The effect of Ta dopant on the electronic and optical properties of anatase TiO2: a first-principles study

Abstract

We study the electronic and optical properties of pure and Ta-doped anatase TiO2 structures using a plane-wave-based first-principles calculation. The pure anatase TiO2 has an indirect band gap of 2.76 eV, while the Ta-doped anatase TiO2 is a metal. Zero-energy dielectric constants of 4.02 and 3.48 were found for E || a and E || c, respectively, in the pure anatase TiO2. Based on the calculated imaginary parts of the dielectric function (ε2), the pure anatase TiO2 has anisotropic interband transition edges of 2.75 eV and 3.55 eV for E || a and E || c respectively, which show an optical dichroism. The Ta-doped anatase TiO2 is found to have metallic behaviour, which is clearly observable through the significantly high electronic absorption in ε2 at the zero energy level. However, the Ta-doped TiO2 also shows anisotropic interband transition edges of 2.55 eV and 3.45 eV for E || a and E || c, respectively, based on ε2. Based on these results, Ta dopant plays an important role for the semiconductor-to-metallic transformation in anatase TiO2. At the same time, Ta dopant also promotes the red-shift of the interband transition edges and enhances the dichroism. This study presents the significant modification in the optical properties of anatase TiO2 due to the presence of Ta dopant based on the dielectric functions.