Band engineering and relative stabilities of hexagonal boron nitride bilayers under biaxial strain

We perform first-principles total-energy calculations to investigate stabilities and electronic properties of hexagonal boron nitride (h-BN) bilayers under biaxial tensile strains. The possible stacking patterns of h-BN bilayers are investigated in detail. We show that the interlayer distances between two layers in h-BN bilayers can be changed under applied strains, and furthermore, they can decrease and increase depending on the stacking patterns of h-BN bilayers. We find that the band gaps are tunable by applying strains. We also find that tensile strains can give rise to a transformation from an indirect- to a direct-gap semiconductor in the case of the most stable stacking bilayer. These results indicate the high importance of h-BN bilayers as future electronic and optoelectronic device materials.