Laser induced optical properties change by photo diffusion of Sb into As2Se3 chalcogenide thin films

The present study reports the effect of Sb deposition onto As2Se3 film and its subsequent photo diffusion into As2Se3 matrix by 532 nm laser. The bilayer Sb/As2Se3 contains Sb as active, optical absorbing and diffusing layer and As2Se3 as barrier layer. The chemical composition and amorphous nature of the as-prepared thin films were examined by energy dispersive X-ray analysis and X-ray diffraction (XRD) respectively. Optical parameters such as transmitivity, absorption coefficient, optical gap, Urbach energy of the studied thin films were studied by absorption spectroscopy. The mechanism of optical absorption follows the rule of indirect allowed transition model proposed by Tauc. It is observed that after photo diffusion, there is a shift of the optical absorption edge to higher photon energy. The absorption of high energy photons enhances the creation of homopolar bonds due to diffusion which increases the density of defect states. The decrease of optical band gap with the addition of Sb to As2Se3 has been explained on the basis of density of states and the increase in disorder in the system. The X-ray photoelectron spectroscopy measurements show the different bonding behavior due to photo induced diffusion. This type of change is generally irreversible in nature which can be used for optical recording purpose.