Physical properties of cost effectively synthesized ZnO nanowires post annealed under various thermal and atmosphere treatments for UV photodetectors

Abstract

Vertically aligned Zinc Oxide nanowires (ZnO NWs) were grown on glass seeded substrates by the chemical bath deposition (CBD) method at a low temperature. Two parameters including temperature and atmosphere were varied while time and heating rate were kept constant. The field emission scanning electron microscopy images show that the ZnO NWs with a hexagonal cross section are grown perpendicular to the seeded glass substrates. The x-ray diffraction results reveal that all the ZnO NW arrays grow preferentially oriented along the c-axis in the direction of (002) plane with a hexagonal wurtzite structure. Photoluminescence measurements of the grown ZnO NWs on all samples exhibit a high ultraviolet (UV) peak intensity compared to a broad visible peak, which can be accounted for the formation of the high crystal quality ZnO NWs. Results show that the UV light emission is greatly enhanced by annealing the as-grown ZnO NWs in O2 ambient. Moreover, transient response measurement reveals that the detectors exhibit a fast photoresponse time of fewer than 5 s. In this annealing case, the quantum efficiency of UV detection reaches about 15%. Finally, a qualified metal-semiconductor-metal (MSM) ZnO photodetector was prepared from the annealed as-grown sample in the pure O2 ambient.