Stability and electronic structures of native defects in single-layer MoS2

The atomic and electronic structures and stability of native defects in a single-layer MoS2 are investigated, based on density-functional theory calculations. Native defects such as a S vacancy (V-S), a S interstitial (S-i), a Mo vacancy (V-Mo), and a Mo interstitial (Mo-i) are considered. The S-i is found to have S-adatom configuration on top of a host S atom, and the Mo-i has Mo-Mo-i split interstitial configuration along the c direction. The formation energies of the native defects in neutral and charged states are calculated. For the charged states, the artificial electrostatic interactions between image charges in supercells are eliminated by a supercell size scaling scheme and a correction scheme that uses a Gaussian model charge. It is found that the V-S has a low formation energy of 1.3-1.5 eV in the Mo-rich limit condition, and the S-i has 1.0 eV in the S-rich limit condition. The V-S is found to be a deep single acceptor with the (0/-) transition level at 1.7 eV above the valence-band maximum (VBM). The S-i is found to be an electrically neutral defect. The Mo-related native defects of V-Mo and Mo-i are found to be high in formation energy above 4 eV. The V-Mo is a deep single acceptor and the Mo-i is a deep single donor, of which the (0/-) acceptor and (+/0) donor transition levels are found at 1.1 and 0.3 eV above the VBM, respectively.