Spectrum of Tunneling Transport through Phonon-Coupled Defect States in a Carbon-Doped Hexagonal Boron Nitride Barrier

Defects in hexagonal boron nitride (<i>h</i>-BN) play important roles in tunneling transport through the <i>h</i>-BN barrier. Here, using carbon-doped <i>h</i>-BN (<i>h</i>-BN:C) as a tunnel barrier containing defects in a controlled manner, we investigated tunneling transport through defects in the <i>h</i>-BN:C/graphene heterostructures. Defect-assisted tunneling through a specific kind of carbon-related defect was observed in all measured devices, where the defect level was always located at ∼0.1 eV above the graphene's charge neutrality point. We revealed a phonon-assisted inelastic process in the defect-assisted tunneling, in which carriers tunnel through the defect with phonon emission. Furthermore, when the <i>h</i>-BN:C barrier was thick (12 layers, ∼4 nm), sequential tunneling through two defects became dominant, where the phonon-assisted inelastic process shows substantial effects between the two defects. This study reveals the contribution of phonons to defect-assisted tunneling transport, which is essential for the development of defect-related van der Waals (vdW) electronic techniques.