Portland State University. Environmental Sciences and Resources
David K. Roe
Date of Award
Doctor of Philosophy (Ph.D.) in Environmental Sciences and Resources: Chemistry
Environmental Science and Management
4, vi, 71 leaves: ill. 28 cm.
Semiconductor films, Cadmium sulfide
Thin layer deposits of cadmium sulfide (CdS) for photovoltaic purposes can be made by cathodic deposition from a nonaqueous solution. There were numerous parameters that were controlled in this electro-deposition. Several of these parameters, including temperature, current density, reactant concentrations and impurity level doping, were studied and optimized. The mechanism of this deposition process is not fully understood, mainly due to the complex chemistry of sulfur. Part of this complexity is the presence of S(,6) and S(,7) along with the major component of S(,8) in sulfur solutions. At 90(DEGREES), these minor species constitute 2% of the total sulfur. Electrochemical studies were made on these species with gold, porous carbon and CdS single crystal electrodes. These showed that S(,6) and S(,7) are electrochemically more reactive than S(,8). Furthermore, they may be the main reacting species in CdS formation, even though they are present at such low levels. Adsorption of all species of sulfur was noted at room temperature and this adsorption may be causing excess sulfur to be incorporated into the CdS deposits. There has been an important development in the measurement of impurity levels of semiconductors called electrochemical photocapacitance spectroscopy. It can be used to analyze impurity levels in a wide variety of semiconductors by shining subband gap light on the semiconductor in a photoelectrochemical cell while measuring the capacitance on the surface. Interpretation of these spectra has previously been qualitative. A quantitative model was developed here along with a computer program utilizing this interpretation. Several types of semiconductors were analyzed by this technique, including these CdS deposits which showed impurity levels that may be due to excess sulfur. Other types of compound semiconductors can also be made by this cathodic deposition. It is hoped that the information gathered here can be used to improve these other semiconductor depositions as well as CdS.
Richard, Jeffrey B., "Cathodic depositions of the compound semiconductor cadmium sulfide" (1985). Dissertations and Theses. Paper 571.