Strain-free MoS 2 /ZrGe 2 N 4 van der Waals Heterostructure: Tunable Electronic Properties with Type-II Band Alignment.

Vertically stacked van der Waals heterostructures (vdW-HS) amplify the scope of 2D materials for emerging technological applications, such as nanodevices and solar cells. Here, we present a first-principles study on the formation energy and electronic properties of the heterobilayer (HBL) MoS 2 /ZrGe 2 N 4 , which forms a strain-free vdW-HS thanks to the identical lattice parameters of its constituents. This system has an indirect band gap with type-II band alignment, with the highest occupied and lowest unoccupied states localized on MoS 2 and ZrGe 2 N 4 , respectively. Biaxial strain, which generally reduces the band gap regardless of compression or expansion, is applied to tune the electronic properties of the HBL. A small amount of tensile strain (>1%) leads to an indirect-to-direct transition, thereby shifting the band edges at the center of the Brillouin zone and leading to optical absorption in the visible region. These results suggest the potential application of HBL MoS 2 /ZrGe 2 N 4 in optoelectronic devices.