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

Abstract

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.

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Fig. 1: Set-up for on-chip ultrafast electrical readout.
Fig. 2: Instantaneous Shockley–Ramo response and tunable HCM.
Fig. 3: Cooling time in samples with different carrier mobilities.
Fig. 4: Electrical readout versus optoelectrical readout.

Data availability

The datasets generated and/or analysed during the current study are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank K. Sasaki and K. Nozaki for fruitful discussions and H. Murofushi for technical support. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan (grant number JPMXP0112101001) and JSPS KAKENHI (grant numbers 19H05790, 20H00354 and 21H05233).

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Contributions

K.Y. and N.K. conceived the experiment. K.Y. designed and built the optical set-up, performed the measurements and analysed the data. K.Y. and N.K. designed the terahertz circuits with support from T.W. and M.H. The devices were fabricated by T.W. and N.K. The hBN material was contributed by K.W. and T.T. The paper was written by K.Y. and N.K., with input from all authors.

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Correspondence to Katsumasa Yoshioka.

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Nature Photonics thanks Alexander Holleitner and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Figs. 1–8, Sections 1–6 and Table 1.

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Yoshioka, K., Wakamura, T., Hashisaka, M. et al. Ultrafast intrinsic optical-to-electrical conversion dynamics in a graphene photodetector. Nat. Photon. 16, 718–723 (2022). https://doi.org/10.1038/s41566-022-01058-z

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