Selection rules for light scattering by folded acoustic phonons in superlattices grown in arbitrary directions

The propagation of acoustic waves in superlattices grown in arbitrary directions is considered, and a general formalism for obtaining wave velocities, selection rules and efficiency of light scattering by folded acoustic phonons is presented. Results based on nine different directions of the phonon wavevector are tabulated. Some errors found in the literature are corrected. The piezoelectric contributions to the phonon frequencies and scattering intensities are analysed. It is shown that their influence is the greatest for propagation along [111]. Changes in the elastic stiffness and Pockels coefficients due to the piezoelectric effect in GaAs are shown to be of the order of 0.1% and 1%, respectively.