Thickness effect of NiO on the performance of ultraviolet sensors with p-NiO/n-ZnO nanowire heterojunction structure

Based on the p-NiO/n-ZnO nanowire (NW) heterojunction structure, a high-performance ultraviolet (UV) sensor has been achieved in this work. The sputtered p-type NiO exhibited good coverage on the hydrothermally-grown n-type ZnO Nano-Wires (NW's). The devices with 250-nm-thick NiO obtained the highest UV light sensitivity (IUV/IDark = 4.98; IVisible/IDark = 3.82 biased at −2 V) under UV (λ = 365 nm) intensity as low as 300 μW/cm2. Such p-n junction with thinner or thicker NiO layer led to worse UV detecting characteristics due to the fully-depleted NiO layer and larger series resistance, respectively. Furthermore, the N2 annealing process can increase the UV light response and suppress the visible light response because of the reduced structural defects in ZnO NWs and the fewer interfacial defects (IUV/IDark = 5.65; IVisible/IDark = 1.35 biased at −2 V).