Photoconductive CdS Films by a Chemical Bath Deposition Process

A new technique for the preparation of thin films by chemical bath deposition is described. The films prepared by this method have many of the advantages of those made by the spray deposition method, such as the ease of coating large areas and simplicity of the process. The stoichiometry is easy to maintain in both these methods. The films are formed on rotating substrates from a bath containing cadmium salt in a complex form. Electrical, photoconducting, and optical properties such as I–V characteristics, decay of photoconductivity, spectral response of photoconductivity, and optical absorption were studied. Addition of cations like Ag, Cu, In, and Zn to the deposition bath makes the films amorphous. Such amorphous layers have a density of state of the order of 10¹⁹–10²⁰/cm³/eV near the Fermi level, as determined by photodecay and field effect measurements. The films produced are strong, adhering tightly to the substrates, show little or no degradation, and are photosensitive as deposited.