Optical absorption edge and Urbach's rule in mixed single crystals of (Ga xIn 1− x) 2Se 3 in the indium rich region

Abstract

The absorption processes at the absorption edge of the ternary system (Ga x In 1− x ) 2Se 3 in the In-rich region were investigated. For all concentrations the absorption coefficient exhibited exponential dependence on photon energy following Urbach's rule. The characteristic Urbach parameters were determined and their temperature and compositional dependence investigated. Analyzing the results along the lines of the general model which takes into account the possible role of several different types of disorder we concluded that the absorption processes in the absorption edge for our mixed solution of binary compounds are the results of the superposition of at least two different mechanisms, one related to the crystal phonons and the other resulting from structural and compositional disorder.