Acoustoelectric studies in cadmium sulphide thin films

Abstract

Mechanical properties of the substrate are shown to exert a primary influence on surface wave propagation in vapour deposited Cadmium Sulphide thin film structures. The implications of substrate anisotropy are numerically explored, and it is shown to be an adequate approximation to regard a suitably oriented CdS-on-Sapphire system as mechanically isotropic with respect to waveguide dispersion.Acoustoelectric coupling dispersion is discussed within an acoustic ray waveguide framework, and it is concluded that no theoretical objection exists to obtaining thin film acoustic surface wave gain rates comparable to those currently obtained in single crystal bulk wave amplifiers.Thermodynamic stabilization is shown to be prerequisite to the successful operation of high field CdS thin film devices. Available techniques for the suppression of impurity and secondary phase effects are discussed, and a post - evaporation heat treatment procedure, aimed both at compensation of native atom astoichiometries and at drift mobility enhancement through copper recrystallization catalysis is described.Observations of thin film high field photocurrent saturation, post- threshold localized field redistribution and acoustoelectric bunching-type noise are diagnosed as characterizing inhomogeneous low gain rate surface wave noise amplification processes.