B₅N₃ and B₇N₅ Monolayers with High Carrier Mobility and Excellent Optical Performance

An ab initio evolutionary search algorithm was combined with density functional theory (DFT) calculations to predict a series of 2-D BN (1 < x/y ≤ 2). Particularly, B₅N₃ and B₇N₅ monolayers have sufficiently low formation enthalpy and excellent dynamic stability that make them promising for synthesis in experiments. Electronic structure calculations reveal that B₅N₃ and B₇N₅ monolayers possess an indirect band gap of 1.99 eV and a direct band gap of 2.40 eV, respectively. The calculated absorption coefficients for B₅N₃ and B₇N₅ monolayers are significantly improved in the low end of the visible region compared with that of 2-D h-BN. Moreover, our calculations reveal that both B₅N₃ and B₇N₅ monolayers have high electron carrier mobilities. The narrow band gaps, high carrier mobilities, strong near-ultraviolet absorption, and high synthesis possibility of B₅N₃ and B₇N₅ monolayers render them promising new materials for application in novel electronics and environmentally benign solar energy conversion.