Tiny silicon rings give huge boost to graphene photodetectors

Using etched silicon rings the width of a human hair, Graphene Flagship scientists have significantly enhanced the responsivity of graphene photodetectors. These devices naturally generate a voltage, avoiding the need for current-to-voltage conversion, and can operate at any wavelength.

The study, published in Nature Communications, was conducted by researchers at Graphene Flagship partners Vienna University of Technology in Austria, IMEC in Belgium, the University of Cambridge in the UK, CNIT in Italy, and Technion – Israel Institute of Technology in Israel, in collaboration with the National Institute for Materials Science, Japan.

The graphene photodetectors developed in this work take advantage of the photothermal effect. Absorbing light causes electrons in the device to increase in temperature, and when this energy dissipates, the diffusion of charge carriers creates a voltage.

“Our devices are able to concentrate the incoming light into a very small volume,” begins Thomas Mueller, Associate Professor at Graphene Flagship partner Vienna University of Technology, who co-led the study. “We placed a graphene photodetector on top of a silicon microring, which circulates the incoming light many times, focusing it onto a small area,” he adds. “This significantly improves the responsivity.”

The technology developed by Graphene Flagship researchers brings graphene-enabled photodetectors to the same level as the state-of-the-art – in-line with today’s standards in terms of responsivity – but with much better overall performance, particularly when it comes to their low energy consumption.

“Thanks to graphene, photodetectors can generate sufficiently large voltages to drive electronic circuits,” says Mueller. Most semiconductor photodetectors used in the datacom industry require current-to-voltage conversion, a highly energy-intensive process. Graphene-based photodetectors avoid this entirely, lowering their carbon footprint and reducing the cost-per-bit of data transfer.

The silicon rings are only 40 micrometres in diameter, which means thousands of them would fit on a one-centimetre silicon chip. Now, Graphene Flagship researchers are looking to target applications in the datacom industry. “Integrated arrays of graphene photodetectors on silicon chips could be effective in data centres, as they are sufficiently fast and very energy efficient,” explains Mueller.

Frank Koppens, Graphene Flagship Work Package Leader for Photonics and Optoelectronics, comments: “This is an ingenious approach and record-high photodetection responsivity has been demonstrated. This is a major step forward and I do expect to see graphene in 5G and future 6G data communications systems."  

Andrea C. Ferrari, Science and Technology Officer of the Graphene Flagship and Chair of its Management Panel, adds: “Graphene-enabled photonics and optoelectronics are coming to the forefront of technology. The Graphene Flagship keeps defining and pushing the state-of-the-art: this work demonstrates that graphene photodetectors can be made much more energy-efficient than alternative technologies, while maintaining a leading performance.”

References

‘High-responsivity graphene photodetectors integrated on silicon microring resonators,’ Nature Communications, 12, 3733 (2021).