Light detector: A graphene photodetector takes advantage of the electric field that is created at the interface between metal contacts (gold) and graphene. When light falls on graphene, the field helps to separate electrons from holes, leading to an electric current.
A single sheet of graphene absorbs 2.3 percent of the light falling on it, a significant amount for a one-atom-thick material. “You have a photodetector that has a number of advantages: it absorbs over a wide wavelength range, it’s very fast, it has a high absorbance, it’s a single atomic layer,” Avouris says. “This combination makes it rather unique.”
Ultrafast photodetectors could find use in future optical communications networks with data rates beyond 40 gigabits per second; right now, optical networks have data rates of about 10 gigabits per second. The photodetectors could also be used in optical computers that compute with electrons but transfer data using light instead of sending it over heat-prone copper wires. Fengnian Xia, a coauthor of the paper, says that graphene would also make a better detector for terahertz radiation, which has shown promise for medical and security imaging.
“Graphene is a great material for electronics,” says Andre Geim, a professor of physics at the University of Manchester, U.K. “Very few people could think about optoelectronics being of any interest with this material. This is like fresh air.”
The researchers get current in response to light pulses at a frequency of 40 gigahertz. Frequencies higher than this are not possible with today’s electronics, says Avouris, but graphene could, in theory, enable photodetectors that work at frequencies even higher than 0.5 terahertz.