Influence of annealing on microstructure and photoluminescence properties of Al-doped ZnO films

Effect of annealing temperature and time on the microstructure and photoluminescence (PL) properties of Al doped ZnO thin films deposited on Si (100) substrates by sol-gel method was investigated. An X-ray diffraction (XRD) was used to analyze the structural properties of the thin films. All the thin films have a preferential c-axis orientation, which are enhances in the annealing process. It is found from the PL measurement that near band edge (NBE) emission and deep-level (DL) emissions are observed in as-grown ZnO : Al thin films. However, the intensity of DLE is much smaller than that of NBE. Enhancement of NBE is clearly observed after thermal annealing in air and the intensity of NBE increases with annealing temperature. Results also show that the PL spectrum is dependent not only on the processing temperature but also on the processing time. The DLE related defects can not be removed by annealing, and on the contrary, the annealing conditions actually favor their formation.