Some physical and optical properties of the a-Se85SbxS15-x film system

Thin films of a-Se85SbxS15-x (x = 0, 3, 6, 9, 12 and 15 at%) were deposited on glass substrates at 300 K by the conventional thermal evaporation techn ique. Systematic investigations of the thermal stability of Se-Sb-S thin fi lms have been performed. The values of K-gl (coefficient of the glass therm al stability) and T-g (the glass transition temperature) were found to vary for different compositions. The optical band gap (E-opt) was found to decr ease with increasing Sb content. The mechanism of optical absorption follow s the rule of indirect allowed transitions. The observed change of E-opt ca n be partially explained using the density of states model in amorphous sol ids proposed by Mott and Davis. it was found that the effect of annealing ( above the glass transition temperature) of the studied films causes a reduc tion in the optical band gap. The relationship between the optical gap and chemical composition in the film systems is discussed in terms of the avera ge coordination number m, the glass transition temperature 7, 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.