Band alignment control in a blue phosphorus/C₂N van der Waals heterojunction using an electric field

Well-controlled band engineering of a blue phosphorus/C2N van der Waals (vdW) heterojunction is investigated by density functional theory (DFT) calculations. The heterojunction has a natural type-II band alignment with a direct band gap value of 1.514 eV, which gives the enormous potential for solar cell applications. When the heterojunction is under solar illumination, the photogenerated electron-hole pairs can separate out on the disparate monolayers effectively. It induces the formation of spatially indirect excitons. Furthermore, it is found that the band gap of this heterojunction exhibits approximately linear variation with respect to the perpendicular external electric field. Very interestingly, a band alignment change from type-II to type-I occurs at an applied electric field of -0.2 V Å-1. This characteristic provides an attractive possibility to obtain novel multifunctional devices.