Optical properties change in Sb/As2Se3 bilayer thin film

Abstract

Bilayer thin films of Sb/As2Se3 were prepared from Sb and As2Se3 by thermal evaporation technique under high vacuum. The optical transmission spectra of the as-prepared As2Se3 and Sb/As2Se3 films were taken by FTIR spectrophotometer. The transmission % is found to be decreased by Sb deposition. It was found that the optical band gap decreased from Eg=1.76 eV for As2Se3 film to Eg=1.72 eV of Sb/As2Se3 (as-prepared) film as the absorption edge shifted to lower photon energies with the deposition of Sb layer on it. The decrease of optical band gap has been explained on the basis of density of states and the increase in disorder in the system. This deposition of Sb layer creates more number of homopolar bonds which are responsible for the decrease in the band gap that we can see in the XPS core level spectra. The XPS core level spectra were obtained with monochromatic Mg Kα X-rays (1253.6 eV) at a vacuum of ~10−9 Torr. The changes were supported by the corresponding changes in the XPS core level spectra of As3d, Se3d, and Sb4d. Due to Sb deposition on As2Se3 film, Sb-Sb bonds are formed at the surface of the bilayer film causing the reduction of the optical band gap.