OUTGOING EXCITONIC RESONANCE IN MULTIPHONON RAMAN-SCATTERING FROM POLAR SEMICONDUCTORS

The theory of scattering process involving both free electron-hole pairs (EHP's) and Wannier-Mott excitons as intermediate states is developed for high-order multiphonon resonant Raman scattering (MPRRS) from polar semiconductors. The combined scattering mechanism removes the disagreement between experiment and theory which appears in the model of MPRRS via high-energy states of discrete excitons because of the hot exciton instability to decay. The binding of free EHP's into the exciton at the last stage of the process explains both the outgoing excitonic resonance and the small decrease in the peak amplitude with the number of phonons observed for high-order MPRRS. The profile of the outgoing excitonic resonance must be asymmetric because of the strong increase in exciton lifetime below the resonance.