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

Abstract

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 (BiSe) and Se vacancy (VSe) 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 (BiS) 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.