bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanoscale InP islands embedded in InGaP
Authors: Kurtenbach A. , Eberl K. , Shitara T.
Published: July 2002

We have prepared small InP islands which are embedded in In0.485Ga0.515P grown on a (100) GaAs substrate by solid-source molecular beam epitaxy. The InP islands form due to the 3.7% lattice mismatch between In0.485Ga0.515P and InP. Atomic force microscopy measurements show that the island size is typically ∼50 nm in diameter and ∼5 nm in height for nominally two monolayers of InP deposited on In0.485Ga0.515P. The energy of the photoluminescence (PL) peak shifts from 1.85 to 1.53 eV as the nominal InP thickness increases from 2 to 10 monolayers. A minimum PL linewidth of 21.6 meV and the maximum intensity of the PL originating from the InP islands is observed for 7.3 monolayers InP.
Ion sources for linac of Moscow Institute for Nuclear Research
Authors: Belov A. S. , Frolov O. T. , Klenov V. S. , Yakushev V. P.
Published: July 2002

Ion sources for 600 MeV linac of Moscow INR are described. It is possible to accelerate in the linac intense unpolarized and polarized proton and negative hydrogen ion beams with average current up to 0.5 mA. The unpolarized proton beam is produced by a duoplasmatron type ion source. After acceleration to 750 keV, a beam with peak current 120 mA within normalized phase space area 0.15 π cm mrad is obtained. The surface-plasma H− ion source operating in noiseless mode produces pulsed H− beam with current 80 mA. Polarized proton beam with peak current 6 mA and polarization 80% is generated by the atomic beam-type polarized proton source.
Cluster ion sources (invited)
Authors: Hagena Otto F.
Published: July 2002

Clusters from gases as well as from metal vapors can be obtained from an expanding nozzle flow with the appropriate set of flow field conditions, characterized by a condensation scaling parameter Γ*. Cluster ion beams are characterized by a low specific charge. Accelerated cluster ion beams allow formation of energetic particle beams in the interesting range of 0.01–10 keV/atom, and the specific characteristics of cluster ion beams have led to new applications in science and technology. In this paper a status report on clusters and cluster ions from nozzle sources is given. As example the construction and results of a source for high-intensity silver cluster beams to be used for thin film formation are described.
Effects of edge plasma turbulence on radial correlation length measurements with BES
Authors: Gianakon T. A. , Fonck R. J. , Callen J. D. , Durst R. D. , Kim J. S. , Paul S. F.
Published: July 2002

The recently developed technique of beam emission spectroscopy (BES) provides a tool to study long-wavelength density turbulence (coherence length ≫ ion gyroradius) in hot tokamak plasmas. To provide an accurate conversion of the measured light intensity fluctuations to a local ñ/n density fluctuation and to assess the influence of density fluctuations in the neutral beam induced by large edge turbulence, a multistate neutral beam excitation/transport code for realistic experimental geometries has been written. Results from this code show that the attenuation of the beam density induced by edge turbulence can give rise to significant levels of common-mode fluctuation power in signals from the plasma core and that the derivation of quantitative values of ñ/n from experimental measurements depends weakly on the radial extent of the density fluctuations.
Remote operation of the TFTR BES experiment from an off-site location
Authors: Fonck R. J. , Cosby G. , Durst R. , Gibney T. , Thompson M. , Paul S. F.
Published: July 2002

The capability of controlling a diagnostic subsystem and interactively participating in the experimental program on Tokamak Fusion Test Reactor (TFTR) from a remote site has been developed and demonstrated on the TFTR BES experiment. Interactive communications are established from multiscreen remote workstations at the University of Wisconsin to the Princeton Plasma Physics Laboratory VAX cluster via multiple terminal sessions across the InterNet national network. Full control of the diagnostic, access to all relevant machine parameters and wave forms, and operations run logs are all available with automatic updates between plasma shots. A real-time count-down shot clock with timer, machine event status, and shot number provides a real-time interface to the TFTR shot sequence. This means of remote participation in a central fusion experiment provides vital experience for extrapolation to implementation on an ignition device to test engineering concepts.
Negative ion volume production model: State of the experimental confirmation
Authors: Berlemont P. , Skinner D. A. , Bacal M.
Published: July 2002

We report the results of simulating two multicusp volume negative ion sources in which plasma parameters, hydrogen vibrational spectra, and in one case the negative ion density, have been measured. We find generally good quantitative and qualitative agreement between experiment and theory for the basic discharge parameters. Good agreement is also found for atomic density, although the wall recombination coefficient γ(H) is 0.05 in one source and 0.5 in the other. The calculated densities of vibrationally excited states with v″≥5 are higher than the measured densities, but the calculated negative ion densities are lower than available measurements. Possible causes for these discrepancies are suggested. Fundamental modifications to the model may be necessary, and we have discussed two possibilities: a suprathermal rotational spectrum, and a spatial gradient in vibrational excitation (due to elastic collisions which can localize the effect of vibrational wall cooling near the wall).
Observation of exciton and biexciton processes in CdxZn1−xSe/ZnSe (x=0.2)
Authors: Wang Li , Simmons Joseph H.
Published: July 2002

Exciton and biexciton transitions have been observed in low-temperature (10 K) photoluminescence from CdxZn1−xSe/ZnSe (x=0.2) multiple quantum well samples grown by molecular beam epitaxy. Transient photoluminescence experiments were conducted to study the dynamics of carrier decay associated with these processes. The formation of exciton and biexciton species is confirmed by examining their energy positions, intensity dependence on excitation power density, spectral line shapes, relative decay lifetimes, and polarization dependence.
Compact hollow cathode Penning surface-plasma sources for steady-state negative ion production
Authors: Belchenko Yu. I. , Bacal M.
Published: July 2002

A compact steady-state negative ion source using a hollow cathode Penning discharge is described. Water-cooled gas-discharge electrodes and permanent Sm-Co magnets were used. Steady-state source operation with a H− beam current intensity of up to 50 mA and discharge power of up to 0.8 kW was achieved. The H− current density in the emission holes was about 50 mA/cm2. The gas efficiency was 3%. The H− yield was proportional to the area of the emission apertures and to the discharge current. About 10 mA of H− beam was accelerated and transported with the source having a smaller emission hole area of 0.3 cm2 in the tests at the Ecole Polytechnique accelerator facility.
Foil deposition alpha collector probe for TFTR’s D-T phase
Authors: Herrmann H. W. , Darrow D. S. , Timberlake J. R. , Zweben S. J. ,   the TFTR Group, Chong G. P. , Pitcher C. S. , Macaulay-Newcombe R. G.
Published: July 2002

A new foil deposition alpha collector sample probe has been developed for TFTR’s D-T phase. D-T fusion produced alpha particles escaping from the plasma are implanted in nickel foils located in a series of collimating ports on the detector. The nickel foils are removed from the tokamak after exposure to one or more plasma discharges and analyzed for helium content. This detector is intended to provide improved alpha particle energy resolution and pitch angle coverage over existing lost alpha detectors, and to provide an absolutely calibrated cross-check with these detectors. The ability to resolve between separate energy components of alpha particle loss is estimated to be ∼20%. A full 360° of pitch angle coverage is provided for by eight channels having an acceptance range of ∼53° per channel. These detectors will be useful in characterizing classical and anomalous alpha losses and any collective alpha instabilities that may be excited during the D-T campaign of TFTR.
First tomographic reconstructions and a study of interference filters for visible-light tomography on RTP
Authors: Ingesson L. C. , Pickalov V. V. , Donné A. J. H. ,   the RTP Team, Schram D. C.
Published: July 2002

An 80-channel visible-light tomography diagnostic is operational on the Rijnhuizen Tokamak Project. This diagnostic uses optical imaging systems from five directions in one poloidal plane to view emission by the plasma. For the application of tomography algorithms, measurements need to be preprocessed to take into account the properties of the imaging system. These properties have been measured and a consistent treatment is demonstrated. An example of a tomographic inversion of a glow-discharge plasma is given. Optical filters can be used to select various wavelength ranges. Because the imaging system gives large angles of incidence on the filter (<16°), a study has been made to determine the minimum useful bandwidth of interference filters to select spectral lines, which was found to be 5 nm.
A passive vibration isolation stack for LIGO: Design, modeling, and testing
Authors: Giaime Joseph , Saha Partha , Shoemaker David , Sievers Lisa
Published: July 2002

Multiple-stage seismic vibration isolation stacks, which consist of alternating layers of stiff masses and compliant springs, can provide significant passive filtering of ground vibration for experiments and equipment that are sensitive to mechanical noise. We describe the design, modeling and testing of a prototype of a stack suitable for use in the Laser Interferometer Gravitational-wave Observatory (LIGO). This is a four-stage elastomer (spring) and stainless steel (mass) stack, consisting of a table resting on three separate legs of three layers each. The viscoelastic properties of elastomer springs are exploited to damp the stack’s normal modes while providing rapid roll-off of stack transmission above these modal frequencies. The stack’s transmission of base motion to top motion was measured in vacuum and compared with three-dimensional finite-element models. In one tested configuration, at 100 Hz, horizontal transmission was 10−7, vertical transmission was 3×10−6, and the cross-coupling terms were between these values.
In situ measurement of AlAs and GaAs refractive index dispersion at epitaxial growth temperature
Authors: Bardinal V. , Legros R. , Fontaine C.
Published: July 2002

In situ molecular beam epitaxy control of III–V optoelectronic device growth has been achieved by dynamic optical reflectometry with tunable excitation wavelength, through the use of a titanium:sapphire laser light source. This new multiwavelength reflectometry method was used to determine the values of the AlAs and GaAs refractive indices at growth temperature (600 °C). Index dispersion between 760 and 960 nm is presented and found to be in good agreement with the existing models.
Development of an imaging vacuum-ultraviolet monochromator in the normal incidence region
Authors: Koog J. , Iwasaki K. , Sato K. , Hamada Y. , Toi K. ,   the JIPP T-IIU Group
Published: July 2002

An imaging vacuum-ultraviolet monochromator has been developed to provide the space-resolved impurity line emissions from magnetically confined plasmas. With minor modifications of a commercial normal incidence monochromator, a pinhole entrance slit and a microchannel plate detector displaced away from the exit slit, the instrument performs two-dimensional spectroscopic observations in the wavelength range from 400 to 2000 Å. Ray tracing has been performed to understand the spatial imaging properties in the practical geometric configuration. The measured spatial resolution is about 0.5 and 1 mrad in dispersion and vertical plane, respectively, with the entrance slit of 0.1 mm width and height. The results of the testing experiments and the measurements carried out on the JIPP T-IIU tokamak plasma are presented and discussed.
Use of emissive probes in high pressure plasma
Authors: Yan Shiluo , Kamal Husain , Amundson Jay , Hershkowitz Noah
Published: July 2002

The characteristics of emissive probes in unmagnetized high pressure (≤1 Torr) argon and helium plasmas, produced by inductively coupled 13.56 MHz rf power, are studied. A procedure is given for interpreting emissive probe current–voltage (I–V) characteristics. The I–V curves indicate the amplitude of the rf fluctuation of the plasma potential. They also show ionization near the emissive probe when the potential drop between the emissive probe and the plasma potential is more than the ionization potential. Experiments show that when the temperature of the emissive probe wire and/or the neutral pressure is increased, ionization becomes significant. An increase in the local ion density due to the additional ionization was demonstrated by the I–V curves of an emissive probe and a nearby Langmuir probe. A simple procedure is presented for interpreting these results.
Full strength compacts by extrusion of glassy metal powder at the supercooled liquid state
Authors: Kawamura Yoshihito , Kato Hidemi , Inoue Akihisa , Masumoto Tsuyoshi
Published: July 2002

We report the production of full strength compacts of metallic glass by warm extrusion of powders at the supercooled liquid state just above the glass transition temperature. The alloy used was Zr65Al10Ni10Cu15 (at. %) which has the lowest viscosity among Zr-based metallic glasses with large supercooled liquid region. The tensile strength and Young’s modulus of the glassy powder compacts were 1520 MPa and 80 GPa, respectively, which are similar to that obtained in the as-cast bulk alloy and melt-spun ribbon. This opens up possibilities of producing high strength amorphous alloys with complex shapes.
Differences between As2 and As4 in the homoepitaxial growth of GaAs(110) by molecular beam epitaxy
Authors: Holmes D. M. , Belk J. G. , Sudijono J. L. , Neave J. H. , Jones T. S. , Joyce B. A.
Published: July 2002

The homoepitaxial growth of GaAs(110) thin films by molecular beam epitaxy has been studied in situ by reflection high-energy diffraction. RHEED specular beam intensity oscillations were recorded over a wide range of growth conditions in which the substrate temperature, growth rate, V/III flux ratio and the relative amount of As2 or As4 in the incident arsenic beam were varied. These conditions were plotted to produce a phase map of the growth conditions for which specular intensity oscillations were recordable. RHEED oscillations were obtained over a much wider range of growth conditions when using As2 compared to growth using As4. It is shown that this is related to the very different incorporation coefficients of the two arsenic species and reflects the requirement of a high arsenic adatom concentration in order to maintain the 1:1 stoichiometry of the nonpolar (110) surface.
Improvement of q-profile measurement by fast observation of pellet ablation at ASDEX Upgrade
Authors: Müller H. W. , Lang P. T. , Büchl K. , Kaufmann M. , Kuteev B. V. , McCarthy P. J. , Mertens V. , Miroshnikov I. , Schneider W. , Zohm H. ,   ASDEX Upgrade Team
Published: July 2002

The q-profile measurement presented in this article is based on the observation of pellets injected into the plasma and viewed with a fast-framing camera. The pellets sublimate in the plasma and the ablated material is ionized. The ions move along the magnetic field lines, while an ablation cloud is forming. This ablation cloud contains a small fraction of neutral particles which emit visible light after collisional excitation. It is therefore possible to visualize the magnetic field lines along which the pellet passes. The inclination angle of the magnetic field lines with respect to the torus midplane can be determined from this observation. The results are compared with the inclination angles delivered by an equilibrium code. Further analysis shows that it is not meaningful to determine the q-profile from the data of only the pellet ablation, in the case of an elongated plasma as in ASDEX Upgrade. However, the accuracy of the q-profile determined by an equilibrium code, especially in the plasma center, can be greatly improved by using the pellet measurements as additional input data.
Characteristics of electron cyclotron resonance plasmas for large area ion source application
Authors: Hwang S. M. , Yang J. G. , Yoon N. S. , Hong J. , Kim B. C. , You K.-I. ,   Hanbit Project Team
Published: July 2002

The characteristics of electron cyclotron resonance (ECR) plasmas at the plug chamber of the “Hanbit” plasma facility have been investigated. The chamber length and diameter are 2.25 m and 1.5 m, respectively, and three pairs of solenoids are used to produce a variety of magnetic field configurations. Two magnetrons of 5 kW maximum output power each are used to produce the ECR plasma, and the microwaves are launched in extraordinary mode (X-mode) and/or right-hand circular polarized mode (R-mode). The dependence of the radial plasma density profile and the energy distribution of end loss ions upon the magnetic field strength and geometry, gas pressure, microwave power, and the mode of microwave are investigated. The plasma parameters are measured by using a position-controllable electrostatic probe, an x-ray spectrometer, and a multigrid ion energy analyzer. Transitions, occurred by threshold magnetron powers between low and high density modes, are found on certain conditions of magnetic field geometry and gas pressure. The density profile and the ion energy distribution are strong functions of magnetic field geometry and gas pressure, respectively.
The status of DESY H− sources
Authors: Peters J.
Published: July 2002

Two different types of H− sources are operating at DESY, a magnetron source and a rf-driven volume source. H− sources for HERA have to run for long uninterrupted periods with a low duty factor and a high reliability. Several necessary improvements are under construction for our rf-driven volume source. The status of both our magnetron and our volume source will be discussed and the first LINAC III experiment with the rf-driven volume source will be reported.
The viscosity of the Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass forming alloy in the supercooled liquid
Authors: Bakke E. , Busch R. , Johnson W. L.
Published: July 2002

The viscosity of the Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass forming alloy in the supercooled liquid was measured using parallel plate rheometry. The measurements were carried out with different heating rates between 0.0167 and 1.167 K/s as well as isothermally. Because of the high thermal stability above the glass transition of this bulk metallic glass former with respect to crystallization, it was possible to measure viscosities in the range from 1010 to 106 poise. This region of viscosities has not been previously measured for supercooled metallic melts. Our measurements suggest that the viscosity of the supercooled liquid of this bulk glass former exhibits a small Vogel–Fulcher temperature relative to the glass transition temperature, similar to silicate glasses.
Systems for remote participation in JT-60 experiments
Authors: Matsuda T. , Tsugita T. , Oshima T. , Sato M. , Sakata S. , Koiwa M. , Hamamatsu K. , Nishitani T. , Saitoh N.
Published: July 2002

Since 1996, the remote participation in JT-60 experiments has been successfully conducted in collaboration with JAERI, Los Alamos National Laboratory and Princeton Plasma Physics Laboratory. The remote analysis system is a computer complex consisting of an analysis server and a data server for access to JT-60 data. Collaborators of the remote participation can analyze JT-60 data by using this system through the Internet. For the remote diagnostic system, an X Window control program has been customized to communicate via the overseas line using a UNIX workstation at the remote site and one in the JT-60 control room. It has a feature of real-time remote control of diagnostic equipment and remote access to CAMAC data. Both systems are used together with the ISDN-based video-conferencing system for real-time communication between the remote laboratory and the JT-60 control room.
Scanning tunneling microscopy based lithography employing amorphous hydrogenated carbon as a high resolution resist mask
Authors: Kragler K. , Günther E. , Leuschner R. , Falk G. , Hammerschmidt A. , von Seggern H. , Saemann–Ischenko G.
Published: July 2002

Amorphous hydrogenated carbon (a–C:H) is introduced as a constituent of a two–layer resist system for lithography with a scanning tunneling microscope (STM) operating in air. The resist is made up of a thin electron sensitive and chemically amplified top resist (≤50 nm) and a–C:H as a thick conducting and etchable bottom resist. In this setup the bottom resist acts as the counter electrode allowing in principle operation on insulating substrates. We show that it is possible to generate structures with high aspect ratios by transfering the developed top resist patterns by means of oxygen reactive ion etching (RIE) into the bottom resist and halogen RIE into silicon substrates. Linewidths between 100 and 50 nm have been observed in the bottom resist as well as in the substrates.
Performance of the grating-crystal monochromator of the ALOISA beamline at the Elettra Synchrotron
Authors: Floreano L. , Naletto G. , Cvetko D. , Gotter R. , Malvezzi M. , Marassi L. , Morgante A. , Santaniello A. , Verdini A. , Tommasini F. , Tondello G.
Published: July 2002

The new beamline ALOISA, now operational at the Elettra Synchrotron, is designed for surface studies by means of several experimental techniques: surface x-ray diffraction and reflectivity, photoemission spectroscopy, photoelectron diffraction, e−-Auger coincidence spectroscopy. A new monochromator has been specifically designed and realized for this multipurpose beamline: it makes use of a channel-cut Si crystal dispersive element for the 3–8 keV range and of a plane mirror-plane grating element for the 200–2000 eV range. Both dispersive elements share the same optical system. In the low energy range (200–900 eV) the spectral resolving power exceeds 5000 while maintaining a throughput higher than 1010 photons/s/200 mA/0.02% BW. In the case of the N2 1s→π* and Ne 1s→3p transitions, the extremely high signal-to-noise ratio of the absorption spectra allowed a very accurate determination of the corresponding natural linewidth (116±2 and 250±10 eV, respectively). Moreover, the vibrational structure of the CO–oxygen 1s→π* transition has been fully resolved. In the high energy range, the measured flux exceeds 1010 photons/s/200 mA up to 6.5 keV with a resolving power of ∼7500.
Time-resolved spectrofluorometer for clinical tissue characterization during endoscopy
Authors: Glanzmann Thomas , Ballini Jean-Pierre , van den Bergh Hubert , Wagnières Georges
Published: July 2002

Time-resolved fluorescence spectroscopy has the potential to provide more information for the detection of early cancer than continuous wave spectroscopy. A new optical fiber-based spectrofluorometer for time-resolved fluorescence spectroscopy of biological tissue during clinical endoscopy is presented. The apparatus is based on a nitrogen laser pumping a dye laser as excitation source and a streak camera coupled with a spectrograph as time-resolved spectrometer. The excitation and fluorescence light is carried by an optical fiber to the tissue under investigation and back to the detector, respectively. This optical fiber can be inserted into the biopsy channel of a conventional endoscope. Hence, the apparatus can be used to perform in situ tissue characterization during endoscopy. The instrument enables the measurement of the decays of entire fluorescence spectra within 15 s with a dynamic range of the spectro-temporal images of up to three orders of magnitude. Luminescence lifetimes from the sub ns up to the ms range can be measured. Spectral and temporal resolution, sensitivity, and dynamic range of the instrumentation were determined. The accuracy of the apparatus was checked by the measurement of the fluorescence lifetimes of various fluorophores with known lifetimes. For the first time, two-dimensional time-resolved spectra with sub-ns temporal resolution of tissue fluorescence of the human bladder, the bronchi, and the esophagus taken during endoscopy are presented as a demonstration of performance of the instrumentation. The excitation wavelengths were 337 nm in the case of the bladder and the esophagus and 480 nm in the case of the bronchi. Lifetime contrasts between normal and neoplastic tissue were found in all three organs. The spectral analysis of the fluorescence decays showed that the fluorescence between 370 and 490 nm, excited at 337 nm, consisted in several overlapping spectra. In the case of the esophagus, the contrast between normal and tumoral tissue was inverse in two different spectral bands proving the importance of the choice of the appropriate spectral range for time-resolved autofluorescence measurements for an optimal contrast. The in vivo fluorescence decay of the photosensitizers 5-aminolevulinic acid hexylester hydrochloride-induced protoporphyrin IX was measured in the human bladder and found to be mono-exponential with a lifetime of 15.9 (±1.2) ns. An in vivo fluorescence lifetime of 8.5 (±0.8) ns was found in the case of the photosensitizer 5, 10, 15, 20-tetra(m-hydroxyphenyl)chlorin (mTHPC) in the esophagus.
A fast-scanning heterodyne radiometer for electron cyclotron emission measurements in HT-7 superconducting tokamak
Authors: Zhang S. Y. , Poznyak V. I. , Ploskirev G. , Kalupin D. , Wan Y. X. , Xie J. K. , Luo J. R. ,   HT-7 Team
Published: July 2002

A fast-scanning heterodyne radiometer employing a backward-wave oscillator (BWO) in 78–118 GHz was developed and installed for electron cyclotron emission (ECE) measurements in HT-7 superconducting tokamak. The radiometer measures 16 ECE frequency points with a scanning time period of 0.65 ms, each of the frequency points can be preset by the program to meet specific interests in physics. The high scanning speed is achieved by carefully choosing a BWO, very finely adjusting the radiometer over the full waveband, and by eliminating some elements that are routinely included in a fast-scanning radiometer system. A horizontal view of the ECE optics was installed to measure electron temperature profiles. The spatial resolution is about 1 cm (Bt=2 T) in the center of the HT-7 minor cross section, determined by the intermediate frequency of 0.1–0.5 GHz in the radiometer. Vertically viewing optics along a perpendicular chord was also installed to study nonthermal ECE spectra. Preliminary measurement results in pellet injection plasma and lower-hybrid current drive plasma were presented.
Room-temperature 1.5 μm luminescence of co-deposited erbium and germanium
Authors: Chen J. H. , Pang D. , Cheong H. M. , Wickboldt P. , Paul W.
Published: July 2002

Nanocrystalline germanium films containing erbium were deposited by thermal evaporation under 0.6 Torr of argon onto crystalline silicon wafer substrates. Weak broad photoluminescence (PL) around 1.5 μm was observed at room temperature. Annealing under 10−7 Torr of vacuum for 3 h at 500 °C produced no change in the PL spectrum. After 1 h oxidation in air at 500 °C the PL intensity increased by an order of magnitude with reduction of the spectral linewidth and appearance of distinct structures, a portion of which is similar to that observed for Er-implanted Si:O. Subsequent increase in oxidation time reduced the PL intensity slightly with no change in the spectral shape. The PL intensity exhibits a sublinear increase with pump power and approaches saturation at 200 mW. Raman spectra before and after anneal are also presented. Annealing increased the average grain size from 5 to 10 nm. The PL spectrum of erbium metal after oxidation in air at 500 °C is quite different from that of these oxidized Ge:Er films.
Evidence for border traps in metal-oxide-semiconductor transistors through 1/f noise
Authors: Ploor M. D. , Schrimpf R. D. , Galloway K. F. , Johnson G. H.
Published: July 2002

1/f noise was measured in n-channel power transistors following high field stressing and high temperature anneals. Negative bias anneals resulted in considerably higher noise than produced by positive bias anneals. Then the bias was switched between positive and negative, the noise level switched between a low and a high level. The noise did not correlate with either interface or oxide trapped charge, but can be explained in terms of border traps and charge compensation. These mechanisms may be sufficient to explain a wide range of noise results in n-channel metal-oxide-semiconductor field effect transistors.
Effect of multiplication layer width on breakdown voltage in InP/InGaAs avalanche photodiode
Authors: Park Chan-Yong , Hyun Kyung-Sook , Kang Seung-Goo , Kim Hong-Man
Published: July 2002

Breakdown voltages of InP/InGaAs avalanche photodiodes have been analyzed with structure parameters, such as multiplication layer width (MLW) and absorption layer thickness. It is shown that there exists a critical MLW, w0, where the breakdown voltage is the lowest. As MLW increases, the breakdown voltage increases slowly in the region of MLW≥w0 while the breakdown voltage decreases in the region of MLW≤w0. It is also revealed that w0 is a function of absorption layer thickness. The measured breakdown voltages having MLWs of 0.15–0.4 μm were reported and compared to the calculated ones, which agreed very well with each other.
InAsSb/InAlAsSb strained quantum-well diode lasers emitting at 3.9 μm
Authors: Choi H. K. , Turner G. W.
Published: July 2002

Strained quantum-well diode lasers emitting at 3.9 μm have been fabricated. The laser structure, grown on a GaSb substrate by molecular beam epitaxy, consists of compressively strained InAsSb active layers and tensile-strained InAlAsSb barrier layers, surrounded by AlAsSb cladding layers. Broad-stripe lasers have exhibited pulsed operation up to 165 K, with threshold current density of 78 A/cm2 at 80 K. The characteristic temperature is 30 K up to 120 K. The devices operated cw up to 123 K, and the maximum cw power at 80 K is 30 mW/facet. Ridge-waveguide lasers have operated cw up to 128 K, with cw threshold current at 80 K of 35 mA.
Microstructure of AlGaAs-oxide heterolayers formed by wet oxidation
Authors: Guha S. , Agahi F. , Pezeshki B. , Kash J. A. , Kisker D. W. , Bojarczuk N. A.
Published: July 2002

We have carried out a transmission electron microscopy based study of AlGaAs–Al(oxide) heterolayers created by lateral sidewall wet oxidation and identify the oxide phase formed as a consequence of the oxidation of AlAs to be γ-Al2O3, with the cubic Fd 3m structure. The oxide-semiconductor interface is weak and porous, possibly due to the high stress loads developed during oxidation, and we propose that the fast oxidation rates are a consequence of reactants transported to the oxidation front along the porous interface.
In situ arsenic-doped polycrystalline silicon as a low thermal budget emitter contact for Si/Si1−xGex heterojunction bipolar transistors
Authors: King C. A. , Johnson R. W. , Pinto M. R. , Luftman H. S. , Munanka J.
Published: July 2002

A low thermal budget emitter contact with low specific contact resistivity (ρc) with the absence of transient enhanced diffusion (TED) effects is essential to fabricate integratable high performance Si/SiGe heterojunction bipolar transistors (HBTs). We report the use of in situ As-doped polycrystalline silicon (polysilicon) from a low base pressure rapid thermal episystem for this purpose and find that it meets all the requirements. We used secondary ion mass spectrometry to find that 18 nm, heavily B-doped layers remain intact after implantation into the surface polysilicon and annealing at 800 °C for 40 s. Similar samples without the surface polylayer displayed extreme broadening of B profile. Kelvin crossbridge resistors together with 2D device simulations revealed that ρc is an extremely low value of 1.2×10−8 Ω cm2 in as-deposited material. Fabrication of simple 30×30 μm2 mesa isolated HBT devices showed IC to be more than two decades higher in devices with only an in situ As-doped polyemitter compared with devices that incorporated a surface implant into the single crystal portion of the emitter before polysilicon deposition. These results demonstrate that this doped polycrystalline silicon material is an excellent choice for emitter contacts to HBT devices.
Evaluation of the surface stoichiometry during molecular beam epitaxy of cubic GaN on (001) GaAs
Authors: Yang H. , Brandt O. , Wassermeier M. , Behrend J. , Schönherr H. P. , Ploog K. H.
Published: July 2002

We use in situ reflection high-energy electron diffraction to investigate the growth kinetics of cubic (001)-GaN/GaAs grown by plasma-assisted molecular beam epitaxy. We find that the GaN surface exhibits three surface reconstructions having (1×1), (2×2), and c(2×2) symmetries, which correspond to Ga adatom coverages of 0, 0.5, and 1, respectively. We demonstrate that the transient behavior of the half-order streak intensity is a sensitive probe of the surface stoichiometry during growth. Particularly, these measurements enable us to directly determine the effective N flux incorporated into the crystal.
High efficiency and fast modulation of Er-doped light emitting Si diodes
Authors: Coffa S. , Franzò G. , Priolo F.
Published: July 2002

We demonstrate that the electrical excitation of Er ions incorporated within the depletion layer of a p+−n+ Si diode allows one to simultaneously obtain efficient pumping of rare earth ions and a fast turnoff time of the electroluminescence signal. In fact it is found that during pumping, under reverse bias at the breakdown, a high internal quantum efficiency (10−4) can be achieved since the Er ions are excited with a cross section of 6×10−17 cm2 and exhibit a decay lifetime of 100 μs at room temperature. On the other hand, when the diode is turned off, the electroluminescence signal dies off in less than 10 μs (a limit set by the time response of the adopted detector). These results are explained by observing that fast nonradiative decay of the excited Er ions can occur by Auger transfer of the energy to a free electron or to an electron bound to an Er-related level in the bandgap. These processes are inhibited within the depletion layer and only set in when, at the turnoff, the excited Er ions are suddenly embedded within the heavily doped (∼1019/cm3) neutral region of the diode.
Electron Auger processes in mid-infrared InAsSb/InGaAs heterostructures
Authors: Hjalmarson H. P. , Kurtz S. R.
Published: July 2002

To investigate the effects of strain and quantum confinement, Auger rates are calculated for an n-type strained InAs0.9Sb0.1/In0.87Ga0.13As mid-infrared laser structure as a function of temperature. Compressive strain in the quantum wells reduces the mass of the holes which leads to a reduction in the Auger rate compared with an unstrained quantum well. The rate reduction is explained in terms of a qualitative analysis of the role of strain. The rate includes contributions from inter-subband Auger transitions which are found to dominate the rate at low temperature.
Gain and differential gain of single layer InAs/GaAs quantum dot injection lasers
Authors: Kirstaedter N. , Schmidt O. G. , Ledentsov N. N. , Bimberg D. , Ustinov V. M. , Egorov A. Yu. , Zhukov A. E. , Maximov M. V. , Kop’ev P. S. , Alferov Zh. I.
Published: July 2002

We present gain measurements and calculations for InAs/GaAs quantum dot injection lasers. Measurements of the modal gain and estimation of the confinement factor by transmission electron microscopy yield an exceptionally large material gain of 6.8(±1)×104 cm−1 at 80 A cm−2. Calculations including realistic quantum dot energy levels, dot size fluctuation, nonthermal coupling of carriers in different dots, and band filling effects corroborate this result. A large maximum differential gain of 2×10−12 cm2 at 20 A cm−2 is found. The width of the gain spectrum is determined by participation of excited quantum dot states. We record a low transparency current density of 20 A cm−2. All experiments are carried out at liquid nitrogen temperature.
The effect of current density and stripe length on resistance saturation during electromigration testing
Authors: Filippi R. G. , Wachnik R. A. , Aochi H. , Lloyd J. R. , Korhonen M. A.
Published: July 2002

Resistance saturation as a function of current density and stripe length has been investigated for a two-level structure with Ti/TiN/AlCu/Ti/TiN stripes and interlevel W stud vias. A simple model relating the resistance change at saturation to the current density and stripe length is formulated for structures with short stripe lengths and blocking boundaries at both ends. Experimental results for stripe lengths of 25, 50, or 100 μm are in good agreement with the model predictions.
Dielectric response of thick low dislocation-density Ge epilayers grown on (001) Si
Authors: Junge Kelly E. , Lange Rüdiger , Dolan Jennifer M. , Zollner Stefan , Dashiell M. , Orner B. A. , Kolodzey J.
Published: July 2002

Spectroscopic ellipsometry was used to measure the dielectric functions of epitaxial and bulk Ge at photon energies from 1.5 to 5.2 eV. The epitaxial Ge was grown at 400 °C by molecular beam epitaxy on (001) Si substrates. The optical response and the interband critical-point parameters of Ge on Si were found to be indistinguishable from that of bulk single crystal Ge, indicating high optical quality. Dislocation density measurements using an iodine etch verified low surface defect densities. We conclude that epitaxial Ge grown on Si at relatively low temperatures is suitable for optical device applications.
Velocity overshoot greater than 107 cm/s at room temperature in sub-0.1-μm silicon-on-insulator devices
Authors: Mizuno Tomohisa , Ohba Ryuji , Ohuchi Kazuya
Published: July 2002

In order to investigate the physical limits of the metal-oxide semiconductor field-effect transistor (MOSFET), we have experimentally studied the non-stationary carrier transport in a high lateral electric field using the n- and p-channel silicon-on-insulator (SOI) transistors. We have experimentally demonstrated that the electron drift velocity ve shows velocity overshoot, that is, over 107 cm/s (1.2×107 cm/s) at room temperature, at less than 0.1-μm channel length Leff, which has been realized under suppressed self-heating conditions. The carrier velocity was obtained by measuring both the transconductance and the gate-to-source capacitance. Moreover, according to the experimental Leff dependence of the carrier velocity, the physical limit of both electron and hole velocity at Leff=0 is estimated to be about 2.5×107 cm/s, which indicates that the transconductance is equal to about 2000 mS/mm.
Enhancement of Schottky barrier height in heterodimensional metal-semiconductor contacts
Authors: Ytterdal T. , Shur M. S. , Hurt M. , Peatman W. C. B.
Published: July 2002

We report on the measurements of the heterodimensional Schottky barrier height in two-dimensional metal-semiconductor field effect transistors (2D MESFETs). Our experimental data indicate approximately 0.1 eV greater barrier height compared to conventional metal-semiconductor contacts of the same materials. The enhancement is explained in terms of two effects—quantization of energy levels of the carriers in the quantum well and broadening of the corresponding wave functions. The increased barrier height leads to a substantial reduction of the gate leakage current in 2D MESFETs.
Healing processes in submicron Al interconnects after electromigration failure
Authors: Hunt A. W. , Riege S. P. , Prybyla J. A.
Published: July 2002

Investigations of the healing of electromigration-induced open-circuit failed submicron Al(0.5%Cu) interconnects were performed using in situ transmission electron microscopy (TEM). The samples consisted of 4000 Å thick Al (0.5%Cu) patterned over a TEM-transparent window into five runners in parallel, with linewidths 0.2, 0.3, 0.5, 0.8, and 1.0 μm. A novel sample design minimized any Joule heating in the runners. Our approach has allowed us to observe voids form, grow, migrate, fail a runner, and heal all with respect to the detailed local microstructure of the runners. In this letter, we focus on our time-resolved observations of the mechanisms of healing.
An optical spectroscopy for detecting quantized polarization waves of excitons
Authors: Madrigal-Melchor J. , Pérez-Rodrı́guez F. , Maytorena J. A. , Mochán W. L.
Published: July 2002

An optical spectroscopy, based upon the determination of the difference between the reflectivity for p-polarized light (Rp) and the squared reflectivity for s-polarized light (Rs2) with an angle of incidence of 45°, is proposed to study the interaction of excitons with the surface potential in semiconductors. It is found that Rp−Rs2 as a function of the wave frequency is quite sensitive to the form of the surface potential. In addition, the generation of longitudinal modes such as the quantized polarization waves of excitons produces resonant dips well-identified in the new spectrum. On the other hand, the transverse resonances present in Rp and Rs disappear in the difference Rp−Rs2.
Doping dependent ZnCdSe/ZnSe-superlattice disordering
Authors: Kuttler M. , Strassburg M. , Stier O. , Pohl U. W. , Bimberg D. , Kurtz E. , Nürnberger J. , Landwehr G. , Behringer M. , Hommel D.
Published: July 2002

The doping dependent intermixing of ZnCdSe/ZnSe superlattices was studied by secondary ion mass spectroscopy. The chlorine or nitrogen doped and undoped structures were grown by molecular beam epitaxy. Heat treatment was performed in the temperature range of 300 to 550 °C under different conditions, namely Zn or N atmosphere, vacuum and protected by a Si3N4 cap. The diffusion of Cd was found to be Fickian for all kinds of doping. While identical Cd diffusion coefficients were observed for the undoped and the chlorine-doped superlattice, a distinct enhancement by three orders of magnitude was found for nitrogen-doped structures. The p-type conductivity, and not the nitrogen itself, was identified to be responsible for the Cd diffusion enhancement by additional implantation studies.
5 W continuous wave power, 0.81-μm-emitting, Al-free active-region diode lasers
Authors: Wade J. K. , Mawst L. J. , Botez D. , Nabiev R. F. , Jansen M.
Published: July 2002

High power, 0.81-μm-emitting, semiconductor diode lasers are used as pump sources for Nd:YAG solid-state lasers. Devices (1-mm-long) consisting of a InGaAsP/In0.5(Ga0.9Al0.1)0.5P/In0.5(Ga0.5Al0.5)0.5P laser structure provide a threshold-current density, Jth, of 290 A/cm2 and a relatively high threshold-current characteristic temperature, T0 (140 K). Uncoated diode lasers (1.2-mm-long) have a maximum continuous wave output power of 5 W (both facets) at 20 °C. The internal power density at catastrophic optical mirror damage (COMD), P̄COMD, is determined to be 9.1 MW/cm2; that is, 1.8 times that for GaAs-active layer, Al-free, uncoated devices. Coated, InGaAsP-active devices are expected to have P̄COMD=18 MW/cm2, more than twice the P̄COMD of AlGaAs-active, 0.81-μm-emitting devices with the same emitting aperture. Therefore, 0.81-μm-emitting, InGaAsP-active diode lasers should operate reliably at powers at least twice those of AlGaAs-based devices with the same contact-stripe geometry.
A positive temperature coefficient of resistivity effect from a paraelectric Pt/(Ba0.5,Sr0.5)TiO3/IrO2 thin-film capacitor
Authors: Hwang Cheol Seong , Lee Byoung Taek , Cho Hag-Ju , Lee Ki Hoon , Kang Chang Seok , Hideki Horii , Lee Sang In , Lee Moon Yong
Published: July 2002

A (Ba0.5,Sr0.5)TiO3 (BST) thin film was deposited on IrO2 thin-film electrode by a rf magnetron sputtering method. Top Pt electrode was deposited on the BST film to make a planar structured capacitor. The BST thin film showed paraelectric behavior at room temperature. A positive temperature coefficient of resistivity (PTCR) effect was observed when the conduction electrons were injected from the IrO2 electrode to BST, while Schottky emission behavior was observed when they were injected from the Pt electrode to BST. The electrical double layer formed at the Pt/BST interface results in the PTCR effect. A model that can explain the asymmetrical conduction behavior with respect to the bias polarity is suggested based on the energy band configurations at the interfaces with the electrodes.
Electron-wave interference effects in a Ga1−xAlxAs single-barrier structure measured by ballistic electron emission spectroscopy
Authors: Guthrie D. K. , First P. N. , Gaylord T. K. , Glytsis E. N. , Leibenguth R. E.
Published: July 2002

Ballistic electron emission spectroscopy (BEES) has been performed on a GaAs/Ga0.8Al0.2As/GaAs single-barrier structure at 77 and 7 K. The single-interface model widely used for such structures was found to be inadequate in describing the BEES second-derivative spectrum. A more complete model that incorporates electron-wave interference effects is shown to describe the data accurately and consistently over many spatial locations and samples. This model reproduces all measured features in the BEES second-derivative spectrum resulting from electron-wave interference. At 77 K (7 K) the conduction band offset for x=0.2 is determined to be 145 meV or Qc=0.58 (150 meV or Qc=0.60) in agreement with accepted values.
High power mid-infrared interband cascade lasers based on type-II quantum wells
Authors: Yang Rui Q. , Yang B. H. , Zhang D. , Lin C.-H. , Murry S. J. , Wu H. , Pei S. S.
Published: July 2002

We report a high power mid-infrared interband cascade laser operating at temperatures up to 170 K. The threshold current densities of this laser are considerably lower than the previously reported values in cascade lasers. The structure was grown by molecular beam epitaxy on a GaSb substrate and comprises 23 periods of active regions separated by digitally graded multilayer injection regions. A peak optical output power of ∼0.5 W/facet and a slope of 211 mW/A per facet, corresponding to a differential external quantum efficiency of 131%, are observed at 80 K and at a wavelength of ∼3.9 μm.
High power InAsSb/InPAsSb/InAs mid-infrared lasers
Authors: Rybaltowski A. , Xiao Y. , Wu D. , Lane B. , Yi H. , Feng H. , Diaz J. , Razeghi M.
Published: July 2002

We demonstrate high-power InAsSb/InPAsSb laser bars (λ≈3.2 μm) consisting of three 100-μm-wide laser stripes of 700 μm cavity length, with peak output power up to 3 W at 90 K, and far-fields for the direction perpendicular to the junction as narrow as 12° full width half maximum. Spectra and far-field patterns of the laser bars are shown to have excellent characteristics for a wide range of operating conditions, suggesting the possibility of even higher light power emission with good beam quality. Joule heating is shown to be the major factor limiting higher power operation.
Effects of coupling and nonresonant tunneling on Coulomb blockade oscillations in an asymmetric double dot structure
Authors: Wang T. H. , Tarucha S.
Published: July 2002

We report on single electron transport through an asymmetric double dot structure with well-defined dot potential profiles. As the two dots are coupled, the conductance exhibits two pronounced types of Coulomb blockade oscillations. An analysis of the small short-period oscillations indicates the presence of interdot interaction. When the coupling strength is reduced, the oscillations become few irregular peaks but they develop into periodic oscillations again as the drain voltage is increased to 0.6 mV. This appearance with increasing drain voltage is well explained by our model which is based on the stochastic Coulomb blockade model and nonresonant tunneling.