Vapour-deposited CdS films and their dependence on the source material

An investigation has been made of the conditions required for the formation of vapour-deposited CdS thin films with reproducible characteristics suitable for use in photovoltaic solar cells. Cathodoluminescence spectroscopy has been used to provide information on differences in composition between the deposited films and the source material from which they were produced, and particular consideration has been given to the influence of the source material structure and stoichiometry on the electrical properties of the resultant films. Under identical deposition conditions, four different high-purity sources were shown to produce films with very different electrical characteristics, but by selecting appropriate deposition conditions (substrate temperature and deposition rate) it was found that each material was capable of generating films with the required characteristics.