Defect-assisted resonant tunneling in graphene/carbon-doped hexagonal boron nitride junctions

Tunneling transport is a powerful probe to study variable quantum properties in van der Waals (vdW) heterostructures. Here, we report defect-assisted resonant tunneling in graphene/carbon-doped hexagonal boron nitride (h-BN:C)/graphite vdW junctions, where carbon, a strong candidate for the origin of defect states in h-BN, was intentionally doped into the h-BN barrier by a carbon annealing process. We observed two kinds of resonant tunneling processes in the same device. One is the elastic process, where carriers tunnel directly between the defect electronic state in the h-BN:C barrier and graphene/graphite electrode layers. The other is the inelastic process accompanied by phonon scattering, where carriers tunnel between the defect electronic state and electrode layers with phonon emission and absorption. From the elastic tunneling process, we determined the energy level of the defect electronic state, which is about 100 meV above the charge neutrality point of graphene. In the inelastic tunneling process, phonons in the vdW heterostructure whose energies are 56, 80, 103, 153, 166, 187, and 201 meV mainly contributed to the tunneling. This defect-assisted resonant tunneling was reproduced in different devices and the obtained defect energy level and phonon energies can be explained by the carbon substitutional defects in the h-BN lattice.