Tuning Coupling Behavior of Stacked Heterostructures Based on MoS₂, WS₂, and WSe₂

The interlayer interaction of vertically stacked heterojunctions is very sensitive to the interlayer spacing, which will affect the coupling between the monolayers and allow band structure modulation. Here, with the aid of density functional theory (DFT) calculations, an interesting phenomenon is found that MoS₂-WS₂, MoS₂-WSe₂, and WS₂-WSe₂ heterostructures turn into direct-gap semiconductors from indirect-gap semiconductors with increasing the interlayer space. Moreover, the electronic structure changing process with interlayer spacing of MoS₂-WS₂, MoS₂-WSe₂, and WS₂-WSe₂ is different from each other. With the help of variable-temperature spectral experiment, different electronic transition properties of MoS₂-WS₂, MoS₂-WSe₂, and WS₂-WSe₂ have been demonstrated. The transition transformation from indirect to direct can be only observed in the MoS₂-WS₂ heterostructure, as the valence band maximum (VBM) at the Γ point in the MoS₂-WSe₂ and WS₂-WSe₂ heterostructure is less sensitive to the interlayer spacing than those from the MoS₂-WS₂ heterostructure. The present work highlights the significance of the temperature tuning in interlayer coupling and advance the research of MoS₂-WS₂, MoS₂-WSe₂, and WS₂-WSe₂ based device applications.