Ultrafast intrinsic optical-to-electrical conversion dynamics in a graphene photodetector

Researchers demonstrated a gate-tunable graphene photodetector with a bandwidth of up to 220 GHz. This was achieved by suppressing the 'RC' time constant using a resistive zinc oxide top gate. Optical-to-electrical conversion in graphene is a central phenomenon for realizing anticipated ultrafast and low-power-consumption information technologies. However, revealing its mechanism and intrinsic timescale require uncharted terahertz electronics and device architectures. Here we succeeded in resolving optical-to-electrical conversion processes in high-quality graphene via the on-chip electrical readout of an ultrafast photothermoelectric current. By suppressing the time constant of a resistor-capacitor circuit using a resistive zinc oxide top gate, we constructed a gate-tunable graphene photodetector with a bandwidth of up to 220 GHz. Measuring the non-local photocurrent dynamics, we found that the photocurrent extraction from the electrode is quasi-instantaneous without a measurable carrier transit time across several-micrometre-long graphene, following the Shockley-Ramo theorem. The time for photocurrent generation is exceptionally tunable from immediate to >4 ps, and its origin is identified as Fermi-level-dependent intraband carrier-carrier scattering. Our results bridge the gap between ultrafast optical science and device engineering, accelerating ultrafast graphene optoelectronic applications.

Automated summary

Researchers have developed a gate-tunable graphene photodetector with a high bandwidth by using a resistive zinc oxide top gate. They found that the optical-to-electrical conversion in graphene is almost instantaneous and can be controlled by adjusting the Fermi level. This study bridges the gap between ultrafast optical science and device engineering, advancing the development of ultrafast graphene optoelectronic applications.