Effects of annealing temperature on photoluminescence of ZnO nanorods hydrothermally grown on a ZnO:Al seed layer

Abstract

Hexagonal zinc oxide (ZnO) nanorod arrays were prepared on ZnO:Al/Si substrates using a hydrothermal method and then annealed at different temperatures. The effects of annealing treatment on the optical and structural properties of ZnO nanorods were studied by photoluminescence (PL), transmittance, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements. SEM images confirmed that the ZnO nanorods were grown on ZnO:Al/Si substrate with (002) preferential orientation. PL spectra showed that the visible emission of a ZnO nanorod crystal converted from yellow band (YB) emission to green band (GB) emission when the annealing temperature exceeded 400°C. The YB emission was caused by –OH surface defect state and the GB emission arose from oxygen vacancy defect. The ratio of emission intensity of GB to ultraviolet (UV) band (Ivisible/IUV) reached maximum (∼9) at 600°C annealing, and it can be concluded that there exists lots of oxygen vacancies in the ZnO crystal. Compared with the ZnO nanorods grown on ZnO seed layer, the ZnO nanorods grown on ZnO:Al seed layer are easier to form oxygen vacancy defects above 400°C annealing in air and have potential applications in ZnO gas sensors.