Raman scattering from Ge<i>x</i>Si1−<i>x</i>/Si strained-layer superlattices

Abstract

Raman spectroscopy has been used to determine built-up deformation in GexSi1−x/Si strained-layer superlattice grown by molecular beam epitaxy. By comparing peak positions in commensurate superlattices and single layers with those from incommensurate thick layers of the same composition we can obtain a quantitative determination of strain. Linewidths are affected by the presence of inhomogeneous strain, dislocations, and disorder. Lines are always narrower in superlattice samples, indicating better crystalline quality. In particular, the Raman line from the Si layers of the strained-layer superlattices is indistinguishable from that from single-crystalline Si in both linewidth and frequency. This is consistent with the expectation that the entire lattice mismatch is accommodated as a homogeneous tetragonal strain in the alloy layers only.