bluuebunny/crossref_metadata_2025 huggingface dataset:
Picosecond optical nonlinearities in a strained InAs/GaAs hetero n-i-p-i structure
Authors: McCallum D. S. , Huang X. R. , Dawson Martin D. , Boggess Thomas F. , Smirl Arthur L. , Hasenberg T. C. , Kost Alan
Published: July 2002

The nonlinear optical properties of a n-i-p-i structure containing strained superlattice quantum wells in the intrinsic regions are studied using picosecond pump and probe pulses of the same photon energy. For pump fluences as low as 1.1 μJ/cm2, a blue shift of the excitonic resonance, caused by the screening of the built-in space-charge field and the accompanying reduction in the quantum-confined Stark effect, is clearly observed. At higher fluences, the onset of bleaching of the excitonic absorption is observed. The nonlinearities associated with the quantum confined Stark effect in the hetero n-i-p-i are directly compared to those arising from excitonic bleaching in identical strained superlattice quantum wells under flatband conditions. The picosecond time resolution allows a more accurate estimation of the carrier density in the hetero n-i-p-i by ignoring the density-dependent recombination and a quantitative comparison between the strength of the nonlinearities in the two structures. Although such comparisons depend on the optical fluence and structure of the hetero n-i-p-i, we find that the magnitudes of the nonlinearities in these two specific structures are comparable on a per carrier basis, although their spectral signatures are quite distinct.
Study of thermoelastic growth during martensitic transformations
Authors: Planes Antoni , Ortín Jordi
Published: July 2002

The possibility of local elastic instabilities is considered in a first-order structural phase transition, typically a thermoelastic martensitic transformation, with associated interfacial and volumic strain energy. They appear, for instance, as the result of shape change accommodation by simultaneous growth of different crystallographic variants. The treatment is phenomenological and deals with growth in both thermoelastic equilibrium and in nonequilibrium conditions produced by the elastic instability. Scaling of the transformed fraction curves against temperature is predicted only in the case of purely thermoelastic growth. The role of the transformation latent heat on the relaxation kinetics is also considered, and it is shown that it tends to increase the characteristic relaxation times as adiabatic conditions are approached, by keeping the system closer to a constant temperature. The analysis also reveals that the energy dissipated in the relaxation process has a double origin: release of elastic energy Wi and entropy production Si. The latter is shown to depend on both temperature rate and thermal conduction in the system.
The influence of underlying metals on the hydrogen evolution from plasma-deposited silicon nitride films
Authors: Kikkawa Takamaro , Endo Nobuhiro
Published: July 2002

The influence of underlying metals on hydrogen evolution from plasma-enhanced chemical vapor deposited silicon nitride (P-SiN) films was investigated. Titanium (Ti), tungsten (W), and tungsten silicide (WSix:x=2.3) cap layers were deposited onto pure-Al, Al-1%Si, Al-0.5%Cu and Al-1%Si-0.5%Cu films on oxidized silicon wafers. The bilayers and Al-alloys were covered with P-SiN films and heated. It was found that the hydrogen evolution rates for the P-SiN films were influenced by the underlying bilayers as well as Al-alloys. Copper (Cu) addition to underlying Al films raised the hydrogen evolution rate peak temperature for the cover P-SiN film, due to the suppression of cover P-SiN film blistering and cracking as a result of Al-Cu hardening. Titanium thin-film capping on the Al-alloy also raised the hydrogen evolution rate peak temperature for the P-SiN film, as results of Ti adhesive layer and thermally stable intermetallic compound formation, TiAl3.
Dispersive photoconduction in Langmuir–Blodgett films of merocyanine dye
Authors: Sugi Michio , Saito Kazuhiro
Published: July 2002

The photoincrement of admittance (photoadmittance) of merocyanine-arachidic acid mixed Langmuir–Blodgett films sandwiched between aluminium electrodes has been measured for frequencies ω/(2π)<1 Hz at room temperature using the monochromatized visible incident. The number of monolayers of the films was 3–19. The photoadmittance is ascribed to photoelectrons from the dye chromophores. The light-intensity dependence obeys a square-root law for thicker films, approaching a linear law as the film thickness decreases. The frequency dependence is found to originate from the dispersive component proportional to ω1−s, which predominates over the d.c. component for thicker films. The value of s≊0.5 is evaluated with a critical length of about 30 nm as characterizing the crossover between the thin-film and the thick-film cases.
Electron trap studies in Al-Ta-O/CdSe thin-film transistors using a hot electron injection method
Authors: Nomura Koji , Ogawa Hisahito
Published: July 2002

Al-Ta-O composite dielectric thin films prepared by rf plasma sputtering under various conditions have been used for gate insulators of CdSe thin-film transistors. The hot electron injection method has been used for investigation of the electron trap properties in these thin-film transistors. It shows clearly that the traps are mainly due to Coulomb attractive centers, i.e., oxygen vacancies. In the best films prepared in this work, capture cross sections of 3.8×10−13 cm2 and trap densities of 1.0 ×1017 cm−3 are obtained. The relationships between gate insulator preparation conditions and the traps of the Al-Ta-O/CdSe thin-film transistors are precisely described in this paper.
High-temperature annealing behavior of μτ products of electrons and holes in a-Si:H
Authors: Wang F. , Schwarz R.
Published: July 2002

The mobility-lifetime products of electrons and holes [(μτ)e and (μτ)h] in undoped hydrogenated amorphous silicon samples have been studied by photoconductivity and ambipolar diffusion length measurements. The density of dangling bonds Nd in the samples is changed over a range of 3×1015–2×1018 cm−3 by annealing at high temperatures. Nd and the Urbach tail slope Eov have been determined by the constant photocurrent method. In addition, the optical gap, the activation energy of dark conductivity, and the exponent governing the intensity dependence of σpc have been measured. The results show that there is a correlation between Nd and Eov which is consistent with equilibrium theory. (μτ)e and (μτ)h change in quite different ways as Nd increases, namely, (μτ)e decreases as a linear function of the inverse of Nd. However, (μτ)h remains almost constant when Nd≤5×1016 cm−3, then decreases fast for higher Nd. The asymmetric dependence of transport properties of electrons and holes on Nd suggests that for electrons recombination through dangling bond states is dominant; but, for holes, recombination mainly proceeds through deep band tail states, especially when Nd is relatively low.
Interactions between implanted Mg and base p-type dopant (Be,Zn,C) in heterojunction bipolar transistor devices
Authors: Amarger V. , Dubon-Chevallier C. , Gao Y. , Descouts B.
Published: July 2002

The interactions, in GaAlAs/GaAs heterojunction bipolar transistor structures, between implanted Mg atoms and different p-type base dopants (Be in layers grown by molecular beam epitaxy, Zn or C in layers grown by organometallic chemical vapor deposition) have been investigated. Different diffusion behaviors have been observed, according to the base dopant, either for the implanted Mg or for the base dopant itself. The resultant hole concentration profile obtained with a C–V electrochemical profiler has also been studied as a function of the base p-type dopant.
A simple technique for simultaneous fabrication of p
+/n diodes and ohmic contacts on n-type InP
Authors: Baber N. , Scheffler H. , Ullrich H. , Wolf T. , Bimberg D.
Published: July 2002

Low leakage current p+/n step junctions with mechanically stable ohmic contacts to p+ layer are fabricated on n-InP wafers simultaneously by a simple procedure consisting of vacuum evaporation of Ni, Zn, and Au followed by a short heat treatment at 340 °C. Current-voltage and capacitance-voltage measurements, secondary ion mass spectroscopy, and deep level transient spectroscopy are employed to characterize the diodes fabricated and to understand their structure.
Temperature dependence of incorporation processes during heavy boron doping in silicon molecular beam epitaxy
Authors: Parry C. P. , Kubiak R. A. , Newstead S. M. , Whall T. E. , Parker E. H. C.
Published: July 2002

Boron doped layers were grown by silicon molecular beam epitaxy to establish incorporation processes at temperatures between 900 and 450 °C. For temperatures exceeding 650 °C a surface accumulated phase of boron was formed when doping levels exceeded solid solubility limits. The properties of this surface phase were used to determine solubility limits for boron in silicon. Above 750 °C, the measured equilibrium solubility limit was in the 1019-cm−3 range in good agreement with previously published annealing data and showing a gradual decrease with decreasing temperature. Below 650 °C, the processes leading to the formation of the surface phase were kinetically limited, manifested by a sharp increase in boron solubility limit, with completely activated levels above 1 × 1020 cm−3 realized. At intermediate growth temperatures the degree of dopant activation was found to be dependent on growth rate. The stability of fully activated highly-doped boron layers, grown at low temperatures, to ex situ annealing is also discussed.
Holograms obtained by laser-assisted oxidation of thin tellurium films
Authors: Shafeev G. A. , Wautelet M.
Published: July 2002

Holograms are recorded by laser-assisted oxidation of thin tellurium films in air. The process of recording is characterized in situ by measuring the evolution of a self-diffracted beam of a cw Ar+ laser. Stationary diffraction efficiency is shown to be independent both on the recording beam power and on the grating period. Amplitude holograms are obtained with an efficiency of 3.2% at a spatial period of 3 μm.
Nucleation and growth of diamond on FeSi2/Si substrates by hot filament chemical vapor deposition
Authors: Godbole V. P. , Narayan J.
Published: July 2002

We have investigated the characteristics of diamond nucleation on silicon substrates alloyed with iron during hot-filament chemical vapor deposition of diamond film. It is shown that the presence of FeSi2 phase enhances nucleation of diamond crystals by more than an order of magnitude compared to bare silicon substrates. The FeSi2 was formed by laser deposition of iron on silicon substrates, followed by thermal annealing at 700 °C. The deposition characteristics of diamond and reaction of iron with silicon substrates were investigated as a function of annealing treatments using Rutherford backscattering, x-ray diffraction, Raman and Auger electron spectroscopy, and transmission electron microscopy. Implications of controlling and enhancing the diamond nucleation in the formation of continuous diamond film are discussed.
Selectively 13C-enriched diamond films studied by nuclear magnetic resonance
Authors: McNamara K. M. , Gleason K. K.
Published: July 2002

The quality of hot-filament chemical-vapor-deposited diamond films has been quantitatively assessed by 1H and 13C nuclear-magnetic-resonance (NMR) spectroscopy. As the carbon mole fraction increases from 0.053 to 0.074 in the gas phase, film quality in terms of sp2 carbon content, bonding disorder, and spin-lattice relaxation times deteriorates, in agreement with the qualitative results of Raman spectroscopy and scanning electron microscopy. Selective isotopic labeling of the acetone reactant and subsequent 13C NMR analysis shows that the carbonyl carbon of acetone is incorporated into the growing diamond films. Secondary-ion mass spectroscopy reveals that heterogeneous exchange reactions, involving the carbonyl carbon at the tantalum filament, are responsible for this phenomena.
Superconductivity related to indium-diffused GaAs
Authors: Li Y. K. , Huang Y. , Fan Z. , Jiang C. , Mei X. B. , Yin B. , Zhou J. M. , Mao J. C. , Fu J. S. , Wu E.
Published: July 2002

Superconductivity in an indium-diffused GaAs system has been investigated by magnetic-field-modulated microwave absorption and ac susceptibility measurements. These show existence of a superconducting phase in some of the samples. Indium was used to solder GaAs on Mo holder or deposit on the surface of GaAs, following the different heat treatments. This indium-diffused GaAs from surface or back side is most likely the origin of the superconductivity.
Electronic properties in Ga-doped CdTe layers grown by metalorganic vapor phase epitaxy
Authors: Ekawa Mitsuru , Yasuda Kazuhito , Ferid Touati , Saji Manabu , Tanaka Akikazu
Published: July 2002

Electronic properties in Ga-doped (100) CdTe layers on (100) GaAs grown by atmospheric pressure metalorganic vapor phase epitaxy were studied. Triethylgallium was used as a dopant source. The source materials were dimethylcadmium (DMCd) and diethyltelluride (DETe). The effects of the DETe/DMCd (VI/II) ratio on the electrical properties were evaluated by Hall measurements. Electron concentration (300 K) was controlled from 3.5×1014 cm−3 to 2.5×1016 cm−3 by the VI/II ratio in the range 0.5 to 2. Higher growth temperature lowered the electron concentration. High electron mobility of 630 cm2/V s (300 K) was obtained for a growth temperature of 375 °C and a VI/II ratio of 2. Good correspondence was observed between electrical and photoluminescence (PL) properties. Both intensity and linewidth of a neutral-donor bound-exciton (D0,X) emission at 1.5932 eV increased with the electron concentration. The ionization energy of the Ga donor was estimated to be about 18 meV from electrical and PL properties. A Ga incorporation mechanism was deduced on the basis of the experimental results.
Internal friction and modulus of nano-ZrO2 solids
Authors: Xie Cunyi , Zhang Lide , Mo Chimei , Zhu Zhengang , Chen Zuyao , Qian Yitai , Li Yian
Published: July 2002

The internal friction (IF) and elastic modulus were measured for bulk samples of nano-ZrO2 from −200 °C to room temperature. An IF peak located on a high background was found for as-compacted bulk nano-ZrO2. At the same time, a large modulus defect appeared. After annealing, the IF background decreased substantially and both the IF peak and the modulus defect disappeared. When the sample was heat treated according to the schedule 700 °C/15 h+900 °C/21 h+1100 °C/18 h, the modulus jumped a factor of 2 comparison with the modulus of an as-compacted sample. The modulus of as-compacted nano-ZrO2 was higher than that of coarse-grained ZrO2 at low temperature. The origin of the IF peak is associated with the atomic relaxation in boundaries. The dramatic increase of the modulus for the annealed nano-ZrO2 is mainly induced by the enhancement of the binding force and the decrease of the mobility of atoms and bonds in boundaries.
X-ray diffraction analysis of Si1−xGex/Si superlattices
Authors: Mai Z. H. , Ouyang J. T. , Cui S. F. , Li J. H. , Wang C. Y. , Li C. R.
Published: July 2002

Si1−xGex/Si strained-layer superlattices grown by molecular-beam epitaxy on Si substrates were investigated by x-ray double-crystal diffraction and x-ray grazing incidence diffraction. Both coherent and incoherent interfaces between the two components of the superlattices were observed. By fitting computer-simulated double-crystal x-ray-diffraction rocking curves to the experimental data, it is determined that there exist graded variations in both the component thickness ratio t1/t2 (t1 and t2 are the thickness of the Si1−xGex and the Si layers, respectively) and the fraction x in one sample. The x-ray grazing incidence diffraction experiments reveal a lattice strain relaxation of about 27% in another sample. The lattice relaxation and the influence of variations of x and t1/t2 on the rocking curves are discussed.
Growth mechanisms of CdTe during molecular beam epitaxy
Authors: Litz Th. , Behr Th. , Hommel D. , Waag A. , Landwehr G.
Published: July 2002

We report here on studies of the growth mechanism of CdTe during molecular beam epitaxy on (100) oriented CdTe substrates by reflection high energy electron diffraction (RHEED). The growth rate of CdTe as a function of the Cd/Te ratio in the impinging molecular beam was investigated in detail. The growth rates were determined by RHEED intensity oscillations. Fluxes were calibrated by film thickness measurements. From the growth rates dependence on the Cd/Te flux ratio we determined the Cd and Te sticking coefficients by comparing the results with kinetic models of molecular beam epitaxial growth. Both Cd and Te sticking coefficients are dependent on the surface concentration of free Cd and Te sites, respectively. The main result is that the influence of a precursor state has to be taken into account to describe the experimental results.
High-power InGaAs-GaAs strained quantum well lasers with InGaP cladding layers on p-type GaAs substrates
Authors: Sin Y. K. , Horikawa H. , Kamijoh T.
Published: July 2002

We report device results from channel guide InGaAs-GaAs strained quantum well lasers with In0.49Ga0.51P cladding layers (λL = 980 nm). Channel guide lasers are demonstrated with a new current blocking scheme using a p-n-p InGaP junction on a p+-GaAs substrate. The laser structure is grown by metalorganic vapor phase epitaxy on the channeled n-InGaP layer. The reverse biased p-n-p InGaP junction is shown to be effective in preserving the current blocking properties for InGaAs-GaAs-InGaP lasers. The uncoated lasers show cw laser thresholds of 11 mA at RT and high output powers of 125 mW.
ac transport in amorphous silicon-nitrogen alloys
Authors: Shimakawa K. , Wakamatsu S. , Kojima M. , Kato H. , Imai A.
Published: July 2002

The frequency-dependent conductivity of sputtered (with and without hydrogen) and glow-discharge amorphous silicon-nitrogen alloy films has been measured in the temperature range 15–330 K. The ac loss decreases with the introduction of hydrogen. The origin of the ac loss is interpreted in terms of electron transfer between dangling-bond states of silicon and nitrogen-related two-level systems.
Gap states in hydrogenated microcrystalline silicon grown by glow discharge technique
Authors: Dusane Suvarna R.
Published: July 2002

The gap state distribution in n-type hydrogenated microcrystalline silicon (μc-Si:H) films deposited by the glow discharge method is determined using deep level transient spectroscopy. The spectra obtained for μc-Si:H films, when compared with those observed in n-type a-Si:H deposited by the same technique, appear to be vastly different and clearly indicate four distinct defect levels. On the other hand the peaks obtained are also not as sharp as those normally observed in crystalline silicon. These observations are important to understand the nature of defects in such material systems with very small grain size.
Oxygen precipitation and defects in heavily doped Czochralski silicon
Authors: Wijaranakula W.
Published: July 2002

The oxygen precipitation and defect formations in Czochralski silicon doped with boron, carbon, and tin were studied after a two-step isochronal anneal in the temperature range between 400 and 900 °C. In silicon lightly doped with boron, a characteristic of isochronal transformation of the bulk defects exhibits two distinctive peaks of maximum defect density at around 550 and 725 °C, respectively. Doping with carbon or boron having a tetrahedral covalent radius smaller than silicon reduces the peak height at 550 °C and simultaneously creates a third characteristic peak at around 850 °C. Based upon the experimental results, the pairing reaction between impurities and point defects, and the relative concentrations between charge defects, it is concluded that oxygen precipitation and defects in silicon heavily doped with boron and carbon-doped silicon are similar. In the case of doping with large impurities such as tin, an enhanced oxygen precipitation was observed. An enhanced oxygen precipitation in tin-doped silicon is hypothesized to be due to a formation of tin-vacancy pairs which act either as the centers of localized lattice relaxation or the nucleaton sites for the precipitate nuclei.
A theoretical model of neutron thermalization in a medium
Authors: Uhm Han S.
Published: July 2002

A simple theoretical model is developed to explain neutron thermalization properties. Assuming that a fast neutron source is located at the origin, the neutron distribution is described as a function of distance from the source. Based on the continuous slowing-down model, it is shown that the thermal neutron flux is a simple function of the diffusion constant D, the reciprocal length κ, and the Fermi age τ of a moderator material. Several points are noteworthy from calculation of the thermal neutron flux. First, theoretical results for polyethylene moderator agree remarkably well with simulation data obtained from a Monte Carlo simulation. Second, the thermal neutron flux at the origin is proportional to the square of moderator density. Third, the volume of the large thermal neutron flux increases drastically as the Fermi age increases. Finally, we also note that theoretical results agree reasonably well with experimental data for a broad range of physical parameters. A simple analytical expression of the thermalization factor of a moderator material is derived and it is found that its theoretical values agree rather closely with measured values.
Hydrodynamic analysis of electron motion in the cathode fall using a Monte Carlo simulation
Authors: Dalvie M. , Farouki R. T. , Hamaguchi S. , Surendra M.
Published: July 2002

The exact mass, momentum, and energy conservation equations for electron transport in a dc glow are derived from the Boltzmann equation. A Monte Carlo particle simulation is used to explicitly calculate the individual terms of the moment equations, and to gain insight into the behavior of the electron distribution function (EDF) moments such as density and average velocity. Pure forward scattering and isotropic scattering are considered as two limiting scattering mechanisms. When forward scattered, the electron fluid shows the maximum change in properties and in transport mechanisms at the field transition point between the cathode fall (CF) and the negative glow. Isotropic scattering, however, results in property changes a short distance inside the sheath. Diffusion of the low-energy, high-density, bulk plasma electrons into the CF causes dilution of the low-density, high-energy beam from the CF before the beam actually arrives at the low-field region. The applicability of commonly used closure relations which yield a fluid description of the system is evaluated. Use of fluid equations to characterize this system with no a priori knowledge of the EDF is limited by kinetic effects, such as heat flow against the temperature gradient, especially in the forward-scattered case where the EDF is very anisotropic. The description of inelastic rates by Arrhenius kinetics is found to be surprisingly accurate with both scattering mechanisms. However, while temperature is an adequate gauge of the characteristic energy under isotropic scattering, the energy of the bulk electron motion must be included under forward scattering. Also, Arrhenius kinetics sometimes produce a spurious double peak in the inelastic rate profile which is not reproduced by the Monte Carlo simulation. The anisotropy of the EDF under the forward-scatter assumption makes it difficult to justify the use of the mobility and heat conduction closure relations. Under isotropic scattering, however, electron inertia is negligible. In that case, under the discharge conditions used here, the drift-diffusion approximation to the flux is good to within a factor of 2. Classical heat conduction theory overestimates the heat flux by a factor of 4 at the sheath edge.
Effects of interface phonon scattering in multiheterointerface structures
Authors: Kim K. W. , Bhatt A. R. , Stroscio Michael A. , Turley P. J. , Teitsworth S. W.
Published: July 2002

In this paper, the commonly used but idealistic formulation of quantized optical-phonon modes for a heterostructure system with only two heterojunctions (i.e., single quantum-well structures) is extended to the more realistic case of multiheterointerface structures. By applying the macroscopic dielectric continuum approach, dispersion relations and interaction Hamiltonians for interface-phonon modes are derived for a double-barrier structure and scattering rates based on these results are used to determine the range of practical validity of the idealistic model using interaction Hamiltonians appropriate for single quantum wells with infinite barrier widths. It is found that when the dimensions of the structures are larger than approximately 30 Å, this simplified description can be applied to multiheterointerface structures in general with reasonable accuracy.
Investigation of the bulk and surface electronic properties of HgCdTe epitaxial layers using photoelectromagnetic, Hall, and photoconductivity measurements
Authors: Sarusi G. , Zemel A. , Eger D. , Ron S. , Shapira Yoram
Published: July 2002

In this work a method is presented that permits the evaluation of the bulk and surface electronic properties of p-type Hg0.77Cd0.23Te epilayers grown by metalorganic chemical-vapor-deposition and liquid-phase-epitaxy growth techniques. The method is based on fitting the generalized photoelectromagnetic expression to the experimental results obtained from photoelectromagnetic, Hall, and photoconductivity measurements. Values of electron mobility, electron diffusion length, bulk lifetime, surface recombination velocities at the front and at the back surfaces of the HgCdTe layer, and the absorption coefficient were derived as a function of temperature. It is found that the Shockley–Read–Hall recombination process is the dominant recombination mechanism both in the bulk and at the surface of the HgCdTe layers. The recombination centers are most likely related to metal vacancies. It is shown that a low value of surface recombination velocity is a fundamental property of the CdTe/HgCdTe interface. In particular, a surface recombination velocity of less than 5000 cm/s was measured at 77 K for HgCdTe with a CdTe cap, which is the lowest value reported for narrow-gap p-type HgCdTe.
Sweeping of trapped flux in superconducting films by a micro-heat-flushing method
Authors: Geng Q. , Minami H. , Chihara K. , Yuyama J. , Goto E.
Published: July 2002

A new technique has been developed to remove flux quanta trapped in superconducting film. It consists of measuring the magnetic field distribution over a superconductor with an rf superconducting quantum interference device (SQUID) and removing the detected trapped flux using laser beam scanning. The trapped flux movement follows the motion of the Ar laser beam exactly. By scanning the laser beam over the trapped flux quanta, the trapped flux is successfully moved to any desired location. Comparison with heat flushing method, the most important advantages of this technique are (i) the flux movement in the superconducting film can be controlled precisely; (ii) by adjusting the laser power so as to change the diameter of the normal hot spot, flux creations caused by the thermoelectric potential of the material can be avoided. These results show that our technique is very useful in the field of Josephson junction electronics and other areas that require extremely low magnetic field environment.
Crystal structure and electron microprobe analyses of a lanthanum lutetium gallium garnet
Authors: Parise J. B. , Harlow R. L. , Shannon R. D. , Kwei G. H. , Allik T. H. , Armstrong J. T.
Published: July 2002

Single-crystal electron microprobe analysis of a lanthanum lutetium gallium garnet has resulted in a composition of La2.37Nd0.07Pb0.01Lu2.54Cr0.01 Ga3.00O12. This composition gives better agreement between observed and calculated total dielectric polarizabilities than previously reported compositions (La2.26–2.32Nd0.04Lu2.57–2.63Ga3.07O12 by x-ray fluorescence and La2.655Nd0.027Lu2.656Ga2.655O12 by inductively coupled plasma analyses), and does not imply the crystal-chemically improbable presence of Lu3+ in the tetrahedral site. X-ray and neutron crystal-structure analyses have confirmed that little or no Lu resides in this site.
Shallow-trap-induced positive absorptive two-beam coupling ‘‘gain’’ and light-induced transparency in nominally undoped barium titanate
Authors: Garrett M. H. , Tayebati P. , Chang J. Y. , Jenssen H. P. , Warde C.
Published: July 2002

We use the asymmetry of beam coupling with respect to the orientation of the polar axis in a nominally undoped barium titanate crystal to determine the electro-optic and absorptive ‘‘gain’’ in the usual beam-coupling geometry. For small grating wave vectors, the electro-optic coupling vanishes but the absorptive coupling remains finite and positive. Positive absorptive coupling at small grating wave vectors is correlated with the light-induced transparency of the crystal described herein. The intensity and grating wave vector dependence of the electro-optic and absorptive coupling, and the light-induced transparency are consistent with a model incorporating deep and shallow levels.
Hydrogenated amorphous carbon films prepared by plasma-enhanced chemical-vapor deposition
Authors: Chou L. H.
Published: July 2002

Hydrogenated amorphous carbon films have been prepared from CH4, H2, and Ar mixtures by plasma-enhanced chemical-vapor deposition. Films with various physical properties were obtained from different deposition conditions. The deposition parameters varied included H2 flow rates, Ar flow rates, total pressures, substrate temperatures, and power densities. Effects of each deposition parameter on the microstructures and the kinetics involved in the formation of each film are discussed. In addition, relations between deposition conditions, microstructures, and the optical properties are reported.
Heteroepitaxial multilayer of YBa2Cu3O7 and PrBa2Cu3O7 on SrTiO3 and LaAlO3 substrates by sputtering
Authors: Qiu X. G. , Li L. , Zhao B. R. , Zhao Y. Y. , Xu P. , Wang C. A. , Li H. C.
Published: July 2002

We have successfully fabricated epitaxially grown YBa2Cu3O7/PrBa2Cu3O7 (YBCO/PBCO) multilayer thin films on SrTiO3 and LaAlO3 substrates by dc/rf magnetron sputtering. The thicknesses of YBCO and PBCO varied from 1 to 8 unit cells. Satellite peaks in x-ray diffraction patterns clearly indicate the formation of periodic modulation structures of different wavelengths. At a certain thickness of the YBCO layer, the zero resistance transition temperature Tc0 decreased with the increase of the PBCO layer thickness. In contrast, Tc0 increased with the increase of the YBCO layer thickness at a constant PBCO layer thickness.
Characteristics of dislocations in beta-barium metaborate bulk crystals investigated via light scattering tomography
Authors: Mao Hongwei , Tan Qiguang , Wu Baichang , Chen Chuangtian
Published: July 2002

General characteristics of dislocations in beta-barium metaborate (BBO) bulk crystals have been investigated via light-scattering tomography (LST). The dislocations induced by inclusions and the residual products which can reflect the interaction process between the dislocation loops were observed in the experiment. Moreover, the decoration of the dislocation lines in BBO crystals with impurity atoms was also demonstrated by LST images.
Co diffusion and growth of buried single-crystal CoSi2 in Si(111) by endotaxy
Authors: Fathauer R. W. , George T. , Pike W. T.
Published: July 2002

At a growth temperature of 800 °C, Co deposited on a Si capping layer exhibits oriented growth on buried CoSi2 grains on Si(111), a process referred to as endotaxy. This occurs preferentially to surface nucleation of CoSi2, provided the thickness of the Si cap is less than a critical value of ≊100 nm for deposition rates of 0.003–0.01 nm/s. The steady-state process is modeled using known values of the Co diffusion coefficient and solid solubility in Si, allowing some conclusions to be drawn regarding parameters relevant to CoSi2 epitaxy. Using this technique, single-crystal continuous layers of CoSi2 can be formed under a high-quality Si capping layer.
Design of multiloop input circuits for high-T
c superconducting quantum interference magnetometers
Authors: Zarembiński S. , Claeson T.
Published: July 2002

A technique is developed for the design of input circuits of superconducting quantum interference devices (SQUIDs) including those based on high transition temperature (Tc) superconductors. A multitransformer SQUID circuit is reduced to a single-loop one with effective values of its loop inductance and applied flux. A numerical model of a multitransformer magnetometer is formed and analyzed. The planar transformer coupling coefficient is evaluated. The multitransformer SQUID structures as a whole are optimized with respect to their performance, taking into account the limits set by fabrication technology. Three gradiometer-type device designs are discussed. The most complex SQUID treated is a second-order gradiometer for magnetoencephalography use which needs only a two superconducting films technology to be realized. Designs are based on available high-Tc superconductor technology. Very competitive performance with high energy resolution and magnetic-field gradient sensitivity is predicted at nitrogen temperature using a multitransformer coupling circuit.
Coverage-time dependence during island growth at a solid surface with application to diamond deposition from the gas phase
Authors: Tomellini M.
Published: July 2002

A model is presented for describing the coverage-time dependence during nucleus growth at a solid surface, derived from Avrami’s statistical approach [M. Avrami, J. Chem. Phys. 7, 1103 (1939); 8, 212 (1940)]. The original formulation of the theory has been modified according to a kinetic scheme which accounts for the time evolution of active sites, germs, and nuclei at the substrate surface. This model has successfully been applied for describing the time dependence of the coverage by diamond experimentally observed at a Si(100) surface.
Scattering of laser beam by acoustohelicon waves in magnetoactive noncentrosymmetric semiconducting crystals
Authors: Jat K. L. , Ghosh S.
Published: July 2002

Using the coupled mode theory, an analytical investigation of scattering of laser beam by an acoustohelicon wave and the consequent amplification of the scattered modes and the acoustohelicon wave is carried out in a longitudinally magnetized semiconductor of a noncentrosymmetric nature. We have assumed the origin of nonlinear interaction to be the second order optical susceptibility arising from the nonlinear induced current density. The numerical estimations are made for n-InSb crystal at 77 K. The threshold pump electric field E0th is found to decrease with increasing wave number and decreasing scattering angle. The nonlinear dispersion characteristics for a right hand circularly polarized mode become positive for E0<E0th and negative for E0≳E0th. The nature of a left hand circularly polarized mode is found to be just the reverse. The steady state gain constants for piezoelectric (gp), deformation (gd), and both cases (gb) are also obtained. The influence of the doping level on nonlinear dispersion characteristics and gain constants has also been considered.
Observation of inverse domains in high T
c superconductors
Authors: Schuster Th. , Koblischka M. R. , Ludescher B. , Kronmüller H.
Published: July 2002

Nucleation of domains of inverse polarity is observed in the remanent state of high Tc superconductors using the high-resolution Faraday effect (HRF). The remanent state consists of domains with trapped flux and of domains with opposite polarity, separated from each other by an annihilation zone. It is shown that the stray fields of microstructural defects contribute to the nucleation process. Using the capability of the HRF technique to observe dynamic processes, experimental evidence for the different signs of the vortices is given. The influence of the pinning forces on this behavior is also shown.
Residual ion current as a limiting factor in plasma opening switch performance
Authors: Goyer J. R. , Kortbawi D. , Roth I. S. , Childers F. K. , Sincerny P. S.
Published: July 2002

Analysis of the plasma opening switch (POS) is performed under the following assumptions: (1) that the switch operates in three different scaling regimes which depend upon the conduction times and currents under investigation, (2) that the predominant loss mechanism is residual ion current which is not interrupted, and (3) that the opening of the switch is due to ion erosion. It will be shown in this paper that these assumptions provide an operational scenario for the POS which matches very closely the limitations observed experimentally on the fast Marx bank EYESS.
Intense electron emission due to picosecond laser-produced plasmas in high gradient electric fields
Authors: Wang X. J. , Tsang T. , Kirk H. , Srinivasan-Rao T. , Fischer J. , Batchelor K. , Russell P. , Fernow R. C.
Published: July 2002

Picosecond laser pulses at a wavelength of 266 nm have been focused onto a solid metal cathode in coincidence with high gradient electric fields to produce high brightness electron beams. At power densities exceeding 109 W/cm2, a solid density plasma is formed and intense bursts of electrons are emitted from the target accompanied by macroscopic surface damage. An inferred ∼1 μC of integrated charge with an average current of ∼20 A is emitted from a radio-frequency cavity driven at electric field gradients of ∼80 MV/m. In another experiment, where a dc extraction field of ∼6 MV/m is used, we observed an electron charge of ∼0.17 μC. Both results are compared with the Schottky effect and the Fowler–Nordheim field emission. We found that this laser-induced intense electron emission shares many features with the explosive electron emission processes. No selective wavelength dependence is observed in the production of the intense electron emission in the dc extraction field. The integrated electrons give an apparent quantum efficiency of ∼1.2%, which is one of the highest reported to date from metal photocathodes at these photon energies.
Effects of free-carrier absorption on time-resolved pump-probe two-photon absorption in semi-insulating semiconductors
Authors: Tomita Yasuo , Shibata Masa-aki , Bergquist Johan
Published: July 2002

Free-carrier absorption induced by picosecond pump excitation is investigated for the time-resolved pump-probe nonlinear transmission process in semi-insulating semiconductors. Time-resolved nonlinear absorption measurements of 1.064 μm, 29 ps pulses with semi-insulating undoped GaAs and Ga-doped CdTe are performed. Because of very small linear absorption at 1.064 μm for Ga-doped CdTe, the effect of the nonlinear free-carrier absorption is found to be noticeable. A theoretical analysis is also made to understand the role of the free-carrier absorption and the linear absorption saturation at large positive time delays of the probe. From the fitting procedure by the theory free-carrier absorption coefficients as well as two-photon absorption coefficients for the two crystals are obtained.
Characterization of processing-induced defects in high-purity InP by photoluminescence
Authors: Mayer K. M. , Makita Y. , Yamada A. , Shibata H. , Beye A. C. , Shimada J.
Published: July 2002

Low-temperature photoluminescence experiments were performed on high-purity InP substrates as a function of heat treatment, flat-profile ion implantation and subsequent annealing procedures. Whereas the well resolved near band edge luminescence proved the superior substrate quality, up to 6 sharp luminescence lines (some of them not reported so far) and one shallow broad-band emission were observed after Si3N4 deposition and various annealing procedures. From the temperature dependence of the luminescence peak intensities the activation energies of the novel lines were determined and discussed in terms of excitons bound to processing-induced complex defects. These assignments are supported by the observation of a strong enhancement of the luminescence after low dose Ar+ ion implantation.
Theory of photo-induced resonant tunneling in heterojunctions
Authors: Apell S. P. , Penn D. R. , Stiles M. D.
Published: July 2002

The theoretical basis for understanding photo-assisted resonant tunneling is generally taken to be the theory by Tien and Gordon [Phys. Rev. 129, 647 (1963)] in which the effect of a photon field on an energy state is to create sidebands at multiples of the photon energy. An alternative mechanism in which bulk photoabsorption is the photoexcitation mechanism is discussed. The two theories take the same form in the weak-field limit, and an expression is given for the relative size of tunneling currents.
Schottky barrier of epitaxial (100)CoGa on GaAs
Authors: Kuo T. C. , Arghavani R. , Wang K. L.
Published: July 2002

Schottky barrier heights in the epitaxial (100) CoGa/n-(100) GaAs diodes were studied by the I-V and internal photoemission methods. Diodes of these epitaxial contacts were shown to exhibit good rectifying behaviors and the forward current was found to follow the thermionic emission theory. Using the temperature dependence of the barrier heights, we show that the Schottky barrier heights are about 0.67 eV by I-V and 0.68 eV by internal photoemission measurements. The Schottky barrier height was found to be constant for contacting to n-type GaAs in the temperature range between 150 and 300 K. From this fact, we conclude that the metal Fermi level is pinned relatively to the GaAs conduction band minimum in this case. This finding is similar to other epitaxial contacting cases, CoSi2/Si and ErSi2/Si, where the Fermi level pins to the nearest semiconductor band [J. Y. Duboz, P. A. Badoz, F. Arnaud d’Avitaya, and E. Rosenche, Phys. Rev. B 40, 10 607 (1989)].
Electron spin resonance investigation of hole trapping in reoxidized nitrided silicon dioxide
Authors: Chaiyasena I. A. , Lenahan P. M. , Dunn G. J.
Published: July 2002

Radiation-induced hole trapping in reoxidized nitrided silicon dioxide (RNO) was studied with electron spin resonance spectroscopy. It is demonstrated that the dominant hole trap in RNO is not the well known E′ center of conventional oxides. This finding confirms our earlier speculation, based on detrapping experiments, that the dominant hole trap in RNO is a species distinctly different from that in conventional oxide.
Spin-wave and effective linewidths of lithium ferrites
Authors: Robinson T. M.
Published: July 2002

The spin-wave linewidth ΔHK of microwave materials may be increased by substituting relaxing ions such as cobalt. However this procedure has the disadvantage that the effective linewidth ΔHeff is also increased. Alternative ways of increasing the spin-wave linewidth of lithium ferrites with saturation magnetizations between 2500 and 5000 G have been investigated with the aim of obtaining high power handling materials with reduced off-resonance magnetic losses. This has been achieved either by hot pressing the material to reduce the grain size (if no titanium is present) or by substituting zinc as well as cobalt. Materials with ΔHK≥20 Oe have been obtained in this way with reduced cobalt content and lower effective linewidths. A broadband method of determining the effective linewidth between 4 and 11 GHz has been developed using the TM010 and TM011 resonant modes of metallized cylinders of the ferrite. These measurements show that the effective linewidths of the materials studied vary linearly with the frequency.
Characterization of potassium tantalum niobate films formed by metalorganic deposition
Authors: Mantese Joseph V. , Micheli Adolph L. , Schubring Norman W. , Catalan Antonio B. , Chen Yen-Lung , Waldo Richard A. , Wong Curtis A.
Published: July 2002

Thin films of potassium tantalum niobate, KTa0.6Nb0.4O3, with a Curie temperature of 20 °C were deposited on a variety of substrates by metalorganic deposition. These films had peak relative permittivities of 16 000 at 20 °C. Hysteresis plots of electric displacement as a function of electric field, taken at 0 °C, revealed a coercive field of 800 V/cm, a spontaneous polarization of 3.9 μC/cm2, and a remnant polarization of 0.5 μC/cm2. The hysteresis loops did not change significantly as the temperature was varied down to −100 °C.
Photoluminescence of CF4/O2 reactive ion etched In0.53Ga0.47As surfaces
Authors: Juang C. , Hsu J. K. , Yen I. S. , Shiau H. S.
Published: July 2002

Surface change due to reactive ion etching of In0.53Gas0.47As epitaxial layers with CF4+O2 plasmas is investigated using photoluminescence techniques. Under low self-induced bias voltages, a point defect layer is generated, while under high self-induced bias voltages, a thin structure disorder is observed along with the point defect. This disorder region is shown to be significantly recovered by a 410 °C thermal annealing.
Interactions between dopants and point defects during nitridation processes
Authors: Vandenbossche Eric , Baccus Bruno
Published: July 2002

The effective diffusivity of substitutional impurities in silicon is reconsidered by involving the point defects. Four basic reactions, including the interstitials and vacancies contributions, are necessary to derive a general formulation of the effective diffusion coefficient. The model has been fitted to data on arsenic diffusion in silicon under nitridation conditions, with a very good agreement. From these experimental results, it has been deduced that arsenic diffuses mostly by a vacancy mechanism with a partial interstitial contribution, which cannot be neglected. It has been also observed that, under these experimental conditions, the point-defects concentrations are a complex function of the observed phosphorus and antimony diffusivities, in contrast with previous approaches. The general behavior of the dopants diffusivities as a function of point-defects concentrations is also presented. This allows the importance of each reaction involved in this analysis to be shown clearly. Finally, the recombination of point defects mediated by dopants pairs has been emphasized over a wide range of conditions for point-defects concentrations.
Liquid-phase epitaxial growth of AlGaAsP with application to InGaP/AlGaAsP single heterostructure diodes
Authors: Wu Meng-Chyi , Chen Chyuan-Wei , Kuo Li-Kuang , Lu Shoei-Chyuan
Published: July 2002

Good quality Al0.28Ga0.72As0.62P0.38 layers lattice matched to GaAs0.61P0.39 epitaxial substrates were grown by liquid-phase epitaxy using a supercooling technique. By selection of the optimum growth condition, we can obtain the undoped layer with a low electron concentration of 1×1016 cm−3. The four major emission peaks observed from the temperature dependence of photoluminescence of the undoped AlGaAsP layer can be identified as the near-band-to-band, donor-to-valence-band, conduction-band-to-acceptor, and donor-to-acceptor-pair transitions. The binding energies of the residual donor and acceptor are 14 and 36 meV, respectively. Effects of Te doping on electrical and optical properties have been examined. The donor ionization energy of Te in the AlGaAsP layer is identified as 24.3 meV. Finally, a p-In0.32Ga0.68P /n-Al0.28Ga0.72As0.62P0.38 single heterostructure diode was fabricated, which exhibits a forward-bias turn-on voltage of 1.6 V and an ideality factor of 2.24.