ACOUSTIC PLASMON BRANCHES IN PHOTOEXCITED SEMICONDUCTORS

We analyze the spectra of electronic elementary excitations in a double component plasma of photoinjected electrons and holes in semiconductors under continuous laser illumination. We show that in the resulting nonequilibrium steady state four types of elementary excitations of the photoinjected carrier system can be identified. Two are the expected single quasi-particle excitations and the higher frequency plasma wave, and two novel ones at low frequencies labelled as acoustic plasma waves that are well defined under particular conditions. These acoustic branches are interpreted as corresponding to the collective motion of each type of carriers interacting through the screened part of Coulomb interaction. © 1990.