Th.--Sci. phys.--Grenoble 1, 1978. N°: 154. / Extr. en partie du Journal de physique ; de Zeitschrift für Physik. A, 278, 1976, 189-199 ; de Nuclear physics. A, 308, 1978, 103-124 ; 313, 1979, 45-76 ; de Physical review. C, 13, 1976, 6 et de Nuclear data tables, 11, 1973, 351-357.

No description available.

No description available.

Inhalation of gallium arsenide (GaAs) particulates represent a potential health hazard in the semiconductor industry. Our results showed that GaAs was soluble under a variety of in vitro conditions. Arsenic levels in phosphate buffer filtrates indicated 78% dissolution by 36 hours. The in vivo dissolution of GaAs was dependent upon particle size, time, and route of administration. Intratracheal (i.t.) instillation of GaAs particulates (10-100 mg/kg) to rats resulted in blood arsenic levels of 5-187 ppm at 14-28 days, depending upon particle size. Dissolution doubled as the mean volume particle diameter was halved. Oral administration of GaAs particulates (10-1000 mg/kg) resulted in blood arsenic levels of 3-18 ppm at 14 days. Gallium was not detected in blood at any dose level by any route of exposure. Indices of toxicity that correlated to GaAs exposure were decreased weight gain and porphyria. These effects were maximal at 100 mg/kg GaAs i.t. Uroporphyrin replaced coproporphyrin as the major urinary metabolite. GaAs (10-100 mg/kg i.t.) resulted in an increase in the lung:body weight ratio (136-228%) at 14-28 days, depending upon particle size. Lungs retained 14-42% of the dose as gallium or arsenic. The increase in lung wet weight was not primarily due to edema although pulmonary edema increased in magnitude as particle size decreased. Lung dry weight, DNA, protein, and lipid content were also elevated 14 days after 100 mg/kg GaAs i.t. (large fraction). At this time and dose, major pathological lesions were a thickening in the alveolar wall, pneumonocyte hyperplasia, and interstitial pneumonia. Gallium, as Ga₂O₃ (65 mg/kg), accounted for the increase in lung lipids. Arsenic, as As₂O₃ (17 mg/kg), was responsible for the remaining changes in lung composition observed with GaAs administration. As₂O₃, but not GaAs, resulted in acute fibrosis at 14 days. With 100 mg/kg GaAs i.t. (smaller fraction), proteinosis, edema, mild fibrosis, and increased reticulin formation were observed over 1-28 days in addition to lesions previously described for the larger fraction. These results showed that oral and i.t. GaAs resulted in systematic arsenic intoxication. Intoxication was proportional to in vivo dissolution which was dependent upon particle size. GaAs i.t. was relatively more toxic to rats than an equivalent oral dose. The finding that urinary uroporphyrin levels were greater than coproporphyrin levels may serve as a sensitive, pretoxic indicator of GaAs exposure.

Thesis (M.M.S.E.)--University of Delaware, 2006. / Principal faculty advisor: Valeria Stoleru, Dept. of Materials Science & Engineering. Includes bibliographical references.

Includes bibliographical references.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Semiconductor multijunction solar cell is a cutting-edge photovoltaic technology aimed at developing a frontier solution to the clean energy demand and environmental problem. Due to the efficient photoabsorption and energy conversion in the visible and near-infrared spectral ranges of the solar spectrum, the multijunction solar cell structures have shown an unprecedented application potential by demonstrating a solar conversion efficiency of over 44 %. Among various multijunction solar cell structural designs, the GaxIn1-xP/GaAs double-junction tandem structure is considered as the most fundamental building block for developing the industry-standard triple- and even more junction photovoltaic cells with super high efficiency. Therefore, obtaining a better and more in-depth understanding of physical properties of the GaxIn1-xP/GaAs double-junction tandem device structure, especially some fundamental optoelectronic processes in the individual structural layer, including photoexcitation, transport and the mid-way recombination of charge carriers, is crucial for further improving the energy conversion efficiency. In this thesis, the mid-way radiative recombination, diffusion transport, localization mechanism, and photocurrent spectra of charge carriers in the GaxIn1-xP/GaAs double-junction tandem solar cells grown on GaAs substrates with different misorientation angles were investigated in detail. Our main findings are summarized as below. Efficient radiative recombination of carriers in the GaxIn1-xP/GaAs double-junction tandem solar cell samples was demonstrated by using electroluminescence (EL) and photoluminescence (PL) techniques. The radiative recombination intensity was shown to be dependent on the intrinsic material-related parameters such as the doping concentration, growth thickness and the substrate misorientation angle both experimentally and theoretically. The radiative recombination was thus revealed to be an important loss channel of carriers in the GaxIn1-xP/GaAs double-junction tandem solar cells. Super strong transverse diffusion of minority carriers in the top GaxIn1-xP subcell was found by the micro-EL image surveying. Theoretical simulation on the experimental data shows that the minority carrier diffusion length is as long as ~93 μm at a forward bias of 2.75 V, which is ~30 times longer than that of unbiased GaxIn1-xP epilayer. Origin of this super transverse diffusion was argued, and its influence on device performance was also discussed. Significant correlations of carrier localization and luminescence behaviors with the substrate misorientation angle in the top GaxIn1-xP subcells were unveiled by excitation intensity- and temperature-dependent PL. The large difference in potential energy profile of GaxIn1-xP layers, caused by the different degrees of atomic ordering, was argued to interpret the observed PL distinctions. Vertical transport and photoresponse mechanisms of charge carriers in the GaxIn1-xP/GaAs double-junction tandem solar cells were studied by temperature- and reverse bias-dependent photocurrent (PC) spectroscopy. Both the temperature and reverse bias were shown to have significant impact on the device photoresponse, in particular on the photoresponse due to the absorption of photons with energy above the bandgap of GaAs and GaxIn1-xP, namely the supra-bandgap photoresponse. A model was proposed to simulate the observed temperature- and reverse-bias dependence of the supra-bandgap photoresponse. / published_or_final_version / Physics / Doctoral / Doctor of Philosophy

No description available.

An investigation is described of the instability of the horizontal free surface of a thin layer of liquid metal. The instability is due to the interaction of imposed electric and magnetic fields which are both initially horizontal. The interaction of fields produces a vertically upward magnetic force within the layer. Various two-dimensional theoretical models of the instability are described. A linear, viscous analysis of free surface instability is presented, and an analytical expression is obtained for the rate of growth of amplitude of a plane sinusoidal wave on the liquid free surface. A nonlinear model of a wave is also discussed on the assumption, later justified by experiment, that the waveform remains approximately sinusoidal providing the ratio of its amplitude and wavelength is small. An exact analysis is presented of a stationary wave in dynamical equilibrium. An experiment is described investigating the instability of a thin layer of liquid gallium. A new method for making instantaneous measurements of two-dimensional wave profiles is presented. Experimental observations are described of waves on an initially undisturbed free surface. It is confirmed that wave corrugations of the orientation predicted by linear theory to grow most quickly are observed to grow more quickly than other wave modes. Qualitative observations indicate the presence of secondary horizontal motions much larger than previous linear analyses have suggested. Quantative results indicate certain stability at non-zero amplitudes of linearly unstable waves if the Weber number is less than 0.12 and the Reynolds number is less than 75. Conversely, separation of gallium from the layer is observed invariably if the Weber number is greater than 0.31 and the Reynolds number is greater than 130.