Theoretical prediction of two-dimensional 1T−MSiN3 (M=V,Nb) with direct bandgap and long carrier lifetime

Motivated by the discoveries on the two-dimensional (2D) ${\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$ family [Y. L. Hong et al., Science 369, 670 (2020)] that can be regarded as 2D transition-metal dinitrides ($M{\text{N}}_{2}$) attached by $\mathrm{Si}\text{\ensuremath{-}}\mathrm{N}$ layers on its two sides, in this work, we propose an emerging 2D $M{\text{SiN}}_{3}$ family, where only one side of $M{\text{N}}_{2}$ monolayer passivated via a $\mathrm{Si}\text{\ensuremath{-}}\mathrm{N}$ layer. Among them, $1T\text{\ensuremath{-}}{\mathrm{VSiN}}_{3}$ and $1T\text{\ensuremath{-}}{\mathrm{NbSiN}}_{3}$ monolayer are determined to be direct-gap semiconductors with a bandgap of 1.24 and 2.92 eV, respectively, calculated on the Heyd-Scuseria-Ernzerhof hybrid functional level. In addition, $1T\text{\ensuremath{-}}{\mathrm{VSiN}}_{3}$ and $1T\text{\ensuremath{-}}{\mathrm{NbSiN}}_{3}$ monolayer are nonmagnetic within its ground state, and can maintain the chemical, dynamical, thermal, as well as mechanical stability. In the framework of quantum many-body perturbation theory, $1T\text{\ensuremath{-}}{\mathrm{VSiN}}_{3}$ and $1T\text{\ensuremath{-}}{\mathrm{NbSiN}}_{3}$ monolayer display strong light-harvesting ability in visible-light region, and have a long carrier lifetime up to the nanosecond level, suggestive of a high light-to-current conversion efficiency. This finding broadens the 2D semiconductors with excellent optical features, and would trigger more interest in this emerging family of $M{\text{SiN}}_{3}$ materials.