Doubly and triply resonant raman scattering by LO phonons in GaAs/AlAs superlattices

We report measurements on a GaAs/AlAs superlattice with a splitting between the n=1 heavy- and light-hole bands nearly equal to the energy of two LO phonons. This condition produces triply resonant Raman scattering (three real intermediate states). The combinations of phonons and the polarization of this resonance can be explained by the dispersion of the phonons of B2 symmetry and the mixing between the hole bands. In one-phonon scattering we attribute a shift in the resonance between the two polarization configurations to doubly resonating impurity-induced Fröhlich scattering.