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

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.