bluuebunny/crossref_metadata_2025 huggingface dataset:
Single-electron effects in slim semiconductor superlattices
Authors: Schmidt T. , Haug R. J. , v. Klitzing K. , Eberl K.
Published: July 2002

We fabricated laterally confined GaAs–AlGaAs superlattices with diameters between 500 nm and 2 μm. With decreasing device diameter, a gap evolves in the current–voltage curve around zero bias and steps show up at the onset of the current. This behavior is interpreted in terms of Coulomb blockade, a depletion of the center of the superlattice, and single-electron tunneling through donor levels.
Electron–plasmon relaxation in quantum wells with inverted subband occupation
Authors: Kisin Mikhail V. , Stroscio Michael A. , Belenky Gregory , Luryi Serge
Published: July 2002

We have considered the electron-plasmon interaction and intersubband resonance screening in a quantum well with inverted subband occupation. We show that in such a system the intersubband plasmon emission leads to an efficient deexcitation of the nonequilibrium initial state and raises the occupation of states at the lower-subband bottom. Downshift and resonance narrowing of the intersubband optical emission spectra are obtained and shown to be influenced by the process of intersubband plasmon excitation.
Direct-coupled second-order superconducting quantum interference device gradiometer from single layer of high temperature superconductor
Authors: Lee Soon-Gul , Hwang Yunseok , Nam Byung-Chang , Kim Jin-Tae , Kim In-Seon
Published: July 2002

We developed a noble design of the planar-type single-layer second-order superconducting quantum interference device (SQUID) gradiometer, and demonstrated that the gradiometer did not respond to a uniform field or the first-order gradient of the field but responded sensitively to the second-order gradient. The device consisted of three parallel-connected pickup loops, each of which is directly coupled to the step-edge junction SQUID. The entire structure was made from a single layer of YBa2Cu3O7 patterned by photolithography with ion milling technique. Response of the device to the field was tested with three identical wire-wound coils coupled to each loop and balancing was achieved by using a small piece of superconductor placed in the center loop. Measured off balance was about 0.6% for the uniform field and 1.4% for the first-order gradient, which were believed not due to intrinsic imbalance but mostly due to slight difference in alignment of the test coils.
Site-selective radiation damage of collapsed carbon nanotubes
Authors: Crespi Vincent H. , Chopra Nasreen G. , Cohen Marvin L. , Zettl A. , Radmilovíc Velimir
Published: July 2002

Carbon nanotubes can flatten into collapsed tubes with bulbs along either edge. The strong anisotropy in the graphitic radiation damage threshold both explains the rapid destruction of face-on flattened nanotubes and can be exploited to selectively modify the structure of edge-on flattened nanotubes, thereby creating one-dimensional sp2 carbon with noncontinuous transverse boundary conditions.
Change in luminescence properties of porous Si by F2 and D2O exposure: In situ photoluminescence, Raman, and Fourier-transform infrared spectral study
Authors: Wadayama T. , Arigane T. , Hatta A.
Published: July 2002

In situ photoluminescence (PL), Raman, and infrared (IR) spectra of porous Si (PS) during F2/D2O exposures were investigated. F2 exposure at 298 K resulted in a peak shift of PL band from 750 to 670 nm with an intensity reduction. IR spectra revealed that the surface hydrogenated Si of the PS was displaced by fluorinated one. By subsequent D2O exposure, the PL band further shifted to a shorter wavelength with a significant intensity increase: IR bands due to surface oxides as well as SiD and SiOD bonds were observed after the exposure. On the contrary, the average size of the Si crystallites in the PS evaluated from Raman spectra remained almost unchanged throughout the exposures. These results suggest that surface chemistry plays a crucial role in the PL of the PS.
Magnetic resonance imaging of hyperpolarized Xe129 produced by spin exchange with diode-laser pumped Cs
Authors: Levron D. , Walter D. K. , Appelt S. , Fitzgerald R. J. , Kahn D. , Korbly S. E. , Sauer K. L. , Happer W. , Earles T. L. , Mawst L. J. , Botez D. , Harvey M. , DiMarco L. , Connolly J. C. , Möller H. E. , Chen X. J. , Cofer G. P. , Johnson G. A.
Published: July 2002

We report the results of experiments leading to the production of an image of a polarized Xe129 sample prepared by spin exchange with Cs, optically pumped with a spectrally narrowed 894.3 nm diode laser. Representative images of the average electron spin polarization are shown. Appreciable cesium electron polarization values were achieved, and a nuclear polarization of about 2.5% was measured for Xe129 The absolute nuclear polarization was measured by water-calibrated free induction decay of the nuclear magnetic resonance signal, and the polarized xenon imaged using a 2 T magnetic resonance imaging system.
Fabrication and physical properties of c-axis oriented thin films of layered perovskite La2−2xSr1+2xMn2O7
Authors: Konishi Y. , Kimura T. , Izumi M. , Kawasaki M. , Tokura Y.
Published: July 2002

We have grown c-axis oriented films of a layered perovskite La2−2xSr1+2xMn2O7 (x=0.4) by pulsed laser deposition under the limited growth condition; above 900 °C and below 100 mTorr for substrate temperature and oxygen pressure (PO2), respectively. Otherwise, epitaxial but composition-unidentified films were deposited. The films show a resistive transition around 100 K in coincidence with the magnetic transition. The value of resistivity at low temperature is larger than that of a single crystal by about two orders of magnitude, perhaps due to the canted spin ordering. The films show gigantic magnetoresistance accompanied with hysteresis.
Room-temperature 1.54 μm electroluminescence from erbium-doped Si/SiGe waveguides
Authors: Neufeld E. , Sticht A. , Luigart A. , Brunner K. , Abstreiter G.
Published: July 2002

In this letter, we demonstrate room-temperature electroluminescence from erbium ions in SiGe waveguide structures. Molecular beam epitaxy was employed to deposit SiGe layers doped with erbium and oxygen on (100)Si. Samples were processed as mesa waveguides and contacted to allow electrical pumping of the erbium ions. The luminescence was collected from the waveguides by a confocal microscope revealing emission from the end facet with a narrow spatial distribution.
Phase transition voltage and response time of an aligned phase–change–guest–host mode of liquid-crystal film
Authors: Wu Jin-Jei , Lee Tzu-Yang , Chen Shu-Hsia , Kuo Chen-Lung
Published: July 2002

We have studied the electro-optical properties of the aligned phase-change–guest–host (PCGH) mode liquid-crystal display. The PCGH material is spread between two glass substrates. Each substrate has previously been coated with a homeotropic alignment layer and has been softly rubbed. Samples with various thickness-to-natural pitch ratio d/p0 are fabricated. It is found that, in some ranges of the d/p0 ratio, the response times and phase transition voltage are affected by the rubbing direction.
Quantum real-space transfer in semiconductor heterostructures
Authors: Yang Rui Q.
Published: July 2002

Quantum real-space transfer of carriers in semiconductor heterostructures, which relies solely on the wave nature of electrons governed by quantum mechanics, is investigated. In quantum-well structures where electron effective mass varies spatially, the confined electron wave function can be modified by changing the longitudinal momentum via an external electric field parallel to the quantum-well plane. This shifts electrons perpendicularly to another layer having a different effective mass. Issues associated with realistic scattering are identified for unambiguously demonstrating this quantum real-space transfer in practical situations. Specific quantum-well structures for realizing the quantum real-space transfer are proposed with calculations. Potential applications of the quantum real-space transfer are discussed.
A phase jump phenomenon in interferometry
Authors: Zhou Weidong , Cai Lilong
Published: July 2002

A phase jump phenomenon in interferometers is reported. When the intensity of one arm of an interferometer changes from greater to less (or less to greater) than that of another, a phase jump of 180° will take place if the phase difference between two beams is fixed as π. We name this phenomenon “phase jump.” Both theoretical analysis and experimental verification are conducted and the results are presented here. The slope of the phase jump is infinite and highly stable. Therefore, this phase jump phenomenon can be used as optical comparators, reference mark, position indexes, pulse generators, edge detection, etc.
Measurement of temperature gradient in diode-laser-pumped high-power solid-state laser by low-coherence reflectometry
Authors: Huang S. L. , Wu W. L. , Huang P. L.
Published: July 2002

A noninvasive technique was developed to measure the temperature distribution in laser gain medium. Both axial and radial temperature distributions of a diode-laser-pumped and intracavity frequency-doubled high-power Nd:YVO4/KTP laser were characterized using a high dynamic range, low-coherence reflectometer. This measurement is important to the design of high-power solid-state lasers both in terms of mode matching and laser-rod doping selection.
Platinum nanodot formation by atomic point contact with a scanning tunneling microscope platinum tip
Authors: Huang D. H. , Nakayama T. , Aono M.
Published: July 2002

Using a platinum tip of a scanning tunneling microscope, ultrasmall nanodots of about 1 to 2 nm in diameter are reproducibly created on the Si(111)7×7 surface at room temperature by applying appropriate voltage pulses between tip and sample. Dynamic processes of the nanodot formation have been monitored by means of the displacement of the tip and the current through the tip. The experimental data suggest that a nanometer-scale bridge is formed between tip and sample, and that the created nanodot is a part of the nanobridge left on the surface. We have also observed relaxation of the tip apex and the created nanodots after the nanobridge is broken.
Scale dependence of submicron polycrystals due to configurational entropy
Authors: Yang Qiang , Yang Wei
Published: July 2002

It is well known that polycrystals exhibit abnormal Hall-Petch dependence when their grain sizes fall into the submicron range. A plausible explanation is that the scale dependence of the yield stress of submicron polycrystals is mediated not only by the internal energy of the dislocation patterns, but also by their configurational entropy. Two-level dislocation arrangements are explored which naturally embed a grain size. Detailed calculations of the internal energy and the configurational entropy are facilitated by the dislocation pileup theory and the Ashby model of geometric necessary dislocations. It is shown that the present model is capable of interpreting the abnormal Hall-Petch dependence for grain sizes in the submicron range.
Direct optical measurement of the valence band offset of p+ Si1−x−yGexCy/p− Si(100) by heterojunction internal photoemission
Authors: Chang C. L. , Rokhinson L. P. , Sturm J. C.
Published: July 2002

Optical absorption measurements have been performed to study the effect of substitutional carbon on the valence band offset of compressively strained p+ Si1−x−yGexCy/(100) p− Si. The compressively strained p+ Si1−x−yGexCy/(100) p− Si heterojunction internal photoemission structures were grown by rapid thermal chemical vapor deposition with substitutional carbon levels up to 2.5%. Carbon decreased the valence band offset by 26±1 meV/% substitutional carbon. Based on previous reports of the effect of carbon on the band gap of Si1−x−yGexCy, our work suggests that the effect of carbon incorporation on the band alignment of compressively strained Si1−x−yGexCy/Si is to reduce the valence band offset, with a negligible effect on the conduction band alignment.
Two-photon transitions between bound-to-continuum states in AlGaAs/GaAs multiple quantum well
Authors: Kang Jin U. , Khurgin Jacob B. , Yang C. C. , Lin H. H. , Stegeman George I.
Published: July 2002

We have experimentally observed room-temperature exciton resonances resulting from interband two-photon transitions between bound-to-continuum states. The excitons exhibit reduced binding energy and broadened resonances compared to that of excitons resulting from two-photon transitions between bound states. This trend is consistent with our theoretical prediction.
Single-sided alignment of electroclinic liquid crystals for active matrix displays
Authors: Hermanns A. , Wilson C. M. , Patel J. Y. , Naciri J. W. , Lindle J. R. , Ratna B. R.
Published: July 2002

Single-sided alignment, in which only one of the two display substrates bears an alignment layer, stands to significantly simplify the manufacture and improve the yield and performance of active matrix displays. Using polybutylene terephthalate alignment layers, we show that single-sided alignment is feasible for electroclinic liquid crystals and can result in faster switching and larger tilt angle. Most importantly, single-sided alignment gave high contrast in excess of 170:1.
Quantum confinement effect in self-assembled, nanometer silicon dots
Authors: Ding S. A. , Ikeda M. , Fukuda M. , Miyazaki S. , Hirose M.
Published: July 2002

The first subband energy at the valence band of self-assembled silicon quantum dots grown by low-pressure chemical vapor deposition on ultrathin SiO2/Si substrates has been measured as an energy shift at the top of the valence band density of states by using high-resolution x-ray photoelectron spectroscopy. The systematic shift of the valence band maximum towards higher binding energy with decreasing the dot size is shown to be consistent with theoretical prediction. The charging effects of the silicon dots and the SiO2 layer by photoelectron emission during the measurements have been taken into account in determining the valence-band-edge energy.
Enhancement of transport critical current densities in Bi2Sr2Ca2Cu3Ox tapes by fission tracks
Authors: Schulz G. W. , Klein C. , Weber H. W. , Moss S. , Zeng R. , Dou S. X. , Sawh R. , Ren Y. , Weinstein R.
Published: July 2002

Bi 2 Sr 2 Ca 2 Cu 3 O x (Bi-2223) tapes were processed by the standard powder-in-tube technique, but small amounts of UO4 were added prior to processing. Both U-doped and undoped tapes were subsequently exposed to a reactor spectrum of neutrons. Whereas the undoped materials show moderate enhancements of the critical current densities Jc due to the pinning action of the fast-neutron-induced collision cascades, Jc in the U-doped tapes increases by factors of 10–20 due to thermal-neutron-induced fission of 235U and the subsequent formation of fission tracks. Since the enhancements are particularly pronounced, when the magnetic field is applied perpendicular to the tape surface, the characteristic Jc anisotropy is strongly reduced in a certain field range. At the same time, the irreversibility field at 77 K is doubled for both field orientations.
Avalanche-induced excess noise in polycrystalline silicon thin-film transistors
Authors: Dimitriadis C. A. , Kamarinos G. , Brini J. , Evangelou E. K. , Gueorguiev V. K.
Published: July 2002

The low-frequency noise behavior of polycrystalline silicon thin-film transistors, operated in the avalanche multiplication region of the output characteristics, is investigated. The avalanche-induced current noise, originating from generation-recombination processes in the depletion region of the drain junction, can be described by the carrier number fluctuation model. Using a model for the excess noise in silicon-on-insulator metal-oxide-semiconductor field-effect transistors operated in the kink regime, an analytical expression for the avalanche-induced current noise is derived taking into account an exponential distribution of the gap states. Comparison of the experimental noise data with the theoretical model indicates that, in addition to the avalanche multiplication, hot-carrier effects contribute significantly to the current increase in the avalanche regime.
Infrared imaging camera based on a Rydberg atom photodetector
Authors: Drabbels Marcel , Noordam L. D.
Published: July 2002

A type of infrared imaging camera is demonstrated that uses gas-phase Rydberg atoms as photocathodes. The camera operates throughout the infrared part of the electromagnetic spectrum: λ=1–100 μm. The first results are presented and the potential of the camera as an ultrafast detector and a wavelength selective detector is discussed.
Nanofaceting of the LiNbO3 surface studied by scanning tunneling microscopy
Authors: Carroll D. L. , Wagner T. , Rühle M.
Published: July 2002

The surfaces of LiNbO3 single crystals have been studied using scanning tunneling microscopy and tunneling spectroscopy. Vacuum reduction was used to provide sufficient conductivity for tunneling. After reduction, the surfaces are dominated by nanoscale. Auger shows the structures to be related to precipitated suboxides of LiNbO3 which can be correlated to asymmetries in Li diffusion within the bulk crystal. These surface nanophases have electronic properties which are strongly dependent on the frequency of applied electric fields.
Issues in general quantum transport with complex potentials
Authors: Ferry D. K. , Barker J. R.
Published: July 2002

Complex potentials have been used previously to simulate dissipative processes in quantum simulations of transport and scattering. A general formulation is presented which shows how such non-Hermitian terms can lead to changes in the dynamics of transport operators, and to the decay of hydrodynamic quantities such as phase, energy, and momentum.
Carrier nonuniformity effects on the internal efficiency of multiquantum-well lasers
Authors: Piprek Joachim , Abraham Patrick , Bowers John E.
Published: July 2002

We investigate quantum efficiency limitations in InGaAsP/InP multiquantum-well (MQW) laser diodes emitting at 1.5 μm. At room temperature, the internal differential efficiency above threshold is found to be reduced mainly by increasing Auger recombination and spontaneous emission within the quantum wells. These carrier loss increments are commonly assumed negligible due to MQW carrier density clamping. Even with clamped average carrier density, increasing nonuniformity of the quantum well carrier population leads to enhanced losses. We analyze these loss enhancements using an advanced laser simulation software. Excellent agreement between measurements and simulations is obtained.
Hydrogen-induced reduction of axial stress in optical fiber cores
Authors: Ky Nguyen Hong , Limberger H. G. , Salathé R. P. , Cochet F. , Dong L.
Published: July 2002

Radial distributions of axial stress across B/Ge- and Sn/Ge-codoped core fibers and a Corning standard single-mode fiber were measured before and after hydrogen loading under different conditions. A significant reduction of axial stress in the core of all investigated fibers is observed after hydrogen loading. The stress reduction in the core of hydrogen-loaded fibers is irreversible and depends strongly on the core dopants and the fiber drawing tension. The hydrogen-induced core stress reduction is believed to be related to the reactions between hydrogen and drawing-induced defects in the fiber core.
Addendum: “Midinfrared vertical-cavity surface-emitting laser” [Appl. Phys. Lett. 71, 3483 (1997)]
Authors: Bewley W. W. , Felix C. L. , Vurgaftman I. , Olafsen L. J. , Aifer E. H. , Meyer J. R.
Published: July 2002

A number of issues related to pulsed-power determinations for midinfrared semiconductor lasers are reexamined. Especially useful is a Green’s function approach to incorporating the temporal dependence of the detector sensitivity. A method for extracting the external differential efficiency when the threshold is “soft” is also presented.
Modal expansion analysis of strained photonic lattices based on vertical cavity surface emitting laser arrays
Authors: Fishman Tal , Kapon Eli , Pier Harald , Hardy Amos
Published: July 2002

The optical modes of lasing photonic lattices incorporating alternating-shear strain were analyzed using a background-resonator mode expansion model. The model correctly explains the observed locking of the photon mode near fields to square or hexagonal-like lattice patterns for subcritical strain values, as well as the abrupt switching between the two mode patterns. Control of the optical mode switching point by adjusting the lattice reflectivity is proposed and analyzed.
Field-enhanced Stokes shifts in tensilely strained carbon-based quantum wells
Authors: Sugawara Y. , Fukatsu S. , Brunner K. , Eberl K.
Published: July 2002

A large, rigid downward shift of excitonic luminescence peak energies was observed with increasing transverse electric field in tensilely strained Si1−yCy/Si(001) symmetric quantum wells, as opposed to theoretical calculations predicting a blueshift due to exciton weakening, which more than balances the redshift due to quantum-confined Stark effects. The observed anomalies are interpreted in terms of field-enhanced Stokes shifts which occur due to carrier relaxation in an inhomogeneously distributed potential of the grown-in Si1−yCy/Si interfaces.
Microwave-induced current steps in intrinsic Josephson junctions patterned on Bi2Sr2CaCu2O8 single crystal
Authors: Wang H. B. , Aruga Y. , Tachiki T. , Mizugaki Y. , Chen J. , Nakajima K. , Yamashita T. , Wu P. H.
Published: July 2002

With a 10 μm×10 μm mesa patterned on Bi2Sr2CaCu2O8 single crystals, we measure the current–voltage (I–V) curves of a stack of intrinsic Josephson junctions. Current steps are observed at an equal voltage spacing of 4 mV when the sample is subjected to microwave radiation at around 7 GHz. With increase of the microwave power, more steps occur while the spacing between neighboring steps does not seem to change. The magnitude of each step depends on the microwave power in an oscillating way. Tuning the microwave frequency causes such steps to occur over separate frequency ranges, and each range is quite narrow. A temperature rise from 4.2 to 14.3 K completely quenches the step structures. Possible explanations for the step structures, based on resonances excited by microwave or geometric resonances in the junction cavity, are discussed.
All-optical reflection modulator using a nonlinear heteronipi structure within an asymmetric Fabry–Perot optical cavity
Authors: Davies P. F. , Phillips C. C. , Roberts C.
Published: July 2002

Reflectivity changes of ∼40% and contrast ratios of ∼100% are reported at optical excitation densities less than 100 μW/cm2 in an AlAs/AlGaAs/GaAs reflection-mode optical modulator. Switching and in-plane transport dynamics as a function of pixel size are also reported. Optical modulation occurs via the quantum-confined Stark effect in GaAs quantum wells grown within a “nipi” doping superlattice and is controlled through microcavity étalon effects. Optical bistability without the need for external electronic biasing circuitry is projected.
Detection of ultrasound using an apertureless near-field scanning optical microscope
Authors: Blodgett David W. , Spicer James B.
Published: July 2002

A method for the detection of ultrasonic vibrations using the apertureless near-field scanning optical microscope (ANSOM) is presented. Due to the changes in tip-sample separation, ultrasonic vibrations are seen as perturbations on the near-field signal. Both contact transducer (5 MHz) and laser-generated ultrasound have been successfully transduced. The linear dependence of the near-field signal on tip-sample separation makes the interpretation of these wave forms similar to that for conventional ultrasonic techniques.
Rapid cooling and magnetic field-induced cooperative effect for the metastable quintet state in a spin crossover complex
Authors: Yu Z. , Liu K. , Tao J. Q. , Zhong Z. J. , You X. Z. , Siu G. G.
Published: July 2002

Our study shows that metastable quintet state of spin crossover complex [Fe(dpp)2(NCS)2]⋅py (dpp=dipyrido[3,2-a:2′,3′-c] phenazine, py=pyridine) at low temperatures may be realized by a rapid cooling. The relaxation from quintet state to singlet spin at low temperatures depends on the both of time and previous history of the sample. The U-shaped dents of the magnetic effective moment depending on the temperature after initial rapid zero-field cooling indicate an obvious affection of magnetic field to the realization of singlet state in the transition range. The observations for this sample are indeed consistent with the fact that cooperative effects play a very important role in the spin transition.
Two-step two-color recording in a photorefractive praseodymium-doped La3Ga5SiO14 crystal
Authors: Nikolajsen T. , Johansen P. M. , Yue X. , Kip D. , Krätzig E.
Published: July 2002

Two-step two-color recording is demonstrated in a photorefractive La3Ga5SiO14:Pr3+ crystal using cw laser radiation. The 488 nm line from an Ar-ion laser is used for gating and gratings are written using a Ti:sapphire laser operating in the range from 788 to 840 nm. The dependence of holographic recording on grating and writing intensity is investigated. A saturation of the sensitivity is found for 2 W/cm2 of grating intensity. A threshold photon energy of 1.53 eV for the second excitation step is observed.
Threshold photoemission analysis of the surface reactions of triethylgallium and trimethylgallium on GaAs(100): A promising technique for kinetics studies
Authors: Viguier N. , Maury F.
Published: July 2002

The decomposition of triethylgallium and trimethylgallium on a As-stabilized GaAs(100) surface has been analyzed by near threshold photoemission. For T⩽200 °C, the negative photocurrent change induced by adsorption of these electron acceptor molecules is directly related to the coverage. The adsorbed diethylgallium species decompose very rapidly above 240 °C to adsorbed Ga atoms, resulting in a positive photocurrent change due to the lower work function of a Ga surface. The activation energy and preexponential factor of this decomposition reaction were derived independently in the temperature range 200–240 °C from the time dependence of the photocurrent emitted from the surface upon exposure to triethylgallium at saturated coverage.
Nonparametric characterization of human breast tissue by the Laguerre expansion of the kernels technique applied on propagating femtosecond laser pulses through biopsy samples
Authors: Zacharakis Giannis , Zolindaki Aggeliki , Sakkalis Vangelis , Filippidis George , Koumantakis Eugenios , Papazoglou Theodore G.
Published: July 2002

Ultrafast laser pulses transmitted through excised human breast tissue have been detected by a streak camera. Experimental data of the temporal spread of the ultrafast pulse during the transmission through the tissue have been analyzed using the Laguerre expansion technique. This method treats the medium of propagation as a “black box system” and using data sets of incident–transmitted pulse, it relates to this system a set of coefficients as well the first-order system kernels. This analysis could present an alternative method of tissue characterization when, due to the limited optical thickness of small biopsy samples, the photon diffusion approximation cannot be used successfully.
Nonlinear thin-layer theory for stratified Kerr medium
Authors: Laine T. A. , Friberg A. T.
Published: July 2002

Exact theory of field propagation in stratified Kerr media is developed. Making use of thin-layer approximation applied to plane waves, we solve the nonlinear Maxwell–Kerr equation within a thin slab. From this we construct the characteristic matrix of the Kerr medium and derive the amplitude-dependent wave vectors. The advantages of the method are that the equations are rigorous, simple to implement, and analogous with the linear theory. We also present a thick-layer approximation and solve a layered example numerically. Both polarizations, transverse electric (TE) and transverse magnetic (TM), are considered separately.
Light emission properties of crystalline SiO2 coated with LiNbO3/LiTaO3 multilayers
Authors: Wu X. L. , Siu G. G.
Published: July 2002

Photoluminescence (PL) properties of the crystalline SiO2 coated with LiNbO3/LiTaO3 multilayers were studied using the 514.5 nm line excitation. The 2.25 eV PL band observed at room temperature can be Gaussian divided into two subbands at 2.19 and 2.30 eV, which can be clearly resolved in the 77 K PL spectrum. The 2.30 eV band is z polarized with a polarization degree of 0.25 and its intensity has a linear dependence on the excitation power. No similar behavior was observed for the 2.19 eV band. Spectral analysis indicates that the two PL bands arise from optical transitions of the self-trapped excitons and E′ defect pairs in the crystalline SiO2 surface, which are induced by the photorefractive effect of the coated multilayers.
Theoretical modeling of carrier and lattice heating effects for frequency chirping in semiconductor lasers
Authors: Tsai Chin-Yi , Chen Chih-Hsiung , Sung Tien-Li , Tsai Chin-Yao , Rorison Judy M.
Published: July 2002

A theoretical model is presented that is capable of simultaneously simulating the frequency response of the photon density, carrier density, electron temperature, hole temperature, populations of nonequilibrium longitudinal optical (LO) and transverse optical (TO) phonons at different wave vectors, and lattice temperature under the modulation of small-signal current. Our results not only provide a more consistent theoretical model for frequency chirping but also illustrate the different roles of carrier and lattice heating in the frequency response of semiconductor lasers.
Surface smoothing of GaAs microstructure by atomic layer epitaxy
Authors: Hirose S. , Yoshida A. , Yamaura M. , Munekata H.
Published: July 2002

We report a method to smooth the rough surface of GaAs microstructures. This method is based on the nucleation process for atomic layer epitaxy which involves the self-limiting two-dimensional (one-monolayer) island formation. The method has been applied successfully to smooth the (111)A surfaces of chemically etched V-grooved GaAs structures as well as the (110) and (111)B side walls of selectively grown GaAs stripe structures.
On the nature of the electric-field effect on YBa2Cu3O7−δ grain boundary junctions employing epitaxial SrTiO3 gate insulators
Authors: Windt M. , Haensel H. , Koelle D. , Gross R.
Published: July 2002

We have fabricated Josephson field-effect transistors based on YBa2Cu3O7−δ bicrystal grain-boundary junctions (GBJs) and epitaxial SrTiO3 films as gate insulators. The SrTiO3 gate insulator shows high products of the breakdown field Ebd and the dielectric constant εr up to Ebdεr=1.3×1010 V/m allowing measurements over a wide range of applied gate electric-field Eg. The critical current Ic of the GBJs is found to depend highly nonlinear on Eg. Remarkably, the measured Ic(Eg) are very similar to the εr(Eg) curves. This strongly suggests that the observed electric-field effect is not due to a field-induced change in carrier concentration but is related to the dielectric properties of the SrTiO3 gate insulator.
Local density of states calculation for a discrete model of a diamond single atom tip
Authors: Miskovsky N. M. , Cutler Paul H.
Published: July 2002

Recent studies of field emission from wide-band-gap semiconductors have concentrated on thin-film and needle geometries. It has been proposed that the emission originates from localized asperities (or crystallites) on the film (which can be of nanometer or even atomic size) or from very sharp tips approaching atomic size in the case of needle geometry. A quantity important in determining the origin of the tunneling electron states is the density of states function. In the present work we have calculated the local density of states at an atomically sharp diamond asperity (or tip) using a tight-binding model. A pyramidal-shaped cluster of 159 atoms is constructed to model the tip. The forces are calculated and used to optimize the atomic geometry of the top six layers of atoms. The bottom layers are fixed to simulate the bulk diamond. Results indicate that the local density of states of the topmost single atom on the tip is significantly different from that of the bulk and suggest that the discrete geometry of the structure plays a role in determining the field-emission characteristics.
Variable energy blast modeling of the stress generation associated with laser ablation
Authors: Siano S. , Pini R. , Salimbeni R.
Published: July 2002

Stress generation induced by laser ablation was modeled by adapting the variable energy blast theory in the condition of laser–target interaction in air that allowed us to obtain the scaling law of the peak and the temporal profile of the pressure pulse. Measurements of the acoustic transient propagating inside the bulk during excimer laser ablation of polyimide, performed by means of polyvinyldenefloride piezoelectric sensors, were successfully compared with the behaviors provided by the theoretical model.
The effect of disorder on excited state dynamics in organic molecular films
Authors: Mäkinen A. J. , Xu S. , Zhang Z. , Diol S. J. , Gao Yongli , Mason M. G. , Muenter A. A. , Mantell D. A. , Melnyk A. R.
Published: July 2002

We have investigated the dynamics of highly excited electron states in thin films of N,N′-diphenethyl-3,4,9,10-perylenetetracarboxylic-diimide (DPEP), a well-known organic photoconductor, with time-resolved photoemission spectroscopy. We observe an extremely fast relaxation process of photoexcitations with a typical lifetime of 30 fs in DPEP films and attribute it to a rapid internal conversion process from S2 and S1 levels to the vibrational manifolds of S1 and S0 states. Interestingly, the relaxation rate is almost twice as fast at low excitation energies in polycrystalline DPEP films as it is in less-ordered DPEP films. We explain this difference by fast transitions within the manifold of extended states that are shown to form in ordered DPEP films.
Ridge waveguides in lithium niobate fabricated by differential etching following spatially selective domain inversion
Authors: Barry Ian E. , Ross Graeme W. , Smith Peter G. R. , Eason Robert W.
Published: July 2002

Ridge structures have been fabricated in z-cut LiNbO3 using the technique of differential etching following spatially selective domain inversion. Waveguides within these ridges have been achieved using the techniques of ion beam implantation, proton exchange, and titanium indiffusion. Using this last method, guides with losses <0.8 dB cm−1 have been realized for light at a wavelength of 1.3 μm. We briefly discuss applications for these structures.
Mn pinning effect in SrS thin-film electroluminescent phosphors
Authors: Xin Y. B. , Tong W. , Summers C. J.
Published: July 2002

An Mn pinning effect which limits the grain size in SrS:Mn thin films is reported. The SrS:Mn films exhibit spectrally identical saturated electroluminescent (EL) and photoluminescent (PL) green emissions at 5400 Å with CIE coordinates of x=0.33 and y=0.64. However, although strong PL emission was obtained, the EL emission was very weak. It is proposed that the weak EL emission is attributed to the small grain size caused by a Mn pinning effect. The mechanisms of the grain growth and Mn pinning effect in SrS are proposed and discussed in this letter.
A simple lateral transport device of strongly interacting electron and hole layers
Authors: Shapira S. , Linfield E. H. , Pepper M.
Published: July 2002

We have fabricated a GaAs device containing independently contacted electron and hole layers with a separation of 14 nm. The device processing avoids the use of self-aligned contacts and is, therefore, greatly simplified. Only basic processing facilities are required, and leakage problems typical of self-aligned contacts are prevented. The resulting increased device yield overcomes a technological barrier, which has so far limited the experimental research of the system.
Electrical and optical characteristics of two color mid wave HgCdTe infrared detectors
Authors: Mason Whitney , Waterman J. R.
Published: July 2002

Two-color mid wave triple-layer heterojunction HgCdTe detectors were studied using temperature-dependent current–voltage (I–V) measurements, temperature-dependent spectral response measurements, and temperature-dependent noise measurements. The reverse biased dark current shows diffusion-limited behavior for T>125 K. The same data show evidence for generation-recombination-type behavior for the longer wavelength junction at temperatures between 100 and 125 K. For temperatures less than 100 K, the measurements are background limited by photon flux, even though these measurements are performed at nominal zero background. The upper junction shows soft reverse breakdown voltages on the order of about 250 mV, while the bottom junction shows no breakdown for V<500 mV. At 80 K, the R0A product is in excess of 1×106 Ω cm2. In forward bias, the current–voltage characteristics of the lower junction are diffusion limited for all temperatures, while at lower temperatures, the upper junction showed generation-recombination behavior. Optical measurements found a cutoff wavelength of about 4 μm for the lower junction and about 4.5 μm for the upper junction. The spectral crosstalk was less than 3%. At 80 K, the frequency-dependent noise of the shorter wavelength junction showed no dependence on bias, while for the longer wavelength junction, the noise at lower frequencies increased with bias. There is no difference in the noise characteristics when either the photon flux or the temperature is increased.
Spatially resolved observation of Coulomb blockade and negative differential conductance on a Ag cluster on the clean GaAs(110) surface
Authors: Jiang C.-S. , Nakayama T. , Aono M.
Published: July 2002

By performing current-image tunneling spectroscopy at room temperature, we have observed the staircase current–voltage (I–V) characteristic and negative differential conductance on a single Ag cluster on a clean GaAs(110) surface. The I–V characteristics have changed spatially with the position of the tip on the cluster. The characteristics are understood in terms of Coulomb blockade and resonance of electron standing-wave states in the cluster with the states of the underlying substrate.
Isotopic substitution of N, O, and Si in the thermal oxidation of nitrogen-deposited silicon
Authors: Baumvol I. J. R. , Salgado T. D. M. , Stedile F. C. , Radtke C. , Krug C.
Published: July 2002

Nitrogen was deposited on the surface of Si(100) wafers by ion implantation at a very low energy (approximately 20 eV), at fluences between 1 and 10×1014 cm−2. The samples were thermally oxidized in dry O2 at temperatures between 800 and 1050 °C. Atomic transport of the chemical species involved in the process was investigated by isotopic tracing of N, O, and Si, using depth profiling with nanometric resolution. The obtained results indicate that: (i) the nitrogen atoms deposited on the Si surface are redistributed during thermal oxidation in O2 within the silicon oxide (oxynitride) film, with maxima at the near-surface and near-interface regions; (ii) during growth, O is fixed not only in the near-interface and near-surface regions like in the thermal growth of SiO2 films on Si, but also in the bulk of the growing oxide (oxynitride) film; and (iii) Si is immobile during the thermal oxidation process. The observed modifications in the mechanisms of thermal growth of SiO2 (SiOxNy) films on Si due to the presence of N are discussed.
Large Schottky barriers for Ni/p-GaN contacts
Authors: Shiojima Kenji , Sugahara Tomoya , Sakai Shiro
Published: July 2002

Large Schottky barriers were measured for Ni contacts formed on low Mg-doped p-GaN. In order to improve leaky Schottky characteristics, low-Mg doping was examined. This provided atomically flat surfaces and a low dislocation density of 5.5×108 cm−2. The Schottky barrier height (qφB) as high as 2.4±0.2 eV and n values of 1.84±0.06 were obtained from current–voltage measurements. These results are in good agreement with the prediction that the sum of qφB of n and p types adds up to the band gap. In the capacitance–voltage measurements, a transient response of capacitance was observed. This indicates that the evaluation of deep levels close to the valence band is possible, which could result in improvement of p-GaN growth.
Resonant second harmonic generation in ZnSe bulk microcavity
Authors: Pellegrini Vittorio , Colombelli Raffaele , Carusotto Iacopo , Beltram Fabio , Rubini Silvia , Lantier Roberta , Franciosi Alfonso , Vinegoni Claudio , Pavesi Lorenzo
Published: July 2002

Room-temperature resonant second harmonic generation is demonstrated in a ZnSe bulk microcavity with Si3N4/SiO2 Bragg reflectors. The resonance occurs at the second harmonic wavelength in the blue-green spectral region and yields an enhancement of one order of magnitude in the second harmonic process. Tunability of the resonant effect between 480 and 500 nm is achieved by varying the angle of incidence.
Temperature dependence of the switching property in τVmin mode ferroelectric liquid crystals
Authors: Sako Teiyu , Kaneko Takashi , Koden Mitsuhiro
Published: July 2002

The temperature dependence of the switching property has been investigated in τVmin mode ferroelectric liquid crystal (FLC) materials, which show a minimum in the response time–voltage curve. From the calculation based on the uniform switching model in an electric field, it is found that τVmin mode FLC materials can be improved to have a temperature-independent switching threshold voltage by optimizing the temperature dependences of dielectric anisotropy and spontaneous polarization. The dielectric anisotropy primarily originates from the smectic C host material and the spontaneous polarization from the chiral dopant one. Accordingly, practical FLC materials with wide operating temperature range have been developed by optimizing the combination of smectic C host and chiral dopant materials.
Deposition-temperature-dependent stress of capping oxide and its effect on Pt/Pb(Zr1−xTix)O3/Pt ferroelectric capacitor
Authors: Koo Bon Jae , Song Yoon Jong , Lee Sung Yung , Jung Dong Jin , Kim Byung Hee , Kim Kinam , Park Youngsoo , Lee June Key
Published: July 2002

Two different interlayer dielectric (ILD) materials, electron cyclotron resonance chemical vapor deposition oxide (ECR-OXIDE) and plasma enhanced chemical vapor deposition TEOS oxide (PE-TEOS), were prepared at 400 and 200 °C respectively, on silicon substrates and Pt/Pb(Zr1−xTix)O3 (PZT)/Pt capacitors. It was found that the ILD deposition temperature is a most important parameter for minimizing the degradation of remnant polarization (Pr) during the ILD deposition. Since the stress of PZT capacitor strongly depends on the ILD deposition temperature, the PZT capacitor with PE-TEOS showed more compressive stress than that with ECR-OXIDE, which results in severe Pr degradation of PZT capacitor with PE-TEOS. This large stress effect of PE-TEOS was confirmed by x-ray diffraction (XRD) patterns in which the d spacing of (111) PZT films with PE-TEOS was much larger than that of PZT films with ECR-OXIDE. Therefore, the low ILD deposition temperature is a key parameter for achieving an ILD integration without any Pr degradation.
Two-dimensional quantum-confined Stark effect in V-groove quantum wires: Excited state spectroscopy and theory
Authors: Weman H. , Martinet E. , Dupertuis M.-A. , Rudra A. , Leifer K. , Kapon E.
Published: July 2002

We report on the electric field effects in photoluminescence (PL) and PL excitation (PLE) measurements of reverse-biased GaAs V-groove quantum wires. We observe large redshifts (9 meV at −65 kV/cm) of PL and PLE peaks as well as field dependent intensity and polarization anisotropy variations, which are analyzed by a two-dimensional quantum confined Stark effect model.
Time-resolved reflectivity characterization of polycrystalline low-temperature-grown GaAs
Authors: Roux Jean-François , Coutaz Jean-Louis , Krotkus Arunas
Published: July 2002

Using femtosecond time resolved reflectivity, we have characterized the dynamics of photoinduced generated carriers in a polycrystalline low-temperature-grown GaAs sample. Our measurements are fitted with an analytical expression reliable for low pump power experiments. The sample, which presents no As precipitates, shows an ultrafast subpicosecond response together with a longer picosecond tail that we attribute to the midgap defect states. Moreover, we have observed the influence of surface roughness on the differential reflected signal.
Linear sensing of speckle-pattern displacements using a photorefractive GaP crystal
Authors: Kamshilin Alexei A. , Iida Yasuhiro , Ashihara Satoshi , Shimura Tsutomu , Kuroda Kazuo
Published: July 2002

Linear transformation of lateral speckle-pattern displacements into the transmitted intensity modulation is achieved in a photorefractive GaP crystal using the polarization self-modulation effect. The optical system is very simple, self-referenced, and as sensitive as an interferometer.
Microsecond photoresponse in liquid crystalline photoconductor doped with C70 under illumination of visible light
Authors: Funahashi Masahiro , Hanna Jun-ichi
Published: July 2002

Steady-state and transient photocurrent measurements were carried out for C70-doped liquid crystalline photoconductor, 2-(4′-octylphenyl)-6-dodecyloxy-naphthalene (8-PNP-O12) in order to clarify its spectral photosensitization in visible region. The C70-doped liquid crystal cells exhibited a photoresponse in visible region of 400–700 nm corresponding to the optical absorption of C70. In the time-of-flight measurement, the fast transient photosignals with fast rise and decay on the order of microseconds were obtained even in a bulk excitation condition, which is governed by the carrier transit. These indicated that C70 can inject both electron and hole into 8-PNP-O12 when photoexcited and does not deteriorate the carrier transport, demonstrating a possible application of liquid crystalline photoconductors to high-speed photosensors with a fast response in microseconds.
Population inversion and far-infrared emission from optically pumped silicon
Authors: Hübers H.-W. , Auen K. , Pavlov S. G. , Orlova E. E. , Zhukavin R. Kh. , Shastin V. N.
Published: July 2002

A mechanism for the generation of population inversion and far-infrared emission in Si with shallow donors is investigated. By optically pumping a phosphorus doped Si crystal with a CO2 laser it was possible to achieve population inversion between the metastable 2p0 state and the 1s(E) and 1s(T) states. Spontaneous emission from these transitions was detected. Frequency measurements of this emission are in agreement with the expected transition frequency. Absorption measurements with a far-infrared probe laser confirm the existence of population inversion between the 2p0 state and the 1s(E) and 1s(T) states.
Shallow donors in Ge-rich GeSi bulk crystals
Authors: Franz M. , Pressel K. , Barz A. , Dold P. , Benz K. W.
Published: July 2002

We report on the change of shallow donor energy levels with alloy composition in Ge-rich Ge1−xSix bulk crystals. For phosphorus, we find a strong, linear increase of the ionization energy with increasing Si content for 0<x<0.1, whereas, for antimony the ionization energy shifts only slightly to higher energies with increasing Si content up to x=0.11. We observe a rapid increase of the antimony ionization energy in the composition range 0.11<x<0.16, where the change in the conduction band minimum from Ge- to Si-like occurs. The different behavior of phosphorus and antimony in Ge-rich GeSi reflects the different short range impurity potentials of these donors and, thus, different mixing of bands.