Quantum dots boost graphene's photodetector dreams
Researchers working at the Institute of Photonic Sciences (ICFO) in Barcelona have built a super-sensitive photodetector by combining graphene with semiconducting quantum dots that outperforms other graphene based devices by a billion times.
Speaking to PhysicsWorld , lead researcher Gerasimos Konstantatos explains: “We managed to successfully combine graphene with semiconducting nanocrystals to create complete new functionalities in terms of light sensing and light conversion to electricity."
Graphene has great potential in photonics applications because it has perfect internal quantum efficiency. This means that every absorbed photon generates an electron hole pair that could be used to generate electricity. However, only three per cent of incident light is absorbed by the material, so some work is still to be done to take advantage of this most useful sounding property.
"In particular, we are looking at placing our photodetectors on ultrathin and flexible substrates or integrating the devices into existing computer chips and cameras," co-leader Frank Koppens said.
The research team made their own graphene flakes using the same technique as the graphene discovering and Nobel Prize winning team of Geim and Novoselov. Then, using Nanoscale lithography, they attached the graphene sheet to two gold electrodes, before adding a thin film of lead-sulphide quantum dots to the mix.
The team chose lead sulphide because it can be made receptive to light in useful wavelength ranges, by tuning its band gap.
Koppens told Physics World: "From [our] measurements, we could very precisely quantify the internal quantum efficiency of the device as being greater than 25% because the quantum dots absorb light so well and because charge transfer between the two materials is so effective," says Koppens.
"We found that we could also optimize this performance with the voltage on the gate or even switch off the response. This 'switchability' might come in useful for pixelated imaging techniques."
The work is published in the May 6 edition of Nature Nanotechnology.