Drifting electron excitation of acoustic phonons: Cerenkov-like effect in n-GaN

Abstract

The process of generation of acoustic phonons by way of drifting electron excitation in polar semiconductors is considered. Similarly to what is present in LO phonons, the emergence of a condensation of the pumped energy in modes around an off-center region of the Brillouin zone is evidenced. The phonons are emitted within a lobe-like distribution with an axis along the direction of the electric field. A numerical calculation for the case of GaN is done, which shows that the phenomenon can be largely enhanced at high carrier densities and in strong piezoelectric materials.