Urbach absorption edge and disordering processes in As2S3 thin films

The temperature studies of transmission spectra for as-deposited and annealed amorphous As2S3 thin films are carried out. The optical absorption spectra in the range of their exponential behaviour are analysed, and the dispersion dependences of refractive index as well as their temperature variation are investigated. The Urbach behaviour of optical absorption edge is revealed, the Urbach absorption edge parameters are determined, and their temperature dependences are studied. The effect of different type of disordering on the optical absorption processes in As2S3 thin films is studied. A comparative analysis of Urbach absorption edge parameters of As2S3 bulk glasses and thin films is performed.

► Urbach behaviour of absorption edge in As2S3 film is observed. ► Temperature dependences of the optical pseudogap and Urbach energy are well described by the Einstein model. ► Transition from 3-D to 2-D As2S3 leads to an increase of structural disorder.