Optical bowing in zinc chalcogenide semiconductor alloys

Alloys of zinc chalcogenides exhibit both some of the smallest (for $\mathrm{Zn}{\mathrm{S}}_{x}{\mathrm{Se}}_{1\ensuremath{-}x}$) and the largest (for $\mathrm{Zn}{\mathrm{S}}_{x}{\mathrm{Te}}_{1\ensuremath{-}x}$) optical bowing observed in isovalent semiconductor systems. A theoretical analysis of this effect, by use of self-consistent band-structure techniques for ordered 50%-50% alloys in the CuAu-I structure, predicts correct bowing parameters and chemical trends, yet suggests a physical model which is altogether different from the virtual-crystal model.