Electric field tunable band-gap crossover in black(blue) phosphorus/g-ZnO van der Waals heterostructures

Abstract

Electrically controlled band-gaps and efficient carrier confinement or separation are crucial in the design of nanoscale light-emitting and photoelectric devices. Here, using hybrid density functional calculations, we studied the electronic and optical properties of graphitic zinc oxide (g-ZnO) and phosphorene van der Waals (vdW) heterostructures. We found that although black(blue) phosphorus/g-ZnO shows an intrinsic type-I(type-II) band alignment with a direct(indirect) band-gap, a vertical electric field can induce type-I-to-type-II transition for the black phosphorus/g-ZnO, and the band edges of blue phosphorus/g-ZnO can be electrically modulated to obtain a direct band-gap at the Γ point. Intriguingly, the heterostructures also showed improved visible-UV light adsorption compared with the single-layers. Our findings reveal that g-ZnO can be used not only as a capping layer to protect the electronic characteristics of phosphorene, but also as the active layer to tune the electronic and optical properties of phosphorene, which may promote potential phosphorene-based applications in the future.