The composition dependence of the optical band gap in Ge doped Se-Te glassy alloy

Bulk glasses with the chemical composition (Se80 Te20)100−x Gex (x = 0, 2, 4, 6) have been prepared from high purity constituent elements. Fragments of the bulk glasses are used to deposit thin films by vacuum thermal evaporation and compositional dependence of the optical and physical properties have been studied. It has been found that optical absorption is due to indirect transition and the optical band gap Eg increases with increasing Ge content in Se-Te glassy alloy. The relationship between the Eg and chemical composition is discussed in terms of cohesive energy and co-ordination number.