Quasi-bonding-induced gap states in metal/two-dimensional semiconductor junctions: Route for Schottky barrier height reduction

The van der Waals interface and interfacial reconstruction between two-dimensional (2D) transition-metal dichalcogenides (TMDCs) and metal electrodes significantly influence their device performance. During the growth of $\mathrm{Mo}{\mathrm{S}}_{2}$ and $\mathrm{W}{\mathrm{S}}_{2}$ on metals, the participation of sulfur atoms leads to the Au(100) surface forming a ${\mathrm{Au}}_{4}{\mathrm{S}}_{4}@\mathrm{Au}(100)\text{\ensuremath{-}}(2\sqrt{2}\ifmmode\times\else\texttimes\fi{}2\sqrt{2})R{45}^{\ensuremath{\circ}}$ reconstructed phase [Luo et al., Nat. Commun. 11, 1011 (2020)]. To reveal the nature of the reconstructed interface interactions, here we perform a comparative study for Au/TMDCs junctions with and without Au(100) surface reconstruction by density-functional theory calculations. Metal-induced gap states are apparent in the unreconstructed junction, while with reconstruction, significant quasi-bonding-induced gap states (QBIGSs) appear above the valence band maximum of TMDCs, which are antibonding states from the quasi-bonding interaction at the ${\mathrm{Au}}_{4}{\mathrm{S}}_{4}$/TMDCs interface. The QBIGS favors the formation of $p$-type contacts and significantly reduce the $p$-type Schottky barrier height (SBH). It is anticipated that QBIGS commonly exist at the chalcogenide-reconstructed metal/TMDCs junctions. This study opens a different route for $p$-type SBH reduction in metal/2D TMDCs junctions.