bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous optical and electrical recovery processes of the photoquenched EL2 defect produced by oxygen and boron ion implantation in gallium arsenide
Authors: Samitier J. , Marco S. , Pérez-Rodríguez A. , Morante J. R. , Boher P. , Renaud M.
Published: July 2002

The optical and electrical recovery processes of the metastable state of the EL2 defect artificially created in n-type GaAs by boron or oxygen implantation are analyzed at 80 K using optical isothermal transient spectroscopy. In both cases, we have found an inhibition of the electrical recovery and the existence of an optical recovery in the range 1.1–1.4 eV, competing with the photoquenching effect. The similar results obtained with both elements and the different behavior observed in comparison with the native EL2 defect has been related to the network damage produced by the implantation process. From the different behavior with the technological process, it can be deduced that the electrical and optical anomalies have a different origin. The electrical inhibition is due to the existence of an interaction between the EL2 defect and other implantation-created defects. However, the optical recovery seems to be related to a change in the microscopic metastable state configuration involving the presence of vacancies.
Paramagnetic defects in neutron-irradiated GaP
Authors: Benchiguer T. , Goltzené A. , Mari B. , Schwab C.
Published: July 2002

Aiming at a better understanding of intrinsic defects in III-V compounds, we reinvestigate fast-neutron-irradiated GaP. The surprising result is the observation of a similar spectrum, formerly ascribed to Asi-related defects in GaAs. Annealing experiments suggest this spectrum involves an impurity, probably boron.
Current-controlled electrical switching caused by the combined properties of ferroelectric KH2PO4 and π-conjugated polymer, poly-p-phenylene vinylene
Authors: Yamamoto Hiromichi
Published: July 2002

For examination of control of conductivity of a single molecule, the dc current-voltage relation has been investigated in a system based on a ferroelectric material, potassium dihydrogen phosphate KH2PO4, and a π-conjugated polymer, poly-p-phenylene vinylene, and its system is demonstrated to cause current-controlled electrical switching that is similar to that of a chalcogenide glass alloy. The switching phenomenon occurs even in repeated runs, although the voltage drop near the critical current value in the first run is unstable compared to that in the following runs. Furthermore, little change in the temperature of the specimen is observed over the entire range in the high- and low-resistivity states. This indicates the negative possibility of a heating effect on the switching phenomenon.
Proposed measurements of the phase-coherence length in a two-dimensional electron gas at high magnetic fields
Authors: Hirai Hiroshi , Komiyama Susumu , Nakamura Kazuo , Nihey Fumiyuki
Published: July 2002

Coherence effects appearing in the two-terminal conductance of a series of quantum point contacts are theoretically studied for zero and finite temperatures and for arbitrary phase coherence lengths in the regime of quantized Hall effects. Experimental geometries to determine the phase coherence length are proposed and the conductance in the geometries is quantitatively analyzed by using the Landauer–Büttiker approach.
Magnesium doping in In0.32Ga0.68P grown by liquid-phase epitaxy
Authors: Chen Chyuan-Wei , Wu Meng-Chyi , Kuo Li-Kuang
Published: July 2002

Mg-doped In0.32Ga0.68P epitaxial layers have been grown on (100) GaAs0.61P0.39 substrates by liquid-phase epitaxy using a supercooling method. The electrical properties of the Mg-doped layers are investigated using capacitance-voltage methods at 300 K. The full width at half maximum value of the 300-K photoluminescence spectrum increases with hole concentration for Mg-doped layers. The 77-K photoluminescence spectra show two peaks and one broad band, and their relative intensities change with various hole concentrations. The Mg acceptor ionization energy obtained from 77-K photoluminescence spectra is in the range from 20 to 38 meV. Finally, the photoluminescence spectra of Mg-doped In0.32Ga0.68P layers with three hole concentrations measured at various temperatures between 20 and 150 K are presented for the gradual evolution of the peaks.
Characterization of high-quality pseudomorphic InGaAs/GaAs quantum wells by luminescence and reflectance techniques
Authors: Pamulapati J. , Bhattacharya P. , Tober R. L. , Loehr J. P. , Singh J.
Published: July 2002

Reflectance and photoluminescence spectroscopy have been used to study the optical properties of high quality InxGa1−xAs/GaAs (0.13≤x≤0.30) single quantum wells. The results show strong agreement with the theoretical model used taking into account the strain potential. The agreement of the theoretical model, though, deviates from the experimental results for large values of excess strain in the well. For the case of the large strain (x=0.30) the reflectance indicates the strain in the well is hydrostatic rather than biaxial. The relevance of this fact is discussed in relation to device performance.
TEr azimuthal modes for a biconic transmission line in the small-gap limit
Authors: Johnson William A. , Mendel Clifford W. , Seidel David B.
Published: July 2002

Azimuthally asymmetric modes in a biconic transmission line with a small-gap angle may be approximated by ‘‘transmission-line-like’’ modes. It is shown that the errors in these approximations are second order in the gap angle and approximate error bounds are provided. As an example demonstrating the application of this analysis in biconic structures, an analysis to characterize of the electromagnetic waves in the vacuum feed of the Particle Beam Fusion Accelerator II is provided.
Analysis of diamond phase in hydrogenated hard carbon film using radio frequency plasma etching
Authors: Shimada Yoshihito , Mutsukura Nobuki , Machi Yoshio
Published: July 2002

The hydrogenated hard carbon films prepared in CH4 radio frequency (rf) discharge, have been examined to characterize the film structure by means of several spectroscopic measurements combined with CF4 rf plasma etching. The CF4 plasma etching can selectively remove the amorphous phase with graphite structure, and can retain the diamond structure in the film. After the CF4 plasma etching for a long time, cylindrical structures and/or particles were formed on the substrate. The top of the cylindrical structure or the particle was diamond, and the bottom part was the Si substrate. It was confirmed that most of the components in the hard carbon film is amorphous phase, and the diamond phases exist at the interface between the film and the substrate.
Dielectric and pyroelectric properties of Pb5Ge3O11 ceramics
Authors: Levstik A. , Golob B. , Kosec M.
Published: July 2002

The pyroelectric coefficient of the (PbO)x(GeO2)(8−x) ceramics as a function of the PbO or GeO2 content close to x=5 was studied. The value of the pyroelectric coefficient increases with increasing content of the PbO up to x=5 and decreases above with an irregularity around x=5. From the frequency dependence of the complex dielectric constant the electric conductivity was determined. The temperature dependence of the electric conductivity is a function of poling. Unpoled ceramics have an activation energy of 0.70 eV. The observed dielectric relaxations in ceramics are equivalent to those in monocrystals.
The degradation of TbFeCo magneto-optic media due to reaction with oxide-containing dielectric materials and substrates
Authors: Yang M. M. , Reith T. M.
Published: July 2002

The interfacial stability of TbFeCo with oxide-containing dielectric materials and substrates is studied, in order to understand the degradation kinetics and thermal activation energy associated with interfacial oxidation of the rare-earth transition film. Auger elemental depth profiles show that interfacial oxidation is responsible for the degradation of Kerr rotation. The glass and oxide-containing dielectric film are the internal source of oxygen. An activation energy of 1.72 eV is obtained for the degradation due to this mechanism.
Nonlinear Bragg reflection waveguide
Authors: Wächter C. , Lederer F. , Leine L. , Trutschel U. , Mann M.
Published: July 2002

The ability of Bragg reflection waveguides to support TE-polarized nonlinear guided waves is studied. The dispersion relation for these waves is derived analytically. The numerical studies address the dependence of their propagation constants upon the interface intensity, the guided field power, and their evolution as they propagate down the guide. The characteristic features of the nonlinear guided waves are identified as power thresholds, instability on positively-sloped branches of the dispersion curve and symmetry breaking with the formation of spatial solitons.
Interfacial reactions between nickel–chromium alloys and aluminum
Authors: Tan Zhengquan , Heald S. M.
Published: July 2002

We have studied the interface structure and reactions of Ni–Cr alloy and Al thin film bilayers using glancing-angle x-ray reflectivity and extended x-ray-absorption fine structure techniques. The Al/Ni–Cr bilayers were prepared by evaporation in ultrahigh vacuum with a clean interface (Clean) or an interface exposed to 600 Langmuir oxygen (O-exposed). No interfacial reaction is observed at room temperature in either the Clean or the O-exposed samples. Upon annealing for 10 minutes, initial reaction occurs at about 250 °C in the Clean sample and 310 °C in the O-exposed sample. The oxygen impurity at the interface retards the initial reaction and also modifies the diffusion behavior. In both Clean and O-exposed systems, the reaction starts between Ni and Al forming NiAl3. The reaction results in a Cr-rich region near the interface which transforms to the bcc structure. Only at higher temperatures do Cr and Al react to form CrAl7. The role of various diffusion channels and oxygen impurity at the interface in relationship to the reaction pattern will be discussed.
Ion-beam induced structural transformations in hydrogenated microcrystalline silicon
Authors: Yedave S. N. , Ogale S. B. , Dusane R. O. , Rajarshi S. V. , Bhide V. G. , Kshirsagar S. T.
Published: July 2002

Ion-implantation induced structural transformations are investigated in hydrogenated microcrystalline silicon (μc-Si:H). Ion-beam processing of the μc-Si:H samples was done using 160 keV Ar+ ions at different dose values, in the range of 1013–1016 ions/cm2. Ion-beam induced transformation from the microcrystalline-to-amorphous phase was examined with the help of x-ray diffraction (XRD) and laser-Raman spectroscopic techniques. The conductivity changes in the samples were also monitored as a function of ion dose. It is observed that at a specific threshold ion dose value, the conductivity decreases by more than an order of magnitude. There are concomitant changes in XRD and laser Raman features. Furthermore the results clearly indicate grain growth under ion-beam irradiation at high dose values.
Implanted Si atoms shifting between Ga sites and As sites by thermal stress in conductive-layer GaAs crystals on semi-insulating substrates
Authors: Saito Yasuyuki
Published: July 2002

Large (0.8 V order) discrepancies of threshold voltage Vth between the predicted Vth values by the Lindhard–Scharff–Schio/tt Gaussian approximate calculation and the Vth of the tungsten nitride (WNx) self-alignment (SA) gate GaAs metal-semiconductor field-effect transistors (MESFETs) were observed. These discrepancies were confirmed by the comparison of the Vth of the WNx-SA-gate MESFETs and the Vth of the (N+: high carrier concentration layers self-aligned of source-drain electrodes)-less conventional MESFETs on 2-in.-diam semi-insulating substrates from liquid-encapsulated-Czochralski-technique-grown 〈100〉 boules. The discrepancy was also analyzed by the capacitance-voltage (C-V) measurement of large-diameter (440 μm) Schottky diodes which were built into the MESFET arrays. It was found that for obtained SA-process carrier depth profiles (Si, 150 keV, 3×1012 cm−2) the carrier concentration at a depth of 0.25 μm decreased from 5.3×1016 to 2.0×1016 cm−3, but, on the other hand, the peak carrier concentration slightly decreased from 12.8×1016 to 12.4×1016 cm−3.

By the calculation for Vth on the basis of the actual C-V carrier depth profiles, it was found that the carrier concentration decrease was comparable to the Vth variation (0.8 V). Furthermore, the Vth variation of the shallow channel implantation (50 keV) was comparable to that of the deep channel implantation (150 keV). As a result of the experiment and analysis, it was found that the large Vth variation for the SA N+ process was caused by reoccupation (Ga sites to As sites) of implanted Si atoms in the channel active-layer crystal by tensile stress formed by the thermal-expansion coefficient difference between chemical-vapor deposition (CVD) phosphosilicate glass (or CVD SiO2) film and (100) GaAs substrate crystal. The Si atom reoccupation quantity was, for the first time, explained by the Si atom compensation ratio equation as a function of the bond length (Si-As and Si-Ga) variation, an equation which was again derived based on Otsuki’s work on the Si atom Gibbs free energy in GaAs crystal, using the data of thermal-expansion coefficients for SiO2, GaAs, and WNx in the report of Katz and Dautremont-Smith [J. Appl. Phys. 67, 6237 (1990)] and in the report of Lahav, Grim, and Blech [J. Appl. Phys. 67, 734 (1990)]. Moreover, the analysis suggests that local stress or local distortion, which is introduced by the implanted Si atom itself into the GaAs crystal, performs an important role for the Si atom electrical activation efficiency.
Excess noise induced in metal resistors as a result of dynamic processes
Authors: Lawson M. F. F. , Spooner T. , Ficalora P. J.
Published: July 2002

Excess noise is induced in thin gold films when the film is put in contact with an electrolytic solution. The magnitude of the noise changes as a function of the concentration of the ions in solution and follows a Temkin adsorption isotherm. Excess noise is also observed in a platinum wire exposed to water undergoing solidification. All measurements are made in the absence of an external applied bias. This implies that a dynamic process moving towards or at equilibrium can induce excess noise in a metal resistor.
Optical transitions in symmetric, compositionally graded triangular AlGaAs quantum wells grown by molecular beam epitaxy
Authors: Giugni Stephen , Tansley T. L. , Green F. , Shwe C. , Gal M.
Published: July 2002

An experimental investigation is reported of optical transitions in narrow, symmetric, triangular well structures. Quantum wells as narrow as 2.5 nm have been grown in AlGaAs using an analog grading strategy in a conventional, solid source molecular beam epitaxy (MBE) system. Linearly graded heterostructures are analyzed in terms of Airy function solutions of the one-dimensional wave equation and energy levels more evenly spaced than in the equivalent square well are predicted. Transition energies obtained from photoluminescence, photoreflectance, and differential photoreflectance measurements agree well with calculated values. The differing spatial extents of wave functions in the triangular well case also modify the relative intensities of the lines identified, in particular the normally faint transition from n=3 heavy hole state to conduction-band ground state (hh3-e1) appears enhanced.
The influence of argon ion bombardment on form birefringence in thin films of titania
Authors: Sprague Robert W. , Hickey Carolyn F. , Hodgkinson Ian J.
Published: July 2002

Thin films of titanium oxide deposited in the presence of oxygen at oblique incidence under argon ion bombardment exhibit birefringence that depends on the energy and relative direction of the ion beam and material flux.
Plasma etch effects on low-temperature selective epitaxial growth of silicon
Authors: Lou Jen-Chung , Oldham William G. , Kawayoshi Harry , Ling Peiching
Published: July 2002

The quality of epitaxial silicon grown on regions exposed to plasma etching using He, CHF3, and CF4 etching gases has been studied. Plasma-etch-induced surface damage leads to defects in the epilayers. Dislocation loops and precipitates at the epi/substrate interface are always observed. High-temperature prebake can further lead to microtwins and threading dislocations. The formation of defects in epilayers is attributed to the ion bombardment induced surface/subsurface defects and the reactive-ion-induced contaminants on exposed Si areas. A 900 °C grown sacrificial oxide film can efficiently remove both near-surface defects and contaminants to get a clean SiO2/Si interface, resulting in high quality Si epilayers. A 5-nm sacrificial oxide is adequate. An air exposure between several plasma etch cycles is also important in suppressing polymer accumulation on substrates.
Epitaxial growth of zinc phosphide
Authors: Suda Toshikazu , Kakishita Kazuhiko
Published: July 2002

We report the first epitaxial growth of Zn3P2. The Zn3P2 epitaxy was obtained on (100) GaAs and ZnSe/GaAs by metalorganic chemical vapor deposition at growth temperatures of 350–400 °C and V/II ratios above 0.8 using dimethylzinc and PH3. The stoichiometry was assessed by x-ray photoelectron spectroscopy at Zn/P=1.5. A Hall mobility of 310 cm2/Vs at 300 K was obtained with a hole concentration of 3.5×1016 cm−3 for Zn3P2 grown at 380 °C. The absorption edge deduced is 1.51 eV at 300 K. Photoluminescence data suggest four acceptor levels (45, 65, 86, and 104 meV at 12.8 K).
Observation of the transverse optical phonon mode in CdS film at 4880 Å excitation
Authors: Dai C. M. , Chuu Der-San
Published: July 2002

The transverse-optical (TO) phonon mode in a CdS film with a thickness less than 410 Å is observed at 4880 Å excitation wavelength which is above the band gap of CdS bulk (2.42 eV) at room temperature. This phenomenon is ascribed to the size quantization of the free carrier in the low-dimensional thin-film structure. The quantum size effect causes a blue shift of the band gap in the as-deposited CdS thin film. The Raman shift of the TO mode of CdS film is around 220 cm−1. The softening energy of the TO phonon mode is about 8 cm−1. It was found that this softening energy is independent of the film thickness.
Determination of the noncharging electron-beam energy on insulators
Authors: Girard P. , Charpenel P. , Martin H.
Published: July 2002

A new method allowing accurate determination of the primary electron energy corresponding to the zero charge deposition on insulators is presented. It consists in evaluating the surface voltage variations under an electron-beam charge deposition, by means of a classical secondary electron spectrometer. Experimental data on lithography photoresists are reported. Comparison is made with classical metrology measurements, i.e., imaging profiles, and a good agreement is found. Experimental results show the angular dependence of the highest noncharge energy. A formulation of the secondary emission coefficient angular dependence is proposed and discussed versus experimental data.
Yield enhancements of secondary negative molecular ions consisting of matrix elements under cesium primary ion bombardment of GaAs
Authors: Tsuji Seiji
Published: July 2002

A high secondary negative molecular ion yield that is high relative to the secondary negative monomer ion yield has been observed. The secondary negative ion spectrum of a GaAs chemical compound semiconductor sputtered by a cesium primary ion under the secondary ion mass spectroscopy dynamic mode was examined and it was found that the secondary negative GaAs dimer ion was as intense as the secondary negative arsenic monomer. The GaAs dimer ion was three times higher in its intensity than another dimer of the As2 ion. Moreover, the secondary matrix trimer ions containing at least one Ga atom have one order higher intensities than the arsenic trimer ions. At a stable state of the sputtering process, yield variations of secondary molecular ions made up of the matrix elements of GaAs have been examined as a function of the primary ion current density. The high yield of secondary molecular ion species consisting of the matrix elements of GaAs and containing at least one Ga atom is considered to be indirectly related to the arsenic depletion on the GaAs surface sputtered by cesium primary ions.
Fluorine-doped indium oxide thin films prepared by chemical vapor deposition
Authors: Maruyama Toshiro , Nakai Tsuyoshi
Published: July 2002

Transparent conductive fluorine-doped indium oxide thin films were prepared by an atmospheric-pressure chemical vapor deposition method. The raw material was [C7H15COO]2 In[H(CF2)4COO]. The polycrystalline films were obtained at a reaction temperature in the range of 350–450 °C. This chemical vapor deposition method incorporates fluorine atoms into a crystalline structure and consequently leads to a high carrier concentration, yielding fluorine-doped indium oxide films of low resistivity. For the 320-nm-thick film deposited at 380 °C, the resistivity was 4.4×10−4 Ω cm, and the sheet resistance was 13.8 Ω/⧠.
Fabrication of highly oriented YBa2Cu4O8 films by alkoxide sol–gel methods
Authors: Katayama Shingo , Sekine Masahiro , Fudouzi Hiroshi , Kuwabara Makoto
Published: July 2002

YBa2Cu4O8 films were fabricated on MgO(100) single-crystal and Ag substrates at atmospheric pressure by the sol–gel method using metal alkoxides. On MgO(100) substrates, YBa2Cu4O8 films were formed at 800 °C through YBa2Cu3O7−x. On Ag substrates, YBa2Cu4O8 films were obtained at a firing temperature as low as 700 °C and highly oriented films were formed at 800 °C. YBa2Cu4O8 films were not formed through YBa2Cu3O7−x in this case. Simultaneous use of the sol–gel method and Ag substrates was remarkably effective for promoting the formation of the YBa2Cu4O8 phase and producing highly oriented films.
Microstructure and magnetic properties developed by hot pressing of cast Pr–Fe–B magnets
Authors: Chen Zhongmin , Shi Zhengxing , Wang Leyi , Fu Hengzhi
Published: July 2002

The hot pressing process of cast Pr19Fe74.5B5Cu1.5 magnets were studied. Microstructure studies reveal that during the hot pressing, the crushing of Pr2Fe14B matrix grains and the relative slip and rotation between the grains take place and the Pr-rich melt is squeezed out of the magnet, leading to fine, dense and well-aligned Pr2Fe14B grains surrounded by a thin Pr-rich phase layer in the fully-deformed magnets. Magnetic properties of Br=9.9 kG, iHc=11.0 kOe and (BH)max=24.0 MG Oe are obtained. The increase of coercivity is attributed to the fine Pr2Fe14B grains and the thin Pr-rich phase layer continuously distributed at the grain boundaries. The increasing remanence results primarily from the development of the easy-axis alignment as well as from the densification of the Pr2Fe14B matrix. The easy-axis alignment is developed by the relative slip and rotation of the crushed Pr2Fe14B grains. A full and slow hot pressing is necessary for developing a good easy-axis alignment and high magnetic properties.
Solid-phase epitaxial growth of Ge-Si alloys made by ion implantation
Authors: Corni F. , Frabboni S. , Ottaviani G. , Queirolo G. , Bisero D. , Bresolin C. , Fabbri R. , Servidori M.
Published: July 2002

Solid-phase epitaxial growth was studied in germanium-implanted 〈100〉 silicon wafers as a function of germanium fluence, annealing temperature, and time. MeV He Rutherford backscattering in channeling conditions, cross-sectional transmission electron microscopy, double-crystal x-ray diffraction, and secondary-ion mass spectroscopy techniques were used to characterize the samples. At low fluences, up to 1×1015 cm−2 at 130 keV, the crystallization kinetics is similar to that measured on self-amorphized silicon. In the high-dose samples, prepared by multiple implants with a total dose of 3.12×1016 cm−2, the growth rate at fixed temperatures decreases. A comparison with literature data, obtained by similar experiments performed on amorphized uniform GexSi100−x films prepared by molecular-beam epitaxy or chemical-vapor deposition, reveals that the concentration gradient, unavoidable in implanted samples mainly at the end of the ion range region, is strictly connected with the observed decrease.
A study of metal-oxide-semiconductor capacitors fabricated on SF6 and SF6+Cl2 reactive-ion-etched Si
Authors: Castán E. , Arias J. , Barbolla J. , Cabruja E. , Lora-Tamayo E.
Published: July 2002

Metal-oxide-semiconductor capacitors have been fabricated on SF6 and SF6+Cl2 reactive-ion-etched silicon in order to study the resulting defects at the Si-SiO2 interface and in the bulk of the silicon substrate. The reactive-ion-etching (RIE) induced damage reveals itself by the presence of positive charge in the oxide, by interfacial states, and by two deep levels in the silicon bulk located at 300 and 335 meV above the valence band and probably related to fluorine atoms. We have studied the effect of the chamber pressure and the plasma composition on the resulting damage. This damage is more important when the chamber pressure is low because of the higher free-mean path of the plasma ions. On the other hand, when the Cl2 concentration in the plasma is raised the densities of interface states and of the deep levels decrease while the positive charge in the oxide increases. Finally, we have shown that a post-RIE thermal annealing can be used to restore the electrical properties of the RIE-damaged silicon surfaces.
Interband tunnel current between states of one, two, and three dimensions
Authors: Gilman J. M. A. , O’Neill A. G.
Published: July 2002

The theory for interband tunnelling has been reviewed and modified to describe more effectively bipolar tunnel currents between states of either one, two or three dimensions. In particular a joint density of states is introduced for those cases where the densities of states on either side of the barrier are so widely disparate that the smaller of the two may lead to current limitation. Theory is compared with experiment which appears to vindicate the procedure.
Planar native-oxide buried-mesa AlxGa1−xAs-In0.5(AlyGa1−y)0.5P- In0.5(AlzGa1−z)0.5P visible-spectrum laser diodes
Authors: Kish F. A. , Caracci S. J. , Maranowski S. A. , Holonyak N. , Hsieh K. C. , Kuo C. P. , Fletcher R. M. , Osentowski T. D. , Craford M. G.
Published: July 2002

Data are presented demonstrating the continuous (cw) room-temperature (23 °C) operation of planar index-guided ‘‘buried-mesa’’ AlxGa1−xAs-In0.5(AlyGa1−y)0.5P- In0.5Ga0.5P heterostructure visible-spectrum laser diodes. The planar ‘‘mesa’’ structure is formed by ‘‘wet’’ oxidation (H2O vapor+N2 carrier gas, 550 °C) of the AlxGa1−xAs on the composite AlxGa1−xAs-In0.5(AlyGa1−y)0.5P upper confining layer (outside of the active stripes). The oxidation process results in a ∼0.5-μm-thick native oxide located (in depth) within ∼3000 Å of the active layer in the region outside of the laser stripes themselves. The oxide possesses excellent current-confinement properties and a low refractive index (n≊1.60), resulting in relatively low-threshold laser operation for narrow-stripe devices. In addition, these devices exhibit transverse-mode confinement and small beam astigmatism because of the refractive index step provided by the deep native oxide.
Neutralization and transport of high-current proton beams in a two-stage linear induction accelerator
Authors: Golkowski Cz. , Kerslick G. S. , Nation J. A. , Ivers J.
Published: July 2002

Experimental results on the propagation and transport efficiency of a 1 MV, 5 kA, 50 ns annular proton beam through a two-stage linear induction accelerator are presented. The beam is generated in a magnetically insulated diode and propagates with high-efficiency along a 0.6 T axial magnetic field to a second accelerating gap located 30 cm downstream. The second accelerating gap increases the beam energy to 1.3 MeV. A full-cusp geometry provides the magnetic insulation in both the diode and the second gap. We report in this paper an 86% (±5%) transport efficiency and an increase of 1.6° in the beam divergence for propagation through the post acceleration gap.
Stopping of multicharged ions in dense and fully ionized hydrogen
Authors: Servajean A. , Gardes D. , Bimbot R. , Dumail M. , Kubica B. , Richard A. , Rivet M. F. , Fleurier C. , Hong D. , Deutsch C. , Maynard G.
Published: July 2002

The enhanced plasma stopping of energetic (MeV/amu) multicharged ions is experimentally confirmed by inserting a fully ionized hydrogen column on a tandem accelerator ion beam line. Relevance to heavy ion driven inertial compression is emphasized. Measured energy losses are quantitatively matched by a theoretical extension of the cold matter stopping formula (Bethe).
Effects of substrate temperature on growth orientation and superconducting properties of YBa2Cu3O7−x films prepared by metalorganic chemical vapor deposition
Authors: Li Y. Q. , Zhao J. , Chern C. S. , Gallois B. , Norris P. , Kear B.
Published: July 2002

The effects of substrate temperature on the structural and superconducting properties of YBa2Cu3O7−x films prepared by metalorganic chemical vapor deposition have been studied in the temperature range of 550 to 690 °C. Highly c-axis oriented films with transition temperatures of 90 K and critical current densities at 77.5 K and 0 T larger than 106 A/cm2 could be produced at substrate temperatures above 650 °C. As the temperature was decreased, the amount of a-axis orientation in the film increased. Films grown at a substrate temperature of 600 °C showed a strong a-axis orientation with a transition temperature of 83.5 K and a critical current density of 4.5×105 A/cm2 at 77.5 K and 0 T.
Laser-induced etching of InP using two laser frequencies simultaneously
Authors: Grebel H. , Pien P.
Published: July 2002

Two different lasers were used simultaneously to etch sinusoidal gratings on InP surfaces employing a thin-film cell configuration under external biasing, in which current was allowed to flow. Irrespective of the laser frequency, large pitch gratings etch faster than small ones when each single grating is etched separately. However, when two gratings are superimposed on each other these characteristics are changed. Also, there is a degradation in the etched profile after prolonged exposure time. This is more pronounced for relatively large pitches than for small pitches. We suggest that the reaction products, the oxide layer, regulate the reaction process in a reverse biased cell.
Dependence of the growth direction of CdTe layers on the orientation of GaAs substrates
Authors: Cinader G. , Raizman A.
Published: July 2002

CdTe layers have been grown by metalorganic vapor deposition on GaAs substrates of different crystallographic orientations. The dependence of the layer direction on the substrate orientation, surface preparation, and growth conditions was investigated. For each substrate direction studied, we have found that two layer orientations can exist. Experimental conditions under which only one layer orientation dominates the growth process, have been found. We propose a model, in terms of twin conjugated directions, explaining our as well as other results appearing in this paper.
Nonexponential deep level transient spectroscopy analysis of moderately doped bulk n-GaAs
Authors: Hardalov Ch. , Yanchev I. , Germanova K. , Ivanov Tzv. , Samurkova L. , Kirov K. , Nigohosian A.
Published: July 2002

A theoretical analysis is carried out of deep level transient spectra (DLTS) obtained on bulk moderately doped n-GaAs. The semiconductor is considered as a disordered one because fluctuations in the concentration of shallow donors and acceptors produce a random potential energy with a root-mean-square (RMS) fluctuation comparable to the mean thermal energy of the electrons. As a result, the energies of the deep levels obey a Gaussian distribution of the same RMS deviation. An original algorithm for the computer simulation of DLTS spectra is presented. The corrections to the peak energy and concentration of deep levels due to the random potential are estimated. Useful theoretical information about the microscopic parameters of the disordered system is presented as well. The degree of compensation of the material is determined.
The Im/Re spectrum method: A new method of detection of resonances of plane or cylindrical targets
Authors: Lenoir O. , Rembert P. , Izbicki J. L. , Pareige P.
Published: July 2002

The detection of resonances of various targets immersed in water is investigated by means of a new signal processing. The fast Fourier transform analysis of the reflected signal allows to obtain the evolution of the ratio between the imaginary part and the real part of the complex number obtained. This ratio strongly depends on the resonant character of the target. Special attention is given to the problem of the time origin in order to have a spectrum well interpretable in term of resonances. Results about a single plane plate, a coated plane plate and a solid cylinder are shown. The method proposed gives at least as much information as the classical ones in the case of an elastic target, and more information in the case of an elastic target coated with an absorbent.
The behavior of LiF-coated metal anodes in pulsed electric fields
Authors: Schwoebel P. R. , Panitz J. A.
Published: July 2002

Investigations of ion emission from LiF-coated metal anodes subjected to pulsed electric fields are reported. For LiF films having a thickness greater than 1000 Å, catastrophic vacuum arcs are initiated by electric-field pulsing. With films having a thickness less than 500 Å field-stress-induced film removal proceeds direct field evaporation of Li+ from the anode surface.
Linear electro-optic effect and temperature coefficient of birefringence in 4-nitro–4′-methylbenzylidene aniline single crystals
Authors: Bailey R. T. , Bourhill G. H. , Cruickshank F. R. , Pugh D. , Sherwood J. N. , Simpson G. S. , Varma K. B. R.
Published: July 2002

A study of the linear electro-optic effect in single crystals of the organic compound, 4-nitro–4′-methylbenzylidene aniline is reported. The reduced half-wave voltages have been found to have values 2.8, 1.3, and 1.1 kV at 632.8, 514.5, and 488.0 nm, respectively and the corresponding values of the largest linear electro-optic coefficient have been calculated. The thermal variation of the birefringence has also been investigated and the temperature variation of the refractive index difference is found to have the value, dΔn/dT = 15.8 × 10−5 K−1.
Photoluminescence of acceptor states in mercury implanted gallium arsenide
Authors: Gillin W. P. , Sealy B. J.
Published: July 2002

We have shown the presence of a free-to-bound photoluminescence peak associated with the presence of mercury sitting substitutionally on a gallium site. The acceptor level for mercury is found to be approximately 58 meV above the valence-band maxima.
Microwave characteristics of all high-T
c edge junctions
Authors: Dai Yuandong , Hu Yifei , Jiang Huaming , Liu Rangjiao , Wang Shiguang
Published: July 2002

We have fabricated the edge junction by using epitaxial multilevel deposition technique. The dc and ac Josephson effects have been observed in liquid nitrogen temperatures. The current-voltage characteristics of the junction are nonhysteretic and have well-defined critical current. The dynamic resistances above the critical current are large and independent of bias current. The dependence of height of the microwave induced steps on the microwave power consists with the prediction of the resistively-shunted-junction model with dc and radio-frequency current bias.
Interface reactions between SiO2-PbO-MO ternary systems and manganese zinc ferrites
Authors: Nitta Atsumi , Nakamura Hideyuki , Komatsu Takayuki , Matusita Kazumasa
Published: July 2002

The interface reactions between Mn-Zn ferrites and SiO2-PbO-MO ternary melts were studied using electron probe microanalysis and x-ray diffraction. In interface reaction between Mn-Zn ferrite and 55SiO2-40PbO-5MnO (in mol %), the intermediate layers were observed in close vicinity to the interface. It was found that these layers were mixtures of Pb2(Mn,Fe)2Si2O9 and Pb8(Mn,Fe)Si6O21 crystals. But no intermediate layers were observed at the interface between the ferrite and 55SiO2-40PbO-5ZnO (in mol %) heat-treated at various temperatures. The two kinds of the intermediate layers were observed at the interface between the ferrite and 55SiO2-40PbO-5FeO1.5 glass. It was found that one of the intermediates was a mixture of Pb2(Mn,Fe)2Si2O9 and Pb8(Mn,Fe)Si6O21, and the other was α-Fe2O3. The interface reaction mechanisms were proposed in this study.
Deep electronic levels at growth interrupted interfaces in low-temperature-grown GaAs and the pressure dependence of these levels
Authors: Samara G. A. , Vook D. W. , Gibbons J. F.
Published: July 2002

Deep electronic energy levels associated with defects confined to interrupted growth interfaces of thin GaAs layers grown by low-temperature (720 K) metalorganic chemical vapor deposition using tertiarybutylarsine and subsequently annealed at 920 K for about 2 min were investigated by transient capacitance spectroscopy at both atmospheric pressure (1 bar) and hydrostatic pressures to 8 kbar. Samples grown under widely different As/Ga ratios in the gas phase were compared, and this ratio was found to have a strong influence on the levels observed. Most of these levels are characteristic of levels seen in GaAs grown from the vapor phase. Analysis of the pressure dependencies of the electron emission rates and capture cross sections shows that most of the levels move higher in energy with pressure and yields the activation volume which accompanies electron emission or capture. These features are unique signatures of the levels and provide new insights into the physics involved. One of the levels is identified as the midgap donor EL2. Its energy exhibits a relatively large increase with pressure, and a large inward (outward) volume relaxation accompanies electron emission (capture) of electrons from (by) it.
XeF (B-X) long-pulse-length laser studies
Authors: Mandl A.
Published: July 2002

A study of the operation of the XeF(B-X) laser under low-electron-beam pump rate and high-energy loading is reported. Measurements have been performed at pump rates of 36, 44, and 66 kW/cm3 with laser output pulse lengths greater than 4 μs in duration and energy loadings up to 280 J/l. Intrinsic laser efficiencies of 2.0% at 66 kW/cm3, 1.7% at 44 kW/cm 3, and 1.5% at 36 kW/cm3 were measured in optimized NF3, Xe, Ne mixtures. Under optimum conditions specific output energies as high as 5.6 J/l were measured. Gain and absorption were also measured.
As desorption from GaAs and AlAs surfaces studied by improved high-energy electron reflectivity measurements
Authors: Yamaguchi Hiroshi , Horikoshi Yoshiji
Published: July 2002

The desorption of As from GaAs (001), (111)B, and AlAs(001) is studied in detail by measuring the electron-beam current reflected from these surfaces. When the As supply to the surface was terminated, the electron specular reflectivity decreases exponentially with time due to the As desorption. The decay rate was much smaller for AlAs (001) than for GaAs (001) and (111)B, which indicates stronger atomic bonding for AlAs than for GaAs. For the GaAs (001) surface, the decay rate and the activation energy for the decay in specular reflectivity change discontinuously at the transition between (2×4) and (3×1) reconstructions. This shows the As desorption process is sensitive to the transition of surface reconstruction. The dependence of the As desorption rate on the thickness of the top GaAs layer in GaAs/AlAs heterostructures indicates an abrupt change of bond strength near the interface.
Chemical and electrical properties of interfaces between deposited insulators and La2CuO4
Authors: Levy A. , Lercel M. J. , Falck J. P. , Kastner M. A. , Bright A. A. , Kleinsasser A. W.
Published: July 2002

Metal-insulator-semiconductor capacitors have been fabricated using plasma enhanced chemical vapor deposition of Si3N4 and SiO2 insulators on La2CuO4 semiconducting single crystals. Auger electron spectroscopy was used to characterize the insulator-semiconductor interface after annealing at several temperatures. Copper segregation and oxygen out-diffusion were observed and the Si3N4-semiconductor interface was found to be more stable than the SiO2-semiconductor one.
Structural properties and transport characteristics of pseudomorphic GaxIn1−xAs/AlyIn1−yAs modulation-doped heterostructures grown by molecular-beam epitaxy
Authors: Tournié E. , Tapfer L. , Bever T. , Ploog K.
Published: July 2002

Non-lattice-matched GaxIn1−xAs/AlyIn1−yAs modulation-doped heterostructures grown on (100) InP by molecular-beam epitaxy suitable for application in field-effect transistors have been studied. A computer simulation of the x-ray diffraction pattern proves to be necessary to obtain precise information about the structural parameters of the samples. The high crystal quality of our samples is demonstrated by the excellent agreement between experimental and simulated x-ray-diffraction curves. The transport characteristics of Ga0.38In0.62As/AlyIn1−yAs heterostructures including the evolution of the mobility and of the two-dimensional electron-gas density with temperature and structural parameters are discussed in relation with the relevant scattering mechanisms. The use of a thin spacer layer makes it possible to obtain very high conductivities. Both x-ray and transport measurements show that the strained GaxIn1−xAs layers are pseudomorphic well above the critical thickness calculated with the mechanical equilibrium model. The highest mobilities (13 100 and 103 000 cm2 V−1 s−1 at 300 and 4 K, respectively), obtained with a sheet carrier density of 1.7×1012 cm−2, are measured on a Ga0.38In0.62As/Al0.51In0.49As heterostructure. They are among the best values reported so far for similar structures.
XeF(C-A) bandwidth control measurements
Authors: Mandl A. , Russell J. A. , Litzenberger L.
Published: July 2002

An electron-beam pumped XeF(C-A) laser has been operated as an injection controlled oscillator. The electron-beam pump rate was 290 kW/cm3 and the pulse length was 600 ns. An etalon controlled dye laser was used as the injection source and reduced the free-running laser linewidth from 16 to 0.003 nm. The intrinsic laser efficiency of the injection controlled XeF(C-A) excimer was 1.8% with a specific output energy of 3 J/ℓ, exceeding the free-running performance.
Microspectroscopic reflectance measurements of textured polycrystalline Si solar cells by scanning spectroreflectometer
Authors: Shimokawa Ryuichi , Saito Ichiro , Katori Kanji , Nagamine Fumiaki , Tsuboi Hideyuki
Published: July 2002

This is the first observation of the microspectroscopic hemispherical reflectances of polycrystalline Si solar cells by the newly-developed scanning spectroreflectometer that represents the surface texturing of small-sized grains. After studying the reflectivity of textured grains with various crystal faces, we found that textured near-(100) grains had lower reflectivity than the other oriented textured grains where the ‘‘near’’ meant crystal faces within the deviation of 15–20 degrees from the defined low index faces. In addition, we proved that if the reflectances of grains are indirectly obtained from the unmetallized dummy wafers, the internal quantum efficiencies of grains are not correctly estimated.
Photoluminescence in strained GaSb/InGaSb quantum wells by metalorganic chemical vapor deposition
Authors: Su Y. K. , Juang F. S. , Su C. H.
Published: July 2002

GaSb/In0.19Ga0.81Sb single quantum well structures have been grown successfully by metalorganic chemical vapor deposition. The conduction band to mj=±3/2 heavy hole (1C-1HH) transition peak was observed in GaSb/In0.19Ga0.81Sb single quantum well (SQW) with the well width of 100–270 Å. From the excitation power dependence of the photoluminescence spectra, the 1C-1HH transition peak was still observed at low excitation power, 0.31 W/cm2, indicating that the carrier confinement in the well is good. From the temperature dependence of emission intensity of the 1C-1HH transition, the nonradiative recombination centers were few and less than that of the D°-A (donor-acceptor) transition arising from the GaSb barrier layers at temperatures below 30 K. This indicates the good quality of our SQW structure. The dependence of the 1C-HH transition energy was compared with the theoretical results using a strained model.
Effects of rapid thermal annealing on the formation of shallow p+n junction by implanting BF2+ ions into thin metal films on Si substrate. I. Thin titanium films
Authors: Juang M. H. , Cheng H. C.
Published: July 2002

High-quality Ti-silicided shallow p+n junctions have been fabricated by implanting BF+2 ions into thin Ti films on Si substrate and subsequent silicidation/drive-in by rapid thermal annealing (RTA) or conventional furnace annealing (CFA) under proper implant and anneal conditions. For both the RTA and CFA techniques, annealing temperatures higher than 800 °C degrade the junction formation because of more severe dopant confinement within the silicides and more serious diffusion of knock-on Ti into junction regions. The high-dose implant greatly enhanced the dopant activation and thus improved the junctions. The high heating rate for RTA caused an immediate formation of Ti–B compounds at high temperatures, while CFA considerably promoted the drive-in efficiency because of its low heating rates and long annealing times. Hence, CFA yielded better low-bias rectifying characteristics than RTA due to larger dopant activation. However, CFA caused much worse high reverse-bias characteristics. A rapid increase of reverse currents with bias voltage was observed for the CFA-treated samples, indicating a severe Ti penetration due to long annealing times.
Generalized perturbation analysis of distortion in semiconductor lasers
Authors: Haldar M. K. , Kooi P. S. , Mendis F. V. C. , Guan Y. L.
Published: July 2002

We have carried out a generalized perturbation analysis of the second-order nonlinear equation for photon density for semiconductor lasers. The second-order equation is obtained with minimal approximations, from the single-mode semiconductor laser rate equations, which unlike previous work, include both the effect of gain compression and the coupling of the spontaneous emission to the lasing mode. After deriving the general perturbation formula, expressions for second harmonic distortion as well as third-order intermodulation distortion are obtained. Unlike previous work which is restricted to two subcarriers, the present work gives results for an arbitrary number of subcarriers.
Molecular dynamic study of grain boundary embrittlement for [101] tilt copper bicrystals induced by bismuth segregation
Authors: Peng Ba-yi , Wu Xi-jun , Zhou Fu-xin , Tang Qi-heng
Published: July 2002

The selective bismuth segregation and the microprocess of fracture for the three [101] tilt copper bicrystals Σ9(2̄1̄2) 38.94°, Σ11(3̄2̄3) 50.48°, and Σ33(5̄4̄5) 58.99° have been studied by a molecular dynamics technique. The results show that the Bi segregation and the fracture behavior of the Cu-Bi bicrystals are strongly dependent on the grain boundary (GB) structure. The Bi segregation is strongly related to the polyhedra constructing the GB cores and the stress fields of the GB dislocations (GBDs), and the GB embrittlement of copper induced by the Bi segregation is determined by the segregated concentration and the distribution of Bi atoms. With the increase of the relative number of pentagonal bipyramids and the localization of the stress fields of the GBDs in the GBs, the bicrystals Σ9, Σ11, and Σ33 show a decreasing propensity for the Bi segregation and subsequent different fracture behaviors. The severe intergranular brittle fracture that happens in the Σ9 bicrystal is mainly caused by the breaking of weakened Cu-Cu bonds, which is related to the highly concentrated Bi segregation at the GB core. In the case of the Σ11 bicrystal, the segregation of Bi atoms at the GB shows an inhomogeneous distribution characteristic, so that the fracture is intergranular but with a large amount of shear deformation. The transgranular fraction that appears in the Σ33 bicrystal is related to the low concentration of the Bi segregation and the dispersive distribution of the Bi atoms along the GB and in the grains.