Near-forward/high-pressure-backward Raman study of Zn1-xBexSe (x similar to 0.5) - evidence for percolation behavior of the long (Zn?Se) bond

The apparently universal 1-bond2-mode percolation behavior in the Raman spectra of zincblende semiconductor alloys is generally observed for the short bond only, and not for the long one. In this work we perform a combined high-pressure-backward/near-forward Raman study of the leading percolation-type (Zn,Be)Se alloy (50at.% Be), which exhibits a distinct percolation doublet in the spectral range of its short Be?Se bond, in search of a Zn?Se analogue. The high-pressure-backward insight is not conclusive per se, but clarifies the perspective behind the near-forward Raman study. The latter reveals an unique Zn?Se phonon-polariton. Its fair contour modeling depending on the scattering angle is achieved within the linear dielectric approach, based on ellipsometry measurement of the ZnBeSe refractive index. Somewhat surprisingly this reveals that the phonon-polariton in question is a fractional' one in that it carries only half of the available Zn?Se oscillator strength, as ideally expected in case of a BeSe-like bimodal Raman behavior of the long Zn?Se bond.