Defect-assisted photocurrent generated in Landau-quantized graphene/carbon-doped h-BN/graphite van der Waals tunnel junctions

Carbon-related defects in hexagonal boron nitride (h-BN) offer discrete energy levels, acting as local probes of the electronic properties of 2D materials through defect-assisted tunneling. This study demonstrates the generation of a defect-assisted photocurrent in a monolayer graphene (MLG)/carbon-doped h-BN/graphite van der Waals tunnel junction. Under a perpendicular magnetic field and mid-infrared light irradiation, a photocurrent was generated only when the condition for cyclotron resonance (inter-Landau level (LL) transition in the MLG) was satisfied. Crucially, this photocurrent is highly selective, appearing only when two conditions are met: the Fermi energy of the MLG lies at the boundary separating the quantum Hall states (QHS) and non-QHS, and an occupied LL is aligned with the energy of a carbon defect level in the h-BN barrier. Our analysis attributes the photocurrent to a bolometric effect: resonant light absorption increases the electron temperature, expanding the area of conductive extended states in QHS, and thus increasing the number of defects contributing to tunneling conductance. These findings introduce a new photodetection technique for atomic-scale photocurrent spectroscopy using an h-BN:C barrier to probe quantum Hall states.