Credit: © 2009 APS

The approximately 3% of incident light that a single layer of graphene absorbs may sound a lot given its thickness, but, for optoelectronics applications, more would be better. The absorption in regular graphene is limited by the small quantity of electronic states available for optical transitions to occur, as well as the low probability of those transitions.

Now, calculations by Chao Zhang and colleagues at the University of Wollongong and the Shanghai Institute of Microsystem and Information Technology have suggested that certain forms of graphene can have a very strong response to light in the far-infrared and terahertz frequencies1. The researchers focused on bilayer graphene nanoribbons, in which the electrons behave as though they are in a one-dimensional conductor. This increases the quantity of states available for optical transitions, as well as the transition probabilities. As a result, the nanoribbon conductivity can increase by 150 times at particular frequencies of light, and at low temperature. These frequencies can in turn be tuned with ribbon width.

The result may have implications for the construction of devices sensitive to low-energy photons, but will require control over the width, chirality and edges of the nanoribbons used.