Amplification of Acoustic Waves through Interaction with Conduction Electrons

Abstract

It is shown, from a Boltzmann equation treatment, that in the presence of a dc electric field it is possible for an acoustic wave to gain energy from the conduction electrons in a material. The criterion for such an amplification of an acoustic wave to take place is that the drift velocity given to the conduction electrons in the direction of propagation by the dc field must exceed the velocity of sound. In metals, dc fields of such a magnitude cannot be maintained, but in semiconductors the necessary conditions can be satisfied and an amplification of the acoustic wave can take place.