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

Abstract 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 ( I UV / I Dark  = 4.98; I Visible / I Dark  = 3.82 biased at −2 V) under UV (λ = 365 nm) intensity as low as 300 μW/cm 2 . 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 N 2 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 ( I UV / I Dark  = 5.65; I Visible / I Dark  = 1.35 biased at −2 V).