Effect of Te addition on the optical properties of As2S3 thin film

Bilayer thin films of Te/As2S3 were prepared from Te and As2S3 by thermal technique under high vacuum. Optical constants were calculated by analysing the transmission spectrum in the spectral range 400–1100 nm. The optical band gap decreases with the addition of Te to As2S3. The decrease of optical band gap has been explained on the basis of density of states and the increase in disorder in the system. We have irradiated the as-deposited films using a diode pumped solid state laser of 532 nm wavelength to study photo-diffusion of Te into As2S3. The changes were characterised by Fourier Transform Infrared and X-ray Photoelectron Spectroscopy (XPS). The optical band gap is found to be decreased with the light irradiation which is proposed due to homopolar bond formation. The core level peaks in XPS spectra give information about different bond formation.