As the graphene market develops, it will be important to highlight even more potential uses. The purpose of this article is to shed light on how graphene can be used as a photodetector.
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The Graphene Council has estimated that graphene could significantly alter the landscape of 45 different industries. Although the more prominent, well-known industries such as batteries, composites, electronics, and medicine are fascinating, it is the smaller, less well-known applications that some argue should be addressed.
What is Photodetector?
A photodetector is an optoelectronic device that can convert an electrical signal from incident light or electromagnetic radiation. Semiconductor photodetectors, also known as photodiodes, are the most common kind of photodetector and are based on PN junctions.
When a semiconductor is exposed to photons with energies above or equal to its bandgap, the absorbed photons cause electrons in the valence band to move into the conduction band, leaving behind holes in the valence band and giving rise to electron-hole pairs in the device's depleted region.
Due to their CMOS compatibility, low cost, and high efficiency, silicon photodetectors are the backbone of modern communication networks. Silicon optical interconnect chips must have an exceptional performance to keep up with the exploding demands of data traffic. These chips should have bandwidths greater than 100 GHz and photodetector responsivities greater than 1 A/W, along with less power consumption.
Due to limitations in the material properties of pure silicon, such as its indirect bandgap of 1.14 eV and its carrier drift velocity of around 1000 cm2/(Vs), devices made from this substance are unable to achieve both of these goals at the same time.
Importance to Introduce Graphene into Photodetectors
Graphene's unique absorption spectrum, which encompasses tetra hertz (THz), far-infrared (FIR), mid-infrared (MIR), near-infrared (NIR), short-wave infrared (SWIR), AND ultraviolet, visible, has been the subject of extensive research into its potential use as the primary building material in ultra-broadband photodetectors.
Graphene is an example of a gapless semimetal. Therefore, it is a highly desirable improvement over silicon because it interacts with long-wavelength light (even microwave). That means photodetectors based on graphene could detect light over a much wider spectrum.
In addition, the high carrier mobility permits ultrafast photon-to-electrical-current conversion. Graphene's high thermal conductivity also ensures that photonic devices use less energy. Graphene's CMOS compatibility allows for its eventual integration with silicon photonics.
World’s Fastest Graphene Photodetector
The increased bandwidth offered by graphene photodetectors over silicon photodetectors is the primary advantage of using graphene in photodetectors. Generally speaking, an increase in bandwidth increases the photodetector's communication potential.
Scientists at the Advanced Microelectronics Center Aachen and AMO GmBH, for instance, have reported graphene-based photodetectors with bandwidths greater than 128 GHz, which could pave the way for the development of communication networks with an optical data transmission rate greater than 180 Gb/s. This photodetector is allegedly the fastest in the world.
As a result of this breakthrough, graphene may soon be used in 5G and even 6G data communications systems.
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Graphene Boosts Next-Generation Telecommunication Devices
With its high charge carrier mobility and lack of a band gap, graphene is well-suited for optical communications at high speeds and over broad bandwidths.
In a recent study, an international team of scientists from AMO Germany created brand-new photodetectors that are integrated with graphene and have high responsiveness while operating at bandwidth of >76 GHz. This is crucial to keep up with the expanding needs of the internet, such as 5G and the Internet of Things.
The THz spectrum is rapidly becoming an integral part of wireless data transmission. A graphene photodetector is capable of absorbing and sensing terahertz light with a wavelength of hundreds of microns. For instance, researchers at ICFO have created a novel graphene-enabled photodetector that can function at room temperature, has a high dynamic range, is fast, and can detect frequencies from 1.8 to 4.2 THz. It is anticipated that this development will pave the way for THz-rate data communication.
Worldwide Initiatives to Commercialize Graphene Photodetectors
AMO, a nonprofit research Centre based in Germany, established spinout Black Semiconductor in 2020 to commercialize graphene-based photodetectors. Black Semiconductor is developing a technology that integrates silicon and graphene to enable the mass production of high-performance photonics on any electronics.
At the Mobile World Congress in 2018, AMO Germany demonstrated the world's first all-graphene optical communication cable, which could achieve a data transfer rate of 25 Gb/s per channel. It is made up of a graphene modulator that encodes electronic data onto an optical carrier. The electronic data is then sent to the receiver made of a graphene photodetector, which is responsible for converting the optical data signal being received back into an electronic signal.
In 2021, Graphenea, Black Semiconductor and AMO Germany joined the ULTRAPHO- Ultra-fast Graphene Photodetectors FTI project, which aims to revolutionize the photonic communication device market by bringing groundbreaking graphene technology to market. The project plans to expand production capacity to 10,000 wafers per year. The project is funded by the European Commission's Horizon 2020 program.
References and Further Reading
Schall, D. et al. (2018). Record high bandwidth integrated graphene photodetectors for communication beyond 180 Gb/s. In Optical Fiber Communication Conference (pp. M2I-4). Optica Publishing Group. Available at https://ieeexplore.ieee.org/document/8385752
Castilla, Sebastián, et al. (2019) "Fast and sensitive terahertz detection using an antenna-integrated graphene pn junction." Nano letters. Available at https://pubs.acs.org/doi/10.1021/acs.nanolett.8b04171
Schall, D. et al. (2017). Graphene photodetectors with a bandwidth> 76 GHz fabricated in a 6 ″wafer process line. Journal of Physics D: Applied Physics. Available at https://iopscience.iop.org/article/10.1088/1361-6463/aa5c67
Project ULTRAPHO- Ultra-fast Graphene Photodetectors (2021). Available at https://www.graphenea.com/blogs/graphene-news/ultra-fast-graphene-photodetectors-to-support-the-data-communications-market
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