Scattering of hot excitons due to optical phonons in quantum wells: Multiphonon resonant Raman process

The hot-exciton scattering rate by optical phonons is calculated in the framework of the envelope-function approximation in narrow quantum wells (QWs). The exciton-phonon Fröhlich-type interaction is considered and the contributions of the confined phonons and interface modes to the total scattering rate are discussed in terms of the in-plane exciton kinetic energy and quantum-well width. To take into account the full symmetry of the optical phonons a phenomenological approach is employed in which the mechanical and electrostatic matching boundary conditions are fulfilled at QW interfaces. It is shown that the main contribution to the scattering rate comes from intrasubband transition assisted by phonons with even electrostatic potential state. The experimental observation in short period GaAs/AlAs superlattices on the phonon symmetries and their relative intensities of multiphonon resonant Raman process is qualitatively explained in terms of the relative role of the confined and interface optical phonons on the exciton scattering rate.