Photo induced optical changes in Sb/As2S3 multilayered film and (As2S3)0.93Sb0.07 film of equal thickness

The increase in optical band gap (photo bleaching) due to light illumination was studied at room temperature as well as at low (4.2 K) temperature for Sb/As2S3 multilayered film of 640 nm thickness by Fourier Transform Infrared Technique. The interdiffusion of Sb into As2S3 matrix results the formation of Sb-As2S3 ternary solid solutions which is explained by the change in optical band gap (Eg), absorption coefficient (α), Tauc parameter (B1/2), Urbach edge (Ee). At the same time, photo darkening phenomena was observed in (As2S3)0.93Sb0.07 film of same thickness both at low and room temperatures. From our X-ray Photoelectron Spectroscopy measurements, we are able to show that some of the As-As, S-S and Sb-Sb bonds are converted into As-S and S-Sb bonds in case of multilayers. We found that the energetically favoured heteropolar bond formation take place by a phonon-assisted mechanism using the lone pair π electrons of S20. But in case of (As2S3)0.93Sb0.07 film, the homopolar bonds are playing a major role.