Properties of Cadmium Sulfide Crystals with High Impurity Concentrations

Photoelectronic properties have been measured for cadmium sulfide single crystals with 10¹⁸ to 10²⁰ cm^-3 iodine, and copper, silver, or gold impurities. Highly photosensitive crystals with broad spectral response have been prepared from the vapor phase by chemical transport. The hypothesis that electrical and luminescence properties are to be associated with the specific acceptor impurity, whereas the photosensitivity is to be associated with other defects, such as cation vacancies, is supported by the following observations. (1) The thermal hole-ionication energy of sensitizing centers decreases with increasing impurity concentration, but the optical electron-ionization energy from copper centers does not change. (2) The optical electron-ionization energy from silver and gold centers is appreciably greater than that from copper centers, but the thermal hole-ionization energy of sensitizing centers is about the same for all three acceptors.