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 v elocities, selection rules and efficiency of light scattering by folde d acoustic phonons is presented. Results based on nine different direc tions of the phonon wavevector are tabulated. Some errors found in the literature are corrected. The piezoelectric contributions to the phon on frequencies and scattering intensities are analysed. It is shown th at their influence is the greatest for propagation along [111]. Change s in the elastic stiffness and Pockels coefficients due to the piezoel ectric effect in GaAs are shown to be of the order of 0.1% and 1%, res pectively.