Is p-Type Doping in SeO₂ Feasible?

The significance of p-type transparent oxide semiconductors (TOS) in the semiconductor industry is paramount, driving advancements in optoelectronic technologies for transparent electronic devices with unique properties. The recent discovery of p-type behavior in SeO₂ has stirred both interest and confusion in the scientific community. In this Letter, we employ density functional theory calculations to unveil the intrinsic insulating characteristics of SeO₂, highlighting substantial challenges in carrier doping. Our electronic structure analyses indicate that the Se 5s² states are energetically positioned too low to effectively interact with the O 2p orbitals, resulting in a valence band maximum (VBM) primarily dominated by the O 2p orbitals. The deep and localized nature of the VBM in SeO₂ limits its potential as a high-mobility p-type TOS. Defect calculations demonstrate that all intrinsic defects in SeO₂ exhibit deep transition levels within the bandgap. The Fermi level consistently resides in the mid-gap region, regardless of synthesis conditions. Furthermore, deep intrinsic acceptors and donors exhibit negative formation energies in the n-type and p-type regions, respectively, facilitating their spontaneous formation and impeding external doping efforts. Thus, the reported p-type conductivity in SeO₂ samples is unlikely intrinsic and is more plausibly attributed to reduced elemental Se, a well-known p-type semiconductor.