bluuebunny/crossref_metadata_2025 huggingface dataset:
Spontaneous pattern on the corroded surface of metal: Phenomenon and theory
Authors: Yang J. J. , Zhou X. Y.
Published: July 2002

A spontaneous pattern was found on the corroded surface of 1Cr18Ni9Ti stainless steel which was subjected to a crude oil containing naphthenic acid at temperature about 330 °C. The high regularity, the periodicity, and SO2 symmetry of the pattern imply that a spontaneous dissipative structure arose in this corrosion system. It was also found that the distribution of chemical elements on the corroded surface was in accordance with the morphologic pattern. A new theory, which is based on the linear perturbation method and in which the shift of boundary is considered, is proposed to characterize the formation of the large-scale spontaneous pattern, reveal the mechanism, and explain this phenomenon in the corrosion system.
Charge-quantization effects on current-voltage characteristics of AlGaAs/GaAs resonant tunneling diodes with spacer layers
Authors: Koenig E. T. , Jogai B. , Paulus M. J. , Huang C. I. , Bozada C. A.
Published: July 2002

An inflection has been observed in the current-voltage characteristics of several AlGaAs/GaAs resonant tunneling diodes with spacer layers. We provide evidence linking this inflection, as well as the negative differential resistance, to quasi-bound energy states localized in the charge accumulation well between the emitter spacer layer and the AlGaAs barrier. There are strong indications that this region acts as the injector of electrons through the quantum well region. We propose a model for the electron transport, and show that the singularities in the current are caused by the quantum well state crossing the accumulation layer quasi-bound states as the bias is ramped.
Comment on ‘‘Thermochemical heat of ablation of solid carbon’’ [J. Appl. Phys. 65, 3425 (1989)]
Authors: Risch Timothy K.
Published: July 2002

We present the results of JANAF and Livermore thermochemical ablation models to demonstrate that the theoretical heat of ablation for solid carbon is 30 kJ/g with a minimum uncertainty of ±3 kJ/g across the temperature range of 2500–4000 K. Proper theoretical computations presented here illustrate that JANAF and Livermore data predict the same heat of ablation for carbon compared to the inherent uncertainties in the theoretical models. Previous heat of ablation calculations by Klein, Berry, and Miles [J. Appl. Phys. 65, 3425 (1989)] purportedly attributing significant differences between JANAF and Livermore data for carbon are shown to be incorrect. Experimental data indicating a heat of ablation of 31.0±1.6 kJ/g for carbon are shown to be consistent with our theoretical calculations provided uncertainties in the above thermochemical models are considered.
X-ray determination of the Debye temperature at high pressure using high-energy synchrotron radiation
Authors: Matsumuro A. , Kobayashi M. , Kikegawa T. , Senoo M.
Published: July 2002

The volume dependence of the x-ray Debye temperature in aluminum at high pressure up to 6 GPa was measured with high-energy synchrotron radiation at the National Laboratory for High Energy Physics. High-pressure high-temperature diffraction experiments were carried out by use of a multianvil press system with the energy-dispersive diffraction method. The Debye temperature was determined from the integrated intensity ratio at different temperatures. In order to avoid the intrinsic anharmonic effects and the influence of the energy shift for the Bragg diffraction due to the thermal expansion, constant volume was maintained in a sample by controlling the pressure at elevated temperatures. The interpolated values of the Debye temperature and the Grüneisen parameter of the atmospheric volume were θD0 =367 K and γ0 =3.0, respectively. Excellent agreement was found upon comparison with the published results of conventional experiments.
Early stages of interface-trap transformation in metal-SiO2-(100)Si structures
Authors: Wang Yu , Ma T. P. , Barker R. C.
Published: July 2002

Interface traps and oxide charge generated by x ray and high-field Fowler–Nordheim (FN) injection are monitored within the first hour after their creation. A characteristic interface-trap peak distribution in the upper half of the Si band gap (∼Ev+0.75 eV) is invariably found immediately after x-ray irradiation or gate-positive FN injection. However, this peak distribution is not observed immediately after gate-negative FN injection; instead, it gradually develops with time after the injection, and is accompanied by a gradual reduction of the positive oxide charge density. In contrast, the interface-trap distribution after x ray or gate-positive FN injection undergoes much less notable changes within the first hour. In addition, the amount of damage measured immediately after FN injection depends strongly on the injection polarity, with gate-positive injection generating more interface traps and less positive charge while the reverse is true for gate-negative injection. These observations may be explained in terms of the differences in the initial trapped hole distribution and subsequent electron-hole interactions under different damage conditions.
Influence of carrier spreading on the current-controlled lateral-mode behavior of twin-stripe lasers
Authors: Watanabe Masanobu , Mukai Seiji , Itoh Hideo , Yajima Hiroyoshi , Saito Masami , Hasegawa Kohei
Published: July 2002

Near- and far-field patterns, lasing efficiency, and spectra of twin-stripe lasers as a function of the injected current ratio were systematically examined with particular interest in their dependence on the carrier spreading which was controlled by the interstripe etched depth. As for lasers lightly etched not deeper than 0.5 μm to the active layer, the near-field peak shifts with current ratio at a higher rate for deeper etching, which leads to the more drastic change of the lasing efficiency. At the same time, the peak direction of the far-field pattern and the peak wavelength also changes at a higher rate for deeper etching. The dependence of these characteristics on the etching depth can be attributed to the higher current isolation for deeper etching. These results mean that laser beam deflection and nonlinear light-current characteristics, which are particularly important for information processing, can be controlled by the interstripe etched depth. As for lasers deeply etched down to 0.3 μm to the active layer, the regions below the stripes lases independently from each other which are ascribed to both the strong isolation of carriers and the considerable dip in the built-in index in the interstripe region.
A metal-oxide-semiconductor field-effect transistor with a 20-nm channel length
Authors: Hartstein A. , Albert N. F. , Bright A. A. , Kaplan S. B. , Robinson B. , Tornello J. A.
Published: July 2002

We have fabricated a Si metal-oxide-semiconductor field-effect transistor with a 20-nm channel length using a novel step/edge technique. An Al gate is evaporated onto a step in the SiO2 gate oxide. A second Al gate, separated from the first by a plasma-enhanced chemical-vapor-deposited SiO2 layer, provides inversion layer extensions of the source and drain contacts. Electrical conductance measurements indicate a channel length approximately equal to the fabricated gate length.
Plasma-cathode-initiated vacuum gap closure
Authors: Sampayan S. E. , Gurbaxani S. H. , Buttram M. T.
Published: July 2002

The properties of vacuum gap closure initiated by a plasma cathode are presented. The plasma cathode consisted of approximately 60 surface flashover sites distributed over a 10-cm2 area. Vacuum gap dimensions were 1×7.5 cm in diameter. Faraday cup measurements indicated an ion density greater than 1012 cm−3, which was controllable by the amplitude of the initiating high-voltage pulse. Although the field-free expansion velocity of the plasma was measured to be 7 cm/μs, plasma-cathode-initiated closure of the vacuum gap indicated closure speeds on the order of 0.5 cm/μs. Also, increased injected ion density and increased anode-cathode potential resulted in increased closure velocity.
Uniformity and composition of TbxFe1−x films prepared by magnetron sputtering using different types of targets
Authors: Murakami Yoshio , Shingyoji Takayuki , Hijikata Kenichi
Published: July 2002

Uniformity and composition of TbxFe1−x films prepared by magnetron sputtering using different types of targets (a composite target and a compound target) is investigated. Composition of the films varies with the position of the substrates placed relative to the target for both types of targets, however the feature of this variation is very different for both targets. It is found that the most important factor which affects compositional variation of TbxFe1−x films is the difference of angular distributions of sputtered Tb and Fe atoms. The angular distributions of Tb and Fe atoms can be qualitatively explained by the difference of angular distribution of sputtered atoms from each metal for the composite target, and by the reflective collision model for the compound target, respectively.
Subnanosecond far infrared photoconductivity from a GaAs/AlGaAs multiquantum well
Authors: de Bekker R. E. M. , Chamberlain J. M. , Claessen L. M. , Wyder P. , Stanaway M. B. , Grimes R. T. , Henini M. , Hughes O. H. , Hill G.
Published: July 2002

The far infrared (FIR) photoconductivity of GaAs/AlGaAs multiquantum wells (MQWs) doped with silicon has been investigated. The spectral response is consistent with extrinsic photoconductivity from shallow donors with an effective Rydberg of approximately 10.5 meV. The time-resolved photoconductivity due to stimulation with a cavity-dump FIR laser is measured. Subnanosecond rise and decay times are implied for the MQWs investigated; these times are shorter than for the corresponding bulk cases. Possible effects of geometric confinement on recombination rates are discussed. For a 150-period MQW, the responsivity at 118 μm is approximately 105 V W−1 .
Formation of several kinds of oxygen-related donors around 500 °C and effects of carbon in Czochralski silicon
Authors: Kamiura Yoichi , Hashimoto Fumio , Yoneta Minoru
Published: July 2002

We have found by resistivity measurements and deep-level transient spectroscopy that four kinds of oxygen-related shallow donors, OD1–OD4, successively appear around 500 °C in the time region 10–106 min and carbon greatly affects their generation behavior in Czochralski silicon. The formation of OD2 and OD3 donors was enhanced by the presence of carbon, while that of OD1 and OD4 donors was retarded. The OD1 donor is identified as the so-called thermal donor that consists of several kinds of double donors observed so far by infrared studies. The OD2 donor is a new kind of donor discovered recently by us. OD3 and OD4 donors, which were formed by very prolonged annealing around 500 °C, are suggested to have correlations with so-called new donors normally generated above 600 °C. The origins of these oxygen-related donors are discussed in relation to oxygen precipitation.
In(As,Sb) sawtooth doping superlattices for long wavelength infrared detection
Authors: Hass K. C. , Kirill D. J.
Published: July 2002

A new superlattice system suitable for infrared detection in the 8–12 μm wavelength range is proposed. The system is a sawtooth doping superlattice (SDS) constructed by alternating n- and p-type δ-doped layers in the narrow gap III-V alloy InAs1−xSbx(x≊0.6). The electronic structure of such materials is examined theoretically using a multiband envelope function formalism. The results indicate that, with relatively modest doping levels (<4×1012 cm−2) and short periods (<300 Å), an InAs0.4Sb0.6SDS exhibiting significant optical absorption out to 12 μm at 77 K should be possible.
Band-gap dynamics and nonlinear propagation of optical pulses in CdTe
Authors: Collet J. H. , Pugnet M. , Rühle W. W. , Nardo L. , Sirvin R.
Published: July 2002

The nonlinear propagation of picosecond pulses in CdTe is investigated. First, the band-gap dynamics is studied in the presence of a dense electron-hole plasma using time-resolved luminescence in the picosecond regime. Good agreement is found between experimental results for band-gap shrinkage and theory for densities of 5×1016–4×1017 cm−3. Second, the nonlinear transmission of optical pulses through CdTe/CdZn0.04Te0.96 heterostructures is investigated for photon energies close to the unexcited band gap. We demonstrate that, depending on the energy of the incident pulse, induced transmission or induced absorption takes place: Self-induced transmission is caused by band filling at high intensity E of the incident pulses (E≂100–200 μJ/cm2). Self-induced absorption is observed at relatively low incident intensity (E≂15–20 μJ/cm2). This effect is related to the band-gap shrinkage of the CdTe epilayer in the presence of a nondegenerate electron-hole plasma. A transmission theory of picosecond pulses propagating in and exciting the sample simultaneously is developed and provides a qualitative description of the experimental data.
Silicon dispersoid nucleation within the aluminum 1.0 wt. % silicon metallization alloy used in very large scale integration
Authors: Tung Chih-Hang , Chang Cheng-Tai , Chang Huei-Chen , Chiu Sloan , Kok Benson , Chang Liang-Hsing
Published: July 2002

The nucleation behavior of silicon precipitates within the aluminum/1.0 weight-percent-silicon (Al/1 wt. % Si) metalization alloy used in integrated circuits is studied by means of classical nucleation theory. The volume free energy and interfacial energy, which dominate nucleation behavior, are estimated, and activation energy barriers are calculated. On the basis of this phenomenological analysis, the relative roles of different nucleation models can be compared for different thermal environments, and the dominant precipitation mechanism can be predicted. The calculated free energy barrier for silicon precipitate nucleation ranges from 0.23 to 727 eV. These values are comparable to the available experimental data in the literature. Modifications can be made for calculations regarding other alloy systems used as very large scale integration metallization materials.
A study of Ni-Ge interdiffusion on GaAs using rapid thermal annealing with temperature standards
Authors: Brooks M. B. , Sigmon T. W.
Published: July 2002

A new technique for probing rapid material interactions at low temperatures has been developed. Rapid thermal annealing at 200 and 250 °C is exploited as a temperature-time probe to study the fast kinetics of Ni-Ge and Ni-Ge-Au contact metallizations on GaAs. Temperature standards are employed to establish known reaction temperatures within −3 to +13 °C of nominal, while anneal times are limited to 30 s or less. Rutherford backscattering analysis of annealed samples indicate that Ge consumption obeys parabolic kinetics, most likely limited by Ni diffusion, consistent with the growth of a NixGe phase. An activation energy estimate ≊0.7 eV is shown to be consistent with the fast interdiffusion observed, which is attributed to a grain boundary mechanism. The presence of Au plays only a limited role in the reaction for the temperatures and times studied.
Strong correlation between new donors and rodlike defects formed at 650 °C in phosphorus-doped, carbon-lean Czochralski silicon preannealed at 450 °C
Authors: Kamiura Yoichi , Hashimoto Fumio , Yoneta Minoru
Published: July 2002

Evidence is presented for strong correlation between new donors and rodlike defects generated at 650 °C in phosphorus-doped, carbon-lean Czochralski silicon preannealed at 450 °C. It is proposed that there are, in general, several types of new donors depending on experimental conditions, and one type of new donor, which is generated preferentially under the above special condition, arises from rodlike defects.
The specific contact resistance of Ohmic contacts to HgTe/Hg1−xCdxTe heterostructures
Authors: Leech Patrick W.
Published: July 2002

The specific contact resistance (ρc) of Ohmic contacts to HgTe/Hg0.4Cd0.6Te heterostructures has been measured using a transmission line model. The lowest measured values of ρc (1.7×10−3 Ω cm2) corresponded to the In/HgTe/Hg 0.4Cd0.6Te and Sn/HgTe/Hg0.4Cd0.6Te systems; while within the range of the other metal contacts examined (Ag, Al, Au, Cr, Cu, Ni, Pt, and Ti), ρc was independent of HgTe/Hg0.4Cd0.6Te interface reactivity. Comparative measurements have also been made with metal junctions formed to Hg0.4Cd0.6Te and HgTe.
A thermodynamic approach for interpreting metallization layer stability and thin-film reactions involving four elements: Application to integrated circuit contact metallurgy
Authors: Bhansali A. S. , Sinclair R. , Morgan A. E.
Published: July 2002

We propose a means of constructing simplified quaternary phase diagrams based on a thermodynamic approach using known and estimated data for Gibbs free energy of formation. Isothermal, isobaric sections of the condensed phase diagrams are built up as tie lines, tie planes, and tie tetrahedra (representing two-, three-, and four-phase equilibrium, respectively) in a regular tetrahedron. This extends the now well-established methodology for ternary systems described, for instance, by Beyers [J. Appl. Phys. 56, 147 (1984); Mat. Res. Soc. Symp. Proc. 47, 143 (1985)]. The procedure is illustrated by reference to Ti-Si-N-O, Al-Si-N-O, Ti-Al-Si-N and Ti-Al-Si-O, systems which are relevant to interactions occurring at various interfaces during the formation of contacts in integrated circuits. These phase diagrams are then used to predict the stability of—or reactions in—metallization layers and thin-film systems involving four elements. In addition, a method is suggested to estimate unknown free energies of formation from observations of thin-film reactions and stability.
Fabrication of InP-based NnpnN heterojunction bipolar transistor
Authors: Chen C. H. , Su Y. K.
Published: July 2002

InGaAs(P)/InP double heterojunction bipolar transistors have been successfully fabricated by inserting an n-type InGaAsP (Eg=0.95 eV) quaternary (0.1 μm, undoped) layer on either side of the base by liquid-phase epitaxy (LPE). As we know, it is the first time to grow this structure by LPE. These devices have been fabricated using a non-self-aligned technology. In this case it can improve the common-emitter current/voltage (IC /VCE) characteristics. Small signal current gain hfe about 100 and dc current gain hFE about 80 at IC=38 mA can be obtained. The ideality factor of emitter-base junction is 1.43.
Significant improvement in the surface smoothness of post-annealed Y-Ba-Cu-O thin films upon silver addition
Authors: Lee Sang Young , Hahn T. S. , Kim Y. H. , Choi S. S.
Published: July 2002

We report the effect of silver addition on the surface quality of rf-sputtered Y-Ba-Cu-O thin films. The Y-Ba-Cu-O-Ag films appear to have very smooth surfaces even if the post-annealing step is employed. The surface roughness of our ex situ grown Y-Ba-Cu-O-Ag film, having a 10.3 wt. % of silver, is within ±1% of the film thickness, which is more than 10 times better than the value of a typical post-annealed high-temperature superconducting film without silver.
Asymmetric Fabry–Perot reflection modulators using red- and blue-shifted electroabsorption effects
Authors: Yan R. H. , Law K. K. , Coldren L. A. , Merz J. L.
Published: July 2002

Applying electric fields along the quantum-confined direction of superlattices generates either red-shift (quantum-confined Stark effect) or blue-shift (field-induced Stark localization in superlattices) electroabsorption effects, and the dominating effect changes from a blue-shift to a red-shift as the superlattice period increases from small values. Both effects are utilized in asymmetric Fabry–Perot structures to implement high-contrast electro-optic modulators. In comparison, the red shift provides lower insertion loss while the blue shift provides lower operating voltage swings.
Optimum (Cs,O)/GaAs interface of negative-electron-affinity GaAs photocathodes
Authors: Lu Qing-Bin , Pan Yong-Xi , Gao Huairong
Published: July 2002

Negative-electron-affinity GaAs photocathodes have been improved by optimizing the (Cs,O)/GaAs interface. An optimum interface can be obtained by annealing the preoxygenated substrate surface at elevated temperatures (∼450 °C) prior to the (Cs,O) activation. Furthermore, the results of experiments with the aid of x-ray photoelectron spectroscopy demonstrate that the direct bonding of oxygen to substrate atoms is most likely the origin of the interfacial barrier to electron escape.
A contact limited precision of the quantized Hall resistance
Authors: Hirai Hiroshi , Komiyama Susumu
Published: July 2002

A four-terminal Hall resistance is analyzed using the Büttiker formalism of contacts. The possible maximum deviation of a quantized Hall resistance from ideal values in a multiterminal device is shown to be limited by the resistances of contacts. A general expression for the possible maximum deviation is derived for a multiterminal configuration with an arbitrary number of terminals in the condition of an arbitrary (integer) number of filled Landau levels. The influence of an inhomogeneous two-dimensional electron gas on the Hall resistance is also discussed.
A method for the measurement of the thermal, dielectric, and pyroelectric properties of thin pyroelectric films and their applications for integrated heat sensors
Authors: Bauer Siegfried , Ploss Bernd
Published: July 2002

A method is described that enables the simultaneous or consecutive determination of the specific heat, the thermal diffusivity, the dielectric constant, and the pyroelectric coefficient of thin pyroelectric films. The sample is heated by the absorption of intensity modulated light at one surface. The pyroelectric current and the transient temperatures of the sample surfaces are recorded as a function of the modulation frequency of the chopped light. The transient temperature recording is performed via thin-film bolometers. Analysis procedures for the determination of the specific heat, the thermal diffusivity, and the spatially varying pyroelectric coefficient are introduced and discussed. A simulation of the performance of integrated pyroelectric ir sensors on silicon chips is performed by a coupling of the pyroelectric material to a heat sink. It is shown that the response of pyroelectric ir sensors integrated on silicon chips is influenced by heat wave interference effects. Experimental results are given using thin pyroelectric PVDF films. It is shown that the use of pyroelectric polymers for integrated pyroelectric sensors is a good choice, due to their low thermal conductivity.
The influence of spontaneous electrochemical effects on dielectric measurements
Authors: Leclerc Gervais , Paquin Louis , Wertheimer M. R. , Yelon A.
Published: July 2002

We discuss the influence of spontaneous voltage and current of electrochemical origin in M1/dielectric/M2 cells on ac permittivity and dc conductivity measurements. It is shown theoretically and experimentally that as long as the ohmic drop in the dielectric dominates, electrochemical effects do not appreciably influence ac behavior, and that they provide a convenient means of estimating the dc conductivity of the dielectric material.
Dynamics of a nonautonomous sine-Gordon system modeling long Josephson junctions
Authors: Cirillo M.
Published: July 2002

We study the dynamics of an ac and dc driven sine-Gordon system extending over a finite spatial interval. We use this system to model fluxon oscillations in long (one-dimensional) Josephson junctions in the presence of an rf current. For three different values of the normalized spatial interval, or junction length, and a fixed value of the loss parameter the response of the junction is scanned over wide regions of the (rf drive amplitude and frequency) plane. In these regions chaotic intermittency, quasiperiodicity and isochronous phase locking are the most interesting dynamical features. We investigate the range of isochronous phase-locking of the soliton oscillations to the external ac drive in parameter space regions where experimental verification of our data can be considered.
Comparison and origin of electronic states of the free GaAs (100) surface and the GaAs/CaF2 interface
Authors: Bousetta A. , Truscott W. S.
Published: July 2002

An in situ assessment technique has been used on forming a metal-insulator-semiconductor structure in which the vacuum of the molecular-beam epitaxy system is used as the insulating film. The electrical characteristics of the metal-vacuum-semiconductor structure were measured in situ at room temperature using the capacitance-voltage (C-V) technique. Investigations were also carried out on the effect of the arsenic volatility on such structures. These results were compared to those obtained on a true MIS capacitor where CaF2 was used as insulator. The C-V hysteresis phenomena recorded on most of the Al/CaF2/GaAs diodes were investigated using a computer program. The results suggest that slow surface states rather than fast ones were responsible for the hysteresis phenomena and an insulator deposited under carefully controlled conditions might reduce defects at the GaAs surface, presumably through structural reordering.
Absorptive electro-optic spatial light modulators with different quantum well profiles
Authors: Sanders G. D. , Bajaj K. K.
Published: July 2002

We present a theory of absorptive electro-optic spatial light modulators based on GaAs/AlGaAs multi-quantum well structures using arbitrary potential well profiles. In particular, we consider three different quantum well profiles: square, parabolic, and asymmetric triangular. We calculate the transition energies, oscillator strengths and absorption co-efficients of the lowest-lying heavy- and light-hole excitons as a function of well width and electric field using a variational approach assuming decoupled valence subbands. For illustrative purposes we select the photon energy of the monochromatic source to be modulated at 1572 meV and aluminum concentration in the barriers to be 0.3. For the sake of comparison among the various modulators with different quantum well profiles we assume that this photon energy coincides with the lowest-heavy-hole exciton transition in the absence of an electric field. We find that the required well widths are 75 Å for the square well, 174 Å for the parabolic well, and 676 Å for the asymmetric triangular well. At zero electric field the values of the exciton oscillator strengths in all three quantum well systems are comparable. However, superior performance in terms of higher contrast ratio is obtained in the case of modulators based on asymmetric triangular wells. For instance, in the case of a square well with excitonic linewidth of 3 meV, a field of approximately 50 kV/cm is required to achieve a 30% decrease in absorption. On the other hand, the field required to achieve the same change in absorption in a parabolic well is 35 kV/cm and in an asymmetric triangular well is −7 kV/cm. The contrast ratio at an electric field of −20 kV/cm is 6.7 for an asymmetric triangular well and 1.02 for a square well in a multi-quantum well sample where the contacts are 2 μm apart.
Arc cathode spot heat transfer and existence diagram
Authors: Minoo H.
Published: July 2002

The heat transfer in the arc cathode spot is treated and an analytical expression is obtained, connecting the power loss by thermal conduction Lt to the velocity, the temperature and the radius of the spot and to the properties of the cathode material. The contribution of Lt to the power balance in the arc cathode region and its incidence on the spot existence diagram are examined in the case of Hg and Cu cathodes.
Visible laser action in N2-laser-pumped Ti vapor
Authors: Ninomiya H. , Hirata K.
Published: July 2002

Ti vapor is produced in a He buffer gas. Ti metal is irradiated by a pulsed YAG laser, and its vapor is optically pumped by a N2 laser at 337 nm. Laser lines at 551.4, 472.3, and 471.0 nm from the Ti 3D01 level which is connected to the ground state by the 337-nm resonance line. Laser lines are reported for the first time at 551.5, 551.3, 431.5, and 547.4 nm from the 3D02, 3D03, or 3G05 levels which are not optically connected to the ground state by the 337 nm line. The laser transitions from the 3D02, 3D03, or 3G05 levels are observed only in a He-Ti mixture.
Transmission electron microscopy investigation of dislocation bending by GaAsP/GaAs strained-layer superlattices on heteroepitaxial GaAs/Si
Authors: Whelan J. S. , George T. , Weber E. R. , Nozaki S. , Wu A. T. , Umeno M.
Published: July 2002

A systematic study, investigating the effects of strained-layer superlattices (SLSs) on threading dislocations present in GaAs/Si heteroepitaxial layers, was conducted. Transmission electron microscope contrast analysis was performed on ∼1% lattice-mismatched GaAs0.72P0.28/GaAs SLSs grown on GaAs/Si substrates.Threading dislocations were found to have Burgers vectors inclined to the GaAs/Si interface. Individual strained layers ranging in thickness from 100 to 250 Å were observed to have negligible effect on dislocation bending. Instead, dislocation bending occurred primarily at the first and last interfaces of the SLS packets. Similarly, effective dislocation bending was observed using 1000 Å layers. Threading dislocation density close to the GaAs/Si heterointerface was found to depend on the SLS packet proximity to the interface.
Ultrasonic second harmonic generation in various crystalline systems. II. Piezoelectric materials: Coupling parameters in terms of elastic and piezoelectric moduli and propagation directions
Authors: Gerlich D. , Breazeale M. A.
Published: July 2002

Expressions for the piezoelectric corrections to the second- and third-order coupling parameters K2 and K3 in cubic, rhombohedral, tetragonal, and orthorhombic crystalline structures are presented. The corrections depend on the linear and nonlinear dielectric constants, second- and third-order piezoelectric moduli (which are related to the elasto-optic, electrostrictive, and the electroacoustic coefficients). The corrections are estimated for the cases of crystalline quartz and lithium niobate.
Formation of MoS2 phase in Al2O3, ZrO2, and SiO2 through ion implantation of constituent elements
Authors: Rai A. K. , Bhattacharya R. S. , Kung S. C.
Published: July 2002

Polycrystalline α-Al2O3 and yttria-stabilized ZrO2 substrates were coimplanted with 175-keV Mo+ and 74-keV S+ at doses of 1×1017 and 74-keV S+ and 2×1017 cm−2, respectively. An amorphous SiO2 substrate was coimplanted with 175-keV Mo+ and 74 keV S+ at doses of 4.97×1016 and 1.02×1017 cm−2, respectively. The energies of Mo+ and S+ ions were chosen to obtain a nearly overlapping depth profiles in all three substrates. Transmission electron microscopy, Rutherford backscattering, and Auger electron spectroscopy techniques were used to characterize the ion-implanted materials. The formation of MoS2 phase was observed in the as-implanted condition as well as after annealing at 700 °C in all substrates. Thermodynamic calculations were performed to predict the equilibrium binary phase formed in Al2O3, ZrO2, and SiO2 under the present implantation and annealing conditions. The predictions agree with the experimental findings.
Low-frequency noise in small InGaAs/InP p-i-n diodes under different bias and illumination conditions
Authors: He L. , Lin Y. , van Rheenen A. D. , van der Ziel A. , Young A. , van der Ziel J. P.
Published: July 2002

Low-frequency noise measurements are reported on small InGaAs/InP p-i-n photodiodes under different bias and illumination conditions. In the first experiment measurements were taken when the diodes were reverse biased and illuminated with incandescent light. At high frequencies the noise is shot noise and at low-frequencies the noise has a spectrum proportional to fγ with γ=−1.0 for one set of two devices and γ=−0.8 for another set of two devices. At low-frequencies the spectral noise intensity is proportional to the current squared. In a second experiment the diodes were forward biased (no illumination) and the spectral intensity of the low-frequency noise was proportional to the current. Under these bias conditions it was possible to extract the parameter αH. The obtained values for this parameter are not compatible with quantum 1/f noise but do seem to coincide with values related to 1/f noise due to recombination centers.
Modal analysis of wake fields and its application to elliptical pill-box cavity with finite aperture
Authors: Kim S. H. , Chen K. W. , Yang J. S.
Published: July 2002

The potential of the wake-field produced by a bunch of relativistic charged particles passing through a pill-box cavity is expressed by using Floquet’s theorem, and an obvious requirement that the energy gain over all acceleration cavity of many pill boxes must be proportional to the number of pill boxes, based on the previous modal approach (BWW theory). It is found that the wake-field is consisted of two classes of modes: the longitudinal modes which are independent of the aperture and the pill-box gap, the hybrid (pill-box) modes which are dependent of the pill-box gap. The wake field is predominated by the fundamental longitudinal mode whose wavelength is on the order of the effective diameter of the cavity, and its magnitude is inversely proportional to the cross sectional area of the cavity for practical cavities with small apertures. Both longitudinal and transverse wake fields due to the longitudinal modes in an elliptical pill box cavity are expressed analytically in a closed series form by solving exactly the longitudinal eigenmode equation in the elliptical cylindrical coordinates in terms of Mathieu functions. It is found that both longitudinal and transverse wake fields whose amplitudes per driving charge are greater than 100 MV/m/μC can be generated in an elliptical cavity.
Investigation of molecular-beam epitaxially grown CdTe on GaAs by x-ray photoelectron spectroscopy
Authors: Waag A. , Wu Y. S. , Bicknell-Tassius R. N. , Gonser-Buntrock C. , Landwehr G.
Published: July 2002

X-ray photoelectron spectroscopy studies of CdTe-GaAs interfaces are reported. The growth start of CdTe on GaAs can be nearly stoichiometric if convenient growth parameters are chosen. The valence-band offset between these two materials is found to be large (470 meV). Cd-Te-metal-GaAs multilayers have been grown with very thin metal films. The CdTe-GaAs band offset is not influenced by such intermediary metal layers. The experimentally obtained value for the valence-band offset is compared with recent theoretical calculations taking into account interface dipoles.
X-ray photoelectron spectroscopy study of fluorine-treated YBa2Cu3O7−δ crystals
Authors: Tressaud A. , Amine K. , Chaminade J. P. , Etourneau J. , Duc Tran Minh , Sartre A.
Published: July 2002

An x-ray photoelectron-spectroscopy study of flux-grown YBa2Cu3O7−δ crystals left in moist atmospheric conditions has shown some aspects of the degradation process. Besides peaks which correspond to YO and BaO bonding in the superconducting phase, higher binding-energy components can be attributed to BaCO3, YOH, and/or YCO3 bonding. An x-ray photoreduction of the copper species is observed in the ultrahigh vacuum. Fluorine-gas treatments carried out at low temperature drastically modify the surface properties of the crystals. The peaks attributed to MO bonding (M=Y, Ba, or Cu) disappear and are substituted by MF bonding with a subsequent increase in Eb. In the F 1s region, the peak corresponding to those bondings is observed around Eb ≂684.5 eV, a value which is in agreement with those claimed for the corresponding inorganic fluorides. The signature of those surface fluorides remains, even when the samples are left for long periods in moist air. Within the F 1s envelope, chemisorbed fluoro species with Eb ≂686.5 eV are observed, especially when the fluorination process is performed at room temperature. These species are eliminated by vacuum annealing at 350 °C. In specific conditions, a high-binding-energy contribution arises (Eb ≂689 eV) which can be ascribed to the formation of surface ‘‘carbon fluoride.’’
Theoretical comparison of electron energy-loss and x-ray absorption near-edge fine structure of the Si L2,3 edge
Authors: Ma H. , Lin S. H. , Carpenter R. W. , Sankey O. F.
Published: July 2002

Various approximations in the calculations of electron energy-loss cross section and x-ray absorption coefficient have been evaluated using the Si L2,3 edge as an example. It was found that the random phase approximation, for which the cross terms are neglected in the expressions of electron energy-loss cross section and x-ray absorption coefficient, is a very good approximation. The dipole approximation in the calculation of the electron energy-loss cross section was found to begin to break down even at small acceptance half angles, such as 12.5 mrad. For energy losses larger than that of the Si L2,3 edge the dipole approximation will break down faster. This approximation also fails for a large scattering angle even at a small energy loss. The electron energy-loss cross section and x-ray absorption coefficient of the Si L2,3 edge has been calculated and compared. The large difference in relative intensity reported experimentally between the two spectra is not confirmed in this study. More experimental comparisons between electron energy loss and x-ray absorption spectra are recommended for Si and other compounds.
Light diffraction by Bleustein–Gulyaev surface acoustic waves in piezoelectric cubic crystals
Authors: Bright Victor M. , Hunt William D.
Published: July 2002

An analytical solution to the boundary-value problem for the existence of a Bleustein–Gulyaev piezoelectric surface acoustic wave in GaAs and other piezoelectric cubic crystals is presented. Numerical solutions for Bleustein–Gulyaev waves in a number of crystals of 4̄3m and 23 symmetry classes are also presented. These include commonly used materials such as GaAs, GaP, InSb, InAs, Bi12GeO20, and Bi4Ge3O12. The results are then used to investigate light diffraction by Bleustein–Gulyaev waves in GaAs. Both plane-wave acousto-optic and guided-optical-wave interaction cases are considered. Numerical solution for a guided-wave acousto-optic collinear interaction in a GaAs-GaAlAs waveguide is presented and discussed. In addition, a simple method of Bleustein–Gulyaev wave detection using optical techniques is developed and illustrated through numerical calculations.
Photoacoustic effect of silicon wafers with a p/n junction in the dc electric field
Authors: Lu Yue-sheng , Zhang Shu-yi , Cheng Jian-chun
Published: July 2002

The piezoelectric photoacoustic effect of silicon wafers with a p/n junction in the dc electric field is studied experimentally and theoretically. Based on the transport properties of semiconductors, four kinds of thermal wave sources are considered: (i) instantaneous intraband nonradiative thermalization, (ii) interband nonradiative bulk recombination of photogenerated carriers (PGC), (iii) interband nonradiative surface recombination of PGC, and (iv) instantaneous Joule thermalization of PGC in the applied electric field. The theoretical results are in good agreement with those of experiment. Both show that the contribution of the Joule thermalization is a major factor and the photoacoustic signal will be strengthened as the dc electric field increases beyond an appropriate value. Therefore, the signal-to-noise ratio and the contrast of photoacoustic imaging of the semiconductor devices can be improved by the dc external electric field.
Atomic resolution images of metal surfaces exposed in oil using a scanning tunneling microscope
Authors: Endo T. , Yamada H. , Sumomogi T. , Kohno K. , Kuwahara K. , Fujita T. , Morita S.
Published: July 2002

Fresh surfaces of polycrystalline Al-49.2%Cu, Al, and In are fabricated in duffusion pump oil, and observed in situ using a scanning tunneling microscope. The current images reflect the atomic arrays on their surfaces. More clear images with atomic resolution are observable about 10 h later compared with those just after the fabrication. Atomic resolution images are observable in oil several days after, with increasing noise.
Electric field induced parallel conduction in GaAs/AlGaAs heterostructures
Authors: Hendriks P. , Zwaal E. A. E. , Dubois J. G. A. , Blom F. A. P. , Wolter J. H.
Published: July 2002

A new mechanism to understand time-dependent features in the conduction of a two-dimensional electron gas (2 DEG) in high electric fields is proposed and discussed. The mechanism is based on the idea that not only the properties of the GaAs/AlGaAs heterostructure have to be included, but also the properties of the transition from the ohmic contact to the heterostructure. We show that the ohmic contact to the heterostructure is fundamentally different from the contact to a bulk semiconductor. In low electric fields electrons cannot move from the contact into the AlGaAs since the conduction band normally lies above the Fermi level. However, when high enough electric fields are applied, the barrier between the contact and AlGaAs is pulled down, allowing conduction in both the AlGaAs and the 2 DEG. We propose a model, in which time-dependent phenomena in the conduction of the 2 DEG can be associated with trapping and detrapping of charge carriers in the AlGaAs. Time-resolved experiments are shown which confirm this hypothesis.
Magnetic properties of the intermetallic compounds MM′X(M=Cr,Mn, M′=Ru,Rh,Pd, and X=P,As)
Authors: Kanomata T. , Kawashima T. , Utsugi H. , Goto T. , Hasegawa H. , Kaneko T.
Published: July 2002

Magnetization, magnetic susceptibility, and crystal structure are investigated on the ternary chromium arsenides CrM′As (M′=Ru,Rh,Pd) and ternary manganese phosphides and arsenides MnM′P(M′=Rh,Pd) and MnM′As(M′=Ru,Pd). MnRhP, MnRuAs, and MnPdAs are ferromagnets with a Curie temperature of Tc=401, 496, and 210 K, respectively. CrRhAs is an antiferromagnet with a Néel temperature of TN=165 K. MnPdP and CrPdAs show spin-glass-like freezing. A magnetic order-order transition is observed for CrRuAs. Susceptibility χ versus temperature curves are well expressed by a formula χ =C′/(T − θ′P)γ for all present compounds. The values of γ are about 3/2 for manganese compounds and CrPdAs, and about 1/2 for CrRuAs and CrRhAs.
Demonstration of new Paul–Straubel trap for trapping single ions
Authors: Yu N. , Nagourney W. , Dehmelt H.
Published: July 2002

New Paul–Straubel traps [H. Straubel, Naturwissenschaften 18, 506 (1955)] have been recently constructed and used to trap single Ba+ ions. Unlike a conventional rf trap, these traps use only a ring electrode surrounded by an uncritical ground electrode structure. The overall simplicity makes it easy to miniaturize the trap and to control the trapping potential spatial orientation. The new design also allows intense heating of the ring electrode with an ion in the trap simply by passing a large current through it. This removes surface layers responsible for large contact potentials varying over the ring surface and greatly reduces the forced micromotion of the ion, which is supposedly ‘‘at rest.’’
Hardening optical coatings to the effects of x rays
Authors: White Richard H. , Edwards David F. , Rathkopf James A.
Published: July 2002

Analyses of the effects of x rays on optical components consisting of a metal reflecting layer, a beryllium heat sink, and a fused silica substrate were done using the computer code xrth. These are compared with calculations for components lacking the beryllium layer. Our analyses show that the addition of the beryllium significantly hardens the system against x rays. The mechanisms for this increased hardness are elucidated by time-dependent temperature and enthalpy plots. The relative effectiveness of beryllium and diamondlike carbon heat sinks is explored. Complex designs which incorporate reflection-enhancing dielectric stacks are also discussed. Some comparisons with experiments are given.
Dependence of the performance of GaAs/AlGaAs quantum well infrared photodetectors on doping and bias
Authors: Gunapala S. D. , Levine B. F. , Pfeiffer L. , West K.
Published: July 2002

We have measured and theoretically analyzed the doping density, ND, dependence of the intersubband absorption coefficient α, the quantum efficiency η, the optical gain g, the dark current ID, and the detectivity D*. We discuss the optimum doping and show that D* depends only weakly on both ND and also the bias voltage, Vb. In particular, we find that the dark current can be reduced by three orders of magnitude, without significantly reducing the detectivity. This would substantially alleviate the undesirable filling of imaging array multiplexer storage capacitors, thereby allowing longer integration times and thus higher sensitivity.
Study of Si/GeSi p-n heterostructures
Authors: Kamjoo K. , Nayak D. K. , Park J. S. , Woo J. C. S. , Wang K. L.
Published: July 2002

The experimental results of a molecular-beam epitaxy grown Si/GeSi p-n heterojunction are reported. It is found that the current flow in these p-n heterojunctions shows a nonideality factor of about 1.5 at room temperature and 2.35 at liquid nitrogen temperature. The nonideal behavior of the Si/GeSi p-n heterojunction is attributed to the charges that are trapped at the heterointerface. Annealing the samples at temperatures higher than the growth temperature results in an increase in the density of defects as well as an increase in the nonideal current. C-V measurements were employed to further investigate the behavior of the charges that are trapped in the interface. From C-V measurements under reverse bias it is found that increasing the annealing time and temperature increases the density of interface traps. In addition, a charge density of about 1012 cm−2 is found to be present at the Si/GeSi interface for the as-grown sample and increases with increasing annealing time and temperature.
Magnetic properties of Fe deposited into anodic aluminum oxide pores as a function of particle size
Authors: AlMawlawi D. , Coombs N. , Moskovits M.
Published: July 2002

A combination of magnetic and electron microscopic measurements on iron deposited in chemically widened anodic aluminum oxide films has allowed us to relate the coercivity of these materials to the dimensions of the metal particles. The coercivity is found to be highly anisotropic and to depend on the aspect ratio of the metallic particles. The functional dependence of Hc on the aspect ratio fits the expression reported by Jacobs and Bean [Phys. Rev. 100, 1060 (1955)] for magnetization reversal by symmetric fanning. This is likely due to the fact that in our unannealed samples the metal deposit consists of a cylindrical assembly of fused single-domain particles. Pore widening by chemical dissolution of the anodic oxide is found to depend quadratically on the time that the sample is soaked in the acid bath.