Graphene in a communications context

News stories about using graphene in computers appear all the time. Less often, there are stories about graphene used in communications. This will probably change.

Graphene is carbon, a specific form of carbon related to graphite (as in the lead of pencils). Graphene is graphite in sheets, very thin sheets precisely one carbon atom thick. Anything at the one atom level is nanoscale (most atoms are less than a nanometer in size and a nanometer is 1/100,000 the width of a human hair), so graphene is part of nanotechnology.

As reported by Nanowerk, recent research at IBM has led to the conclusion that graphene has many desirable properties for communications – if it can be manufactured at the right quality, in the right quantity.

The specific use of graphene in IBM’s research is in photodetectors, a device that converts light into electrical energy. This same capability in graphene is why it’s also under research for use in solar cells [SciTechStory: Progress toward graphene solar cells]. In both cases, the researchers are looking to graphene as a replacement for the use of silicon. In communications, photodetectors are used in fiber-optic systems to convert light from the optical system to electricity – it could be as a converter, or a switch.

When struck with light (photons) traditional semiconductors such as silicon form what are called electron-hole pairs (it’s not really a ‘hole’ but a gap between the layers or bands of a semiconductor). In the presence of an electric field (supplied from outside the semiconductor), an electric current is formed in the gap, which then can be drawn to electrodes – hence the switch from light to electricity. When combined with a metal in the form of palladium-titanium electrodes, graphene can do this too, but unlike silicon it does not require an external source of current – a big operational advantage. Moreover, it does the light/electricity conversion very quickly, with operating speeds greater than 500 GHz.

A key contribution of this research was to figure out how to attach the electrodes to the graphene sheet – in essence by creating ‘fingers’ of metal that extend further onto the sheet and creating a much larger photosensitive area.

The IBM team says that the unique band structure of graphene can enable an ultrawide range of operational wavelengths, at least from 300 nm to 6 µm. Xia says that, in combination with its intrinsically high operating speed, this enables the graphene photodetector to be a promising candidate for a variety of applications including optical communications, remote sensing, environmental monitoring, terahertz detection, and surveillance.

[Source: Nanowerk]

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