EXCITONIC EFFECTS IN 2-LO-PHONON RESONANT RAMAN-SCATTERING

The role of electron-hole correlation in resonant Raman scattering by two LO-phonons is analyzed. A theoretical model including excitons bel onging to the discrete and continuous spectra as virtual intermediate states in the Raman process and valid for incident energies below and above the gap is developed. For the exciton-phonon coupling the Frohli ch Hamiltonian is considered. The most important contribution to the R aman scattering efficiency corresponds to the continuous-->discrete--> discrete exciton transition, followed by the discrete-->discrete-->dis crete and the continuous-->continuous-->discrete ones. The model is te sted for GaP, where the scattering efficiency data are available aroun d the E0 critical point, and both the absolute value and the profile o f the scattering efficiency are reproduced without adjustable paramete rs.