Effects of Al doping concentration on optical parameters of ZnO:Al thin films by sol–gel technique

ZnO:Al thin films doped with different aluminum concentration were deposited on (0 0 0 1) sapphire substrates by sol–gel technique. Kramers–Kronig relationship was used to determine the optical parameters of ZnO:Al thin films in wavelengths with a range of 300–600 nm. Calculated results show that all optical parameters keep constant in the visible region. The refractive index, the extinction coefficient and the real and imaginary components of dielectric are ∼1.6, ∼0.08, ∼2.5, and ∼0.27, respectively. Optical constants change distinctly near the optical absorption edge. In the ultraviolet region, doping concentration strongly affects the optical parameters of ZnO:Al thin films. Optical parameters tend to decrease with increasing doping concentration.