Tracking Ultrafast Photocurrent Generation and Transport in hBN-Encapsulated Graphene Using On-Chip THz Spectroscopy

We investigate ultrafast photocurrent generation and transport in high-quality graphene photodetector (PD) with its intrinsic time scale using on-chip THz spectroscopy and ZnO gate structure with the minimum capacitive coupling. We successfully readout photothermoelectric current with the 3 dB bandwidth of 220 GHz, which is previously limited to around 70 GHz due to bandwidth limitation of readout electronics and the large RC time constant of the device. As a result, we comprehensively understood how incident light is converted to electrical current in graphene, which is crucial information for developing ultrafast graphene optoelectronics towards the next generation of telecom and datacom.