The plasma spectrum effect on acoustic wave amplification by carrier drift in semiconductors

TL;DR

This paper investigates how plasma oscillations influence acoustic wave amplification in semiconductors with carrier drift, revealing significant effects when plasma frequency is comparable to electron scattering rates.

Contribution

It develops a continuum hydrodynamical model to analyze plasma effects on acoustic wave amplification, extending previous conductivity-based approaches.

Findings

Amplification factor can be orders of magnitude larger with plasma effects.

Optimal drift velocity is significantly reduced when plasma frequency is high.

Results align with conductivity models when plasma frequency is low.

Abstract

The effect of plasma oscillations on acoustic wave amplification by carrier drift in semiconductors is discussed. A continuum theory is developed on the basis of hydrodynamical equations for the conduction electrons, the equations for the elastic vibrations of the crystal, and the Poisson equation. It is shown that if the plasma frequency is much lower than the reciprocal value of the electron relaxation time for the scattering on phonons and impurities, the results are in agreement with available calculations based on the electrical conductivity - diffusion equation. However, in the opposite case the amplification factor is orders of magnitude larger compared to the value predicted by those calculations, while the optimum drift velocity is much smaller.