First-principles calculations of aluminium nitride monolayer with chemical functionalization

Using density functional theory computations, the structures and electronic properties of hydrogenated and fluorinated aluminium nitride (AlN) were systematically investigated. We found that fully hydrogenated AlN (H-AlN-H) is an indirect-bandgap semiconductor which is similar to an AlN monolayer. Interestingly, Janus functionalized AlN (F-AlN-H) is a direct-bandgap semiconductor with a bandgap of 3.076 eV. F-AlN-H bilayer is also a direct-bandgap semiconductor, but its bandgap (only 0.187 eV) is much smaller than that of F-AlN-H monolayer. In addition, the gap values of both the F-AlN-H monolayer and the F-AlN-H bilayer can be continuously modulated by a perpendicular electric field; semiconductor-metal transition can even be obtained by applying a small electric field in the F-AlN-H bilayer. Our results are expected to shed light on the fabrication of electronic and optoelectronic devices based on AlN monolayer.