Band gap tuning in aluminum doped two-dimensional hexagonal boron nitride

Recently boron nitride received a lot of attention due to its applications in optoelectronic devices, multi-function composites, and biological materials. Using first-principles calculations, we show that the band gap in aluminum doped two-dimensional hexagonal boron nitride (2D-h-BN) layers strongly depends on Al concentration. We found that increasing Al concentration diminishes the electronic band gap due to the formation of unoccupied intermediate states in the h-BN gap. For Al concentration of 12.5%, the electronic band gap of the doped h-BN becomes 4.1 eV compared to 5.955 eV in the original undoped bulk h-BN material. Such a significant band gap reduction makes doped boron nitride promising for using in deep UV optoelectmnic devices. The impact of interatomic distances between substitutional Al defects in 2D-h-BN was also investigated. The position of defect related intermediate bands (and the band gap of the doped material) depends on the interatomic distances between the substitutional Al atoms. To take into account different structural arrangements of Al defects at the BN monolayer, we performed statistical studies for the band gap distribution in doped materials. We also found that increasing concentration of Al substitutional defects makes the Al-doped h-BN monolayer thermodynamically more stable which is in favor for using heavily doped h-BN in optoelectronic devices.