Their device uses an absorbing layer of quantum dots atop of a charge carrier sheet of graphene to achieve a gain of around 108 electrons per photon.
According to the team at the Institut de Ciencies Fotoniques in Barcelona, the technology could find a use in digital cameras, night-vision goggles or other sensing applications.
Graphene is an attractive material for optoelectronics and photodetection applications because it offers a broad spectral bandwidth and fast response times. However, weak light absorption and the absence of a gain mechanism that can generate multiple charge carriers from one incident photon have limited the responsivity of graphene-based photodetectors.
The researchers, therefore, turned to quantum dots, which are nanoscale-size crystals that have the unique property of absorbing different wavelengths of light depending on their size.
To build their photodetector, the team first created a graphene substrate using the standard graphite sticky tape procedure, to which it affixed tiny gold electrodes using nanoscale lithography. Following that, the team applied lead sulphide crystals to its device via a spray bottle. Because the crystals weren’t filtered, they came in a variety of sizes, which accounted for virtually all of the different wavelengths of light.
After testing and tuning, the team found that it was able to achieve 25 per cent internal quantum efficiency.