Type II GaS/AlN van der Waals heterostructure: Vertical strain, in-plane biaxial strain and electric field effect

Abstract

In this work, the geometrical structure, stability, electronic and optical properties of the GaS/AlN van der Waals heterostructure have been explored based on first principles calculations considering the effect of vertical strain, in-plane biaxial strain and the electric field. It is demonstrated that, the GaS/AlN van der Waals heterostructure possesses an intrinsic typical type-II band alignment with an indirect band gap of 1.65 eV. Due to the difference of work functions between monolayer GaS and AlN, the electrons transfer from AlN layer to GaS layer, causing a build-in electric field which facilitates the separation of free electrons and holes. The band gap value of the heterostructure is insensitive to the vertical strain, while in-plain biaxial strain is an effective way to tune the band gap. The band gap value is in the range of 0.68–1.82 eV under in-plane biaxial strain of −5%–5%. The band offsets of the heterostructure can be increased by positive electric field and decreased by negative electric field. Meanwhile, the type-II band alignment of the heterostructure is retained under vertical strain, in-plane biaxial strain and the electric field. In addition, for the heterostructure, compare to constituent layers, the optical absorption is enhanced in visible region. These results render GaS/AlN heterostructure as a good candidate for photovoltaic devices. • GaS/AlN van der Waals heterostructure possesses a typical type-II band alignment with an indirect band gap of 1.65 eV. • The band gap of the heterostructure can be effectively tuned by strains and electric field. • The type-II band alignment of the heterostructure is retained under strains and electric field. • Compare to constituent layers, the optical absorption coefficient of the heterostructure is enhanced in visible region.