Abstract
The photoluminescence of zinc oxide nanowires was investigated via the thermal annealing treatment in oxygen-rich and oxygen-poor conditions. Dramatic changes in the relative intensity of the ultraviolet and the green visible luminescence were observed following different annealing treatments. The changes in photoluminescence bear little correlation to the changes in the oxygen-to-zinc ratios that were revealed using Raman scattering and other characterization techniques. The chemisorption of oxygen and the subsequent surface band bending, instead of the oxygen vacancy concentration, are shown to be the mechanism that determines the observed changes in photoluminescence.
Highlights
The luminescence of zinc oxide (ZnO) exhibits a band edge ultraviolet (UV) emission peak related to the exciton luminescence and a broad green luminescence (GL) band related to deep level defects
Prior to the annealing treatments, the morphology and crystallization of the as-grown sample were characterized by using scanning electron micrograph (SEM) and X-ray diffraction (XRD)
The oxygen-to-zinc ratio was barely modified by the oxygen annealing, and it was reduced by the vacuum annealing
Summary
The luminescence of zinc oxide (ZnO) exhibits a band edge ultraviolet (UV) emission peak related to the exciton luminescence and a broad green luminescence (GL) band related to deep level defects. The different growth methods and postgrowth treatments result in different surface conditions, and the concentration and spatial distribution of native or foreign defects vary among samples. When comparing such PL data, caution needs to be exercised since all these factors can contribute to the characteristics of PL. The relative intensity of the green luminescence band increased significantly after the oxygen annealing and decreased after the vacuum annealing. This result is inconsistent with the assumption that a higher level of oxygen deficiency (in forms of Vo) gives rise to a higher. Concentration of recombination centers for GL; can be elucidated by taking the effect of surface band bending into consideration
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