Lead monoxide $\alpha$-PbO: electronic properties and point defect formation

The electronic properties of polycrystalline lead oxide consisting of a network of single-crystalline $\alpha$-PbO platelets and the formation of the native point defects in $\alpha$-PbO crystal lattice are studied using first principles calculations. The $\alpha$-PbO lattice consists of coupled layers interaction between which is too low to produce high efficiency interlayer charge transfer. In practice, the polycrystalline nature of $\alpha$-PbO causes the formation of lattice defects in such a high concentration that defect-related conductivity becomes the dominant factor in the interlayer charge transition. We found that the formation energy for the O vacancies is low, such vacancies are occupied by two electrons in the zero charge state and tend to donate their electrons to the Pb vacancies that leads to ionization of both vacancies.The vacancies introduce localized states in the band gap which can affect charge transport. The O vacancy forms a defect state at 1.03 eV above the valence band which can act as a deep trap for electrons, while the Pb vacancy forms a shallow trap for holes located just 0.1 eV above the valence band. Charge de-trapping from O vacancies can be accounted for the experimentally found dark current decay in ITO/PbO/Au structures.