Effects of annealing and dopant concentration on the optical characteristics of ZnO: Al thin films by sol-gel technique

ZnO:Al thin films doped with different aluminum concentrations were deposited on (0001) sapphire substrates by the sol-gel technique. Thermal annealing of ZnO:Al films was carried out in an argon ambient at various annealing temperatures from 600 to 950 degrees C. The effects of thermal annealing and dopant concentration on the optical properties of ZnO:Al thin films were investigated. It is found that near band edge UV emission is enhanced by increasing the annealing temperature and dopant concentration. But defect-related deep-level emission decreases with the increasing dopant concentration and thermal annealing has little influence as the deep-level emission. The optical band gap of ZnO:Al films increases from 3.21 to 3.25 eV on increasing the dopant concentration from 0.01% to 1%. The optical transmittance decreases in the visible region, while it increases in the ultraviolet region with an increase in the annealing temperature. (c) 2006 Elsevier B.V. All rights reserved.