Structural and electronic properties of tri-layer Van der Waals heterostructure

With the significant progress of the research on two-dimensional (2D) materials, van der Waals heterojunctions constructed by stacking several 2D materials are becoming one of the new methods to explore novel low-dimensional materials and modulate the expected new properties. In this paper, we design and investigate four types of tri-layer van der Waals heterojunctions, bilayer-black-phosphorous(BP)/MoS₂, bilayer-blue-phosphorous(BlueP)/MoS₂, BP/graphene/MoS₂ and BlueP/graphene/MoS₂, in terms of their structure, energy bands, local density of states and differential charge density by the way of first principles calculation. Firstly, the formation energy of the tri-layer heterostructures are lower than the corresponding bilayer ones, so that these four structures are relatively easy to prepare in the experiments and have the possibility for practical application. Secondly, the band gap of the four tri-layer heterostructures are narrower than their corresponding bilayer heterojunctions. For the former two structures, it can be attributed to the same more BP or BlueP layers coupled together, as is one of the most effective means to control the spectral response range of photodetectors and make the band gap more easily modulated. For the latter two tri-layer structures, the significantly reduced band gap results not only from the simple graphene incorporation but also from the interaction of graphene with other two layers. More importantly, BP and BlueP can still maintain their band structure and band gap value, indicating that graphene can be used as a promising candidate material to mediate between phosphorene and metal electrodes for improving the contact performance while maintaining the electronic properties of phosphorene. As can be stressed, the band gap of graphene becomes finite, suggesting that the tri-layer van der Waals heterojunction may be the more effective way to modulate the property of graphene. Thirdly, the density of states of the four tri-layer van der Waals heterostructures have no element overlap near the Fermi level, indicating that the different layers do not chemically interact to destroy their original properties. It thus provides an effective method to manufacture low-dimensional optoelectronic devices based on van der Waals force. Finally, the analysis of the differential charge density proves that charge transport occurs at the heterojunction interface and a built-in electric field is formed. As a whole, the above investigations provide a new design for the construction of low-dimensional van der Waals heterojunction photovoltaic devices and photodetector devices.