  In this paper we study in detail the effect of the rotational alignment
between a hexagonal boron nitride (hBN) slab and the graphene layers in the
vertical current of a a graphene-hBN-graphene device. We show how for small
rotational angles, the transference of momentum by the hBN crystal lattice
leads to multiple peaks in the I-V curve of the device, giving origin to
multiple regions displaying negative differential conductance. We also study
the effect of scattering by phonons in the vertical current an see how the
opening up of inelastic tunneling events allowed by spontaneous emission of
optical phonons leads to sharp peaks in the second derivative of the current.
