Electronic and optical properties and quantum tuning effects of As/Hfs₂ van der Waals heterostructure

Abstract

Stacking two or more monolayer materials to form van der Waals heterostructures is an effective strategy to realize ideal electronic and optoelectronic devices. In this work, we use As and HfS₂ monolayers to construct As/Hfs₂ heterostructures by six stacking manners, and from among them the most stable structure is selected to study its electronic and optic-electronic properties and quantum regulation effects by hybrid functional HSE06 systematically. It is found that the As/Hfs₂ intrinsic heterostructure is a II-type band aligned semiconductor, and its band gap can be significantly reduced (~ 0.84 eV) in comparison with two monolayers (band gap > 2.0 eV), especially the valence band offset and conduction band offset can increase up to 1.48 eV and 1.31 eV, respectively, which is very favorable for developing high-performance optoelectronic devices and solar cells. The vertical strain can effectively adjust the band structure of heterostructure. The band gap increases by tensile strain, accompanied with an indirect-direct band gap transition. However, by compressive strain, the band gap decreases rapidly until the metal phase occurs. The applied external electric field can flexibly adjust the band gap and band alignment mode of heterostructure, so that the heterostructure can realize the transformation between I-, II-, and III-type band alignments. In addition, intrinsic As/Hfs₂ heterostructure has ability to strongly absorb light in the visible light region, and can be further enhanced by external electric field and vertical strain. These results suggest that the intrinsic As/Hfs₂ heterostructure promises to have potential applications in the fields of electronic, optoelectronic devices and photovoltaic cells.