High performance graphene photodetectors set speed record

Graphene-based technologies are proving integral to the new generation of communications -- enabling high performance optical communication systems through ultra-fast and compact optoelectronic devices. Researchers from the Graphene Flagship working at TU Vienna, Austria and AMO, Germany, have demonstrated ultrafast photodetectors that have the highest reported bandwidth for graphene-based devices, enabling data rates of up to 100 Gbit/s. The research, recently published in Nano Letters, points the way towards graphene applications in high-speed communications systems.

Simone Schuler, a researcher at TU Vienna, explained the importance of increasing data capabilities. "These kinds of photodetectors are typically used in optical data links, which form the back-bone of the internet. The maximum operation speed of a photodetector defines the maximum data rate the detector can receive. So, the faster the photodetector the more data it can receive."

Graphene's properties make it ideal for next-generation optoelectronics and optical communications systems. Its excellent electrical properties and broadband optical absorption are highly suited for high-performance optoelectronic devices, and it can be readily integrated with silicon photonic systems. The photodetector demonstrated here is highly sensitive, due to its very compact structure. This enables the use of such detectors alongside other opto-electronic devices including switches in functionally dense, integrated chips. "This could open the path towards a complete integration on one CMOS chip. Graphene will be the enabling material for realising high performance photodetectors on a silicon platform," added Schuler.

In the new photodetectors, light is guided into a slot waveguide that is covered with graphene. Under specific electrical conditions in the graphene, in which the graphene acts as semiconductor junction, the light in the waveguide generates a current in the graphene via the photothermoelectric effect, converting light into an electrical signal. The sensitivity of the detector can be tuned electrically without compromising the speed, enabling the high bandwidth and ultrafast data rate.

Speaking about this new photodetector design, another of the paper's authors, Daniel Neumaier of AMO, Germany said "This is an important step towards high performance on-chip photo-detectors, demonstrating that competitive speed and sensitivity can be achieved in graphene photodetectors in a highly controlled way." On-chip integration of different graphene-enable technologies is an important focus of the Graphene Flagship. Neumaier leads the Graphene Flagship Electronics and Photonics Integration Division and Work Package Electronic Devices, and is a member of the Flagship Management Panel and Executive Board

This research is a prime example of the way graphene can provide improvements over existing optoelectronic technologies, both in terms of performance and compactness. Frank Koppens, of the Institute of Photonic Sciences, Spain, is leader of the Flagship's Optoelectronics and Photonics Work Package. "This work has shown record-high performance and operation with zero dark current. It's a major step forward for the Flagship program that aims at developing the components (detectors, modulators) for a fully CMOS-integrated optical data-communication platform," he said.

Andrea Ferrari, Science and Technology Officer of the Graphene Flagship and Chair of its Management Panel, stated "Graphene photonics and optoelectronics is clearly one of the strongest areas for mid-term development. The Graphene Flagship has made significant investment in pioneering large scale integration of optoelectronic components based on graphene and related materials. This is a key step to enable their widespread uptake in the future of data com and IoT areas. This result clearly shows that we are on the right track on our technology roadmap"