$\mathrm{BaAs_3}$: A narrow gap 2D semiconductor with vacancy-induced semiconductor-metal transition

Searching for novel two-dimensional (2D) materials is highly desired in the field of nanoelectronics. We here propose a new 2D crystal barium tri-arsenide ($\mathrm{BaAs_3}$) with a series of encouraging functionalities. Being kinetically and thermally stable, the monolayer and bilayer forms of $\mathrm{BaAs_3}$ possess narrow indirect band gaps of 0.87 eV and 0.40 eV, respectively, with high hole mobilities on the order of ~$\mathrm{10^3\ cm^{2}\,V^{-1}\,s^{-1}}$. The electronic properties of 2D $\mathrm{BaAs_3}$ can be manipulated by controlling the layer thickness. The favorable cleavage energy reveals that layered $\mathrm{BaAs_3}$ can be produced as a freestanding 2D material. Furthermore, by introducing vacancy defects monolayer $\mathrm{BaAs_3}$ can be transformed from a semiconductor to a metal. 2D $\mathrm{BaAs_3}$ may find promising applications in nanoelectronic devices.