Some Physical and Optical Properties of the a-Se85SbxS15-x Film System

Abstract

Thin films of a-Se 85 Sb x S 15-x (x = 0, 3, 6, 9, 12 and 15 at%) were deposited on glass substrates at 300 K by the conventional thermal evaporation technique. Systematic investigations of the thermal stability of Se-Sb-S thin films have been performed. The values of K gl (coefficient of the glass thermal stability) and Tg (the glass transition temperature) were found to vary for different compositions. The optical band gap (E opt ) was found to decrease with increasing Sb content. The mechanism of optical absorption follows the rule of indirect allowed transitions. The observed change of E opt can be partially explained using the density of states model in amorphous solids proposed by Mott and Davis. It was found that the effect of annealing (above the glass transition temperature) of the studied films causes a reduction in the optical band gap. The relationship between the optical gap and chemical composition in the film systems is discussed in terms of the average coordination number m, the glass transition temperature Tg and cohesive energy CE. The optical energy gap E opt and cohesive energy CE are found to be in a negative correlation in the present system.