Ultrafast Photocurrent Generated by Suspended Graphene


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Graphene could be used as photodetector. Photo by Mranthem

The superfast photoelectric response rate of graphene has now been measured in new research.

Graphene, if irradiated with a laser, can generate an electric signal of only a few picoseconds duration (10-12 seconds). These results were published on the 31st of January 2012, in Nature Communications. Emission of a signal with Terahertz frequency was also observed. This confirms the exceptional properties of this material, which can be used in several technological applications.


Graphene is a carbon-based material. Its structure is made of only one layer of carbon atoms; each carbon atom is bonded to three other atoms, with a bond angle of 120º. As all atoms lay in the same plan, graphene has a 2-D planar structure.

Graphene is one of the most studied and interesting materials, due to its outstanding physical properties. It shows remarkable mechanical behavior; as tests showed that it is the strongest material ever measured.

Graphene is also an excellent electrical conductor. It has a very high carrier mobility; this means the charges, such as electrons, can move very easily and quickly within the lattice. Graphene has interesting optical properties as well; we can see it through a microscope, despite the fact that it’s a material that is only one atom thick.

All these characteristics make graphene a very suitable material for optoelectronic devices, such as photodetectors.

What are Photodetectors?

Photodetectors are devices which can convert a light signal into voltage/electricity. Usually electromagnetic radiations of appropriate wavelength l, with photons of specific energy, are employed to generate the electric signal (photocurrent).

In recent years, there has been an increasing interest in developing fast photodetectors, that is devices able to perform the light-current conversion in very short times, of the order of less than one billionth of a second (10-9 seconds). These ultrafast devices can be employed in sectors such as computers or telecommunications.

In this field, graphene always seemed a very promising material. However, it was not possible to verify this, as there was no instrument with sufficiently high time resolution, capable of measuring such a fast photoelectric response.

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