Optical and Tunable Electronic Properties of AlAs/InSe Van Der Waals Heterostructures

The formation of heterostructures from different two-dimensional (2D) materials stacked on top of each other has become a current research hotspot. Heterojunctions can retain the characteristics of their constituent materials and produce new characteristics. Stacking AlAs monolayers on InSe monolayers to form AlAs/InSe heterojunctions is an effective way to improve the defects of its constituent materials. This project is based on density functional theory, using the first-principles plane wave ultra-soft pseudo-potential method to calculate the geometric structure, electronic properties and optical properties of AlAs/InSe heterostructures. By changing the stacking method of the heterojunction and adjusting the distance between layers, the most stable theoretical model is found. The density of states (DOS) and energy band gap are calculated, and the properties of AlAs/InSe heterojunction are analyzed by applying external conditions. The results show that the AlAs monolayer has an indirect band gap of 1.88 eV, the InSe monolayer has an indirect band gap of 2.02 eV, and the band gap of the AlAs/InSe heterostructure is significantly reduced, with a value of 1.28 eV and typical Type-II band arrangement. When the layer spacing is adjusted or an external electric field and strain are applied, the band gap value of the heterostructure can be effectively changed. Interestingly, when an electric field of 5 V/nm is applied, the heterostructure realizes the transition from Type-II to Type-I. And when the electric field intensity continues to increase, AlAs/InSe heterojunction can complete the transition from semiconductor to metal. At the same time, it is found that a similar situation occurred in the heterojunction when strain was applied. Taking into account the underestimation of the semiconductor band gap by the Perdew-Burke-Ernzerhof (PBE) functional, the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional is used to calculate the optical properties and obtain more accurate results. Compared with the isolated monolayer, the absorbance of the AlAs/InSe heterostructure is significantly improved, especially in the ultraviolet region. In summary, the research results show that the new two-dimensional AlAs/InSe heterojunction can be a strong candidate for optoelectronic materials and UV detector parts.