Dirac Point Photo-Thermionic Response at the Graphene-Boron Nitride Interface

The unique inter- and intra-layer transport processes in graphene-boron nitride-graphene heterostructures give a unique snapshot of non-equilibrium electronic phases in this Dirac electronic system, and unveil new design principles based on the high level of control of the hot carrier distribution. Utilizing a near-infrared scanning pulsed laser, we explore the inter- and intra-layer photocurrent of a pixel consisting of two graphene layers separated by an ultrathin tunneling barrier. We find that the interlayer photocurrent increases super-linearly with excitation power, consistent with carriers being thermally driven over the interlayer barrier. The inter-layer photocurrent also exhibits a striking enhancement of the conductance near the Dirac point, which indicates a tunable electronic temperature that is sensitive to the doping and quality of each graphene layer. Furthermore, the intra-layer photocurrent is consistent with, but not fully described by, a thermoelectric current driven by a spatial temperature distribution generated from the Gaussian laser spot. The evolution of hot electronic charge carriers in Dirac electronic systems, such as graphene, may highlight the intriguing hot carrier dynamics of non-conventional electronic states, such as the Dirac fluid.