bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous Sb doping and formation of self-aligned TiSi2 by codeposition of Ti and Sb
Authors: Li X.-H. , Gong S. F. , Hentzell H. T. G. , Hagel J. , Robertsson A.
Published: July 2002

Thin Ti films containing Sb were deposited on silicon by electron-beam evaporation. The films were annealed in three steps at different temperatures in order to achieve simultaneous Sb doping and self-aligned TiSi2 formation. Sb behavior during the Ti silicide formation and silicide structures were investigated with Auger electron spectroscopy, transmission electron microscopy, and secondary ion mass spectroscopy. Shallow n+-p junctions have been obtained by using a modified self-aligned TiSi2 process.
Raman study of cw laser-induced crystallization of a-Si:H films on quartz and sapphire substrates
Authors: Mavi H. S. , Jain K. P. , Shukla A. K. , Abbi S. C. , Beserman R.
Published: July 2002

A Raman-scattering study of amorphous-to-crystalline transition in a-Si:H films on quartz and sapphire substrates induced by cw laser annealing is reported. The threshold power density for crystallization is much greater for a-Si:H films on sapphire than on quartz substrates. It is determined that crystallization occurs in a-Si:H films on quartz substrates due to a bulk-induced solid phase process. Crystallization in a-Si:H films on sapphire substrates is due to liquid phase epitaxy. It was found that annealing with laser powers significantly greater than the threshold powers causes substantial stresses at the interface.
Thin thermal oxides of silicon and the orientation effect: An empirical approach
Authors: Taft E. A.
Published: July 2002

Within a linear-parabolic model of oxide growth on silicon in dry oxygen a set of linear and of parabolic rate constants has been constructed. Data from multiple sources have been collected and correlated with some general concepts. One activation energy for the linear rate constants was found to apply to all silicon orientations. The activation energies for the parabolic rate constants for the several silicon orientations are different. In the fitting of data it is found that the oxygen pressure dependence of oxidation is sublinear and the coefficient for 〈100〉 silicon is not the same as for 〈111〉 silicon. Numerical values for these temperature- independent coefficients are chosen. An initial rapid oxidation appears essentially as a small, limited, growth step. Comparisons of calculated oxidation curves are made with reported orientation effect data.
Useful angular selectivity in oblique columnar aluminum
Authors: Ditchburn R. J. , Smith G. B.
Published: July 2002

A useful magnitude of angular selective transmittance of incident unpolarized light is demonstrated in obliquely deposited aluminum. Required deposition procedures and anisotropic optical properties are discussed. Angular selectivity is very strong at visible wavelengths but both experiment and theory indicate that a single oblique layer with well defined columns gives high transmittance at near-infrared wavelengths compared with normal films. There are ways of reducing this to enhance the energy control capability. Both solar and luminous angular selectivity are reported.
Conductivity in undoped and doped molecular solid films of metallophthalocyanines
Authors: Beqqali O. El , Sadoun M. Al , Guillaud G. , Gamoudi M. , Benkaddour M. , Skal A. S. , Maitrot M.
Published: July 2002

Many universal models of ac conductivity have been given in the literature and applied to molecular materials. They are compared with experimental data from deliberately doped phthalocyanines. The variation of conductivity of these samples with temperature is not accounted for by the universal models.
Band-to-band and free-carrier absorption coefficients in heavily doped silicon at 4 K and at room temperature
Authors: Jain S. C. , Nathan A. , Briglio D. R. , Roulston D. J. , Selvakumar C. R. , Yang T.
Published: July 2002

Using the raw experimental data of Schmid and the known values of band-gap narrowing and Fermi energies for different doping concentrations, the band-to-band and free-carrier absorption coefficients in heavily doped Si are calculated. The behavior of boron-doped Si is different from that of arsenic doped Si. Near threshold, our values of the absorption coefficients are significantly different from those derived by Schmid from the same data. The enhancement of band-to-band transitions due to impurity or free-carrier scattering is not as important in heavily doped Si as in heavily doped Ge. Numerically fitted empirical expressions for the absorption coefficients, suitable for computer simulation studies of opto-electronic devices are given.
Pulsed laser-induced electron and positive-ion emission from Cu(100) under ultrahigh-vacuum conditions near the threshold for surface damage
Authors: Strupp Paul G. , Stair Peter C. , Weitz Eric
Published: July 2002

Results are presented from an experimental study of pulsed laser-induced electron and positive-ion emission at 590 nm from single-crystal Cu(100) under ultrahigh-vacuum conditions near the threshold for surface damage. Below 60 MW/cm2 the electron emission is consistent with a three-photon photoemission mechanism. Above 60 MW/cm2 thermionic electron emission becomes dominant. Positive ions are produced with a threshold of approximately 60 MW/cm2 and a slope of 9.5 in a log(yield) vs log(power) plot. The kinetic energy distribution of the ions is nonthermal with a maximum at approximately 0.7 eV. Ion production is most likely due to collisions of thermally desorbed atoms with electrons above the surface. Evidence is presented that suggests a critical role of substrate-emitted electrons in the formation of a laser-induced surface plasma near its low power threshold. It is also found that electron and ion yields from a given spot on the surface decrease with the number of laser pulses and spot receives. The yield from a previously unirradiated spot decreases by an order of magnitude over the course of approximately the first 25 laser pulses approaching a constant level for subsequent pulses. Enhanced yields from new spots could be eliminated by additional annealing of the surface prior to laser irradiation. These observations are consistent with enhanced charged particle yield from surface defects which are reduced in number by subsequent annealing by the laser.
An equation of state for shock loaded powders
Authors: Petrie M. W. , Page N. W.
Published: July 2002

A simple analytical model is developed for the shock Hugoniot of a powdered material. Previous models have exhibited decreasing accuracy when applied to powders and porous materials of high initial porosity. This deficiency has been avoided in the present model. A special feature of this model is provision for a cold pressure loading relation which covers the full range of consolidation mechanics including relative particle movement, elastic and plastic deformation, fracture and bulk compression. This empirical cold loading relation is incorporated into a Mie–Grüneisen treatment of the shock process. This ensures that the model correctly describes behavior for all starting porosities and shock strengths and as such is suitable for use with all powdered and porous materials. A limiting density ratio is prediced at high shock strengths. The accuracy of the model is demonstrated by comparison with previously published shock compaction data.
Radio frequency thermal plasma chemical vapor deposition of superconducting Y1Ba2Cu3O7−x films
Authors: Zhu H. , Lau Y. C. , Pfender E.
Published: July 2002

Superconducting YBa2Cu3O7−x thick films have been grown in situ on polycrystalline CaO stabilized ZrO2 substrates by radio frequency thermal plasma chemical vapor deposition at ∼0.1 μm/min. Mixed aqueous nitrate solutions of yttrium, barium, and copper were used as precursors. Different substrate temperatures of 450, 500, and 600 °C were used for deposition. The as-deposited films were black, dense, smooth, and superconducting with onset Tc’s higher than 80 K. X-ray diffraction shows that the films were highly textured with the c axis normal to the substrate. Energy dispersive x-ray spectroscopy was used to analyze the film composition. From direct current magnetization measurements, the critical current density was found to be 1 × 106 A/cm2 at 10 K and zero field for a film deposited at 450 °C.
Phase matching for second harmonic generation in KNbO3:Ta crystals with Nd:YAG- and GaAs-laser wavelengths
Authors: Schmidt N. , Voigt P. , Hellermann B. , Betzler K. , Hesse H. , Kapphan S.
Published: July 2002

Noncritical phase-matched second harmonic generation was measured in optically biaxial KNb1−xTaxO3 mixed crystals in the orthorhombic phase. For Nd:YAG-(1064 nm) the coefficient d31 of the tensor of the nonlinear susceptibility was applied, while for the GaAs-laser (905 nm) the coefficient d32 was used. For both laser wavelengths the phase-matching temperature decreases with increasing Ta-concentration. Noncritical phase-matching at room temperature can be reached with the GaAs-laser for a Ta concentration of ≊9%. The corresponding value for the Nd:YAG laser is ≊14%.
Passive mode-locking of an Alexandrite laser for picosecond pulse generation
Authors: Völker F. , Lü Q. , Weber H.
Published: July 2002

The Alexandrite laser belongs to the class of vibronical lasers. The broad spectral laser gain of Alexandrite laser gain of Alexandrite suggests the possibility to generate femto-second laser pulses with passive mode locking. Experiments showed, however, that a limit of pulsewidth shortening is reached near 10 ps. This effect is caused by the limited mode-locking capability of the passive absorber. The results of eight different passive absorbers used to generate mode locking are presented. The effect of bandwidth narrowing of the laser emission spectrum of Alexandrite on pulsewidth and pulse-train energy was measured for these absorbers. The dependence of laser output energy with the temperature on the active medium was also investigated.
Deep-level photoluminescence studies on Si-doped, metalorganic chemical vapor deposition grown AlxGa1−xAs
Authors: Visser E. P. , Tang X. , Wieleman R. W. , Giling L. J.
Published: July 2002

Deep-level photoluminescence (PL) studies were performed on Si-doped, metal organic chemical vapor deposition grown AlxGa1−xAs as a function of the most important growth parameters. The SiH4 input mole fraction, the V/III ratio, and the Al fraction were varied over a wide range, resulting in net charge carrier concentrations n ranging between 1.8×1016 and 4.5×1018 cm−3, Hall mobilities μH between 220 and 2400 cm2/V s, and a solid Al fraction x between 0 and 0.72. Two novel PL emissions for AlxGa1−xAs in the energy range of 1.05–1.35 eV were recorded. By a systematic analysis of the growth conditions these emissions were attributed to SiGa–SiAs and SiGa–VGa complexes. The behavior of the broad PL emission at 0.8 eV as a function of the growth parameters was studied systematically. It was demonstrated that this emission is not related to the DX center. Instead, there are strong indications that it should be attributed to an internal transition within a native, or oxygen-related defect.
Comparison of zirconia thin films sputtered from metal and compound targets by reactive ion-beam process
Authors: Kao A. S.
Published: July 2002

Reactive ion-beam deposition of zirconia films is carried out to demonstrate the characteristic difference between the sputtered species from a metallic zirconium target and a compound zirconia target, and their effects on the structural properties of deposited films. Films deposited from the compound target have compositions much closer to the ideal stoichiometry of zirconia, and have higher stresses and are mechanically harder, due to the ionic nature of the sputtered species and their inherently low mobility on the substrate surface. In contrast, adatoms sputtered from the metal target are chemically less active but have a higher mobility which facilitates the relief of film stress by low-energy Ar+ bombardment during deposition. This stress modification process requires a much greater dosage of Ar+ flux when a compound target is used. X-ray diffraction analysis indicates that all of the zirconia films deposited from the metal target are amorphous, whereas the monoclinic phase is observed in the films from the compound target at sputtering energies of 500 and 1000 eV. However, the monoclinic crystallites diminish as additional energy is imparted to the growing film from either a higher sputtering energy or a greater flux of Ar+ bombardment. The polymorphic transformation of zirconia films is examined by isochronal annealing of the films in a temperature range from 150 to 600 °C. The phase transformation of the zirconia films shows that the monoclinic zirconia persists after annealing while the amorphous matrix transforms into a cubic structure in the temperature regime from 300 to 450 °C.
The design of GaAs/AlAs resonant tunneling diodes with peak current densities over 2×105 A cm−2
Authors: Wolak E. , Özbay E. , Park B. G. , Diamond S. K. , Bloom David M. , Harris James S.
Published: July 2002

A coherent transport model is described which accommodates bandstructure nonparabolicity by using a ‘‘local energy parabolic band approximation.’’ The model and a knowledge of its limitations is used to design resonant tunneling diodes in the GaAs/AlAs material system with measured peak current densities of 2.5(2.8)×105 A cm−2 concurrent with peak-to-valley ratios as high as 1.8 (3.1) at room temperature (77 K).
Matrix method to determine a steady solution of the Boltzmann equation in III-V compound semiconductors
Authors: Gontrand C.
Published: July 2002

A matrix method is used to solve the Boltzmann equation for hot carriers. This method is independent of initial conditions and is very fast computed. Then a steady-state solution is performed. Distribution functions, drift velocities, and energies versus the electric field, for instance, can be obtained. We compare our results to a Monte Carlo code as a check, taking GaAs material as an example.
Thermally stimulated current of amorphous selenium
Authors: Kang T. W. , Tong C. , Leem J. Y. , Kim T. W.
Published: July 2002

Deep trap properties such as activation energy, capture cross section, and polarity in the amorphous selenium bulk are investigated using a thermally stimulated current (TSC). Two peaks are found near 220 and 330 K in the TSC curve, and the activation energies corresponding to these two peaks are distributed from 0.20 to 0.22 eV and from 1.04 to 1.10 eV. It is found that the trapped carriers near the temperature 220 K are mainly holes.
The temperature dependence of the contact resistivity of the Si/Ni(Mg) nonspiking contact scheme on p-GaAs
Authors: Han C. C. , Wang X. Z. , Lau S. S. , Potemski R. M. , Tischler M. A. , Kuech T. F.
Published: July 2002

The temperature dependence of the contact resistivity of the Si/Ni(Mg) nonspiking contact scheme on p-GaAs has been investigated. This contact scheme has been shown to form planar contact interfaces with contact resistivities less than 1 × 10−6 Ω cm2. This investigation demonstrates that the contact resistivity can be modeled by a sum of two components in series: (i) a contact resistivity due to the metal-GaAs interface and (ii) a contact resistivity due to the high-low junction formed between the highly doped regrown GaAs layer and the substrate. For degenerately doped samples (4.5 × 1019 cm−3), the contact resistivity is nearly independent of the temperature from 300 to about 30 K, indicating that the dominant resistivity is that across the metal-semiconductor tunneling barrier. For samples with lower doping concentrations (≤ 1.5 × 1018 cm−3), the contact resistivity increases with decreasing temperature, suggesting the dominance of the contact resistivity due to the high-low junction.
Electrical properties of InPxOy -InP metal-insulator-semiconductor structures
Authors: Hattori K. , Torii Y.
Published: July 2002

The electrical properties of n-type InP metal-insulator-semiconductor (MIS) structures have been investigated. As gate insulators, InPxOy layers are formed by a new method. In the method, a Px′Oy′ layer is deposited on InP by evaporation of P2O5 powder. The reaction between the Px′Oy′ layer and InP substrate yields an InPxOy layer. The InPxOy layers 500–1450 Å thick exhibit high resistivities ρ and low dielectric dissipations D, i.e., ρ≊2×1015 Ω cm and D≤0.01 in the frequency range 0.02–100 kHz at room temperature. The hysteresis in the capacitance-voltage curves of a typical InP MIS structure is found to be less than 0.6 V and an ion-drift type. The interfacial properties of InP MIS structures are shown to be well explained by the statistical model in the conductance method. A typical value of the minimum surface state density is evaluated as 3.3×1011 cm−2 eV−1 at about 0.26 eV below the conduction-band edge. The distribution of the electron capture cross sections σ of surface states is also obtained, e.g., σ=1.6×10−16 cm2 at 0.4 eV below the conduction-band edge.
Electron-beam-irradiation effects in bulk YBa2Cu3O7−x
Authors: Basu S. N. , Mitchell T. E. , Nastasi M.
Published: July 2002

Irradiation effects on thin foils of bulk YBa2Cu3O7−x have been studied in a transmission electron microscope using 100-, 150-, 200-, 250-, and 300-keV electrons at 83 and 300 K. The disordering of the oxygen atoms and vacancies in the O(4) and O(5) sites in the Cu-O planes during irradiation was monitored by measuring the splitting of the (11̄0) diffraction spots in the [001] diffraction pattern. The results show that YBa2Cu3O7−x is insensitive to 100-keV electron irradiation. Irradiation by higher-energy electrons leads to irradiation-induced oxygen disordering of the oxygen atoms and vacancies, mainly by single displacement events. The excellent fit of the data to a disordering model suggests that the displacement threshold energy for oxygen in YBa2Cu3O7−x is around 18 eV and that irradiation-assisted oxygen reordering occurs in YBa2Cu3O7−x at 300 K, but not at 83 K.
Zinc diffusion into GaAs, Al0.2Ga0.8As, and GaAs0.6P0.4 from MOCVD (ZnO)x(SiO2)1−x films
Authors: Lawrence David J. , Smith Frank T. , Lee S.-Tong
Published: July 2002

A simple and reproducible process for the open-tube diffusion of zinc from (ZnO)x(SiO2)1−x source films into GaAs, Al0.2Ga0.8As and GaAs0.6P0.4 is reported. (ZnO)x(SiO2)1−x films were deposited onto compound semiconductor substrates by metalorganic chemical vapor deposition. A capping layer of SiO2 was deposited on top of the source films. The diffusions were performed in flowing nitrogen at 650 °C. Diffusion depths from 0.2 μm to several micrometers were readily achieved. The diffusion front in n-type substrates is abrupt and the average hole concentration for diffused layers in GaAs is approximately 8 × 1019/cm3. The dependence of the diffusion depth on the source film composition (x=0.04–x=1.00) is presented. The dependence of the diffusion depth on the source film thickness and the SiO2 cap layer thickness is also reported.
Practical measurement of diffusion constants in sintered zirconias by using a light-scattering method
Authors: Suemoto T. , Arashi H.
Published: July 2002

A practical method to determine the ionic diffusion coefficient and activation energy by using quasielastic light scattering (QELS) is presented. It is shown that a temperature dependence curve of the QELS intensity at a fixed frequency can be well fitted by Jonscher’s formula and that the diffusion parameters can be obtained from this curve fitting. This method is successfully applied not only to crystals with high optical quality, as reported earlier, but also to opaque ceramics, which are more important than the crystals from a practical point of view. The composition dependence of the ionic diffusion coefficient is studied in sintered YbSZ to show the usefulness of this method.
Temperature distribution during heating using a high repetition rate pulsed laser
Authors: Haba Belgacem , Hussey Brian W. , Gupta Arunava
Published: July 2002

A general equation has been derived for computing the temperature distribution produced in a substrate heated by a high repetition rate pulsed laser. The theoretical predictions have been compared with experimental results obtained for etching of Mn-Zn ferrite in KOH solution using a copper vapor laser. The effects of the laser power and substrate scan speed on the temperature distribution have been investigated, and the predicted melt-zone boundaries have been compared with the experimentally observed width, depth, and shape of the etched grooves.
Electric field induced emission as a diagnostic tool for measurement of local electric field strengths
Authors: Dharamsi A. N. , Schoenbach K. H.
Published: July 2002

The phenomenon of electric field induced (EFI) emission is examined in several diatomic and polyatomic molecules. The possibility of using this phenomenon as a diagnostic tool to measure, nonintrusively, the strength and direction of local electric fields in plasmas is discussed. An estimate of the EFI signal emitted in a typical application plasma is given. This yields a lower bound on the detector sensitivity necessary to exploit EFI emission in practical applications. It is concluded that, at present, the EFI signal could be measured by some very sensitive infrared detection schemes available. Current progress in infrared detector technology, if maintained, could result in the possibility of utilizing EFI emission on a more routine basis. This would allow measurement of electric fields in plasmas of species that are not suitable candidates for any of the other currently available schemes which measure such fields.
A novel three-guide optical coupler using a taper-formed waveguide
Authors: Cai Yuanmin , Mizumoto Tetsuya , Saito Takeshi , Naito Yoshiyuki
Published: July 2002

A novel taper-formed three-guide coupler is presented. Its unique power coupling characteristics are experimentally demonstrated. By virtue of adopting the taper-formed waveguide, the severe restrictions imposed on the device fabrication process are greatly relaxed. This makes the coupler advantageous to application in a variety of integrated optics, such as power splitters and combiners, and as constituent elements of devices like optical isolators.
Scaling of the electron-beam-pumped xenon chloride laser
Authors: Cartland Harry E. , Johnson Thomas H.
Published: July 2002

A comprehensive kinetics and extraction model of electron-beam-excited xenon chloride lasers is used to examine the feasibility of constructing a megajoule-class excimer laser. The ratio of small-signal gain to absorption scales nearly logarithmically with pump rate over the range studied, 10 kW/cm3 to 1 MW/cm3, and limits extraction efficiency to 20%–50%. Active volume dimensions are practically constrained to 1–2 m in length and to ∼2 m in width, with efficient extraction possible for pulse lengths of 2 μs or less. Single modules operating in the technologically conservative, low-pump-power (≤100 kW/cm3 ) regime should be capable of producing pulse energies of 40 kJ.
Photovoltaic spatial light modulator
Authors: Hong John H. , Vachss Frederick , Campbell Scott , Yeh Pochi
Published: July 2002

A novel concept for implementing a high-resolution spatial light modulator using a thin slab of photorefractive LiNbO3 crystal is described. This method uses the photovoltaic effect to impress phase information onto the crystal without the use of holography where coherent reference beams are required. Experimental demonstration as well as an analysis of the operation and performance of the device are given.
Thermal effects on cavity stability of chromium- and neodymium-doped gadolinium scandium gallium garnet laser under solar-simulator pumping
Authors: Kim Kyong H. , Venable Demetrius D. , Brown Lamarr A. , Lee Ja H.
Published: July 2002

A chromium- and neodymium-codoped gadolinium scandium gallium garnet (Cr:Nd:GSGG) crystal was tested for pulsed- and continuous-wave (cw) laser operations with a flashlamp and solar simulator as pumping sources. The crystal has been considered as a good candidate for a solar-pumped laser because of its broad absorption bands over the solar spectrum. However, it was observed experimentally and theoretically that its cw laser operation is difficult at high pump powers because too many thermal lensing effects are induced. Only at low solar-simulator beam intensities of up to 1500 solar constants (203 W/cm2 ) was cw laser operation lasting longer than 10 min achieved. For higher pump beam intensities of up to 2500 solar constants (338 W/cm2 ), a quasi-cw-laser operation was obtained with continuously chopped pumping with a duty cycle of 0.5 and a repetition rate of 13 Hz. The experimental result was compared with the calculated stability condition of the laser resonator for various pump powers and showed that the thermal focusing of the Cr:Nd:GSGG is 15–8 times greater than that of the neodymium-doped yttrium aluminum garnet (Nd:YAG) laser for the pump beam intensities from 1000 to 3000 solar constants.
Synthesis of diamond films on titanium substrates by hot-filament chemical vapor deposition
Authors: Park Soon-Sup , Lee Jai-Young
Published: July 2002

Synthetic diamond film has been deposited on a polycrystalline titanium substrate using a hot-filament chemical vapor deposition method in order to study the role of substrate pretreatment and carbide formation for the diamond nucleation and subsequent growth. The substrate pretreatment, roughening by diamond powder, affects both nucleation behavior and subsequent growth of diamond. The TiC is formed on the Ti substrate during deposition. It is observed that scratches which existed on the initial Ti surface disappear after the TiC has formed; this TiC has a rough and porous structure. The TiC layer formed in this experimental condition does not influence the nucleation behavior. The nucleation behavior depends entirely on the initial surface condition of the Ti substrate, i.e., whether or not it was scratched with the diamond powder. It is suggested that changes in the surface nature due to the scratching process can create the new nucleation sites which have strong binding energies and that the formation of these new sites can alter the nucleation behavior.
Theory and simulation of a high-power microwave convertor for current-density-modulated, annular, relativistic electron beams
Authors: Lemke Raymond W. , Bacon Larry D.
Published: July 2002

The efficiency of converting the kinetic energy of a current-density-modulated, annular, relativistic electron beam into high-power microwaves depends on details of the beam, and the convertor geometry. The latter issue is investigated in this paper for a particular choice of convertor. Maxwell’s equations are solved for the case in which a structure comprised of a cylindrical cavity coupled to a waveguide by an impedance transformer is excited by a symmetric, transverse magnetic wave. The field solutions are employed to determine the effect that the transformer/waveguide system has on the resonant properties of the cavity. An example is given in which the analytic model is used to obtain maximum power output in a numerical simulation.
Self-consistent analysis of lattice-matched and pseudomorphic quantum-well emission transistors
Authors: Hong Kyushik , Pavlidis Dimitris
Published: July 2002

A self-consistent analysis of the quantum-well emission transistor (QWET) is presented allowing an exact calculation of the device quantum properties. Poisson’s and Schrödinger’s equation are solved numerically using a finite-difference method on a self-consistent basis. Pseudomorphic AlGaAs/InGaAs designs with 15%–20% excess In are suggested for improving the device performance. Design with doping in various parts of the QWET are also studied. This analysis reveals that the device performance is less optimistic than previously predicted by analytic approaches. By introducing the pseudomorphic channel principle, while maintaining a reasonably low Al content for the gate and collector layers, it is, however, possible to obtain satisfactory performance. Optimum pseudomorphic designs showed high current driving capability (2×105 A/cm2), high transconductance (3S/mm) and small intrinsic delay time (2 ps).
The role of geometric considerations in the diamond-cubic boron nitride heteroepitaxial system
Authors: Braun M. W. H. , Kong H. S. , Glass J. T. , Davis R. F.
Published: July 2002

We report the methods and results of a theoretical study of the diamond-cubic boron nitride [BNcub] heteroepitaxial system. We introduce a general, geometric reciprocal space technique for evaluating candidate epitaxial configurations, and a novel system of essentially geometric criteria to order them from most to least likely to occur. In the diamond- BNcub system, it is found that low index like planes require a relatively small strain of 1.37% from bulk parameters. The unlike epitaxial configuration which pairs diamond{100} with BNcub{221} and yields two-dimensional coincidence with the same strain is favored above other low index mixed configurations. The essentially geometric nature of this epitaxial system is highlighted.
Harmonic mixing in a superconductor-insulator-normal metal tunnel junction receiver
Authors: Chernin L. M. , Blundell R.
Published: July 2002

We have investigated the theoretical performance of a subharmonically pumped Pb/Bi/In-oxide-Ag superconductor-insulator-normal metal mixer and found excellent receiver noise performance for signal frequencies above the gap frequency, Δ/h, if the junction is biased at zero volts. This type of mixer needs no pair current suppression and can use local oscillator power more efficiently than a fundamental mixer.
Defects in a-SiO2 deposited from a tetraethoxysilane-oxygen plasma
Authors: Devine R. A. B. , Tissier A.
Published: July 2002

We have studied intrinsic and extrinsic paramagnetic defects in as-deposited and annealed samples of amorphous SiO2 produced by plasma enhanced chemical vapor deposition using tetraethoxysilane and O2. In as-deposited samples the total paramagnetic defect density is 1.7×1018 cm−3 decreasing to 3× 1016 cm−3 after annealing for 10 min in N2 at 800 °C. We identify silicon dangling bond defects (O3 ≡Si•) and, tentatively, nonbridging oxygen-hole centers (O3 ≡SiO•), O−2 ions, C2H•5 radicals, and CO−2 radicals. We observe a defect having a g factor of 2.0040 which we cannot identify.
Validation of homogenization theory for the electrical parameters of lossy transversely periodic composite materials
Authors: Olsen Robert G. , Vanhoff Barry
Published: July 2002

A computer program which utilizes a finite difference implementation of the homogenization method for calculating effective electrical parameters of transversely periodic composite materials has been developed. Computed results have been compared to measurements and to variational bounds on the parameters. The lower bound is often a reasonable approximation to the effective parameters but not always. Measurements and theory are in excellent agreement except for the imaginary part of the permittivity of composites containing a lossy material. Although the agreement in this case is within the limits of experimental error, it is believed that inhomogeneities in the lossy material contributed to the discrepancy.
Dielectric and pyroelectric properties of lithium sodium niobate ceramics at low temperature
Authors: Wang C. L. , Zhang P. L. , Zhong W. L. , Zhao H. S.
Published: July 2002

The dielectric and pyroelectric properties of lithium sodium niobate ceramics are investigated between the temperature range 320–120 K. The result is indicative of a first-order ferroelectric-ferroelectric phase transition at low temperature with a large thermal hysteresis. At temperatures near the phase transition, an unusual pyroelectric response is observed, which is attributed to the coexistence of the two ferroelectric phases. The result is in agreement with the measurement we made on the lithium sodium niobate single crystals.
Observation of the type I–type II crossover in GaAs/AlAs short-period superlattices by optical spin orientation
Authors: Bandet J. , Bacquet G. , Fabre F. , Frandon J. , Taouint R. , Planel R. , Le Roux G.
Published: July 2002

An optical spin orientation investigation of GaAs/AlAs short-period superlattices (SLs) near the type I–type II transition is reported. We used samples with intentional grading of GaAs and AlAs thicknesses in the plane of the layers. The optical spin orientation results, as a function of the investigated region, are compared with those of well-defined type-I or type-II SLs. A drastic change is observed in the Hanle profiles, which allows us to determine with precision the Γ-X crossover.
Identification of the energy levels of Si:Rh
Authors: Zhou Jie , Wu Ji-an , Lu Li-wu , Han Zhi-yong
Published: July 2002

Two thermostable levels E(0.31) and E(0.58) related to Rh in Si were observed using deep level transient spectroscopy and double correlation deep level transient spectroscopy techniques. By means of thermal annealing and electron irradiation, the microscopic natures of these levels were identified for the first time. The levels E(0.31) and E(0.58) arise from by the same impurity center but have different charge states. Their microstructures are not related to a pure substitutional Rh atom, but correspond to a complex. This result is compared to our self-consistent theoretical calculation.
Space-charge-limited current measurements in semi-insulating GaAs
Authors: Eizenberg Moshe , Hovel Harold J.
Published: July 2002

The electronic properties of undoped semi-insulating GaAs were studied by measurements of current injection under a planar configuration which is sensitive to the near-surface region. The I-V characteristics were measured as a function of temperature in the range of 295–360 K for the as-received state and also following a heat treatment of 850 °C /20 min using a Si3N4 cap. In order to understand the observed characteristics, a computer program was developed to simulate the current both in the ohmic and space-charge-limited regimes. The combination of the electrical measurements and simulation enabled the determination of the parameters controlling the resistivity of the semi-insulating samples, and shed light on the trap distributions and concentrations. It was found that the normally assumed three-level compensation model is inadequate to explain the observed behavior. Two other deep donors lying at 0.56 and 0.40 eV below the conduction band are suggested by the data (in addition to EL2); these two donor levels control the resistivity. In some instances, the influence of a deep acceptor is also observed.
Ohmic contacts to heavily carbon-doped p-AlxGa1−xAs
Authors: Katz A. , Abernathy C. R. , Pearton S. J. , Weir B. E. , Savin W.
Published: July 2002

Two different metallization schemes, AuBe(80 nm) and Pt(75 nm)/Ti(50 nm), were investigated as potential ohmic contacts for highly carbon-doped p-AlxGa1−xAs. The best contact resistance values of 0.015 and 0.025 Ω mm were achieved by applying the Pt/Ti scheme onto 1×1020 and 1×1019 cm−3 C-doped AlGaAs, respectively, followed by rapid thermal processing at 450 °C. The AuBe contacts yielded their lowest values of 0.025 and 0.05 Ω mm for the same doping levels as a result of rapid thermal processing at 425 °C. The heat treatment at 450 °C caused only limited reactions in both the Pt/Ti and Ti/AlGaAs interfaces and did not lead to significant degradation of the stable microstructure.
Studies of photogeneration of charge in polysilanes using thermally stimulated current measurements
Authors: Samuel L. M. , Dove D. B. , Sanda P. N. , Miller R. D. , Thompson D.
Published: July 2002

Studies of photogeneration of charge in polysilanes resulting from multiple pulse excitation in thermally stimulated current (TSC) measurements are reported. The amount of charge that was photogenerated at 80 K and collected during the heating of the sample up to 300 K, ranged from 1×10−9 to 4×10−8 C/cm2 for electric fields of 10–30 V/μm and illumination energy up to 2.5 mJ/cm2 and was found to be dependent both on the electric fields applied during illumination and thermal ramping and on the illumination energy. The results are compared to an idealized model that qualitatively describes for photogeneration of the charge at 80 K and its collection during the TSC measurement. According to this model, multiple pulse excitation at 80 K leads to a buildup of photogenerated charge density in the surface region of the sample and as the temperature is increased, electron-hole recombination occurs, limiting the amount of charge collected by the external circuit.
Laser spot scanning in photoelectrochemical systems, relation between spot size and spatial resolution of the photocurrent
Authors: Eriksson S. , Carlsson P. , Holmström B. , Uosaki K.
Published: July 2002

Laser spot scanning studies of single-crystalline p-InSe in contact with a neutral aqueous solution reveal a dramatic difference in lateral resolution between the material ‘‘as cleaved’’ and after platinization by brief dipping in a dilute H2PtCl6 solution. A model is developed to explain these observations, and the resolution is calculated as a function of the diffusion coefficient and the life time of minority carriers, and of the charge transfer rate. The improvement of the resolution is found to be due to the increase of the rate of hydrogen evolution at the illuminated semiconductor by Pt catalyst. The model also provides numerical values for the charge transfer rate in the noncatalyzed and the catalyzed cases.
Molecular-beam epitaxy growth and i
n s
i
t
u arsenic doping of p-on-n HgCdTe heterojunctions
Authors: Arias Jose , Zandian M. , Pasko J. G. , Shin S. H. , Bubulac L. O. , DeWames R. E. , Tennant W. E.
Published: July 2002

In this paper we present, results on the growth of in situ doped p-on-n heterojunctions on HgCdTe epilayers grown on (211)B GaAs substrates by molecular-beam epitaxy (MBE). Long wavelength infrared (LWIR) photodiodes made with these grown junctions are of high performance. The n-type MBE HgCdTe/GaAs alloy epilayer in these structures was grown at Ts=185 °C and it was doped with indium (high 1014 cm−3 range) atoms. This epilayer was directly followed by the growth, at Ts=165 °C, of an arsenic-doped (1017–1018 cm−3 ) HgTe/CdTe superlattice structure which was necessary to incorporate the arsenic atoms as acceptors. After the structure was grown, a Hg annealing step was needed to interdiffuse the superlattice and obtain the arsenic-doped p-type HgCdTe layer above the indium-doped layer. LWIR mesa diodes made with this material have 77 K R0A values of 5×103, 81, 8.5, and 1.1 Ω cm2 for cutoff wavelengths of 8.0, 10.2, 10.8, and 13.5 μm, respectively; the 77 K quantum efficiency values for these diodes were greater than 55%. These recent results represent a significant step toward the demonstration of MBE as a viable growth technique for the in situ fabrication of large area LWIR focal plane arrays.
Improvement in the thickness uniformity of silicon-on-insulator layers formed by dual electron beam recrystallization
Authors: Hopper G. F. , McMahon R. A. , Barfoot K. M.
Published: July 2002

Simple modifications to the processing of the capping layer in structures used for the preparation of silicon-on-insulator films by liquid phase recrystallization using the dual electron beam method are shown to reduce nonuniformities in the recrystallized layers. A model has been developed to explain the nature of thickness variations in recrystallized layers in terms of the geometry of the starting structure, the condition of the capping layer and the recrystallization conditions.
Laser plasma x-ray emission studies using a pinhole transmission grating spectrometer
Authors: Wang Xiaofang , Chen Shisheng , Xu Zhizhan , Pachtman A. , Li Yaoling , Qian Aidi
Published: July 2002

The powerful diagnostic capabilities of the pinhole transmission grating spectrometer (PTGS) have been utilized in studying laser plasma soft x-ray (SXR) emission and the following results are presented: (1) Studies of the SXR emission from C, Al, SiO2, Cu, Se, Mo, Sn, Er, W, and Au targets irradiated by a 1.06-μm laser beam with average power density 5×1014 W/cm2 and 300 ps duration indicate the strong dependence of the SXR emission on the atomic number Z. (2) Comparative experiments of Al or Au plasma SXR emission show that changes of the laser intensity have a more remarkable influence on low-Z plasma SXR emission than on high Z’s. (3) Experiments on target configurations (foil, multilayer, and half-cylindrical-groove target) reveal that the foil target is least effective for short-wavelength SXR emission, while the half-cylindrical target not only converges the plasma in the groove region, but also most effectively enhances the short-wavelength SXR emission or increases the electron temperature therein. (4) The PTGS is also complementarily used with the grazing incidence grating spectrograph in the SXR lasing experiments to determine the essential parameters of the line-focused laser-produced plasmas.
Effect of zinc diffusion from overgrown p-InP layers on semi-insulating InP
Authors: Cheng W. H. , Kuwamoto H. , Appelbaum A. , Renner D. , Zehr S. W.
Published: July 2002

Characteristics of Fe-doped semi-insulating (SI) InP layers with overgrown Zn-doped p-type layers have been investigated by scanning electron microscope, secondary-ion mass spectrometry (SIMS), and capacitance-voltage (C-V) and current-voltage (I-V) measurements. Resistivity of the structures determined from the measured I-V characteristics was found to be strongly dependent on the Zn doping concentration. The SIMS depth profiles showed Zn accumulation at the SI/p-InP interface and the peak concentration of the Zn accumulation increased with the doping level and overgrowth time of the p-InP layers. This accumulation of Zn at the SI/p-InP interface correlated with reduction in SI layer resistivity. Accumulation of Zn at the SI/p-InP interface may be minimized by short growth time with low or medium doping of p-InP layers. These growth conditions resulted in high SI layer resistivity. Possible mechanisms for the accumulation of Zn are discussed.
Flow conditioning for improved optical propagation of beams through regions bounded by surfaces of high solidity
Authors: Robey H. F. , Albrecht G. F. , Freitas B. L.
Published: July 2002

A flow conditioning system has been designed to maximize the thermal homogeneity in an enclosed region through which a laser beam must propagate. In the present application, such an enclosed region exists between the Nd:glass disks of a high average power solid-state laser amplifier. Experiments have been conducted on a test facility to quantify the magnitude of the beam losses due to thermal scattering. It is shown that the intensity of the incoherent light which is thermally scattered from this region can be reduced to less than 0.1% of the incident-beam intensity under apropriate flow and cooling conditions.
Improved bounds on elastic and transport properties of fiber-reinforced composites: Effect of polydispersivity in fiber radius
Authors: Miller C. A. , Torquato S.
Published: July 2002

Improved rigorous bounds on the effective elastic and transport properties of a transversely isotropic fiber-reinforced material composed of oriented, infinitely long, multisized circular cylinders distributed throughout a matrix are computed. Specifically, we evaluate such bounds on the effective axial shear modulus (which includes, by mathematical analogy, the transverse conductivity), effective transverse bulk modulus, and the effective transverse shear modulus. These are generally demonstrated to provide significant improvement over the Hill–Hashin bounds which incorporate only volume-fraction information. Although the upper bounds diverge from the lower bounds when the cylinders are much stiffer than the matrix, the improved lower bounds still yield relatively accurate estimates of the effective properties. Generally, increasing the degree of polydispersivity in cylinder size increases the effective transverse conductivity (or axial shear modulus) and effective transverse bulk modulus, and decreases (slightly) the effective transverse shear modulus for cases in which the fibers are more conducting or stiffer than the matrix.
Production of a large-diameter uniform plasma by electron cyclotron resonance heating with a small-diameter Lisitano coil
Authors: Komori A. , Takada Y. , Yonesu A. , Kawai Y.
Published: July 2002

A large-diameter uniform plasma is produced by electron cyclotron resonance heating with a slotted Lisitano coil of 9 cm in diameter by locating the resonance apart from the Lisitano coil. Although the plasma production with a Lisitano coil has been performed extensively by placing the resonance near the Lisitano coil, the influence of the resonance location has not received as much attention. When the resonance is located further than 8 cm from the Lisitano coil, the uniform plasma of ∼40 cm in diameter at densities of ∼1.2×1011 cm−3 is produced over the vacuum chamber with an inner radius of 46 cm. The microwave is propagated in the whole space between the resonance and the Lisitano coil, and spatial electric-field distributions of the microwave play an important role on forming the radially uniform plasma.
Diffusion of magnetic fields in a toroidal conducting shell of circular cross section
Authors: Dialetis D. , Len L. K. , Golden J. , Kapetanakos C. A.
Published: July 2002

The diffusion of an external magnetic field through a toroidal conducting shell is studied under the assumption of a small aspect ratio. The external magnetic field can have an arbitrary field index and magnetic flux on the minor axis of the torus. The diffused field, field index, magnetic flux, and wall current are computed analytically and compared with the numerical results from the TRIDIF code. The analytical and numerical results are in good agreement. Measurements in the toroidal chamber of the NRL modified betatron gave a delay time of 34 μsec, which is less than 10% from the theoretical prediction of 37 μsec.
Magnetic x-ray dichroism in core level photoemission from ferromagnets (abstract)
Authors: Baumgarten L. , Schneider C. M. , Ebert H. , Petersen H. , Schäfers F. , Kirschner J.
Published: July 2002

We report on the novel effect of magnetic dichroism in core level photoemission from ferromagnets with circularly polarized synchrotron radiation in the soft x-ray range. Depending on the relative orientation of photon spin and sample magnetization (parallel or antiparallel), a single core level emission line may be resolved into two lines of different intensities. The mechanism is shown to be due to spin-selective dipole transitions from exchange-split core levels in the presence of spin-orbit interaction. Experiments on the 2p1/2 and 2p3/2levels of Fe are compared to fully relativistic photoemission calculations. Rather good qualitative and quantitative agreement is found. The effect does not rely on the spin-split empty density of states near the Fermi energy, but probes the exchange splitting of core levels directly. Because of its surface sensitivity, x-ray dichroism in photoemission may serve as a new powerful tool in surface and interface magnetism.
Monte Carlo studies of magnetic critical phenomena using histogram techniques (invited)
Authors: Ferrenberg Alan M. , Landau D. P. , Peczak P.
Published: July 2002

Recent developments in the use of histograms (measured discrete probability distributions) now make it possible to determine critical properties with high accuracy using Monte Carlo (MC) simulations combined with finite-size scaling analyses. The advantages and limitations of the use of histograms for extracting the maximum information from MC simulation data are described. Results from extensive MC studies of the critical properties of two important magnetic systems, the d=3 ferromagnetic Ising and Heisenberg models, are presented. It is shown that the careful use of histogram techniques can provide results comparable or superior to these obtained with other numerical methods while maintaining all the advantages of standard MC techniques.