  Two-dimensional (2D) semiconductors have shown great promise in
(opto)electronic applications. However, their developments are limited by a
large Schottky barrier (SB) at the metal-semiconductor junction (MSJ), which is
difficult to tune by using conventional metals due to the strong Fermi level
pinning (FLP) effect. Here we show that, this problem can be overcome by using
2D metals, which are bounded with 2D semiconductors through van der Waals (vdW)
interaction. This success relies on a weak FLP at the vdW MSJ, which is
attributed to the suppression of metal-induced gap states. Consequently, the SB
becomes tunable and can vanish with proper 2D metals (e.g. H-NbS2). This work
not only offers new insights into the fundamental properties of
heterojunctions, but also uncovers great potential of 2D metals in device
applications.
