Physics of intrinsic point defects in bismuth oxychalcogenides: A first-principles investigation

As quasi two-dimensional semiconductors, bismuth oxychalcogenides (BOXs) have been demonstrated as potential candidates for high-speed and low-power electronics because of their exceptional environmental stability and high carrier mobility. Here, thermodynamics of growth and a series of intrinsic defects in BOXs are studied using first-principles calculations. Comparing the chemical potential phase diagrams of BOXs, we find that it is easier to grow Bi₂O₂Se than to grow Bi₂O₂S or Bi₂O₂Te. It is most difficult to grow stable Bi₂O₂Te because of the existence of various binary phases. Under Se-poor conditions, the intrinsic point defects of Bi replacing Se (Bi_Se) and Se vacancy (V_Se) can form easily and behave as donors because of low formation energy, which is the reason for the n-type character of as-grown Bi₂O₂Se in experiments. For Bi₂O₂S, the donor point defect of Bi substituting S (Bi_S) is also dominant, leading to an n-type carrier. This study of thermodynamics and the physics of intrinsic point defects provides a valuable understanding of BOXs.