Selection rules for light scattering by folded acoustic phonons in low-index Si-based superlattices

We consider the propagation of acoustic waves in Si-based heterojunctions (HJs), quantum wells (QWs) and superlattices (SLs) grown in arbitrary directions, and present a general formalism for obtaining wave velocities, selection rules, and efficiency of Raman scattering (RS) and Brillouin scattering (BS) by folded acoustic-phonons. Results based on nine different directions for the phonon wavevector are tabulated.