Near-Forward Raman Selection Rules For The Phonon-Polariton In (Zn, Be)Se Alloys

The Raman selection rules of the (Zn-Se, Be-Se)-mixed phonon-polariton (PP) created by "alloying" in the three-mode [1 x (Zn-Se), 2 x (Be-Se)] Zn1-xBexSe system, whose dramatic S-like dispersion (similar to 200 cm(-1)) covers the large frequency gap between the Zn-Se and Be-Se spectral ranges, are studied in its wave vector (q) dependence by near-forward Raman scattering. Both the "collapse" regime away from the Gamma point (q = 0) and the "reinforcement" regime near C are addressed, using appropriate laser lines and Be contents. We find that in both regimes the considered PP, in fact a transverse mode with the mixed mechanical-electrical character, obeys the same nominal Raman selection rules as its purely mechanical variant observed in the standard backscattering geometry. The discussion is supported by contour modeling of the multi-PP Raman line-shapes in their q-dependence within the linear dielectric approach. Published by AIP Publishing.