Self-Assembled Al Nanostructure/ZnO Quantum Dot Heterostructures for High Responsivity and Fast UV Photodetector

Owing to their excellent characteristics of intrinsic anti-interference from the visible region [ 1 ], filter free [ 2 ], and high radiation hardness [ 3 ], UV photodetectors (PDs) have been widely witnessed in civilian and military fields, including intersatellite communications [ 4 ], optical imaging [ 5 ], flame sensing [ 6 ], environmental monitoring [ 7 , 8 ], and missile detection [ 9 ]. Among various UV photo-electronic materials (i.e., GaN, SiC, SnO 2 , and TiO 2 [ 10 , 11 ]), ZnO has great potential to fabricate high-performance UV photodetectors because of its wide direct bandgap of ~ 3.37 eV, high saturated carrier drift rate, large exciton energy (60 meV) [ 12 , 13 ]. Whereas, the conventional ZnO single crystal and thin-film photodetectors commonly suffer from a large dislocation density, excessive grain boundaries, and high-cost fabrication, resulting in radical deterioration of photoresponse for the devices [ 14 ]. Meanwhile, the solution-processed ZnO nanostructures (NSs) (i.e., quantum dots (QDs), nanowires, and nanodisks) emerged with high adjustability, physical flexibility, and low cost, offering a promising approach to achieve the high-performance detectors in practical fabrication [ 10 ]. Additionally, the high specific surface area of the ZnO NSs allows additional oxygen absorption, and a relatively lower dark current and high on/off ratio can correspondingly be expected with extended low-conductive depletion regions [ 10 , 15 ]. However, the dimension of the ZnO NSs inevitably limits the light utilization and carrier transportation, which have become a huge challenge for the fabrication of ultra-sensitive photodetectors working with a fast response [ 15 ].