Percolation-controlled conduction in chalcogenide glass semiconductors

The applicability of effective-medium percolation theory (EMPT) to the composition dependence of the electrical conductivity is discussed for binary and multicomponent chalcogenide glasses. Calculations assuming a random mixture of atoms, which are applied to explain the experiment for As-Te films by Ast, do not agree with experiments on all the systems considered. By assuming a strong chemical ordering which forms microscopic molecular species, the conductivity over the measured compositional range can be well described with EMPT in the As-Se, As-S, and As₂{Se}₃$-${Sb}₂Se₃ systems, except for Te-Se, As₂{Se}₃$-${As}₂Te₃, and As₂{S}2.63$-Te which contain the isomorphous Te, Se, and S atoms. Chalcogenide glasses can be classified roughly into three groups: a "random mixture of atoms" type, a "strong chemical ordering" type, and an "isomorphous-atom" type. It is suggested that EMPT has broad application in structural studies of chalcogenide glasses.