Showing papers by "Solid State Physics Laboratory published in 1986"
TL;DR: A review of the wide variety of predictions that results from a Landau-type of description of the nematic-isotropic phase transition is given in this paper, which includes a discussion of the nature of the order parameter and of the various types of possible phases.
291 citations
TL;DR: In this article, the authors show how to choose a stepping probability for an irreversible random walk such that only strictly selfavoiding configurations are generated, which corresponds to the non-branching version of the dielectric breakdown model.
Abstract: We show how to choose a stepping probability for an irreversible random walk such that only strictly self-avoiding configurations are generated. This probability is linked to the solution of the Laplace equation with appropriate boundary conditions and corresponds to the nonbranching version of the dielectric breakdown model. We have performed an exact enumeration for this so-called Laplacian random walk (LRW) on a square lattice (N ≤ 18). We find a smooth variation of the exponent ν as a function of the parameter η. For η = 0 this walk corresponds to the IGSAW. A self-consistent scaling theory is formulated for η = 0 that predicts an upper critical dimensionality dc = 3.
40 citations
TL;DR: Amorphous Al 6 Fe, icosahedral Al-Fe and crystalline Al m Fe have been investigated by X-ray diffraction, electron diffraction and Mossbauer effect measurements as mentioned in this paper.
38 citations
TL;DR: In this article, the X-ray reflectivity form the surface of a liquid crystal with terminally polar (cyano substituted) molecules has been studied using a high-resolution triple-axis Xray spectrometer in combination with a synchrotron source.
Abstract: The X-ray reflectivity form the surface of a liquid crystal with terminally polar (cyano substituted) molecules has been studied using a high-resolution triple-axis X-ray spectrometer in combination with a synchrotron source. It is demonstrated that at the surface of the smectic A1 phase a few antiferroelectric double layers develop that can be distinguished from the bulk single layer structure. A model is developed that separates the electron density in a contribution from the molecular form factor, and from the structure factor of the mono- and the bilayers, respectively. With only a few adjustable parameters it accounts for the rather complex observed reflection curve. It shows that (i) the first molecular layer has tails up rather than heads up, (ii) the smectic order parameter of the first mono- and bilayer is saturated, (iii) the antiferroelectric bilayering does decay rather abruptly and not exponentially Etude RX de la surface d'un cristal liquide pres de la transition nematique-smectique A1. Developpement en surface de quelques doubles couches antiferroelectriques qui peuvent etre distinguees de la structure en simples couches du materiau massif
25 citations
TL;DR: In this paper, the effective series resistance of n + -p junction solar cells has been measured as a function of operating current using open circuit voltage decay (OCVD), and Rajkanan and Shewchun (R−S) techniques.
16 citations
TL;DR: In this paper, the phase diagram and electrical resistivity of liquid Na-Ga alloys were studied experimentally, and the electrical resistivities were shown to be within the metallic regime.
Abstract: The phase diagram and the electrical resistivity of liquid Na-Ga alloys were studied experimentally. Compound formation in the solid state was observed at 20 at.% and at 37 at.% Na. The latter composition closely corresponds to the stoichiometric compound Na22Ga39, reported recently by Ling and Belin. The present DSC and electrical resistivity measurements do not show the existence of a region of immiscibility around 70 at.% Na. The electrical resistivity ϱ shows a maximum value of 203.9 μΩ cm in the isothermal curve at 560° for an alloy containing 57 at.% Na. In the neighbourhood of this composition, the temperature derivative dϱ dT becomes slightly negative. The values of ϱ and dϱ dT remain within the metallic regime; yet, a description by the diffraction model is complicated by a lack of information on both liquid structure and ion-electron potentials.
15 citations
TL;DR: In this paper, the electrical resistivity parallel and perpendicular to c-axis, mobility and carrier concentration of diselenide single crystals have been determined and growth spirals observed for the first time on the as grown faces of these crystals are also presented.
Abstract: Tin diselenide single crystals have been grown by the physical vapour transport (PVT) method. Optical absorption studies give an indirect allowed transition at 1.03 eV at room temperature. The electrical resistivity parallel and perpendicular to c-axis, mobility and carrier concentration have been determined. Dependence of resistivity parallel to c-axis on temperature gives an activation energy of 0.072 eV. Growth spirals observed for the first time on the as grown faces of these crystals are also presented here.
14 citations
TL;DR: In this paper, the diffuse phase transition of fluorite-type superionic conductors was studied in terms of the Bragg-Williams and the quasichemical approximation, compared with experimental data taken from the literature.
13 citations
13 citations
TL;DR: In this paper, the effect of Zener current due to the internal field emission in the space charge region of an n+p junction on the zero-bias resistance area product R o A of narrow-bandgap HgCdTe photodiodes has been investigated theoretically.
Abstract: The effect of Zener current, due to the internal field emission in the space-charge region of an n+-p junction, on the zero-bias resistance-area product R o A of narrow-bandgap HgCdTe photodiodes has been investigated theoretically. It is shown that the contribution of this mechanism in these photodiodes could appreciably lower the R o A product in the temperature range of 10 to 100 K.
12 citations
TL;DR: There is a discrepancy between the numbers of dipoles as observed with the dielectric relaxation techniques and the spectroscopic EPR method, and it appears that this discrepancy is caused by the fact that inDielectric experiments the dipoles are detected through their dynamical properties, whereas the EPR results provide a static picture.
Abstract: In this paper we present the results of a series of combined experiments on solid solutions ${\mathrm{Ba}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Gd}}_{\mathrm{x}}$${\mathrm{F}}_{2+\mathrm{x}}$ employing the following techniques: (a) ionic thermocurrents (ITC's); (b) dielectric capacitance and loss measurements at 1000 Hz; and (c) EPR. In line with earlier results on solid solutions ${\mathrm{Sr}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Gd}}_{\mathrm{x}}$${\mathrm{F}}_{2+\mathrm{x}}$ we find a discrepancy between the numbers of dipoles as observed with the dielectric relaxation techniques [(a) and (b)] and the spectroscopic EPR method, respectively. It appears that this discrepancy is caused by the fact that in dielectric experiments the dipoles are detected through their dynamical properties, whereas the EPR results provide a static picture. With ITC we only observe those dipoles which are isolated from the remaining defect system. The most important feature of our EPR data is that trigonal ${\mathrm{Gd}}^{3+}$ ions are by far the dominant defects present in ${\mathrm{Ba}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Gd}}_{\mathrm{x}}$${\mathrm{F}}_{2+\mathrm{x}}$ even for 0x0.05. This has important consequences for the conductivity processes in heavily doped materials. The defect properties of the system ${\mathrm{Ba}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Gd}}_{\mathrm{x}}$${\mathrm{F}}_{2+\mathrm{x}}$ deviate from those observed for cubic solid solutions consisting of ${\mathrm{CaF}}_{2}$ and rare-earth fluorides, which show extensive preferential clustering.
TL;DR: In this paper, the theory of open-circuit voltage decay (OCVD) technique for the determination of excess carrier lifetime in p-n-junction single-crystal solar cells is discussed.
Abstract: Publisher Summary This chapter discusses the theory of open-circuit voltage decay (OCVD) technique for the determination of excess carrier lifetime in p-n-junction single-crystal solar cells. It also discusses the OCVD obtained by electrical as well as optical injection of excess carriers. The OCVD is a popular technique for measurement of excess carrier lifetime in p-n-junction diodes. In a solar cell, the excess carriers can be injected electrically by a forward current or optically by illuminating it. OCVD technique is used in studying the switching behavior of diodes and solar cells and design of electronic pulse circuits, charge storage devices, and varactor diodes for frequency multiplication. Some limitations of the OCVD method for lifetime determination and small signal OCVD include variation of lifetime, diode factor and its variation, and high injection effects. The effect of high injection is to modify the excess carrier lifetime as well as the diode factor. In addition, it causes a saturation of the junction voltage.
TL;DR: In this paper, the effect of recombination in the emitter was investigated and it was found that recombination becomes important at high levels of injection and makes the voltage decay faster.
Abstract: The open circuit voltage decay (OCVD) in p - n junction diodes at high levels of injection is discussed in this paper. Theoretical results are given for thick base diodes and for BSF solar cells including the effect of recombination in the emitter. It is found that the recombination in the emitter becomes important at high levels of injection and makes the voltage decay faster. The experimental results in BSF solar cells at high levels of injection are also reported and found to be in good agreement with the theoretical results derived in this paper.
TL;DR: PbS films have been prepared by reactive evaporation for the first time as mentioned in this paper, and they have a carrier concentration of ≈ 6 × 1017 cm−3 and the mobility is temperature activated.
Journal Article•
TL;DR: It is concluded that a circular-aperture geometry leads to a minimum cold shield shading effect for a square mosaic array.
Abstract: Cold shield shading effects in a 2-D array have been calculated for square- and circular-aperture geometries of the cold radiation shield. It is concluded that a circular-aperture geometry leads to a minimum cold shield shading effect for a square mosaic array.
TL;DR: In this paper, an analytical model for the threshold voltage for ion-implanted short-channel IGFET's is presented and the coupled two-dimensional Poisson's equation under the gate is solved rigorously.
Abstract: An analytical model for the threshold voltage for ion-implanted short-channel IGFET's is presented. The coupled two-dimensional Poisson's equation under the gate is solved rigorously. A closed-form analytical expression is derived for threshold voltage as a function of the material parameters and device geometry.
TL;DR: In this paper, cold shield shading effects in a 2D array have been calculated for square-and circular-aperture geometries of the cold radiation shield, and it is concluded that a circular-approach geometry leads to a minimum cold shielding shading effect for a square mosaic array.
TL;DR: In this paper, the preparation technique of µc-SiH films using R.F. capacitive glow discharge of hydrogen-diluted silane is described. And the electrical and optical properties of the films are also reported.
Abstract: Microcrystalline silicon films have been found quite useful in amorphous silicon solar cells as a contact material in n-i-p cells. Microcrystalline silicon films are obtained when amorphous silicon films are prepared by R.F. glow discharge of SiH4 + H2 at higher power ratings. These films possess higher conductivity as well as high transmission than amorphous silicon films. The present paper reports the preparation technique ofµc-SiH films using R.F. capacitive glow discharge of hydrogen-diluted silane. X-ray studies andtem studies of the films indicate microcrystallinity of the films. The electrical and optical properties are also reported.
TL;DR: In this article, the salient features of various epitaxial growth techniques used for growing InP and lattice matched InP-based materials are reviewed and compared with those of Si and GaAs.
TL;DR: In this paper, the 57Fe Mossbauer effect was investigated on the solid solutions of Li0.5ZnxTixFe2.5−2xO4 (x=0 to 0.6) at 300K.
Abstract: The paper reports the57Fe Mossbauer effect investigations on the solid solutions of Li0.5ZnxTixFe2.5−2xO4 (x=0 to 0. 6) at 300K. The samples with x⩽0.4 exhibit well defined Zeeman pattern consisting of two sextets corresponding to Fe3+ ions at tetrahedral and octahedral sites. The composition with x=0.5 shows a strong ferrimagnetic relaxation whereas the composition with x=0.6 exhibits paramagnetic behaviour. The internal magnetic field at57Fe nuclei decreases with increasing x at both the sublattices. This variation is explained in terms of cation distribution and super-exchange interactions. The s-electron density has been observed to be independent of substitution level.
TL;DR: The semi-empirical model of Miedema and Van der Woude was used to extract information from Mossbauer isomer shift data about the packing in amorphous FexB1-x-alloys.
Abstract: The semi-empirical model of Miedema and Van der Woude is used to extract information from Mossbauer isomer shift data about the packing in amorphous FexB1-x-alloys (10at%
TL;DR: PbI 2 has been purified using zone refining technique by giving 20 passes and single crystals of pure and doped PbI2 were grown by the zone melting and Bridgman-Stockbarger technique as mentioned in this paper.
TL;DR: In this paper, the cold shield shading effects in a linear detector array for an elliptical aperture geometry with varying major-to-minor axis ratio were investigated and the results suggest that an elliptial aperture geometry is a better design than a rectangular aperture.
TL;DR: In this paper, photo-emission measurements were performed on melt-quenched amorphous Fe(Zr, B) and (Fe, Ni)B alloys, and the atomic and electronic structure of Fe90Zr10 and Fe88B12 glasses were found to be different.
Abstract: 57Fe Mossbauer and photoemission measurements were performed on meltquenched amorphous Fe(Zr, B) and (Fe, Ni)B alloys. The atomic and electronic structure of Fe90Zr10 and Fe88B12 glasses were found to be different. Half of the Zr content could be replaced by B in the Fe90Zr10 glass without changing its structure. Mossbauer investigation of the amorphous (Fe1−xNix)100−yBy (0<=x<=0.80, 12<=y<=40) system indicates preferential arrangement of Fe and Ni atoms on the transition metal sites. According to the present XPS measurements there is a remarkable shift of 0.5 eV to higher binding energies of the B ls core level energy in the Ni rich glasses compared to Fe88B12 corresponding to a stronger binding between the Ni and the B atoms than that of Fe and B.
TL;DR: In this paper, the quadrupole splitting in alloys is determined by the structural and electronic properties of the alloy, and only in cases where the density of states at the Fermi level is constant or known as a function of the concentration is known.
Abstract: The quadrupole splitting in alloys is determined by the structural and electronic properties of the alloy. Only in cases where the density of states at the Fermi level is constant or known as a function of the concentration, relevant structural information can be obtained from the quadrupole splitting.
TL;DR: Diammonium Hydrogen Citrate single crystals have been grown from aqueous solution The etch technique for defect studies is applied to these crystals Propionic acid is shown to be a reliable etchant capable of bringing out dislocations intersecting the (001) face Various other interesting features observed during etching are also presented and discussed as mentioned in this paper.
Abstract: Diammonium Hydrogen Citrate single crystals have been grown from aqueous solution The etch technique for defect studies is applied to these crystals Propionic acid is shown to be a reliable etchant capable of bringing out dislocations intersecting the (001) face Various other interesting features observed during etching are also presented and discussed
TL;DR: In this article, changes in the performance of CuxS/Cd1−yZnyS solar cells have been studied after annealing in air, nitrogen, and hydrogen.
TL;DR: In this article, the dopant profile of the impurity implanted in silicon is measured by anodic oxidation and stripping (AOS) in an especially designed electrochemical cell followed by surface Hall and conduc-tivity measurements.
Abstract: N- and p-type silicon slices are ion implanted at room temperature with various doses and energies up to 200 keV by a 400 kV ion implanter. The implanted slices are then subjected to a two step thermal annealing in nitrogen ambient. Electrical methods are used for the depth profiling of these slices. The dopant profile of the impurity implanted in silicon is measured by anodic oxidation and stripping (AOS) in an especially designed electrochemical cell followed by surface Hall and conduc-tivity measurements. The AOS technique useful for high dopant concentration is supplemented by capacitance-voltage (C-U) measurements of the impurity distribution at low concentrations. C-U technique is employed by making Schottky barrier diodes (SBD) with Al and Au metalliza-tions. The failure physics of Al-SBD is explained by a model based on kinetics of diffusion whereas the results of Au-SBD are reported and discussed.
N- und p-leitende Siliziumscheiben werden bei Zimmertemperatur mit unterschiedlichen Dosen und Energien bis zu 200 keV mittels eines 400 kV-Ionenimplanters implantiert. Die implantierten Scheiben werden dann einer Zweistufentemperung in Stickstoffatmosphare ausgesetzt. Elektrische Methoden werden fur die Tiefenprofilierung dieser Scheiben benutzt. Das Dotieningsprofil der implantierten Storstellen in Silizium wird mittels anodischer Oxydation und Abatzen (AOS) in einer speziell entwickelten elektrochemischen Zelle und einer nachfolgenden Oberflachen-Hall-und-Leit-fahigkeitsmessung bestimmt. Die AOS-Technik, die fuir hohe Dotierungskonzentrationen geeignet ist, wird durch Kapazitats-Spannungs-(C-U)-Messungen der Storstellenverteilung bei niedrigen Konzentrationen vervollstandigt. An Schottky-Barrierendioden (SBD) mit Al- und Au-Metalli-sierung werden C-U Messungen durchgefuhrt. Das Versagen der Al-SBD wird mit einem Modell erklart, das auf der Diffusionskinetik beruht, wahrend die Ergebnisse der Au-SBD mitgeteilt und diskutiert werden.
TL;DR: In this article, an energy-dispersive X-ray diffraction spectra of boron-rich amorphous FeB alloys is presented.
TL;DR: In this article, the second harmonic response of indigenously developed X-band GaAs was treated and the circuit requirements and experimental results obtained in a conventional resonant disc type oscillator circuit were discussed in details.
Abstract: GaAs Gunn devices are being increasingly used in the harmonic mode to deliver appreciable power in the mm-wave band. In this paper, the second harmonic response of indigenously developed X-band Gunn devices are treated. The circuit requirements and experimental results obtained in a conventional resonant disc type oscillator circuit are discussed in details.