Coupled Plasmon — Polar Phonon Modes in Semiconductors: Spatial Dispersion and Other Properties

Abstract

It is the purpose of this paper to present a survey on the characteristic properties of the collective excitations of the free electron gas. These excitations are termed plasmons. They are in contrast to excitations of single electrons, so called single particle excitations (SPE). Classically the plasmon is described by a synchronous motion of all free electrons against the positive background of the ions. At infinite wavelength, i.e. wavevector K=O, this motion is solely determined by Coulomb forces and the free electron gas oscillates with the plasma frequency $\Omega _{\text{p}}^2 = n{\text{ }}{e^2}/m{\varepsilon _O}$ against the positive ionic background. For finite wavelength, i.e. K≠O, the electron gas no longer oscillates homogeneously, but density gradients build up. In addition to the motion caused by Coulomb forces then diffusion type motion will occur and the eigenfrequency of the plasmon will change with wavevector:Ω (K). This is what is termed spatial dispersion.