Intrinsic stoichiometry and oxygen-induced p-type conductivity of pyrite FeS₂

The stoichiometry and ubiquitous observation of p-type conductivity of synthetic pyrite FeS₂ thin films are investigated via first-principles computations of native (vacancies, interstitials, antisites) and extrinsic (O_S, O_i) point defects. Native defects have high formation energies and are predicted to occur in low concentrations within the Fe- and S-rich limits, showing that pyrite should be intrinsically stoichiometric. Under sufficiently oxidizing conditions, O_S becomes the most dominant defect type and induces p-type conductivity. At the experimental oxygen impurity concentration, the hole concentration is predicted to be O(1019) cm^-3, in agreement with Hall measurements reported in the literature. Therefore, we attribute the unintentional p-type conductivity of pyrite to oxygen impurities and propose that improvements in device performance may be achieved under more reducing conditions.