Nature of the band gap of Tl2O3

The ground state electronic structure of thallic oxide has been a source of controversy in the literature, with Tl2O3 reported to be either a degenerate n-type semiconductor or an intrinsic semimetal with no band gap. Using a screened hybrid density functional theory (DFT) approach, we show that Tl2O3 is a semiconductor with a predicted band gap of 0.33 eV. We rationalize the large optical band gaps reported in experimental studies and demonstrate that previous standard DFT approaches wrongly predict Tl2O3 to be a semimetal. Doubly ionized oxygen vacancies are shown to be the origin of the high carrier concentrations seen experimentally.