First-principles study of electric field and strain modulation in GaS-BSe vdW heterostructured bilayer for bandstructure engineering

Inspired by previous studies on the electronic properties of the two-dimensional (2D) hexagonal structure group III-VI binary monolayers, this work further explores possible heterostructures and their potential applications. People have been focusing on transition metal dichalcogenides (TMDCs) based materials for a long time, while the low mobility greatly hinders their further application. After years of exploration and research, the related composite forms and synthesis methods for constructing a heterostructure with ideal band alignment have been well developed. Based on the density functional theory (DFT), we here combine monolayer GaS and BSe through vdW interaction to obtain a new heterostructure form with well-defined type-II alignment. This work proves for the first time that GaS-BSe heterostructures can fully meet all ideal criteria and has a better mobility than pristine structures. We found that the applied electric field can adjust the band alignment between type-I and type-II, while the applied strain can maintain two heterostructures within a relatively wide type-II range, thereby effectively separating the light-induced carriers in space. The tensile strain applied structure can promote light absorption within the solar spectrum. When an external strain is applied, the predicted efficiency of s-GaS can be as high as 21%. This work provides a promising route to design new vdW heterostructures based on group III-VI monolayers and s-GaS with high flexibility and tunability, and is a potential candidate for new electronic devices and photocatalysts.