bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatially resolved critical current limitations in YBa2Cu3O7 multilayer structures
Authors: Hollin C. A. , Abell J. S. , Goodyear S. W. , Chew N. G. , Humphreys R. G.
Published: July 2002

Current flow in YBa2Cu3O7/PrBa2Cu3O7 multilayer structures has been studied using low temperature, scanning electron microscope, beam-induced voltage contrast. Specialized data acquisition has been used to limit thermalization effects and improve resolution. For both via hole contacts and crossovers, the lowest critical current densities were found at steps where the superconductor tracks climb up or down over patterned edges of the insulator.
Observation of residual strain in dynamically excited electrostrictors
Authors: Vohra S. T. , Fabiny L. , Bucholtz F.
Published: July 2002

We measured the dynamic small strain effects in electrostrictive ceramics with a high resolution fiber optic interferometer. The dynamic strain response of both a lead magnesium niobate (PMN) and a lead zirconate titanate (PZT)-based electrostrictive ceramic exhibited a residual signal which cannot be understood by the simple scalar strain-polarization relationship, e+QP2. The magnitude of the residual signal decreased as a function of increasing temperature indicating that the residual strain signal has origins in the remnant electric polarization of the material. The magnitude of the residual strain was generally higher for the PZT-based electrostrictor than for the PMN based sample. The observed residual strain signal represents a novel phenomenon previously unseen in the dynamical strain response of electrostrictive ceramics.
X-ray stimulated Raman scattering in Li and He
Authors: Hudis E. , Shkolnikov P. L. , Kaplan A. E.
Published: July 2002

We propose to use initially neutral Li and He gases to observe x-ray stimulating Raman scattering. We solve the Maxwell–Bloch equations for the Raman scattering in the presence of a strong photoionization atomic depletion and show that very high conversion efficiencies can be obtained, although the required intensities are significantly high to cause very fast photoionization.
Reliability and microstructure of Al-Si-V-Pd alloy films for use in ultralarge scale integration
Authors: Dirks A. G. , Augur R. A.
Published: July 2002

New data on a highly reliable interconnect material based on aluminum will be presented. As compared with conventional Al-Si-Cu alloy films, quaternary Al-Si-V-Pd films with only 0.1 at. % vanadium and 0.1 at. % palladium combine excellent plasma etchability with good corrosion resistance. Electromigration tests of Al-Si-V-Pd films have shown a surprisingly high stability at 180 °C. Studies of microstructural attributes show: (a) for Al-Si-V-Pd relative to Al-Si, texture is not significantly changed and average grain size is slightly increased, and (b) the dominant factor leading to a highly stable microstructure is the combined presence of finely dispersed, small precipitates of both (Al,V) and (Al,Pd) phases.
Observation of carrier heating in a 1.5 μm band multi-quantum-well semiconductor laser amplifier by time-resolved measurement for amplified spontaneous emission spectrum
Authors: Nido Masaaki , Suzuki Akira
Published: July 2002

The time development of electron temperature in 1.5 μm band multi-quantum-well (MQW) semiconductor laser amplifier is observed. The time development of an amplified spontaneous emission (ASE) spectrum triggered by a pump optical pulse with a 1.54 μm wavelength is observed with a time resolution of 2 ps. The electron temperature estimated from the ASE spectrum showed a fast rise up to 480 K, due to stimulated emission induced by the pump optical pulse, followed by a two-step decrease with a time scale over 20 ps. The slow carrier cooling shows that the carrier is heated due to the carrier transport in the MQW.
Resonant coupling of orbital angular momentum components in the barrier with analogous components in the well in InxGa1−xAs-GaAs quantum wells
Authors: Reynolds D. C. , Jogai B. , Yu P. W. , Evans K. R. , Stutz C. E.
Published: July 2002

When narrow InGaAs-GaAs quantum wells (QWs) are resonantly excited by the GaAs free exciton in the barrier, the intensity of the heavy-hole free exciton (HHFE) in the well oscillates with applied magnetic field. In the presence of a magnetic field, the magnetically field split angular momentum components of the GaAs barrier free exciton resonantly excite magnetically field split angular momentum components of the HHFE in the well. The angular momentum components of the HHFE in the well are expected to move in and out of resonance with the angular momentum components of the free exciton in the barrier as the magnetic field changes resulting in the observed intensity oscillations of the HHFE emission. When the QW is excited at energies slightly above the GaAs band-gap energy the HHFE emission intensity is greatly reduced and the intensity oscillations with magnetic field disappear.
Phase locking in two-junction systems of high-temperature superconductor-normal metal-superconductor junctions
Authors: Reintsema C. D. , Ono R. H. , Harvey T. E. , Missert N. , Vale L. R.
Published: July 2002

Mutual phase locking between two high-temperature step-edge superconducting-normal metal-superconducting junctions has been investigated using a two-junction circuit with a nonsuperconducting feedback path. The strength of the phase-locked state has been characterized as a function of locking frequency and temperature. Results are presented for a planar circuit as well as for a multilayer circuit incorporating a superconducting ground plane. The observed behavior was significantly enhanced for the circuit over a ground plane. Characterization of the phase locked state at 4 K yielded locking strengths as large as ‖IL‖/Īc=9%, and maximum locking frequencies to 1.06 THz. The magnitude of the locking strength decreased rapidly with increasing temperature with complete loss of coherence occurring at temperatures greater than 35 K.
Formation of probe microscope tips in silicon by focused ion beams
Authors: Vasile Michael J. , Biddick Christopher , Huggins Harold
Published: July 2002

A combination of lithographic patterning, liquid phase anisotropic etching, and focused ion beam milling has been used to prototype the production of scanning probe microscope tips in single-crystal silicon. The results show that tips with geometry equivalent to those made with iridium or tungsten wires can be made without the deleterious random effects of grain structure. The tips subtend a maximum cone angle of 20° and protrude 3.5 μm above the surface of a Si pyramid bounded by (111) planes.
Suppression of microstructural coarsening and creep deformation in a lead-free solder
Authors: McCormack M. , Jin S. , Kammlott G. W.
Published: July 2002

Bi-43% Sn eutectic solder [melting point (m.p.)∼139 °C] undergoes extensive microstructural coarsening and severe creep deformation under stresses at temperatures near 100 °C. It is shown that a relatively uniform dispersion in the solder of essentially insoluble particles such as iron can be accomplished by use of a magnetic field, and that the presence of these dispersoid particles significantly reduces microstructural coarsening and resultant accelerating tertiary creep rates. The useful service ranges of this Bi-Sn lead-free solder can thus be raised to much higher homologous temperatures, allowing its use at or exposure to elevated temperatures (near 100 °C) which are typical for the widely used, lead-containing, eutectic Pb-63-Sn solder alloy (m.p.∼183 °C), but with a greatly reduced creep rate.
Enhancement of optical absorption induced by disorder in three-dimensional random superlattices
Authors: Wang E. G. , Xu J. H. , Su W. P. , Ting C. S.
Published: July 2002

The effect of disorder on the optical absorption of the realistic random superlattice has been investigated based on a three-dimensional tight-binding Hamiltonian. It is found that the absorption intensity close to the band edge of the random superlattice is considerably enhanced, which can be explained by optical matrix elements of the relevant eigenfunctions localized strongly over 2–4 monolayers. An energy-level crossing behavior at the conduction-band bottom is also obtained.
Numerical study of temperature effect on carrier dynamics in multiple quantum well narrow wires
Authors: Endoh Akira , Arimoto Hiroshi , Sugiyama Yoshihiro , Kitada Hideki , Muto Shunichi
Published: July 2002

To clarify the effect of temperature on the wire width dependence of the photoluminescence (PL) decay time in multiple quantum well narrow wires, we performed numerical calculations of carrier dynamics using a simple damage model in which nonradiative recombination centers caused by fabrication damage near the wire sidewalls are considered. The drastic reduction of PL decay time around a 100-nm-wide wire at low temperature is explained by our damage model by the presence of an optically inactive layer, i.e., a so-called ‘‘dead layer’’ in which carriers vanish almost immediately due to heavy damage before reaching the sidewall. Our calculations show that the length of the ‘‘dead layer’’ changes with temperature even though the length of the damaged layer, in which defects are formed during fabrication process, is independent of temperature.
As-grown superconducting Bi2Si2Ca2Cu3Ox thin films with T
czero of 102 K prepared by rf magnetron sputtering
Authors: Ohbayashi Kazushige , Ohtsuki Takehiko , Matsushita Hiroshi , Nishiwaki Hideaki , Takai Yoshiaki , Hayakawa Hisao
Published: July 2002

As-grown high-quality superconducting thin films of the Bi2Sr2Ca2Cu3Ox were prepared by rf magnetron sputtering with a regulated shuttering technique. 2223 phase films with a 2201 phase buffer layer were deposited on MgO(100) substrates under rigorous control of the film composition, especially of bismuth contents. As a source of bismuth a sufficiently presputtered Bi2O3 target was used. At the preparation, Bi-Sr-Cu-O and Ca-Cu-O blocks were deposited alternately, no post-treatment steps were performed. The zero resistivity critical temperature of the as-grown film was 102.5 K and the critical current density at 4.2 K was 1.5×107 A/cm2. The growth rate was about 360 Å/h.
Laser-assisted thermochemical processing of diamond
Authors: Miyazawa Hajime , Miyake Shojiro , Watanabe Syuichi , Murakawa Masao , Miyazaki Toshiyuki
Published: July 2002

A new technique of contamination-free thermochemical processing of diamond is proposed. A diamond plate, which is placed on a metal plate, is treated thermochemically from its lower surface, in liquid, using a laser as the heat source. A focused Q-switched YAG laser beam was introduced, which passed through the liquid and diamond, onto the metal plate. The laser beam heats up the metal, and thereby, the lower surface of the diamond is etched by thermochemical interaction with the liquid. Comparison of the liquids, de-ionized water, and KOH solution, proved that KOH solution is preferable to water with respect to the stability of machining and smoothness of the prepared surface.
Electron distribution in a periodically line-doped GaAs
Authors: Takagaki Y. , Friedland K. J. , Ploog K.
Published: July 2002

The electrostatic potential and the electron distribution in periodically wirelike Si-doped GaAs are calculated within the semiclassical approximation for a distance between the wires of D=8–16 nm. It is shown that the mutual coupling between channels is significant for these wire separations. The electron distribution is most homogenized when the average electron density is ns∼5×1015 m−2, nearly independent of D. The existence of one-dimensional bound states is found to be unlikely even for ns∼8×1016 m−2 when D=8 nm, indicating that the electron distribution modulation is sustained by two-dimensional states.
Polarization of intersecting particles
Authors: Paley A. V. , Radchik A. V. , Smith G. B. , Vagov A. V.
Published: July 2002

An exact expression for the polarizability of intersecting circular cylinders has been derived covering all degrees of intersection and arbitrary complex dielectric constants for the particle material. This enables a comparison between the induced dipole moment on two particles of almost identical shape; a cardioid and a particular pair of overlapping cylinders. The absorption spectra in the small particle limit are extremely sensitive to the detailed shape of the surfaces near the point of intersection.
Active mode locking of a diode laser by a resonant tunneling diode
Authors: Grumann E. , Golub J. E. , Matusovsky M. , Rosenbluh M.
Published: July 2002

We use an oscillating resonant tunneling diode as the driver of an external cavity diode laser to produce active mode locked light pulses in the picosecond range. We demonstrate dc voltage-controlled uniform temporal positioning, or time shifting, or the laser pulses with reference to a synthesizer based reference signal. This may be very useful for picosecond time-resolved applications.
Efficient photogeneration of charge carriers in a layered photoreceptor using a conjugated polymer
Authors: Osaheni John A. , Jenekhe Samson A. , Perlstein Jerry
Published: July 2002

The field-dependent quantum efficiency φ(E) for photogeneration of charge carriers in a bilayer photoreceptor consisting of a poly(p-phenylene benzobisthiazole) charge generation layer and a hole transporting layer has been measured by the xerographic photodischarge technique. φ(E) varied from 0.10 at low fields (<105 V/cm) to 0.32 at 106 V/cm. The conjugated polymer-based photoreceptors have a photosensitivity of 13 ergs/cm2 and negligible dark decay (∼0.2 V/s). Photocarrier generation in the bilayer devices is suggested to be due to field-assisted dissociation of exciplexes formed between the conjugated polymer and the hole transporting molecule.
Transient space-charge-limited currents: The time-of-flight and post-transit analysis in hydrogenated amorphous silicon
Authors: Schauer F. , Eliat A. , Nesládek M. , Adriaenssens G. J.
Published: July 2002

Through evaluation of the post-transit part of the transient space-charge-limited currents (SCLC), it becomes possible to determine the hydrogenated amorphous silicon (a-Si:H) density of localized states (DOS) over a wide range of energies. The use of SCLC conditions results in the enhancement of the occupation of the deep states and hence in the corresponding increase of the signal. In combination with standard SCLC time-of-flight, and since it can be used for both electrons and holes, the method is suitable for the elucidation of the complete DOS distribution, for the examination of the emission times of deep traps, and for the determination of carrier drift mobilities, all on the same p-i-n structure (which may be a standard solar cell).
Chemical effect of ternary additions on amorphization in Fe-C systems by mechanical alloying
Authors: Omuro K. , Miura H.
Published: July 2002

Mechanical alloying (MA) of elemental powder mixtures of Fe83C17 and Fe58A25C17 (at. %) (A=Cr, Mo, Mn, or Ni) is performed using a planetary ball mill. In the MA processing, the ternary additions Cr, Mo, and Mn lead to the amorphization of MA products. Due to their higher affinity for C and solubility in Fe, they markedly promote the dissolution of C in the Fe-rich phase under stronger interaction between atoms A and C, in contrast to the addition Ni with lower affinity for C. Also, such additions, Cr, Mo, and Mn, dissolved in the Fe phase together with C suppress the diffusion of C over large distance in MA products and retard recovery processes, like nucleation of competing more stable carbides.
Modal analysis of a Talbot cavity
Authors: Leger James R. , Mowry Greg , Chen Diana
Published: July 2002

Modal analyses of Talbot cavity eigenmodes are performed for a finite diode laser array using a simple finite external mirror and a patterned external mirror. At a full round-trip Talbot length, the in-phase and oscillating-phase modes of the cavity with a simple flat mirror have slightly different thresholds. The increased modal separation from a patterned-mirror Talbot resonator is shown to be larger than a flat-mirror resonator with a round-trip distance of half a Talbot length. In all these cases, steady-state oscillation is shown to consist of either the in-phase or oscillating-phase mode. The inherent flaw of the Talbot resonator suggested by P. Latimer [Appl. Phys. Lett. 62, 217 (1993)] is thus shown to be a simple matter of modal separation rather than a ‘‘violation of the widespread assumption of grating self-imaging.’’
Sensitive plasma etching endpoint detection using tunable diode laser absorption spectroscopy
Authors: Sun H. C. , Patel V. , Singh B. , Ng C. K. , Whittaker E. A.
Published: July 2002

We report the use of a tunable diode laser locked to a molecular vibrational absorption line as a sensitive plasma etching endpoint detector. Measurements were made on multilayer silicon wafers etched in a SF6 plasma discharge. We show that polycrystalline silicon to silicon dioxide endpoint transitions on wafers with exposed area as small as 33 mm2 should be observable by detecting the etch end product SiF4. The method shows considerable potential as an endpoint detection technique for applications such as contact hole etching wherein very small areas are being etched.
Phase control of a nonlinear coherent coupler: The multi-beat-length twisted birefringent fiber
Authors: Ferro P. , Trillo S. , Wabnitz S.
Published: July 2002

We demonstrate that the switching power in a multi-beat-length and mismatched nonlinear coherent coupler may be controlled by means of a small variation of the relative phase of two equally intense input beams.
Feasibility of the artificial ultrahigh mobility materials
Authors: Li S. , Khurgin J. B.
Published: July 2002

It is shown that in three-dimensional semiconductor superlattices, the effective mass near the Fermi level can be made substantially smaller than in bulk materials. This results in a higher carrier mobility. A novel high transconductance field-effect transistor is proposed and modeled based on this higher mobility.
Incidence of cavitation in the fragmentation process of extracorporeal shock wave lithotriptors
Authors: Rink K. , Delacrétaz G. , Pittomvils G. , Boving R. , Lafaut J. P.
Published: July 2002

The fragmentation mechanism occurring in extracorporeal shock wave lithotripsy (ESWL) is investigated using a fiber optic stress sensing technique. With our technique, we demonstrate that cavitation is a major cause of fragmentation in ESWL procedures. When a target is placed in the operating area of the lithotriptor, two shock waves are detected. The first detected shock wave corresponds to the incoming shock wave generated by the lithotriptor. The second shock wave, detected some hundreds of microseconds later, is generated in situ. It results from the collapse of a cavitation bubble, formed by the reflection of the incoming shock wave at the target boundary. This cavitation induced shock wave generates the largest stress in the target area according to our stress sensing measurements.
Stress balance in soft porous media
Authors: Kirmanen J. , Kataja M. , Timonen J.
Published: July 2002

The applicability of Terzaghi’s principle of effective stress for soft porous media is assessed [K. Terzaghi, From Theory to Practice in Soil Mechanics (Wiley, New York, 1960)]. We present experimental results for highly compressible fibrous media showing cross deviation from Terzaghi’s principle and propose a phenomenological formula for a generalized effective stress under one-dimensional static compression.
Crystal structure and optical properties of polymorphic octasilacubane
Authors: Tachibana Hiroaki , Goto Midori , Matsumoto Mutsuyoshi , Kishida Hideo , Tokura Yoshinori
Published: July 2002

Single crystal x-ray crystallographic analysis of tert-butyloctasilacubane showed that a new polymorphic form (β form) exists with a slightly modified shape of the Si cage as compared with the previously reported form (α form) [K. Furukawa, M. Fujino, and N. Matsumoto, Appl. Phys. Lett. 60, 2744 (1991)]. Spectroscopic investigations of the single crystal indicate that the electronic band gap and luminescence band position differ by ∼0.4 eV between the polymorphs, signaling the sensitivity of the electronic structure to the distortion of the octasilacubane framework.
Quantum ballistic channel as an ultrahigh frequency generator
Authors: Fedichkin L. , V’yurkov V.
Published: July 2002

A novel application of a quantum ballistic channel as an ultrahigh frequency oscillator is proposed. The generation frequency is about a reciprocal transit time of an electron across the channel. It achieves 1 THz for channel length about 0.2 μm. The most attractive feature of a quantum ballistic channel is that it can be easily integrated into traditional microelectronic waveguides.
Observation of resonant tunneling through localized continuum states in electron wave interference diodes
Authors: Carnahan R. E. , Maldonado M. A. , Martin K. P. , Higgins R. J. , van der Wagt J. P. A. , Harris J. S.
Published: July 2002

A 13 layer aperiodic semiconductor superlattice electron wave interference filter, designed with thin-film optical interference filter techniques by using the analogies between electromagnetic wave propagation in dielectrics and ballistic electron wave propagation in semiconductors, was realized in the GaAs/AlGaAs material system. Current-voltage measurements at 300 and 77 K show negative differential resistance peaks (with peak-to-valley current ratios of 1.25 and 3.9, respectively) that represent observation of tunneling through an above barrier localized quasibound state. We show that electron wave interference devices could compete with resonant tunneling diodes as high frequency oscillators based on dc device characteristics and theoretical subpicosecond tunneling traversal times.
Photoluminescence of chemically vapor deposited Si on silica aerogels
Authors: Cao Wanqing , Hunt Arlon J.
Published: July 2002

We have prepared in situ porous Si by the decomposition of SiH4 at 500 °C on an aerogel substrate. Electron microscopy studies indicate that the as-deposited Si is primarily amorphous while the sample annealed in Ar at 800 °C has various nanometer-sized crystalline Si particles. Visible photoluminescence (PL) can be observed only from the annealed sample and the PL peak red shifts with the annealing temperature from 800° to 1000 °C. The results support the quantum confinement theory as the luminescence mechanism in porous Si.
Polarization-independent wavelength filter using a grating-assisted vertical directional coupler in InP
Authors: Heismann F. , Buhl L. L. , Miller B. I. , Newkirk M. , Koren U. , Young M. G. , Alferness R. C.
Published: July 2002

We demonstrate a polarization-insensitive optical bandpass filter in indium phosphide (InP) with a 3 dB bandwidth of 1.5 nm at a center wavelength of 1.498 μm. The 5-mm-long filter is based on a grating-assisted vertical directional coupler and features a novel double-periodic coupling grating.
Conductance study of silicon nitride/InP capacitors with an In2S3 interface control layer
Authors: Sundararaman C. S. , Milhelich P. , Masut R. A. , Currie J. F.
Published: July 2002

Conductance measurements of the SiNx/n-InP interface with an In2S3 interface control layer show the presence of electron traps, with capture cross section of 5.6×10−18 cm2, near the conduction band that increase in density towards the band edge. Carrier accumulation at the interface and response from bulk traps lead to single time constant conductance peaks. The loss is dominated by interface states in accumulation and by bulk states in depletion and weak inversion. The study indicates that low interface trap densities are achieved in the InP band gap for Ec−E≳0.24 eV in agreement with capacitance-voltage results.
Charge state of the natural EX defect in thermal SiO2
Authors: Stesmans A. , Scheerlinck F. , Afanas’ev V.
Published: July 2002

K-band electron spin resonance and high-frequency capacitance-voltage measurements have been combined to analyze the charge state of the intrinsic delocalized EX defect naturally generated in thermal SiO2 on (111) and (001) Si. The data provide strong evidence for the positive charge state of the defect when electron spin resonance active (paramagnetic): the EX centers account, within a factor of 2, for all detected positive charge in the Si-dioxide films. Passivation of the EX defects into a diamagnetic state through hydrogenation is found to go hand in hand with the charge neutralization of the centers.
Effects of ZrO2 on the texturing and properties of melt-processed Y1Ba2Cu3O7−δ
Authors: Juang J. Y. , Wu C. L. , Wang S. J. , Chu M. L. , Wu K. H. , Uen T. M. , Gou Y. S. , Chang H. L. , Wang C. , Tsai M. J.
Published: July 2002

The addition of ZrO2 is found to be very effective as the nucleation sites to promote the oriented growth of Y1Ba2Cu3O7−δ (YBCO) during peritectic solidification. Extended regions of well- textured YBCO grains with superior superconducting properties of the YBCO bulk are readily obtained by a single-step melt process at much lower process temperatures. At 77 K, the platelike Josephson weak-link behaviors observed in pure melt-processed YBCO have been effectively eliminated, indicating that the coherency between the spherulitic superconducting YBCO grains may have been greatly improved by ZrO2 additions.
Electro-optic side-chain polyimide system with large optical nonlinearity and high thermal stability
Authors: Sotoyama Wataru , Tatsuura Satoshi , Yoshimura Tetsuzo
Published: July 2002

We report electro-optic (EO) efficiency and thermal stability of a poled polyimide system with nonlinear optical dyes as side chains. The side-chain polyimide system is synthesized from a dianhydride containing azobenzene dye and a diamine. The dye in the polymer is chemically stable for temperatures below 250 °C. The polymer can be poled simultaneously with or after imidization of the polyamic acid. Our sample poled after imidization shows a large EO coefficient (r33=10.8 pm/V at λ=1.3 μm) and long-term thermal stability at 120 °C.
Position-dependent exciton-photon mode splitting in a microcavity
Authors: Frey A. , Jungk G. , Hey R.
Published: July 2002

Exciton-photon mode interaction of In0.1Ga0.9As quantum wells (QWs) in a λ/2 microcavity has been studied using classical linear dispersion theory. In a system consisting of a GaAs cavity with one QW surrounded by Al0.3Ga0.7As/AlAs and GaAs/AlAs Bragg reflectors grown by molecular beam epitaxy, the interaction is found to be strongest at the ends of the cavity and is vanishing in the center of it. The behavior in the center position is changed by inserting a second QW into the cavity. Reflectance and photoluminescence measurements show modulation effects by QW absorption in accordance with the calculations.
Spatial distribution of oxygen in luminescent porous silicon films
Authors: Teschke Omar
Published: July 2002

Transmission electron microscopy associated with electron energy loss spectroscopy imaging was used to determine structural spatial variations and compositional variation in heavily doped (0.006 Ω cm) and lightly doped (0.4 Ω cm) luminescent porous silicon films.
Transport critical current density of melt textured YBa2Cu3O7−x rods prepared by zone melting using a high temperature gradient
Authors: Brand M. , Elschner S. , Gauss S. , Assmus W.
Published: July 2002

We have developed a quasicontinuous crucible free zone melting method for texturing YBCO bulk material. Dense sintered rods with a length of 10 cm were partially molten in the hot zone of a 5 zone furnace and recrystallized in the large temperature gradient (140 °C/cm) limiting this zone. Suitable additions of Y2BaCuO5 (20 mol %) and PtO2 (1 wt %) to the starting material and a growth rate of not more than 1 mm/h were necessary to obtain stable growth conditions. After natural grain selection we obtained 8-cm-long rods with a uniform orientation of the crystallographic axes within 2°. The angle between c direction and rod axis typically was 55°. The critical current density at 77 K measured with continuous current over a length of 4.5 cm was 1.3×104 A/cm2 in zero field and 8×103 A/cm2 in 0.5 T. These values confirm the absence of grain boundaries.
High critical current density NbN/AlN/NbN tunnel junctions fabricated on ambient temperature MgO substrates
Authors: Wang Zhen , Kawakami Akira , Uzawa Yoshinori , Komiyama Bokuji
Published: July 2002

NbN/AlN/NbN tunnel junctions are fabricated at ambient temperature on MgO substrates, and a critical current density of 8 kA/cm2 is obtained in junctions with 1.5–nm–thick AlN barriers. Even though the NbN/AlN/NbN trilayers are deposited without intentional heating, the junctions show a large gap voltage (Vg=5 mV), sharp quasiparticle current rise (ΔVg=0.16 mV), and small subgap leakage current (Vm=25 mV and Rsg/RN=9). This report shows that high-quality NbN/AlN/NbN tunnel junctions can be made at ambient substrate temperature.
Heavy ion beam pumped visible laser
Authors: Ulrich A. , Wieser J. , Brunnhuber A. , Krötz W.
Published: July 2002

Heavy ion beam pumped laser action was observed in the visible spectral range. This result is encouraging for the potential development of shorter wavelength lasers pumped by heavy ion beams. The laser operated on the 585.25-nm neon line in He-Ne-Ar, He-Ne-Kr, and He-Ne-Xe mixtures. The laser gas pressure was, typically, 800 hPa and the mixing ratio 92% He, 6% Ne, and 2% Ar (Kr,Xe). Quasicontinuous laser action was obtained using a chopped beam of 120-MeV 35 Cl ions for pumping. Preliminary spectroscopic studies of the laser medium show selective excitation of the 585.25-nm line.
Electric-field-dependent electroreflectance spectra of visible-band-gap (InAlGa)P quantum-well structures
Authors: Fritz I. J. , Blum O. , Schneider R. P. , Howard A. J. , Follstaedt D. M.
Published: July 2002

We present results from the first studies of electric-field effects on optical transitions in visible-band-gap InGaP/InAlGaP multiple-quantum-well (MQW) structures. These structures, grown at 775 °C by metalorganic vapor phase epitaxy on (100) GaAs substrates misoriented 6° towards P(111〉〈111〉A, consist of nominally undoped MQWs surrounded by doped In0.49Al0.51P cladding layers to form p-i-n diodes. The Stark shifts of various allowed and forbidden quantum-well transitions were observed in bias-dependent electroreflectance spectra of In0.49Ga0.51P/In0.49(Al0.5Ga0.5)0.51P MQW samples with 10-nm-thick layers. We find the magnitude of these shifts to depend on the details of the Mg doping profile, confirming the importance of Mg diffusion and unintentional background doping in these materials. Our results show that (InAlGa)P materials are promising for visible-wavelength electro-optic modulator applications.
Determination of density of trap states at Y2O3-stabilized ZrO2/Si interface of YBa2Cu3O7−δ /Y2O3-stabilized ZrO2/Si capacitors
Authors: Qiao Jianmin , Wang Kuohsu , Yang Cary Y.
Published: July 2002

YBa2Cu3O7−δ/yttria-stabilized zirconia (YSZ)/silicon superconductor-insulator-semiconductor capacitors are characterized with current-voltage and capacitance-voltage (C-V) measurements at different temperatures between 223 and 80 K. As a result of ‘‘freezing’’ of mobile ions in YSZ, effects of trapped charge at the YSZ/Si interface dominate the device electrical properties at superconducting temperatures. Density of interface states and its temperature dependence are determined using a modified high frequency C-V method, in which the temperature dependences of band gap, Fermi level, and active dopant and intrinsic carrier concentrations are considered. At superconducting temperatures, e.g., 80 K, the interface state density within the band gap is reduced to lower than 1×1011 cm−2 eV at midgap. The low interface state density at the YSZ/Si interface is important for acceptable performance and reliability devices made up of such capacitors.
Crystal structure and magnetic properties of LaCo13−xSix compounds
Authors: Rao G. H. , Liang J. K. , Zhang Y. L. , Cheng X. R. , Tang W. H.
Published: July 2002

Tetragonal LaCo13−xSix compounds have been obtained by annealing cubic LaCo13−xSix compounds. The space group for the tetragonal structure is I4/mcm. Atomic ordering occurs in the tetragonal LaCo13−xSix compounds, i.e., Si atoms show a strong preference for occupying a specific crystallographic position. The tetragonal LaCo13−xSix compounds are ferromagnetic with Curie temperatures higher than 900 K. The magnetic moment per Co atom in the tetragonal LaCo13−xSix compounds decreases with Si content, which can be explained by the rigid-band model. The tetragonal LaCo13−xSix compounds are expected to be promising candidates for permanent magnets purpose.
Hydrodynamic approach to noise spectra in unipolar semiconductor structures
Authors: Gruz̆inskis V. , Starikov E. , Shiktorov P. , Reggiani L. , Varani L.
Published: July 2002

By using a closed hydrodynamic approach coupled with the field-impedance method we evaluate the spectra of the small-signal impedance (admittance) and of the voltage (current) density of submillimeter n+nn+ diode generators. The calculations, which are performed for the case of InP with applied fields near the onset of self-oscillations, indicate the presence of a sharp peak of the current spectral density at the generation frequency.
Steady-state performance of microcavity surface-emitting lasers with quantum confinement of electrons and photons
Authors: Vurgaftman Igor , Singh Jasprit
Published: July 2002

In conventional surface-emitting lasers, the photon density of states is essentially that of a bulk material and, therefore, spontaneous emission rates are the same as in bulk. However, in an ideal laser, one would like to have a single photon mode coincident with the peak in the material gain so that zero-threshold lasing occurs. This possibility is examined for a surface-emitting microcavity laser. The photon density of states for realistic GaAs-based microcavity structures (4 μm length and 0.5–4 μm lateral width) is derived from solutions to the wave equation in the cavity. This density of states is used to study the properties of microcavity lasers with compressively strained quantum well active media by using the exact form of spontaneous emission rate in the rate equations. It is found that when the lateral dimension approaches 0.5 μm, all optical power is present in a single resonant photon mode (the lasing mode), although additional leaky and propagating modes exist. The spontaneous emission factors and threshold current densities are derived for a few microcavity lasers. It is found that for microcavities with lateral dimensions and aspect ratios practical in experimental realization, the ideal ‘‘thresholdless’’ behavior is not observed, although the threshold current density is reduced to ≊60 A/cm2 compared with 160 A/cm2 calculated for lasers with cross sections typical for conventional surface-emitting lasers.
Epitaxial solid-solution films of immiscible MgO and CaO
Authors: Hellman E. S. , Hartford E. H.
Published: July 2002

Metastable solid solutions in the MgO-CaO system grow readily on MgO at 300 °C by molecular beam epitaxy. The epitaxy displays both the reflection high-energy electron diffraction oscillations characteristic of layer-by-layer growth and the lattice rotations which have been related to island nucleation. Mg1−xCaxO solid solutions grow despite a larger miscibility gap than in any system for which epitaxial solid solutions have been grown. Epitaxial quenching of nonequilibrium solid solutions is possible because of the very low growth temperatures for rock-salt oxides.
High quality ArF laser ablation of photoincubated polyethylene
Authors: Dyer P. E. , Karnakis D. M.
Published: July 2002

The interaction of ArF excimer laser radiation with polyethylene has been investigated using HeNe laser probe beam deflection, energy transmission of thin films, and scanning electron microscopy of the irradiated site. The ‘‘incubation’’ of ultraviolet absorbing chromophores by photoinduced modification appears to play a major role in controlling ablation of this weakly absorbing polymer (∼500 cm−1 at 193 nm). Analytical solution of the photon transport equation including an integrated exposure term to account for incubation provides a good description of the transmission results.
Temperature-insensitive offset reduction in a Hall effect device
Authors: Mani R. G. , von Klitzing K.
Published: July 2002

A double current technique applied to a double boundary device produces dual boundary specific Hall effects even above room temperature. It is shown that current compensation allows in situ cancellation of the offset voltage in the Hall effect, originating from effective contact misalignments. Thus, this method reduces the temperature-dependent offset originating from the T dependence of the resistance, and improves the sensitivity of the Hall element to the external magnetic field. Possible applications such as field sensing elements, contactless switches, and position sensors are cited.
Nonlinear reflection at a dielectric-carbon suspension interface: Macroscopic theory and experiment
Authors: Lawson C. M. , Michael R. R.
Published: July 2002

We report on a theoretical investigation of the nonlinear reflection that has been experimentally observed when Nd:YAG laser pulses interact with a dielectric-carbon particle suspension interface. This interaction leads to plasma formation, laser induced cavitation, and the formation of a vapor layer at the dielectric interface. This vapor layer results in total internal reflection. The theoretical fit to the experimental data shows that the calculated fluence threshold of the plasma formation process is 1 J/cm2. The theory also shows that the formation time of the vapor interface is on the order of a few nanoseconds and depends on the concentration of the carbon particles in the suspension.
Temperature dependence of the electron energy gap of high T
C superconductors studied by work function spectroscopy
Authors: Westermeyr S. , Müller R. , Scholtes J. , Oechsner H.
Published: July 2002

Work function measurements with the so-called onset technique have been used to study the temperature-dependent behavior of the electron energy gap of YBa2Cu3O7−x superconducting films. In the temperature range from TC down to 30 K a BCS-like behavior with gap width 2Δ0 at T=0 between 38 and 62 meV is found.
Time-resolved spectroscopy of visibly emitting porous silicon
Authors: Gaponenko S. V. , Germanenko I. N. , Petrov E. P. , Stupak A. P. , Bondarenko V. P. , Dorofeev A. M.
Published: July 2002

Time-resolved emission spectra and photoluminescence decay kinetics are analyzed in porous Si samples exhibiting a noticeable inhomogeneous broadening under steady-state selective excitation. The gated emission spectra are found to be substantially narrower compared to a steady-state one, with a pronounced redshift with time. Considerable dependence of the decay parameters upon the emission wavelength is found. The decay time distribution analysis applied leads to a model where the nonradiative decay mechanism is attributed to traps of the same type, the number of traps per Si grain obeying the Poissonian statistics.
Interface formation in InAs/AlSb and InAs/AlAs/AlSb quantum wells grown by molecular-beam epitaxy
Authors: Wagner J. , Schmitz J. , Behr D. , Ralston J. D. , Koidl P.
Published: July 2002

We have used resonant Raman scattering from both longitudinal-optical phonons and interface modes to study the chemical bonding across the InAs/AlSb interface in InAs/AlSb quantum wells grown by molecular-beam epitaxy. The effusion cell shutter sequence at the interfaces was selected for the deposition of either one monolayer of InSb or two to three monolayers of AlAs. In all cases an InSb-like interface mode is observed, indicating the preferential formation of In—Sb interface bonds irrespective of the shutter sequence. The deposition of two or three monolayers of AlAs at the InAs/AlSb interface results in the formation of pseudoternary AlSb1−xAsx barriers rather than binary AlAs interfaces and AlSb barriers, indicating a strong exchange among the group-V atoms. Normal (AlSb on InAs) and inverted (InAs on AlSb) InAs/AlSb interfaces have also been compared, revealing a much stronger InSb-like interface mode for the growth of AlSb on InAs than for the case of InAs grown on AlSb.
Strong intensity attenuation of Raman scattering in proton-exchanged LiNbO3 crystals
Authors: Wu Xinglong , Zhang Ming-sheng , Feng Duan
Published: July 2002

Raman spectroscopy of protonated LiNbO3 crystal has been performed as a function of proton-exchange time. At right angle scattering geometries, a strong (more than 50 times) intensity attenuation of Raman scattering was found in samples after 12–14 h proton treatment. A similar situation exists in the protonated LiTaO3 crystal after 8–10 h proton treatment. We attribute this anomalous attenuation tentatively to phonon localization-related effects, resulting from the strongly disordered distribution of protons in the sample.
Low-frequency line shapes in guided acoustic-wave Brillouin scattering
Authors: Greene Benjamin I. , Saeta Peter N.
Published: July 2002

Guided acoustic-wave Brillouin scattering (GAWBS) measurements were performed on 20-cm lengths of optical fibers with particular attention focused on the lowest lying resonance. In 125-μm-diam silica fibers, this resonance was observed to occur at ∼22 MHz and have a line shape which varied erratically from sample to sample. Significant line shape fluctuations were evident even between sequential samples from the same fiber spool. We speculate that the observed effects are attributable to 0.01–0.1 μm distributed geometric deviations from a perfect cylinder.
Slow current transients in metal–oxide–semiconductor capacitors
Authors: Yao Ze-Qiang , Dimitrijev Sima , Tanner Philip , Harrison H. Barry
Published: July 2002

Glitches of positive current at negative voltages have been observed during current–voltage measurements of metal–oxide semiconductor capacitors. The magnitude of the glitches depends on both stepping rate and duration of holding the metal electrode at the most negative potential before stepping towards positive potentials is initiated. Current versus time measurements show a voltage-dependent time constant, generally ≳100 ms. Charging/discharging of border traps is suggested as a possible cause for this effect.
Alternating-current excitation of InP based δ layers
Authors: Mareš J. J. , Feng X. , Koch F. , Krištofik J.
Published: July 2002

We have studied a nonlinear response of a field-effect transistor multi δ-layer structure to an external alternating-current signal. A specific resonance behavior of the source-drain resistance was observed in the MHz range depending on the orientation of the magnetic field. The results are discussed within the framework of a model of electron gas heating due to the parametric resonance between the ac electrical signal and the sound wave generated by an ac electrical signal by means of the piezoelectric effect.
Hot electron luminescence in In0.53Ga0.47As transistor channel
Authors: Mastrapasqua M. , Berthold G. , Canali C. , Luryi S. , Zanoni E. , Manfredi M. , Sivco D. L. , Cho A. Y.
Published: July 2002

Measurements of light emission are reported in the 1.1–2.5 eV energy range, by hot electrons in the In0.53Ga0.47As channel of a complementary charge injection transistor. By comparing electrical characteristics and light emission, there is the ability to identify the intraconduction band transitions as the main light emission mechanism. Hot-electron effective temperatures up to 2200 K have been determined from high energy exponential tails of the electroluminescence spectra.
Low thermal budget in situ removal of oxygen and carbon on silicon for silicon epitaxy in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor
Authors: Sanganeria Mahesh K. , Öztürk Mehmet C. , Violette Katherine E. , Harris Gari , Lee C. Archie , Maher Dennis M.
Published: July 2002

In this letter, we present experimental evidence on desorption of O and C from a Si surface resulting in impurity levels below the detection levels of secondary ion mass spectroscopy. We then propose a surface preperation method for silicon epitaxy that consists of an ex situ clean and an in situ low thermal budget prebake in an ultrahigh vacuum rapid thermal chemical vapor deposition (UHV-RTCVD) reactor. The ex situ clean consists of a standard RCA clean followed by a dilute HF dip and rinse in de-ionized water. The in situ clean is either carried out in vacuum or in a low partial pressure of 10% Si2H6 in H2. The experiments were conducted in an UHV-RTCVD reactor equipped with oil-free vacuum pumps. We propose that the responsible mechanism is desorption of oxygen and hydrocarbons from the Si surface due to the low partial pressures of these contaminants in the growth chamber. If Si2H6 is used during the prebake, a sufficiently low growth rate is required in order to provide sufficient time for desorption and avoid Si overgrowth on the O and C sites.
Anomalous electrical and optical properties of polymeric carbons
Authors: Chellappa V. , Jang B. Z.
Published: July 2002

Semiconducting polymeric carbons were prepared by pyrolyzing phenol formaldehyde resin in a nitrogen atmosphere between 500 to 800 °C for 0.5 to 48 h. Their logarithmic resistivity values were found to vary linearly with the temperature in the range of 20 to 200 °C. Properties such as switching, radiative recombination, and Mott’s minimum metallic conductivity were observed in these materials. These three characteristics, which are common with the inorganic amorphous semiconductors, suggest that these polymeric carbons can be included in the class of materials which satisfy the Ioffe–Regel condition, kL≊1 (where k is the electron wave vector and L is the mean-free path). The switching and the radiative recombination phenomena observed in these materials provide experimental proof for the double injection model proposed by N. F. Mott [Adv. Phys. 16, 4 (1967)] for describing conduction processes in amorphous chalcogenide semiconductors.
Electrical characterization of surface defects in GaSb created by hydrogen plasma
Authors: Dutta P. S. , Sangunni K. S. , Bhat H. L. , Kumar Vikram
Published: July 2002

Using steady state and transient capacitance measurements, the electrical characteristics of a defect layer on the surface of bulk GaSb created during the hydrogen plasma treatment is presented. The trap density, activation energies, and the thickness of the defect layer have been calculated. The trap densities are comparable in magnitude to the carrier concentration. The defects introduce multiple energy levels in the band gap. Typical defect layer thicknesses range from a few angstroms to a fraction of a micron.
Nonlinear single wavelength polarization switching in InGaAs/InP quantum well waveguides
Authors: Gontijo I. , Neilson D. T. , Ehrlich J. E. , Walker A. C. , Kennedy G. T. , Sibbett W.
Published: July 2002

The existence of two polarization dependent band edges in InGaAs/InP quantum well material has been used to demonstrate single wavelength all-optical switching in a nonlinear guided wave Fabry–Perot resonator. The device had a single quantum well embedded in the optical waveguide and was characterized as a function of input pump power and laser wavelength using laser pulses of about 45 ps duration at a repetition rate of 82 MHz. A signal gain factor of over two was obtained for pump pulses of 1.2 pJ and the optimum operating wavelength of 1.51 μm was found to coincide with the heavy hole exciton absorption resonance.
Effect of negative gain suppression on the stability of laser diodes
Authors: Bennett S. , Snowden C. M. , Iezekiel S.
Published: July 2002

The stability of homogeneously pumped single-section laser diodes is analyzed theoretically and it is found that under certain bias conditions negative gain suppression factor laser diodes (NGSFLDs) self-pulsate. An analytical condition for self-pulsation in homogeneously pumped single-section laser diodes is derived. The dynamics of self-pulsating NGSFLDs under direct modulation are analyzed and a quasiperiodic route to chaos is found.