Graphene
Graphene is a layer of carbon just one atom thick that has a range of unique electronic, mechanical and optical properties that could have great technological promise. Indeed, since its discovery in 2004.
Photocurrent production
Researchers have created optical devices using graphene. Researchers of Massachusetts Institute of Technology and Harvard University have found hot-carrier regime which is very unusual and is normally only seen at extremely low temperatures or in very non-linear processes, also in graphene it occurs at all temperatures from very low up to room temperature and in the linear regime when the material is excited with a laser. Graphene does not behave like a conventional semiconductor when exposed to light but instead produces hot carriers that generate a photocurrent which is usually driven by an electrostatic potential difference. Such processes form the basis of modern optoelectronics devices. It has been proved that thermoelectric processes could be at play in the material.
Process
According to the researchers, such high values of photocurrent are a result of the photo thermoelectric effect. When you shine a light on graphene, the electrons in the material heat up, and remain hot, while the underlying carbon lattice remains cool, it is these hot electrons that then produce a current. The electrons in the excited graphene cannot cool down easily because they couple poorly to the carbon lattice and so cannot transfer their heat to it
Researchers performed precise spatially resolved optical-excitation microscopy and electron-transport measurements by shining laser light with a wavelength of 850 nm onto the graphene p–n interfaces and measured the photocurrent produced in the devices as the laser spot was scanned over the samples. They found that a strong photocurrent was produced at the p–n contact which increased as the power of the laser beam was increased.
Applications
The finding could be useful for creating new types of ultra fast and highly efficient photo detectors and energy-harvesting devices such as solar cells.