Enhanced Hot Carrier Up-Conversion in Graphene By Quantum Dot Coating

Graphene with unique linear band structure and enhanced electron-electron interaction exhibits peculiar hot-carrier generation. The thermalized hot carriers in graphene have potential to achieve high energy which is well above energy of the incident photons. Together with its outstanding optical and electrical properties, the exotic thermalization of hot carriers makes graphene a promising material for applications in optical up-conversion devices and ultrafast photonics. However, the excitation efficiency of hot carriers is limited by its weak absorption and atomically thin light-matter interaction length. Here, the efficient hot-carrier amplification is demonstrated in graphene by adjacent quantum dots (QD). With pump-probe experiments, this hot carrier amplification is found to stem from the charge collection of the two-photon excited hot carriers in QD. Taking advantages of strong absorption of QD, the hot-carrier excitation efficiency of graphene can be efficiently improved under near-infrared sub-bandgap excitation of QD. The transferred hot carriers are with energy higher than those originally excited in graphene, leading to raised hot-carrier temperature and enhanced hot-carrier up-conversion. This research demonstrates QD's immense potential to realize high efficiency hot-carrier injection in graphene-based devices, which will promote their ability for hot-carrier-driven devices, optical up-conversion devices and high-frequency optoelectronics.