On the compositional dependence of the optical gap in amorphous semiconducting alloys

Abstract

It is found that the optical gap E AB for amorphous A-B alloys can be determined by the energy gap E A for element A and E AB for the element B in the equation E AB ( Y) = YE A + (1− Y) E B where Y is the volume fraction of element A. Calculations based on a random bond network agree with experiments for SiGe, SbSe, and AsTe films (class A). Calculations based on a chemically ordered bond network which tends to form microscopic molecular species gree with experimental results for the AsSe, AsS, GeTe and Sb 2Se 3As 2Se 3 systems (class B). In contrast to the above systems, agreement with experiment is not obtained for the TeSe, As 2Te 3As 2Se 3 and GeTe 2GeSe 2 systems which contain atoms of both Te and Se (class C). The classification into three types (classes A, B and C) is consistent with the calculation based on effective medium percolation theory which interprets the compositional dependence of the conductivity of chalcogenide glasses.