Uncovering Interlayer Electronic Coupling in Two-Dimensional van der Waals Semiconductors

Interlayer electronic coupling or hybridization in two-dimensional (2D) van der Waals semiconductors has a nontrivial impact on layer-dependent properties. However, the underlying mechanisms governing interlayer coupling in 2D semiconductor systems remain poorly understood, hindering precise control of their layer-dependent properties for device applications. Herein, we present a comprehensive classification of interlayer electronic coupling and reveal how it impacts the layer-dependent electronic and optical properties across a series of 2D semiconductors based on density-functional theory (DFT) calculations. Our results indicate that the interlayer coupling strength of these 2D semiconductors is governed by the overlapping degree of out-of-plane orbitals, which is determined by the type and coupling distance of valence electronic states. The strongly coupling 2D semiconductors dominated by out-of-plane orbital interactions exhibit significant variation in bandgap and a notable shift in absorption peaks with the change of layer number. Conversely, the weakly coupling 2D semiconductors originate from in-plane orbital interactions or large coupling distance, making their bandgaps and optical absorption peaks insensitive to the change of layer number. This work sheds light on the interlayer electronic coupling mechanism in 2D semiconductors and suggests the possibility of modulating their electronic and optoelectronic properties for advanced device applications by utilizing the interlayer coupling effect.