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

Abstract

© 2015 Elsevier B.V. We present a Raman scattering study of LO phonon-coupled modes in Be-doped, p-type In0.53Ga0.47As with hole densities ranging from 2.2×1017 to 2.4×1019 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.