Light Scattering from Plasmas and Single-Particle Excitations in Cadmium Sulfide near Resonance

Coupled phonon-plasmon excitations and single-particle excitations in CdS have been observed by means of inelastic light-scattering experiments using argon and krypton ion lasers with emission frequencies near that of the CdS band gap. The coupled-mode frequencies, linewidths, and cross sections have been measured as functions of temperature, laser frequency, and carrier concentrations and have been compared with theoretical predictions. The simultaneous observation of coupled one-LO-phonon excitations and uncoupled two-LO-phonon excitations is explained in terms of plasmon dispersion and damping which uncouple the plasmon and LO phonon at wave vectors near $q_{\mathrm{FT}}$, the Fermi-Thomas wave vector.