Folded acoustic phonons in Si/GexSi1−xstrained-layer superlattices

Abstract

We present a detailed Raman scattering study of folded longitudinal acoustic modes in Si/${\mathrm{Ge}}_{\mathrm{x}}$ ${\mathrm{Si}}_{1\mathrm{-}\mathrm{x}}$ strained-layer superlattices with 0.2≤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≥275 Å) 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.