Theory of positron diffusion in semiconductors.

Abstract

We have developed a theory for positron diffusion in the presence of positron--acoustic-phonon interaction in semiconductors. Our treatment of the positron--acoustic-phonon interaction is based on an analogy with hole--acoustic-phonon interaction in contrast to existing theories which are based on electron--acoustic-phonon interaction. We treat the positron--acoustic-phonon interaction on the basis of the deformation-potential approximation and calculate the relaxation rate by using a self-consistent Green's-function method. We find that transverse phonons play a very important role in the diffusion process, along with the longitudinal phonons. This effect is not predicted by previous theories. The present theory is applied to calculate positron--acoustic-phonon relaxation rates and diffusion coefficients for Si, Ge, and GaAs. We find that the contribution of transverse phonons to the diffusion coefficient depends on the deformation-potential constants and also on the type of semiconductor, but is almost independent of temperature.