First-principles calculations of electronic and optical properties of orthorhombic Bi2Se3 nano thin film

Abstract This study explored the electronic and optical properties of nano-thin film orthorhombic bismuth selenide (Bi2Se3) using first-principles approach. The thin films were modelled in the [001] direction using slab geometry supercell with vacuum along z-direction so that periodic images and slab can be managed independently. We obtained band gap of 0.730 eV, 0.566 eV and 0.690 eV for 1, 2 and 3 slabs respectively. It shows dependence of band structure to the thickness of the films. The reduced band gap in Bi2Se3 films is due to the effect of quantum confinement. The electron contributions were increased as the thickness of the thin film increased. We also found that the thickness of Bi2Se3 thin film influences its optical properties. Higher thickness provides higher static dielectric function, refractive index, extinction coefficient, absorption coefficient and loss function. This study demonstrates Bi2Se3 thin film has good optical properties that are useful for optoelectronic applications.