First principle calculation of Se-vacancy monolayer 2H–MoSe2

Abstract

The photocurrent of intrinsic and Se-vacancy monolayer 2H–MoSe2 in zigzag direction is calculated by using first-principles method based on the Keldysh nonequilibrium Green's functional theory. Furthermore, the photo response for the circular photogalvanic effect (CPGE) and linear photogalvanic effect (LPGE) at different photon energies are investigated. The results show that the photon energy of 2.5 eV is a turning point. Lower than the photon energy of 2.5 eV, the CPGE of intrinsic monolayer 2H–MoSe2 is steadily larger than its LPGE counterpart by the amount of the absorbed photon energy. However, the curve becomes steeper as the photon energy approaches 2.5 eV and reaches the maximum at 2.7 eV. The CPGE and LPGE curves of the Se-vacancy 2H–MoSe2 also change around 2.5 eV, i.e., the CPGE is slightly smaller than LPGE with the photon energy lower than 2.5 eV and absorbs enough photon energy to become larger than LPGE with the photon energy larger than 2.5 eV. These results can be explained by the electron transition between the valence and conduction bands, which is proportional to the density of states according to the Fermi's Golden rule. In addition, we also study the relationship between the photocurrent of LPGE and CPGE and the polarization angles θ and φ. Our results have the potential to be utilized in the optimization of monolayer transition metal dihalide-based photodetectors.