bluuebunny/crossref_metadata_2025 huggingface dataset:
A derivative method for interface state density determination at the silicon-silicon dioxide interface
Authors: Vitkavage S. C. , Irene E. A.
Published: July 2002

We report on an improved method of displaying the interface state density versus energy plots that is particularly useful for observing subtle changes in curve shape caused by the presence of states at a particular energy level. Essentially, the derivative of the density of interface states with respect to energy is plotted versus energy. An example which is presented using this technique is the monitoring of the effectiveness of cleaning and annealing treatments on Ar ion-beam-bombarded silicon. Subtle changes in the interface state distribution can be observed.
Extended four-photon mixing approach to modulational instability
Authors: Kitayama Ken-ichi , Okamoto Katsunari , Yoshinaga Hisao
Published: July 2002

Analysis of modulational instability in optical fibers based on a phase-matched four-photon mixing approach is extended by taking into account higher-order dispersion. Fourth-order dispersion governs the modulation frequency in a region near zero-dispersion wavelength, resulting in frequency saturation. The frequency decreases as group delay dispersion becomes dominant in comparison to the fourth-order dispersion. To deepen the modulation, a phase-matching condition for four-photon mixing must be satisfied. A technique is studied which uses externally controllable birefringence of optical fibers to achieve phase-matching at a given modulation frequency.
Light-induced degradation of hydrogenated amorphous silicon films deposited at different rf powers
Authors: Acharya P. K. , Malhotra L. K. , Chopra K. L.
Published: July 2002

Light-induced degradation has been investigated in glow-discharge deposited hydrogenated amorphous silicon (a-Si:H) films (≊1 μm), deposited at different rf powers by glow-discharge decomposition of pure silane. Changes in electrical, ellipsometric, and infrared parameters have been observed by exposing the films to white light of intensity 350 mW/cm2 for 4 h. The initial dangling bond density increases and the rate of change of the dangling bond density decreases in films successively deposited at higher powers up to 50 W. However, at still higher power (75 W), a reverse behavior has been observed. Spectroscopic ellipsometry shows maximum void fraction in films deposited at 50 W. Light soaking results in an increase in void fraction and hence, the dangling bond density. The unaltered position of ε2 max suggests that the tetrahedral coordination of the silicon network remains unchanged on light exposure. The IR transmittance difference curves indicate changes on light soaking in the stretching mode vibrations only in 50-W deposited film and in the rocking mode for all films except that deposited at 5 W. A greater change (maximum change for 50-W film) in the state of bonds has been observed for samples having a greater initial void fraction.
Equilibration of nonstoichiometric Ta-Si deposits on polycrystalline silicon at high temperatures
Authors: Baiocchi F. A. , Lifshitz N. , Sheng T. T. , Murarka S. P.
Published: July 2002

The formation of tantalum disilicide from either a metal- or silicon-rich amorphous film was studied to provide information on the kinetics of phase formation and the corresponding details of atom diffusion. A thin-film structure consisting of ∼3000 Å of cosputtered Ta-Si on ∼4000 Å of annealed polycrystalline silicon (which will be referred to as ‘‘silicon’’) on ∼1250 Å of silicon dioxide was deposited over monocrystalline Si(100) wafers. The deposition variables probed were (1) arsenic doped versus undoped silicon, (2) Si/Ta atom ratios of 3.2 and 1.3, and (3) capping silicon dioxide layers versus no capping present during the anneals. One hour anneals were performed in vacuum between 850 and 1000 °C at 50 °C intervals. Rutherford backscattering spectrometry and transmission electron microscopy measurements show that the metal-rich film consumes an appropriate amount of silicon to form the stable tantalum disilicide phase even at the lowest anneal temperature. On the other hand, the rate of formation of TaSi2 from the Si-rich film is affected by both the presence of capping oxide and dopant in the underlying silicon. The main mechanism for Si ejection in the uncapped specimens is evaporation from the surface. In the capped specimens, the main Si loss mechanism is growth of a Si layer between the silicon and tantalum disilicide. In this case, formation of TaSi2 and simultaneous growth of the Si layer is enhanced by the presence of arsenic dopant.
Low-temperature p-n junction space-charge-region thickness including the effects of doping-dependent dielectric permittivity
Authors: Liou J. J. , Lindholm F. A.
Published: July 2002

This paper studies the thickness of silicon p-n junction space-charge regions at low temperature including the effects of doping-dependent dielectric permittivity ε(N), which is important for heavily doped semiconductor materials because of the presence of unionized impurity atoms that are subjected to polarization. The treatment is applicable for p-n junctions under all voltages and is not based on the conventional depletion approximation which assumes free carriers are negligible in the space-charge region. Comparison of the present thickness model including ε(N) and the conventional depletion model is included.
Stable multifilament structures in semiconductor materials based on a kinetic model
Authors: Kardell K. , Radehaus Ch. , Dohmen R. , Purwins H.-G.
Published: July 2002

A new model for pattern formation in semiconductor materials is proposed based essentially on kinetic processes of charge carriers. This model leads to a set of coupled nonlinear reaction-diffusion equations with two components: the electron density in the conduction band and the occupation density of a trap level. The model possesses a variety of stable solutions including stable multifilament structures.
High midplane accessibility stellarator windings for high-current toroidal accelerators
Authors: Marsh S. J. , Golden J. , Kapetanakos C. A. , Anderson David
Published: July 2002

We have developed two strong focusing field configurations that provide high midplane accessibility and therefore are compatible with presently contemplated extraction schemes for high-current, toroidal accelerators. When these windings are attached to a modified betatron accelerator, the bandwidth of the device is slightly smaller than the bandwidth of a modified betatron with unsplit stellarator windings. However, the bandwidth of the two new configurations is more than sufficient even for modest (20–30 kA) winding currents.
Magneto-optic circulator for optical fiber transmission (abstract)
Authors: Yan Xuejin , Xiao Shangqing
Published: July 2002

We have developed a polarization-independent optical circulator for optical transmission systems whose overall dimensions are 25×18×18 mm. The configuration of the circulator is shown in Fig. 1. The insertion losses and the isolations of the circulator are about 2.0–2.2 and 20–21 dB, respectively, at 1.3 μm wavelength. The circulator has four ports. The nonreciprocal paths of the circulator are 1–3, 2–4, 3–2, and 4–1. The prisms of the polarization separator of the circulator were pestered with a kind of estersil. The refraction index of the estersil is 1.46 at 1.3 μm wavelength. The polarization separator separates the incident beam into two polarized beams with polarization planes perpendicular to each other. The distance of the two beams is 3.2 mm. A Faraday rotator consists of an yttrium-iron-garnet (YIG) crystal and Sm-Co permanent magnets. The size of the YIG block is 2.25 (mm) length×4.5(mm) width×1.5(mm) thickness. The two polarized beams are transmitted along the longitudinal direction of the YIG crystal block. The applied magnetic field of the YIG crystal is produced by Sm-Co permanent magnets. The half-wave plate of the circulator is made of a white mica.
Neutron diffraction study of the Néel transition in Cr(0.5% V)
Authors: Noakes D. R. , Holden T. M. , de Camargo P. C. , Fawcett E. , de V. DuPlessis P.
Published: July 2002

While pure chromium undergoes a first-order antiferromagnetic transition, thermal expansion measurements have indicated that the addition of small amounts of vanadium and molybdenum make the Néel transition continuous. A neutron diffraction study of a single crystal of Cr(0.5% V) showed no discontinuity in magnetic Bragg satellite intensity at the Néel temperature, TN=254 K, that would indicate a first-order transition. Complicated behavior of the satellite intensities near the transition temperature is attributed to inhomogeneous strain in the sample. The satellite intensity showed a linear temperature dependence over a range of at least 100 K below TN.
A miniature transformer/dc-dc converter for implantable medical devices
Authors: Mohammed Osama A. , Jones W. Kinzy
Published: July 2002

This paper presents a new technique for the design of a miniature dc-dc converter used in energy producing implantable devices such as defibrillators and advanced pacemakers. This converter is inserted in such a device and is used to boost the voltage from a low voltage implanted battery to high voltage energy storage capacitors in a short period of time. The stored energy is then delivered, when needed, through an energy delivery circuit in order to stimulate or defibrillate the heart. The converter takes the form of a flyback topology which includes a miniature transformer and a specialized control circuit. The transformer was designed using a new numerical synthesis method which utilizes finite elements and dynamic programming for predicting the geometries of the transformer’s magnetic circuit. The final transformer design satisfied the performance criteria and provided means for selecting the converter components. The obtained performance results for the transformer and the dc-dc converter were in excellent agreement with laboratory performance tests.
Superconductivity in Bi-Sr-Ca-Cu-O (invited)
Authors: McGuire T. R. , Shivashankar S. A. , La Placa S. J. , Chandrashekhar G. V. , Boehme R. F. , Shaw T. M. , Yee D. S. , Shafer M. W. , Cuomo J. J.
Published: July 2002

We report on the structure and superconducting properties of a single phase polycrystalline composition given by Bi2.2Sr1.7Ca1.2Cu2O8+δ as well as measurements on single crystals. X-ray and electron diffraction analyses of both single-crystal and single phase materials show an incommensurately modulated orthorhombic superlattice, derivable from a pseudotetragonal substructure. The various compositions have the common feature that the major portion of the superconductivity disappears above 85 K but there is a small tail in the diamagnetic susceptibility extending to 110 K, above which the sample becomes paramagnetic. Single crystals, grown by the flux method, exhibit the same incommensurately modulated pseudotetragonal structure as the ceramic, but show a higher diamagnetic shielding and in some cases also have tails. The critical currents in the (ab) plane are only about one-fifth of the value found for YBa2Cu3O7 crystals and the anisotropy is smaller. These reduced values may be an intrinsic property of the modulated superlattice but more likely are due to stacking faults and other defects in the crystals.
Direction dependence of microwave ferromagnetic resonance transmission along the surface of Fe-Si-B foils
Authors: Kakuno K.
Published: July 2002

Microwave transmission along the surface of metal-metalloid foils was examined with a ferromagnetic resonance transmission spectrometer, and a dependence on the static and microwave magnetic field directions was observed. The resonant transmission of microwave radiation depended strongly on the angle between the direction of the static magnetic field and that of the fine grooves running along the surface of the sample. The transmission intensity was a maximum when the static magnetic field was parallel to the grooves. It also depended on the relation between the directions of the static and the microwave magnetic fields.
Experimental-statistical method for synthesis of multicomponent narrow-resonance linewidth yttrium-iron-garnet
Authors: Kojuharoff V. , Nedkov I. , Andreev N.
Published: July 2002

The study of the combined influence of substituting ions in multicomponent systems of the type Y3−2xCa2xFe5−x−y−zIny AlzVkO12 is a comparatively difficult task requiring many experiments. Moreover, construction of composition-properties diagrams for such multifactor systems is practically impossible using conventional methods. We used computer processing of the data from a number of experiments in order to determine the overall influence of the substituting components on the microwave properties of such garnets. This enabled us to build mathematical models of the type: Yk=∑bixi+∑bij xixj+∑bijxix jxk. Based on the solution of the equation, triple diagrams were constructed corresponding to strictly defined microwave properties of the system. Thus, the conditions for synthesis are significantly eased and the range for possible microwave applications is increased.
The structural and the magnetic properties of the solid solutions GecFe3−cO4 (abstract)
Authors: Beach G. V. , Camishov V. M. , Men A. N. , Petrov Yu. A.
Published: July 2002

The physicochemical properties of the compound oxide solid solutions versus the composition and the presence of defects are to be described in terms of the cluster components method.1 The binary solid solution, containing the cation with three different charge magnitudes (+2; +3; +4) is considered as the simplest system. The changes of the crystalline lattice parameter (a) and the saturation magnetic moment (σ) of the spinel solution versus the concentration of Ge are studied. We also consider that the concentration dependencies a and σ on the Ge concentration should be interpreted with regard to the defect structure and the character of the redistribution of Fe2+ on the nonequivalent positions. The conducted analysis allows to assume that the obtained solutions are defect due to the volatility of Ge. In this case the part of Fe2+ occupies the tetrapositions. As the result, σ exceeds the magnitudes obtained according to the Néel model with the C concentrations between 0 and 0.5, if Fe3O4 and GeFe3O4 are the pure components. The research of the pycnometric density agrees with the data on the defect structure.
Dzyaloshinsky–Moriya interaction in the spin-glass system Cu95−xAuxMn5: Hall effect and ac susceptibility
Authors: Barnard R. D. , Al-Naimi R. F.
Published: July 2002

The effect of gradually changing the background matrix in which Mn ions are imbedded has been investigated in the spin-glass system Cu95−xAuxMn5 by means of low-field Hall effect and ac susceptibility measurements. For the Cu-rich alloys a substantial positive anomalous Hall coefficient is found arising from skew scattering of Dzyaloshinsky–Moriya origin which peaks in each case at the freezing temperature. The concentration x=∼50% appears to be critical in that (a) the anomalous Hall coefficient changes sign, (b) peff undergoes a change of 0.30, and (c) a fairly sudden change of the ordinary Hall coefficient occurs. These results suggest the Mn ions suddenly acquire additional orbital angular momentum at this composition.
Single-target magnetron sputter deposition of high-T
c superconducting Bi-Sr-Ca-Cu-O thin films
Authors: Dhere Neelkanth G. , Goral John P. , Mason Alice R. , Dhere Ramesh G. , Ono Ronald H.
Published: July 2002

Single-target RF magnetron sputtering was used to deposit superconducting thin films of Bi-Sr-Ca-Cu-O with a Tc0 above 80 K. Varying PO2 modified the concentrations of Bi, Cu, and O in the films by 10%–20%. Higher annealing temperatures, especially with brief melting, favored the formation of the higher Tc phases. Tetragonal phases (6- and 75-K Tc ), with a=3.8097 Å, c=24.607 Å, and Bi2 Sr2 CuO6 composition, and a=3.812 Å, c=30.66 Å, and Bi2 Sr2−x Ca1+x Cu2 O8 composition, were identified. 70–84 K films contained large proportions of a new tetragonal phase, with a=3.81 Å and c=55.23 Å.
A backside hydrogenation technique for defect passivation in silicon solar cells
Authors: Sopori B. L.
Published: July 2002

A novel technique is described for confinement of hydrogen in silicon solar cells during a high-temperature process. It is shown that hydrogen implanted at low energies on the backside of a solar cell can be confined within the cell through a metallization process consisting of deposition of aluminum and a subsequent alloying. The alloying of aluminum is done by a rapid optical processing technique. The passivation effects of hydrogen are identified in terms of improvements in the cell parameters of small area solar cells. It is shown that if the processing is done without the aluminum cap, the hydrogen is driven out of silicon with no passivation effects. This method can render hydrogen passivation compatible with standard solar cell process techniques.
A possible model: Photothermal excitation via an excited state in the Si:Pd level
Authors: Fu J. , Wang Z.-G. , Wan S. K. , Lin L. Y.
Published: July 2002

The electron photoionization cross-section spectra of the Si:Pd EA level at various temperatures are obtained for the first time. It is shown that the cross-section spectra around the threshold energy shift to lower energy when the temperature rises. Instead of the variation of the energy gap or the broadening effect of lattice relaxation, photothermal excitation via an excited state at 45 meV below the bottom of the conduction band causes this energy shift. The energy from the ground state to the excited state derived from both optical and thermal data is 370 meV.
Influence of substrate-induced misfit stresses on the miscibility gap in epitaxial layers: Application to III-V alloys
Authors: Larché F. C. , Johnson William C. , Chiang C. S. , Martin G.
Published: July 2002

We have examined the influence of the substrate on the stability with respect to decomposition of thin epitaxial layers. We show that the misfit stresses induced by the substrate can interact strongly with the coherency strains engendered by composition fluctuations. This interaction may lead to changes in the critical temperature of several hundred degrees as compared to predictions that consider the coherency strains alone. Results are applied to a III-V pseudobinary alloy that permit experimental confirmation.
An exact, closed-form expression of the integral chord-length distribution for the calculation of single-event upsets induced by cosmic rays
Authors: Luke Keung L. , Buehler Martin G.
Published: July 2002

In a previous paper [J. Appl. Phys. 50, 3799 (1979)] Bradford derived a distribution function for the chord lengths through a rectangular parallelepiped (a×b×c, a≤b≤c). This chord-length distribution describes the path-length distribution of cosmic-ray particles in an object exposed to the isotropic cosmic-ray flux outside the earth’s magnetosphere. It is an essential quantity needed for computing the rate of single-event upsets (SEUs) induced in space-borne random-access memory cells by cosmic rays. While Bradford’s distribution is exact for chord length x within the range 0<x≤b, it is only approximate for b<x≤w, where w=(a2+b2+c2)1/2. In this paper we present an exact distribution which is valid for all values of chord length (0<x≤w). The extent to which the two distributions differ is explored. It is found that the two distributions agree exactly for 0<x≤b, but are very different for b<x≤w, and that this difference can lead to serious errors when Bradford’s distribution is used for computing the SEU rate. We also present an integral for computing the SEU rate in which the actual shape of the SEU cross-section curve is explicitly taken into consideration. Our formulation is much easier to evaluate numerically than the one proposed recently by Shoga et al. [IEEE Trans. Nucl. Sci. NS-34, 1256 (1987)].
Equivalence of electrons and holes in a-Si p-s-n diodes
Authors: Kusian W. , Pfleiderer H. , Bullemer B.
Published: July 2002

Amorphous-silicon (a-Si:H) solar cells have the structure of short p-i-n diodes, with an electric field extending through the i layer. The photocurrent is voltage dependent. Primary and secondary photocurrents occur. We modify the diode structure by low-level doping of the i layer in order to obtain p-s-n diodes. The s layer has the type ν or π, i.e., is slightly n or p doped. The transition p-i-n→p-s-n deforms the associated spectral photocurrent-voltage characteristics. Certain asymmetries build up. A type transfer of π→ν inverts the symmetry pattern. The reversal of the illumination direction has almost the same effect. Electrons and holes therefore play equivalent roles in p-s-n diodes and p-i-n solar cells. An elementary photocarrier-collection model provides a basic understanding of all the observed phenomena.
The temperature dependence of polycrystalline Si bulk and surface conductivity
Authors: Alpern Y. , Shappir J.
Published: July 2002

The temperature dependence of polycrystalline Si conductivity is studied. The conductivity is analyzed in terms of activation energy Ea and a prefactor σ0. The correlation between Ea and σ0 is shown to be consistent with the assumption of a linear relation between the grain boundary potential barrier height and the temperature. Field effect is used to measure surface conductivity, which is shown to have similar properties.
Low-field electron transport at room temperature in Ga1−xAlxAs alloys
Authors: Choi Choon Tae , Lee Hyung Jae
Published: July 2002

Various electron scattering mechanisms were evaluated consistent with the material parameters in Ga1−xAlxAs alloys at room temperature. A three-conduction-band model is necessary only in the range of x=0.3–0.42. Except for a narrow x range in each band,the intraband scattering by polar optical phonons dominates in the whole interval. In this narrow range, the interband scattering is dominant, but does not affect significantly the overall variation of Hall mobility with composition. The Hall mobility and scattering factor together with the Fermi energy are provided for varied conditions for use in assessing the alloys in a routine way.
Large-scale quantum well domain structures
Authors: Khurgin Jacob
Published: July 2002

New structures, based on asymmetric quantum wells, large-scale quantum well domains (LSQWDs) are proposed. Different implementations of LSQWDs are evaluated. The importance of LSQWDs specific property of orderly reversal of second-order nonlinear optical susceptibility for applications in integrated optics is shown. Examples of LSQWD-based devices are given.
Time-dependent fracture strength of solid bodies
Authors: Ettouney Osama M. , Hsiao C. C.
Published: July 2002

Statistical theories in fracture kinetics constitute a very important role in investigating the fracture strength of solids and their utilization in modern engineering. In this paper, a review of some of the recent concepts and models is provided. The main concern is the effect of the breaking stress on the time-to-break. Based upon the consideration of the fraction of integrity of a medium, a number of models have been evaluated and compared. Two basic considerations used for evaluation and comparison are Zhurkov’s empirical kinetic relationship and Hsiao’s statistical absolute reaction rate model. Other considerations reducible from these two are also given for comparison. Using a well-known numerical analysis method, it appears that the nonlinear mathematical consideration is more realistic in describing the time-dependent fracture strength behavior of a medium over any linear ones. The computed results seem to fit reasonably well with the general observations.
Numerical study of the impedance mismatch effect in laser-irradiated layered targets
Authors: Kaushik T. C. , Godwal B. K.
Published: July 2002

The effect of impedance mismatch on shock-pressure enhancement in laser-irradiated layered targets has been investigated by numerical simulation of the entire time history of shock generation. The model is a simple, one-dimensional, single-temperature Lagrangian hydrodynamic code incorporating a simplified laser-absorption model and an equation of state suitable to describe the thermodynamic state of matter in a wide range of density and temperature. Effects of change in layer materials and other experimental parameters on the attainable shock pressure and compression have been studied. From an exhaustive study of such targets, it is found that it is possible to enhance the attainable values of compression (ρ/ρ0) and shock pressure with a given laser pulse by suitable optimization of the target. A pressure of more than 60 Mbar can be generated with a 1014 W/cm2, 300-ps rise-time laser pulse in such targets. In order to generalize the applicability of the results, within existing experimental uncertainties of measurements, and facilitate a suitable target design for any laser system, simple scaling laws are obtained in terms of parameters like intensity and rise time of the laser pulse.
Rotational slip in III-V heterostructures grown by molecular-beam epitaxy
Authors: Lind M. D. , Sullivan G. J. , Liu T. Y. , Kroemer H.
Published: July 2002

We report the observation of rotational slip as a mechanism for relieving strain in Ga1−xInxAs/GaAs and GaAs/Si heterostructures grown by molecular-beam epitaxy. Rotational slip causes a tilt of the epitaxial layer with respect to the substrate. With increasing layer thickness it is accompanied by misfit dislocations and crazing on the surface of the layer.
As4 to Ga flux ratio dependence of the optical and electrical properties of Ge-doped GaAs grown by molecular-beam epitaxy
Authors: Makita Yunosuke , Tanaka Hideki , Mori Masahiko , Ohnishi Nobukazu , Phelan Paul , Shigetomi Shigeru , Shibata Hajime , Matsumori Tokue
Published: July 2002

A drastic change of the conduction type from p to n with an increase of the As4 to Ga flux ratio, γ, was observed for the first time in the photoluminescence spectra of amphoteric impurity (Ge)-doped GaAs made by molecular-beam epitaxy. The sample with the lowest γ (γ=1.0) presented a purely p-type emission associated with pairs between the excited states of acceptors. The sample with the highest γ (γ=10.6) indicated a totally n-type emission reflecting an increase of quasi Fermi energy. Results show that by precisely controlling the flux ratio, γ, one can reliably make use of substantially amphoteric atoms of Ge both as p- and n-type impurities for the fabrication of GaAs by molecular-beam epitaxy.
The hole photoionization cross section of EL2 in GaAs1−xPx
Authors: Silverberg P. , Omling P. , Samuelson L.
Published: July 2002

The hole photoionization cross section σ0p of EL2 is determined at T=80 K for different x in GaAs1−xPx. From these data, the energy position of the EL2 level relative to the valence band is determined for different alloy compositions. The results are compared with the previously determined energy positions of the EL2 level relative to the conduction band and with the corresponding change in the direct band gap with alloy composition.
Effects of irradiation-induced lattice defects on the quantum Hall effect in GaAs-AlxGa1−xAs heterostructures
Authors: Adrian H. , Möhle W. , Bliek L. , Weimann G. , Schlapp W.
Published: July 2002

GaAs-AlxGa1−xAs heterostructures were irradiated with 6-MeV protons at low temperature to study systematically the influence of lattice disorder in two-dimensional electron systems on resistivity, mobility, carrier concentration n, and quantum Hall-effect structures. The additional irradiation-induced scattering centers lead to a linear decrease of n with the proton fluence and to a broadening of the quantum Hall plateaus, which is qualitatively explained in the framework of localization in magnetic fields.
Rotational viscosity in ferroelectric liquid crystals estimated from transient light scattering and dielectric properties
Authors: Ozaki M. , Hatai T. , Nakao K. , Yoshino K.
Published: July 2002

A new method for the estimation of rotational viscosity of ferroelectric liquid crystals using transient light scattering (TSM) is reported. The relation between rotational viscosity, spontaneous polarization, and dielectric dispersion frequency is studied as a function of the racemization. The rotational viscosity is almost independent of spontaneous polarization and there is no obvious correlation between rotational viscosity and dispersion frequency. The dispersion frequency is confirmed to be inversely proportional to the square of the helical pitch. The rotational viscosity calculated from this relation is consistent with that from the new TSM method.
Raman scattering evaluation of Pb2CrO5 thin film on a glass substrate
Authors: Yoshida Shinzo , Toda Kohji
Published: July 2002

Pb2CrO5 thin films on glass substrates deposited by an electron-beam evaporation technique are examined for the possibility of obtaining a highly crystallized film at various substrate and annealing temperatures. The crystal structure of the film is evaluated by Raman scattering and x-ray diffraction techniques.
Selective titanium disilicide by low-pressure chemical vapor deposition
Authors: Reynolds G. J. , Cooper III C. B. , Gaczi P. J.
Published: July 2002

TiSi2 was deposited onto both Si and SiO2 substrates by low-pressure chemical vapor deposition. By using both TiCl4 and SiH4 as source gases, the reaction could be controlled to yield either selective TiSi2 on Si substrates only, or blanket silicide films. Experimental conditions providing for selective deposition were investigated. Mass spectroscopy data and thermodynamic calculations were in good agreement with each other and provided rational explanations of observed phenomena. Reaction of TiCl4 vapor with Si yields TiSi2, but is accompanied by excessive Si consumption. This etching reaction may be moderated by increasing the reactor pressure while keeping the substrate temperature around 900 K, and by the introduction of H2 and/or SiH4 into the reactant gas mixture.
Determination of shallow minority-acceptor concentration in multiply doped silicon
Authors: Bambakidis G. , Brown G. J.
Published: July 2002

A method is presented, based on photothermal ionization spectroscopy (PTIS), for determining the shallow minority-acceptor concentration in multiply doped silicon, over the concentration range 1013/cm3–1015/cm3. The method is an extension of a model developed previously for the PTIS response in a multiply doped semiconductor, which accounts for the experimentally observed change in signature, from negative to positive, of the lower-energy lines of the deeper acceptor as the temperature is increased. It uses a calculated curve of the dependence on the shallow-acceptor concentration of the temperature at which the change in signature occurs, for a given line, and compares it to a determination of this temperature from actual spectra for the sample. The method is applied to the determination of boron concentration in the Si(Ga,B) system.
Electrical behavior of a static hole inversion layer at the i-AlAs/n-GaAs heterojunction
Authors: Qian Q.-D. , Melloch M. R. , Cooper J. A.
Published: July 2002

The photocapacitance-voltage and current-voltage characteristics of p+-GaAs/i-AlAs/n-GaAs heterojunction enhancement mode capacitors have been studied in the temperature range from 9.5 to 273 K. Under steady-state illumination, the emission mechanisms for a photopopulated hole inversion layer are found to be thermionic field emission at high temperatures and tunneling at low temperatures. Estimates are made of the minority-carrier recombination lifetime, valence-band discontinuity, and the tunneling effective mass for holes in the AlAs barrier layer. The decay of inversion hole concentration after terminating the photoinjection process is measured with a capacitance transient technique, which is sensitive to current levels below 1 pA. The dominant decay mechanisms at this current level are found to be injection to the substrate at low-inversion bias voltages and emission over the AlAs barrier via the Frenkel–Poole mechanism at high-inversion bias voltages.
Ablation of gallstones using excimer laser pulses
Authors: Mitchell N. F. , Novak R. , Lunney J. G.
Published: July 2002

Ablation of gallstones using a pulsed KrF excimer laser was studied in both air and water. Acoustic and optical signals were monitored as a function of incident laser fluence. The etch depth per pulse was found to be proportional to the logarithm of the laser fluence. A threshold for plasma generation was observed at a fluence of 0.5 J cm−2, beyond which the etch rate saturates and eventually decreases. Considerable etching was seen below this fluence. This process may have applications in a clinical setting.
Deep levels in p-type AlGaAs/GaAs heterostructures
Authors: Reemtsma J.-H. , Kugler S. , Heime K. , Schlapp W. , Weimann G.
Published: July 2002

p-AlGaAs/GaAs heterostructures were investigated by means of photoconductivity and low-frequency noise measurements. Both methods were performed with ungated structures using ohmic contacts prepared by alloying (sample I) or diffusion (sample II). Three hole traps (0.39, 0.53, and 0.57 eV) were detected by the photoconductivity measurements in both samples. Low-frequency noise measurements showed different results for both samples. In sample I one hole trap at 0.42 eV and in sample II one hole trap at 0.25 eV was found. Possible origins of the traps are discussed.
Vertical element redistribution in Ni78B11Si11 amorphous films deposited on Si as revealed by scanning Auger microprobe and cross-sectional transmission electron microscopy
Authors: Sobue S. , Okuyama F.
Published: July 2002

The vertical element redistribution in Ni78B11Si11 amorphous films deposited on Si wafers was surveyed by means of scanning Auger microprobe and cross-sectional transmission electron microscopy in order to obtain a better understanding of the crystallization process of amorphous alloys. The diffusion of Si and Ni atoms across the film-substrate interface commencing at ∼250 °C drove B atoms toward the surface, thereby dividing the film into Si- and B-rich regions. The crystallization started at ∼300 °C in the Si-rich region, and the crystallized zone grew with increasing temperature, until the B-rich outer region was transformed into a polycrystalline state at ∼350 °C. These findings indicated that the crystallization temperature was a strong function of compositional structure, thus allowing us to conclude that a local compositional variation is generally a precondition for the nucleation of the crystalline phase in the amorphous matrix.
Ferromagnetic resonance measurements on epitaxial grown Fe/ZnSe and Co/ZnSe films on GaAs substrates
Authors: Oliver S. A. , Vittoria C. , Krebs J. J. , Jonker B. T. , Prinz G. A.
Published: July 2002

Ferromagnetic resonance (FMR) measurements have been performed over a broad frequency range on epitaxial films of Co and bcc α-Fe grown onto epilayers of ZnSe by molecular-beam-epitaxy techniques on (001) and (110) GaAs substrates. In-plane and perpendicular FMR results were used in deducing the magnetic parameters and spin-wave resonance (SWR) dispersion of the films. The magnetic parameters deduced for Fe films agree with previous results obtained on the (001) Fe/ZnSe film. Well-resolved SWR modes were observed in the Fe/ZnSe films, allowing extraction of the exchange stiffness constant. Few spin-wave excitations were observed for the Co/ZnSe films. Both (110) Fe/ZnSe and (110) Co/ZnSe show evidence for surface spin-wave excitations. These excitations are attributed to variations in the internal field near the interface.
Passivation of HgCdTe with CdS thin films: Correlation of device characteristics with surface spectroscopy
Authors: Ziegler John P. , Lindquist John M. , Hemminger John C.
Published: July 2002

We present results on the passivation of HgCdTe with thin films of CdS grown anodically from nonaqueous polysulfide electrolytes. Electrochemical measurements have been carried out to develop an understanding of the film growth. Capacitance-voltage measurements on metal-insulator-semiconductor (MIS) device structures that incorporated a ZnS cap and Pd gate metal over the CdS are used to compare electrical properties of the interface with Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) depth profiles. The surface spectroscopies were carried out using a sample temperature of 170 K, which allowed us to easily observe Hg by Auger electron spectroscopy. XPS and AES results show that Hg and Te are partially incorporated into the CdS layer, as sulfides that did not completely dissolve during the film growth. The interdiffusion of Zn into the interface resulted in large hysteresis in the C-V data. By minimizing the Zn interdiffusion, MIS devices with low hysteresis (∼0.25 V) that are bake stable to ∼95 °C have been fabricated and analyzed.
Raman scattering as a contactless room-temperature test of the quality of YBa2Cu3O7−x thin films
Authors: Farrow L. A. , Chan Siu-Wai , Greene L. H. , Feldmann W. L.
Published: July 2002

The room-temperature Raman spectrum of YBa2Cu3O7−x is sensitive both to stoichiometry and to the transition from the semiconducting to the superconducting state as a function of oxygen annealing. In particular, it is shown that a good quality film with a Tc of ∼90 K and a sharp resistivity transition has not been produced if the frequency of the O(1) stretch along the c axis shifts from 500 cm−1 to lower frequencies. In this paper, two types of processing failures are illustrated: (1) lack of sufficient oxygen and (2) incorrect stoichiometry. No attempt has been made to predict Tc from the Raman data for less than optimum films.
Anomalous capacitance in selenium Schottky diodes
Authors: Champness C. H. , Pan J.
Published: July 2002

In measurements of capacitance as a function of bias on selenium-metal diodes, an anomalous minimum has been observed at frequencies below about 1 kHz. As the frequency is increased, the minimum disappears. For Se-Bi, Se-Au, Se-Tl, and Se-Mg diodes, prepared by evaporation of the metal on a layer of crystallized selenium, the voltage at which the minimum occurs shifts systematically with the magnitude of the barrier height, as determined from capacitance at reverse-bias and current-voltage characteristics. However, no singularities have been observed in parallel incremental resistance at these particular voltages. A simple equivalent circuit model is proposed, which phenomenologically accounts essentially for the observed facts.
Light scattering by air heated from an aerosol due to pulsed irradiation
Authors: Sutton George W. , Wong Kai
Published: July 2002

The problem of the scattering by air which has been locally heated by aerosols irradiated by a short pulse, for example, by a pulsed laser, is addressed through the use of the heat conduction equation and scattering theory. The resulting air scattering cross section increases as with the square of the absorbed fluence. After a pulse, it increases to a maximum and then decays as the inverse of time. For absorbed fluences greater than 2 J/cm2, the air scattering cross section can exceed that of the aerosol itself. For multiple irradiation pulses, the air scattering cross section reaches a maximum asymptotic limit. For an aerosol cloud, the air scattering cross section decays exponentially after the thermal wave from an aerosol reaches one-third of the interparticle spacing.
Influence of the preepitaxial annealing and polycrystalline silicon deposition processes on oxygen precipitation and internal gettering in N/N+(100) epitaxial silicon wafers
Authors: Wijaranakula W. , Matlock J. H.
Published: July 2002

Standard substrate wafers and substrate wafers having a thin polycrystalline silicon layer deposited on the backside were heavily doped with antimony at the concentration of 4×1018 atoms/cm3, and then annealed at temperatures ranging between 500 and 950 °C prior to epitaxial deposition. As-deposited wafers were annealed at 1050 °C in dry oxygen ambient for 16 h. Enhanced precipitation of oxygen in epitaxial wafers having polysilicon backside substrate was observed when preannealing was performed in the temperature range above 750 °C. This was found to be directly related to the thermal process used in polysilicon deposition. An improvement in minority-carrier generation lifetime was noticed in the preannealed epitaxial wafers. In comparison to standard epitaxial wafers, little or no improvement in the gettering effectiveness in epitaxial wafers having polysilicon backside substrate was observed. The reason can be due to the formation of microtwins, and recrystallization of the polycrystalline silicon grains occurred during epitaxial deposition. This can lead to stress relaxation in the polysilicon backside layer and degradation of gettering effectiveness.
Neuromagnetic localization performed by using planar gradiometer configurations
Authors: Bruno A. C. , Romani G. L.
Published: July 2002

The spatial discrimination of planar and axial gradiometers is compared by using a spatial filtering model. By measuring somatosensory evoked fields, equivalent current dipoles were localized with the use of planar gradiometer outputs. The planar configurations were obtained by combining, in a proper way, the outputs of a four-channel biomagnetic system. It was observed that with a proper signal-to-noise ratio, the use of the planar configurations did not significantly affect the localization precision.
SiGe/Si superlattices on implanted buried-oxide structures
Authors: Kamins T. I. , Wang K. L. , Park Jin , Davis G. E.
Published: July 2002

In an attempt to reduce the number of threading dislocations propagating through a silicon epitaxial layer grown on an implanted buried-oxide structure, a SiGe/Si superlattice was placed between the initial silicon surface layer and the subsequently grown silicon epitaxial layer. Both the superlattice and the silicon epitaxial layer were formed by molecular-beam epitaxy. Some of the threading dislocations are bent parallel to the superlattice as they propagate through the structure. Some of these are annihilated by interacting with other dislocations while others bend toward the surface again after propagating parallel to the superlattice for some distance. The effect of the superlattice is limited, and many of the dislocations continue propagating through the superlattice toward the surface of the silicon epitaxial layer.
A comparison between calculation procedures for photoelectrical method of determination of charge distribution in metal-oxide-semiconductor dielectric layers
Authors: Balasiński A. , Duszak M. , Iniewski K.
Published: July 2002

Photoelectrical methods are widely used to determine charge distribution in the oxide layer of metal-oxide-semiconductor structures. Implementation of techniques proposed so far requires complicated numerical calculations. In this work, a new, simple analytical method of charge distribution extraction from experimental photoelectrical current-voltage curves is presented. The method is based on the relationships derived from the other photoelectrical techniques and, therefore, is consistent with them. An example confirming the validity of the proposed method is also shown.
Strong traps for deuterium in krypton-implanted nickel
Authors: Frank R. C. , Pearce J. L. , Watson E. T. , Rehn L. E. , Baldo P.
Published: July 2002

Experiments were carried out to investigate strong traps (binding enthalpies>0.50 eV) for deuterium that were found earlier when pure nickel was implanted with argon and krypton at temperatures ≤500 °C. In one experiment, three different areas of a nickel specimen were implanted with a fluence of 2×1016 cm−2 krypton at 600, 700, and 800 °C; a second experiment involved implanting krypton at three different fluences (2, 6, and 20×1015 cm−2) in nickel at 500 °C. Retained deuterium was monitored during subsequent isochronal anneals using nuclear reaction analysis. In a third experiment, depth profiles for both implanted krypton and trapped deuterium were determined simultaneously using secondary ion mass spectrometry. Traps for deuterium in krypton-implanted nickel were found with binding enthalpies ranging from 0.5 to 1.1 eV. At implantation temperatures <500 °C, the traps are in the same location as the krypton atoms. At implantation temperatures >700 °C, the traps are found where the krypton was originally implanted in spite of the fact that a significant fraction of the krypton apparently escapes through the surface during the implantation process. The observed fluence and temperature dependence indicate that the traps with binding enthalpies between 0.5 and 1.1 eV are associated with the surfaces of cavities formed during the implantation.
Thermal analysis of the Bi-Sr-Ca-Cu-O system by an electrical property
Authors: Park Jin Seong , Kim Ho Gi
Published: July 2002

The formation of the high-temperature superconducting phase in the Bi-Sr-Ca-Cu-O system has been investigated by measuring the electrical properties with temperature in an oxygen atmosphere. A few intermediate phases are measured with increasing temperature. CaCO3 and Sr(NO3)2 are decomposed below 600 °C. The weight loss continues with increasing temperature even after the decomposition of CaCO3 and Sr(NO3)2. The high-temperature superconducting phase comes into being above 830 °C in the case of the initial composition of Bi4Sr3Ca3Cu4Ox. The stability region of the superconducting phase is between 890–895 and 855–895 °C in the mixed Bi4Sr4Ca2Cu4Ox composition and Bi4Sr3Ca3Cu4Ox, respectively.
Effect of room-temperature stress on the critical current of NbTi
Authors: Bray S. L. , Ekin J. W.
Published: July 2002

The effect of axial tensile stress, applied at room temperature, on the critical current of NbTi superconducting wire was measured and compared with the effect of tensile stress applied at liquid-helium temperature (∼4 K). The results of these measurements indicate that the effect on the critical current is independent of the temperature at which the stress is applied. Thus, the existing 4-K data base can be used to determine Ic degradation from room-temperature fabrication stress, cool-down stress introduced by differential contraction, as well as 4-K stress generated by the Lorentz force when the magnetic is energized. To generalize these results for arbitrary matrix-to-superconductor volume ratios, the data are presented in terms of the stress on the NbTi portion of the composite conductor. Methods for determining the stress on the NbTi from the total composite load are presented.
Low-frequency noise of planar dc SQUIDs made of various Josephson junctions
Authors: Matsuda M. , Matachi A. , Kuriki S. , Hasegawa H.
Published: July 2002

The noise characteristics at low frequencies are studied for various planar dc SQUIDs made of junctions with different barrier materials of a-Si, aluminum oxide, and niobium oxide. It is found that fluctuations of the parameters of individual junctions contribute to the flux noise of the SQUIDs in a magnitude of the same order with the apparent flux noise. The magnitude of the flux noise due to the parameter fluctuations depends on the barrier material and on the inductance parameter βL . We have observed a telegraph noise in the voltage time trace and a Lorentzian in the voltage power spectrum for a current-biased SQUID. As a source of the parameter fluctuations, capture and emission of electrons at the trapping sites in the barrier are indicated.
Absorption cross sections in the far-IR spectrum of elemental shallow donors and acceptors in germanium
Authors: Rotsaert E. , Clauws P. , Vennik J. , Van Goethem L.
Published: July 2002

The integrated absorption cross section of the main lines in the far-IR spectrum of the group-V donors Sb, P, and As and the group-III acceptors B, Al, Ga, and In in germanium has been determined for impurity densities in the range of 1012–1014 atoms/cm3. The cross sections and consequently the experimental oscillator strengths for transitions from the ground state, decrease gradually with increasing ground-state energy. In compensated samples the electric field due to the ionized impurities strongly affects the relative line strengths; neutralizing by band-gap illumination allows one to minimize the effect of the electric field and to observe simultaneously the majority and minority impurities, allowing one to calculate the compensation.