Portland State University. Environmental Sciences and Resources Ph. D. Program.
David K. Roe
Date of Award
Doctor of Philosophy (Ph.D.) in Environmental Sciences and Resources: Chemistry
Environmental Science and Management
3, viii, 67 leaves: ill. 28 cm.
Semiconductor films, Cadmium sulfide, Cadmium selenide
Cadmium sulfide and cadmium selenide are important materials for applications such as photoconductive cells, photovoltaic cells and other electrooptical devices. Generally, these devices use single crystals. However, reasonable efficiencies have been observed by using polycrystalline films on conducting substrates, which are easier to make and provide considerable savings on materials and energy. Polycrystalline CdS/CdSe films have been made by sputtering and solution spraying, compound evaporation, chemical vapor deposition, and many others. A recent technique involves the electrochemical deposition of CdS and CdSe from nonaqueous solvents. Preparation of these films is based upon the cathodic deposition from a nonaqueous solution of a cadmium salt and elemental sulfur and/or selenium. Although the technique is simple, no mechanistic information is known to optimize the conditions in which films of controlled stoichiometry, doping and crystallinity are made. This research has the purpose to understand the mechanism of the formation of polycrystalline films of CdS and CdSe by electrochemical deposition in dimethylsulfoxide. This approach to the problem makes use of electrochemical techniques such as rotating ring disc electrode, linear scan voltammetry, high pressure liquid chromatography coupled with ultraviolet and electrochemical detection. By the rotating ring disc electrode technique, we have studied the kinetic parameters for the reduction of sulfur, selenium, cadmium, and the electroChemical formation of CdS and CdSe for temperatures from 25 - lOO°C. The results show that rates of initie.l electron transfer for the reduction of these species are moderately rapid, and secondly, that the reverse reaction is irreversible and involves additional steps. Studies of solubility of selenium with temperature reveal that its solubility is enhanced by the addition of sulfur. Understanding the electrochemical behavior of sulfur-selenium mixtures is of great importance to produce mixed semiconductive films with more adequate bandgaps for use with solar spectrum. Electrochemistry of sulfur-selenium mixtures are no different from that of sulfur alone. High pressure liquid chromatography separations with spectroscopic and electrochemical detectors have shown that sulfur solutions contain 86 and 87 fractions which are not electrochemically active.
Aparicio-Razo, Mario, "A mechanistic study of the electrochemical formation of CdS CdSe semiconducting films" (1983). Dissertations and Theses. Paper 448.