Tuning Valleys and Wave Functions of van der Waals Heterostructures by Varying the Number of Layers: A First‐Principles Study

In van der Waals heterostructures of 2D transition‐metal dichalcogenides (2D TMDCs) electron and hole states are spatially localized in different layers forming long‐lived interlayer excitons. Here, the influence of additional electron or hole layers on the electronic properties of a MoS2/WSe2 heterobilayer (HBL), which is a direct bandgap material, is investigated from first principles. Additional layers modify the interlayer hybridization, mostly affecting the quasiparticle energy and real‐space extend of hole states at the Γ and electron states at the Q valleys. For a sufficient number of additional layers, the band edges move from K to Q or Γ, respectively. Adding electron layers to the HBL leads to more delocalized K and Q states, while Γ states do not extend much beyond the HBL, even when more hole layers are added. These results suggest a simple and yet powerful way to tune band edges and the real‐space extent of the electron and hole wave functions in TMDC heterostructures, potentially affecting strongly the lifetime and dynamics of interlayer excitons. van der Waals heterobilayers, e.g., MoS2/WSe2, offer long‐lived interlayer excitons and direct bandgaps, due to type‐II band alignment. These properties can further be tuned by addition of more electron or hole layers. If more electron layers are added to MoS2/WSe2, the spread of wave function suggests delocalization of interlayer excitons throughout the whole stack, possibly extending the life of excitons.