First-principles insights into efficient band gap engineering of the blue phosphorus/g-C ₃ N bilayer heterostructure via an external vertical strain

In this contribution, using DFT calculations, we take systematic insights into the modified structural and electronic properties of two-dimensional (2D) blue phosphorus (blueP)/graphene-like (g-C ₃ N) heterostructure via an external vertical strain. First, four types of representative stacking configurations are considered, i.e., I, II, III and IV pattern, respectively. The calculated results indicate that the III configuration behaves more energetically, structurally and dynamic stable, under which it is chosen for the following calculations. The lattice constants of the individual blueP and g-C ₃ N monolayers, along with their calculated band gaps, are consistent with the previous reported works, supporting the reliability of our theoretical models and computational details. Besides, the relatively large difference in the work function (W _F ) between the isolated blueP and C ₃ N monolayers illustrates a charge transfer from g-C ₃ N to blueP layer, in good accordance to the analysis of charge density difference and Mulliken atomic population of 0.16 e. A built-in electric field (E _int ) has been formed due to the charge transfer at the interface region, which can efficiently hinder the recombination of photongenerated electron-hole pairs, suggesting its significant application prospect in novel optoelectronic devices. A type-II band alignment is presented for the blueP/g-C ₃ N heterostructure, demonstrating it great significance for the application in photoelectronic materials. Furthermore, tunable interlayer distances from 2.2 to 5.0 Å are employed to obtain modulated electronic properties for the blueP/g-C ₃ N heterostructure. Interestingly, there occurs a semiconductor-to-metal transition when D larger than 4.6 Å, indicating its promising application in the field of electronics and nano-electronics. Moreover, tailored work functions can also be acquired by changing the interlayer distance. These findings together predict significant potential for the blueP/g-C ₃ N heterostructure with tunable interlayer distances applied as next-generation nanoelectronic and optoelectronic devices, along with a photocatalyst.