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Browsing by Author "Uppal, P. N."

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    Compositional depth profiles of chemiplated Cu2S/(Zn,Cd)S heterojunction solar cells
    Uppal, P. N.; Burton, Larry C.; Rivaud, Lydia; Greene, J. E. (American Institute of Physics, 1983)
    Atomic absorption spectroscopy combined with controlled chemical etching and Auger electron spectroscopy profiling with ion beametching have been used to obtain composition versus depth analyses of Cu2S/(Zn,Cd)S heterojunctionsolar cells formed by an aqueous cation exchange, or chemiplating, process. The Cu2S films, ranging from 0.5 to 6 _m in thickness, were polycrystalline and exhibited a (001) preferred orientation on either textured polycrystalline or cleaved single crystal (Zn,Cd)S substrates. The profiling results showed that the interfacial regions were compositionally graded over very large distances ranging from tens to hundreds of nonometers depending on the Cu2S film thickness. This is much wider than observed for comparable Cu2S/CdS cells. Moreover, excess Zn in the form of both elemental Zn and ZnS was always found in the interfacial region and may be responsible for the short circuit current being lower than expected for these cells.
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    Cross diffusion of Cd and Zn in Cu2S formed on Zn x Cd1_x S thin films
    Burton, Larry C.; Uppal, P. N.; Dwight, D. W. (American Institute of Physics, 1982)
    Cadmium and zinc compositions in Cu 2S formed on Zn x Cd1_x S films (0
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    X-ray and XPS studies of evaporated cuxs thin-films
    Uppal, P. N.; Burton, Larry C. (American Institute of Physics, 1983-04-01)
    The structural changes in Cu x S films have been monitored by x_ray diffraction and correlated to the chemical changes taking place on the Cu x S surface, the latter monitored by XPS. The results show: evaporated Cu x S films contained chalcocite, free copper phases, and probably a third phase (of sulfur); resistivity is related to the amounts of free Cu and S in the film; air heat treatments converted chalcocite to Cu deficient phases and resulted in the disappearance of the sulfide and predominance of CuSO4_nH2O and CuO; argon heat treatment tended to react Cu and S to form Cu x S; Cd is detected on the surface of Cu x S deposited onto CdS and is significantly increased in amount by heat treatments. These results can be related to chemical processes occurring on Cu x S/CdS and Cu x S/(Zn,Cd)S solar cells. For the CdS cell, oxides and sulfates of Cu and Cd are found on the Cu x S surface and the sulfates are enhanced by the heat treatment in moist air. CuO and CuSO4 are formed in the absence of Cd, and dominate the Cu x S surface.