Quasiparticle and excitonic effects in WSi2N4 monolayer

Abstract

Very recently, a new two-dimensional material, named WSi2N4, has been successfully synthesized in an experiment, which has high stability and semiconducting nature [Science 369, 670–674 (2020)]. Motivated by this achievement, herein, the electronic and excitonic optical properties of WSi2N4 monolayer are systematically investigate by employing the density functional theory (DFT) combined with many-body perturbation theory (MBPT). The phonon dispersion spectrum guarantees the dynamical stability of the monolayer. The electronic band structure indicates that WSi2N4 monolayer is a semiconductor with an indirect band gap of 2.06 eV. This value is corrected to be 3.37 eV at the G0W0 level of theory. The optical spectrum achieved from solving the Bethe-Salpeter equation on top of the GW shows an optical band gap of 2.99 eV, which corresponds to a strongly bound bright exciton with a binding energy of 1.34 eV. Such large binding energy together with high effective mass (0.56 m0) and small Bohr radius (2.26 Å) suggest that the excitons in WSi2N4 monolayer have the Frenkel exciton characteristics, which means the excitonic states are highly stable at room temperature. This study discloses the underlying physics behind the electronic and optical properties of WSi2N4 monolayer and suggests it as an appropriate candidate for optoelectronic applications at room temperature.