PROPAGATION AND LOCALIZATION OF VERTICALLY POLARIZED PLASMON-LO PHONON COLLECTIVE EXCITATIONS IN DOPED GaAs/AlAs SUPERLATTICES

摘要

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 character-istical asymmetries of the Raman lines corresponding to the coupled modes were found in samples with different electron densities. It was shown that the observed asymmetries are caused by the dispersions of the coupled plasmon-LO phonon excitations. In accordance with the theoretical predictions, the coupled modes reveal either a plasmon or a phonon character, depending on the electron density. The transition from propagating to localized superlatice plasmons was observed with the increase of the doping concentration.