Photoresponse Imaging of Hot Carrier Dynamics in Graphene-Boron Nitride-Graphene Heterostructures

The space and time evolution of hot charge carriers in Dirac electronic systems, such as graphene, may highlight the intriguing electron dynamics of Dirac fluids. Utilizing a near-infrared scanning pulsed laser, we spatially and temporally resolved the interlayer photocurrent between two graphene layers separated by an ultrathin tunneling barrier. We found the interlayer photocurrent I increases super-linearly with excitation power P, exhibiting clear power law growth of I ~ P²_. This behavior is uniform across the heterostructure area and depends on temperature and applied bias voltage. Further, we utilized a two-pulse photoresponse measurement to access the interlayer charge carrier dynamics and extracted two timescales of the photoresponse, t₁ on the order of 200 fs, and t₂ about 2 ps, which we attributed to fast electron-electron scattering and slow electron-phonon interactions within a single graphene layer. These time scales are accessible due to the unique interlayer transport processes in the graphene-boron nitride-graphene heterostructure, which may allow detailed investigation of non-equilibrium correlated electron phases in this Dirac electronic system.