Ultrasonic amplification characteristics and nonlinearity in CdS

By using CdS crystals, studies are carried out on the gain and the nonlinear characteristics of ultrasonic amplification in the frequency range15\sim195Mc. A gain of 94 db at 135 Mc is obtained. Saturation characteristics and generation of higher harmonics up to 405 Mc are observed. The observed relation between the gain and the drift field is unsymmetric with respect to the drift field and the plots of the maximum gain versus frequency do not agree with the theory developed by White. When the conductivity of the crystal is low, these disagreements become considerable. Taking into account the effects of phase shift between the space charge waves formed by conduction electrons and by trapped electrons, we develop a modified expression for the gain. Agreement between the theory and the experiments is satisfactory.