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.
