Attosecond-fast internal photoemission

Abstract

The photoelectric effect has a sister process relevant in optoelectronics called internal photoemission1,2,3. Here an electron is photoemitted from a metal into a semiconductor4,5. While the photoelectric effect takes place within less than 100 attoseconds (1 as = 10−18 seconds)6,7, the attosecond timescale has so far not been measured for internal photoemission. Based on the new method CHArge transfer time MEasurement via Laser pulse duration-dependent saturation fluEnce determinatiON—CHAMELEON—we show that the atomically thin semimetal graphene coupled to bulk silicon carbide, forming a Schottky junction, allows charge transfer times as fast as (300 ± 200) as. These results are supported by a simple quantum mechanical model simulation. With the obtained cut-off bandwidth of 3.3 PHz (1 PHz = 1015 Hz) for the charge transfer rate, this semimetal/semiconductor interface represents a functional solid-state interface offering the speed and design space required for future light-wave signal processing.

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Fig. 1: Experimental configuration and photocurrent generation mechanisms.
Fig. 2: Measured photocurrent and model simulation results.
Fig. 3: Extraction of the charge transfer times from graphene to SiC.

Data availability

Source data for Figs. 2 and 3 are provided with the article. All other data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.

Code availability

The custom computer code for these simulations is available from the corresponding authors on reasonable request.

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Acknowledgements

This work has been supported in part by the European Research Council (Consolidator Grant “NearFieldAtto”), Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 953 “Synthetic Carbon Allotropes”, project 182849149 and project WE 3542/7-1) and the PETACom project financed by the Future and Emerging Technologies Open H2020 programme. C.H. is part of the Max Planck School of Photonics supported by BMBF, Max Planck Society and Fraunhofer Society. P.H. greatfully acknowledges a fellowship from the Max Planck Institute of the Science of Light (MPL).

Author information

C.H., T.H., M.H., H.B.W. and P.H. conceived the study. C.H. and M.H. conducted the photocurrent measurements. C.H. analysed the data and provided the plots. M.H. fabricated the samples. C.H. performed the numerical simulations. All authors discussed the obtained results and contributed to the writing of the manuscript. H.B.W. and P.H. co-supervised the experiments.

Correspondence to Christian Heide or Peter Hommelhoff.

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Extended data

Extended Data Fig. 1 Bias-controlled electric field at the Schottky junction.

a, Applying no or a slightly positive bias voltage VB reduces the DC electric field at the Schottky junction, hampering a fast charge transfer. b, A large reverse bias voltage leads to a greater band bending in SiC and hence a larger DC electric field at the interface, increasing the charge transfer rate dramatically (Fig. 3).

Extended Data Fig. 2 Photocurrent for various experimental conditions.

a,b, Photocurrent (a) and efficiency (b) versus laser pulse fluence F as a function of τp and VB. Coloured circles show the data points, while the solid lines are fits including the contributions from PIPE, PTI and 2P-PIPE as explained in Fig. 2b,c. The resulting saturation fluences Fs are indicated by black solid dots. Different colours represent different bias voltages from +0.1 to –6 V (grey to red, see legend). Increasing the negative bias voltage enhances the PIPE extraction rate. As a consequence, Fs is shifted to higher values. Since the saturation is shifted, the superlinear PTI contribution becomes more visible (larger bump). Increasing τp reduces PTI since a high electron temperature can only be reached with short laser pulses, and the saturation is shifted to higher values as well.

Supplementary information

Supplementary Information

Supplementary Information and Figs. 1–7.

Source data

Source Data Fig. 2

Numerical data: measured current versus laser fluence for 0 V and –6 V.

Source Data Fig. 3

Numerical data: saturation fluence versus GDD for –6, –4, –0.3, –0.1 and 0 V.

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Heide, C., Hauck, M., Higuchi, T. et al. Attosecond-fast internal photoemission. Nat. Photonics (2020). https://doi.org/10.1038/s41566-019-0580-6

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