S. , Egawa K. , Umemura T. , Uchikawa F. , Nakabayashi S.
Published: July 2002

Y1Ba2Cu3O7−x superconducting thin films which have isotropic Jc-B properties were prepared onto SrTiO3 (100) substrates at 700 °C by metalorganic chemical vapor deposition. The Jc did not depend on directions of the field either perpendicular or parallel to the c axis of the films and the films had a high Jc of 6.1×104 and 7.1×104 A/cm2 at 77 K and 5 T perpendicular and parallel to the c axis, respectively. Transmission electron microscopy observation and x-ray energy dispersive spectroscopy analysis indicated that the films contained many fine Y2BaCuO5-like precipitates with diameter of ∼10 nm and they were distributed uniformly with the density Np as high as 1023/m3.
Concentration profiles of surface atoms during epitaxial growth on vicinal surfaces
Authors: Shitara T. , Suzuki T. , Vvedensky D. D. , Nishinaga T.
Published: July 2002

Concentration profiles of surface atoms have been obtained from Monte Carlo simulations of epitaxial growth and compared with predictions based upon the original Burton–Cabrera–Frank (BCF) theory and with a modified BCF theory. The modification is a BCF-type equation for a quantity that involves the concentrations of surface atoms in each of the possible environments and accounts for the fact that all atoms, not simply free adatoms, can participate in surface diffusion. Even at temperatures beyond those where growth becomes dominated by step advancement, the modified BCF equation provides a more accurate description of the adatom concentration profiles than that obtained using only the free adatom concentration, which is the central quantity in the original BCF theory. This is due to step detachment processes combined with the meandering of the steps, which leads to an effective source of free adatoms that is not taken into account in the original BCF approach.
Heteroepitaxy of β-FeSi2 on unstrained and strained Si(100) surfaces
Authors: Peale D. R. , Haight R. , Ott J.
Published: July 2002

We have investigated factors influencing the heteroepitaxial growth of semiconducting β-FeSi2 on both unstrained and strained Si(100) surfaces under ultrahigh vacuum conditions using low energy electron diffraction, x-ray photoelectron spectroscopy, and scanning electron microscopy. We show that epitaxy and clear LEED patterns may be obtained by forming a template layer of FeSi2 followed by additional codeposition of reactants upon the template layer. Further improvement in the quality of the silicide layer is achieved by employing strained Si substrates. The dependence of the epitaxial silicide domain size on the lattice mismatch between the silicon substrate and the silicide layer is demonstrated.
Passivation of deep level states caused by misfit dislocations in InGaAs on patterned GaAs
Authors: Matragrano M. J. , Watson G. P. , Ast D. G. , Anderson T. J. , Pathangey B.
Published: July 2002

Deep level transient spectroscopy (DLTS) and cathodoluminescence (CL) were used to study the hydrogen passivation of misfit dislocations in In0.06Ga0.94As/GaAs heterostructures. The CL observations indicate that hydrogen plasma exposure passivates most, but not all, of the dark line defects existing in the specimen prior to hydrogenation. The concentration of deep level defect states that cannot be passivated is below the detection limit of the DLTS instrument (approximately 4×1012 cm−3). We find the passivation is stable after anneals at temperatures as high as 600 °C, indicating that hydrogen passivation of misfit dislocations is at least as stable as that of the isolated point defect studied previously with DLTS [W. C. Dautremont-Smith, J. C. Nabity, V. Swaminathan, M. Stavola, J. Chevalier, C. W. Tu, and S. J. Pearton, Appl. Phys. Lett. 49 1098 (1986)].
Screw dislocations in substrates used for high temperature superconductor thin films
Authors: Eissler D. , Wang H. S. , Dietsche W.
Published: July 2002

Substrates for high temperature superconductor (HTSC) thin films were chemically etched in order to obtain pits and hillocks at the sites of the dislocations. The structures were imaged by both an atomic force microscope and an optical microscope. We found that the dislocation density in the bare substrate is comparable to the screw dislocation density in the HTSC films. Based on the shape and orientation of the pits we identify the defects in the substrate as screw dislocations.
80–111 GHz quasi-optical measurement of the complex conductivities of YBa2Cu3O7 superconducting thin films
Authors: Zhang Dawei , Plant D. V. , Fetterman H. R. , Glass N. E. , Cheung J. T. , Kobrin P. H.
Published: July 2002

Complex conductivities of YBa2Cu3O7 high-temperature superconducting thin films were measured from 80 to 111 GHz using quasi-optical techniques. From transmission measurements, a peak was obtained in σ1 versus temperature. Measurements of the frequency dependence of this peak position found it shifted to higher temperatures with increasing frequency. The data for both σ1 and σ2, as a function of frequency, were fitted using a BCS/effective medium model. This fit indicates that the observed peak in σ1 is a result of the temperature dependence of the carrier mean free path combined with effects resulting from the granularity of the films.
Phase locking in a multichannel radial array CO2 laser
Authors: Yelden E. F. , Seguin H. J. J. , Capjack C. E. , Reshef H.
Published: July 2002

Phase locking in an extended-area, multichannel, radial array, carbon dioxide laser has been investigated. Preliminary self-phase-locking percentages as high as 62% were achieved with the device. The phase-locking mechanism was determined to be the mutual optical coupling present within the central region of this geometry. As such, this region acted as a core oscillator to initiate a fundamental optical mode within each individual discharge slot.
Self-aligned buried-heterostructure lasers grown entirely by metalorganic vapor phase epitaxy
Authors: Kondo Y. , Sato K. , Yamamoto M.
Published: July 2002

The effects of n-type dopant on InP embedding regrowth by metalorganic vapor phase epitaxy (MOVPE) are studied. It is found that the growth of the n-InP layer on the mesa structure is completely suppressed under a Se concentration of more than 8×1018 cm−3 and a mesa structure having a width of 1.1 μm. Using this novel MOVPE technique, a buried heterostructure laser diode is successfully fabricated without a selective growth mask. This achieves a threshold current as low as 14 mA, an external differential efficiency of 0.18 W/A, and an output power of more than 15 mW, at 25 °C.
Efficient laser performance of Nd:GdLiF4: A new laser crystal
Authors: Zhang X. X. , Bass M. , Villaverde A. B. , Lefaucheur J. , Pham A. , Chai B. H. T.
Published: July 2002

Laser action of Nd3+ doped GdLiF4 (GLF) has been demonstrated for both pulsed and cw laser pumped operation. A slope efficiency of 60% was obtained in either manner of operation. The spectroscopic properties and laser performance of Nd:GLF are very similar to those of Nd:YLF. GLF, on the other hand, can be doped with much higher Nd3+ concentration.
p
+/n/n
+ InP solar cells directly on Si substrates
Authors: Lee M. K. , Wuu D. S. , Horng R. H.
Published: July 2002

p +/n/n+ InP solar cells have been fabricated directly on (100) Si substrates by low-pressure organometallic vapor phase epitaxy. The best experimental cell without an antireflection coating exhibits an air mass one efficiency of 11.9%. The corresponding open-circuit voltage, short-circuit current, and fill factor are 0.78 V, 22.47 mA/cm2, and 0.63, respectively. An electrical characterization identifying loss mechanism is proposed.
Study of characteristics of photoluminescence spectra in double-barrier resonant tunneling structures
Authors: Wang T. H. , Mei X. B. , Jiang C. , Huang Y. , Zhou J. M. , Yang G. Z.
Published: July 2002

We have investigated photoluminescence of double-barrier diodes under various bias voltages and observed the saturation of the broadening of the photoluminescence lines. We have also studied the integrated photoluminescence intensity with increasing applied voltages near resonant voltages for high quality samples at low temperature (4.2 K). The results of the 77 K photoluminescence experiments confirm those at 4.2 K. The saturation of the broadening is due to weak hole localization; however, the saturation of the integrated photoluminescence intensity is mainly due to reduced nonradiative recombination. Our results suggest that the hole localization may arise from interface roughness.
Peltier refrigerator using a high T
c superconductor
Authors: Fee M. G.
Published: July 2002

A prototype Peltier refrigerator junction for operation at around liquid nitrogen temperatures has been built consisting of a thermoelectrically active bismuth-antimonide alloy leg and a thermoelectrically passive superconducting YBa2Cu3O7−δ leg. The junction has shown a maximum cooling of 5.35 K below a heat sink held at 79 K. Improvements in materials and design and operation in a magnetic field could result in cooling of up to 16 K.
Effect of growth conditions on the electrical and optical properties of AlxIn1−xAs (0.48<x<0.7)-Ga0.47In0.53As heterostructures
Authors: Brown A. S. , Henige J. A. , Schmitz A. E. , Larson L. E.
Published: July 2002

An increase of the Al- content of AlInAs layers above that of the composition which is lattice matched to InP (Al0.48In0.52As) has been shown to lead to increased Schottky barrier height [Lin et al., Appl. Phys. Lett. 49, 1593 (1986)]. This technique has been used to realize improved gate-to-drain breakdown voltage in AlInAs-GaInAs modulation-doped transistors designed for power applications. This letter reports the observation of an optimum growth temperature regime for the Al-rich Schottky layers in the modulation-doped structure. Growth in this regime results in the highest conductivity for modulation-doped structures as well as the highest quality interface formation as determined from low temperature photoluminescence measurements.
Uniformity of GexSi1−x epitaxial layers grown by ultrahigh vacuum chemical-vapor deposition
Authors: Greve D. W. , McLaughlin G. , Capano M. A. , Racanelli M.
Published: July 2002

We report on the uniformity of composition and thickness of epitaxial GexSi1−x layers grown by ultrahigh vacuum chemical-vapor deposition. Double-crystal x-ray diffractometry showed that variations in thickness are less than ±2.2% and variations in composition less than ±2.5% from center to edge of a 75 mm wafer. The variations observed are consistent with the predictions of Monte Carlo simulations.
Memory effect of an organic photoconductor and its application to a neuron model
Authors: Fujii Akiteru , Yoneyama Mitsuru , Ishihara Kei , Maeda Shuichi , Murayama Tetsuo
Published: July 2002

A new type of organic photoconductor composed of 9-ethylcarbazole-3-carbaldehyde diphenylhydrazone (DPH) dispersed in a polycarbonate polymer (PCR) film, when in the presence of thio-Michler’s ketone (TMK), was found to exhibit a sustained state of enhanced conductivity following visible irradiation. At room temperature, the enhanced current is observed to decay slowly over a period of a day and when heated it rapidly returns to its original state. A potential application of this ‘‘memory’’ effect to an artificial neuron model, using such memory-type organic photoconductors as optically controllable interconnections, is discussed. A liquid-crystal cell is used to demonstrate a nonlinear-saturated response dependent on a weighted input electric signal.
Band edge shifts of p-type copper indium diselenide electrodes in aqueous electrolytes
Authors: Siripala Withana , Vedel Jacques , Lincot Daniel , Cahen David
Published: July 2002

Impedance measurements were used to evaluate the relative band edge positions of single crystal p-CuInSe2 electrodes in various aqueous electrolytes, by measuring the extrapolated flatband potentials, Vfb. We find that Vfb can be shifted, depending on the extent of the potential scan and on the pH of the electrolyte used, over a range of up to 1.7 V (between pH 0–pH 14). In the pH range 0–6, Vfb can be fixed at intermediate values, which, in their turn, are determined by the pH of the electrolyte.
Hot-electron electroluminescence in AlGaAs/GaAs heterojunction bipolar transistors
Authors: Zanoni Enrico , Vendrame Loris , Pavan Paolo , Manfredi Manfredo , Bigliardi Stefano , Malik Roger , Canali Claudio
Published: July 2002

When biased in the active region at high collector voltages, AlGaAs/GaAs single heterojunction bipolar transistors have been observed to emit light in the 1.1–2.5 eV energy range. The spectral distribution of the emitted radiation results from the superimposition of (i) two peaks at about 1.4 and 2.1 eV, due to band-to-band recombination of cold electrons and holes, and (ii) a nearly exponential tail due to hot-electron-induced electroluminescence, whose intensity depends on reverse collector-base voltage. Moreover, a linear correlation has been found between the intensity of the hot-electron-induced electroluminescence and the current generated by impact ionization.
Strong piezoelectricity in nanosized silicon nitride prepared by laser-induced chemical vapor deposition
Authors: Wang Wei-Xiang , Li Dao-Huo , Liu Zong-Cai , Liu Song-Hao
Published: July 2002

It has been found for the first time that laser-induced chemical vapor deposition (LICVD) processed nano-Si3N4 possesses strong piezoelectric effects. The piezoelectricity of LICVD nano-Si3N4 stems from the charge accumulation in the interfaces and the surfaces of microvoids.