Graphene contacts to a HfSe 2 /SnS 2 heterostructure.

Two-dimensional (2D) heterostructures and all-2D contacts are of high interest for electronic device applications, and the SnS2 /HfSe2 bilayer heterostructure with graphene contacts has some unique, advantageous properties. The SnS2 /HfSe2 heterostructure is interesting because of the strong intermixing of the two conduction bands and the large work function of the SnS2 . The band lineup of the well separated materials indicates a type II heterostructure, but the conduction band minimum of the SnS2 /HfSe2 bilayer is a coherent superposition of the orbitals from the two layers with a spectral weight of 60% on the SnS2 and 40% on the HfSe2 for AA stacking. These relative weights can be either increased or reversed by an applied vertical field. A 3×3 supercell of graphene and a 2×2 supercell of SnS2 /HfSe2 have a lattice mismatch of 0.1% and both the SnS2 /HfSe2 conduction band at M and the graphene Dirac point at K are zone-folded to Γ. Placing graphene on the SnS2 /HfSe2 bilayer results in large n-type charge transfer doping of the SnS2 /HfSe2 bilayer, on the order of 1013 /cm2 , and the charge transfer is accompanied by a negative Schottky barrier contact for electron injection from the graphene into the SnS2 /HfSe2 bilayer conduction band. Binding energies and the anti-crossing gaps of the graphene and the SnS2 /HfSe2 electronic bands both show that the coupling of graphene to the HfSe2 layer is significantly larger than its coupling to the SnS2 layer. A tunneling Hamiltonian estimate of the contact resistance of the graphene to the SnS2 /HfSe2 heterostructure predicts an excellent low-resistance contact.