Current oscillations in CdS caused by acoustoelectric domain motion

Current oscillations caused by acoustoelectric domain motion were investigated in semiconducting and photoconducting CdS at room temperature. Oscillatory behaviors of the current are closely connected with the domain motion. Four different kinds of behavior of the domain were observed in several samples. In the homogeneous semiconducting CdS, the domain is built up through local amplification of thermal phonons due to spatial fluctuations of phonon-density distribution. Its "formation site" depends upon the applied electric field. In the inhomogeneous ones, the domain is usually formed at the region of electric-field concentration. In the homogeneous photoconducting CdS, damped oscillations of the current were observed. The domain formation may be attributed to amplification of acoustic shock wave generated at the cathode. In the inhomogeneous ones with a high-resistivity region near the anode, the domain is formed at the high-resistivity region and it seems to be dragged by some acoustic stimulations such as shock-excited acoustic waves. Formation time of the domain was also investigated in the homogeneous semiconducting CdS. Conductivity dependence of it seems to support the quantum theory but exclude White\´s formulation.