bluuebunny/crossref_metadata_2025 huggingface dataset:
Floating gate effects in high-power semiconductor-metal eutectic composite transistors
Authors: Rossoni P. G. , Levinson M. , Ditchek B. M.
Published: July 2002

Novel field-effect transistors (FETs) with unusual high-power capabilities have been demonstrated previously. They are fabricated using the grown-in metal-semiconductor junctions of semiconductor-metal eutectic composite materials. Here, computer modeling has been used to examine the relation between their exceptional resistance to avalanche breakdown and the effects of floating gate junctions between the gate and drain. Calculations are presented that show how composite geometry and materials parameters could be optimized to give extremely large off-state blocking voltages combined with low series resistance. These transistors should, in principle, be capable of an on-state power dissipation lower than that of any conventional high-voltage FET device.
Elongated quadrupole ion traps for frequency standard applications
Authors: Murphy A. B.
Published: July 2002

The use of a novel nonaxisymmetric quadrupole ion trap for frequency standard applications is suggested. The properties of such an elongated trap are examined using a cold-ion-cloud model. It is shown that increasing the elongation of the trap, while keeping either the smallest dimension or the volume of the trap constant, substantially increases the ratio of the number of ions that can be stored to the magnitude of the second-order Doppler shift of the ions. This indicates that a frequency standard incorporating an elongated rf ion trap can achieve greater precision than one based on the currently favored circular rf or Paul trap.
Laser-induced breakdown studies of laboratory air at 0.266, 0.355, 0.532, and 1.06 μm
Authors: Tambay Rekha , Thareja R. K.
Published: July 2002

We report laser-induced breakdown studies of laboratory air using 0.266, 0.355, 0.532, and 1.06 μm radiation for focal spot varying from 30 to 100 μm. The breakdown intensities were measured for two pulse widths for all four wavelengths. We observe a t−0.5p dependence of pulse width on threshold field at 0.532, 0.355, and 0.266 μm while for 1.06 μm the pulse width dependence of t−0.35p is observed.
Electric-field-induced birefringence properties of high-refractive-index glasses exhibiting large Kerr nonlinearities
Authors: Borrelli N. F. , Aitken B. G. , Newhouse M. A. , Hall D. W.
Published: July 2002

The electro-optic Kerr effect and its wavelength dispersion have been measured in glasses representing several compositional systems. The measured Kerr effect was found to be large for glasses having large refractive indices, including: (i) glasses containing high concentrations of the heavy metals Pb, Bi, and Tl; (ii) glasses with high Nb, Ta, and Ti content; and (iii) tellurite glasses. Comparison of the third-order nonlinear susceptibility, χeff(ω = ω + 0 + 0), obtained from the measured electro-optic data, to values estimated from literature values of the optical frequency value, χeff(ω = ω + ω − ω) suggest an opposition of the electronic and nuclear contributions to the low-frequency electro-optic effect for the glasses containing Ti, Ta, or Nb.
Modeling of H− surface conversion sources; binary (H-Ba) and ternary (H-Cs/W) converter arrangements
Authors: van Os C. F. A. , Kunkel W. B. , Leguijt C. , Los J.
Published: July 2002

The production process for the formation of H− ions in a surface conversion source is sputtering of hydrogen atoms from the converter surface layers by incident positive ions, followed by electron attachment via resonant charge exchange with the converter surface. The sputtering process is in direct relation to the converter surface composition. New experimental data led us to identify two different classes of converters: metallic converters, like solid barium(binary) and adlayer converters, like cesium on tungsten (ternary). For a binary converter the hydrogen in the surface layers is directly sputtered by the incoming ions. Consequently, the negative ion yield scales with the hydrogen concentration in the surface layers. In the cesium/tungsten system (ternary) the hydrogen at the surface is believed to be sandwiched between the cesium adlayer and the tungsten surface. Hence, the negative ion yield scales with the sputter coefficient of hydrogen on adsorbed cesium. This is experimentally confirmed.
Flatband voltage shift of amorphous silicon nitride metal-insulator-semiconductor diodes
Authors: Miyashita H. , Watabe Y.
Published: July 2002

The relation between the flatband voltage shift of amorphous silicon nitride metal-insulator-semiconductor (a-SiN:H MIS) diodes and a-SiN:H deposition conditions is investigated. Significant hysteresis loops are observed in the capacitance-voltage (C-V) characteristics for some MIS diodes. This means that the bias scanning sequence and the a-SiN:H deposition conditions affect the flatband voltage. The dependence of the flatband voltage on bias stress time is also studied in connection with the deposition conditions. A logarithmic time dependence of the flatband voltage is seen for MIS diodes for which a-SiN:H was deposited at a high NH3/SiH4 gas ratio. These effects are induced from Si-dangling bonds which exist in a-SiN:H films.
Preparation of Tl2Ba2CaCu2O8 superconducting thin films on sapphire substrates via a two-step chemical deposition process
Authors: Collins B. T. , Ladd J. A. , Matey J. R.
Published: July 2002

Single-phase Tl2Ba2CaCu2O8 thin films have been deposited on single-crystal sapphire substrates, (11̄02) orientation, via a two-step chemical deposition process. Ba-Ca-Cu-O precursor films were prepared by spin coating a (Ba-Ca-Cu)-2-ethylhexanoate solution followed by a firing in oxygen at 850 °C. Thallium was incorporated by heating the film in a confined surface configuration with an unfired pellet of Tl2Ba2CaCu2Ox composition at 870 °C for 0.1 h. The resultant films (1 μm thick) were oriented with the c axis normal to the substrate. The structural and chemical composition of the films was monitored by x-ray diffraction, electron microprobe, and energy dispersive x-ray analysis. The superconducting properties were characterized by resistance and mutual inductance versus temperature measurements. Zero resistance temperatures as high as 95 K have been observed.
Critical current and flux pinning near T
c of a YBa2Cu3O7 thin film
Authors: Qiu X. G. , Cui C. G. , Li S. L. , Liu M. X. , Li J. , Zhang Y. Z. , Zhao Y. Y. , Xu P. , Li L. , Chen L. F. , Chen P. F. , Li N. , Liu G. T.
Published: July 2002

The voltage V versus current I of a high-quality YBa2Cu3O7−x thin film with zero-resistance temperature equal to 90.8 K was measured at temperatures near Tc (85, 87, and 90 K, respectively) under different magnetic fields (0–7 T). A significant result is that the critical-current density of the film reached 1.37×104 A/cm2 (zero field) even at 90 K, implying that strong pinning centers exist in our sample. However, a small applied magnetic field will diminish the critical-current densities remarkably. The pinning-force densities are found to follow Kramer’s scaling law in both perpendicular and parallel directions of the magnetic fields to the c axis of the film. A possible influence of thermally activated flux creep on the pinning mechanism is confirmed.
High-speed modulation and nonlinear damping effect in InGaAs/GaAs lasers
Authors: Dutta N. K. , Lopata J. , Sivco D. L. , Cho A. Y.
Published: July 2002

The high-speed modulation characteristics of ridge waveguide InGaAs/GaAs strained quantum well lasers have been investigated. The lasers have bandwidth of 12 GHz at 21 mW of output power. The differential gain coefficient, the nonlinear damping factor (κ factor) and the gain suppression coefficient (ε) are found to be 6.4 × 10−16 cm2, 0.6 ns and 6.2 × 10−17 cm3, respectively. The above differential gain coefficient and κ factor for InGaAs/GaAs strained quantum-well lasers are a factor of 2 larger than that for unstrained InGaAs/InP quantum-well lasers. The ε value for these strained and unstrained quantum-well lasers are comparable.
Study on high reliability TbFeCoNb magneto-optical recording disk
Authors: Kirino Fumiyoshi , Ogihara Noriyuki , Ohta Norio
Published: July 2002

We studied the magnetic properties, corrosion resistance, and disk properties, using TbFeCoNb film for magneto-optical film. Adding 2–3 at. % Nb to TbFeCo, the magnetic properties did not change, and the recorded domain on the disk using TbFeCoNb film is the same as on a TbFeCo film. TbFeCoNb film has high corrosion resistance for wet corrosion and pitting corrosion. The dependency of corrosion on the forming process is studied. The magnetic properties are dependent on the process such as rotational process and pass-by process, but the corrosion resistance is independent. As a result, we have a high reliability and high-performance magneto-optical disk. Write/erase repetition cycles are more than 107. After this disk was held in 60 °C−90% RH (relative humidity) for 2000 h, carrier-to-noise ratio (C/N), and defect error rate had not changed.
Cumulative effect near ablation threshold of polymer by 308-nm excimer laser pulse
Authors: Guo Hongping , Lou Qihong
Published: July 2002

Excimer lasers are finding increasing use in the area of laser material processing. In this paper, near-threshold behavior of the ablation processes was investigated using light deflection spectroscopy as a detection method. The cumulative effects of polymethylmethacrylate near ablation threshold were studied in detail.
Drag pressures of a set of alternating-polarity magnets over a superconductor tile
Authors: Komori Mochimitsu , Kitamura Tadashi
Published: July 2002

Drag pressures of a levitation mechanism are investigated. The levitation mechanism consists of a high-Tc superconductor tile (type II superconductor) and a set of alternating-polarity bar magnets of the same size. Relationships of the drag pressure to the distance between the magnets and the superconductor tile and to the width of a bar magnet are investigated. The drag pressure becomes small rapidly with increasing distance. The drag pressure becomes large with the superconductor-magnets distance decreasing. If the distance is fixed there exist a width of a bar magnet providing a maximum drag pressure. The drag pressure is also measured when the superconductor is moved in the direction of the alternating polarity.
Anomalous Sb redistribution during the preparation of delta-doping layers in silicon
Authors: Slijkerman W. F. J. , Zagwijn P. M. , van der Veen J. F. , van de Walle G. F. A. , Gravesteijn D. J.
Published: July 2002

We have studied Sb segregation at the moving crystal-amorphous Si(001) interface during preparation of Sb delta-doping layers. X-ray reflectivity measurements reveal a broadening of the delta-doping profile as a result of segregation during amorphous Si crystallization. From ion backscattering measurements, in conjunction with channeling and blocking, it is inferred that bulk diffusion constants are too low to account for the observed segregation behavior. The observed broadening is ascribed to enhanced diffusion at the c-Si/a-Si interface. This interfacial diffusion coefficient is determined to be at least two orders of magnitude larger than the diffusion coefficient in bulk a-Si. Possible causes of this enhancement are discussed.
Structural characterization of CdS epilayers by channeling Rutherford backscattering spectrometry
Authors: Leo G. , Drigo A. V. , Lovergine N. , Mancini A. M.
Published: July 2002

We report on the structural characterization by Rutherford backscattering spectrometry in channeling geometry of CdS epitaxial layers grown on the highly lattice-mismatched CdTe substrates by chemical vapor deposition. The overall layer quality has been investigated for different CdS thicknesses, as well as the occurrence of small misalignments of the crystallographic directions from point-to-point in the layers. A crystallographic study of the hexagonal (wurtzite) lattice is also presented: two principal planes parallel to the c axis have been determined experimentally, i.e., (101̄0) and (112̄0), together with their in-plane axial directions. This allows investigation of the occurrence of 30° rotation effects in the crystal lattice as observed by scanning electron microscopy.
Low-frequency asymptotics for eddy currents in a conducting half-space in the absence and presence of inhomogeneities
Authors: Nair Satish M. , Rose James H.
Published: July 2002

The low-frequency asymptotics of an electric field generated inside a conducting half-space by an external time-varying current source are derived. The conductivity of the half-space may be either uniform or it may contain inhomogeneities (i.e., regions in which the conductivity varies). The dependence of the low-frequency asymptotics on the dimensionality of the current source and the inhomogeneity are exhibited. We display those leading terms in the expansion that are given exactly by the quasistatic approximation. It is shown that in the case of variable conductivity, the asymptotics of the electric fields inside the half-space are determined by a Fredholm integral equation of the second kind. For the general case, the solution of this integral equation is identical to solving a classical boundary-value problem of electrostatics. We also show that there is an important class of problems for which the low-frequency asymptotics are trivial and are given explicitly in terms of the external field via the Born approximation.
Twice sum-frequency mixing of a dual-wavelength Nd:YALO3 laser to get 413.7-nm violet coherent radiation in LiIO3 crystal
Authors: Shen H. Y. , Lin W. X. , Zeng R. R. , Zhou Y. P. , Yu G. F. , Huang C. H. , Zeng Z. D. , Zhang W. J.
Published: July 2002

A new method to obtain 413.7-nm violet coherent radiation by second-order sum-frequency mixing of the outputs (1341.4 and 1079.5 nm) of a double-wavelength Nd:YALO3 (Nd:YAP) laser in two LiIO3 crystals is reported. First, a 598.1-nm orange coherent radiation is obtained by sum-frequency mixing (SFM) of 1341.4- and 1079.5-nm radiations in a LiIO3 crystal, and then the 598.1- and 1341.4-nm radiations are mixed again in a second LiIO3 crystal to get 413.7-nm radiation. The phase-matching angles are obtained for both SFM processes. The experimental results agree well with calculated results.
Revealing process-induced strain fields in GaAs/AlGaAs lasers via electron irradiation in a scanning electron microscope
Authors: Jakubowicz A.
Published: July 2002

An electron beam induced current study has been performed on single quantum well graded index separate confinement heterostructure GaAs/AlGaAs ridge geometry lasers. It has been shown that electron irradiation in the keV range combined with the electron beam induced current technique can be used to reveal process-induced strain fields and to study strain-related degradation phenomena in these devices on a microscopic scale. This technique has revealed a strain field below the ridge and below an opening in the metal layer. Enhanced susceptibility to degradation processes has been detected close to the lower corners of the ridge. It is shown that a correct interpretation of electron beam induced current images requires, including as contrast mechanism, local fluctuations in the distribution of the electric potential in the device and capture properties of quantum wells; (in the past, electron beam induced current images of degraded lasers were interpreted under the assumption that the contrast reflects the distribution of defects which act as recombination centers). A possible role of process-induced strain fields in the formation of fluctuations in the material’s built-in electric potential distribution within the active part of the laser during degradation is discussed.
Rotational dynamics of passive high T
c superconducting bearings
Authors: Weeks David E.
Published: July 2002

The rotational dynamics of passive high Tc superconducting bearings are discussed. Rotor deceleration as a function of time is measured using a bare rotor, a rotor with paddles, and a rotor with a small magnetic chip used to induce magnetic asymmetry. All three cases are fit to within experimental error using solutions to a first order differential equation where the decelerating torque is given by a constant term described by the critical-state Bean model, plus a term linear in the rotational frequency described by the Stokes ‘‘slow flow’’ approximation to the Navier–Stokes equations in the limit of small Reynolds number.
The dependence of stiction and friction on roughness in thin-film magnetic recording disks
Authors: Raman V. , Tang Wing T. , Jen D. , Reith T. R.
Published: July 2002

The influence of surface roughness in determining the tribological behavior of carbon coated thin-film magnetic recording disks have been investigated. Contact start/stop and low-speed drag tests were performed on unlubricated disks as well as disks that were coated with different thickness of a perfluoropolyether lubricant. Measurements of stiction and friction were made on disks with different surface roughness and using Al2O3–TiC sliders. Experimental results show that both stiction and friction are reasonably independent of the surface roughness above a certain value but show a sharp increase for tests on the smoother disks. The experimental findings are explained on the basis of currently accepted models for stiction that considers surface tension and viscous properties of the surfaces and possible effects arising from contamination.
An equation of state applied to plastics, rubbers, glasses, and polymers
Authors: Kumari Mithlesh , Dass Narsingh
Published: July 2002

In the present paper, the equation of state suggested by the authors has been applied in the case of plastics, rubbers, glasses, and polymers. The maximum pressure range and the minimum pressure range used in the present study are 0–100 and 0–24 kbar, respectively. A good agreement is found between the calculated and experimental values of V(P,T0)/V(0,T0) in case of all the materials studied here.
In situ doped polycrystalline silicon selective growth using the SiH2Cl2/H2/HCl/PH3 gas system
Authors: Ohshita Yoshio , Kitajima Hiroshi
Published: July 2002

The in situ heavy phosphorus doping effects on polycrystalline-silicon selective deposition were studied using the SiH2Cl2/H2/PH3/HCl/gas system. By increasing the PH3 flow rate, the growth rate was drastically decreased and selectivity was improved. The results indicated that the growth rate was determined by the impurity surface coverage. The correlation between the growth rate and the PH3 flow rate was well explained by Frumkin–Temkin type adsorption model.
Effects of oxygen content and oxide layer thickness on interface state densities for metal-oxynitride-oxide-silicon devices
Authors: Xu Dan , Kapoor Vik J.
Published: July 2002

The interface state density of metal-oxynitride-oxide-silicon (MNOS) devices was investigated as a function of the tunnel oxide thickness and the amount of oxygen in the oxynitride films. Nitrous oxide gas was used to introduce oxygen into the oxynitride film during the deposition process. As 17 at. % oxygen was introduced into the oxynitride film, the lowest oxide-silicon interface state density increased from 3.0 to 3.5×1011 cm−2 eV−1 for 90-Å oxide MNOS devices, and decreased from 5.1 to 3.65×1011 cm−2 eV−1 for 20 Å oxide devices. The increase in interface state density with increasing oxygen for 90-Å oxide devices may be due to an increase in the loss of hydrogen passivation at the interfacial regions as more oxygen is introduced into the film. The higher interface state density for the 20 vs 90 Å oxide samples, for a given oxygen content of the oxynitride films, may be due to additional contributions from the trapping states near or at the oxide-oxynitride interface. However, the decrease in the interface state density for increasing oxygen concentration for 20-Å oxide MNOS devices may be due to passivation of trapping states at the oxide-oxynitride interface by oxygen. The silicon dangling bonds responsible for these trapping states may be compensated by oxygen introduced during the deposition process.
Comparison of Bi-system 2223 and 2212 thick superconducting tapes: Grain alignment, current density, and strain effects
Authors: Sekine H. , Schwartz J. , Kuroda T. , Inoue K. , Maeda H. , Numata K. , Yamamoto H.
Published: July 2002

Bi-Sr-Ca-Cu-O (2212) and Bi-Pb-Sr-Ca-Cu-O (2223) superconductors were fabricated into silver-sheathed tapes by cold rolling and sintering. The resulting samples are compared in terms of microstructural alignment, critical current density, and strain dependence. Although both samples show good grain alignment, that of the 2212 phase is superior due to partial melting during heat treatment. This microstructural superiority is reflected in superior Jc as well. The single-filament and multifilament 2212 tapes have Jc ≳ 5 × 104 A/cm2 and Jc ≳ 1.5 × 104 A/cm2 at 20 T, respectively. Each material shows a similar dependence of Jc upon strain, with the 2223 phase exhibiting slightly more degradation. Furthermore, multifilamentary tapes were less affected by strain than single-filament tapes. A multifilamentary tape at 4.2 K, 0.5 T showed only a weak dependence upon strain, indicating that the strain dependence of the Bi system at low temperature may not be severe.
X-ray and phenomenological study of lanthanum-modified lead zirconate-titanates in the vicinity of the relaxor phase transition region
Authors: Rossetti G. A. , Nishimura T. , Cross L. E.
Published: July 2002

X-ray diffraction analyses of chemically derived Pb1−xLax(Zr0.65Ti0.35)1−x/4O3 powders were combined with a phenomenological theory to investigate the corresponding single-crystal thermodynamic properties of compositions approaching the relaxor ferroelectric phase transition region (x=0–0.04). The temperature dependence of the electrostrictive strain component, x4, could be described by the Landau–Ginsburg–Devonshire phenomenological theory taking Tc = 357 °C independent of La content (x). The single-domain, single-crystal elastic Gibbs free-energy density was calculated as a function of temperature and composition. The calculated results were discussed in relation to a simple superparaelectric model of relaxor behavior involving the temperature stabilization of noninteracting polar microregions.
Optical investigation in ultrathin InAs/InP quantum wells grown by hydride vapor-phase epitaxy
Authors: Banvillet H. , Gil E. , Cadoret R. , Disseix P. , Ferdjani K. , Vasson A. , Vasson A. M. , Tabata A. , Benyattou T. , Guillot G.
Published: July 2002

Single and multiple InAs/InP strained quantum wells have been grown by hydride vapor-phase epitaxy (HVPE). A compact set of vent/run valves monitored by manifold switches and a computer allowed the vapor species to be changed. InAs growth times of 4–24 s followed by etching times of 7–14 s, in an InCl, HCl, and H2 atmosphere, were used to control the thickness and interface abruptness. Low-temperature photoluminescence (PL) spectra have revealed emissions either in the form of a single peak or well-resolved multiple peaks attributed to monolayer variation in quantum-well thickness. The thinnest well obtained, observed for the first time by HVPE, has a PL energy transition at 1.28 eV. Experimental data agree well with theoretical calculations, taking into account strain effects on band structure and effective masses. The full widths at half maximum indicate good interfacial abruptness.
Optical characterization of selectively intermixed GaAs/GaAlAs quantum wires by Ga+ masked implantation
Authors: Vieu C. , Schneider M. , Mailly D. , Planel R. , Launois H. , Marzin J. Y. , Descouts B.
Published: July 2002

Quantum wires were fabricated by selective intermixing of a GaAs/GaAlAs quantum well through masked Ga+ implantation and rapid thermal annealing. The evolution of the luminescence spectra of the wires with the width of the implantation masks, enabled us to characterize the lateral selectivity of our process as well as the degree of one-dimensional confinement. The lateral extent of the intermixing was estimated at 20 nm giving rise to an important penetration of aluminum into the wires. From numerical simulations of the spatial distribution of implantation-induced damage, it was concluded that some lateral diffusion of the defects occurred during annealing. However it has been possible to assess the confinement energies to be around 4 meV. The linewidth of the wires’ emission turned out to increase with decreasing mask size, indicating the presence of some fluctuations of the confining potential along the wires. The roughness of the lateral definition of the wires was evaluated at 20 nm, of the same order of magnitude as the dimension of the intermixed region under the mask. Under these conditions optical excitation spectroscopy failed to detect the different one-dimensional subbands. Finally the potentialities of this method of fabrication of quantum wires are inspected.
Hydrogenation of InAs on GaAs heterostructures
Authors: Theys B. , Lusson A. , Chevallier J. , Grattepain C. , Kalem S. , Stutzmann M.
Published: July 2002

Atomic hydrogen has been introduced from a plasma source into InAs layers grown by molecular beam epitaxy on GaAs substrates. It is shown that hydrogen diffuses very fast into this material. The presence of hydrogen modifies the electronic transport properties, the near-band-edge luminescence spectra, and the far-infrared reflectivity spectra. The most striking effect is that, unlike other III-V compounds, the free-carrier density increases by one order of magnitude after hydrogenation. These phenomena are reversible and thermal annealing restores the original properties of the samples. Finally, models are proposed to explain the experimental results.
Monte Carlo modeling of electron transport in a Si metal-oxide-semiconductor inversion layer including quantum state and bulk scattering
Authors: Imanaga Syunji , Hayafuji Yoshinori
Published: July 2002

Electron transport in a Si metal-oxide-semiconductor (MOS) inversion layer was investigated by Monte Carlo particle simulation. Two models were used: (1) Electrons in the MOS inversion layer were treated as being two dimensional, taking account of the three lowest subbands. (2) Electrons in the MOS inversion layer were treated in one of two ways, depending on their energy: Electrons with energy less than the threshold energy Eth were treated as being two dimensional, while electrons with energy larger than Eth were treated as being in bulk Si. The simulated results of the dependence of the drift velocity on the tangential electric field Et and the electric field En normal to the MOS inversion layer were compared with the experimental results obtained by using the time-of-flight method of Cooper and Nelson [J. Appl. Phys. 54, 1445 (1983)]. As a result, we found that the simulation result of the first model diverges from the experimental results as Et increases and En decreases, and that the second model agrees well with the experimental results. These simulation results suggest that it is important to take account both of the behavior of two-dimensional electrons and bulk Si electrons in the MOS inversion layer.
Experimental determination of the attenuation coefficient of surface electromagnetic waves
Authors: Klopfleisch M. , Schellenberger U.
Published: July 2002

The experimental determination of attenuation coefficients of surface electromagnetic waves (SEW) excited by using the evanescent wave coupling technique (two prism technique) proves to be elusive. In an experimental study of the SEW attenuation we could show that the electromagnetic surface modes are obscured by bulk electromagnetic waves. The influence of these bulk waves on the decoupled electromagnetic intensity was detected by its diffraction on a screen placed in front of the coupling prism. A simple half-quantitative description can be given in the framework of the Fresnel–Huyghens principle. The experimental arrangement modified by the additional screen allows the determination of the propagation lengths unambiguously. The measured propagation length for optically thick gold films agree with results obtained by infrared ellipsometric measurements.
Effect of post-growth annealing on the recombination centers in C-doped p+-GaAs/n-AlGaAs heterojunctions
Authors: Watanabe Kazuo , Yamazaki Hajime , Yamada Kohji
Published: July 2002

Recombination current in carbon-doped p+-GaAs/n-AlGaAs junction diodes can be reduced by post-growth annealing of the epilayers at 600 and 700 °C but not at 500 °C. The reduction of recombination current at 600 °C under the face-to-face or SiO2 capped condition is by far larger than that under high-AsH3 flow, i.e., arsenic overpressure condition. The reduction can be primarily attributed to the reduction in the 0.55-eV deep levels of recombination centers, which may be an oxygen related complex level with As atoms. The reduction of recombination current at 600 °C is a little smaller when cooling after annealing proceeds slowly, which may be mainly due to around 0.5 eV levels being created during slow cooling. Degradation in the carrier and dopant profiles near junction is not detected even after 700 °C annealing. Annealing at temperatures of 600 °C or higher followed by fast cooling without arsenic overpressure ambient is thus promising for the reduction of recombination centers.
WSi2 and CoSi2 as diffusion sources for shallow-junction formation in silicon
Authors: Probst V. , Schaber H. , Mitwalsky A. , Kabza H. , Van den hove L. , Maex K.
Published: July 2002

The redistribution of B and As ions implanted into thin layers of WSi2 and CoSi2 on poly- or monocrystalline Si and the outdiffusion into the Si substrate during furnace annealing (FA) and rapid thermal processing (RTP) were investigated by several analytical techniques. Shallow junctions (depth xj < 100 nm) with interface concentrations Cint close to the solid solubility of the respective dopant in Si (Cint≳3×1020 cm−3 for As; (Cint ≳ 8 × 1019 cm−3 for B) were obtained with RTP. For FA above 800 °C, the diffusion of B from CoSi2 into Si results in a drop of Cint < 2 × 1019 cm−3 because of strong B segregation and probably reactive loss at the SiO2/CoSi2 interface. No evidence on metal-dopant-compound formation could be found. The dopant redistribution is demonstrated to be a superposition of lattice and grain-boundary diffusion, solubility limits, layer inhomogeneities, dopant segregation at the interface and grain boundaries, and probably phase transformation of the dopants segregated at the SiO2/silicide interface. Electrical results such as, e.g., CoSi2 diode leakage currents (≊1 nA/ cm2) and contact resistances ( 2–5 × 10−7 Ω cm2 for RTP) clearly show that the formation of shallow silicided junctions by diffusion from an implanted silicide is a highly useful technological approach.
Temperature influence on the damage induced in Si+-implanted InP
Authors: Zheng P. , Ruault M.-O. , Gasgnier M. , Descouts B. , Krauz P.
Published: July 2002

In situ transmission electron microscopy observations during 50-keV Si+ ion implantation in InP were performed from 15 to 600 K. The implantation dose temperature dependence of the cluster density was studied in the 15–400-K range, and the results are discussed. It is shown that the result of increasing damage is either amorphization (T≤400 K) or phase precipitation (T≥500 K). The threshold fluence for these phenomena increases with the implantation temperature (from 8 × 1011 Si/cm2 at 15 K to 4 × 1015 Si/cm2 at 600 K). The formation of an amorphous layer is ascribed to the defect zone overlap of the displacement cascade outskirts. The precipitate structure and evolution are studied.
An investigation of the diffusion of silicon in delta-doped gallium arsenide, as determined using high-resolution secondary ion mass spectrometry
Authors: Nutt H. C. , Smith R. S. , Towers M. , Rees P. K. , James D. J.
Published: July 2002

Silicon delta-doped samples of various densities were grown by molecular-beam epitaxy and analyzed using high-resolution secondary ion mass spectrometry. A marked difference was observed between profiles produced from samples doped below a surface density of 1.3×1013 cm−2, where all the silicon was incorporated on gallium sites, and highly doped samples, where autocompensation had occurred. All samples were grown at nominally 580 °C and all the doped planes showed some degree of broadening. A computer model of a two-step diffusion process was developed which produced a set of diffusion coefficients for the lower-doped samples. The diffusion coefficient associated with the post deposition growth for these low-doped samples was approximately 4.2×10−17 cm2 s−1. The more highly doped samples, because of their complicated profiles, were modeled using a graphical technique. This technique revealed the presence of a much larger diffusion coefficient, which is tentatively assigned to silicon diffusing as nearest-neighbor pairs.
Cross-polarization coupling via reflection-type degenerate four-wave mixing in compound semiconductor photorefractive crystals
Authors: Roy Amitava , Singh K.
Published: July 2002

The photorefractive (PR) degenerate four-wave mixing (DFWM) of polarized electromagnetic waves in cubic isotropic crystals is considered. Effects of cross-polarization coupling have been investigated in the case of DFWM in absorbing, semi-insulating compound semiconductor PR crystals in reflection geometry. Considering the pump beam depletion, nonlinear coupled wave equations are obtained and have been solved numerically by a shooting method. Numerical results obtained from computer calculations are presented in graphical form. It is observed that the intensity of a particular polarization component can be appreciably increased by a proper choice of input beam polarization angle, crystal orientation, and crystal thickness.
Rectification in heavily doped p-type GaAs/AlAs heterojunctions
Authors: Yoffe G. W.
Published: July 2002

Experimental and theoretical studies of heavily doped p-type single GaAs/AlAs heterojunctions have been performed. Abrupt junctions doped at 1018 cm−3 exhibited marked rectifying behavior, in agreement with calculations based on thermionic emission theory. At a doping level of 1019 cm−3, the current-voltage characteristics were more symmetric, as tunneling current dominated. Grading the junction was found to make the characteristics more linear and symmetric. The results explain the high series resistance of vertical-cavity surface-emitting lasers and demonstrate the need for compositional grading in the p-type multilayer mirrors in those devices.
In situ pulsed laser deposition of Nd1.85Ce0.15CuO4−y
Authors: Horwitz J. S. , Chrisey D. B. , Osofsky M. S. , Grabowski K. S. , Vanderah T. A.
Published: July 2002

Thin films of the electron-charge-carrying high-temperature superconductor, Nd1.85Ce0.15CuO4−y have been deposited by pulsed laser deposition on to 〈100〉 MgO and SrTiO3 substrates. Film composition, structure, and transport properties were measured as a function of deposition conditions (substrate temperature, oxygen deposition pressure, and postdeposition annealing conditions). C-axis oriented, single-phase films were formed at high substrate temperatures (900 °C) in high background pressures of oxygen (200 mTorr), but were semiconducting when quenched to room temperature in either oxygen or nitrogen. A reduced oxygen background pressure during deposition at 900 °C resulted in films that were transparent and insulating due to the loss of copper. Films which were deposited at 900 °C (Poxygen≥200 mTorr) and then slowly cooled in a vacuum were superconducting with a maximum Tc (onset) of 15 K and Tc(R = 0) of 11 K.
Transmission electron microscopy study of V-Sr-Tl-O system
Authors: Li J. Q. , Liu Z. Y. , Huang Y. Z. , Zhao Z. X.
Published: July 2002

We have investigated the structure of V-Sr-Tl-O system with transmission electron microscopy. The majority phase in VSrTl0.2Oy samples with a sharp resistivity drop around 165 K is identified as V2Sr0.6TlδOy with δ ranging from 0.01 to 0.04. This phase has a hexagonal structure, with point group 6/mmm, space group P6/mmm, and lattice parameters a=0.569 nm and c=1.284 nm. Upon in situ cooling from room temperature to 130 K, no evidence of structure change is observed. When the crystals of V2Sr0.6TlδOy are heated in situ, two superstructures are formed.
Resonant nuclear Bragg diffraction from epitaxial 57Fe2O3 on natural Fe2O3
Authors: Tischler J. Z. , Larson B. C.
Published: July 2002

We have used a 57Co Mössbauer source to measure the resonant nuclear scattering properties of epitaxial 57Fe2O3 grown on natural Fe2O3 substrates. Isotopically enriched 57Fe2O3 layers were grown on 〈111〉 oriented Fe2O3 by chemical vapor transport; Mo Kα rocking curve measurements showed the mosaic spread of the epitaxial layers to be ∼15 arcs. The resonant nuclear scattering properties were characterized by absolute integrated intensity measurements of the (electronic and nuclear resonant) 666 reflection and the (pure nuclear resonant) 777 reflection as a function of energy near the resonance. The energy widths of the diffracted intensities were found to be ∼40 neV (∼10Γ) and the integrated intensities were found to lie between the values calculated from kinematic and dynamic diffraction theories. The results indicate that epitaxial crystals such as these can be used for resonant nuclear monochromators to obtain resonant x-ray beams from synchrotron sources.
Thin-film BiPbSrCaCuO direct current superconducting quantum interfering devices operating at 78 K
Authors: Xu H. D. , Wang H. Z. , Xue S. Q. , Shi X. Q. , Huang X. M. , Yang C. B. , Cao X. N.
Published: July 2002

Direct current SQUIDs (superconducting quantum interference devices) have been successfully fabricated by using a Pb-doped BiSrCaCuO superconducting thin film made by mixed evaporation of a single source composed of related components with a resistance heater. The dc SQUID comprises a square washer with a small hole. These SQUIDs show perfectly periodic voltage-flux characteristics without magnetic shield, that is, typically, the flux noise and energy resolution at a frequency range from dc to 1 Hz and at 78 K being 1.7×10−3 Φ0/√Hz and 3.6×10−26 J/Hz, respectively. Meanwhile, we have found out that one of the SQUIDs still was able to operate on flux-locked mode without bias currents and showed voltage-flux second harmonic characteristics. This phenomenon is not well understood, but it may be related to I-V (current-voltage) characteristics of the dc SQUID.
89Y nuclear magnetic resonance study of hyperfine interactions in (R
xY1−x)Fe2
Authors: Alves K. M. B. , Guimarães A. P.
Published: July 2002

89Y pulsed nuclear magnetic resonance measurements have been performed at low temperatures in (RxY1−x)Fe2 compounds, where R is a heavy rare-earth (Gd, Tb, Dy, Ho, Er, and Tm) in the range 0≤x≤0.05. The spectra were measured at 4.2 K, except for Dy (77.4 K). The spectra were analyzed in terms of direct and indirect (through common Fe neighbors) transferred hf interactions. The direct transferred hf field amounts to a few kOe per rare earth 1st neighbor; the indirect contributions of the first two shells are smaller by a factor of 10. We have found that a model that restricts the transferred hyperfine interactions to the indirect hf field or considers the first three neighbor shells in the same way is not satisfactory to explain the changes in the hyperfine field at Y nuclei.
Multiple images theory in superlattices
Authors: Elabsy A. M.
Published: July 2002

A multiple images potential energy model for a charge carrier located in a single quantum well (QW) of a superlattice is derived. The new model is applied to a hydrogenic charge carrier in a GaAs QW of GaAs/AlxGa1−xAs superlattice. It is found that the present model is more pronounced for studying the energy states of impurities in narrow QWs than for wide ones.
Ultrasonic measurements on silver(Ag)-high T
c superconductor (YBa2Cu3O7−δ) composites at high pressures up to 0.4 GPa
Authors: Xu Ji-an , Wang Ru-ju , Manghnani Murli H. , Misra Anupam , Song Yi , Gaines James R.
Published: July 2002

The longitudinal and transverse velocities of various Ag-YBa2Cu3O7−δ composite samples have been measured under high pressure in nitrogen gas (up to 0.4 GPa) using ultrasonic techniques. A systematic relationship between the elastic properties and the composition of these composites is observed. The sound velocities of pure YBa2Cu3O7−δ derived from our experimental data are in good agreement with previous results obtained on single crystalline and oriented polycrystalline samples
Artificial magnetostatic and electrostatic modes
Authors: Peuzin J. C.
Published: July 2002

Outer surfaces of simple objects such as plates, cylinders, spheres, etc. may be approximately reproduced (in an infinite number of ways) by closely assembling a number of insulated metal stripes or wires. If those stripes or wires are then suitably connected through purely reactive impedances, one obtains a system that exhibits either ‘‘magnetostatic’’ or ‘‘electrostatic’’ modes. These modes are analogous to those predicted and observed in solid bodies of corresponding shapes (plate, cylinder, sphere, etc.) made of respectively magnetic or dielectric materials. The proposed systems can thus constitute models on which a number of basic features characterizing the magnetostatic or electrostatic modes can be easily demonstrated and studied. Two specific examples, the ‘‘magnetic’’ plate, and the ‘‘magnetic’’ cylinder, will be described in detail in this paper, both theoretically and experimentally. Other models exhibiting electrostatic modes will also be presented but only on the theoretical side.
Second-harmonic generation by Cerenkov-type phase matching in a poled polymer waveguide
Authors: Sugihara O. , Kunioka S. , Nonaka Y. , Aizawa R. , Koike Y. , Kinoshita T. , Sasaki K.
Published: July 2002

A copolymer of methyl methacrylate and azo-dye-substituted methacrylate is corona-poled. Cerenkov-type second-harmonic generation (SHG) of Nd:YAG laser is observed in the poled polymer waveguide even though there is strong absorption of the SHG wavelength. The total SHG conversion efficiency is 1.72 × 10−3%, and the net SHG conversion efficiency in the waveguide is 0.21%.
Behaviors of ionization wave packets within finite positive columns
Authors: Ohe K. , Kimura T.
Published: July 2002

Behavior of ionization wave packets was investigated in wave-free positive columns of Ne-N2 and He. The position of envelope wave packet launching was displaced with an excitor along the tube axis, while phases of included carrier waves shifted only a little. The anode end of positive column played an important role in propagation of the carrier wave, causing such a phase shift. The influence of anode end on the wave behavior was explained by a phenomenological model.
Characteristics of the electroluminescence and photoluminescence emission of erbium ions doped in InP and the energy transfer mechanism
Authors: Isshiki Hideo , Saito Riichiro , Kimura Tadamasa , Ikoma Toshiaki
Published: July 2002

The characteristics of impact excitation of the 1.54-μm emission due to intrashell transitions of 4f electrons of erbium atoms (4I13/2 →4 I15/2) doped into InP were investigated in comparison with the photoluminescence (PL) emission of the same peak from the same sample. The thermal quenching of this Er-related electroluminescence (EL) emission was found to be very small in contrast to the large thermal quenching of the PL emission. The EL emission intensity at room temperature was half that at 77 K, and the temperature dependence of the emission energy and the spectral width was very small. Due to almost temperature-independent nature of the impact excitation process, the quenching of the EL emission intensity reflected directly that of the fluorescence efficiency of this intrashell transitions of Er 4f electrons. Using this result, the temperature dependence of the PL energy transfer efficiency was also obtained. It was also found that the fine structure of the 1.54-μm emission was different between EL and PL. It was speculated that Er atoms on different lattice sites, which were in different crystal fields, were excited depending on excitation processes.
Thermal magnon fluctuations in guided-wave Faraday rotation
Authors: Shen T. P. , Rogovin D.
Published: July 2002

We examine theoretically the role of thermodynamic spin fluctuations in optical guided waves propagating on a ferromagnetic film and undergoing Faraday rot ation. Using the equipartition theorem, we obtain the noise equivalent power (NEP) for these thermally excited magnetostatic spin waves, as a function of film thickness and applied magnetic field. These considerations place limiting sizes and modulation sensitivities on optical signal processing devices that are based on the Faraday effect. For example, if 1 mW of optical guided wave power propagates in a 1-μm film, then 46 pW of optical power are mode converted by these thermal spin waves and appear as optical noise. The NEP for all thermal spin waves in a 1-μm Bi-doped yttrium iron garnet film deposited on a gadolinium gallium garnet substrate is 30 nW and drops by a factor of two for a 10-μm film.
A new measurement method for trap properties in insulators and semiconductors: Using electric field stimulated trap-to-band tunneling transitions in SiO2
Authors: Thompson Scott E. , Nishida Toshikazu
Published: July 2002

A new experimental technique for characterization of traps in insulators and semiconductors and its speed-up derivative are presented which use trap-to-band tunneling emission of electrons. Equations are given which allow the energy levels to be calculated from experimental emission decay data. The expressions are valid for electrically active defects with a discrete energy level or a distribution of levels. The numerical error in calculating the energy level from experimental data is 1%–2% for a given set of energy-band parameters such as the effective masses and the parabolicity of the dispersion relation in the energy gap. The techniques are applied to electron traps in thermally grown integrated-circuit grade SiO2 to illustrate their accurate and utility. An energy distribution of shallow charged oxide traps is found throughout about 0–3 eV below the oxide conduction band edge with a peak density of states at about 0.9 to 1.0 eV. The centroid of the charged oxide traps is about 82 Å from the SiO2/Si interface. The same density–energy curve is observed for oxide traps in many thermally grown dry oxide films thicker than 150 Å. A decrease in the density of the charged oxide traps is found for oxides less than 100 Å. A distribution of capture cross sections versus trap energy depth, ranging from 10−15 to 10−17 cm2, is measured at low oxide electric field (1.1 MV/cm). The shallower traps have a larger capture cross section than the deeper traps. The measured energy level at the peak density is consistent with the recent theoretical anticipation of Robertson and Rudra and Fowler for an oxygen vacancy which relaxes to form a silicon–silicon bond in the oxide [(Si—O)3≡Si—Si≡(O—Si)3].
Morphology and hole transport of butadiene derivative
Authors: Enokida Toshio , Hirohashi Ryo
Published: July 2002

Morphology and hole-carrier mobilities of 1,1-bis(p-diethyl-aminophenyl)-4, 4-diphenyl-1, 3-butadiene (DEAB) derivative have been investigated. Annealing on a DEAB film and the temperature of glass transition, crystallization and the melting point on this amorphous film were measured by a differential scanning calorimeter and their polymorphic states discussed. Hole-carrier mobilities in excess of 10−3 (cm2/V s) have been observed at room temperature. The electric field and temperature dependences of the hole mobility can be described as exp(βE1/2) and exp(T0/T)2 and are discussed according to Arrhenius, Poole–Frenkel formulations and non-Arrhenius type of temperature dependence assuming Gaussian distribution of the hopping sites.