STUDY OF AN ACOUSTOELECTRIC INSTABILITY IN PIEZOELECTRIC SEMICONDUCTORS

Abstract

The coupling between the acoustic transverse phonons and the electron drift current, in piezoelectric semiconductors, has long been known to give rise to a negative acoustoelectric current, thereby leading to a decreased conductivity with respect to the value derived from the Ohm law. Increasing the electric field above a threshold causes the differential conductivity to become eventually negative, which triggers off an instability. The latter has been characterized experimentally by a mm-wide, high-field soliton moving at transverse sound velocity and by low-frequency current oscillations. However it is shown here to consist actually of a high-amplitude acoustoelectric microwave-packet. Because the electric permitivity is inferred to be renormalized to zero, the properties of this solution, including its vibrational frequency and amplitude, are shown to be shaped by the nonlinear piezoelectric interaction. All experimental features turn out to be accounted for satisfactorily within the framework of the present analysis. The relatively long initial transient regime, exhibiting interesting observations by Brillouin scattering, is also addressed.