PORTLAND, Ore. IBM Research has demonstrated an optical link using a graphene photodetector fabricated on a silicon-on-insulator (SOI) substrate. The 10 Gbit per second receiver uses a novel interdigitated source and drain on a field-effect transistor (FET) with graphene as the channel.
The vertical-incidence metal-graphene-metal photodetector achieved 6.1 milliamps per watt at the communications wavelength of 1.55 microns, but was shown to be useful over a very wide bandwidth of 300 nanometers to 6 microns, making the graphene optical link a promising candidate not only for communications, but for remote sensing, environmental monitoring and surveillance.
Today, photodetectors at these wavelengths require a III-V semiconductor such as gallium nitride, but by fabricating graphene on conventional SOI substrates, IBM aims to usher in an age of photonic circuitry that can be manufactured on conventional CMOS lines.
Last year, IBM demonstrated that graphene could be used to fabricate photodetectors that run as fast as 40 Gbps and predicted that by going to palladium electrodes near terahertz speed could eventually be achieved.
To achieve the world's first optical data link using graphene, IBM fabricated an asymetrical metal-graphene-metal FET that used palladium and titanium as the source and drain electrodes, respectively, and graphene as the channel. Photons hitting the graphene create electron-hole pairs which would ordinarily recombine in the absence of a strong electric field, but are prevented from doing so by the interdigitated source and drain which intensifies the built-in potential profile of the different metals within the channel.