bluuebunny/crossref_metadata_2025 huggingface dataset:
Second-order nonlinearity of nonpoled polymeric thin films doped with pyrylium salts with blue window characteristics
Authors: Nakayama Hideki , Matsushima Ryoka , Okamoto Naomichi , Mizuno Atsushi , Sugihara Okihiro , Egami Chikara
Published: July 2002

A novel nonlinear organic ionic material, or pyrylium salt dye, is synthesized and doped in the polymer matrix. These guest-host-type polymer films, which have no absorption in the blue-wavelength region, have second harmonic generation (SHG) activities without the electric-field poling process. The nonlinear optical coefficient d33 is estimated as 1.10 pm/V at a 15 wt % of dye concentration. The nonlinearity is stable at room temperature and at 120 °C. The SHG device is fabricated using the nonpoled polymer film, and Cerenkov-type phase-matched SHG is observed.
Effect of postdeposition anneal on the resistivitity of p-type polycrystalline diamond films
Authors: Sahli S. , Aslam D. M.
Published: July 2002

A four-point probe method is used to study the effect of a 10 min anneal in N2 at 600 °C on the resistivity of B-doped chemical vapor deposited diamond samples as a function of doping and film quality, as determined by Raman spectroscopy. Measurements on diamond films deposited on oxidized Si having resistivities in the ranges of 0.27–535 Ω cm, show that the increase of resistivity after the anneal is more prominent for films with low doping and high quality. There seems to be a doping level above which the effect of anneal is not observable. the dependence of the effect of anneal on the doping level and diamond quality is reported.
Influence of the buffer layers on the morphology and the transport properties in InAs/(Al,Ga)Sb quantum wells grown by molecular beam epitaxy
Authors: Blank H.-R. , Thomas M. , Wong K. C. , Kroemer H.
Published: July 2002

The growth of modulation-doped InAs/(Al,Ga)Sb quantum wells on GaAs substrates employing molecular beam epitaxy requires care in the nucleation and the use of buffer layers to achieve high quality material. Despite a 7% lattice mismatch between the substrate and the active layers, fully relaxed epitaxial growth can be accomplished, and quantum wells with electron sheet concentrations of 7×1012 cm−2 having low-temperature mobilities as high as 300 000 cm2/V s have been routinely fabricated recently in our laboratory. In the present work the combination of atomic force microscopy and van der Pauw measurements is used to investigate and explain the strong influence of the buffer layers on the morphology in the quantum well that is shown to be responsible for the great differences in the observed low-temperature mobilities.
Optimization of gate dopant concentration and microstructure for improved electrical and reliability characteristics of ultrathin oxides and N2O oxynitrides
Authors: Chou Anthony I. , Lai Kafai , Kumar Kiran , Lee Jack C. , Gardner Mark , Fulford Jim
Published: July 2002

We study the effects of gate dopant species (boron, arsenic, or phosphorous) concentration (1×1019 cm−3–1×1021 cm−3) and microstructure (as-deposited amorphous or polycrystalline silicon gate) on the electrical and reliability characteristics of ultrathin oxides and N2O oxynitrides (60 Å). In order to minimize polysilicon depletion, a high gate dopant concentration is desirable. However, for devices with BF2 doped gates, it is found that because of boron penetration through the thin gate oxide, device characteristics degrade as the gate doping concentration increases, thus an intermediate gate doping must be chosen. In contrast, samples with arsenic and phosphorous doped gates show no degradation as the doping level increases. Optimization of gate microstructure for N2O and O2 dielectrics is also discussed.
Time evolution of structural changes and second-order optical nonlinearity of hemicyanine doped silica film
Authors: Xu Lei , Liu Liying , Yu Jing , Wang Wencheng , Li Fuming
Published: July 2002

Hemicyanine-doped silica film was fabricated by sol–gel technique. Time evolution of structural changes in hemicyanine and their influence on the second-order optical nonlinearity were investigated through UV-visible absorption and second-harmonic generation (SHG) measurements. We found that the conversion of protonated hemicyanine to monomeric and aggregated hemicyanine occurred within 4 h after film deposition. During this period of time the SHG signal continued to rise and finally reached the maximum. The growth of optical nonlinearity was mainly due to deprotonation of hemicyanine molecules. Blueshift of the absorption peaks for both aggregate and monomer were found during the drying of the film.
Potential of confocal microscopes to resolve in the 50–100 nm range
Authors: Schrader M. , Hell S. W. , van der Voort H. T. M.
Published: July 2002

We determine the resolution of high-performance confocal microscopes by measuring the three-dimensional point–spread function (3D-PSF) of an optimized confocal setup. The 3D-PSF is standardized by recording the scattered light of pointlike objects. For a wavelength of 543 nm and a specified numerical aperture of 1.4 (oil), we find an axial and lateral focal full width at half-maximum (FWHM) of 460±20 and 145±10 nm, respectively. A high signal-to-noise ratio is obtained by using recording times comparable to those of near-field scanning optical microscopy. We further reduce the effective PSF extent by means of a three-dimensional deconvolution technique exploiting the information gained from the measurement of the focus. We show that it is possible to obtain an axial and lateral FWHM of the far-field effective PSF after deconvolution of 80 and 40 nm, respectively.
Measurement of optical gain at 670 nm in an oxazine-doped polyimide planar waveguide
Authors: Weiss Martin N. , Srivastava Ramakant , Correia Ricardo R. B. , Martins-Filho J. F. , de Araujo Cid B.
Published: July 2002

Optical gain measurements have been performed on several of the lower order modes of a multimode polyimide planar waveguide doped with the laser dye cresyl violet 670. A transverse pumping geometry was employed, resulting in larger gain for higher order modes. In a 21-mm-long device, an amplification of 14.4 dB was achieved for the sixth order guided mode at a wavelength of 670 nm. The photostability performance of the waveguide is comparable to the results reported for rhodamine-doped organically modified silica gels.
Small-astigmatism, low-noise, and high-power self-sustained pulsation multiple-quantum-well laser diodes with a real refractive index guided self-aligned structure
Authors: Takayama T. , Imafuji O. , Hashimoto T. , Yuri M. , Yoshikawa A. , Itoh K.
Published: July 2002

We demonstrated low-noise and high-power GaAlAs laser diodes with small astigmatism. The low-noise characteristics are realized by self-sustained pulsation due to the saturable absorption of a single-quantum-well located close to the triple-quantum-well active layer. The high-power and small-astigmatism characteristics are achieved by using a real refractive index guided self-aligned structure. The lasers showed a relative intensity noise less than −130 dB/Hz under 10% optical feedback in a very wide output-power range (5–35 mW), a stable fundamental transverse mode up to 150 mW, and astigmatism less than 1 μm.
Microwave surface resistance of YBa2Cu3Cu3O7−x films on polycrystalline ceramic substrates with textured buffer layers
Authors: Findikoglu A. T. , Foltyn S. R. , Arendt P. N. , Groves J. R. , Jia Q. X. , Peterson E. J. , Wu X. D. , Reagor D. W.
Published: July 2002

We have used a parallel-plate resonator technique to measure the microwave surface resist- ance Rs of YBa2Cu3O7−x (YBCO) films on buffered ceramic substrates at around 10 GHz, and studied the correlation between their Rs and materials properties. A 0.4-μm-thick YBCO film (with an in-plane mosaic spread of 7°) grown on a polycrystalline alumina substrate with an ion-beam-assisted-deposited yttria-stabilized zirconia buffer layer showed an Rs of 1.89 mΩ at 76 K and 0.21 mΩ at 4 K. We have observed a strong correlation between the Rs of the samples and the in-plane mosaic spread of the YBCO films. This correlation can be explained qualitatively in terms of a simple model in which the weak links between the grains of the YBCO film form an electrical network of Josephson junctions.
Polycrystalline silicon formation by pulsed rapid thermal annealing of amorphous silicon
Authors: Kuo Yue , Kozlowski P. M.
Published: July 2002

A method of forming polycrystalline silicon (polysilicon) from amorphous silicon in several seconds is presented in this letter. This solid-phase crystallization process was carried out with the pulsed rapid thermal annealing method using a metal as the seed. The crystal-growth process was monitored with an optical microscope and the polysilicon structure was confirmed by a micro-Raman shift measurement. Polysilicon film within a 30-micrometer channel was formed using 3 pulses of 1-s 800 °C heating/5-s cooling. It took more than 13 h using a 500 °C furnace annealing method to form polysilicon film within a 12-micrometer channel. Since the substrate is only exposed to the high temperature for a very short period of time, heat effects in the substrate are minimized. This method has the potential for use in the fabrication of small geometry devices, such as thin film transistors, on large-area, low temperature glass substrates.
Fourth-harmonic generation of picosecond glass laser pulses with cesium lithium borate crystals
Authors: Sharma Lalit B. , Daido H. , Kato Y. , Nakai S. , Zhang T. , Mori Y. , Sasaki T.
Published: July 2002

We report the fourth-harmonic generation of 1.5 ps, 1.053 μm glass laser pulses, where group velocity mismatch plays a significant role, at intensities up to 100 GW/cm2 using newly developed crystal, cesium lithium borate (CsLiB6O10). Type-I doubler and type-I quadrupler were used in the fourth harmonic generation experimental scheme. Energy conversion efficiencies of 24% and 53% have been achieved for frequency quadrupling and doubling of the fundamental glass laser pulses, respectively.
Enhanced nitrogen incorporation and improved breakdown endurance in nitrided gate oxides prepared by anodic oxidation followed by rapid thermal nitridation in N2O
Authors: Jeng Ming-Jer , Hwu Jenn-Gwo
Published: July 2002

Room-temperature anodic oxidation (ANO) followed by rapid thermal nitridation in N2O was used as new method to prepare thin nitrided oxides. It was found that the ANO nitrided oxides demonstrate better interfacial property and breakdown endurance than rapid thermal oxidation (RTO) nitrided oxides. The concentration of nitrogen incorporated in ANO nitrided oxide is larger than that in RTO nitrided oxides. It is believed that the loose density and the existence of hydrogen related species in anodic oxides formed by room-temperature anodization cause nitrogen to diffuse easier into oxide and pile up at Si/SiO2 interface during N2O nitridation. In addition, the self-readjustment of anodization current through the weak path in oxide is beneficial to thin gate oxides.
Mechanisms of carrier and energy injection in three-terminal laser structures
Authors: Tolstikhin Valery I. , Khrenov Gregory Yu.
Published: July 2002

The mechanisms of injection in the recently proposed three-terminal laser structures and the ability to effectively tune the energy yield associated with a single injected electron are analyzed, by means of the ensemble Monte Carlo simulations, with respect to a high-speed modulation using dynamic carrier heating.
A proposed high-gradient laser-driven electron accelerator using crossed cylindrical laser focusing
Authors: Huang Y. C. , Byer R. L.
Published: July 2002

We propose a dielectric-based, crossed-laser-beam electron linear accelerator structure operating in a vacuum that is capable of providing 1 TeV electrons in approximately 1 km. The accelerator structure employs cylindrical laser focusing that allows for simplifying the fabrication process, accelerating more electrons, reducing the electron phase slip, minimizing the transverse wake-fields, and spreading the structural thermal loading. We present a 0.7 GeV/m average-gradient accelerator structure, repeated every 390 μm, subject to the laser damage fluence 2 J/cm2 on the optical components for 100 fs laser pulses.
Ti/MgO superlattices epitaxially grown on sapphire (00.1) and MgO(001) substrates
Authors: Kado Tetsuo
Published: July 2002

Epitaxial metal/insulator superlattices composed of Ti and MgO have been prepared on MgO(001) buffer layers grown on MgO(001) substrates and MgO(111) buffer layers grown on sapphire (00.1) substrates by electron beam evaporation in ultrahigh vacuum. 1–4-nm-thick Ti layers and 1–2-nm-thick MgO layers have been grown alternatively for 20 periods on the buffer layers at 273 K and at a growth rate below 0.02 nm/s. The reflection high energy electron diffraction and x-ray diffraction measurements reveal that the crystal structures of Ti in the superlattices grown on MgO(001) and on sapphire (00.1) substrates are face-centered tetragonal structure and hexagonal closed-packed structure, respectively.
High Q merit factor, low frequency acoustic resonant modes from a Pt{100} single crystal
Authors: Mitrelias T. , Kelling S. , Gruyters M. , King D. A.
Published: July 2002

A spectroscopic technique, acoustic wave resonance spectroscopy (AWRS), has been developed to study the influence of long wavelength acoustic phonon excitations on surface chemical processes. Results are presented which demonstrate the sensitivity of AWRS to the state and composition of a Pt{100} single crystal sample, using an ultrahigh frequency and amplitude resolution acoustic spectrometer, a vector analyzer. A novel part of the ultrahigh vacuum compatible excitation system is a retractable piezo holder allowing the lithium niobate piezo transducer to be moved in situ into the bonding position against the side of the sample. Very sharp acoustic resonant modes with a Q merit factor of 1×104 appear only when the sample is clean. Carbon contamination reduces drastically both the intensity and the density of the peaks.
Experimental characterization of reactive ion etched germanium diffraction gratings at 10.6 μm
Authors: Stiens J. , Ranson W. , Cottam R. , De Tandt C. , Vounckx R. , Kotov V. , Shkerdin G. , Dhoedt B. , Baets R.
Published: July 2002

An experimental study of diffraction gratings reactive ion etched in germanium is performed. Gratings are designed for the 10.6 μm infrared CO2 laser. Different etchants have been compared to pattern 3-μm-deep grooves in the germanium layers evaporated on a GaAs substrate. The experimental diffraction efficiency (maximum 30%) of the prototype gratings are in good accordance with the theoretical predictions. The U-shaped grooves have still to be further optimized.
Gain spectra and stimulated emission in epitaxial (In,Al) GaN thin films
Authors: Wiesmann D. , Brener I. , Pfeiffer L. , Khan M. A. , Sun C. J.
Published: July 2002

We measured the emission of (In,Al) GaN films under high intensity optical pumping both in the direction parallel and perpendicular to the film growth. In the edge emission geometry we determine the gain magnitude from the variable stripe length method. We use the spontaneous emission collected perpendicular to the layer plane to calculate the spectral dependence of the gain. Finally, we compare the emission spectra with those obtained for high quality GaAs thin films and find that the observation of a stimulated emission peak perpendicular to the nitride layer plane is predominantly due to scattering of the in-plane stimulated emission.
Red luminescence from strain-induced GaInP quantum dots
Authors: Sopanen M. , Taskinen M. , Lipsanen H. , Ahopelto J.
Published: July 2002

The strain of self-organized InP islands is used to induced quantum dots in near-surface GaInP/AlGaInP quantum wells. To obtain quantum dot luminescence in a widely tunable wavelength range of 630–700 nm, the composition and thickness of the GaInP quantum well is varied. The effect of different cap layer materials, i.e., GaAs, AlGaAs, GaInP, and AlGaInP on the InP island formation and quantum dot luminescence properties is investigated. The luminescence intensity ratio of the quantum dot peak to the quantum well peak is found to be highest when a GaAs cap is used.
Influence of redistribution of electrons in the conduction band on the lattice parameters of AlxGa1−xAs
Authors: Ba̧k-Misiuk J. , Leszczyński M. , Paszkowicz W. , Domagal/a J.
Published: July 2002

Lattice parameters of GaAs layers were measured using the Bond method. For samples heavily doped with S and Se, we observed an increase of lattice parameters with respect to the undoped samples. The results are compared with those observed for AlxGa1−xAs:S (Wagner et al.) and both are explained by the influence of free electrons and their redistribution in the conduction band. For Al0.39Ga0.61As, the following values of deformation potentials of the conduction-band minima were obtained: DΓ=−6.7 eV, DL=1.4 eV, and DX=1 eV.
Microlithographic techniques for laser assisted fabrication of bioelectronic devices
Authors: Di Fabrizio E. , Gentili M. , Morales P. , Pilloton R. , Mela J. , Santucci S. , Sese A.
Published: July 2002

Microlithographic techniques are described for the fabrication of removable stencils to be used in micropatterning by laser deposition of organic and biological matter. Patterned layers are shown together with same atomic force microscope preliminary characterization. Also, a lithographically fabricated micron size glucose biosenser is shown, together with first assays of its performance.
Study of CoCrPt/NiAl thin films on (001) MgO single crystals
Authors: Tang L. , Lee L.-L. , Laughlin D. E. , Lambeth D. N.
Published: July 2002

The microstructure and in-plane magnetic properties of Co72Cr10Pt18/NiAl thin films sputter deposited on (001) single crystal MgO substrates have been investigated. The orientation relationship between the NiAl underlayer and the MgO substrate is determined to be [001](100)NiAl//[001](110)MgO. The CoCrPt films grow in a fibrous manner on the (001) NiAl underlayer and the orientation relationship between the two layers is determined to be [101̄1]CoCrPt//[001]NiAl, and (12̄10)CoCrPt//(100)NiAl (variant 1), or (12̄10)CoCrPt//(010)NiAl (variant 2). The CoCrPt film has two sets of in-plane magnetization easy axes. The major easy axes are along the MgO[100] (i.e., NiAl[11̄0]) and the MgO[010] (i.e., NiAl[110]) directions and the secondary easy axes are along the MgO[110] (i.e., NiAl[100]) and the [1̄10] (i.e., NiAl[010]) directions.
Far-field and beam characteristics of vertical-cavity surface-emitting lasers
Authors: Zhao Y.-G. , Zhang Y.-S. , Huang X.-L. , Zhang L.-T. , Chen W.-X. , Cong L.-F. , Jin C.-Z. , Hu X.-W. , Wang W.
Published: July 2002

We have determined the far-field patterns and beam parameters of vertical-cavity surface-emitting lasers (VCSELs) with different structures. The results show that the window diameter and the active-layer aperture of VCSELs strongly influence laser far-field distributions and beam characteristics; for VCSELs with small window ω=5 μm, only one dominant lobe has been observed in the far-field profiles, even though injected current was increased up to 2 Ith; and the smaller the ratio of the window diameter to the active-layer aperture, the larger is the far-field divergence. The laser structure dependence of the K factor has also been studied.
Dynamic studies of charge-separated-state enhancement of the optical nonlinearity of a porphyrin heterodimer
Authors: Si Jinhai , Wang Yougui , Yang Qiguang , Ye Peixian , Tian Hongjian , Zhou Qingfu , Xu Huijun
Published: July 2002

Light-induced enhancement of the third-order nonlinear optical susceptibility of a heterodimer consisting of two different porphyrin monomers, a zinctetra(4-sulfonatophenyl)porphyrin and a zinctetra(4-N-methyl-pyridyl)porphyrin, was observed when the sample was optically pumped by a 30 ps, 532 nm pump pulse. The temporal behavior of the enhancement was studied. It was found that the enhancement was due predominantly to the population of the charge-separated state with a large electronic third-order nonlinear optical susceptibility
Electroluminescence of epitaxial perylene films
Authors: Toda Y. , Yanagi H.
Published: July 2002

A multilayered electroluminescent device was constructed with ordered perylene thin films as an emission layer. The epitaxial perylene film was prepared by vapor deposition onto the KCl (001) surface, then removed from the KCl substrate and sandwiched between the hole-transport layer coated on an indium tin oxide electrode and Al top electrode. In this epitaxial layer, the perylene molecules oriented their molecular planes perpendicular to the electrode surfaces. This epitaxial device emitted an electroluminescence in the longer wavelengths of 560–580 nm due to the ordered dimeric structure. On the other hand, the device with polycrystalline perylene films exhibited an electroluminescence mainly below 500 nm.
Dispersive surface plasmon microscopy for the characterization of ultrathin organic films
Authors: Knobloch Harald , von Szada-Borryszkowski Günther , Woigk Sabine , Helms Andreas , Brehmer Ludwig
Published: July 2002

We report on experiments, applying a novel microscopy method for ultrathin-film characterization which uses the dispersion properties of plasmon surface polaritons (PSP) as a contrast giving mechanism. In contrast to prior methods, we apply white light instead of a laser for resonant PSP excitation. For a given incident angle and an area of given thickness, a narrow spectral band of the incident light is at resonance for PSP excitation. Therefore, we obtain images with areas of different thickness appearing in different color. As an example, we present microscopic images taken from a thin Cu–phthalocyanine film, evaporated onto solid support through a mask. In addition, we compare the obtained images to theoretical considerations on the contrast mechanism.
Fast modeling of the low-pressure capacitively coupled radio-frequency discharge based on the nonlocal approach
Authors: Berezhnoi S. V. , Kaganovich I. D. , Tsendin L. D. , Schweigert V. A.
Published: July 2002

The results of modeling a low-pressure capacitively coupled radio-frequency (rf) discharge based on the nonlocal approach are reported. The approximation employed enables fast modeling (FM) of the electron distribution function. The solution of the full problem, which consists of calculation of the electron distribution, rf, and stationary electric fields, and of the plasma density profile, for simple atomic gas takes ∼10 min on the IBM PC 486DX2/66. To check the validity of the FM the full scale Monte Carlo modeling was performed. The results of the fast and the full scale modeling are in agreement.
Functional InP/InGaAs lateral double barrier heterostructure resonant tunneling diodes by using etch and regrowth
Authors: Broekaert T. P. E. , Randall J. N. , Beam III E. A. , Jovanovic D. , Seabaugh A. C. , Smith B. D.
Published: July 2002

A planar integrated lateral double barrier heterostructure resonant tunneling diode is demonstrated. Resonances in the current–voltage (I–V) characteristics are observed that have peak-to-valley current ratios as high as 3.5 at 4.2 K and are attributed to resonant tunneling in a two-dimensional/one-dimensional/two-dimensional system. The device structure consists of a lateral double barrier heterostructure embedded in an InP/InGaAs/InP modulation-doped field-effect transistor structure. The lateral heterostructure uses InP barriers and an InGaAs quantum well fabricated by epitaxial etch and regrowth techniques. This device and fabrication process forms the basis for lateral resonant tunneling transistors.
Epitaxial growth of (Sr1−xCax)CuO2 thin film with the infinite-layer structure by metal-organic chemical vapor deposition
Authors: Chang K.-W. , Wessels B. W. , Studebaker D. , Marks T. J.
Published: July 2002

Phase-pure epitaxial (Sr1−xCax)CuO2 thin films having the infinite-layer crystal structure were grown on SrTiO3 (100) substrates by low pressure metal-organic chemical vapor deposition using fluorinated metal-organic precursors. The substrate temperature and reactant gas (O2, H2O) partial pressure are crucial for stabilizing the tetragonal infinite-layer structure. Films with compositions over the range x=0–0.3 can be stabilized. In-plane epitaxy was confirmed by x-ray diffraction φ scan. The films were semiconducting but exhibit resistivity anomalies. The orthorhombic phases of Sr2CuO3 and SrCuO2 were stabilized at 700 °C and 750 °C, respectively.
Ginzburg–Landau theory of Josephson field effect transistors
Authors: Betouras J. J. , Joynt Robert , Dong Zi-Wen , Venkatesan T. , Hadley Peter
Published: July 2002

A theoretical model of high-Tc Josephson field effect transistors (JoFETs) based on a Ginzburg–Landau free energy expression whose parameters are field- and spatially-dependent is developed. This model is used to explain experimental data on JoFETs made by the hole-overdoped Ca-SBCO bicrystal junctions (three terminal devices). The measurements showed a large modulation of the critical current as a function of the applied voltage due to charge modulation in the bicrystal junction. The experimental data agree with the solutions of the theoretical model. This provides an explanation of the large field effect, based on the strong suppression of the carrier density near the grain boundary junction in the absence of applied field, and the subsequent modulation of the density by the field.
c-axis tunneling in multilayers NdBa2Cu3O7−δ junctions with PrBa2Cu3O7−δ barriers
Authors: Alvarez G. A. , Utagawa T. , Enomoto Y.
Published: July 2002

This letter reports c-axis tunneling spectroscopy investigations of high quality junctions fabricated from c-axis oriented NdBa2Cu3O7−δ/PrBa2Cu3O7−δ/NdBa2Cu3O7−δ multilayers deposited by pulsed laser deposition. The conductance spectra as a function of temperature show a smooth crossover from tunneling to metallic junction behavior. A temperature dependent BCS-like gap giving 2Δ/kBTc=6 was observed. The current–voltage characteristics exhibit supercurrent and quasiparticle tunneling that is commonly observed for superconductor–insulator–superconductor junctions.
Non-Markovian gain of a quantum-well laser with many-body effects
Authors: Ahn Doyeol
Published: July 2002

The optical gain of a quantum-well laser is studied taking into account the valence-band mixing, non-Markovian relaxation, and the many-body effects. Plasma screening and excitonic effects are taken into account in the time-dependent Hartree–Fock approximation. Conventional gain spectra calculated with the Lorentzian line shape function show two erroneous phenomena: unnatural absorption region below the band-gap energy and mismatch of the transparency point in the gain spectra with the Fermi-level separation, the latter suggesting that the carriers and the photons are not in thermal (or quasi) equilibrium. It is shown that the non-Markovian gain model with many-body effects removes the two errors associated with the Lorentzian line shape function with the proper choice of the correlation time.
Thick AlxGa1−xAs: An intrinsically percolating barrier owing to its microscopic structural inhomogeneity
Authors: Kim D. S. , Ko H. S. , Kim Y. M. , Rhee S. J. , Hong S. C. , Yee Y. H. , Yee D. S. , Woo J. C. , Choi H. J. , Ihm J. , Woo D. H. , Kang K. N.
Published: July 2002

A significant charge transfer, which differs from tunneling, over thick AlxGa1−xAs barrier in GaAs/AlxGa1−xAs asymmetric double quantum wells is studied by cw photoluminescence excitation (PLE) and time-resolved photoluminescence. It is found that 300-Å-thick Al0.3Ga0.7As barrier is universally ‘‘leaky’’ with transport time of ∼300 ps, while AlAs and AlAs/GaAs digital alloy barriers with same thickness are not. Aided by a model calculation, we suggest that the intrinsic inhomogeneities in the alloy, which recent x-ray and scanning tunneling microscope studies revealed, may be responsible.
Activation of luminescence in polycrystalline silicon thin films by ultrasound treatment
Authors: Koshka J. , Ostapenko S. , Ruf T. , Zhang J. M.
Published: July 2002

A dramatic increase of infrared photoluminescence (PL) intensity by a factor of 2 orders of magnitude is observed after a few minutes at 250 °C of ultrasound treatment (UST) applied to polycrystalline silicon thin films on glass substrates. In films obtained by solid-phase crystallization of amorphous silicon at 550 °C, UST enhances the PL band intensity at 0.7 eV, and also activates a new luminescence maximum at about 0.9 eV. We prove that the 0.9 eV PL band is related to the amorphous fraction of poly-Si films. Due to similarities in spectral shape and temperature behavior, this UST activated luminescence is attributed to a ‘‘defect’’ PL band previously observed in hydrogenated amorphous Si. This conclusion is confirmed by using a set of films with controlled fractions of the amorphous to crystalline phase. A mechanism of ultrasound stimulated hydrogen detrapping followed by hydrogen diffusion and passivation of nonradiative centers (e.g., dangling bonds) in polycrystalline and amorphous Si films is discussed.
Linear measurement of weak 1.57 μm optical pulse train by heterodyne autocorrelation
Authors: Tomaru Tatsuya , Kitajima Shigeki , Inoue Hiroaki
Published: July 2002

A technique for measuring optical pulses, using heterodyne autocorrelation rather than a nonlinear process, is proposed. This method gives not only the pulse width, but also information about optical phase in a simple way. Practical measurement is demonstrated with linearly chirped weak optical pulse train from an actively model-locked external-cavity semiconductor laser. Pulse width and chirp are quantified.
Multisoliton generation by laser modes in a frequency doubling medium
Authors: Agin Pascal , Stegeman George I.
Published: July 2002

We demonstrate that the number of solitons generated by laser modes with multiple power maxima in a phase-matchable, second-order, nonlinear optical medium can be explained by a model based on field overlap and neighboring soliton interactions.
In situ infrared transmission spectroscopy of nucleation and growth of amorphous hydrogenated silicon
Authors: Knobloch Jürgen , Hess Peter
Published: July 2002

We present a series of IR transmission spectra with submonolayer resolution of the initial growth of amorphous hydrogenated silicon (a-Si:H) deposited by F2 laser (157 nm) chemical vapor deposition. The film thickness was measured simultaneously using a quartz crystal microbalance with appropriate sensitivity. The presented technique allows the evolution of the H content and bonding configuration on a silicon substrate to be monitored during nucleation and growth. It provides a comparable or even higher sensitivity than that achieved by reflection absorption spectroscopy using metal surfaces or methods applying multilayer ‘‘optical cavity’’ structures to enhance the IR absorption.
Surface morphology and growth mechanism of YBa2Cu3O7−y films by metalorganic chemical vapor deposition using liquid sources
Authors: Yoshida Y. , Ito Y. , Hirabayashi I. , Nagai H. , Takai Y.
Published: July 2002

We have investigated surface morphology of YBa2Cu3O7−y thin films prepared by chemical vapor deposition (CVD) using liquid metalorganic (MO) sources on MgO(100) single crystalline substrates by atomic force microscopy (AFM). An abrupt change in the terrace width was observed at the deposition temperature of around 750 °C. An anomalous decrease in the efficiency of incorporation of the yttrium component into the film was also found above the same temperature. It suggests that the appearance of liquid phase on the growing surface and the growth mode change from the conventional vapor growth to the VLS (vapor–liquid–solid) growth mode at this temperature.
Synthesis of carbon nanotubes from bulk polymer
Authors: Cho Woo-Seok , Hamada Etsuo , Kondo Yukihito , Takayanagi Kunio
Published: July 2002

Carbon nanotubes have been synthesized by heat treating the polymer at 400 °C in air which was obtained by polyesterification between citric acid and ethylene glycol. Transmission electron micrographs and an electron diffraction pattern showed the formation of carbon nanotubes. The diameter of the tubes ranged from 5 to 20 nm, whereas the lengths were less than 1 μm.
Influence of disorder on luminescence from pseudorandomized strained Si1−xGex/Si superlattices
Authors: Miyake Y. , Shiraki Y. , Fukatsu S.
Published: July 2002

Carrier localization in a disordered potential was studied in type-I strained Si1−xGex/Si superlattices (SLs) where layer widths have been artificially pseudorandomized. The photoluminescence (PL) intensity under a transverse bias voltage varies monotonically and exhibits a folded increase as the bias is increased as opposed to an ordered SL where only steady drop-off of PL intensity, symmetric with respect to bias polarity, was observed with increasing field strength. The results indicate that electron and hole wave functions are located spatially apart at zero bias due to disorder-induced localization. We point out that such a wave-function displacement is even pronounced for type-II SL potentials in the presence of monolayer thickness fluctuation.
Synthesis of nanocrystalline gallium nitride in silica aerogels
Authors: Goodwin T. J. , Leppert V. J. , Smith C. A. , Risbud S. H. , Niemeyer M. , Power P. P. , Lee H. W. H. , Hrubesh L. W.
Published: July 2002

Nanocrystals of gallium nitride were synthesized in silica aerogel host matrices by pyrolysis of dimeric dimethylgallium-diphenylamide precursor sequestered in the nanometer scale aerogel pores. Powder x-ray diffraction (XRD) and selected area electron-diffraction results verify the formation of hexagonal gallium nitride material in the aerogels, and Scherrer-broadening analysis of the XRD data indicate the gallium nitride particle size is ∼20 nm. Transmission electron microscopy results show that the gallium nitride nanoparticles have diameters between 10 and 40 nm with an average diameter of 23 nm. The synthesis parameters for the gallium nitride nanocrystals in the aerogel hosts are discussed.
Direct current heating in superconductor–insulator–superconductor tunnel devices for THz mixing applications
Authors: Dieleman P. , Klapwijk T. M. , Kovtonyuk S. , van de Stadt H.
Published: July 2002

DC heating effects in superconductor–insulator–superconductor (SIS) tunnel junctions are studied by comparing junctions sandwiched between niobium or aluminum layers. With niobium a temperature rise of several Kelvin is observed, which is reduced by an order of magnitude by using aluminum. A simple model satisfactorily explains this observation and predicts a 30% increase in the subgap current due to the elevated temperature. At the operating voltage for heterodyne mixing the receiver noise temperature increases by only 2%.
A vacuum ultraviolet flash lamp with extremely broadened emission spectra
Authors: Kubodera Shoichi , Kitahara Mitsuo , Kawanaka Junji , Sasaki Wataru , Kurosawa Kou
Published: July 2002

We have developed a vacuum ultraviolet (VUV) flash lamp using a binary rare gas mixture excited by a pulsed silent discharge. In a Kr/Xe silent discharge, the VUV emission spectral width was extended up to 26 nm full width at half-maximum (FWHM) at a center wavelength of 162 nm. According to kinetic analyses, such a spectral extension in mixed rare gases is attributed to the simultaneous emissions from heteronuclear rare gas excimers (KrXe*) and homonuclear rare gas excimers (Kr2* and Xe2*).
Image upconversion via unidirectional anti-Stokes generation by reverse-circularly polarized pump beams
Authors: Xia X.-W. , Wada S. , Akagawa K. , Tashiro H.
Published: July 2002

Two-dimensional image transfer with frequency upconversion from the pump to the anti-Stokes beam has been realized using polarization coupling in rotational Raman scattering. With two pump beams of counter-rotating circular polarization from a Q-switched Nd:YAG laser, images carried in either pump can be transferred to the anti-Stokes beam through pump-phonon coupling in a hydrogen cell. Image addition has also been demonstrated when different objects are inserted simultaneously in two pump beams. The potential for imaging through scattering media with this technique is discussed.
High-efficiency and high-speed silicon metal–semiconductor–metal photodetectors operating in the infrared
Authors: Chen Erli , Chou Stephen Y.
Published: July 2002

A silicon metal–semiconductor–metal photodetector with high-efficiency and high-speed in the infrared is reported. The high performance is achieved by using a Si-on-insulator substrate with a patterned nanometer-scale scattering reflector buried underneath a 170-nm-thick Si active layer. This scattering reflector causes light to be trapped inside the thin Si active layer, resulting in a fast and efficient carrier-collection by the electrodes. The impulse response of the photodetector, measured by electro-optic sampling at 780 nm wavelength, has a full width at half-maximum of 5.4 ps, corresponding to a 3-dB bandwidth of 82 GHz. At both 633 and 850 nm wavelengths, the responsivities of the photodetector with the buried backside reflector are at least an order of magnitude larger than those without the reflector.
Short-pulse, extreme-ultraviolet continuum emission from a table-top laser plasma light source
Authors: Meighan O. , Gray A. , Mosnier J.-P. , Whitty W. , Costello J. T. , Lewis C. L. S. , MacPhee A. , Allott R. , Turcu I. C. E. , Lamb A.
Published: July 2002

We have observed extreme-ultraviolet (XUV) “line-free” continuum emission from laser plasmas of high atomic number elements using targets irradiated with 248 nm laser pulses of 7 ps duration at a power density of ∼1013 W/cm2. Using both dispersive spectroscopy and streak camera detection, the spectral and temporal evolution of XUV continuum emission for several target atomic numbers has been measured on a time scale with an upper limit of several hundred picoseconds limited by amplified spontaneous emission.
Observation of visible light emission from Co-silicided junctions with leakage current
Authors: Watanabe J. , Goto K. , Nakamura T.
Published: July 2002

We have observed visible light emission from Co-silicided junctions by emission microscopy. It was found that leakage current across the junction was accompanied by weak emission of light arising from spots distributed spatially on the electrode. In addition, the emission characteristics depended on the annealing temperature of the metallization process. It can be concluded that a plausible leakage origin is anomalous diffusion of Co, resulting in a locally high electric field. We also measured the energy dependence of the emission intensity and found that the emission intensity increases with decreasing photon energy.
Temperature dependent electron beam induced current experiments on chalcopyrite thin film solar cells
Authors: Scheer R. , Wilhelm M. , Stolt L.
Published: July 2002

Electron-beam-induced current (EBIC) profiles of Mo/CuInX2/CdS/ZnO thin film solar cells with X=Se, S were recorded at different temperatures. We measure the collection efficiency of cells as a function of the beam energy and subsequently identify the depth dependent collection function. For a CuInS2 based cell, charge collection is maintained by diffusion transport of minority carriers to the junction with an effective diffusion length of 1.3±0.2 μm. This value is independent on temperature between 123 and 373 K. A CuInSe2 based cell exhibits increased collection of charge carriers created at the back contact on decreasing temperature. The temperature variation of the EBIC profiles is discussed considering the effect of bulk and grain boundary recombination.
Anisotropic sintered Sm2(Fe,M)17Nx magnets made by rotational alignment
Authors: Yang Jun , Mao Ou , Girt Er. , Altounian Z. , Ström-Olsen J. O.
Published: July 2002

Anisotropic bulk Sm2(Fe,M)17Nx magnets were prepared by rotation aligning easy plane Sm2(Fe,M)17 powders followed by sintering and nitriding. Vanadium substitution for iron can help the c-axis alignment compared to the binary Sm2Fe17 compound. Magnets with an energy product of 15 MG Oe and an intrinsic coercivity of 7 kOe were obtained on a single phase Sm2Fe16.15V0.85Nx compound with a density of 91% of theoretical density.
Stable and intense blue-green emission in porous silicon achieved by amine immersion and rapid thermal oxidation
Authors: Li Gu-Bo , Liao Liang-Sheng , Liu Xiao-Bing , Hou Xiao-Yuan , Wang Xun
Published: July 2002

Porous silicon treated by amine immersion and then rapid thermal oxidation results in a photoluminescence peak shift from ∼650 nm (red light) to a stable and intense ∼520 nm blue-green light. The amine immersion may catalyze a process during rapid thermal oxidation that both reduces the sizes of Si cores and more effectively saturates the dangling bonds on the inner surfaces of the porous silicon.
Generation of 10-THz transients from a subpicosecond optical pulse and a 1-THz field in quantum wells
Authors: Citrin D. S.
Published: July 2002

A quantum well simultaneously subjected to a 1 kV/cm, 1 THz field, and a 100 fs optical pulse is shown to result in emission of a sub-ps strong upshifted ∼10 THz transient.
Dynamics of dual-wavelength emission from a coupled semiconductor microcavity laser
Authors: Michler P. , Hilpert M. , Reiner G.
Published: July 2002

We present an experimental demonstration of the dynamics of dual-wavelength emission from a coupled semiconductor microcavity laser after femtosecond optical excitation at 20 K. The coupled microcavity laser is comprised of two λ sized Al0.2Ga0.8As/Al0.5Ga0.5As cavities, separated by a common mirror. The bottom cavity contains three 10 nm thick GaAs quantum wells (QWs) whereas the top cavity contains three 16 nm thick GaAs QWs. Time-resolved measurements of the stimulated emission show pulses as short as 4.8 ps (10 ps) and peak delays as short as 13 ps (16 ps) for the shorter (longer) emission wavelength. Fast pulse fall times of 1 ps are observed for the pulses of the shorter emission wavelength which can be explained by the simultaneous interaction of the two photon modes with both gain regions of the two types of QWs.
High-gain p-i-n infrared photosensors with Bragg reflectors on amorphous silicon–germanium alloy
Authors: Ho Jyh-Jier , Fang Y. K. , Wu Kuen-Hsien , Tsai C. S.
Published: July 2002

An amorphous silicon–germanium alloy (α-SiGe:H) infrared photosensor with a Bragg reflector to obtain high optical gain and responsivity is demonstrated. The Bragg reflector containing α-Si:H and α-SiGe:H layers was grown on the top of p-i-n structure with an amorphous silicon/germanium alloy. All of the amorphous silicon and amorphous silicon–germanium layers were deposited by a low-temperature plasma enhanced chemical vapor phase deposition system. The experimental results of the new structures exhibit a much superior performance to that of conventional p-i-n avalanche photosensor structures. That is, the structure with a Bragg reflector shows a significant improvement in optical gain from 80 to 328 under the incident optical power of 1 μW, and the full width at half maximum can be reduced from 250 to 150 nm.
Parallel quantum-point-contacts as high-frequency-mixers
Authors: Haubrich A. G. C. , Wharam D. A. , Kriegelstein H. , Manus S. , Lorke A. , Kotthaus J. P. , Gossard A. C.
Published: July 2002

The results of high-frequency mixing experiments performed upon parallel quantum point contacts defined in the two-dimensional electron gas of an AlxGa1−xAs/GaAs heterostructure are presented. The parallel geometry, fabricated using a novel double-resist technology, enables the point-contact device to be impedance matched over a wide frequency range and, in addition, increases the power levels of the mixing signal while simultaneously reducing the parasitic source-drain capacitance. Here, we consider two parallel quantum point-contact devices with 155 and 110 point contacts, respectively; both devices operated successfully at liquid helium and liquid nitrogen temperatures with a minimal conversion loss of 13 dB.
Subband electron densities of Si δ-doped pseudomorphic In0.2Ga0.8As/GaAs heterostructures
Authors: Li G. , Babinski A. , Jagadish C.
Published: July 2002

Magnetotransport properties of Si δ-doped pseudomorphic In0.2Ga0.8As/GaAs heterostructures grown by metalorganic vapor phase epitaxy have been investigated in magnetic fields up to 12 T in the dark at 1.7 K. Different δ-doping configurations, in which the same Si δ-doped layer was placed at different positions with respect to the In0.2Ga0.8As well, have been studied to clarify their effect on subband electron densities in the well. Very high electron densities of >4×1012 cm−2 were obtained when placing a Si δ-doped layer at the well center or the well–barrier interface. We found that one subband was occupied in the well-center-doped structure, but when the Si δ-doped layer was at the well–barrier interface, the second subband in the well became occupied. The electron density of Si δ-modulation-doped In0.2Ga0.8As/GaAs heterostructures, in which the cap barrier or the buffer barrier was Si δ doped, was in the order of <1.2×1012 cm−2. The Si δ doping in both of the barriers led to an increase of the electron density by almost a factor of 2. Owing to an incomplete transfer of the electrons from the Si δ-doped layers to the well, parallel conduction was observed in the Si δ-modulation-doped structures.
High resolution imaging of thin-film recording heads by superparamagnetic magnetic force microscopy tips
Authors: Liou S. H. , Malhotra S. S. , Moreland John , Hopkins P. F.
Published: July 2002

We have used superparamagnetic magnetic force microscopy (MFM) tips to obtain high spatial resolution MFM images of recording heads. Profiles of the magnetic field gradient above a thin-film recording head under 3 mA bias current to the head and various tip-head distance conditions are presented. At a low tip-head distance, the gap width, gap location, and gap-field structure can be well resolved in these MFM images. Superparamagnetic tips show promise for the magnetic imaging of recording heads with gap widths below 200 nm.
Direct imaging of current sharing in (BiPb)2Sr2Ca2Cu3Ox composite conductors
Authors: Peterson T. B. , Welp U. , Crabtree G. W. , Vasanthamohan N. , Singh J. P. , Lanagan M. T. , Vlasko-Vlasov V. K. , Nikitenko V. I.
Published: July 2002

Using a high-resolution magneto-optical imaging technique, we study the flow of transport currents around cracks in monofilament (BiPb)2Sr2Ca2Cu2Ox composite conductors. Shunting through the Ag clad is directly observed. The current in the silver decays exponentially with distance from the crack as expected in a one dimensional distributed resistance model. At 77 K, the transfer length, λ, is approximately 0.56 mm, implying an interface resistivity of 7.5×10−8 Ω cm2. This transfer length is found to increase slightly with increasing temperature.
Ionization rates and critical fields in 4H silicon carbide
Authors: Konstantinov A. O. , Wahab Q. , Nordell N. , Lindefelt U.
Published: July 2002

Epitaxial p-n diodes in 4H SiC are fabricated showing a good uniformity of avalanche multiplication and breakdown. Peripheral breakdown is overcome using the positive angle beveling technique. Photomultiplication measurements were performed to determine electron and hole ionization rates. For the electric field parallel to the c-axis impact ionization is strongly dominated by holes. A hole to electron ionization coefficient ratio of up to 50 is observed. It is attributed to the discontinuity of the conduction band of 4H SiC for the direction along the c axis. Theoretical values of critical fields and breakdown voltages in 4H SiC are calculated using the ionization rates obtained.