NTT Achieves World’s Fastest Zero-bias Operation of a Graphene Photodetector

Rhea-AI Summary

NTT Corporation has partnered with the National Institute for Materials Science to achieve a world record in graphene photodetector speed, demonstrating zero-bias operation at 220 GHz. This breakthrough clarifies the optical-to-electrical conversion process in graphene, which is crucial for high-speed applications. The research underlines a key trade-off between operating speed and sensitivity for various photodetector applications. Findings from this study, published in Nature Photonics, aim to optimize graphene photodetectors for future mass production, addressing challenges in current manufacturing methods.

Positive

• Demonstrated world record speed of 220 GHz for graphene photodetectors, surpassing previous limits.
• Clarified the optical-to-electrical conversion process in graphene, enhancing understanding for future applications.
• Potential for optimization of photodetectors based on the trade-off between speed and sensitivity.

Negative

• Current graphene used is not suitable for mass production, hindering immediate commercial applications.

New Research Demonstrates the Promise of Graphene as a Broadband High-Speed Photodetector Material

TOKYO--(BUSINESS WIRE)-- NTT Corporation (“NTT”) and the National Institute for Materials Science (NIMS) have jointly achieved the world's fastest zero-bias operation¹ (220 GHz) of a graphene photodetector (PD) ². Furthermore, the research conducted by NTT and NIMS clarified the optical-to-electrical (O-E) conversion process in graphene for the first time. Graphene has high sensitivity and high-speed electrical response to a wide range of electromagnetic waves, from terahertz (THz) to ultraviolet (UV). Thus, it is a promising photodetection material for enabling high-speed O-E conversion at wavelength ranges where existing semiconductor devices cannot operate. However, until now, the demonstrated zero-bias operating speed has been limited to 70 GHz due to conventional device structure and measurement equipment. For this reason, the challenge for graphene PDs is to demonstrate 200-GHz operation speeds and clarify graphene's inherent properties, such the process of optical-to-electrical conversion.

In this study, NTT and NIMS demonstrated high-speed operation with a 3dB bandwidth of 220 GHz by removing the current delay caused by the device structure by using zinc oxide (ZnO) thin film as the gate material and by using on-chip THz spectroscopy technology to read out the current at high speed. The research also found a trade-off between operating speed and sensitivity by comparing the characteristics of PDs fabricated with graphene of different qualities. The findings will enable graphene PDs to be optimized according to their intended use, such as in optical sensors prioritizing sensitivity or O-E signal converters prioritizing speed. This groundbreaking research was published online in the British scientific journal Nature Photonics on August 25^th, 2022.

The research group studied O-E conversion in graphene, focusing on the photothermoelectric (PTE) effect³, which enables zero-bias operation required to improve power consumption and the signal-to-noise ratio. Furthermore, the research showed that, contrary to conventional understanding, the response time of the current is almost independent of the size of the PD. Moreover, the time from light irradiation to current generation can be varied 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-speed broadband PD. However, the graphene in this experiment was exfoliated from graphite, making it unsuitable for mass production. In the future, NTT researchers will evaluate PDs using large-area graphene that can be mass-produced. Researchers have actively been creating materials that do not exist in nature by layering graphene and other two-dimensional materials (single or multi-layered atomic layer materials). Researchers will also search for materials that can achieve even faster operation by making the most of this technology. You can read the full details about this innovation here.

¹ In graphene especially, zero-bias operation is essential to improve power consumption and signal-to-noise ratio.
² A device that electrically detects light by converting optical signals into electrical signals.
³ Changing the temperature by irradiating the material with light to generate voltage.

About NTT

NTT is a global technology and business solutions provider helping clients accelerate growth and innovate digital business models. We provide digital business consulting, technology and managed services for cybersecurity, applications, workplace, cloud, data center and networks – all supported by our deep industry expertise and innovation. As a top-five global IT services provider, our diverse teams deliver services in 190+ countries and regions. We serve 85% of the Fortune Global 100 companies and thousands of other clients and communities. With a 120-year heritage of service and social responsibility, we advocate and act for our clients and a sustainable world. For more information on NTT, visit https://www.global.ntt/.

NTT and the NTT logo are registered trademarks or trademarks of NIPPON TELEGRAPH AND TELEPHONE CORPORATION and/or its affiliates. All other referenced product names are trademarks of their respective owners. © 2022 NIPPON TELEGRAPH AND TELEPHONE CORPORATION

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Media Contact:

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For NTT

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Source: NTT Corporation

FAQ

What was the achievement of NTT Corporation regarding graphene photodetectors?

NTT Corporation achieved a world record operational speed of 220 GHz for graphene photodetectors in collaboration with the National Institute for Materials Science.

How does the new graphene photodetector improve optical-to-electrical conversion?

The research clarifies the optical-to-electrical conversion process in graphene, which is crucial for high-speed applications.

What is the significance of the 220 GHz speed achieved by NTT Corporation?

The 220 GHz speed represents a significant advancement from the previous limitation of 70 GHz, enabling faster and more efficient photodetectors.

When was the research on graphene photodetectors published?

The research was published on August 25, 2022, in the British journal Nature Photonics.

What challenges does NTT face in manufacturing graphene photodetectors?

The current graphene used in experiments is not suitable for mass production, which poses a challenge for commercial applications.