RAMAN-SCATTERING FROM COUPLED PLASMON-PHONON MODES IN HGTE

An inelastic-light-scattering experiment from the (100) face of p-type HgTe, a zero-band-gap semiconductor, is reported. The spectral features, which involve coupling of the longitudinal phonon mode with the multicomponent plasma comprised of light electrons in the 8c conduction band and heavy holes in the 8v valence band, are analyzed by calculating Im[μ-1(q,)], where μ(q) is the frequency- and wave-vector-dependent dielectric function of the medium. The sharp peak at 138 cm-1 is ascribed to forbidden LO-phonon scattering. The partially screened allowed LO phonon appears as a broad peak around 127 cm-1, which is higher than the TO-phonon frequency (118 cm-1). The hole carriers give rise to additional features in the spectrum around 160 cm-1. The results of infrared-reflectivity measurements by Grynberg et al. are also discussed in light of Raman data. While the ir spectra can be analyzed using μ(), it is seen that a finite wave vector involved in the light-scattering experiment modifies the phonon-plasmon spectrum profoundly. © 1990 The American Physical Society.