Tuning the Schottky Barrier at the Graphene/MoS₂ Interface by Electron Doping: Density Functional Theory and Many-Body Calculations

Abstract

Using ab initio calculations we investigate the energy level alignment at the graphene/MoS 2 heterostructure and the use of electron doping as a strategy to lower the Schottky barrier and achieve a low-resistance Ohmic contact. For the neutral heterostructure, density functional theory (DFT) with a generalized gradient approximation predicts a Schottky barrier height of 0.18 eV, whereas the G 0 W 0 method increases this value to 0.60 eV. While the DFT band gap of MoS 2 does not change when the heterostructure is formed, the G 0 W 0 gap is reduced by 0.30 eV as a result of the enhanced screening by the graphene layer. In contrast to the case of metal substrates, where the band alignment is governed by Pauli repulsion-induced interface dipoles, the graphene/MoS 2 heterostructure shows only a negligible interface dipole. As a consequence, the band alignment at the neutral heterostructure is not changed when the two layers are brought into contact. We systematically follow the band alignment as a function of doping concentration and find that the Fermi level of the graphene crosses the MoS 2 conduction band at a doping concentration of around 10 12 cm –2 . The variation of the energy levels with doping concentration is shown to be mainly governed by the electrostatic potential resulting from the doping charge.