Tunable bandgap structures of two-dimensional boron nitride

Electronic structures of two-dimensional (2D) hexagonal boron nitride (h-BN) with different planar strain distributions have been studied using the first principles methods. We found that the 2D h-BN without strain has a large direct bandgap and its bandgap structure strongly depends on the strength and direction of the strain. The bandgap width can be reduced significantly under both symmetrical and asymmetrical strain distributions. Moreover, the bandgap feature exhibits strong anisotropic behaviors. The bandgap remains direct under large symmetrical tensile strain or asymmetrical tensile strain perpendicular to B-N bonds. However, a small amount of symmetrical compressive strain larger than 1.5% or asymmetrical tensile strain parallel to B-N bonds larger than 1.2% turns the direct bandgap into indirect. Our results indicate that optical and electronic transport properties of 2D h-BN can be effectively tuned by applying different planar forces, offering a unique route for designing nanoscale tunable ultrathin optoelectronic devices only one atomic layer thick. c 2008 American Institute of Physics. [DOI: 10.1063/1.3006138]