Large-scale spin-polarized DFT calculation of electronic properties of GaAs with defects

We report a spin-polarized density functional theory (spin-polarized DFT) study of the electronic properties of defected GaAs bulk modeled by a supercell of 216 atoms. MetaGGA (mBJ-LDA) is used to describe the exchange-correlation and the PAW method is used to integrate spin–orbit (SO) interaction to suitably account for the broken inversion-symmetry of GaAs. We note that the band-gap and the split-off band at Γ of the clean (no defects) GaAs bulk are in agreement with that of the experiment and with other sophisticated yet very expensive methods, GW and HSE. For the GaAs bulk with defects, we found that at ~1% concentration of As-antisite (AsGa), mid-gap state appears. The structural origin of this state is a AsGa-centered tetrahedral cluster and not the AsGa point defect alone. The energy level of the mid-gap state, obtained with respect to the conduction band minimum, is 0.791 eV, in excellent agreement with the below band-gap excitation at 0.790 eV. This energy level reduces to 0.645 eV when SO interaction is neglected, indicating the significance of SO effects in the stabilizing mid-gap states. The defected GaAs also exhibits split-off band at Γ with a value similar to that of clean GaAs.