Theory of the One-Phonon Resonance Raman Effect

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Abstract
Resonant enhancements of Raman scattering cross sections for photons near electronic resonances are calculated for ordinary allowed scattering and for intraband Fröhlich scattering, which is of higher order in the wave vectors and thus forbidden. Exciton effects are included exactly in the hydrogenic approximation via numerical calculations using the Green's-function formulation. Much greater enhancements are found for forbidden than for allowed lines, and it is shown that forbidden lines can become comparable to allowed lines near resonance with large Wannier excitons. It is predicted to be feasible to observe one-LO-phonon lines in crystals (e.g., TlCl and TlBr) in which such transitions are always forbidden. Comparison with experiment for CdS is presented.