Resonance Raman scattering from defects in CdSe

Resonance Raman scattering (RRS) in CdSe is investigated in the region of the A excitonic transition. Three new Raman lines at 182, 195, and 208 ${\mathrm{cm}}^{\mathrm{-}1}$ are observed which become stronger than even the line due to the longitudinal optic (LO) phonon under appropriately resonant conditions. The modes at 182 and 195 ${\mathrm{cm}}^{\mathrm{-}1}$ show resonant enhancement at 1.8206 eV whereas the mode at 208 ${\mathrm{cm}}^{\mathrm{-}1}$ and the LO phonon exhibit maximum intensity at 1.8222 eV. The polarized luminescence spectra show that these energies correspond to the excitons bound to two different donors having different site symmetries. The peaks at 182 and 195 ${\mathrm{cm}}^{\mathrm{-}1}$ are assigned to electronic Raman scattering from the levels of a donor complex which does not have the full symmetry of the lattice. Possible mechanisms for the mode at 208 ${\mathrm{cm}}^{\mathrm{-}1}$ are discussed.