A two-dimensional MoSe2/MoSi2N4 van der Waals heterostructure with high carrier mobility and diversified regulation of its electronic properties

Abstract

Two-dimensional (2D) van der Waals heterostructures (vdWHs), composed of two or more 2D monolayer (ML) materials, provide more opportunities for the application of 2D materials. Here, we have designed a 2D vertical MoSe₂/MoSi₂N₄ vdWH and estimated its electronic and optical properties as well as the effects of applying strain and electric fields (E-fields) using first-principles calculations within density functional theory. We have indicated that the MoSe₂/MoSi₂N₄ vdWH is a type-I direct bandgap vdWH with a bandgap of 1.39 eV, in which both the valence band maximum and conduction band minimum are mainly contributed by the MoSe₂ ML. Intriguingly, the hole mobility in this vdWH is one order of magnitude higher than that in an isolated MoSe₂ ML, up to 10⁴ cm² V⁻¹ s⁻¹, which is attributed to its larger in-plane stiffness and smaller deformation potential. Furthermore, the optical absorption is greatly improved compared to both the isolated MoSe₂ and MoSi₂N₄ MLs. The electronic properties of such a vdWH can well respond to the application of strain and external electric fields, leading to a transition not only between type-I and type-II vdWHs but also between direct and indirect bandgap semiconductors. The tensile strain can enhance the optical absorption in the visible region, while the compressive strain has made optical absorption more superior in the ultraviolet region. Both positive and negative E-fields can transform the system to a type-II vdWH, and especially the positive E-field enables the properties of type-II and direct bandgap vdWHs to coexist. Our findings provide strategies to enhance the performance of MoSe₂ MLs in optoelectronic devices and also broaden the application of MoSi₂N₄ MLs.