  Point defects in the binary group-IV monochalcogenide monolayers of SnS,
SnSe, GeS, GeSe are investigated using density-functional-theory calculations.
Several stable configurations are found for oxygen defects, however we give
evidence that these materials are less prone to oxidation than phosphorene,
with which monochalcogenides are isoelectronic and share the same orthorhombic
structure. Concurrent oxygen defects are expected to be vacancies and
substitutional oxygen. We show that it is energetically favorable oxygen be
incorporated into the layers substituting for a chalcogen (O S/Se defects), and
different from most of the other defects investigated, this defect preserves
the electronic structure of the material. Thus, we suggest that annealing
treatments can be useful for the treatment of functional materials where loss
mechanisms due to the presence of defects are undesirable.
