Continuous Oscillations of Acoustoelectric Current in CdS

Abstract

It is shown that a dc electric field can generate continuous oscillations of current in a CdS crystal provided a region of higher resistivity exists near the positive electrode of the sample. Frequency measurement reveals the existence of two kinds of periods. One corresponds to a round-trip of sound waves in the sample and the other to a forward transit of waves. A possible explanation of these oscillations is offered on the basis of an acoustoelectric current accompanying the ultrasonic flux. Oscillations are self-sustained by the ultrasonic traveling-wave amplification in a low resistivity region and the non-ohmic property of a high resistivity region where the amplified ultrasonic flux is converted into acoustoelectric current. Agreement between experiment and theory is semiquantitatively good.