bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of iron based precipitates in GaAs layers grown by molecular-beam epitaxy
Authors: Bench M. W. , Carter C. B. , Wang Feng , Cohen P. I.
Published: July 2002

GaAs layers that contain small Fe-based precipitates have been grown using molecular-beam epitaxy. The layers were produced either by codepositing Fe during GaAs growth or by first depositing a thin layer of an Fe-Ga alloy and then growing a capping layer of GaAs. Microstructural characterization of the layers was performed by using transmission electron microscopy. For those samples in which the Fe alloy layer was deposited, the layer disappeared after GaAs growth, leaving behind Fe-containing precipitates distributed throughout the GaAs overlayer. Precipitates were also formed in Fe codeposited samples. The sizes and number densities of the precipitates were dependent on the growth method used, with mean diameters ranging from 21 to 47 nm and number densities from 1013–1015 per cm3. The phase, orientation, and morphology of the particles were also dependent on the growth conditions used, with FeAs and Fe being observed.
Capacitance bridge for low-temperature, high-resolution dielectric measurements
Authors: Foote M. C. , Anderson A. C.
Published: July 2002

A stable capacitance bridge has been designed to measure changes both in capacitance and in loss of three-terminal capacitors at temperatures ranging from 0.01 to 100 K. The circuit uses commercially available components, and has a resolution of better than 10−6. Also described is an anomalous voltage dependence present at low temperatures in capacitors which have electrodes applied using an evaporative or similar technique.
New scanning transmission electron microscope microanalytical system
Authors: Parker N. William , Mittleman Richard K. , Crewe Albert V.
Published: July 2002

We have designed and built an improved, dedicated analytical scanning transmission electron microscope (STEM). A novel feature of this microscope is a magnetic lens above the accelerating gun, allowing the specimen probe to achieve very high current densities while retaining the high spatial resolution of the STEM. Integrated with this microscope, we have also implemented an image processing system which allows rapid analysis of the digitized microscope output signals. This processing system also allows the graphic simulation of planar materials (such as intercalated graphite) to derive diffraction pattern simulations for comparison with the experimental data. An image database system allows over 2000 images to be easily managed.
Oscillating vane for measuring speed of gas flow
Authors: Jonsson H. H. , Vonnegut B.
Published: July 2002

Experiments with an oscillatory vane in a wind tunnel reveal that the vane’s oscillation frequency is directly proportional to the square root of the dynamic pressure of the flow. The linear relationship is observed for flow speeds up to the speed of sound in air, argon, and helium. The vane’s oscillations are a measure of mass flow, or if used on an aircraft, of indicated air speed. In constant density media the oscillation frequency is directly proportional to flow speed, and a simple count of the oscillations is a measure of distance traveled. At given ambient temperature and pressure, the vane’s frequency is the same at the speed of sound for all gases, irrespective of their molecular weight.
Identification of individual bistable defects in avalanche photodiodes
Authors: Buchinger F. , Kyle A. , Lee J. K. P. , Webb C. , Dautet H.
Published: July 2002

The effects of individual bistable defects on the dark counting rate of avalanche photodiodes have been monitored and their temperature dependence studied. The presence of a bistable defect in the diode is indicated by the repeated random switching of the counting rate between two well-defined rates. Four of the defects studied were produced via reaction with a single neutron from a Be–Am source, while two were found to exist without irradiation. Results were analyzed in terms of the activation energies of the electron generating capabilities of the defects, and the effective potential barriers between the two structural configurations of the bistable states. Among the six defects studied, two of them could be of the same type.
Crystalline quality of strain-free GaAs-on-Si structures formed by annealing under ultrahigh pressure
Authors: Ishiwara Hiroshi , Hoshino Tomohisa , Katahama Hisashi
Published: July 2002

Crystalline quality and residual strain in GaAs films epitaxially grown on Si substrates have been investigated after annealing them under ultrahigh pressures up to 2.1 GPa. The strain in the films decreased linearly with increase of pressure and it became zero at a pressure around 1.9 GPa. The strain depended weakly on the annealing temperature in the range from 300 to 500 °C. A slight increase in the channeling minimum yield in Rutherford backscattering spectrometry was observed in the samples with broad-area GaAs films. However, the degradation in the crystalline quality was avoided by etching the GaAs films in a stripe pattern with 10 μm width.
Monolithic integration of multiple wavelength vertical-cavity surface-emitting lasers by mask molecular beam epitaxy
Authors: Saito Hideaki , Ogura Ichiro , Sugimoto Yoshimasa , Kasahara Kenichi
Published: July 2002

Mask molecular beam epitaxy has been used to monolithically integrate vertical-cavity surface-emitting lasers (VCSELs) emitting at two wavelengths. This technique allows successive selective and nonselective growth in a chamber by using a movable mask. Varying the cavity thickness at selected areas enables the growth of VCSELs spaced 500 μm apart and emitting at wavelengths 10 nm apart. Both lasers have threshold current densities of 1.3–1.4 kA/cm2, a range comparable to that of typical VCSELs grown by conventional molecular beam epitaxy.
Potassium titanyl phosphate thin films on fused quartz for optical waveguide applications
Authors: Lundquist P. M. , Zhou H. , Hahn D. N. , Ketterson J. B. , Wong G. K. , Hagerman M. E. , Poeppelmeier K. R. , Ong H. C. , Xiong F. , Chang R. P. H.
Published: July 2002

Thin films of potassium titanyl phosphate (KTiOPO4) for photonic applications have been fabricated on fused quartz substrates by pulsed excimer laser ablation. The textured films were optically uniaxial with the symmetry axis oriented normal to the film surface. The principle component of the second order electric susceptibility was oriented parallel to this symmetry axis and was determined to be about 16 times the magnitude of quartz for the fundamental wavelength of 1.064 μm. This configuration, with the largest nonlinear optical response for polarizations perpendicular to the film surface, is desirable in TM guided wave applications. Planar optical waveguide measurements were performed and the linear waveguide loss was measured. The frequency dependence of χ(2)(ω) was determined and found to be uniform for visible second harmonic wavelengths.
Thin-film temperature rise estimates during low energy ion bombardment in a plasma reactor
Authors: Naeem M. D. , Chidambarrao D.
Published: July 2002

Theoretical estimates of the temperature distributions are obtained in structures where thin copper films mounted on special membrane wafer transmission electron microscopy (TEM) specimens are exposed to low energy (63–114 eV) ion bombardment in a magnetically enhanced (ME) plasma reactor. The substrate temperatures are experimentally measured as a function of rf power in the plasma reactor and of time. The temperature rise in the copper films is obtained based on a two-dimensional heat transfer finite element analysis with input of a heat flux at the surface due to ion bombardment. The results indicate that copper heating due to ion bombardment is minimal because of rapid heat transfer through the underlying structure and the observed microstructural changes in copper films during plasma processing must be attributed to other causes.
Conducting atomic force microscopy of alkane layers on graphite
Authors: Klein David L. , McEuen Paul L.
Published: July 2002

We have used an atomic force microscope with a conducting tip to investigate the layering of hexadecane on graphite. Discrete jumps were observed in both the tip–sample conductance and separation as individual liquid layers are penetrated. These conductance measurements extend solvation studies to higher force scales than have been previously achieved, and can be used to determine when the tip makes contact with the substrate. The layering also enables the formation of stable tunneling junctions.
Light propagation, optical modulation, and beam steering in waveguides with quantum well voltage tunable claddings
Authors: Harwit Alex , Fernandez R. , Kinell D. K. , Eades W. D.
Published: July 2002

We present results on devices fabricated in a waveguide system utilizing a voltage tunable quantum well cladding layer. A (GaAs/AlGaAs) beam steering device produced an angular shift of 2.4° under an applied voltage of 20 V. It is shown numerically that electro-optic modulators fabricated in such a material configuration can have simultaneously improved contrast ratios and insertion losses if the ratio of light propagating in the cladding and in the core regions can be controlled. A proof of concept device is demonstrated in which an electric field is used to change the distribution of light propagating in the waveguide.
Surface morphology of metalorganic vapor phase epitaxy grown strained-layer InxGa1−xAs on GaAs observed by atomic force microscopy
Authors: Hsu C. C. , Xu J. B. , Wilson I. H. , Wang S. M.
Published: July 2002

We have studied the surface morphology and growth mechanism of metalorganic vapor phase epitaxy grown strained-layer InxGa1−xAs (x=0.2 or 0.5) on GaAs with atomic force microscopy. Morphological instability of monolayer steps was observed on a 10 nm thick strained-layer In0.2Ga0.8As. Three-dimensional (3D) growth was observed for x=0.5 when grown at 650 °C. By lowering the growth temperature to 600 °C, the growth mode is 2-D for 5 nm films (x=0.5). Monolayer steps and 2D islands can be seen. Increasing the layer thickness to 7.5 nm at 600 °C caused the growth of 3D islands and the generation of misfit dislocations.
Theoretical study of strained InGaP quantum-well lasers
Authors: Ahn Doyeol
Published: July 2002

The effects of biaxial compressive and tensile strains on the optical gain and threshold current density of 70 Å strained InGaP–In(AlGa)P quantum-well lasers are studied theoretically. Due to strain effects on the density of states and optical dipole matrix elements, compressive strain produces the largest gain (TE) for carrier density N<5×1018 cm−3 while the TM mode gain of a tensile strained quantum well is the largest when N≳5×1018 cm−3. Calculated threshold current densities of compressive- and tensile-strained quantum wells are both lower than unstrained case. For cavity length longer than 500 μm, a quantum well with compressive strain has the lowest threshold current density. In this case, calculated threshold density shows reasonable agreement with the experiment.
Effect of dispersion on the reflectivity of an asymmetric Fabry–Pérot étalon
Authors: Hefferman J. F. , Hegarty J.
Published: July 2002

We have shown that the spectral properties of an asymmetric Fabry–Pérot étalon, with a multiple quantum well cavity, are very sensitive to dispersion in the refractive index. We also show that this effect can be used to measure the dispersion around the exciton absorption features in the GaAs/Al0.35Ga0.65As multiple quantum well.
Reply to ‘‘Comment on ‘VISAR analysis in the presence of large intensity changes: Application to the expanding ring’ ’’ [Rev. Sci. Instrum. 6
0, 3832 (1989)]
Authors: Gourdin William H.
Published: July 2002

The published method to correct VISAR data is applicable to those cases in which an existing instrument would require radical modification in order to eliminate the behavior addressed in the original article.
Three-stage lattice relaxation of Ge islands on Si(111) measured by tunneling microscopy
Authors: Theiss Silva K. , Chen D. M. , Golovchenko J. A.
Published: July 2002

We use the tunneling microscope to measure the surface lattice spacing of Ge islands grown on Si(111) as a function of their height. It changes in three stages: (I) (0–50 layers tall) Rapid relaxation from near the bulk Si value, at the end of which the lattice spacing atop some of the islands exceeds that of bulk Ge. (II) (50–80 layers) Rapid decrease in surface lattice spacing, to nearly 2% below the bulk Ge value. (III) (≳80 layers) Gradual relaxation to the bulk value. Additional observations of dislocations and analysis of island widths are used to explain this behavior.
Ultralow interface recombination velocity in ordered–disordered GaInP2 double heterostructures
Authors: van Geelen A. , Thomeer R. A. J. , Giling L. J.
Published: July 2002

The minority charge-carrier lifetime of undoped GaInP2 has been investigated in disordered–ordered–disordered GaInP2 double heterostructures. It is found that minority charge carriers can be confined to the ordered GaInP2 if the growth is performed on a (100) 6° off towards [111̄] substrate. Minority charge-carrier lifetimes of 1.2±0.35 μs are measured. These high lifetimes are the result of the extremely low interface recombination velocity of the disordered–ordered GaInP2 interface.
Effect of spin-orbit split-off band on optical gain in AlGaInP/GaInP strained quantum wells
Authors: Domen K. , Ishikawa H. , Sugawara M. , Kondo M. , Tanahashi T.
Published: July 2002

The optical gains in AlGaInP/GaInP strained quantum wells using valence band structures by the second-order k⋅p method, with and without spin-orbit split-off (SO) band effect have been calculated. It was easy to overestimate the optical gain without considering the SO-band effect, because a small spin-orbit splitting energy for GaInP makes higher nonparabolicity of the valence bands. The SO-band effect is particularly significant under tensile strain, since the SO band makes the effective mass very large due to the large interaction between the SO and light hole bands.
Bifilar helical wiggler magnet inductance
Authors: Fajans J.
Published: July 2002

A formula for the inductance of a bifilar helical wiggler magnet is given.
An elliptical spectrograph/fiber-array/streak camera system for remote time-resolved spectral measurements in the x-ray region
Authors: Hammel B. A. , Ruggles L. E.
Published: July 2002

An elliptical spectrograph and a scintillator/fiber-array detection system have been developed to provide time-resolved measurements of the x-ray spectra from a Z-pinch plasma. The elliptical spectrograph (1.2-m focal distance, eccentricity=0.9586) observes the 1-keV region, covering a range of λ/2d=0.5–0.9. The detector consists of a thin scintillator butt-coupled to a fiber optic array which transmits the signal to a streak camera in a remote location. This system provides continuous time history with temporal resolution of ∼3 ns, and a spectral resolving power of ∼165. The detection scheme is limited to spectral lines with intensities greater than ∼106 W/sr-eV.
Impedance monitor to protect the thyratron in metal vapor lasers
Authors: Lin C. E. , Yang C. Y. , Wang T. C. , Huang C. L.
Published: July 2002

It is found that the appearance of high reverse-voltage spikes on the thyratron anode in the discharge of metal vapor lasers due to high laser impedances can easily be monitored by a dc current meter in series with the bypass inductor of the discharge circuit. Experiments are demonstrated using a copper vapor laser. Results show that the proposed impedance monitor is effective, reliable, and economical. The meter deflection corresponding to acceptable, well-behaved thyratron operation can be obtained easily by the residual ionization-control method using a clean laser tube. By keeping the deflection within a specified limit, the lifetime of thyratron can greatly be extended.
High-brightness and high-resolution RHEED system
Authors: van Gorkum A. A. , Smits M. R. T. , Larsen P. K. , Raue R.
Published: July 2002

A RHEED system, consisting of a high-resolution (75-μm FWHM) and high-brightness (10-μA) electron gun, and a phosphor screen with high resolution and good linearity, was developed. The system is based on concepts from projection television. The results show that this setup is particularly useful for obtaining quantitative RHEED patterns.
Measuring axially varying beam position using B-dot monitors
Authors: Shokair Isaac R.
Published: July 2002

For charged-particle beam experiments, it is often necessary to measure the transverse position of a beam that is undergoing oscillations as it propagates axially in a conducting tube. This is usually done using small wire loops called B-dot monitors which measure the change of magnetic flux. If the monitors are located at a radius R, which is of the same order as the wavelength of the beam oscillations, the B-dot signal and the beam transverse position are related in a nonlocal manner. We consider this situation here and derive an integral equation relating the beam position to the B-dot signals, for arbitrary displacement profiles, in the limit of small beam displacements. Solutions of this equation are obtained for special cases along with a numerical method for solving the general problem.
Two-dimensional plasma-electron temperature measurements
Authors: Goodman Daniel L.
Published: July 2002

A system to measure the two-dimensional cold-electron temperature profile in a magnetic confinement laboratory plasma is described. Using a digital storage CCD camera, image intensifier, and optical transmission filters, a two-dimensional helium-line emission-ratio measurement shows plasma features which are not possible to resolve using only a single detector or an array of detectors. The system is especially useful for nonaxisymmetric magnetic geometries, where the three-dimensional equilibria make interpretation of more standard measurements difficult. Other two-dimensional plasma-profile measurements including density and ionization source measurements are also possible using the system.
Environmental facility for synchrotron radiation topography
Authors: Gillespie K. , Littlejohn A. , Roberts K. J. , Sheen D. B. , Sherwood J. N.
Published: July 2002

A versatile environmental facility for in situ x-ray topographic (white radiation) investigations of the perfection of nearly perfect single crystals is described. The system is built to UHV standards and can be optimized to investigate the defect structure in many materials at variable pressure and temperature. High quality data have been obtained with this facility during the decomposition of nickel sulphate hexahydrate and calcite. In the former case, in contradiction to what has previously been believed, the results clearly show that dislocations are not involved in the nucleation of the reaction process.
An improved double fluorescence detector for fluorescence EXAFS measurements
Authors: Heald S. M.
Published: July 2002

In many cases the fluorescence EXAFS signal is contaminated with fluorescence from nearby elements. If this fluorescence is of lower energy than the element of interest, x-ray filters are not effective. One method for dealing with this problem is the double fluorescence method described by Wong and Rao. This paper describes an improved version of this double fluorescence scheme that greatly improves its efficiency. Data are presented for a sample of 1/2% Hf in Ni3 Al, and 1.6% CuO in NiO. When standard fluorescence is used, both signals are almost completely obscured by the ≂100× larger Ni K fluorescence signal. With the double fluorescence detector the Hf L3 and Cu K-edge signals are clearly observed, and good spectra can be obtained in about an hour.
Nb/Al–AlOx–Al/Ta/Nb Josephson junctions for x-ray detection
Authors: Morohashi Shin’ichi , Gotoh Kohtaroh , Yokoyama Naoki
Published: July 2002

Nb/Al–AlOx–Al/Ta/Nb Josephson junctions for use as energy resolving x-ray detectors have been fabricated. The junctions have been designed to raise both creation and collection efficiency of quasiparticles. The current–voltage characteristics of the junctions have been investigated on the Al deposition dependence, and found that the characteristics are strongly dependent on the Al deposition rate during the fabrication. The subgap leakage current of those junctions fabricated at higher Al deposition rates exhibit very low leakage current (less than 200 nA at a bias voltage of 100 μV measured at 0.5 K).
Buffer layer/film interactions in the growth of Tl2Ba2Ca1Cu2Ox films on CeO2 buffered sapphire
Authors: Bramley A. P. , Morley S. M. , Grovenor C. R. M. , Pecz B.
Published: July 2002

Tl2Ba2Ca1Cu2Ox thin films have been grown on highly textured CeO2 layers deposited onto R-plane sapphire substrates. The Tl2Ba2Ca1Cu2Ox films have critical temperature (Tc) values around 95 K and current density (Jc) values up to 8×104 A/cm2. The films are c-axis oriented even though we have identified the formation of a polycrystalline BaCe(Tl)O3 layer by reaction between the buffer layer and the superconducting precursor during the thalliation process.
Studies on the process of reaction in crystals by synchrotron radiation: Dehydration of α-AlOOH (abstract)
Authors: Hagiya K. , Ohmasa M. , Ryuta J. , Saito S. , Sasaki S.
Published: July 2002

In order to study the process of reaction in crystals, it is necessary to observe decomposition of precursor and formation of the product during the transformation. Since such change is related to the structures of both the phases, x-ray diffraction is the most powerful method for this purpose. However, not only Bragg reflections but diffuse scattering or satellite reflections are observed occasionally in the early stage of the process and intensities of those scattering are extremely weak although they are important to analyze the process. Therefore, use of synchrotron radiation is desirable to study those problems. There are many compounds which show topotaxy during phase transformation. Since the product of such transformation is formed in an oriented manner under the influence of the structure of the precursor, diffraction patterns of the product are similar to those of a single crystal and anomaly of the diffraction can be easily detected. We have consequently studied the process of dehydration in α-AlOOH which indicates topotaxy in the process of dehydration. α-AlOOH transforms to α-Al2O3 at about 500 °C when it is heated in air. Lima-de-Faria (1963) found that the products revealed distinct satellite reflections along c* direction on x-ray diffraction patterns when the samples are quenched to room temperature in the early stage of reaction. Similar phenomena are also known in dehydration of α-FeOOH to α-Fe2O3 (both of them are isostructural to α-AlOOH and α-Al2O3, respectively). No interpretation has yet been established to the origin of the satellites. We have analyzed the averaged structure, interpreted the satellite reflections and change of profile of the satellites, and have elucidated the process of the reaction. The results indicate that the origin of the satellites is ascribed to the modulation of Al content along c direction and the change of the profile to the change in the mode of the modulation.
MBE apparatus for i
n s
i
t
u grazing incidence x-ray diffraction
Authors: Akimoto K. , Mizuki J. , Hirosawa I. , Matsui J.
Published: July 2002

A molecular beam epitaxy (MBE) apparatus furnished with two E-gun evaporators, two Knudsen cells and RHEED, was built for in situ grazing incidence x-ray diffraction studies. By adopting horizontal sample setting geometry, the entire ultrahigh vacuum chamber was rotated simply with the aid of a spring, and a large sample area was irradiated by the x-rays. Using this apparatus, we observed the 7×7 superstructure on a Si(111) surface and at a SiO2/Si(111) interface.
Spectrally and temporally resolved laser emission from vertical cavity surface emitting lasers
Authors: Sinclair M. B. , Gourley P. L. , Brennan T. M. , Hammons B. E. , Dawson L. R.
Published: July 2002

The laser emission spectra of several vertical cavity surface emitting lasers, following pulsed laser excitation, have been measured with a temporal resolution of <1 ps. With broadband excitation, emission was observed from multiple longitudinal modes when pumped well above threshold. The output-pulse decay times of modes located near the edges of the high reflecting zone were significantly shorter than the decay times of modes located near zone center. The zone-edge modes were not observed when narrow-band photoexcitation was used, indicating that broadband excitation results in seeding of the laser cavity.
In situ real time measurement of the incubation time for silicon nucleation on silicon dioxide in a rapid thermal process
Authors: Hu Y. Z. , Diehl D. J. , Liu Q. , Zhao C. Y. , Irene E. A.
Published: July 2002

Real time ellipsometry and atomic force microscopy (AFM) were used to measure critical nucleation parameters for polycrystalline silicon deposition on an amorphous SiO2 layer by rapid thermal chemical vapor deposition (RTCVD) using disilane (5% in helium). A particularly important parameter for selective epitaxial deposition is the time for nuclei to form, the incubation time. Quantitation of the nucleation parameters, such as the nuclei density, nuclei growth rate, nuclei coalescence, and an operational incubation time were determined from the real time ellipsometric measurements and confirmed by AFM. For a substrate temperature of 700 °C and at a chamber pressure of 0.2 Torr, the nuclei densities of 1.4×1010 nuclei/cm2, incubation time of 26 s and nuclei layer growth rates of 20 nm/min were obtained.
Pitot tube as a calibration device for turbulence measurement
Authors: Kassab Sadek Z.
Published: July 2002

This note is to demonstrate that one can correct hot-wire turbulence measurements simply by using a Pitot tube to obtain the mean velocity distribution in fully developed, turbulent pipe flow. The basic idea is simply a combination of two independent derivations given in the late sixties. A test case is given to prove the idea.
MEDEA II two-pulse generator development
Authors: Bieniosek F. M. , Honig J. , Theby E. A.
Published: July 2002

This article discusses improvements in the efficiency, output power, and operational flexibility of MEDEA II, a double-pulse electron beam accelerator at McDonnell Douglas Research Laboratories. A modified charging circuit, based on the triple-resonance pulse transformer concept, was implemented on both of MEDEA II’s two stages. The output switches were modified to increase maximum output voltages, and a new, second output switch with asymmetric breakdown characteristics was developed. To avoid degradation of the second-pulse output waveform at the diode, a keep-alive circuit was installed. The effects of diode closure on double-pulse operation are also discussed.
Measurement of Allan variance and phase noise at fractions of a millihertz
Authors: Conroy Bruce L. , Le Duc
Published: July 2002

Although the measurement of Allan variance of oscillators is well documented, there is a need for a simplified system for finding the degradation of phase noise and Allan variance step-by-step through a system. This article describes an instrumentation system for simultaneous measurement of additive phase noise and degradation in Allan variance through a transmitter system. Also included are measurements of a 20-kW X-band transmitter showing the effect of adding a pass tube regulator.
Passivation of an n-type GaAs surface with an As2S3 film
Authors: Mada Yoichi , Wada Kazumi
Published: July 2002

This letter describes the passivation of an n-type GaAs surface using an arsenic trisulfide (As2S3) film. Metal–insulator—semiconductor diodes were fabricated with an evaporated As2S3 film as an insulator. In the inversion region, the capacitance–voltage curve shows deep depletion, that coincides with the depletion theory. In the accumulation region, surface Fermi level movement is blocked 0.25 eV below the conduction-band minimum due to a high density of interface states. The minimum interface state density is found to be about 1–2×1011 eV−1 cm−2.
Millimeter wave distributed metal-semiconductor-metal photodetectors
Authors: Böttcher E. H. , Bimberg D.
Published: July 2002

We propose and analyze a method for distributed photodetection using waveguide-coupled metal-semiconductor-metal (MSM) photodetectors. The electrode configuration is a coplanar strip waveguide capacitively loaded with the interdigitated MSM structure. The slow wave character of this structure allows for matching the velocity of the guided electrical wave to that of the optical waveguide resulting in virtually capacitance-free photodetection. In the context of actual device structures and operating conditions, the bandwidth limitation due to velocity mismatch and the influence of transmission line loss and dispersion on the high-frequency response are calculated and is found to be close to 1 THz. Thus, the detector structure is suitable for fully exploiting the transit-time-limited bandwidth potential of ≥200 GHz which is attainable by using interdigitated electrodes with ≤0.1 μm spacing and width.
High speed metal-semiconductor-metal photodetector manufactured on GaAs by low-temperature photoassisted metalorganic chemical vapor deposition
Authors: Boutros K. S. , Roberts J. C. , Bedair S. M. , Carruthers T. F. , Frankel M. Y.
Published: July 2002

We report on the photoassisted metalorganic chemical vapor deposition (MOCVD) of high resistivity gallium-arsenide at low-temperature (LT-GaAs). The as-grown GaAs exhibits a resistivity of ∼106 Ω cm and has been used as the active layer of a metal-semiconductor-metal (MSM) Schottky-barrier photodetector. The impulse response of the detector is 4 ps with a dark current of 4 nA at a bias of 2 V. These results are comparable to those obtained from LT-GaAs grown by molecular beam epitaxy (MBE).
A sensitive modified Mach–Zehnder interferometer for studying electro-optic properties
Authors: Pan W. Y. , Jang S. J.
Published: July 2002

A modified Mach–Zehnder interferometer has been built for measuring the electro-optic properties of crystals. The system is capable of resolving an optical path length change of 5×10−3 Å. The electro-optic R33 coefficient of the LiNbO3 crystal has been measured; the result is in excellent agreement with the previously reported values.
Damping of mechanical vibration by superconducting Y
B
a
2
C
u
3
O
7−
x in a magnetic field
Authors: Terentiev A. N. , Harrison J. P. , Liang Ruixing , Bonn D. A. , Hardy W. N.
Published: July 2002

As the load capacity of magnetic bearings using high-Tc superconductors increases, the inherent damping decreases. Damping of externally generated vibration is an important unsolved problem. A proposal is made for an active damping system, based upon the strong temperature dependence of the magnetic flux dissipation in a high-Tc superconductor in the region of the phase transformation a few degrees below the transition temperature. The damping system would be distinct from the levitated system. The strong temperature dependence of the dissipation is demonstrated with a single crystal of yttrium barium copper oxide, but a melt-processed ceramic sample would behave in the same way.
Doping of p-type shallow junctions using electron beam evaporation of boron layers for compatibility with complementary-metal-oxide-semiconductor technology
Authors: Zagozdzon-Wosik W. , Pan D. , Davis M. F. , Rusakova I. , Zhang Z.-H. , Rhodes K.
Published: July 2002

Electron-beam evaporation was used as a low-temperature deposition process of boron and boron/amorphous-silicon layers as dopant sources in rapid thermal diffusion. High efficiency of doping is attributed to high dopant supply from the boron layer to the silicon substrate. Oxygen ambient leads to layer consumption and thus opens possibility for the source removal after diffusion. Dopant activation results in high carrier concentration within the junctions. High concentrations of dopant cause generation of precipitates at the B/Si substrate interface but not at the B/Si cap interface. The process is compatible with the complementary-metal-oxide-semiconductor technology since the low temperature of the source deposition facilitates masking of the dopant by a patterned photoresist and its subsequent lift-off removal from the silicon surface.
Anisotropic roughness in Ge/Si superlattices
Authors: Headrick R. L. , Baribeau J.-M. , Strausser Y. E.
Published: July 2002

We discuss measurements of buried interfaces utilizing x-ray specular reflectivity profiles, and high-resolution x-ray reflectivity measurement of diffuse scattering. Interface structure is compared to atomic force microscopy characterization of the morphology of the Si cap layer overlying the buried structures. The results show that the morphology of roughness on the growth surface is greatly influenced by substrate miscut, and tends to form one-dimensional undulations. Roughness along the miscut direction is highly replicated from interface to interface, but roughness perpendicular to the miscut evolves more rapidly during the growth process. This effect is characterized by a reduced vertical correlation length in x-ray diffuse scattering in one azimuthal orientation.
Photoluminescence vibrational structure of Si center in chemical-vapor deposited diamond
Authors: Gorokhovsky A. A. , Turukhin A. V. , Alfano R. R. , Phillips W.
Published: July 2002

Photoluminescence spectra from the Si impurity center in diamond films grown by chemical-vapor deposition techniques were studied at temperatures between 9 and 300 K. Laser excitation at 514.5 nm, and resonant with the zero-phonon absorption line at 737 nm (1.6823 eV), were used. Luminescence lines become narrowed at resonance excitation, and the vibrational structure of the Si center was observed with a major phonon replica at 767 nm (1.6165 eV). The observed vibrational energy of 515 cm−1 supports a diatomic quasi-molecular Si2 center structure. Temperature dependencies of the linewidth of the zero-phonon line and its phonon replica were measured and the origins of the broadening are discussed.
Three-dimensional electron probe roughness analysis of InP sidewalls processed by reactive ion beam etching
Authors: Matsutani Akihiro , Koyama Fumio , Iga Kenichi
Published: July 2002

A quantitative three-dimensional measurement of sidewall roughness of InP etched by chlorine-based reactive ion beam etching (RIBE) is presented. An electron probe surface roughness analyzer using four secondary electron detectors was employed. The minimum value of average sidewall roughness under the optimized etching condition was as small as 1 nm, where the etching condition was an ion extraction voltage of 400 V and a Cl2 gas pressure of 1.2×10−3 Torr. It is found that the etched sidewall roughness can be reduced by lowering ion extraction voltage with a relatively higher gas pressure.
A portable alt-azimuth solar simulator for evaluation of daylighting devices
Authors: Jackson Andrew , Pitcher David , Gerritsen Hendrik J.
Published: July 2002

The construction and functioning of a portable alt-azimuth solar simulator and demonstration model is described. The instrument was designed to be used with a slide projector as its light source, as this is readily available in most labs. An arrangement of movable mirrors and a pivoting window allow the user to simulate a wide range of altitude and azimuth combinations of the sun. Upon insertion of a daylighting device in the window, the intensity, position, and coloration of the redistributed simulated sunlight on the ceiling and walls, as well as the presence and intensity of glare, can be visually inspected. Instrumentation consisting of a photovoltaic cell and a 20 segment bar graph display allow direct read out (in lux) of the illumination levels in the model. The scaling up from the simulator model to a full size room is simple and straightforward.
A differential reflection high energy electron diffraction measurement system
Authors: Chang C. E. , Chin T. P. , Tu C. W.
Published: July 2002

An economical, real-time differential reflection high energy electron diffraction (RHEED) measurement system which is effective in a high-noise environment is described. Two fiber optic cables sample the RHEED intensities from the phosphorescent screen in a molecular beam epitaxy (MBE) growth chamber. The first cable observes the RHEED oscillations with the inherent background noise while the second cable monitors the background noise. The differential RHEED unit subtracts the RHEED signal combined with the background noise from the background noise, leaving only the RHEED signal. The resultant ‘‘clean’’ RHEED oscillation is displayed on an IBM compatible computer.
Mapping the composition of planetary surfaces by Auger electron spectroscopy
Authors: Lin R. P. , Gopalan R.
Published: July 2002

We explore the feasibility of Auger electron spectroscopy as a remote sensing technique to map the composition of the sunlit surfaces of planetary bodies without atmospheres. Solar x rays eject photoelectrons from the planetary surface. The resulting ions relax by emission of fluorescence x rays or Auger electrons, with energies characteristic of the element which is ionized. The spectrum of Auger electrons and photoelectrons is computed for a variety of elements and for representative lunar rock types illuminated by soft x-ray line and continuum emission typical of solar long-lived coronal active regions. The Auger electron lines for O, Si, Mg, Al, Fe, and Ca in lunar rocks stand well above the continuum background from photoelectrons and backscattered interplanetary electrons, with typical line-to-continuum ratios of ∼20 to ≳103. An ideal Auger electron spectroscopy instrument to map the elemental composition of planetary surfaces should have a combination of high energy resolution (≲2 eV) and large geometric factor (≳0.1 cm2 sr). This technique could be applied to the Moon, Mercury, asteroids, comets, and perhaps the moons of outer planets.
Compact, semi-sealed-off, high-repetition-rate transversely excited atmospheric-pressure CO2 laser with a surface-wire-corona preionization
Authors: Sugii Masakatsu , Komi Takao , Hara Hiroshi
Published: July 2002

This article describes the design and operating characteristics of a reasonably compact, semi-sealed-off, high-efficiency transversely excited atmospheric-pressure CO2 laser operating at prfs <150 Hz by a stable discharge system using a new type of surface-wire-corona preionizer. An efficient laser operation at a slope efficiency of 10.2% with a maximum average power of 42 W (100 Hz) has been achieved from a discharge volume of 57.5 cc with an active length of 26 cm. With CO and H2 as additive, ≳2.1×106 shots has been achieved on a single gas fill and an estimated half-power lifetime of 2×107 shots made.
Covariance of density and velocity fields of a gas-solid suspension
Authors: Zhu C. , Slaughter M. C. , Soo S. L.
Published: July 2002

This note concerns the accuracy of measurement of local particle density (cloud density in number or mass per unit volume) of a gas-solid suspension in pipe flow, inasmuch as such a system is susceptible to fluctuations in density and velocity.
Demagnetization of porous compacts of iron-alloy powder under shock compression
Authors: Oda Hideaki , Sato Takashi , Kondo Ken-ichi
Published: July 2002

Demagnetization of porous green compacts consisting of iron-alloy powder was observed under shock compression in the range of 4.0–13.5 GPa and 660–2040 K. The total reduction of the initial magnetization occurs under shock conditions with pressures exceeding 9 GPa and a temperature of 1300 K, and the possible mechanism for the observed demagnetization is consistent with the whole and/or partial α- to γ-phase transition in the powder, depending on the localization of heat at the particle surfaces. The mechanism is also consistent with the anomalous low value of residual magnetic flux density of the recovered material which was overcompacted under undesirable conditions.
Triggered vacuum flashover switch for high-power applications
Authors: Kellogg J. C. , Boller J. R. , Commisso R. J. , Jenkins D. J. , Ford R. D. , Lupton W. H. , Shipman J. D.
Published: July 2002

A command triggered, high-power, surface-flashover closing switch that operates in vacuum has been developed for use on a prototype inductive-storage pulsed power generator, Pawn. This vacuum flashover switch isolates the high-pressure-gas tamped wire fuse from a second opening switch. The switch consists of an insulating ring sandwiched between electrodes. Plasma and ultraviolet light from eight small spark discharges driven by a 5 keV pulse initiate a flashover across the switch insulator. The entire triggering unit resides inside one of Pawn’s metallic conductors. The switch can be triggered after holding off voltage for ≂15 μs. Normally, switch closure occurs at 22–45 kV. Time to closure at a voltage of ≂30 kV is ≂320 ns, with a typical jitter of ±50 ns. Peak current is typically ≂1 MA. Current density in the switch is approximately 25 kA/cm2. The average risetime of the fuse output current pulse can be varied by a factor of 2 by triggering the switch at different closing voltages.
1 Gb/s Si high quantum efficiency monolithically integrable λ=0.88 μm detector
Authors: Levine B. F. , Wynn J. D. , Klemens F. P. , Sarusi G.
Published: July 2002

We propose and demonstrate a 1 Gb/s high quantum efficiency Si MSM metal-semiconductor-metal detector which is complementary metal-oxide semiconductor compatible. The detector absorbs over 50% of the light entering the active layer at a wavelength of λ=0.88 μm.
Influence of carrier kinetics on subpicosecond gain dynamics in diode laser amplifiers
Authors: Schuster S. , Haug H.
Published: July 2002

For a bulk GaAs semiconductor laser amplifier the evolution of the optical gain after a 200 fs pulse excitation is calculated by including carrier–carrier and LO-phonon–carrier scattering in terms of the Boltzmann collision integrals. For an injected light pulse in the gain (absorption) region the optical gain shows a transient decrease (increase) followed by relaxation towards a lower (higher) level. Around the transparency point the broadening of the optical transition due to the decay of the induced interband polarization yields a transient decrease of the optical gain although the carrier density does not change. This behavior agrees qualitatively well with measurements of M. P. Kesler and E. P. Ippen [Appl. Phys. Lett. 51, 1765 (1987)]. The temperature relaxation after the excitation is examined.
Simple cooled CCD camera for beam diagnostics
Authors: Cambel Vladimír , Sudek Ján , Kovalenko Alexander Dmitrievich , Datskov Vladimir Ivanovich , Voevodin Mikhail Alexandrovich
Published: July 2002

A simple system for beam positioning and spatial distribution diagnostics based on a cooled charge coupled device (CCD) camera, scintillation screen, and optics has been developed. Standard methods of recording beam profiles are different for low and high intensity beams, which complicates readout techniques. The main advantage of our system is its adaptability for intensity range 103–1012 particles/cm2/pulse. The system was tested at the Dubna synchrophasotron complex. Protons and nuclei beam profile and position monitoring in mentioned intensity range and energy range of 10 MeV to 10 GeV was provided. A CCD camera is used in wavelengths interval 400–1100 nm. The hardware, software, and cryogenics of this system are described. Effects of fixed pattern noise and dependence of nonuniformity of response on wavelength are shown and some results of beam diagnostic are presented.
Biased-voltage controlled thinning for bonded silicon-on-insulator wafers
Authors: Huang Qing-An , Chen Jun-Ning , Fu Xing-Hua , Zhang Hui-Zhen , Tong Qin-Yi
Published: July 2002

A novel method for the preparation of bonded and etch-back silicon-on-insulator is presented and demonstrated in which the surface of the to be thinned silicon wafer near the oxide is biased to inversion, so the bulk of this silicon wafer can be removed by anodic etching using the depletion layer as an etch stop. The high etching selectivity between the bulk silicon wafer and the depletion layer makes it possible to produce a micron/submicron-thick active silicon layer with good thickness uniformity across a 3 in. silicon-on-insulator wafer.
Many-body Coulomb effects in room-temperature II–VI quantum well semiconductor lasers
Authors: Chow W. W. , Koch S. W.
Published: July 2002

This letter investigates the gain medium properties in II–VI blue-green quantum well semiconductor lasers, including band structure and carrier interactions in the electron-hole plasma are found to be significantly more important than in infrared III–V lasers. In particular, the interband Coulombic enhancement of the optical transitions, together with a band gap renormalization result in an increase in gain and a reduction in the antiguiding or linewidth enhancement factor.
p
+ doping of Si by Al diffusion upon annealing Al/n-Si(111)7×7
Authors: Wen H. J. , Prietsch M. , Bauer A. , Cuberes M. T. , Manke I. , Kaindl G.
Published: July 2002

A novel method for the formation of a p+-layer underneath a Si(111)7×7 surface is presented. It is based on annealing of an epitaxial Al/n-Si(111) interface up to complete desorption of the Al film. This leads to a strong potential variation within the substrate, as observed in Si-2p core-level photoemission spectra with variable sampling depth, while scanning-tunneling microscopy reveals an unchanged 7×7 reconstructed surface. These observations are consistent with a p+ doping of (4±2)×1018/cm3 and a lowering of the surface Fermi level by (0.06±0.02) eV.
Reduced interface state density after photocurrent oscillations and electrochemical hydrogenation of n-Si(111): A surface photovoltage investigation
Authors: Rauscher S. , Dittrich Th. , Aggour M. , Rappich J. , Flietner H. , Lewerenz H. J.
Published: July 2002

The electrochemical H-termination process of n-Si(111) surfaces in aqueous 0.1 M NH4F pH 4.0 solution was optimized for a two step procedure consisting of the surface smoothing during oxidation in the photocurrent oscillating potential region followed by the oxide etching and passivation of the surface atoms with hydrogen. The hydrogen termination was monitored in situ measuring the dark current transient and evaluated using pulsed surface photovoltage technique. An unusually low density of interface states it=1×1010 eV−1 cm−2 was obtained by the hydrogen termination on n-Si(111) surfaces following this procedure with better results than applying an electropolishing treatment.
Saturation behavior of the defect density in hydrogenated amorphous silicon by continuous and pulsed light illumination
Authors: Yoon Jong-Hwan , Kim H. L.
Published: July 2002

Measurements of the saturated defect density in hydrogenated amorphous silicon by continuous and pulsed light illumination are reported. It is observed that the saturation value of the defect density by pulsed light illumination is about one order of magnitude higher than by continuous light illumination in device quality films. It has been suggested that this result would be due to the difference in the light-induced defect annealing rate between two cases, in which it is found that the light-induced annealing rate by pulsed light is lower than by continuous light with a similar intensity.
Effects of electron cyclotron resonance etching on the ambient (100) GaAs surface
Authors: Glembocki O. J. , Tuchman J. A. , Ko K. K. , Pang S. W. , Giordana A. , Kaplan R. , Stutz C. E.
Published: July 2002

Photoreflectance has been used to study the electronic behavior of the ambient (100) GaAs surface and its modification by etching in a Cl2/Ar plasma generated by an electron-cyclotron resonance (ECR) source. We observed two pinning positions for ambient (100) GaAs, with n-GaAs pinning near midgap and p-GaAs pinning near the valance band. ECR etching shifts the Fermi level of p-GaAs toward midgap, but has little effect on n-GaAs. The surface modification is most influenced by the rf power. Auger electron spectroscopy indicates that the etching increases As at the GaAs/oxide interface. We suggest that the Ga/As ratio controls the position of the Fermi level.