Optical phonons and polaritons in ZnSiP2

Reflectivity measurements have been made on single crystal ZnSiP 2 using polarized infrared radiation in the wavelength range 4-250 mu m. The data have been analyzed using classical dispersion theory to obtain mode frequencies, strengths and damping factors. A simple group theoretical analysis has been performed and six of the seven predicted infrared active modes have been observed. The polariton dispersion curves have been calculated and the possible use of ZnSiP 2 in resonant Raman scattering from polaritons for the generation of tunable far infrared radiation is discussed.