DEPOSITION OF CADMIUM-SULFIDE FILMS BY DECOMPOSITION OF THIOUREA IN BASIC SOLUTIONS

Cadmium sulfide films were deposited on silicon wafer substrates by homogeneous decomposition of thiourea in basic solutions of amine complexed cadmium. The film morphology depended on the presence or absence of a cadmium hydroxide precipitate in solution and the presence or absence of a thin cadmium hydroxide film on the substrate. In the presence of the bulk precipitate, powdery poorly adherent films were formed; while in the absence of precipitate but with the cadmium hydroxide film, adherent, dense, specularly reflecting films were formed. In the absence of either bulk precipitate or substrate film, poor surface coverage was observed. X-ray photoelectron spectroscopy was used to detect the formation of the cadmium hydroxide film. Kinetic studies of the film growth demonstrated that film formation was essentially complete before the appearance of a bulk cadmium sulfide precipitate. After an initiation period, during which no discernable cadmium sulfide deposition occurred, the nucleation event occurred followed by crystal growth and no further nucleation of crystals. The behavior was very similar to the burst type nucleation found in homogeneous precipitation of powders. Analysis of the kinetic data supported decomposition of thiourea by the CdS film.