Strain-tunable band alignment of blue phosphorus-WX_2 (X= S/Se/Te) vertical heterostructures: from first-principles study

摘要

In the scope of two-dimensional (2D) material study, blue phosphorus (BP) is a new graphene-like layered structure that has been successfully synthesized in the experiment after it was theoretically proved to be thermostable. These 2D structured functional materials have great potential in the next-generation nanoscale electronic devices for their unique features. Here, we composite BP and monolayer WX_2 (X= S/Se/Te) based on van der Waals force (vdW) interaction to obtain well-defined type-Ⅱ band alignment heterostructures. A systematic theoretic study was conducted to explore the interlayer coupling effects and the bands' re-alignment of the BP-WX_2 heterostructure after the strain was applied. Nowadays, many researches have proved that 2D materials can be used to degrade pollutants or used as a potential photovoltaic cell material to obtain high performance. We here twist BP and WX_2 (X= S/Se/Te) into different angles to lay a theoretical framework on the band alignment and carriers' separation. It reveals that the electronic properties of freestanding BP and WX_2 can be roughly preserved in the corresponding heterostructures. Upon applying strain, band alignment exhibits significant adjustability through varying external strain. The heterostructures are type-Ⅱ in a certain strain range, within which the carriers can be effectively separated spatially. These heterostructures undergo a transition from semiconductor to metal when a certain strain is imposed. This work not only provides a deep insight into the construction of heterostructures, but presents a new possibility for strain engineering that is both flexible and feasible and can be used for diverse applications.