bluuebunny/crossref_metadata_2025 huggingface dataset:
Epitaxial electrodeposition of CdTe films on InP from aqueous solutions: Role of a chemically deposited CdS intermediate layer
Authors: Lincot D. , Kampmann A. , Mokili B. , Vedel J. , Cortes R. , Froment M.
Published: July 2002

Epitaxial (111) CdTe films have been grown on (1̄ 1̄ 1̄) InP single crystals by one step electrodeposition in aqueous acidic solution, at a temperature of 85 °C, and a growth rate of about 0.7 μm h−1. Reflexion high-energy electron diffraction and five-circle x-ray diffraction techniques have been used to characterize the interface structure and epitaxial quality. The epitaxy of CdTe (fcc a=6.49 Å) takes place with a direct continuation of the InP lattice (fcc a=5.87 Å), with no rotation of the respective crystallographic directions. The epitaxy is markedly improved when the InP substrate is covered with a thin film (20–30 nm) of epitaxial CdS grown by chemical bath deposition which acts as an interfacial buffer layer.
Microwave compatible YBa2Cu3O7−x films on ferrimagnetic garnet substrates
Authors: Piqué A. , Harshavardhan K. S. , Moses J. , Mathur M. , Belohoubek E. , Venkatesan T. , Denlinger E. J. , Kalokitis D. , Fathy A. , Pendrick V. , Rajeswari M. , Jiang Wu
Published: July 2002

High quality epitaxial YBa2Cu3O7−x (YBCO) thin films have been deposited onto ferrimagnetic yttrium iron garnet (100) substrates using a double buffer layer lattice engineering scheme. The YBCO films are c-axis oriented and show superconductive transition temperatures of 88–89 K with transition widths ≤0.5 K. The films also exhibited Jc’s of 2.7×106 A/cm2 in zero field and 1.1 ×106 A/cm2 in 2000 G at 77 K. Dielectric resonator measurements indicated unloaded Q values of 29 000 at 77 K and 24 GHz for unpatterned films. These values correspond to a surface resistance (RS) of 500 μΩ at 77 K, 10 GHz, which is the lowest obtained to date for a YBCO film on a ferrimagnetic substrate. Such films could be used for fabricating miniature-high-temperature superconducting microwave elements such as nonreciprocal and passive microwave devices, making possible, their integration on a single ferrimagnetic wafer.
Design of a detection coil system for a biaxial vibrating sample magnetometer and some applications
Authors: Bernards J. P. C.
Published: July 2002

A theoretical expression for the sensitivity of a detection coil for a vibrating sample magnetometer (VSM) is derived. This expression is used to design a detection coil system for a biaxial VSM for measuring the magnetization components in the direction of the applied field (x direction) and perpendicular to the applied field (y direction). This detection coil system is optimized with respect to the sensitivity, cross talk, and their position dependences. Both an eight-coil detection system and a 12-coil detection system are described. With the eight-coil detection system, experiments have been performed showing that, in an electromagnet VSM, images contribute significantly to the measured signals. The 12-coil configuration has the lowest position dependences and cross talk. An example shows that the average position dependences in the xy plane can be five times better compared to the eight-coil configuration with comparable sensitivities. For both detection directions the signal varies less than 1% within a circle in the xy plane with a radius of 3 mm. For a displacement in the z direction and detection in the x direction the position dependence is larger (about 2% for a displacement of 3 mm). Finally, some examples demonstrate the usefulness of a biaxial VSM for the magnetic characterization of recording materials.
Computer simulation for a large-field electron-beam-reducing image projector
Authors: Nakasuji Mamoru , Suzuki Syouhei , Shimizu Hiroyasu
Published: July 2002

Computer simulation is used to optimize the design of a large-field electron image projector system. Aberrations from mask to target are smaller than 0.02 μm in distortion and 0.12 μm in beam resolution for a 27×27 mm2 field size, 3:1 reduction system, with a 4-m optical path distance. The lenses are given nonuniform bores. The bottom of mask-side lens and the top of wafer-side lens are reduced in diameter to 1/4 of the other bore diameters. The axial direction tolerance for lenses, mask, and target positions is found to be much larger than errors that are anticipated to occur during assembly. The reduction factor can be adjusted to the value designed by adjusting lens positions or mask and target positions, and can be adjusted for the wafer linear distortion through adjusting the lens current ratio of two lenses. We have identified, but not solved, two remaining problems in the lithography system. One is the large emittance electron gun and the other is a condenser lenses spherical aberration.
An angle-resolved translational energy spectrometer for investigating low-energy, highly charged ion–atom (molecule) collisions
Authors: Vancura J. , Perotti J. J. , Flidr J. , Kostroun V. O.
Published: July 2002

An experimental apparatus for investigating low-collision energy gas-phase reactions of highly charged ions with atoms and molecules by angle-resolved translational energy spectroscopy is described. The basic function of the apparatus is to slow down highly charged ions extracted at 2–3 kV from the Cornell superconducting solenoid, cryogenic electron beam ion source (CEBIS) to energies below 100 qeV. The slowing down and monochromatization of the beam is done by an ion optical system that consists of two 180° hemispherical electrostatic analyzers with a tuneable deceleration lens located between them. The low-energy beam available for experiments has an angular spread of 0.5° and an energy spread of 0.4 qeV. The ion optical system is mounted on a 508 mm by 576 mm electrically isolated platform inside a large vacuum chamber, and the modular nature of the apparatus allows for quick and easy rearrangement of the ion optical elements for different experiments. A brief overview of in-plane scattering kinematics is given.
Dominant mechanisms for the temperature sensitivity of 1.3 μm InP-based strained-layer multiple-quantum-well lasers
Authors: Seki Shunji , Oohasi Hiromi , Sugiura Hideo , Hirono Takuo , Yokoyama Kiyoyuki
Published: July 2002

We study the dominant mechanism for the temperature sensitivity of the differential quantum efficiency and threshold current of 1.3 μm InP-based strained-layer multiple-quantum-well (MQW) lasers. We show that the temperature dependence of both properties is separated into two regions at critical temperature c). Below c, the temperature dependence of internal loss in the QWs plays a very important role in determining the temperature sensitivity of the differential quantum efficiency. On the other hand, above c, its temperature sensitivity is affected more by the internal loss in the separate confinement heterostructure (SCH) region. Excellent correlation is observed between the spillover of holes into the SCH region and c. It is also shown that the Auger recombination current plays a more significant role in determining the temperature dependence of threshold current below c. However, above c, electrostatic band-profile deformation, which causes a significant increase in loss and radiative recombination current in the SCH region, plays the more dominant role than the Auger recombination current.
New diffractometer for thin-film structure analysis under grazing incidence condition
Authors: Horii Yoshimasa , Tomita Hirofumi , Komiya Satoshi
Published: July 2002

We designed and constructed a new x-ray diffractometer under grazing incidence condition. This diffractometer is mainly composed of two goniometers; (1) a goniometer for grazing incidence angle control and (2) a goniometer for a sample rotation. The axes of the goniometers are orthogonal to each other. Furthermore, a detector moves parallel and vertical to the sample surface. Therefore, lattice constants of vertical and parallel components can be identified. We will describe components and accuracy of our designed diffractometer for grazing incidence x-ray diffraction and show applications for TiSi2 (several 10 nm thickness) and GaAs (20 monolayer) on Si.
Growth and characterization studies of Fe4N thin films prepared by ion beam assisted evaporation
Authors: Chatbi H. , Vergnat M. , Bauer Ph. , Marchal G.
Published: July 2002

Thin films of iron nitrides have been prepared using an ion beam assisted evaporation method. X-ray diffraction and Mössbauer spectrometry show that the films generally consist in a mixture of Fe and Fe4N phases. For high source powers and temperatures higher than 300 °C it was possible to obtain the pure Fe4N phase.
A new multidimensional diagnostic method for measuring the properties of intense ion beams
Authors: Yasuike Kazuhito , Miyamoto Shuji , Nakai Sadao
Published: July 2002

A new arrayed pinhole camera (APC) diagnostic method for intense ion beams has been developed. The APC diagnostic technique permits the acquisition of the angular divergences and the ion fluxes of high intensity ion beams, in one shot, with a spatial resolution on the source of better than 1 mm and an effective angular divergence resolution of better than 10 mrad. A prototype time integrated APC has been designed and evaluated. The demonstration experiments have been performed on a Reiden-IV, 1 MV and 1 Ω pulsed power machine [1 T W (tera-watt or trillion watts)]. Proton beams of 0.7 MeV, with a pulse duration of ∼50 ns and an ion current density of about 100 A/cm2, were generated in an applied-Br type ion diode source using paraffin-filled grooves. These experimental results show that the APC can measure nonuniformities in the ion beam intensity generated from the ion source and the dependence of beam angular divergence on ion beam intensity.
High resolution x-ray absorption spectroscopy with absolute energy calibration for the determination of absorption edge energies
Authors: Kraft S. , Stümpel J. , Becker P. , Kuetgens U.
Published: July 2002

The general characteristics and spectrometric features of a high resolution four-crystal reflection x-ray monochromator with wavelength analysis installed at the HASYLAB beam line L at DESY are presented. The monochromator is part of a spectrometer developed to calibrate x-ray absorption edge spectra in the energy range of 6–36 keV with a relative uncertainty ΔE/E from 10−5 to 10−6. This requires an extremely effective suppression of harmonics and also a negligible instrumental influence in order to obtain almost intrinsic spectra. As the results show, the monochromator fulfills the requirements, including very high stability. An example of the calibration procedure for the copper K edge is given as well as a comparison of the remeasured absorption edge energies with the previously tabulated data.
Quantitative analysis of lateral force microscopy experiments
Authors: Schwarz U. D. , Köster P. , Wiesendanger R.
Published: July 2002

The analysis of lateral force microscopy experiments is discussed with emphasis on calibration issues and the statistical treatment of the original data in order to obtain reliable quantitative results. This includes an extensive discussion about the statistical and systematical errors which have to be considered if experimental results obtained under different experimental conditions (such as different cantilevers, samples, humidities, with or without lubricant, etc.) have to be compared. The proposed data analysis procedure is exemplified using data acquired on germanium sulfide and highly oriented pyrolytic graphite.
532 nm pumped optical parametric oscillator in bulk periodically poled lithium niobate
Authors: Pruneri V. , Webjörn J. , Russell P. St. J. , Hanna D. C.
Published: July 2002

We report a quasi-phase-matched optical parametric oscillator (OPO) pumped by the second harmonic of a single frequency Q-switched Nd:YAG laser. Both the frequency doubling to 532 nm and the parametric oscillation are performed in periodically poled lithium niobate crystals with a nonlinearity of ∼15 pm/V. The OPO has been operated in ‘‘singly resonant’’ and ‘‘doubly resonant’’ configurations. The threshold in the singly resonant case was ∼0.14 J/cm2, more than one order of magnitude below the damage limit. OPO tuning from 945 to 1225 nm was achieved by changing both the period of domain reversal (from 6.8 to 6.85 μm) and the temperature of the crystal.
Simultaneous measurements of heat capacity and spin-lattice relaxation time in high magnetic field at low temperature
Authors: Andraka B. , Takano Y.
Published: July 2002

We propose a method to measure heat capacities at low temperature and in high magnetic field. The method is based on an improved version of the thermal relaxation technique and can also be used to measure the nuclear spin-lattice relaxation time T1 and the nuclear heat capacity. As an example, we present the results of an experiment that measured the electronic heat capacity and T1 of pure copper at temperatures below 1 K in a 10 T field.
Surface-mode stimulated emission from optically pumped GaInN at room temperature
Authors: Kim S. T. , Amano H. , Akasaki I.
Published: July 2002

In this letter, we report the surface-mode stimulated emission from optically pumped Ga0.11In0.89N at room temperature. The GaInN was deposited on the intermediate layer of GaN grown on the AlN buffer layer over sapphire substrate using horizontal metalorganic vapor phase epitaxy method. The peak wavelength and the full width at half-maximum of surface-mode stimulated emission was 406 nm and 25.6 meV, respectively, and the threshold of excitation power density was about 0.52 MW/cm2.
A high current, battery-operated power supply with power control through an on–off fast switch
Authors: Reschiglian P. , Valcher S. , Locatelli C. , Rossi F. N. , Melucci D. , Torsi G.
Published: July 2002

A simple high current power supply is described. It can be assembled from readily available and relatively cheap components which can be itemized as follows: (1) commercial batteries; (2) fast high current switch; (3) feedback sensor; (4) PC with peripherals for controlling the switch. The apparatus was assembled for heating at very high heating rate with a low resistant load such as a graphite or vitreous carbon tube used as an atomizer in electrothermal atomization-atomic absorption spectroscopy measurements. The high heating rate must, however, be combined with a fairly good control of the temperature of the tube at various levels. This was obtained with a PC and relative peripherals which, directly or through a feedback circuit, control the switch. The system can be easily modified and adapted for other kinds of measurements as long as the high noise of the switching does not interfere with signal recovery. With the atomic spectrometer used (Perkin–Elmer Model 1100B), however, no worsening of the signal noise was observed. The level of current that can be used is mainly determined by the switch since, within a certain range, the voltage and the internal resistance of the power supply can be changed by the type of batteries and the way they are connected.
Epitaxial silicon growth using supersonic jets of disilane: A model study of energetic jet deposition
Authors: Pacheco K. A. , Ferguson B. A. , Li C. , John S. , Banerjee S. , Mullins C. B.
Published: July 2002

High (2 eV) and low kinetic energy supersonic jets of disilane as well as ultrahigh vacuum chemical vapor deposition have been employed to grow epitaxial silicon thin films on Si(100) wafers at temperatures ranging from 500 to 650 °C. The growth properties and film uniformity are compared in order to characterize the high energy technique. High translational energy disilane supersonic jets increase the efficiency of deposition by increasing the disilane reaction probability. The growth profiles from the high energy jet are sharply peaked due to a focusing of the precursor along the jet centerline.
Enhanced local surface conductivity measurements by scanning tunneling microscopy
Authors: Müller F. , Müller A.-D. , Meissner O. , Heilmann A. , Hietschold M.
Published: July 2002

A scanning tunneling microscope with a completely digital control is described which is able to determine in addition to the sample topography the local reactance of the surface by using a mathematical procedure. The new types of information allow a more detailed discussion of surface properties. The measurements were carried out at gold films on silicon wafers. On a plasma polymer gold composite surface typical reactance differences will be demonstrated.
Optical interferometric signal generator based on electrical phase-locked loop technique
Authors: Chang Lih-Wuu , Lee Ching-Ting , Chien Pie-Yau
Published: July 2002

To simulate a phase-modulated interferometer, a novel electrical signal generator has been demonstrated. There are two phase-locked loop (PLL) circuits used in our system to process the phase signal. The first PLL is adopted as a voltage-controlled phase shifter, and the second PLL is used to amplify the phase signal to get a phase shift with a dynamic range over ±16π rad. This system can be further modulated with sinusoidal, sawtooth, and triangular wave forms for interferometric signal detection.
Photomodulated thermoreflectance detection of hydrogen gas using optically thin palladium film on silicon oxide
Authors: Kalli K. , Othonos A. , Christofides C. , Spetz A. , Lundström I.
Published: July 2002

The sensitivity of various thicknesses of optically thin film palladium layers evaporated onto silicon oxide substrate is investigated in the presence of a hydrogen/air atmosphere at room temperature. The magnitude of the resulting reflectivity change is measured using an excite-probe technique, through laser excited photothermal modulation of a probe beam. This allows for the recovery of information from both the amplitude and phase channels of the hydrogen sensor output. Data indicates that concentrations of 0.1% hydrogen in the presence of a balanced air mixture and at room temperature may be measured with an 8 nm palladium film. The presence of inhomogeneities in the palladium layers leads to anomalous behavior.
Properties of extraordinary mode interferometry for plasma density measurements
Authors: Ejiri A. , Kawahata K. , Okajima S.
Published: July 2002

Extraordinary mode interferometry with the frequency lower than the electron cyclotron frequency has been applied to the core plasma of the JIPP TII-U tokamak. The system is operated as a reflectometer when the density exceeds the cutoff for the extraordinary mode. The measured fringe shift is in good agreement with the calculated fringe shift using the density profile obtained by a six-chord HCN laser interferometer. Advantages and disadvantages of extraordinary mode interferometry are shown numerically and experimentally. To overcome the disadvantages, a dual (ordinary and extraordinary) mode interferometer is proposed as a divertor diagnostic. There are two attractive choices for this scheme. One choice double the operational density range but does not compensate for changes in the length of the transmission line. The other can compensate for transmission line changes, but with a density range limited by the O-mode cutoff.
Si1−xGex/Si asymmetric 2×2 electro-optical switch of total internal reflection type
Authors: Gao Yong , Liu Xiding , Li Guozheng , Liu Enke , Zhang Xiangjiu , Lu Xuekun , Hu Jihuang , Wang Xun
Published: July 2002

Based on plasma dispersion of Si1−xGex, we have fabricated asymmetric 2×2 switches of total internal reflection type, in which Si1−xGex was grown by molecular beam epitaxy. The optimum intersecting angle is 4°, and the crosstalk is less than −10.6 dB at 76 mA injection current. The insertion loss is 2.8 dB, and the switch time is 0.6 μs.
Visible-spectrum (λ=650 nm) photopumped (pulsed, 300 K) laser operation of a vertical-cavity AlAs–AlGaAs/InAlP–InGaP quantum well heterostructure utilizing native oxide mirrors
Authors: Ries M. J. , Holonyak N. , Chen E. I. , Maranowski S. A. , Islam M. R. , Holmes A. L. , Dupuis R. D.
Published: July 2002

Data are presented on the 300 K photopumped (pulsed) laser operation of a visible-spectrum (λ=650 nm) AlAs–AlGaAs/InAlP–InGaP quantum-well heterostructure (QWH) crystal that utilizes high-index-contrast AlAs-native-oxide/Al0.6Ga0.4As distributed Bragg reflector mirrors. The mirrors are formed by the lateral oxidation (H2O+N2, 425 °C) of two sets of four ‘‘buried’’ AlAs layers that are separated by Al0.6Ga0.4As. These mirrors, which create a high-Q cavity in the vertical direction, ‘‘sandwich’’ a one-wavelength InAlP–InGaP QW active region, thus forming a compact microcavity that ‘‘tunes’’ the carrier scattering and recombination into a narrow spectrum (∼25 Å) and supports laser operation in the vertical direction.
A high-field/high-frequency heterodyne induction-mode electron paramagnetic resonance spectrometer operating at 360 GHz
Authors: Fuchs Martin R. , Prisner Thomas F. , Möbius Klaus
Published: July 2002

We present design details of and first measurements with a novel continuous wave (cw) high-field/high-frequency electron paramagnetic resonance spectrometer operating at a microwave frequency of 360 GHz and a magnetic field of up to 14 T. The spectrometer design incorporates a heterodyne mixer detection scheme with a quasi-optical transmission line and a bimodal induction mode Fabry–Perot cavity. First cw experiments on polycrystalline 1,1-diphenyl-2-picryl-hydrazyl and bisdiphenylene-β-phenylallyl benzolate in polystyrene at room temperature and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl in frozen solution at 190 K demonstrate the high Zeeman resolution achievable and allow an estimate of the present detection sensitivity of 4×109 spins/G at a detection bandwidth of 1 Hz.
Two new all-organic complexes with electrical bistable states
Authors: Xu W. , Chen G. R. , Li R. J. , Hua Z. Y.
Published: July 2002

Two all-organic complexes, MC+TCNQ and BBDN+TCNQ, with electrical bistable states at room temperature have been discovered. The resistivity of these thin films prepared in vacuum can be transferred from high to low under a voltage of few volts. The transition time is <100 ns. Therefore, both materials are suitable for making write-once read-only memories.
Radiative recombination in near-surface strained Si1−xGex/Si quantum wells
Authors: Fukatsu S. , Akiyama H. , Shiraki Y. , Sakaki H.
Published: July 2002

Influence of the surface on the radiative recombination is studied in near-surface (NS) strained Si1−xGex/Si quantum wells (QWs). The luminescence intensity of NSQWs is clearly diminished as the Si cap thickness decreases due to carrier capture to the surface. However, the luminescence diminution discloses a saturable behavior with increasing excitation density. Time-resolved measurements reveal selective electron capture to surface traps as being the controlling process in the luminescence attenuation, and there is no signature of quantum mechanical hole tunneling to the surface. Results of potential-biased luminescence lend further support to the electron-controlled picture of the luminescence attenuation in Si-based near-surface geometry.
Characterization of buried thin films with resonant soft x-ray fluorescence
Authors: Carlisle J. A. , Terminello L. J. , Hudson E. A. , Perera R. C. C. , Underwood J. H. , Callcott T. A. , Jia J. J. , Ederer D. L. , Himpsel F. J. , Samant M. G.
Published: July 2002

The geometric and electronic structure of a buried monolayer of boron nitride (BN) has been probed using resonant soft x-ray fluorescence (SXF). By using the strong π* resonance feature in the resonant fluorescence spectrum near the B (1s) threshold, we were able to detect the BN thin film and examine changes in its electronic structure when the monolayer is placed between different materials. Our results demonstrate the capability of the resonant SXF technique for probing the element-specific electronic structure of a buried thin film nondestructively.
Effect of encapsulant material on the diffusion of beryllium in molecular beam epitaxy gallium arsenide
Authors: Haddara Yaser M. , Deal Michael D. , Bravman John C.
Published: July 2002

Experiments were done that illustrate the role of the wafer surface in the transient diffusion of Be in GaAs. Samples were doped during molecular beam epitaxial growth and annealed at 900 °C for 15 min and 2 h under two different caps. In some of the annealed samples, the dopant was initially located near the surface. Other samples had the dopant initially located in a buried layer. Both types of samples were analyzed by secondary ion mass spectrometry measurement. The variations in the diffusion behavior for these different experimental conditions can all be qualitatively explained by a model which accounts for three important effects: the transient evolution of point defect populations; the injection of Ga vacancies by an oxide cap; and the efficiency of the surface in restoring point defect equilibria.
Lateral structuring of III-V quantum well systems with pulsed-laser-induced transient thermal gratings
Authors: Kelly M. K. , Nebel C. E. , Stutzmann M. , Böhm G.
Published: July 2002

A two-dimensional quantum well structure grown by molecular beam epitaxy has been laterally structured with an interference pattern from a high-energy pulsed laser. The resulting thermal grating produces a reduction in the carrier density, which causes a lateral modulation in the band levels, with a period of 380 nm. Photoluminescence spectroscopy has been used for characterization.
Room-temperature photoenhanced wet etching of GaN
Authors: Minsky M. S. , White M. , Hu E. L.
Published: July 2002

Laser-enhanced, room-temperature wet etching of GaN using either dilute HCl:H2O (1:10) or 45% KOH:H2O(1:3) is reported. Etch rates of a few hundred Å/min (HCl) and up to a few thousand Å/min (KOH) have been measured for unintentionally doped n-type films of thickness (1–2 μm) grown by MOCVD on a sapphire substrate. The etching is thought to take place photoelectrochemically with holes and electrons generated by incident illumination from 4.5 mW of HeCd laser power enhancing the oxidation and reduction reactions in an electrochemical cell.
Superconducting quantum interference devices based on YBaCuO nanobridges
Authors: Pedyash M. V. , Blank D. H. A. , Rogalla H.
Published: July 2002

Direct current SQUIDs based on YBaCuO thin film nanobridges have been investigated. Critical current densities Jc of the devices are up to 3×106 A/cm2 at T=77 K and show a temperature dependence of (1−T/Tc)1.6±0.1. High values of the voltage-flux modulation are observed (8 μV peak to peak at 77 K, 45 μV at 4.2 K). The temperature dependence of the SQUID modulation is found to be essentially different from the one of the conventional weak link SQUID. We discuss our results by considering degradation of the nanobridge area during structuring, which leads to a transition from SNS to SS′S type junction with decreasing temperature.
High etch rates of SiC in magnetron enhanced SF6 plasmas
Authors: McLane G. F. , Flemish J. R.
Published: July 2002

Magnetron enhanced reactive ion etching of SiC has been investigated in SF6 plasmas. Etch rate was determined as a function of cathode power density (0.1–0.5 W/cm2), pressure (1–5 mTorr), and flow rate (5–15 sccm). The highest SiC etch rates yet reported (450 nm/min) were achieved, at low cathode bias voltage (100 V). Anisotropic etch profiles were obtained with smooth etch surfaces free of micromasking. Addition of O2 to the SF6 feed gas did not increase the etch rate.
Study of a novel C60−2,6-bis(2,2-bicyanovinyl)pyridine complex thin film
Authors: Ouyang M. , Wang K. Z. , Zhang H. X. , Xue Z. Q. , Huang C. H. , Qiang D.
Published: July 2002

A novel complex thin film of 2,6-bis(2,2-bicyanovinyl)pyridine (BDCP) and C60 has been fabricated by vacuum coevaporation of BDCP and C60 from two different evaporation sources. The C60-BDCP thin films have shown totally different optical and electronic properties from the films of both the BDCP and C60. Stable and reproducible electric bistable properties have been observed in sandwichlike device Ag/C60-BDCP/Ag. The films are characterized by several methods including high-resolution scanning electron microscopy, x-ray diffraction, UV-visible absorption and infrared transmission spectroscopy.
Temperature dependence of the threshold current in gain-coupled distributed feedback lasers with periodically etched quantum wells: Mechanism for an appearance of infinite T
Authors: Makino T. , Lu H. , Evans J. D.
Published: July 2002

A phenomenological model describing the temperature dependence of the threshold current of 1.3 μm gain-coupled distributed feedback (DFB) lasers with periodically etched strained-layer quantum wells is presented and compared to experimental results. The model can predict the minimum threshold current as a function of temperature (infinite T0), which has been observed experimentally. The mechanism for the appearance of this minimum is explained by the decrease of the detuning of the DFB-mode wavelength from the material gain-peak wavelength as the temperature increases. The condition for single-mode operation is also discussed with use of the effective gain of DFB laser structures.
Enhanced microhardness in Zr65.0Al7.5Ni10.0Cu17.5 amorphous rods on coprecipitation of nanocrystallites through supersaturated intermediate solid phase particles
Authors: Frankwicz P. S. , Ram S. , Fecht H.-J.
Published: July 2002

Amorphous rods of 4 mm diameter of Zr65.0Al7.5Ni10.0Cu17.5 crystallize in a very fine microstructure, with an average size of the crystallites of 19 nm, on an isochronal heating over 655–860 K for a short period of 300 s. The multiple primary crystallization occurs with subsequent precipitation transformation of Zr-rich supersaturated tetragonal Ni11Zr9- type (T phase) and cubic NiZr2- type (I phase) phases to a thermally stable three phase mixture of α-Zr (hexagonal), T and I phase finely dispersed one into another. It results in an enhanced microhardness of 6.9 GPa in the crystallized sample in comparison to 4.6 GPa in the amorphous sample, 5.7 GPa in the well-crystallized bulk ingots, or 1.75 GPa or lower in the pure Zr or other elemental starting components. The results are discussed with the refined microstructure and the formalism of the local precipitations of α-Zr nanocrystallites in the locally phase separated microscopic domains of related supersaturated intermediate phases.
AlGaAs/GaAs light-emitting diode on a Si substrate with a self-formed GaAs islands active region grown by droplet epitaxy
Authors: Hasegawa Y. , Egawa T. , Jimbo T. , Umeno M.
Published: July 2002

We report the preliminary results on self-formed GaAs islands grown on the GaAs/Si substrate by metalorganic chemical vapor deposition using droplet epitaxy. Atomic force microscope observation shows that the GaAs islands exhibit a conical shape with heights of 90–170 nm, diameters of 600–750 nm, and densities of 107 cm−2, which are controlled by the trimethylgallium flow rate. In addition, an AlGaAs/GaAs light-emitting diode (LED) on Si with a self-formed GaAs island active region was fabricated by the use of this technique. The LED was operated up to 27 μW at 190 mA under direct current conditions at room temperature.
Spectral effects in short pulse pump-probe measurements
Authors: Mo/rk J. , Mecozzi A. , Hultgren C.
Published: July 2002

Spectral effects arising from linear gain dispersion are shown to strongly influence the ultrafast gain dynamics measured in active semiconductor waveguides using the pump-and-probe technique. Measurements on a AlGaAs amplifier under varying amounts of gain dispersion are in good agreement with a simple analytical theory derived from semiclassical density matrix equations.
Large non-biased all-optical bistability in an electroabsorption modulator using p-i-n-i-p diode and asymmetric Fabry–Perot cavity structure
Authors: Kwon O. K. , Kim K. , Hyun K. S. , Baek J. H. , Lee B. , Lee E. H.
Published: July 2002

We have constructed a non-biased all-optical bistable device using electroabsorption in multiple quantum wells (MQWs). The device is made of a serial connection of two identical double p-i-n (p-i-n-i-p) diode structures within asymmetric Fabry–Perot (AFP) cavity. This scheme ensures both large internal electric field swing and full exploitation of the light intensity. From the measurement of the diode properties, the non-biased bistability parameters—reflection change of 19%, contrast ratio of 17:1, and bistable loop width of 70%—were obtained.
The onset of secondary phase precipitation during synthesis of heteroepitaxial Si1−x−yGexCy on Si(100)
Authors: Herbots Nicole , Ye Peihua , Jacobsson Harald , Xiang Joan , Hearne Sean , Cave Nigel
Published: July 2002

An upper temperature limit of 450 °C has been established for growth of heteroepitaxial Si1−x−yGexCy solid solutions with substitutional C on Si(100) by combined ion and molecular beam deposition (CIMD). At 450 °C infrared absorption spectroscopy shows that C is on substitutional sites and no SiC precipitates are detected, whereas at 560 °C the substitutional C signal is much smaller but SiC precipitates are still not detected. High resolution transmission electron microscopy shows that Si1−x−yGexCy films deposited at 560 °C exhibit Ge deficient, coherent, secondary phase clusters in the cubic diamond matrix, which are not seen in films deposited at 450 °C. These observations suggest that the clusters are C-rich, Ge-deficient precursors to SiC, with a lattice which is distorted but free of extended defects. Ion channeling results indicate that the Si1−x−yGexCy films might have a distribution of different bond lengths.
Space-charge-limited currents in nonstoichiometric GaAs
Authors: Ibbetson J. P. , Mishra U. K.
Published: July 2002

A study of space-charge-limited transport in nonstoichiometric (NS) GaAs is presented. The NS-GaAs was grown at 250 °C by molecular beam epitaxy and subsequently annealed at 700 °C so that the room-temperature low-field conductivity is due almost entirely to electrons thermally excited to the conduction band from deep traps. Experimental current–voltage characteristics of an n+ GaAs/NS-GaAs homojunction structure display an unusual current saturation whose onset occurs at an electric field of ∼5 kV/cm. We argue that this behavior is due to a combination of electron velocity saturation and the high concentration of compensated traps in annealed NS-GaAs.
Low temperature selective silicon epitaxy by ultra high vacuum rapid thermal chemical vapor deposition using Si2H6, H2 and Cl2
Authors: Violette Katherine E. , O’Neil Patricia A. , Öztürk Mehmet C. , Christensen Kim , Maher Dennis M.
Published: July 2002

We present the use of the Si2H6/H2/CL2 chemistry for selective silicon epitaxy by rapid thermal chemical vapor deposition (RTCVD). The experiments were carried out in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor. Epitaxial layers were grown selectively with growth rates above 150 nm/min at 800 °C and 24 mTorr using 10% Si2H6 and H2 and Cl2 with a minimum Si:Cl ratio of 1. Excellent selectivity with respect to SiO2 and Si3N4 was obtained indicating that very low Cl2 partial pressures are sufficient to preserve selectivity. In situ doping results with B2H6 show that sharp doping transitions and a wide range of B concentrations can be obtained with a slight B incorporation rate reduction with Cl2 addition. Our results indicate that UHV-RTCVD with the Si2H6/H2/Cl2 chemistry yields highly selective Si epitaxy with growth rates well within the practical throughput limits of single wafer manufacturing and with a potential to reduce the Cl content below the levels used in conventional SiH2Cl2 based selective epitaxy processes.
Resonance oscillations of a permanent magnet levitated above granular superconductors
Authors: Kordyuk A. A. , Nemoshkalenko V. V.
Published: July 2002

We have studied the interaction of alternating magnetic fields with granular high temperature superconductors (HTSC) with a magnetization distribution in the HTSC volume. The expressions for resonance frequencies of a permanent magnet levitated above a HTSC sample were found for five oscillation modes. An original method for determination of the superconducting grains’ volume fraction is proposed.
Broad wavelength tunability of grating-coupled external cavity midinfrared semiconductor lasers
Authors: Le H. Q. , Turner G. W. , Ochoa J. R. , Manfra M. J. , Cook C. C. , Zhang Y.-H.
Published: July 2002

Midinfrared InAs-based and GaSb-based semiconductor lasers with wavelengths from 3.3 to 4 μm have been used in a grating-tuned external cavity configuration. At 80 K, a tuning range up to ∼8% of the center wavelength has been obtained. Power of 0.2 W peak, 20 mW average has been demonstrated for multimode operation with ∼1–2 nm linewidth.
Suppression of wavy growth in metalorganic vapor phase epitaxy grown GaInAs/InP superlattices
Authors: Bangert U. , Harvey A. J. , Dieker C. , Hardtdegen H.
Published: July 2002

The effects of growth temperature, V–III partial pressure ratio in the gas phase, and the nature of the carrier gas on the morphology of lattice matched InGaAs/InP multiple quantum well stacks are investigated. Preliminary results of an extension of this study to strained InGaAs/InP systems are presented.
Direct observation of hydrogen-related luminescent states in subsurface region of homoepitaxial diamond films
Authors: Hayashi Kazushi , Watanabe Hideyuki , Yamanaka Sadanori , Okushi Hideyo , Kajimura Koji , Sekiguchi Takashi
Published: July 2002

We found hydrogen-related luminescence in the subsurface region of chemical vapor deposited homoepitaxial diamond films by means of cathodoluminescence. A specific broad peak at around 540 nm is observed in the hydrogenated films, but not in the conventional oxidized films. The gap states related to the peak observed at around 540 nm are found to exist spatially in the surface region. The fact is consistent with the hydrogen distribution previously determined by secondary ion mass spectroscopy. The result indicates the existence of hydrogen-related luminescent states in the subsurface region of as-deposited homoepitaxial diamond films.
InAs channel heterostructure-field effect transistors with InAs/AlSb short-period superlattice barriers
Authors: Bolognesi C. R. , Bryce J. E. , Chow D. H.
Published: July 2002

We report on the implementation of InAs-channel heterostructure-field-effect transistors (HFETs) fabricated with InAs/AlSb short-period superlattice barriers. The InAs/AlSb superlattice barrier structure is advantageous for InAs/AlSb HFETs because of its improved chemical stability against oxidation when compared to pure AlSb, and its compatibility with silicon as an n-type dopant during growth by molecular beam epitaxy. The structures examined here consist of a 200-Å-wide InAs quantum well inserted between 25/25 Å InAs/AlSb superlattice barriers that provide a 0.5 eV conduction band discontinuity between the quantum well and the superlattice barrier. Fabricated HFET devices display complete channel modulation, confirming the field-effect operation at room temperature. In addition, we demonstrate the modulation doping of an InAs quantum well clad by silicon-doped InAs/AlSb superlattice barriers.
Dissociative and selective adsorption of H2S on the GaAs(001)-(4×2) surface
Authors: Chung Chan-Hwa , Yi Sang I. , Henry Weinberg W.
Published: July 2002

The adsorption of H2S on the GaAs(001)-(4×2) surface has been studied using high-resolution electron energy loss spectroscopy and temperature-programmed desorption. The H2S adsorption is predominantly dissociative at 100 K, producing mercaptan (HS-) and H- species, the latter of which are bonded only to As. After annealing to 700 K, vacant gallium sites, which are available for further sulfur chemisorption, are monitored by post-exposure of atomic hydrogen. Several cycles of H2S exposure and thermal annealing build up more S-Ga bonding on the surface and yield a completely sulfur-saturated layer on which only sulfur is available for post-hydrogenation.
Meyer–Neldel behavior of deep level parameters in heterojunctions to Cu(In,Ga)(S,Se)2
Authors: Herberholz R. , Walter T. , Müller C. , Friedlmeier T. , Schock H. W. , Saad M. , Lux-Steiner M. Ch. , Alberts V.
Published: July 2002

Admittance spectroscopy was measured on Cu(In,Ga)(S,Se)2 thin film and single crystal heterojunctions. The emission rates of defects for various near-stoichiometric compositions follow a Meyer–Neldel rule, showing increasing attempt-to-escape frequencies with increasing defect depth. Defects in highly (In,Ga)-rich material showed lower attempt-to-escape frequencies and follow a separate Meyer–Neldel relation. Repetitive air annealing of a CuInSe2 heterojunction revealed a shift of the depth and capture cross section of an observed defect.
Rapid relaxation of hot carriers in GaAs fractional-layer superlattice quantum wires
Authors: Chavez-Pirson A. , Ando H. , Saito H. , Kobayashi N. , Kanbe H.
Published: July 2002

We measure the hot carrier relaxation in two GaAs quantum wire arrays made from fractional-layer superlattices (FLS). Using femtosecond optical pump–probe spectroscopy, we measure the differential transmission spectra for various pump–probe time delays from which we determine the carrier thermalization times. Although the two FLS structures have different degrees of one-dimensional confinement at the band edge, we observe rapid (<2 ps) and efficient carrier relaxation in both cases with no sign of the inhibited relaxation predicted for ideal one-dimensional structures. We believe that FLS quantum wire structures avoid relaxation bottlenecks because the shape of the FLS confinement potential produces high energy states which are two dimensional in character and which facilitate rapid energy relaxation.
Elastic characterization of a supported porous silicon layer by Brillouin scattering
Authors: Andrews G. T. , Zuk J. , Kiefte H. , Clouter M. J. , Nossarzewska-Orlowska E.
Published: July 2002

Brillouin spectroscopy was used to study surface acoustic waves on a supported layer of (111)-oriented porous silicon having a thickness of 2.7 μm and a porosity of 30%. The Rayleigh surface wave velocities were found to be significantly lower than corresponding velocities for crystalline silicon. A complete set of elastic constants for the porous layer was determined from the measured directional dependence of the surface wave velocity in the (111) plane. The best-fit constants are C11=56.0±0.7 GPa, C12=6.7±0.3 GPa and C44=37.0±0.8 GPa. The anisotropy factor, η=1.50 indicates that the porous layer is elastically anisotropic.
Observation of folded acoustic phonons in nanocrystalline silicon/amorphous silicon multilayers
Authors: Wu X. L. , Siu G. G. , Stokes M. J. , Tong S. , Yan F. , Liu X. N. , Bao X. M. , Jiang S. S. , Zhang X. K. , Feng D.
Published: July 2002

We report in this letter the observation of folded acoustic phonons in hydrogenated nanocrystalline silicon/amorphous silicon multilayers with visible emission, which are prepared in a plasma enhanced chemical vapor deposition system. In the low-frequency range of 10–100 cm−1, the obtained Raman spectra clearly show some folded doublets from longitudinal acoustic phonons. Using the elastic continuum model, we calculated their frequencies and the obtained results were in agreement with the experimental ones. In addition, some broad folded doublets and additional peaks were clearly observed in the sample with thin nancorystalline sublayers. We attributed them to the mixing of longitudinal and transverse acoustic phonons due to the layered structure. A confined acoustic mode was also proposed to be responsible for the strongly folded longitudinal acoustic phonon peak at 61 cm−1.
Monitoring HgCdTe layer uniformity by the differential absorption technique
Authors: Ariel V. , Garber V. , Bahir G. , Krishnamurthy S. , Sher A.
Published: July 2002

In this letter, we demonstrate how the differential absorption technique can be applied to study band gap uniformity in HgCdTe samples. The transmission of HgCdTe wafers is measured at room temperature and data filtering is used to remove both the interference fringes and high-frequency noise. This data treatment approach produces reliable transmission data for HgCdTe layers as thin as 8 μm. In addition, the spectrum of the interference fringes is used to estimate the HgCdTe layer thickness with an accuracy of ±0.1 μm. The absorption coefficient is differentiated twice with respect to the photon energy and an approximate value of the band gap is estimated from extrema of the derivatives. By applying this procedure to different points on the same HgCdTe wafer, we can determine both lateral and transverse fluctuations of the semiconductor band gap. The initial results indicate that the accuracy of the differential absorption technique is around ±0.5 meV for HgCdTe wafers. The differential absorption technique appears suitable for routine characterization of HgCdTe wafers because it is simple, nondestructive, and applicable at room temperature.
Noncontact probing of metal-oxide-semiconductor inversion layer mobility
Authors: Son Joo-Hiuk , Jeong Seongtae , Bokor Jeffrey
Published: July 2002

We have measured absorption of terahertz radiation pulses by metal-oxide-semiconductor (MOS) inversion layers and thereby determined carrier mobility without the need for source and drain contacts. This has allowed for the determination of inversion layer mobility prior to subsequent high temperature processing. An unannealed MOS sample was found to have a mobility value of 400 cm2/V s, which increased to 700 cm2/V s after a 950 °C anneal.
Studies of film growth processes and surface structural characterization of ferroelectric memory-compatible SrBi2Ta2O9 layered perovskites via in situ, real-time ion-beam analysis
Authors: Auciello O. , Krauss A. R. , Im J. , Gruen D. M. , Irene E. A. , Chang R. P. H. , McGuire G. E.
Published: July 2002

In situ, real-time studies of layered perovskite SrBi2Ta2O9 (SBT) film growth processes were performed using a time-of-flight ion scattering and recoil spectroscopy (TOF ISARS) technique. These studies revealed two important features related to the synthesis of SBT films via ion-beam sputter-deposition, namely: (a) atomic oxygen originating from a multicomponent SBT target during the sputtering process is incorporated in the growing film more efficiently than molecular oxygen; and (b) the SBT surface appears to be terminated in an incomplete (Bi2O2)2+layer with a top surface of oxygen atoms, which may be responsible for the high resistance to polarization fatigue exhibited by Pt/SBT/Pt capacitors.
Thermal stability of engineered Schottky barriers in Al/Si/GaAs(001) diodes
Authors: Sorba L. , Yildirim S. , Lazzarino M. , Franciosi A. , Chiola D. , Beltram F.
Published: July 2002

Schottky barriers as high (low) as 1.0–1.1 eV (0.2–0.3 eV) obtained in Al/n-GaAs(001) diodes by fabricating Si bilayers at the interface under an excess cation (anion) flux were subjected to sequential annealing cycles in the 100–450 °C temperature range. X-ray photoemission and current–voltage studies indicate a higher stability for high-barrier diodes, which retain 90% of the Si-induced interface dipole after a 450 °C anneal, as compared to only 32% for the low-barrier devices. Qualitatively different microscopic degradation mechanisms were identified in the two cases.