Geometric, electronic, and optical properties of MoS₂/WSSe van der Waals heterojunctions: a first-principles study

Van der Waals (vdW) heterojunctions constructed by vertical stacking two-dimensional transition metal dichalcogenides hold exciting promise in realizing future atomically thin electronic and optoelectronic devices. Recently, a Janus WSSe structure has been successfully synthesized by using chemical vapor deposition, selective epitaxy atomic replacement, and pulsed laser deposition methods. Herein, based on first-principles calculations, we introduce the structures and performances of MoS₂/WSSe vdW heterojunctions with different interfaces and stacking modes. The vdW heterojunctions possess indirect band gaps for S–S interfaces, while direct band gaps for Se–S interfaces. Besides, the potential drop indicates an efficient separation of photogenerated charges. Interestingly, the opposite built-in electric fields formed in the vdW heterojunctions with a S–S interface and a Se–S interface suggest different charge transfer paths, which would motivate further theoretical and experimental investigations on charge transfer dynamics. Moreover, the electronic property is adjustable by applying external in-plane strains, accomplishing with indirect to direct bandgap transition and semiconductor to metal transition. The findings are helpful for the design of multi-functional high-performance electronic and optoelectronic devices based on the MoS₂/WSSe vdW heterojunctions. (paper)