Fabrication of p-NiO/n-ZnO heterojunction devices for ultraviolet photodetectors via thermal oxidation and hydrothermal growth processes

In this research work, a p-NiO/n-ZnO heterostructure was fabricated using thermal oxidation and hydrothermal growth processes. The p-NiO films were oxidized at different temperatures. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and UV–visible spectral analysis were used to characterize the p-NiO/n-ZnO heterostructure. The results indicated that the NiO films oxidized at higher temperature have wider optical band gap and lower defect density. In particular, by comparing the photoresponse properties of the UV photodetectors oxidized at different temperatures we suggest that the oxidation temperatures have a great influence on the photoresponse time. The defect density of NiO film decreases with increasing oxidation temperature. And the defect density affects the photoresponse characteristics that the decay time decreases with the decreasing of defect density as the NiO oxidation temperature increases. This work could serve as a valuable guideline for designing and improving the p-NiO/n-ZnO UV photodetectors in a low-cost and large-scale way.