Graphene // Light-detectors made of Graphene
cientists at the Faculty of Electrical Engineering and Information Technology at the Vienna Uni-
versity of Technology (TU Vienna, Austria) develo- ped light-detectors made of graphene and analyzed their astonishing properties.
“Light detectors which convert light into electronic signals have been around for a long time. But when they are made of graphene, they react faster than most other materials could,” Alexander Urich ex- plains. He investigated the optical and electronic properties of graphene together with Thomas Müller and Professor Karl Unterrainer at TU Vienna.
Last year the scientists had already shown that gra- phene can convert light into electronic signals with remarkable speed. However, the reaction time of the material could not be determined – the photoelec- tric effect in graphene is so fast that it just cannot be measured by the usual measuring methods. But now, sophisticated technological tricks could shed some light on the properties of graphene. At TU Vienna, la- ser pulses were fired at the graphene photo-detector in quick succession, and the resulting photo-current was measured. If the time delay between the laser pulses is changed, the detector’s maximum frequen- cy can be determined.
“Using this method we could show that our detectors can be used up to a frequency of 262 GHz,” Thomas Müller (TU Vienna) says. This corresponds to a
theoretical upper bound for data transfer using graphene photo-detectors of more than 30 giga- bytes per second. It has yet to be determined to what extent this is technically feasible, but this result clearly shows the remarkable capability of graphene and its potential for optoelectronic applications.
The main reason for the fact that graphene-photo- detectors can operate at such high frequencies is the short life-span of the charge carriers in graphene. The electrons which are removed from their fixed position and contribute to the electrical current settle down at another fixed position after a few picose- conds.
Alexander Urich, Karl Unterrainer, and Thomas Mueller: Intrinsic Response Time of Graphene Photodetectors, In: NANO Letters ASAP, May 31, 2011, DOI:10.1021/ nl2011388: http://dx.doi.org/10.1021/nl2011388
Image cover: Graphene: Light makes the electrons flow. © TU Vienna
Background: Alexander Urich and Thomas Müller with a chip contai- ning graphene, © TU Vienna
Right: Professor Karl Unterrainer, Thomas Müller, Alexander Urich (from left), © TU Vienna
11-06/07 :: June/July 2011