Interaction of optical and interface phonons and their anisotropy in GaAs/AlAs superlattices: Experiment and calculations

The angular anisotropy of interface phonons and their interaction with optical phonons in (001) GaAs/AlAs superlattices are calculated and experimentally studied. Experiments were performed by Raman light scattering in different scattering geometries for phonons with the wave vector directed normally to the superlattice and along its layers. Phonon frequencies were calculated by the extended Born method taking the Coulomb interaction into account in the rigid-ion approximation. Raman scattering spectra were calculated in the Volkenshtein bond-polarizability approximation. Calculations confirmed that the angular anisotropy of phonons observed in experiments appears due to interaction (mixing) of optical phonons, in which atoms are mainly displaced normally to superlattices, with interface phonons (TO-IF modes). In the scattering geometry, when the wave vector lies in the plane of superlattice layers, the mixed TO-IF modes are observed under nonresonance conditions. The Raman spectra for TO-IF modes depend on the mixing of atoms at heteroboundaries.