Raman Scattering from Plasmon-LO-Phonon Coupled Modes in n-ZnSe

Raman scattering spectra from plasmon-LO-phonon coupled modes in n-ZnSe crystals have been measured. Upper- and lower-branches of the coupled modes have been observed clearly in polarized Raman spectra. It is found that the scattering intensity of the coupled modes depends on the magnitude of the momentum transfer of electrons. This result indicates that the charge density fluctuation mechanism as well as the deformation potential and electro-optic mechanisms contribute to the Raman scattering from the coupled modes in ZnSe. Calculated line-shapes reproduce the observed spectra well. From the line-shape fitting, carrier concentration and plasmon damping constant are determined.