Nature of the band gap ofTl2O3

Abstract

The ground state electronic structure of thallic oxide has been a source of controversy in the literature, with Tl${}_{2}$O${}_{3}$ 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 Tl${}_{2}$O${}_{3}$ is a semiconductor with a predicted band gap of 0.33 $\mathrm{eV}$. We rationalize the large optical band gaps reported in experimental studies and demonstrate that previous ``standard'' DFT approaches wrongly predict Tl${}_{2}$O${}_{3}$ to be a semimetal. Doubly ionized oxygen vacancies are shown to be the origin of the high carrier concentrations seen experimentally.