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) MoSi2N4 family [Y. L. Hong et al., Science 369, 670 (2020)] that can be regarded as 2D transition-metal dinitrides (MN2) attached by Si-N layers on its two sides, in this work, we propose an emerging 2D MSiN3 family, where only one side of MN2 monolayer passivated via a Si-N layer. Among them, 1T-VSiN3 and 1T-NbSiN3 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-VSiN3 and 1T-NbSiN3 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-VSiN3 and 1T-NbSiN3 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 MSiN3 materials.