bluuebunny/crossref_metadata_2025 huggingface dataset:
Tunneling between totally quantized levels in GaAs/AlGaAs asymmetric triple-barrier heterostructures in high magnetic fields
Authors: Asahi H. , Tewordt M. , Syme R. T. , Kelly M. J. , Law V. J. , Mace D. R. , Frost J. E. F. , Ritchie D. A. , Jones G. A. C. , Pepper M.
Published: July 2002

Electron transport is studied in GaAs/AlGaAs asymmetric triple-barrier resonant tunneling structures in a high magnetic field perpendicular to the interfaces. Besides the resonance peaks arising from tunneling between two quantum wells, a series of fine structure is observed in the valley region of the current-voltage characteristics, which is attributed to electron transitions between well defined totally quantized levels (Landau levels) in the two wells, together with the emission of a longitudinal optical phonon. In the voltage region of the main current peak, any structures which shift with magnetic field are not observed, suggesting that the tunneling in this bias region is mainly determined by Δn=0 elastic transitions.
Oxygen tracer diffusion through BaF2 and MgO overcoats on YBa2Cu3O7−Δ
Authors: Wong S. B. , Vajo J. J. , Hunter A. T. , Nieh C. W.
Published: July 2002

The movement of oxygen through MgO and BaF2 overcoats on YBa2Cu3O7−Δ has been studied using 18O tracer diffusion techniques. By analyzing the 18O and 16O signals from secondary-ion mass spectrometry depth profiles, the motion of small concentrations of oxygen in both insulating and oxygenated hosts has been tracked. BaF2 was found to be transparent to oxygen diffusion while MgO blocked its motion during 10 min 500–600 °C anneals. Uncovered YBa2Cu3O7−Δ films were also found to exchange up to 90% of their oxygen during similar anneals. These results have important ramifications for reoxygenation steps during device fabrications.
Large excitonic nonlinearity in InAs quantum sheets
Authors: Brandt O. , Lage H. , Ploog K.
Published: July 2002

We measure the nonlinearity of the excitonic absorption in isolated InAs planes inserted in a bulk-like GaAs matrix. In cw pump and probe experiments absorption changes as high as 37% are observed at a pumping intensity of 80 W/cm2. The corresponding saturation intensity is 400 W/cm2. The nonlinear absorption cross section is determined to be 1×10−12 cm2, which is in excellent agreement with the theoretical prediction.
Monolithic integration of a new optoelectronic device based on a modulation-doped heterostructure
Authors: Honda Y. , Suemune I. , Yamanishi M.
Published: July 2002

Monolithic integration of a new type of optoelectronic device which functions not only as a lateral-current-injection laser but also as a junction field-effect transistor based on a modulation-doped heterostructure is proposed and demonstrated for the first time. The static and dynamic modulation characteristics of the integrated device were studied. The dynamic on/off ratio of 9 in the light output was observed with the preliminary modulation experiment at the repetition frequency of 50 MHz.
Microstructural characterization of Nb3Al ultrafine multifilamentary superconducting wire by analytical electron microscopy
Authors: Wadayama Y. , Suzuki T. , Aihara K. , Tada N. , Kamata K. , Sakai S. , Inoue K.
Published: July 2002

Microstructural characterization of the longitudinal cross section of Nb3Al wires fabricated by an Nb tube composite process is presented. The wire was produced by cold reduction and a subsequent reaction between Nb matrix and Al-Mg core (final size: ∼φ 80 nm) at 950 °C×5 min+750 °C×72 h. The A15 superconducting compound (grain size: 100 nm) and unreacted fibrous Nb were observed in the microstructure. Nb2Al or other phases rarely appeared. The average Al concentration at the A15 grain was 22–23 at. % from x-ray microanalysis. The critical current density Jc of composite processed wire depended on the grain size of A15, with fine grains providing a high Jc value.
Theoretical study of a vacuum ultraviolet F2 excimer lamp (157 nm) excited by microwave discharge
Authors: Hatakeyama Toshiro , Kannari Fumihiko , Obara Minoru
Published: July 2002

A high-efficiency operation of a vacuum ultraviolet (VUV) incoherent light source of a F2 excimer lamp [157 nm:F2(D′)-F2(A′)] excited by a pulsed microwave discharge has theoretically been studied. Despite the low-pressure (300 Torr) operation, an intrinsic efficiency of 10.6% and a F2(D′) formation efficiency of 17.4% were found to be obtainable at an optimum F2 concentration (0.5%) using He/F2 mixtures. The F2(D′) state is mainly produced by energy transfer reaction from F*. Using a 300 Torr mixture of He/F2=99.5/0.5(%), a photon extraction efficiency of 60.9% is achievable with a low energy loss (39.1%) by collisional quenching. The corresponding optical output of 50.0 μJ/cm3 is achievable at an excitation rate of 100 W/cm3 and an excitation pulse width of 9.0 μs. Since it can be operated at high repetition frequency of up to 55 kHz using conventional devices, an average output power of 2.75 W/cm3 is achievable.
Efficient Cr,Nd:Gd3Sc2Ga3O12 laser at 1.06 μm pumped by visible GaInP/AlGaInP laser diodes
Authors: Scheps Richard
Published: July 2002

The 1.06 μm Nd transition in co-doped Cr,Nd:Gd3Sc2Ga3O12 (Cr,Nd:GSGG) is obtained by diode pumping Cr3+ at 670 nm and is shown to produce efficient, low-threshold laser operation. Both cw and long-pulse diode pumping were demonstrated, with pump power levels as high as 300 mW cw and 1 W pulsed. The lowest threshold power measured was 938 μW, and the highest output power obtained was 43 mW cw and 173 mW pulsed. The best slope efficiency obtained was 42.1%, 78% of the theoretical maximum. Loss measurements indicate a value of 0.4% cm−1.
Low-temperature magnetotransport experiments in pseudomorphic GaAs/Ga0.87In0.13As/Al0.40Ga0.60As semiconductor-insulator-semiconductor field-effect transistors
Authors: Schmidt P. E. , Barbier E. , Rossmanith M. , Dobers M.
Published: July 2002

Low-temperature magnetotransport measurements on a molecular-beam-epitaxy-grown pseudomorphic GaAs-Ga0.87In0.13As-AlxGa1−xAs-GaAs semiconductor-insulator-semiconductor field-effect transistor are reported. In magnetic fields up to 12 T, the sample reveals clearly the integer quantum Hall effect. By varying the gate voltage, the sheet electron concentration of the two-dimensional electron gas can be tuned from depletion to 2×1012 cm−2. The dependence of the electron concentration and the mobility is studied as a function of the gate voltage.
Simulation of effects of uniaxial stress on the deep level transient spectroscopy spectra of the DX center in AlGaAs alloys
Authors: Li Ming-fu , Yu Peter Y. , Weber E. R.
Published: July 2002

Recently the effect of uniaxial stress on the deep level transient spectroscopy (DLTS) of the DX center in AlGaAs alloys have been reported by two separate groups. In both experiments no splitting of the DLTS peak was observed. We have analyzed the experimental results in terms of a large lattice relaxation model in which the DX center can have either a positive or a negative Coulomb energy U. We found that if the symmetry of the DX center depended on its charge state then its DLTS peak was not split by uniaxial stress in contrast to other defects with large lattice relaxation (such as the A center in Si).
High-quality Y1Ba2Cu3O7−x thin films on polycrystalline MgO by temperature-controlled chemical vapor deposition
Authors: Feng Aiguo , Chen Ling , Piazza Timothy W. , Li Hongwen , Kaloyeros Alain E. , Hazelton Drew W. , Luo Li , Dye Robert C.
Published: July 2002

Y1Ba2Cu3O7−x superconducting thin films were grown in situ on polycrystalline MgO substrates by a chemical vapor deposition process that closely couples the sublimation temperatures of the elemental sources to that of the substrate during deposition. It was found that the best quality films were achieved with a controlled ramping of the substrate temperature from 850  °C, at the onset of deposition, down to 750 °C at the end of deposition. The films were analyzed by Rutherford backscattering (RBS), scanning electron microscopy (SEM), x-ray diffractometry (XRD), and four-point resistivity probe. The results of these studies showed that the films were highly c-axis oriented, had near-stoichiometric composition, and exhibited Tc,onset=90 K, Tco=85 K, and had a Jc=2×105 A/cm2 at 77 K in zero magnetic field. A model is proposed for the effect of such temperature control on the CVD growth mechanism of high-quality YBCO films.
Raman scattering resonant with excitons in CdZnTe/ZnTe multiple quantum wells
Authors: Lee D. , Zucker J. E. , Johnson A. M. , Feldman R. D. , Austin R. F.
Published: July 2002

We have studied CdZnTe/ZnTe multiple quantum wells which have alloy wells and strained layers. Low-temperature Raman spectra reveal a strain-induced shift of the longitudinal optic phonon energy consistent with a strain coherently shared between well and barrier layers. In resonant Raman profiles, we observe strong incoming and outgoing resonances at the n=1 heavy hole exciton transition that are well correlated with features in the photoluminescence and excitation spectra. Scattering by the CdTe-like phonon indicates an energy range for exciton localization by alloy fluctuations. The behavior of the ZnTe-like phonon near resonance is interpreted with exciton-polariton relaxation.
Enhancement of SiO2/GaAs interface properties by electron cyclotron resonance plasma-enhanced chemical vapor deposition and Ga outdiffusion control
Authors: Sugitani Suehiro , Asai Kazuyoshi
Published: July 2002

High quality electron cyclotron resonance plasma-enhanced chemical vapor deposition SiO2 film and annealing are investigated in an effort to enhance SiO2/GaAs interface properties. Dramatic reduction of interface state density is achieved by reducing nitrogen and hydrogen impurities in the SiO2 film and optimizing the annealing temperature. A minimum interface state density of 3×1010 eV−1 cm−2 is obtained in SiO2/GaAs annealed at 690 °C for 30 min. Secondary-ion mass spectroscopy data suggest that the reduction in interface state density may be related to the amount of Ga outdiffusion into the SiO2 film.
Saturable absorption in intracavity loss modulated quantum well lasers
Authors: O’Gorman J. , Levi A. F. J. , Tanbun-Ek T. , Logan R. A.
Published: July 2002

Voltage, temperature, and intensity dependence of saturable absorption in InGaAs/InP multiple quantum wells are investigated and related to the lasing characteristics of intracavity loss modulated InGaAs/InP quantum well lasers. Bistability in the static laser light output/absorber voltage characteristic arises from the shape of the measured absorption/voltage/intensity surface of the quantum well absorber. This surface is little changed in the temperature range 0–100 °C. A consequence of this fact is that an intracavity absorber modulates laser threshold more efficiently at higher substrate temperatures.
Equivalent circuit model for current filamentation in p-i-n diodes
Authors: Symanczyk R. , Jäger D. , Schöll E.
Published: July 2002

In semiconductor materials with S-shaped negative differential conductivity, pattern formation due to current filament formation is observed. We present experimental results of filamentation in Si p-i-n diodes and propose an equivalent circuit to describe the observed structures. The electrical circuit is based upon numerical results of electrical field−current density characteristics in p-i-n diodes. From this model we derive an equation, which describes the current density distribution in the device as a solitary structure. The proposed analytical solution, which is well known from the theory of pulse propagation in nerve fibers, leads to expressions for the peak current density and the width of a filament.
Field dependence of critical currents in polycrystalline Bi-Pb-Sr-Ca-Cu-O superconductors
Authors: Jin S. , Tiefel T. H. , van Dover R. B. , Graebner J. E. , Siegrist T. , Kammlott G. W. , Fastnacht R. A.
Published: July 2002

The field dependence of Jc in partial-melt-processed Bi1.6Pb0.3Sb0.1Sr2Ca2Cu3Ox has been investigated. The samples have a dense, polycrystalline microstructure of the (2223) phase with no significant crystallographic texture, and exhibit Tc(χ)∼105 K and transport Jc(H=0)∼104 A/cm2 at 4.2 K. In high magnetic fields (e.g., H=5 T), the transport Jc is somewhat reduced but is still of substantial value. While the high-angle grain boundaries in the present, partial-melt-processed samples are by no means weakly coupled, the field dependence of the critical current density [Jc(0)/Jc(5 T)∼10] is somewhat stronger than in c-axis textured samples [Jc(0)/Jc(5 T)∼3]. The grain boundaries in the present polycrystalline samples may thus be viewed, on the average, as ‘‘mild’’ weak links. These results clearly indicate the necessity for grain texturing if the full Jc capability of the BSCCO-type superconductors is to be exploited.
Control of microscopic superconducting channel by proximity effect
Authors: Totsuji Hiroo
Published: July 2002

A possibility to control a thin superconducting channel through the proximity effect is analyzed on the basis of simple one-dimensional solutions of the equation for the order parameter in the dirty limit. By estimating the transconductance, the feasibility of the three-terminal device based on such a mechanism is discussed.
Laterally injected low-threshold lasers by impurity-induced disordering
Authors: Zou W. X. , Law K.-K. , Merz J. L. , Fu R. J. , Hong C. S.
Published: July 2002

Novel laterally injected lasers were fabricated by impurity-induced disordering (IID). The laterally injected IID (LID) lasers have a self-aligned structure and planar configuration; its processing procedures are almost identical to that used for our recently reported vertically injected IID lasers, and are considerably simpler than those of any other laterally injected laser yet reported. The LID lasers have a minimum threshold current Ith=3.2 mA (typical Ith=4 mA) and a maximum light output 11 mW, with a differential quantum efficiency ηd=32% per facet under room-temperature continuous-wave operation. The LID lasers can also be injected vertically by deliberately using an n+-doped (instead of semi-insulating) GaAs substrate and making additional ohmic contacts on the bottom surface of the wafer. A number of interesting aspects about the LID lasers were revealed by comparing the L-I characteristics of the laser under different injection modes, and by studying the I-V characteristics of different combinations of the top and bottom ohmic contacts.
Sharp phosphorus spikes in silicon grown by fast gas-switching chemical vapor deposition at reduced and atmospheric pressure
Authors: Roksnoer P. J. , Maes J. W. F. M. , Vink A. T. , Vriezema C. J. , Zalm P. C.
Published: July 2002

Sharp phosphorus doping spikes in silicon were grown by fast-gas-switching chemical vapor deposition at temperatures between 800 and 850 °C using disilane and phosphine in 0.03, 0.1, and 1 atm hydrogen carrier gas. The phosphine doping gas was added while growing silicon at a rate of 0.15–0.5 nm/s. High depth resolution secondary ion mass spectrometry measurements have revealed sharp and high concentration dopant profiles. Peak phosphorus concentrations up to 7×1019 cm−3 and a full width at half maximum of 7 nm were obtained. Electrical measurements show that at these concentrations about 40% of the dopant atoms is electrically active in structures grown at 1 atm. Formation of doping tails is shown to be suppressed at atmospheric hydrogen pressure.
Perturbation of the cathode fall in direct-current glow discharges by particulate contamination
Authors: Choi Seung J. , McCaughey Michael J. , Sommerer Timothy J. , Kushner Mark J.
Published: July 2002

Particulate (or ‘‘dust’’) contamination of plasma materials processing discharges is known to reduce yields of the product and to perturb electron transport. Dust preferentially accumulates near the cathode sheath-plasma boundary where energetic electrons accelerated in the cathode fall emanate into the negative glow. In this letter, we theoretically investigate the penetration of the electron flux generated in dc cathode falls through the particulate ‘‘barriers’’ formed by dust contamination. We find that at constant current densities, the plasma responds to the reduction in ionization rate coefficients caused by the particulates by increasing the electric field in the cathode fall. In doing so, the cathode fall voltage increases and cathode fall thickness decreases.
Epitaxy on vicinal surfaces: The critical flux and the diffusion coefficients
Authors: Lu Yan-Ten , Metiu Horia
Published: July 2002

We examine epitaxial deposition on stepped surfaces to determine how the transition from step flow to island growth depends on the diffusion coefficients, terrace width, and the incident flux.
1.55 μm high-power large optical cavity lasers
Authors: Zhong J. C. , Zhu B. R. , Li R. H. , Zhao Y. J. , Pillai R.
Published: July 2002

A high-power 1.55 μm large optical cavity (LOC) laser structure is successfully prepared for the first time by reasonably designing its configuration and by using a proper single step liquid phase epitaxy (LPE) so as to realize lasers with peak output power higher than 2 W per facet in pulsed operation at room temperature. The devices are also characterized by their lower threshold current ( Jth≤2.7 KA/cm2 for broad area contact structure) and high-temperature stability (T0≊130 K). At the same time they are of long-lived operation and are an ideal source of light in this spectral region.
New integrated acousto-optic matrix algebra processor architecture
Authors: Kar-Roy A. , Tsai C. S.
Published: July 2002

A new integrated optic matrix algebra processor architecture that utilizes guided-wave multifrequency acoustooptic (AO) Bragg diffractions is proposed. The architecture is potentially capable of performing matrix-vector multiplications faster than any AO architecture reported heretofore, and matrix-matrix multiplications at rates comparable to the fastest bulk-wave AO architecture. An integrated AO processor module has been realilzed in a Y-cut LiNbO3 substrate 1.0×10.0×28.0 mm3 in size to demonstrate the multiplication of a 4×4 matrix with a 4-element vector at the optical wavelength of 0.6328 μm.
Laser-induced fluorescence on Hg+ in Hg-Ar discharges
Authors: Wamsley R. C. , O’Brian T. R. , Mitsuhashi K. , Lawler J. E.
Published: July 2002

The density of ground-state mercury ions in the cathode region of a fluorescent-lamp-like discharge is measured using laser-induced fluorescence (LIF) at 194.2 nm. LIF is used to make relative density measurements with good spatial resolution and a wide dynamic range while a previously reported absorption technique is used to provide the absolute normalization for these maps.
Creation of E′ defects in vitreous SiO2 by energetic electrons produced by x irradiation
Authors: Kerwin D. B. , Galeener F. L.
Published: July 2002

From experiments using synchrotron radiation, we present evidence that the spin-active defects created in v-SiO2 by x irradiation are predominantly the result of energetic electron damage, rather than the relaxation of the photoionized atoms.
Anomalous Hall effect and the anomalous infrared absorption in n-type bulk Hg0.8Cd0.2Te
Authors: Tian J. G. , Zhang C. P. , Zhang G. Y.
Published: July 2002

The anomalous Hall effects and the anomalous infrared absorption dependence on temperature have been observed in n-type bulk Hg0.8Cd0.2Te in the temperature range between 5 and 300 K. The existence of p-type inclusions in an n-type matrix is considered as the cause of the anomalies. IR spectrum measurement is suggested to be employed to investigate the anomalous effects in bulk HgCdTe crystal.
Molecular beam epitaxy of GaAs on Si-on-insulator
Authors: Zhu Wenhua , Yu Yuehui , Lin Chenglu , Li Aizhen , Zou Shichang , Hemment P. L. F.
Published: July 2002

Epitaxial GaAs films have been grown by molecular beam epitaxy (MBE) on Si-on-insulator (SOI) formed by ion beam synthesis. Rutherford backscattering and channeling, x-ray double-crystal diffraction, and infrared reflection measurements have been used to characterize the epitaxial GaAs films. Experimental results show that the crystal quality of the GaAs films improves markedly towards the GaAs surface for thicker films where the minimum channeling yield drops to 10%. Infrared reflection spectra prove that crystalline GaAs films have been deposited on the SOI structures. Refractive index profiles of the GaAs films on SOI structures can be obtained by computer fitting the interference spectra. The results indicate that the crystal quality of these GaAs films is comparable to similar GaAs films deposited directly on Si by MBE.
Strong anisotropy of the resistive transition in Bi-Sr-Ca-Cu-O thin films prepared by metalorganic chemical vapor deposition
Authors: Yuhya Shigenori , Nakao Koichi , Sugimoto Tsunemi , Baar David J. , Shiohara Yuh , Tanaka Shoji
Published: July 2002

The resistivity of the Bi-Sr-Ca-Cu-O thin films deposited by MOCVD (metalorganic chemical vapor deposition) has been investigated. Samples of thickness from 5 to 300 nm have been studied. Zero resistance temperatures (Tc0) for all samples were about 70 K. For all samples, Tc0 was nearly independent of magnetic fields up to 6 Tesla applied parallel to the film surface. In contrast, Tc0 decreased significantly in fields applied perpendicular to the film surface. We suspect this difference to originate in the nonpenetration of flux quanta (due to the large effective lower critical field for thin film in the parallel field case) and in the potential barrier to flux penetration at the surface of the thin films in addition to the natural anisotropy of the Bi-based superconductors.
High T
c bulk superconductor wigglers
Authors: Matsuzawa Hidenori , Ishibashi Yoshiharu , Ariizumi Masato , Saegusa Hiroshi
Published: July 2002

In the present letter, high Tc bulk superconductor wigglers were proposed as one of the novel applications of high Tc superconductor lenses (Supertrons). Their operation was also shown experimentally. The bismuth-based bulk superconductor wiggler had sinusoidal surfaces with a period length of 35 mm and an amplitude of 2 mm. The wiggler deflected intense electron beams of 340 keV, 1 kA, and 10 ns of duration time with an amplitude of about 1.5 mm.
Pressure studies of tunneling processes through a doped barrier
Authors: Suski T. , Gschlössl C. , Demmerle W. , Smoliner J. , Gornik E. , Böhm G. , Weimann G.
Published: July 2002

We have investigated the influence of hydrostatic pressure on the tunneling processes between two independently contacted two-dimensional electron gas systems which are separated by a doped AlGaAs barrier. For magnetotunneling data, the pressure dependence of the GaAs effective mass m* was determined between p=0 and 10 kbar. In this range, we find a linear pressure dependence of d(m*/me)/dp=8×10−4 kbar−1 for the electrons in the two-dimensional channels. At higher pressures several new resonances are observed, which correspond to transition energies in the order of 4 meV. These effects are most probably explained by local phonon modes related to the DX centers inside the barrier.
First operation of a multi-electron-beam Cherenkov free-electron laser oscillator
Authors: Wang Qingyuan , Yu Shanfu , Xun Peijue , Liu Shenggang , Hu Kesong , Chen Yutao , Wang Pinshan
Published: July 2002

The first experimental demonstration of the physical mechanism underlying multi-electron-beam Cherenkov free-electron lasers has been carried out. Electron beams of a total beam current of 280 A at 500 kV were introduced into a multi-dielectric cavity and stimulated Cherenkov radiation of 1.7 MW at 33.4 GHz was generated. The interaction efficiency was about 1.2%.
Arsenic implantation to oxide filled trench isolation structure
Authors: Fuse G. , Iwasaki H. , Onoda M.
Published: July 2002

We have studied crystal defects of devices with oxide filled trench isolation introduced by high dose (∼1015 cm−2) arsenic implantation at 40–80 keV and the dependence of their growth on oxidation conditions. Cross-sectional views of the devices are observed by transmission electron microscopy. Solid phase epitaxial regrowth becomes very slow at the edge of the silicon island. Oxidation of the silicon substrate is influenced by the stress generated in the oxide filled trench structure. Defect density after oxidation (1) is higher for pyrogenic H2+O2 oxidation than for dry oxidation, (2) is lower at the edge than in the central region of the silicon island, and (3) decreases significantly for a low energy arsenic implantation (40 keV).
Comparison of As species (As4 and As2) in molecular beam epitaxial growth of AlxGa1−xAs (x=0.2–0.7) on (100) GaAs
Authors: Hayakawa T. , Morishima M. , Nagai M. , Horie H. , Matsumoto K.
Published: July 2002

Systematic studies have been made for the first time on the basic properties of AlxGa1−xAs (x=0.2–0.7) grown by molecular beam epitaxy in the wide growth temperature range of 540–780 °C with As4 and As2. The forbidden growth temperature region (FTR), where the specular smooth surface cannot be obtained, has been found to depend strongly upon both the As species and the AlAs mole fraction x. FTR does not change with x in the case of As4; however, in the case of As2, FTR does not exist for x=0.2 and it increases with x from 0.3–0.7. Photoluminescence of n-Al0.3Ga0.7As (Si=1×1018 cm−3) grown with As2 shows lower intensity and higher sensitivity to growth temperature than those of samples grown with As4. Deep level transient spectroscopy has been measured on n-Al0.7Ga0.3As (Si=2×1016 cm−3). New electron traps are found in layers grown with As2.
Nonlinear optical study of quasi-one-dimensional platinum complexes: Two-photon excitonic resonance effect
Authors: Iwasa Y. , Funatsu E. , Hasegawa T. , Koda T. , Yamashita M.
Published: July 2002

Third-harmonic generation measurements have been made for the first time on oriented films of halogen-bridged mixed-valence platinum complexes for the pump wavelength region from 0.6 to 1.0 μm. The ‖χ(3)(−3ω;ω,ω,ω)‖ spectra obtained by the Maker’s fringe method show a distinct peak at about 1.8 eV with the peak value of about 4×10−11 esu. From comparison with the electroabsorption data, this peak has been identified with the two-photon resonance peak with the forbidden exciton in the Pt-halogen chains. One-dimensional exciton states in this compound take an important role in the third-order optical nonlinearity, similar to the case in conjugated polymers.
Wave propagation and damping in an electron cyclotron resonance plasma reactor
Authors: Miyake Shoji , Chen Wei , Kawai Yoshinobu
Published: July 2002

Propagation and damping of 2.45 GHz input microwaves in an electron cyclotron resonance (ECR) hydrogen plasma reactor were measured in a mirror magnetic field. Without plasma production the wave propagated in the chamber with a wavelength nearly equal to the one in a vacuum. When the hydrogen plasma was sustained at a pressure of 3.3×10−1 Pa, the wavelength was shortened to several cm and the wave was strongly damped near the resonance zone in the axial direction where the electron temperature as well as the plasma density indicated maximum values. The experimental result approximately agreed with the cold plasma dispersion relation for an electron cyclotron wave.
Effect of hydrogenation on hole intersubband absorption in δ-doped Si layers
Authors: Arbet-Engels V. , Wang K. L. , Karunasiri R. P. G. , Park J. S.
Published: July 2002

The effect of hydrogen passivation on the intersubband absorption in δ-doped multiple Si layers is studied. The passivation is carried out using a dc plasma of hydrogen in a quartz reactor. Fourier transform infrared spectroscopy is used to measure the absorption spectra and the effectiveness of the passivation of boron acceptors. The intersubband absorption intensity is reduced considerably upon H passivation and the effectiveness of the hydrogenation is a function of the boron concentration in the δ layers and the duration of the exposition to the H plasma. A resonance peak at 1870 cm−1 is observed after passivation, characteristics of a boron-hydrogen complex. After annealing the samples in nitrogen at sufficiently high temperature, the absorption intensity recovers nearly to its initial value and the process of hydrogenation is reversed. The activation energy of the dissociation of the boron-hydrogen complex is calculated and found to be 1.9±0.1 eV, in reasonable agreement with the B-H complex dissociation energy in bulk Si.
Atomic layer epitaxy of GaAs using nitrogen carrier gas
Authors: Yokoyama Haruki , Shinohara Masanori , Inoue Naohisa
Published: July 2002

Atomic layer epitaxy (ALE) of GaAs is achieved in a relatively wide temperature range from 490 to 520 °C by using nitrogen carrier gas. For hydrogen carrier gas, the corresponding temperature range is only from 490 to 500 °C. The upper temperature limits for ALE correspond to the decomposition temperatures of TMG in each carrier gas. Gas analysis reveals that using nitrogen expands the temperature range by suppressing TMG decomposition.
Direct probing of electron movement in superlattices by subpicosecond luminescence
Authors: Deveaud B. , Clérot F. , Chomette A. , Lambert B. , Auvray P. , Gauneau M. , Regreny A.
Published: July 2002

Vertical transport in GaAs/AlGaAs superlattices is probed in structures with graded composition. Such structures allow both to impose a quasi electric field to the carriers and to evidence the carrier movement by the temporal changes in the luminescence line shape. The fit of this line shape by a drift-diffusion model gives the transport properties of electrons. High mobility of the electrons is evidenced for the shortest period superlattices, in agreement with previous optical measurements. The importance of the transfer to the satellite valleys and of the finite capture time in the large well included as a marker are evidenced.
Observation of second-order kinetic damage in sodium salicylate due to soft x rays
Authors: Husk D. E. , Tarrio C. , Benitez E. L. , Schnatterly S. E.
Published: July 2002

We have observed the dose dependence of the bulk quantum efficiency for luminescence of sodium salicylate as a function of the photon energy from 7 to 150 eV. We show that the damage is a second-order or higher kinetic process in the number of electron-hole pairs and is not reversible. We predict that the threshold for damage occurs at 7.2 eV, or twice the band gap of sodium salicylate.
Polarization switching in spun birefringent fiber
Authors: Ferro P. , Haelterman M. , Trillo S. , Wabnitz S. , Daino B.
Published: July 2002

We have experimentally observed the relatively low-power self-switching of polarization ellipticity along the profile of initially circularly polarized picosecond pulses in a spun birefringent fiber. The switching and pulse breakup effects originate from the intensity-dependent modulation of the birefringence beat length.
Uniform p-type impurity-doped multiquantum well AlGaInP semiconductor lasers with a lasing wavelength of 633 nm at 20 °C
Authors: Tanaka T. , Yanagisawa H. , Kakibayashi H. , Minagawa S. , Kajimura T.
Published: July 2002

Impurity doping into a GaInP/AlGaInP multiquantum well (MQW) active layer is applied to suppress the occurrence of the ordered structure of column III elements. Calculation of the quantized energy level in an ordered and disordered GaInP quantum well (QW) shows that uniform p-type impurity doping into a MQW structure is more effective than modulation doping for shortening the lasing wavelength. The lasing wavelength of p-doped MQW lasers with a 3-nm-thick GaInP QW can be shortened to 633.2 nm at an output power of 2 mW at 20 °C. A maximum lasing temperature of 46 °C for a 630 nm band AlGaInP MQW laser with a cavity length of 450 μm is obtained.
Surface electronic states of low-temperature H-plasma cleaned Si(100)
Authors: Cho Jaewon , Schneider T. P. , VanderWeide J. , Jeon Hyeongtag , Nemanich R. J.
Published: July 2002

The surface of low-temperature H-plasma cleaned Si(100) was studied by angle-resolved UV photoemission spectroscopy. The cleaning process involved an ex situ wet chemical preclean followed by an in situ H-plasma exposure at a substrate temperature of 300 °C. After the in situ H-plasma exposure, a 2×1 ordered surface was obtained which exhibited two hydrogen-induced surface states/resonances in the UV photoemission spectra. The temperature dependence of the spectra showed that the Si-H monohydride started to dissociate at a temperature below 500 °C, and the dangling-bond surface states were identified. The spectroscopic properties of the low-temperature H-plasma surface were essentially identical to surfaces prepared by ultrahigh vacuum high-temperature annealing followed by H passivation.
Mechanisms of phase transitions in ion-doped silicon layers
Authors: Danilin A. B. , Mordkovich V. N.
Published: July 2002

A model is suggested for amorphization of Si layers under ion bombardment and also for recrystallization of amorphous layers subjected to heat or radiation-heat treatment. The model is based on regularities governing the kinetics of solid-phase chemical reactions. The amorphization rate is shown to be determined by the divacancy formation rate, while the recrystallization rate by the rate of formation of Si two-atoms complexes at the amorphous layer-crystal matrix interface.
Development and application of a microbeam plasma generator
Authors: Koinuma Hideomi , Ohkubo Hiroyuki , Hashimoto Takuya , Inomata Kiyoto , Shiraishi Tadashi , Miyanaga Akiharu , Hayashi Shigenori
Published: July 2002

A microbeam plasma was successfully generated by using an originally designed capacitively coupled rf plasma reactor which was composed of a needle cathode (1 mm φ), a cylindrical anode (3 mm φ), and a quartz tubing inserted between the cathode and anode. When the reactor was operated in open air and helium was steadily fed as a discharge gas, a plasma beam (φ<2 mm) blew out into air. Conditions for generating a stable plasma were investigated. Preliminary results are presented on the etching of Si by this beam plasma, as well as an emission analysis of the etching plasma.
Weak link dominated anisotropy of critical current density in polycrystalline Y1Ba2Cu3O7−x thin films
Authors: Yang F. , Narumi E. , Patel S. , Shaw D. T.
Published: July 2002

The c-axis oriented Y1Ba2Cu3O7−x thin films with different thicknesses ranging from 1000 to 4000 Å have been fabricated on polycrystalline yttria-stabilized zirconia substrates by pulse laser deposition. The thickness of the film has noticeable influence on the behavior of transport critical current densities at low magnetic field. With the thickness being reduced from 4000 to 1000 Å, the Jc(H) anisotropy changes from Jc(H∥c) ≳ Jc(H⊥c) to Jc(H∥c) < Jc(H⊥c)in the region of field less than 2 kOe. It reveals that the geometric nature of grains and grain boundaries which form Josephson weak links determines Jc(H) behavior of polycrystalline Y1Ba2Cu3O7−x thin films in the magnetic field up to several kOe.
Space-charge effects in photovoltaic double barrier quantum well infrared detectors
Authors: Schneider H. , Larkins E. C. , Ralston J. D. , Schwarz K. , Fuchs F. , Koidl P.
Published: July 2002

We show that the spatial distribution of the dopants strongly influences the transport asymmetry and the photovoltage observed in double barrier quantum well intersubband photodetectors. This influence can be quantitatively explained by the local space-charge fields arising from an asymmetry of the doping profile with respect to the well centers. The resulting transport model correctly predicts both the observed transport asymmetry of the photocurrent and the opposite asymmetry of the dark current.
Mid-infrared field-tunable intersubband electroluminescence at room temperature by photon-assisted tunneling in coupled-quantum wells
Authors: Faist Jerome , Capasso Federico , Sirtori Carlo , Sivco Debbie , Hutchinson Albert L. , Chu Sung-Nee G. , Cho Alfred Y.
Published: July 2002

Electroluminescence associated with intersubband transition energies greater than the optical phonon energy and at temperatures as high as 300 K is reported. The mid-infrared (λ∼5 μm) luminescence is generated by electron injection into AlInAs/GaInAs coupled-quantum wells via an AlInAs/GaInAs pseudoquaternary graded gap alloy. Optical powers up to a few nanowatts and linear in the drive current have been measured. The large Stark shift of the luminescence peak demonstrates the photon-assisted tunneling nature of the transition. The temperature independence of the luminescence slope efficiency in the 10–100 K range and the linearity of the optical power versus drive current provide strong evidence of population inversion.
Nanocrystal seeding: A low temperature route to polycrystalline Si films
Authors: Heath J. R. , Gates S. M. , Chess C. A.
Published: July 2002

A novel method is presented for growth of polycrystalline silicon films on amorphous substrates at temperatures of 540–575 °C. Grain nucleation and grain growth are performed in two steps, using Si nanocrystals as nuclei (‘‘seeds’’). The nanocrystal seeds are produced by excimer laser photolysis of disilane in a room temperature flow cell. Film (grain) growth occurs epitaxially on the seeds in a separate thermal chemical vapor deposition (CVD) step, with growth rates 10–100 times higher than similar CVD growth rates on crystal Si. Grain size and CVD growth rates are dependent on seed coverage, for seed coverage <0.2 monolayers.
Deposition of fluoropolymer thin films by vacuum-ultraviolet laser ablation
Authors: Ueno Y. , Fujii T. , Kannari F.
Published: July 2002

Crystalline thin films of polytetrafluoroethylene were deposited on Si(100) wafers by F2 laser (157 nm) ablation in 200 mTorr Ar gas atmosphere. X-ray photoemission spectra indicated that the composition of the deposited films was similar to the source material. The surface morphology of films deposited at room temperature contained numerous fibrous structures in size of 100–400 nm, but they were smoothed out at elevated wafer temperature of ∼370 K, while the crystalline feature was still maintained. The refractive index was ∼1.35 at 633 nm.
Photothermally modulated stray field imaging of magnetic materials
Authors: Hoppstädter D. , Netzelmann U.
Published: July 2002

Magnetic stray fields of ferromagnetic surfaces were modulated by focused laser beam heating using a chopped Ar-laser beam. The changes of the magnetic flux close to the surface due to the temperature dependence of the magnetization are measured by a pickup coil. Modulation frequencies were between 100 Hz and 30 kHz. The heating beam and pickup coil were rastered over the sample surfaces to produce microscopic images. A lateral resolution of about 10 μm has been achieved, which is determined mainly by the size of the laser beam. The technique was applied to samples of iron containing cementite and austenite phases. The phase signals are revealing the different signs of the local magnetization. Measurements as a function of the external magnetic field show the reversal of the magnetization in the ferromagnetic phases.
Three-dimensional electrostatic potential, and potential-energy barrier, near a tip-base junction
Authors: Pan Li-Hong , Sullivan Thomas E. , Peridier Vallorie J. , Cutler Paul H. , Miskovsky Nicholas M.
Published: July 2002

The geometry of an atomically sharp or nearly atomically sharp tip in proximity to a planar anode may be closely approximated in the prolate-spheroidal coordinate system. An exact three-dimensional electrostatic-potential solution for a free charge in such a tip/base junction is given in this letter, including calculations for both the symmetrical on-axis case and the asymmetric off-axis case. An exact solution for the potential-energy barrier is also given; this solution has immediate applications in three-dimensional tunneling studies and in calculations of electron trajectories in micron- and submicron-sized field-emitter arrays.
Development of anisotropic microtwin distributions in GaAs grown on 4°-off (001) Si by molecular beam epitaxy
Authors: Wei X. L. , Aindow M.
Published: July 2002

Transmission electron microscopy has been used to confirm that the microtwins in GaAs grown on 4°-off (001) Si by molecular beam epitaxy form preferentially on one of the {111} planes. A Schmid factor analysis of the stresses in the deposit shows that the favored plane is the one on which the resolved shear stress is highest, supporting a deformation twinning model for twin formation in two dimensional growth of GaAs on offcut Si substrates.
Common-mode rejectors for pulse power diagnostics
Authors: Mathew J.
Published: July 2002

Pulse power diagnostics are usually prone to common-mode noise pickup. A way of suppressing this noise is to introduce a common-mode rejector in each suspected signal line. Two types of rejectors will be described in this article. One handles signals with rise times exceeding 10 ns, or equivalently with frequencies less than 35 MHz. The other is suitable for signals with subnanosecond rise times. Both were optimized to yield the highest rejection achievable. The method of winding employed and the interlead separation were found to be quite important for proper operation of the common-mode rejector. Some of the underlying mechanisms of ground noise generation are also briefly investigated.
An accurate method for refractive index measurements of liquids using two Michelson laser interferometers
Authors: St-Arnaud J. M. , Ge J. , Orbriot J. , Bose T. K. , Marteau Ph.
Published: July 2002

This article describes how a thin wedge can be combined with two Michelson laser interferometers to determine precisely the refractive index of liquids. The precision of our experimental technique is such that the refractive index values obtained with this method can yield results with a statistical error of 5×10−6. The experimental refractive index values of ethanol, CCl4, toluene, benzene, and CS2 obtained by using bidistilled water as a reference are reported.
High-power microwave pulse generator
Authors: White G. O. , Chen L. , Patton C. E. , Tinkoff R. L.
Published: July 2002

An inexpensive alternative to commercial high-power microwave pulse generators is described. The present high-power microwave pulse generator utilizes a surplus MIT model 3 Mark II hard tube modulator and 2J51 magnetron. The basic design and technical details of the pulse generator are presented. The pulse generator is designed to produce 8.5–9.6 GHz pulses with pulse lengths ranging from 2 to 4 μs, with a nominal power output of 20 kW and a maximum duty cycle of 0.001.
Applications of real time digital acquisition of ultrasonic borehole televiewer data on a personal computer
Authors: Schmitt Douglas R. , Holm Lars , MacKinnon James S.
Published: July 2002

A personal computer based hardware has been developed for the real time, rapid digitization of echo amplitudes and times-of-flight of ultrasonic pulses produced by existing analog ultrasonic borehole imaging systems. Both amplitude and travel-time B-scan images are mapped circumferentially around the wellbore wall with reference to magnetic north. 12-bit analog to digital conversion of pulse amplitudes provides a resolution of approximately 1 mV out of a peak amplitude voltage of 1 V; travel times are determined to within 100 ns to a maximum time of 512 μs after which it is assumed that no signal will be detected. This information provides high-resolution digital images of the borehole wall and cross section which are useful for delineation of open fractures, discrimination of complex cross sections, and calculation of wellbore volumes.
New microwave ion source for plasma-wall interaction studies
Authors: Tokiguchi K. , Gotoh Y. , Yamaki T. , Amemiya K.
Published: July 2002

To obtain high-flux hydrogen atoms equivalent to the irradiation condition at the surface of the first-wall or divertor plate in a nuclear fusion reactor, a new microwave ion source was constructed and its operation was demonstrated. The source was designed so that H3+ ions are efficiently produced through the ion-molecule reaction between H2+ ions and H2 molecules. Extracted ion beams were mass analyzed and pure H3+ ions were introduced into the ultrahigh-vacuum target chamber. The obtainable irradiation current of H3+ ions was 1.5 mA at 3 keV. The beam diameter at the target was about 1 cm. Maximum flux density of hydrogen atoms at an energy of 1 keV exceeded 4×1016 H/cm2 s, which is high enough for plasma-wall interaction studies.
Sensitive electron paramagnetic resonance spectrometer for studying defects in semiconductors
Authors: Altink H. E. , Gregorkiewicz T. , Ammerlaan C. A. J.
Published: July 2002

The construction of a state-of-the-art electron paramagnetic resonance spectrometer for application to the studies of defects in semiconductors is described. The spectrometer is of superheterodyne type with low-frequency modulation of the magnetic field and working in dispersion. The use of a microwave synthesizer and a low-noise GaAs field-effect transistor amplifier results in ultrahigh sensitivity of the spectrometer which is experimentally shown to be 3×108 centers cm−3 with the test measurement being performed at 4.2 K for the easily saturable typical shallow donor center phosphorus in silicon. It is shown that this high sensitivity can be attributed to the use of the microwave synthesizer. The sensitivity of the spectrometer is improved by a factor 30 when a microwave synthesizer is used as microwave source instead of a quartz crystal stabilized klystron.
Application of a microscope to Brillouin scattering spectroscopy
Authors: Takagi Yasunari , Kurihara Kazuyuki
Published: July 2002

In order to make a microscopic observation of the surface elastic wave on inhomogeneous opaque materials, an apparatus for Brillouin scattering spectroscopy was constructed utilizing a commercial microscope. An optical system which serves both as an inlet of a laser beam and as an outlet of the scattered light was made and incorporated in the microscope. The apparatus was proved to be particularly useful to make microscopic-scale observations of surface elastic waves on metal films.
Cascading lock-in amplification: Application to wavelength modulation spectroscopy
Authors: Holcomb M. J. , Little W. A.
Published: July 2002

We have developed a new method of signal detection that permits the direct measurement of the wavelength derivative transmittance or reflectance spectra of any sample that can be studied by optical spectroscopy. This method uses multiple lock-in amplifiers where the output of one lock-in is, in turn, measured by another. In doing this we can achieve both high signal-to-noise ratios and eliminate variations in the background response of the spectrometer to approximately one part in 104, while keeping the spectrometer simple in design.
Development of a 500 keV, 22 A D− ion source for the neutral beam injector for JT-60U
Authors: Okumura Y. , Fujiwara Y. , Honda A. , Inoue T. , Kuriyama M. , Miyamoto K. , Miyamoto N. , Mogaki K. , Nagase A. , Ohara Y. , Usui K. , Watanabe K.
Published: July 2002

The first results of the performance test of the large negative ion source for a JT-60U negative-ion-based neutral beam injector (N-NBI) are presented. The ion source consists of a cesium seeded multicusp plasma generator, where negative ions are produced via volume and surface processes, a 110 cm×45 cm multiaperture extractor, and a three-stage electrostatic accelerator. After negative ion production and voltage holding tests in test stands, the ion source was installed in the N-NBI system and the full power test began. Up to now, the ion source has produced 400 keV, 5.9 A (2.4 MW) D− ion beams, the world highest D− current and beam power, with a pulse duration of 0.1 s.
New method of calculating the correction factors for the measurement of sheet resistivity of a square sample with a square four-point probe
Authors: Shi Junsheng , Sun Yicai
Published: July 2002

The finite element method was employed to calculate the correction factors for the measurement of sheet resistivity of a square sample with a square four-point probe. This method is simpler than methods of image and conformal transformation, and can be used for calculating the correction factors for four-point resistivity measurement of an arbitrarily shaped sample with an arbitrary four-probe array.