Nonlinear Theory of Current Oscillation in Piezoelectric Semiconductors

Abstract

A nonlinear theory is given of the current oscillation in semiconducting cadmium sulfide at room temperature when the drift velocity of electrons exceeds the velocity of sound. It is assumed that a high field domain of a rectangular shape due to the amplification of thermal phonons builds up near the cathode and travels with the sound velocity toward the anode without changing the domain width, while the region outside the domain remains ohmic. The electrons and phonons inside the domain are assumed to obey the nonlinear coupled equations employed in the discussion of current saturation in a previous paper. When reasonable values of the domain width and the “nonlinear relaxation time” of amplified phonons are chosen, the theory explains semiquantitatively (1) the wave form of current oscillation, (2) the negative resistance in current-voltage characteristics, and (3) the time dependence of electric field distribution in the sample.