The Unusual Mechanism of Partial Fermi Level Pinning at Metal–MoS2 Interfaces

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.