Effect of dispersion of "vertically" polarized collective plasmon-LO-phonon excitations on Raman scattering of strongly coupled GaAs/AlAs superlattices

The coupled plasmon-LO phonon collective excitations polarized normal to the layers were studied by Raman scattering in doped GaAs/AlAs superlattices with broad minibands. Different asymmetries of the Raman lines showing a different character (plasmon or phonon) of the coupled modes were found in accordance with theoretical predictions in samples with different electron densities. A strong influence of the superlattice miniband structure on the localization of the collective excitations was observed. Different strengths of the localization were found for the collective modes with different characteristical frequencies.