First-principles study of the effect of BiGa heteroantisites in GaAs:Bi alloy

First-principles calculations have been carried out to study effects of BiGa heteroantisite defects in GaAs:Bi on the related electronic structures. Our results show that the heteroantisite defect BiGa can be formed after the isovalent impurity BiAs reaches the solubility limit. This BiGa defect is a deep level donor, and the related defect band is composed of 6s state of BiGa hybridized with 4p states of the nearest As atoms. It is also found that the bandgap of GaAs:Bi alloy varies slightly with the increase of Bi compositions, as well as the relative position of the defect level. The co-existing, especially when BiGa and BiAs stay in the first-nearest neighbor, counteract the reduction of the bandgap caused by isovalent impurities BiAs in GaAs:Bi alloy. These results suggest that heteroantisite defect BiGa does not contribute to the reduction of the bandgap of GaAs:Bi alloy, and might be not an ideal candidate for the bandgap engineering of GaAs:Bi alloy.