Folded acoustic phonons in Si/GexSi1-x strained-layer superlattices.

Abstract

We present a detailed Raman scattering study of folded longitudinal acoustic modes in Si/${\mathrm{Ge}}_{\mathrm{x}}$${\mathrm{Si}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$ strained-layer superlattices with 0.2\ensuremath{\le}x<0.5. Rytov's theory of acoustic vibrations in layered media was found to model accurately the observed Raman line frequencies and intensities. Studies of large-period (d\ensuremath{\ge}275 A\r{}) superlattices, where the scattering wave vector of the photon lies outside the mini-Brillouin-zone, have allowed observation of umklapp-mediated Brillouin and Raman lines involving the folding of the photon wave vector.