Inorganic photodetectors, which are typically made from silicon or gallium nitride based p-n junction photodiodes, are unsuitable for certain applications because of their high cost and low responsivity (<0.2A/W). Forming graphene-based heterostructures with bulk semiconductors is very promising for competitive commercial photodetectors.

The key for pushing a graphene UV photodetector to the limit is dynamically doping graphene by UV light itself. In the first step, we inset the h-BN layer into the graphene/GaN heterostructure for suppressing the static charge transfer from GaN to graphene. The interfaced h-BN layer increases the barrier height at the graphene/GaN heterojunction and enhances the performance of our device.

Furthermore, coating the graphene/BN/GaN heterostructure with ZnO quantum dots brings the photo-induced doping technique to this UV photodetector. ZnO quantum dots can absorb the UV light efficiently as they have a band gap larger than 3.1 eV and a large exciton binding energy larger than 60 meV as a result of the quantum confinement effect. The absorbed photons in ZnO quantum dots produce a large amount of electron-hole pairs. The photo-induced holes in ZnO can effectively inject into the graphene layer and move the Fermi level of graphene down, which enlarges the barrier height between graphene and GaN and improves the performance of graphene/GaN photodetector.

By optimizing the photo-induced doping technique, we have a chance of pushing the graphene UV photodetector to the limit. The photo-doped graphene/GaN heterostructure has a great future for commercial UV photodetector applications.

Full details are reported in Nanotechnology.