Photoinjected carrier's acoustic plasma oscillations

Abstract

Resorting to the Nonequilibrium Statistical Operator Method (NSOM) we calculate the Raman spectrum of the double (electrons and holes) photoinjected plasma in direct-gap polar semiconductors. It allows us to identify four types of elementary excitations in the photoexcited carrier system. Besides the expected Raman bands corresponding to single quasi-particle excitations and a higher frequency plasma wave (labelled optical), there appear two low-frequency bands. They show a linear energy dispersion relation and are labelled acoustic plasma oscillations. While the optical plasma branch is ascribed to the out of phase collective movement of both types of carriers interacting through the bare Coulomb interaction, the acoustic branches are ascribed to the in-phase oscillation of each type of carriers interacting through the screened part of Coulomb interaction.