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

TL;DR

This study reveals the ultrafast intrinsic optical-to-electrical conversion process in graphene photodetectors, demonstrating a bandwidth of 220 GHz and identifying carrier scattering as a key factor in photocurrent generation.

Contribution

The paper introduces a gate-tunable graphene photodetector with suppressed RC time constant, enabling direct measurement of ultrafast photocurrent dynamics at terahertz frequencies.

Findings

Photocurrent extraction is instantaneous, with no measurable carrier transit time.

Photocurrent generation time is tunable from immediate to over 4 ps.

Carrier-carrier scattering depends on Fermi level, affecting ultrafast response.

Abstract

Optical-to-electrical (O-E) conversion in graphene is a central phenomenon for realizing anticipated ultrafast and low-power-consumption information technologies. However, revealing its mechanism and intrinsic time scale require uncharted terahertz (THz) electronics and device architectures. Here, we succeeded in resolving O-E conversion processes in high-quality graphene by on-chip electrical readout of ultrafast photothermoelectric current. By suppressing the RC time constant using a resistive zinc oxide top gate, we constructed a gate-tunable graphene photodetector with a bandwidth of up to 220 GHz. By measuring nonlocal photocurrent dynamics, we found that the photocurrent extraction from the electrode is instantaneous without a measurable carrier transit time across several-micrometer-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.