NTT Achieves World’s Fastest Unbiased Operation for Graphene Photodetector

A new study demonstrates the promising potential of graphene as a high-bandwidth photodetector material

TOKYO, September 26, 2022–(COMMERCIAL WIRE)–NTT Corporation (“NTT”) and the National Institute of Materials Science (NIMS) jointly achieved the world’s fastest impartial operation1 (220 GHz) for a graphene photodetectortwo. Furthermore, the NTT and NIMS study elucidates for the first time the optical-to-electrical (EO) conversion process in graphene. Graphene has a high-speed electrical response and high sensitivity to a wide range of electromagnetic waves, ranging from terahertz (THz) to ultraviolet (UV). Therefore, it is a promising photodetection material that enables high-speed EO conversion in wavelength ranges in which current semiconductors cannot operate. However, until now, the proven speed of unbiased operation was limited to 70 GHz due to the structure of conventional measurement devices and equipment. For this reason, the challenge for graphene photodetectors was to demonstrate operating speeds of 200 GHz and to clarify the inherent properties of graphene, such as the optical-to-electrical conversion process.

In this study, NTT and NIMS demonstrated high-speed 220 GHz operation with 3dB bandwidth by eliminating the current slowdown caused by the structure of devices with a thin layer of zinc oxide (ZnO) as the gate material. and THz on the chip. spectroscopy technology to read high-speed current. The study also found the trade-off between speed of operation and sensitivity by comparing the characteristics of photodetectors made of graphene of different grades. The findings will allow graphene photodetectors to be optimized for their intended use, such as sensitivity-prioritizing optical sensors or speed-prioritizing OE signal converters. This groundbreaking study was published online in the British scientific journal photonics of nature on August 25, 2022.

The research group investigated the conversion of EO to graphene, focusing on the photothermoelectric effect.3, which allows operation without the necessary bias to improve eco-efficiency and signal-to-noise ratio. Furthermore, the study showed that, contrary to available knowledge, the current response time is almost independent of the size of the photodetector. Also, the time between light irradiation and current generation can change significantly (from less than 100 fs to more than 4 ps), depending on the carrier density.

These results demonstrate the potential of graphene as a high bandwidth photodetector. However, the graphene in this experiment was exfoliated from the graphite, making it unusable for mass production. In the future, the NTT researchers will evaluate photodetectors using large-area graphene that can be mass-produced. Researchers have actively created materials that do not exist in nature by layering graphene and other two-dimensional materials (materials with single or multiatomic layers). Researchers will continue to try to find materials capable of even faster operation by taking full advantage of this technology. Find all the detailed information about this innovation by clicking here.

1 Especially with graphene, bias-free operation is essential to improve power consumption and signal-to-noise ratio.
two A device that electrically detects light by converting optical signals into electrical signals.
3 Change of temperature by irradiating material with light to generate voltage.

About NTT

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Media Contact:
Stephen Russell
wired communications®
for NTT

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