Investigation of indium oxide band structure with DFT method

Band gap of indium oxide is still a wonderful matter. Based on optical measurements the presence of an indirect band gap has been suggested, which is 0.9 to 1.1 eV smaller than the direct band gap at the 𝛤 point. This could be caused by strong mixing of O 2p and In 4d orbitals in 𝛤. We have performed density functional theory calculations using the LDA-U and the GGA-U methods to demonstrate the contribution of the In 4d states and the effect of spin-orbit coupling on the valence band structure. Although an indirect band gap is obtained, the energy difference between the overall valence band maximum and the highest occupied level at the 𝛤 point is less than 50 meV. It is concluded that the experimental observationcannot be related to the electronic structure of the defect free bulk material