Effect of Damping on the Plasmon‐Phonon Coupling in CdS and Gap

Abstract

Abstract The influence of dampings of the free carrier motion and polar lattice vibration on the coupled plasmon‐phonon states is studied both semi‐phenomenologically and experimentally. It turns out that the correct frequencies and damping rates of the normal modes are the roots of the dielectric function ε(ω) for complex ‐values and the dielectric function takes a factorized form. Scattering of the free carriers mainly counteracts the well known coupling mechanism by the electric fields of the two subsystems, and reduces the forbidden frequency gap. Infrared reflection spectra of differently doped CdS and GaP samples and Raman spectra of GaP are analyzed by fitting the optical spectra end calculating the complex roots of ε( ). The analysis shows that the shifts of the normal mode frequencies due to the high scattering rates of free carriers in these materials is beyond the limits of experimental error and that the effect of coupling is completely suppressed in heavily doped Gap. An overall fit of the reflection spectra with a frequency‐independent free carrier damping rate fails in the frequency region of the coupled plasmon‐Phonon modes and at frequencies below them.