Density functional theory calculations are performed to unravel the nature of the contact between metal electrodes and monolayer MoS2. Schottky barriers are shown to be present for a variety of metals with the work functions spanning over 4.2−6.1 eV. Except for the p-type Schottky contact with platinum, the Fermi levels in all of the studied metal−MoS2 complexes are situated above the midgap of MoS2. The mechanism of the Fermi level pinning at metal− MoS2 contact is shown to be unique for metal−2D- semiconductor interfaces, remarkably different from the well- known Bardeen pinning effect, metal-induced gap states, and defect/disorder induced gap states, which are applicable to traditional metal−semiconductor junctions. At metal−MoS2 interfaces, the Fermi level is partially pinned as a result of two interface behaviors: first by a metal work function modification by interface dipole formation due to the charge redistribution, and second by the production of gap states mainly of Mo d-orbitals character by the weakened intralayer S−Mo bonding due to the interface metal−S interaction. This finding would provide guidance to develop approaches to form Ohmic contact to MoS2.
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