First-principles study of point defects and doping limits in CaO

The simple oxide CaO is a promising quantum-defect host due to its ultrawide band gap and scarcity of spinful nuclei in the crystal lattice. Here, we present results of HSE hybrid-functional calculations for intrinsic point defects in CaO. We discuss the electronic behavior of calcium and oxygen vacancies, calcium and oxygen interstitials, and calcium-oxygen antisites. We identify the dominant defects, and determine the Fermi-level pinning energies of CaO. Calcium and oxygen vacancies are found to be major electron and hole killers, respectively. Interestingly, we find that most band-gap regions of CaO are allowed to place the Fermi level, except those very close to the band edges. We have additionally investigated hydrogen impurities in CaO, considering that wide-band-gap oxides are prone to lack of control of doping due to presence of unintentional hydrogen impurities.