There may be an element of ludic absurdity in the science of graphene that is at first only partially sensed but which finally breaks through with the force of a giant fireball fiercely burning one hundred and fifty million kilometres above our heads.
Yet, for all its absurdity, graphene researchers seem to have an unvarying ability to surprise us anew and on a near daily basis. Therefore the news that a graphene photodetector is a billion times more efficient than previous graphene devices requires a degree of journalistic dampening, lest we all begin to think there is no further room for improvement; because as sure as eggs are eggs, this latest report on the tremendous gains wrought by the research groups at ICFO will, in time, be shown to be only a scaffold around which greater progress is made.
The latest piece of research to be published in Nature Nanotechnology showcases the work of Professors Gerasimos Konstantatos and Frank Koppens, both of whom are NEST Fellows at the ICFO. Their development of an ultra-sensitive hybrid photodetector that functions within the visible and infrared bands of the electromagnetic spectrum brings graphene devices once again to the fore. Improvements on earlier graphene photodetectors have been produced by incorporating nanocrystals (colloidal quantum dots) into the fabric of the graphene. It is this graphene-nanocrystal combination has led to the production of a device which is a billion times more sensitive than any existing graphene photodetector to date.
Graphene’s well documented band width makes it an excellent candidate for photoelectronic devices. However, the absence of a gain mechanism that can generate multiple charge carriers from one incident photon have until now limited the responsiveness of graphene photodetectors. Konstantatos and Koppens technique of spraying tiny crystals of lead sulphide onto the surface of monolayer and bi layer graphene shows a demonstrable gain of ~108 electrons per photon, a phenomenal increase on the responsiveness of unadulterated graphene.
This discovery, which also features in the latest online edition of The Economist, inaugurates the possibility of the development of low-cost photodetectors with possible applications ranging from biomedical imaging and night vision, to remote sensing and metrology.
The discovery of the graphene photodetector is an important advance for scientists that have been responding to the calls from industry for lower cost devices. As the Institute of Photonic Sciences suggest,
The reported hybrid device consists of low-cost materials that can be integrated with existing silicon technologies, and can be readily deposited onto any sort of substrates- rigid or flexible, crystalline or amorphous. The search for low-cost, ultra-sensitive photodetectors, in particular for light that is not visible with the naked eye (such as infrared light) has been a pressing challenge for physicists and engineers.