Microscopic theory of optic-phonon Raman scattering in quantum-well systems

A microscopic theory of Raman scattering by optic phonons is worked out systematically, on the basis of recent advances in our knowledge of the electronic and phonon structure of quantum-well systems. With our recently reformulated analytical expressions for the optical modes, explicit expressions for the Raman tensor for the various phonon modes (interfaces as well as bulklike LO and TO modes) are derived, displaying in full the selection rules regarding polarization configuration, phonon parity, and the phonon-scattering mechanisms. As the theoretical results show, certain specific features of quantum-well wave functions are of special importance for a quantitative theory. Thus heavy- and light-hole mixing effects, and the angular momentum state of the excitons, can play a decisive role in determining the predominant scattering channels. These are illustrated by numerically calculated results for various intra- and intersubband scattering channels. Special emphasis has been given to the Fröhlich-interaction-induced scattering, which is dipole allowed in multiple quantum wells owing to the barrier penetrations and heavy- and light-hole mixing.