OUTGOING EXCITONIC RESONANCE IN MULTIPHONON RAMAN-SCATTERING FROM POLAR SEMICONDUCTORS

The theory of scattering process involving both free electron-hole pai rs (EHP's) and Wannier-Mott excitons as intermediate states is develop ed for high-order multiphonon resonant Raman scattering (MPRRS) from p olar semiconductors. The combined scattering mechanism removes the dis agreement between experiment and theory which appears in the model of MPRRS via high-energy states of discrete excitons because of the hot e xciton instability to decay. The binding of free EHP's into the excito n at the last stage of the process explains both the outgoing excitoni c resonance and the small decrease in the peak amplitude with the numb er of phonons observed for high-order MPRRS. The profile of the outgoi ng excitonic resonance must be asymmetric because of the strong increa se in exciton lifetime below the resonance.