Inelastic light scattering by collective charge-density excitations in semi-infinite semiconductor superlattices

An analytic expression for the resonant, inelastic light scattering cross section from collective charge-density excitations of a semi-infinite semiconductor superlattice is derived. Raman intensities of bulk and surface modes of an n-type GaAs-${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As sample are analyzed. Calculations show that intersubband surface plasmons have higher intensity than intrasubband ones and should be easier to observe experimentally. The line shapes of bulk spectra are explained in terms of photon broadening and broken translational symmetry in the superlattice direction. A new band of intersubband surface modes, with frequencies below the longitudinal-optical phonon frequency, is found.