Is p-Type Doping in TeO₂ Feasible?

Abstract

Wide-bandgap two-dimensional (2D) β-TeO2 has been reported as a high-mobility p-type transparent semiconductor (Nat. Electron. 2021, 4, 277-283), attracting significant attention. This “breakthrough” not only challenges the conventional characterization of TeO2 as an insulator but also conflicts with the anticipated difficulty in hole doping of TeO2 by established chemical trends. Notably, the reported Fermi level of 0.9 eV above the valence band maximum actually suggests that the material is an insulator, contradicting the high hole density obtained by Hall effect measurement. Furthermore, the detected residual Se and the possible reduced elemental Te in the 2D β-TeO2 samples introduces complexity, considering that elemental Se, Te, and Te1-x Se x themselves are high-mobility p-type semiconductors. Therefore, doubts regarding the true cause of the p-type conductivity observed in the 2D β-TeO2 samples arise. In this Letter, we employ density functional theory calculations to illustrate that TeO2, whether in its bulk forms of α-, β-, or γ-TeO2, or in the 2D β-TeO2 nanosheets, inherently exhibits insulating properties and poses challenges in carrier doping due to its shallow conduction band minimum and deep valence band maximum. Our findings shed light on the insulating properties and doping difficulty of TeO2, contrasting with the claimed p-type conductivity in the 2D β-TeO2 samples, prompting inquiries into the true origin of the p-type conductivity.