Compatibility between Schottky–Mott Limit and High Carrier-Injection Efficiency in Metal–van der Waals Semiconductor Junctions

For a traditional bulk metal–semiconductor junction, owing to the Fermi level pinning (FLP), the Schottky barrier height (SBH) cannot be effectively tuned by varying the metal work function. This phenomenon is proven to be true even in two-dimensional (2D) van der Waals (vdW) semiconductors. However, some recent experiments showed an ideal metal–vdW semiconductor junction (MVSJ) is free of FLP, thus, can achieve Schottky–Mott limit (SML) and high interface current simultaneously. Here, we address this contradiction by showing that intrinsic FLP persists in stable ideal MVSJs due to wave function hybridization, which prevents the simultaneous achievement of SML and high interface current. Although FLP can be reduced by decreasing the metal–semiconductor interactions (e.g., artificially increasing the interfacial distance), this inevitably raises contact resistance and degrades charge injection efficiency. Our basic understanding thus provides significant insights on the FLP issue in 2D semiconductor interfaces, and more experimental study on this issue is called for.