MULTIPLE-PHONON SCATTERING NEAR THE DIRECT ABSORPTION-EDGE IN H-2-PBI2

We have measured resonant Raman spectra of a layer semiconductor, 2H-PbI2, in the exciton and band-to-band transition regions. The structure of multiple scattering by LO phonon found in the spectrum above the band edge is consistent with the model proposed by martin and Varma. The observed broadness of the multi-phonon Raman line is considered to originate from the very large anisotropy in the dispersion of the LO phonon which is characteristic of a layer semiconductor. The polarization memory of the scattered light suggests that the polariton of the higher order exciton is created in the course of the cascade scattering process by the LO phonon. © 1979.