bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport properties of photoelectrons in Bi12SiO2
Authors: Grousson R. , Henry M. , Mallick S.
Published: February 2003

An optical method for studying the transport properties of photogenerated electrons in the photoconducting electro-optic crystal of Bi12SiO20 is described. The physical model in which the free electrons are assumed to hop from the donor sites to the trapping sites and thus create a space-charge field has been developed. The crystal is mounted in a transverse configuration with the light beam propagating along the [11̄0] axis and the electric field applied along the [110] axis. By measuring the photoinduced birefrigence variations, we determine the quantum efficiency φ of generating a free electron by an absorbed photon, the range μτ of a photoelectron, and the dark conductivity of the material. φ varies from 1.00 to 0.03 when the incident wavelength changes from 400 to 700 nm. The range μτ is found to be 5.2×10−6 cm2/V and the dark conductivity 2×10−15 (Ω cm)−1.
Measurement of the optical constants of Al above the melting point at λ=10.6 μm
Authors: Dreehsen H. G. , Hartwich C. , Schaefer J. H. , Uhlenbusch J.
Published: February 2003

The index of refraction, the extinction coefficient, and the absorptance of pure aluminum of technical quality were experimentally determined as a function of temperature for the CO2-laser wavelength. For the measurements, an ellipsometric setup was used. The absorptance jumps from 5% to 38% discontinuously at the melting point, where this result is weakly dependent on the laser power.
Effect of stress on the polarization of stimulated emission from injection lasers
Authors: Dutta N. K. , Craft D. C.
Published: February 2003

The role of stress on the polarization of stimulated emission is discussed in this paper. The stimulated emission from injection lasers is usually polarized in the TE mode. However, in the presence of a sufficiently high stress in the active region, TM polarized stimulated emission at threshold can be observed. We find that for some InGaAsP buried heterostructure lasers with a kink in the light-current characteristic, the kink represents the onset of a TM polarized stimulated emission. X-ray diffraction measurements show that the active region of these devices are under stress. We show that the change in polarization characteristics associated with the light-current kinks can be due to (i) higher optical gain of the TM emission than TE in the presence of stress and (ii) larger reflectivity of the higher-order TM modes. This mechanism is supported by the observation of higher-order TM modes than TE and the observation that the TM gain is unsaturated above TE threshold. We also find that the TM kinks occur at lower currents as the external pressure is increased. In the absence of stress in the active region, stimulated emission in higher-order TE modes associated with light-current kinks is observed in buried heterostructure lasers with large active region. Our results show that the observation of stimulated TM emission in real index guided laser structures is indicative of internal stress in the active region of these devices.
Damaged and reconstructed regions in silicon after heavy arsenic implantation
Authors: Cerofolini G. F. , Meda L. , Queirolo G. , Armigliato A. , Solmi S. , Nava F. , Ottaviani G.
Published: February 2003

High-dose, high-current arsenic implantation in silicon produces a partial recrystallization during the implantation process. The phenomenon presents the disadvantage that the recrystallized region is highly defective and remains nearly unchanged during subsequent low temperature thermal treatments. Instead, in implantation conditions leading to an amorphous layer, similar treatments should give rise to a solid-phase epitaxial regrowth. In this work the nature of the damaged region is investigated by electrical, analytical and structural techniques.
Temperature dependence of boron infrared-absorption line intensity in extrinsic silicon
Authors: Fischer David W.
Published: February 2003

The temperature dependence of the integrated peak areas for lines 1, 2, and 4 of the boron P3/2 IR-absorption spectrum in silicon is shown to reflect the variation in the concentration of neutral boron centers in accordance with published models. At about 15 K the peak intensity begins to drop rapidly, coinciding with the onset of thermal activation of the boron level. Above 30 K the peak intensities are partly influenced by the thermal activation of deeper acceptor centers.
The evaluation of the crystallinity of laser annealed polycrystalline silicon-on-silicon structures by Raman-microprobe polarization measurements
Authors: Nakashima S. , Inoue Y. , Mitsuishi A.
Published: February 2003

Raman-microprobe polarization measurements have been performed on amorphized and cw-laser-annealed polycrystalline silicon films which are directly deposited on crystalline silicon substrates. Distribution of local Raman intensity has been measured across the laser-annealed stripes. In order to characterize the perfection in the crystallographic orientation of the recrystallized zone, we have introduced a quantity which is related to the depolarization factor. The analysis with this quantity has enabled us to determine the extent to which the crystal orientations of grains in the annealed zone are aligned along those of the underlying substrate and to estimate the regrowth mechanisms involved in the laser-annealing conditions.
Si-doped GaAs epitaxial layers grown by metalorganic chemical vapor deposition
Authors: Okamoto K. , Onozawa S. , Imai T.
Published: February 2003

Silane is used as a doping gas for epitaxial growth of GaAs by metalorganic chemical vapor deposition (MOCVD). The electron concentration mainly depends on the silane flux, but the doping efficiency is affected by the partial pressure of arsine. The Si-doped epitaxial layers show a broadband spectrum of photoluminescence at 915 nm in addition to band-edge spectrum, which originates from self-activated complex of (V)Ga–SiGa. It appears from the dependence of 915-nm spectrum on the arsine molar fraction that Ga vacancies increase with the increase of the partial pressure of arsine in the epitaxial growth of GaAs by MOCVD.
Effect of Se vapor pressure and thermal dissociation process on excitonic-emission lines in molecular beam epitaxially grown high-purity zinc selenide
Authors: Taguchi Tsunemasa , Yao Takafumi
Published: February 2003

It has been found that two dominant bound-exciton (BE) emission lines at 2.7954 and 2.7815 eV in the not-deliberately-doped ZnSe single crystal layers grown by molecular beam epitaxy, can be strongly affected by heat treatment in controlled Se vapor pressure. The emission intensity of the 2.7954-eV line was shown to decrease remarkably with increasing Se vapor pressure and from its temperature dependence the line is ascribed to the recombination of excitons bound to a neutral donor whose ionization energy is about 36 meV. On the other hand, the 2.7815-eV line, which is due to the recombination of a neutral acceptor BE, became more intense and sharp with increasing Se vapor pressure. The characteristics of the principal BE lines variable with Se vapor pressure are discussed.
Limitations to the application of the electron-beam-induced current in hydrogen-passivated silicon grain boundaries
Authors: Yacobi B. G. , Matson R. J. , Herrington C. R. , Tsuo Y. S.
Published: February 2003

The electron-beam-induced current (EBIC) mode of a scanning electron microscope is used to investigate the effect of hydrogen passivation on silicon grain boundaries. A reduction in the grain boundary surface recombination velocity is observed by EBIC linescans after passivation. The EBIC signal decays with repeated linescans across hydrogen-passivated grain boundaries. This is probably associated with the electron-beam-induced breaking of passivated bonds in the grain boundary. Subsequent annealing at about 200 °C restores the hydrogen passivation effect on grain boundaries.
C-V hysteresis in metal-oxide-semiconductor structures resulting from Pt doping of the gate oxide
Authors: Golja Bogdan , Nassibian Armenag G.
Published: February 2003

Experimental results of hysteresis on platinum-diffused 〈111〉 and 〈100〉 metal-oxide-semiconductor (MOS) capacitors are presented. The platinum diffusions were performed through the front surface with no oxide present and on wafers with 50 and 100 Å oxides already grown. The diffusion conditions were also varied, some being carried out in a nitrogen ambient and others in an oxygen ambient. The temperature and time were fixed at 1000 °C and 60 min, respectively. The findings confirm the hysteresis effects of platinum in the oxide-silicon system and suggest that its introduction may be controlled by the presence of an oxide, in much the same way that B or P diffusions are controlled. This being the case, the charge retention properties of platinum-diffused MOS structures may be exploited by present day integrated circuit fabrication procedures.
Direct evidence for a charge-controlled dipolar structure of the EL2 complex center in semi-insulating GaAs
Authors: Fillard J. P. , Bonnafe J. , Castagne M.
Published: February 2003

EL2 center is a key defect controlling the electrical and optical properties of semi-insulating GaAs. Controversial hypotheses were proposed to establish its quantum scheme and to relate it to possible chemical or structural origins. Very recently a model was proposed that included a shallow donor impurity and a lattice defect; these two charged centers are associated in a dipolar structure corresponding to two different possible configurations depending on the charge state of the dipole. This should explain unexpected phenomena such as the persistent photocapacitance, photoconductivity, and photoluminescence quenching. Here we bring some direct experimental evidence supporting and completing the proposed theoretical model. The two distinct energy-level schemes related to the two different configurations are selectively revealed in electrical thermally-stimulated conductivity experiments and this conclusively confirms the model.
Addendum to ‘‘New optical recording material for video disc system’’ [J. Appl. Phys. 54, 1256 (1983)]
Authors: Watanabe Kenjirou , Nakane Yasuaki , Yanada Tetsunosuke , Miyaoka Senri
Published: February 2003

Previous work has established that the optical characteristics of Sb2Se3 films are influenced by an amorphous-crystalline transition at 170 °C. This paper comments on the change in optical characteristics in an optical recording material composed of Sb2Se3 and Bi2Te3 layers caused by alloying between the layers above 250 °C.
Slow fracture model based on strained silicate structures
Authors: Michalske T. A. , Bunker B. C.
Published: February 2003

Slow crack growth data, molecular-orbital calculations, and vibrational spectroscopy results are used to develop an atomistic model for environmentally controlled fracture of silica glass. The model is based on chemically active bond defects generated by the strain field of the crack tip. Molecular-orbital results suggest that bond angle deformations are most effective in increasing the chemical activity of the Si–O–Si bond. Vibrational spectra identify silica polymorphs containing highly strained bonding configurations. A comparison of strained bond reactivity with crack growth results shows that strained silica polymorphs can be used to model the crack tip chemical reactions controlling slow fracture. Based on model complexes, a two-dimensional fracture model involving kink site nucleation and motion is developed. The model shows that the stress intensity dependence of the crack growth rate is controlled by the energy required to form chemically active defects in the silica structure. The absolute rate of fracture depends on the combined rates of active bond formation and chemical attack at strain induced defects. Crack growth data suggest that for silica, strain activation occurs prior to the adsorption of environmental chemicals.
Ge diffusion at Ge/GaAs heterojunctions
Authors: Sarma K. , Dalby R. , Rose K. , Aina O. , Katz W. , Lewis N.
Published: February 2003

Interdiffusions at Ge/GaAs heterojunctions formed by the epitaxial deposition of Ge films on GaAs have been studied for temperatures ranging from 650–800 °C. The diffusion coefficients of Ge in GaAs have been found to be 1.6×10−5 exp(−2.06/kT) for Cr: and Si:doped GaAs. After the diffusion heat treatment, Ge was found to be p type and ohmic.
Carrier transport at grain boundaries in semiconductors
Authors: Mataré H. F.
Published: February 2003

This review describes the characteristics of dislocations in dislocation arrays and grain boundaries as they appear in imperfect and polycrystalline semiconductors. To further the understanding of the electronic features of these structures, metallurgical and crystallographic aspects of grain boundaries are reviewed. Grain-boundary diffusion is discussed as part of the metallurgy of bicrystal interfaces. Carrier transport at grain boundaries is described as it has been developed from the studies on germanium and III-V-compound bicrystals. Important features are lateral blocking layers, longitudinal or sheet conduction, space-charge extension with lateral bias, recombination and photovoltaic effects. Attention is focused on the activity to understand grain-boundary effects in silicon and their influence on electronic materials properties, a research area of particular importance during recent years. The application of silicon polycrystals in solar cells and in microcircuitry in the form of polycrystalline thin films has enhanced the understanding of dislocations and grain boundaries as they are considered here. Propositions for future research conclude this review.
Measurement of adherence of residually stressed thin films by indentation. I. Mechanics of interface delamination
Authors: Marshall D. B. , Evans A. G.
Published: February 2003

A fracture analysis of indentation-induced delamination of thin films is presented. The analysis is based on a model system in which the section of film above the delaminating crack is treated as a rigidly clamped disc, and the crack extension force is derived from changes in strain energy of the system as the crack extends. Residual deposition stresses influence the cracking response by inducing buckling of the film above the crack and by providing an additional crack driving force once buckling occurs. A relation for the equilibrium crack length is derived in terms of the indenter load and geometry, the film thickness and mechanical properties, the residual stress level, and the fracture toughness of the interface. The analysis provides a basis for using controlled indentation cracking as a quantitative measure of interface toughness and for evaluating contact-induced damage in thin films.
Role of surface adsorption in the surface-induced alignment of nematic liquid crystals on evaporated SiO films
Authors: Yokoyama H. , Kobayashi S. , Kamei H.
Published: February 2003

It is shown that a layer of liquid crystal molecules adsorbed on an evaporated SiO film plays an important role in aligning the bulk of the liquid crystal, apart from the topographical structure of the SiO film. On an SiO film evaporated from the substrate normal, various textural patterns were observed depending on how the liquid crystal was introduced onto the film. These patterns were invariably stable against the nematic-isotropic phase transition, indicating the presence of a firmly adsorbed layer of liquid crystal molecules. In particular, when the liquid crystal was injected into the cell with a unidirectional flow in the nematic phase, a stable quasi-homogeneous alignment could be obtained. For this sample, the structure of the SiO film-liquid crystal interface was studied in detail to compare its aligning mechanism with that of an obliquely evaporated SiO film, by measuring the wall-induced pretransitional birefringence and the contact angle of the isotropic liquid resting on the substrate in equilibrium with the nematic phase. The results of these measurements are in close agreement with the previous observations for an SiO film evaporated at 60° from the substrate normal, implying that the molecular processes occurring on both types of SiO films are not so much different, and concomitantly the presence of such an adsorbed layer even on the 60° evaporated SiO film. The effect of the adsorbed layer on the liquid crystal alignment on an obliquely evaporated SiO film is discussed with a particular emphasis on the temperature variation of the tilt angle. Finally, it is qualitatively argued on the basis of the present measurements that the molecules in the adsorbed layer are oriented with a considerable randomness on the molecular level rather than well aligned.
Proton nuclear magnetic resonance study on hydrogen incorporation in amorphous-microcrystalline mixed-phase hydrogenated silicon
Authors: Hayashi Shigenobu , Hayamizu Kikuko , Yamasaki Satoshi , Matsuda Akihisa , Tanaka Kazunobu
Published: February 2003

The behavior of hydrogen in the amorphous-microcrystalline mixed-phase hydrogenated silicon (μc-Si:H) deposited by glow-discharge (GD) decomposition of SiH4 has been characterized by 1H NMR. The 1H spectra consist of two components with different linewidths. The full width at half maximum (FWHM) of the narrow component is about 0.5 kHz at a resonance frequency of 90 MHz, which is much narrower than that has been observed in GD hydrogenated amorphous silicon (a-Si:H) deposited under a conventional low rf power condition. It has been demonstrated that the 0.5-kHz FWHM component originates from the hydrogens in motional narrowing state, and such fast-moving hydrogens are incorporated both in μc-Si:H and high-power deposited a-Si:H. It has also been indicated through annealing study in vacuo that the moving hydrogen has different natures between μc-Si:H and high-power deposited a-Si:H.
Diffusion of ion-implanted As in SiO2
Authors: van Ommen A. H.
Published: February 2003

We investigated the diffusion of ion-implanted As in SiO2 with Rutherford backscattering spectrometry. By applying different annealing ambients and also encapsulating with a Si3N4 layer, we were able to distinguish three types of diffusion for implanted As in SiO2. These are correlated to two chemical states of As in SiO2. One state, with As completely immobile in SiO2, is typical for implanted As and occurs when no extra oxygen is supplied during annealing. This type of As is associated with As on oxygen sites in the SiO2 network. When extra oxygen is supplied during annealing, As is incorporated on Si sites and exhibits the normal diffusion coefficient of As in SiO2. Diffusion occurs by a mobile arsenic-oxygen complex formed by a reaction with the extra oxygen. When annealing is carried out in an O2/H2O mixture, enhanced diffusion of As is observed; this is attributed to the introduction of hydroxyl groups in the SiO2 network which tend to weaken the structure. When, in addition to the As, P is also implanted, As becomes immobile in all annealing ambients.
Low-temperature redistribution of As in Si during Ni silicide formation
Authors: Ohdomari I. , Akiyama M. , Maeda T. , Hori M. , Takebayashi C. , Ogura A. , Chikyo T. , Kimura I. , Yoneda K. , Tu K. N.
Published: February 2003

We have investigated the redistribution of implanted As during Ni2Si formation at 275 and 300 °C and NiSi formation at 400 to 700 °C with neutron activation analysis and Hall effect measurement. Some of the implanted As atoms were found to redistribute themselves near the silicide-Si interface during both Ni2Si and NiSi formation. The depth of the redistribution extends about 100 Å into Si and is affected slightly by the formation temperature of NiSi. A fraction of the redistributed As is electrically active and the fraction increases with the annealing temperature. The maximum electrical activity of redistributed As during NiSi formation at 700 °C is estimated to be 6.5%.
Solid phase growth of disk-shaped PtSi clusters on lightly nitridized Si substrates
Authors: Joubert P. , Henry L. , Riviere D.
Published: February 2003

An interfacial silicon nitride layer was produced by sputter etching of the silicon substrate with pure nitrogen before platinum deposition. The thickness of the layer thus obtained ranges from 30 to 60 Å. It varies linearly with the energy of the incident nitrogen ions. Platinum deposited upon these thin nitride layers and annealed at temperatures higher than 500 °C reacts locally with silicon to form disk-shaped PtSi clusters. The cluster radii always increase linearly with annealing time. The growth rate depends neither upon the substrate orientation and its doping level, nor upon the thickness of the platinum film. It is inversely proportional to the thickness of the nitride layer and varies with temperature with an activation energy of 1.9 eV. Such a growth could be explained by the diffusion of platinum through the nitride layer in the locally stressed region of the growth front.
X-ray diffraction study and electrical characterization of boron-implanted low-pressure chemical vapor deposited polycrystalline silicon layers
Authors: Hendriks M. , Delhez R. , de Keijser Th. H. , Radelaar S. , Habraken F. H. P. M. , Kuiper A. E. T. , Boudewijn P. R.
Published: February 2003

The distribution of dopant atoms and the structure and the electrical properties of low-pressure chemical vapor deposited (LPCVD) polycrystalline silicon layers were studied as a function of layer thickness (0.35–2.0 μm), annealing temperature (800–1100 °C), and boron implantation dose (1015–1016 cm−2). The distribution of boron atoms was determined by secondary ion mass spectrometry. By means of x-ray diffraction, information about (i) preferred orientation of crystallites, (ii) crystallite size and short-range strain form the peak broadening, and (iii) lattice parameter from the peak position was obtained. The lateral grain size was determined by transmission electron microscopy. For electrical characterization Hall-effect measurements and resistivity measurements were performed. The redistribution of implanted boron in LPCVD polycrystalline silicon proceeds faster than in monocrystalline silicon, as expected. The as-deposited films exhibit an anisotropic structure: a 〈110〉 fiber texture was found and the crystallites with 〈110〉 perpendicular to the surface are larger than crystallites with other orientations. With increasing layer thickness the 〈110〉 texture becomes more pronounced and the 〈110〉 oriented crystallites increase in size, whereas the size of crystallites with other orientations slightly decreases. Annealing leads to a weaker texture and larger crystallites. Implantation and subsequent annealing at 800 °C results in a weaker 〈110〉 texture and smaller crystallites. A significant increase in crystallite size for the implanted layers is noted after the 1100 °C anneal only. Because of the multitude of parameters the interpretation of the electrical data is necessarily qualitative. The minimum in the mobility after annealing the implanted samples at 1000 °C correlates with a pronounced change in lattice parameter but its origin is not yet understood. The increase in mobility after the 1100 °C anneal can be explained by the significant increase in crystallite size mentioned above.
Effects of hydrogenation and doping on the conductivity and density of defect states in amorphous silicon
Authors: Savvides N.
Published: February 2003

The temperature dependence of the dc conductivity σ has been measured in the temperature range T=100–500 K for a series of a-SiHx:B thin-film specimens prepared by magnetron reactive sputtering. Two groups of specimens were measured: (a) undoped specimens containing hydrogen concentration varying from zero to about 30 at. %, and (b) doped specimens containing 10 at. % hydrogen and boron concentration in the range 0.1–10 at. %. Activated band conduction (log σ∼T−1) was observed at high temperatures in undoped specimens containing about 5–10 at. % hydrogen. For all other specimens there is an extended temperature range of log σ∼T−1/4 consistent with charge transport by Mott’s variable range hopping mechanism. The density of states N(EF) at the Fermi level undergoes appreciable changes with increasing concentrations of hydrogen and boron. These changes are interpreted as evidence of substantial structural disorder in hydrogen-rich and heavily doped a-SiHx:B films.
Intensity dependence of diffusion length in amorphous silicon by surface photovoltage measurements
Authors: Moore A. R. , Kane D. E.
Published: February 2003

The dependence of minority carrier diffusion length Lp on light intensity in undoped amorphous silicon can be obtained by surface photovoltage (SPV) measurements alone. The sample is first illuminated with a light bias but unbiased electrically. Then it is voltage-biased electrically, but unbiased optically. By combining SPV measurements made under both conditions, and interpreting with the aid of a regional approximation theory, the effect of the surface space-charge region can be allowed for, and the intensity dependence of Lp revealed. In the equation for light dependence Lp∝I S, S was found experimentally to vary from −0.038 to −0.015, depending on the sample. This relatively weak dependence means that the main cause of the observed change in the apparent diffusion length as the bias light intensity increases can be ascribed to the collapse of the surface space-charge region. We also obtain estimates of the characteristic energy slopes of the density of states near the center of the gap. Values of 290–737 mV were found for a series of samples. This corresponds to an almost uniform distribution in energy within a few tenths of a volt on the valence-band side of the equilibrium Fermi level.
Substitutional doping of photochemically-deposited amorphous hydrogenated silicon
Authors: Mishima Y. , Hirose M. , Osaka Y. , Ashida Y.
Published: February 2003

Physical properties of amorphous hydrogenated silicon produced by the direct photolysis of disilane have been investigated as a function of the doping ratio of phosphine and diborane. Boron doping resulted in a smooth increase of conductivity, while phosphorus doping revealed anomalous behavior of conductivity. Correspondingly, the growth rate was increased by boron doping and lowered by phosphorus doping. This was attributed to a remarkable difference in the optical absorption cross sections of phosphine and diborane.
Carrier collection efficiency of Schottky diodes on triode dc sputtered hydrogenated amorphous silicon: Transport properties of holes
Authors: Arene E. , Baixeras J. , Mencaraglia D.
Published: February 2003

Spectral response of Schottky diodes has been used to determine the product μpτp (mobility-lifetime product of holes) of sputtered undoped and n-doped hydrogenated amorphous silicon. It is shown that the diffusion of holes in the space-charge region can be neglected in the calculation of the collection efficiency. Further, the influence of H content as well as dopant content on the transport properties of the holes has been investigated. Our results clearly demonstrate that (i) the incorporation of hydrogen leads to an increase of μpτp, and (ii) the n-type doping results in a drastic decrease of μpτp. Moreover, the behavior of the transport properties of the holes has been interpreted in the framework of the recombination model first proposed by Rose. For our samples, the variation of μpτp is controlled through the hole lifetime by the deep gap states which act as recombination centers. This interpretation has been confirmed by the influence of the photon flux intensity on the collection efficiency.
Activation of shallow, high-dose BF+2 implants into silicon by rapid thermal processing
Authors: Powell R. A.
Published: February 2003

Rapid thermal processing has been used to activate shallow p+ layers (∼0.1–0.15 μm) following BF+2 implantation (49 keV, 2–6×1015 cm−2) into amorphized silicon. For doses of 2×1015 cm−2, the shallow as-implanted boron profile was preserved, unlike the case of furnace annealing (900 °C, 30 min). Sheet resistance of 85 Ω/sq following rapid annealing was close to that calculated assuming 100% activation of dopants in their as-implanted distribution. At 6×1015 cm−2 dose, however, these same rapid annealing conditions (10–15 sec exposure to a 1250 °C heater) produce considerable dopant redistribution (≳2000 Å) with peak carrier concentration of ∼1020 cc−1, which is far below the as-implanted value of ∼1021 cc−1. A two-step anneal is described which permits shallow junctions of ∼1500 Å to be obtained for the 6×1015 cm−2 dose implants; however, maximum carrier concentration was still ≲1020 cc−1. The present data suggests that the concentration limit for activation of implanted boron encountered when furnace annealing is applicable even when annealing is carried out on a much shorter time scale of 10 sec versus 30 min.
Size effects on polar optical phonon scattering of 1-D and 2-D electron gas in synthetic semiconductors
Authors: Leburton J. P.
Published: February 2003

The total scattering rate and the transition probability for electron-phonon interaction in 1-D and 2-D semiconductor materials are calculated in taking into account the finite dimensions of the structure. Although noticeable, size effects on the scattering rate are generally small, with more pronounced features for 1-D structures than for 2-D structures. For 2-D layers, our theory agrees with recent experimental results whereas it contradicts the previous theory predicting large size effects and mass-independent electron-phonon scattering rates. In 1-D structures singularities in the phonon emission rate appear as a natural consequence of the 1-D density of states. However, for high energy the 1-D emission rate is found smaller than the corresponding 3-D rate. An additional consequence of the confinement is the quenching of the phonon absorption rate.
Effects of iron on coil systems with cylindrical symmetry using Legendre polynomials
Authors: Caldwell J.
Published: February 2003

This paper considers the calculation of the scalar potential of a system of axisymmetric conductors. The method used includes the effects of iron on the coil systems into the Legendre polynomial expansion. The collocation approach used is specifically oriented towards cylindrical symmetry. The iron is divided into small cylindrical elements which are used to obtain the coefficients of the Legendre polynomial expansion of the potential due to the iron. A check on the accuracy of the method is obtained by comparing the results with the analytical results for the case of constant permeability.
Magnetic and magneto-optical properties of amorphous GdFePb films
Authors: Hartmann M. , Hansen P. , Willich P.
Published: February 2003

Amorphous alloys of composition (Gd,Fe)1−yPby with 0≤y≤0.18 have been prepared by co-deposition from three electron-gun sources onto glass substrates. The characterization of the films has been performed by electron probe microanalysis and by SIMS depth profiling. The magnetic and magneto-optical properties have been investigated in the temperature range of 4.2 K ≤T≤TC. From the temperature dependence of the saturation magnetization the compensation temperature is found to decrease strongly with increasing y, while the Curie temperature is less affected. The magneto-optical Faraday and Kerr rotation display a considerable increase with increasing Pb-content. The temperature behavior can be interpreted in terms of the mean-field analysis, indicating a pronounced influence of the Pb on the iron moment and the exchange constants.
Photoelectron paramagnetic resonance studies of ionization transitions of chromium impurities in ZnS and GaAs
Authors: Godlewski M.
Published: February 2003

The photoelectron paramagnetic resonance (photo-EPR) technique is applied to studies of photoionization transitions of chromium impurities in ZnS and GaAs lattices. The different dynamic photo-EPR experiments are discussed enabling an unambiguous interpretation of the nature of photoionization transitions to be made and a determination of the chromium centers ionization energies (Eopt, Eth, Erel) to be carried out.
Rapid thermal annealing of ion-implanted semiconductors
Authors: Narayan J. , Holland O. W.
Published: February 2003

Annealing of ion implantation damage (in the form of amorphous layers and/or the layers containing only dislocation loops) in silicon and gallium arsenide has been studied by electron microscopy techniques and the effects on dopant distribution have been investigated by Rutherford backscattering and secondary ion mass spectrometry techniques. The annealing of amorphous layers occurs by solid-phase-epitaxial growth and that of dislocation loops involves primarily loop coalescence as a result of conservative climb and glide processes. The annealing of isolated loops occurs primarily by a bulk diffusion process. Almost a ‘‘complete’’ annealing of displacement damage is possible for shallow implants provided loop coalescence does not lead to the formation of a crossgrid of dislocations. For deep implants, the free surface cannot provide an effective sink for defects as in the case of shallow implants. Dopant profiles can be controlled to less than 500 Å in layers having good electrical properties. The enhanced diffusion of dopants which is observed is probably due to entrapment of point defects in the annealing regions.
Defects introduced in silicon wafers during rapid isothermal annealing: Thermoelastic and thermoplastic effects
Authors: Bentini G. G. , Correra L. , Donolato C.
Published: February 2003

The temperature and stress distribution induced in silicon wafers during ‘‘rapid isothermal’’ annealing have been calculated for two commonly used heating methods: (a) by a strip heater and (b) by uniform irradiation with an energy flux. Analytical expressions have been obtained for the temperature and stress profiles which show that thermoelastic effects, originated by the temperature drop at the sample edge, are much higher in case (b). The conditions of plastic deformation and consequent damage introduction have been established by comparing the yield stress with the value of stress resolved on the {111} planes in the 〈110〉 slip directions. As a result, the topographic distribution of the slip lines, the extension of the peripheral damaged region, and the temperature threshold for damage introduction have been evaluated for 2- and 4-in. wafers. Rapid isothermal annealing experiments have been performed to check the results of the calculations. Two-inch silicon wafers were irradiated uniformly for 15 sec in the temperature range from 930 to 1400 °C by using a shuttered electron gun. The threshold temperature for damage onset was found to lie in the interval 1030–1090 °C; the observed geometrical distribution of the slip lines and their extension were consistent with theoretical estimates.
Investigation into the photocurrent quadrature signal of photoelectrochemical cells
Authors: Flaisher Harvey , Tenne Reshef
Published: February 2003

It is well known that for certain photoelectrochemical cells, the flat-band voltage calculated from the photocurrent onset is actually false and can differ from the true flat-band voltage by several hundred millivolts. We have observed this phenomenon for the cadmium selenide/aqueous polysulfide, as well as for other photoelectrochemical cells. In addition, we have observed a phase shift in the photocurrent signal at the voltage where the false onset occurs and we attribute this shift to the electronic filling of surface states. A kinetic model is used in conjunction with an equivalent circuit in order to verify this hypothesis. Results of the theoretical model agree satisfactorily with experimental data. Experimental guidelines for increasing the reliability of photocurrent onset measurements are presented.
Laser annealing of ZnO thin films
Authors: Bertolotti M. , Ferrari A. , Jaskow A. , Palma A. , Verona E.
Published: February 2003

Thermal furnace and CO2 laser annealing experiments on ZnO thin films are reported. Both the refractive index of the films and the effective refractive index of guided optical modes increase with thermal furnace annealing. However, the losses of guided modes increase, too. Laser annealing performed by scanning with a CO2 laser beam does not affect refractive index but produces a marked decrease for guided mode losses.
Hydrogen-induced oxide surface charging in palladium-gate metal-oxide-semiconductor devices
Authors: Armgarth M. , Nylander C. , Svensson C. , Lundström I.
Published: February 2003

Hydrogen-induced oxide surface charging occurs in palladium-gate metal-oxide-semiconductor devices. This has been concluded from high-frequency capacitance-voltage measurements, especially in the inversion region. Measurements of transient currents induced by changes in bias, and microscopic ellipsometry on the oxide surface, support the idea of hydrogen-induced charges. It is concluded that the surface charges are protons.
Numerical simulations of positively-biased probes and dielectric-conductor disks in a plasma
Authors: Brandon S. T. , Kessel R. L. , Enoch J. , Armstrong T. P.
Published: February 2003

A cylindrical particle-in-cell (PIC) plasma simulation code applicable to plasma densities encountered in low earth orbit has been refined. The basic configuration simulated consists of a conductor, partially covered with dielectric material, placed upon a conducting ground plate. The plasma is Maxwellian for both ions and electrons at large distances. Current-versus-voltage curves have been computed by following in time a randomly loaded initial system in which the conductor was held at a specific voltage. The resulting time stationary state is identified as the solution of the boundary value problem. These results have been compared to experimental values showing quantitatively correct behavior. Techniques allowing the simulation of dielectric charging using PIC time scales are discussed. A method of simulating large ion-to-electron mass ratios by moving the ions once every n time steps, where n is the square root of the desired mass ratio, has been developed. Enhanced diagnostics have allowed a more detailed study of the plasma behavior near the conductor (hole) and dielectric.
Z-pinch instability in an electrically exploding thin-shelled tube
Authors: Hechtman Charles D. , Cheo Bernard R-S.
Published: February 2003

A Z-pinch instability is observed experimentally on an electrically exploding thin-shelled tube and theory is developed to predict the wavelength of the instability.
Device for simultaneous measurement of the Peltier and Seebeck coefficients: Verification of the Kelvin relation
Authors: Jiménez J. , Rojas E. , Zamora M.
Published: February 2003

We have designed and built an experimental device, which we called a ‘‘thermoelectric bridge.’’ Its primary purpose is simultaneous measurement of the relative Peltier and Seebeck coefficients. The systematic errors for both coefficients are equal with this device and manipulation is not necessary between the measurement of one coefficient and the other. Thus, this device is especially suitable for verifying their linear relation postulated by Lord Kelvin. Also, simultaneous measurement of thermal conductivity is described in the text. A sample is made up of the couple nickel-platinum, taking measurements in the range of −20–60 °C and establishing the dependence of each coefficient with temperature, with nearly equal random errors ±0.2%, and systematic errors estimated at −0.5%. The aforementioned Kelvin relation is verified in this range from these results, proving that the behavioral deviations are ≤0.3% contained in the uncertainty ±0.5% caused by the propagation of errors.
Self-epitaxial deposition of high-T
C Nb3Al thin films
Authors: Tanabe K. , Michikami O.
Published: February 2003

A self-epitaxial method has been applied to the preparation of Nb3Al thin films by magnetron sputtering, utilizing a composition variation with sputtering gas pressure. The effects of the deposition parameters of both the epitaxial layer and the lower Nb-rich layer on film properties have been investigated. The A15 phase boundary is extended by 2 at. % Al, as compared with conventional deposition, to a stoichiometric composition. An epitaxial temperature of about 400 °C and a correlation between TC enhancement and ordering in the lower layer are found. The growth of a nearly stoichiometric A15 phase over a thickness of more than 100 nm is confirmed by x-ray diffraction, Auger analysis, and tunneling measurements, although the latter reveals evidence of some material inhomogeneity. Thickness dependence of film properties different from those for coevaporated films suggest the important roles of a homoepitaxial process as well as the suppression of second-phase nucleation at the self-epitaxial interface. The highest TC observed in this work is 17.7 K and the transition width is typically 0.1–0.3 K. A comparison of the compositional dependence of TC for both films and bulk Nb3Al suggests that the inferior TC values in our sputtered films are attributable to lack of long-range order.
Interactions of strongly coupled superconducting microbridges
Authors: Escudero R. , Smith H. J. T.
Published: February 2003

An electronic analog simulation of two coupled superconducting microbridges is shown to give similar results to the numerical solution. For strongly coupled microbridges some new phenomena are revealed. Strongly coupled thin-film microbridges were prepared by a new technique and their current-voltage characteristics confirm some of the predictions that are indicated by the analog simulation.
Low-frequency losses at high fields in multifilamentary superconductors
Authors: Zaleski A. J. , Orlando T. P. , Zieba A. , Schwartz B. B. , Foner S.
Published: February 2003

Low-frequency (∼1 Hz) ac loss measurements were made at applied fields up to 20 T with field modulation amplitudes of up to 1 T. Results for the alternative in situ and powder metallurgy (P/M) processed Nb3Sn and Nb–Al wires are presented for single-strand and multistrand geometries. Loss measurements for commercial continuous-fiber Nb3Sn wires manufactured by Holec and Supercon also are presented and show that the effective fiber size determined by these ac-loss measurements corresponds to that measured optically. The effective fiber size for alternative processed wires was intermediate between the wire size and the fiber size, and the losses (and effective fiber size) were reduced by twisting. Multistrand geometries showed further reductions in losses. The smallest effective fiber size at high field was measured for P/M processed Nb–Al. The losses were fully hysteretic and the ac losses were used to determine the critical-current density at low fields where it was difficult to measure directly.
Pressure and temperature dependence of the electromechanical properties of polarized polyvinylidene fluoride films
Authors: Destruel P. , Rojas F. Soto , Tougne D. , Hoang-The-Giam
Published: February 2003

The piezoelectric resonance method was adopted in order to measure piezoelectric and elastic constants of polyvinylidene fluoride films over the temperature range from −40 to 60 °C and at pressure up to 3 kbar. We have shown that the glass transition temperature increases with pressure, dTg/dP being approximately equal to 17 °C/kbar at atmospheric pressure. We have demonstrated that the electromechanical coupling factor K32 is not independent of temperature. Previous measurements, carried out at atmospheric pressure, which indicated the invariance of K32 with temperature, corresponded to a particular case of more general thermodynamic behavior.
Charge dependence of secondary electron emission coefficients
Authors: Hird B. , Pepin C. , Kelly G.
Published: February 2003

No significant difference is found between the secondary emission coefficients of negative ions compared to positive ions for ions of the same element, measured at the same energy and on the same stainless-steel surface.
Energy and momentum conservation relations in a dispersive medium
Authors: Seshadri S. R. , Schill Robert A.
Published: February 2003

A variational method is presented for determining the real and the imaginary parts of the changes in the wave vector and the wave angular frequency in a dispersive medium capable of supporting weakly decaying or growing waves.
Approximation for the Fermi–Dirac integral with applications to degenerately doped solar cells and other semiconductor devices
Authors: Abidi S. T. H. , Mohammad S. Noor
Published: February 2003

An analytical formula for evaluating Fermi–Dirac integral of order 1/2 has been proposed. The formula exhibits essentially the same form as that of Joyce and Dixon, but is accurate enough to be used in the heavily doped regions of semiconductor devices as well as in those cases where the degeneracy occurs at nonequilibrium. It has been shown that the accuracy with which the derivative can be evaluated by differentiation of the proposed series is remarkable and the error never exceeds 0.4%. To justify its applicability the formula has been used to calculate the effective charge carrier concentration of degenerate heavily doped material.
Severe limitations upon the ultracentrifuge gravitational red-shift experiment
Authors: Weber F. Neff
Published: February 2003

A description of the ultracentrifuge gravitational red-shift experiment is given. The experiment attempts to simulate the cosmological gravitational red shift, resulting from a relatively small gravitational field operating relatively long distances, by an effective gravitational field of 106 g produced in the ultracentrifuge operating on laser light for short distances. Definitive results from the experiment were not achieved, nor was a transverse Doppler effect detected. The present paper sets forth the reasons for these problems and calculates the experimental conditions that would be necessary to overcome them.
Generalized rate equations and modulation characteristics of external-cavity semiconductor lasers
Authors: Agrawal Govind P.
Published: February 2003

Modulation characteristics such as the power response and the dynamic frequency shift (chirp) of an external-cavity semiconductor laser are analyzed using a set of generalized rate equations for a single longitudinal mode selected by the coupled-cavity device. The general formalism is applied to the specific case where the external cavity consists of a rod of graded-index material (GRINROD cavity). Particular attention is paid to the chirp reduction and its optimization in the presence of intercavity coupling. The results are in reasonable agreement with the recent experimental observations.
Analysis of astigmatism of gain guided laser with a tapered-stripe geometry
Authors: Mamine Takayoshi , Oda Tatsuji , Yoneyama Osamu
Published: February 2003

The astigmatism of the tapered-stripe (TAPS) laser has been analyzed. Calculating the near-field spot size and the radius of curvature in the tapered-stripe region, the astigmatism is determined by using the expression of D=Re [1+(λRe/ πw2e)2]−1. In our formalism we assume that the gain profile is parabola and the near-field spot size at the facet is determined by the diffusion length of injected carriers. So far as these assumptions are valid, it is concluded that the amount of astigmatism is reduced with the length of tapered stripe, using the refractive index change due to the band-edge absorption of −10−2. The fundamental characteristics of the gain guided laser with TAPS structure such as the astigmatism, far-field radiation pattern, and the spontaneous emission factor are shown to be controlled by properly designing the stripe geometry and the thickness of the active layer.
Effects of a cold electron beam on the parametric decay of a Langmuir wave
Authors: Willett Joseph E. , Aktas Yildirim
Published: February 2003

A formalism for the parametric decay of a Langmuir wave into a backscattered Langmuir wave and an electrostatic ion wave in an electron beam-plasma system is developed. Explicit growth rates and dispersion relations for the ion wave modified by mode coupling and a nearly monoenergetic electron beam are derived. A numerical study of the effects of the beam on the growth rate for this resonant backscatter decay instability is presented.