Raman scattering involving umklapp processes inSiGexSi1−xsuperlattices

Raman scattering from folded acoustic phonons in $\frac{\mathrm{Si}}{{\mathrm{Ge}}_x{\mathrm{Si}}_{1-x}}$ strained-layer superlattices grown by molecular-beam epitaxy is reported. The superlattice periodicity was chosen so that the transferred photon momentum exceeds the minizone momentum $\frac{\pi }{d}$, where $d$ is the superperiodicity. The observed peaks agree very well with calculations involving umklapp and folding of the scattered phonons into the minizone.