Propagation of ultrasonic waves in bulk gallium nitride (GaN) semiconductor in the presence of high-frequency electric field

The propagation of ultrasound is studied in bulk GaN semiconductor in the presence of a strong AC field oscillating at a frequency much higher than that of the ultrasound. Analytical expressions have been obtained for the attenuation coefficient (α) and the renormalised velocity (v) of the acoustic wave. It is shown that the dependencies of the ultrasonic absorption coefficient of the conduction electrons and the renormalised sound velocity on the field amplitude and the sound frequency have an oscillatory character which can be used to determine the effective mass and mobility of the material. The threshold field Emin=3.3×102V/cm needed to observe the oscillation is two orders smaller than that needed in the case of CdS.