Visible—near-uv optical spectra ofa−GexSe1−x

Dielectric function spectra from 2 to 5 eV are reported for a series of $a-{\mathrm{Ge}}_x{\mathrm{Se}}_{1-x}$ films in the compositional range $0.20<~x<~0.52$. The spectra show two broad absorption features which shift systematically with changes in composition. From these shifts we determine the compositional changes in the lone-pair to antibonding band gap and in the bonding to antibonding band gap. The results are compared with theoretically predicted band-center and bandwidth changes.