Effect of oxygen annealing on the ultraviolet photoresponse of p-NiO-nanoflower/n-ZnO-nanowire heterostructures

A transparent ultraviolet (UV) sensor using nanoheterojunctions (NHJs) composed of p-type NiO nanoflowers (NFs) and n-type ZnO nanowires (NWs) was prepared through a sequential low-temperature hydrothermal-growth process. The devices that were annealed in an oxygen (O ₂) ambient exhibited better rectification behavior (I _forward/I _reverse = 427), a lower forward threshold voltage (V _th = 0.98 V), a lower leakage current (1.68 × 10 ^-5 A/cm ²), and superior sensitivity (I _UV/I _dark = 57-8; Ivisible/Idark = 1 -25) to UV light (λ = 325 nm) than the unannealed devices. The remarkably improved device performances and optoelectronic characteristics of the annealed p-NiO-NF/n-ZnO-NW NHJs can be associated with their fewer structural defects, fewer interfacial defects, and better crystallinity A stable and repeatable operation of dynamic photoresponse was also observed in the annealed devices. The excellent sensitivity and repeatable photoresponse to UV light of the hydrothermally grown p-NiO-NF/n-ZnO-NW NHJs annealed in a suitable O ₂ ambient indicate that they can be applied to nano-integrated optoelectronic devices.