Crystallographic orientation dependence of electrical response of acoustoelectric oscillators

The crystallographic orientation dependence of the direct voltage/current characteristics, the amplitude of the r.f. output and the field dependence of the frequency were studied in CdS acoustoelectric oscillators. The electromechanical coupling is dependent on the crystallographic orientation. Two types of oscillators were prepared orientated in such a direction that nearly an order of magnitude difference in the electromechanical coupling was obtained. Changes in the frequency of the electrical output with the applied field were measured, and were compared with those predicted by a linear theory. In the weak-coupling oscillators, the field dependence of the frequency was much less than expected from linear theory. At higher drift fields, a negative dispersion was observed in which the frequency decreased with increasing drift field. This behaviour was contrary to linear predictions, and was attributed to the rise in temperature of the crystal and also to nonlinear processes associated with the interaction between the electrons and the acoustic waves.In applications requiring high frequency-stability, a weak-coupling orientation is more suitable because of its lower dispersion.