Raman scattering study of LO phonon-plasmon coupled modes in p-type InGaAs

Abstract We present a Raman scattering study of LO phonon-coupled modes in Be-doped, p -type In 0.53 Ga 0.47 As with hole densities ranging from 2.2 × 10 17 to 2.4 × 10 19  cm −3 . Two separate phonon-like coupled modes are observed in the optical-phonon spectral region, corresponding to InAs-like and GaAs-like overdamped modes. With increasing free-hole density, these modes exhibit a redshift and their frequencies approach the respective TO frequencies. Unlike the case of n -type material, no high-frequency L + coupled mode could be detected. The Raman spectra are analyzed using a dielectric model based on the Lindhard–Mermin susceptibility that takes into account HH and LH intraband transitions as well as HH–LH interband transitions. The model yields good quality fits to the experimental spectra. It is shown that the inter-valence-band processes introduces an additional damping channel that causes the L + mode to be damped out. The comparison between the Raman spectra and the theoretical line-shape calculations suggests the presence of a residual strain and a reduced sublattice interaction in the most heavily doped samples.