Effects of annealing temperature and Al doping concentration on optical properties of ZnO thin films by sol-gel technique

ZnO:Al thin films doped with different aluminum concentration are deposited on(0001) sapphire substrates by the sol-gel technique. Thermal annealing of ZnO thin films is carried out in argon atmosphere from 600 to 950 ℃. The effects of annealing temperature and dopant concentration on the optical properties of ZnO:Al thin films are investigated. Results show that the UV peak intensity is enhanced as increasing annealing temperature and dopant concentration while green emission related with deep level defects is decreased. The optical band gap increases from 3.21 eV to 3.25 eV as increasing dopant concentration from 0.01% up to 1%. The optical absorption in the visible region increases with increasing annealing temperature while decreases in the ultraviolet region. The optical transmittanc