Resonant Raman Scattering at the Critical Points of Semiconductors

We formulate a theory of the one-phonon resonant Raman scattering of light in semiconductors. Emphasis is placed on the scattering near the critical points. Resonance enhancement is found at the saddle points just as in the case of the $M_0$ edge. The effect of the electron-hole interaction on the scattering is discussed within the framework of the Slater-Koster interaction. An enhancement is predicted near the saddle points. The treatment is extended to include the effect of metastable excitons. Again an enhancement is predicted in addition to resonant scattering near the metastable exciton energies. It is suggested that more careful experiments are needed in the III-V and II-VI compounds to make contact with the theory.