  Using first-principles calculations, we study the structural and electronic
properties of the bilayer SnS/graphene, bilayer SnS/bilayer graphene
(AA-stacked), bilayer SnS/bilayer graphene (AB-stacked) and monolayer
SnS/graphene/monolayer SnS van der Waals (vdW) heterostructures. Electronic
properties of all components of the vdW heterostructures are well preserved,
which reflects the weakness of the vdW interaction. In the cases of bilayer
SnS/graphene and bilayer SnS/bilayer graphene (AA-stacked), an Ohmic contact is
formed which can be turned first into p-type and then into n-type Schottky
contacts via application of an external electric field. Calculations show that
an Ohmic contact is also formed at the interface of bilayer SnS/bilayer
graphene (AB-stacked) heterostructure, but interestingly, by applying the
perpendicular electric field a transition from semimetal/semiconductor contact
to semiconductor/semiconductor one occurs which can enhance its optical
properties. Alternatively, in the monolayer SnS/graphene/monolayer SnS vdW
heterosructure, a p-type Schottky contact is established that changes into
Ohmic contact under an applied electric field. Our results clearly indicate
that the electronic properties of the vdW heterostructures can be tuned
efficiently by external electric field, which is important in designing of new
nanoelectronic devices.
