Deposition of Piezoelectric Cadmium Sulfide Films from a Single Source of Cadmium and Sulfur Vapor

Abstract

This paper describes a simple method of depositing from a single source films of CdS with reproducible properties. These films are highly oriented and highly resistive so that they function effectively as piezoelectric transducers. The CdS is grown on a heated substrate from Cd and S vapor produced from a source utilizing a single heater. To equalize the rates of evaporation, the S is sealed in a vessel with a small exit orifice. A major advantage of the single heater source is that variations in heat input to the source during the evaporation period have little effect on the ratio of the vapor pressures, and therefore the stoichiometry remains constant. Films of CdS up to 6 μ thick with resistivities of 1010 Ω cm have been grown. The films are piezoelectrically active with coupling constants of about 0.12. They can be grown to generate predominantly either the shear or longitudinal mode of vibration. In either case, the unwanted mode is better than 48 dB down from the wanted mode. The method has a high yield rate of good films.