A study of electron transport processes in cadmium sulphide using the acoustoelectric effect

Abstract

The current saturation associated with the acoustoelectric effect has been investigated in photoconducting crystals of cadmium sulphide. Under normal band gap irradiation the current-voltage characteristic measured under pulsed conditions shows a departure from Ohm's law at a critical field, E(_c), of the order of l0(^3)v cm(^-1). The current saturation is associated with the internal generation of acoustic flux which occurs when the electron drift velocity, v(_d), exceeds the velocity of sound, v(_s), in the crystal. In consequence the critical field for saturation is determined by the drift mobility µ(_d) = v(_s) /E(_c). The work described in this thesis concerns the measurement of the drift mobility and its relationship to the experimentally determined Hall mobility, fd^, as a function of conductivity and temperature. In uniform samples the critical field at room temperature was independent of conductivity over the range 10(^-4) to 10(^-2) ohm(^-1)cm(^-1). The corresponding values of µ(_d)were all about 300 cm(^2)v(^-1)sec(^-1) in most of the samples studied and agreed well with the measured values of the Hall mobility. With non-uniform samples, however, the critical field varied strongly with the intensity of incident illumination. Under saturated conditions potential probe measurements on uniform samples revealed the presence of a stationary high field domain near the positive electrode.