Study of the Dispersion Relations of the Coupled Phonon-Damped Plasmon Mode inn-GaAs by Light Scattering

Abstract

Recent developments of the study on the coupled LO phonon-electron system are described. A special attention is paid to the behavior of a coupled mode in the Landau damping region in n·GaAs. Capability of the light scattering is also discussed for getting information about the semiconductor surfaces as well as the dispersion and damping of the mode. The study of electron and phonon interactions is of fundamental im­ portance in polar semiconductors. The longitudinal optical (LO) phonons interact with carriers through longitudinal polarization field, causing the well known polaron effects!) as well as a shift of the LO phonon frequency. 2>•3> The existence of the coupled LO phonon-plasmon modes was first predicted by Yokota in the long wavelength limit. 4> Gurevich et al. independently discussed the dispersion of the coupled modes in connection with the possibility of superconductivity in semiconductors. 5) The LO phonon-plasmon system was further studied theoretically for the degenerate polar semiconductors, G),7) where the usual self consistent field method is reliable. 8) Such a treatment is closely related to the theory of the coupled electron-ion system in simple metals. 9>• 10> Fallowing the invention of the laser sources, the opening of the Renaissance was notified in the light scattering spectroscopy which had been a valuable tool in the investigation of vibrational and rotational energy levels of molecules as well as the determination of phonon frequencies in crystalline solids.11> Accordingly theoretical aspects of light scattering also entered upon a new phase. Many exciting effects have been discovered in the field of light scatter­ ing in this decade. Elementary excitations such as phonons, plasmons, magnons and polaritons as well as single particle excitations have been studied extensively_l2)~ 15) Experimental researches on LO phonon and high density