Realization of Large Scale, 2D van der Waals Heterojunction of SnS₂ /SnS by Reversible Sulfurization

2D van der Waals heterojunction provides an attractive opportunity for realizing novel electronic or optoelectronic devices. It remains challenging to realize high-quality heterostructures through scalable methods such as molecular epitaxy growth (MBE). Here, growth of few-layer SnS thin films is reported on mica and Nb-doped SrTiO₃ (100) substrates by MBE. Then the top layer of SnS film is uniformly sulfurized to monolayer SnS₂ in a sulfur atmosphere, resulting in a high-quality SnS₂ /SnS 2D heterojunction. Furthermore, the SnS₂ layer can be recovered to SnS by annealing SnS₂ /SnS without sulfur supply, indicating the heterojunction formation is reversible. The scanning tunneling spectroscopy measurements on SnS₂ /SnS heterostructure indicate the type-II band alignment in SnS₂ /SnS. The work provides a promising approach to construct artificial 2D heterojunctions with desired properties, which could be extended to other sulfide and selenide systems.