Electronic structure and tunability of 2D hexagonal boron arsenide
Group theory and density functional theory methods are combined to obtain compact and accurate $k\cdot p$ Hamiltonians that describe the bandstructures around the $K$ and $\Gamma$ points for the 2D material hexagonal boron arsenide (h-BAs) predicted to be an important low-bandgap material for electric, thermoelectric, and piezoelectric properties that supplements the well-studied 2D material hexagonal boron nitride. Hexagonal boron arsenide is a direct bandgap material with band extrema at the $K$ point. The bandgap becomes indirect with a conduction-band minimum at the $\Gamma$ point subject to a strong electric field or biaxial strain. At even higher electric field strengths (approximately 0.75 V/$\r{A}$) or a large strain ($14$~\%) 2D hexagonal boron arsenide becomes metallic. Our $k\cdot p$ models include to leading orders the influence of strain, electric, and magnetic fields. Excellent qualitative and quantitative agreement between density functional theory and $k\cdot p$ predictions are demonstrated for different types of strain and electric fields.