Figure 1. Atomic and electronic structures of MoS₂/WS₂ heterostructures.

(a) Illustration of the heterostructure, where a WS₂ monolayer lies on top of a MoS₂ monolayer. Electron and hole carriers excited by incident light separate by hole transfer into the WS₂. (b) Band structure of the heterostructure, showing an indirect bandgap from Γ to K. The smallest direct transition with appreciable absorption is from the (VBM-1) state to the CBM in the vicinity of K. (c) Band structure in the vicinity of K-point in the Brillouin zone. From the K-point at the centre, right and left are directions toward Γ and M points, respectively. The incident light excites electron in |MoS₂〉 to the conduction band minimum, and hole is transferred into |WS₂〉. The energy of the valence band maximum at the K-point is set to zero. Colour indicates the degree of projection of each state onto the MoS₂ layer. A projection of one (pink) indicates complete localization of the state to the MoS₂ layer and that of zero (blue) indicates localization to the WS₂ layer. (d,e) Isosurface plots of two valence band charge density at the K-point. The local VBM, which we denote |WS₂〉, presents almost entirely localized charge to WS₂ (d), but the (VBM-1) state, which we denote|MoS₂〉, is almost entirely localized to MoS₂ (e).