Interfacial Band Engineering in ZnO-Carbon Quantum Dot Hybrids for Next-Generation Ultraviolet Photodetectors

Planar zinc oxide (ZnO) based ultraviolet (UV) photodetectors are emerging for low-power optoelectronic applications but often suffer from limited responsivity due to surface recombination and inefficient carrier separation. In this work, we demonstrate vertically aligned ZnO nanorods (ZNRs) coated with nitrogen-doped carbon quantum dots (NCQDs) hybrid UV photodetector. Compared to the (zinc oxide thin film) ZTF device, which exhibits a photocurrent density on the order of 10^-5 Acm^-2 at ±1 V, the ZNR device shows improved light absorption and directional charge transport, yielding a photocurrent density of ∼10^-4 Acm^-2 and an external quantum efficiency (EQE) of ∼75%. Upon incorporation of NCQDs, the photocurrent density increases by more than two orders of magnitude, reaching the 10^-2 Acm^-2 range, accompanied by a responsivity exceeding 2 AW^-1 and an EQE approaching 730%. This pronounced enhancement is attributed to stepwise conduction band alignment that promotes electron accumulation in the ZnO channel, along with CQD-induced surface passivation and long-lived interfacial trapping. These results highlight the importance of vertically oriented architecture, interfacial band engineering and controlled carrier trapping in realizing high-gain ZnO-based UV photodetectors, offering a scalable strategy for low-power next-generation optoelectronic platforms.