  Placing graphene on SnS2 results in significant charge transfer, on the order
of 10^13/cm^2, from the graphene to the SnS2, and the charge transfer results
in a negative Schottky barrier contact for electron injection from the graphene
into the SnS2 conduction band. However, due to the s-px,y composition of the
SnS2 conduction band, the coupling between the SnS2 and the graphene is
relatively weak. A third layer, HfSe2, placed between the SnS2 and the
graphene, serves as a matrix element matching layer, since it has strong
coupling to both the graphene and the SnS2. It increases the coupling to the
graphene by a factor of 10, and it has little effect on the negative Schottky
barrier height, since the conduction band wavefucntion of the SnS2 / HfSe2 is a
coherent superposition of the orbitals from the two individual layers, such
that there is no energy barrier for an electron to move between the two layers.
This paper first investigates the electronic properties of the heterostructure
bilayer SnS2 / HfSe2 in the presence of an applied vertical electric field, and
then it investigates the trilayer systems of BN / SnS2 / HfSe2 and graphene /
SnS2 / HfSe2. A tunneling Hamiltonian estimate of the the contact resistance of
the graphene to the SnS2 / HfSe2 heterostructure indicates an excellent
low-resistance contact.

Materials Science