Investigation of Optical Parameters of Different Rates Al doped ZnO by Electrochemical Deposition

Abstract

In this study, pure ZnO and Al-doped ZnO thin films with different doping ratios were fabricated using the electrochemical deposition method, and their fundamental optical parameters were examined in detail. The Al doping ratios were set to 2.5%, 5%, 7.5% and 10%. The wavelength range selected for optical analysis was 300–700 nm. Accordingly, all Al-doped ZnO thin films exhibited higher absorption compared to the pure ZnO film, with the maximum absorption observed for the 2.5% Al-doped ZnO thin film. As the doping ratio increased, the absorption decreased. The incorporation of Al reduced the transmittance of the ZnO thin films. The average transmittance values of ZnO, 2.5% Al-doped ZnO, 5% Al-doped ZnO, 7.5% Al-doped ZnO, and 10% Al-doped ZnO thin films were 95%, 79%, 82%, 83% and 83%, respectively. The optical band gap (Eg) of the Al-doped ZnO thin films was higher than that of the pure ZnO thin film. The Eg values for ZnO, 2.5% Al-doped ZnO, 5% Al-doped ZnO, 7.5% Al-doped ZnO and 10% Al-doped ZnO thin films were 3.51, 4.01, 4.00, 3.99 and 3.98 eV, respectively. The highest extinction coefficient (k) for all films was observed at 300 nm. While the k value of the pure ZnO film at 300 nm was 0.004, the corresponding values for 2.5%, 5%, 7.5% and 10% Al-doped ZnO thin films were 0.046, 0.039, 0.039, 0.041 and 0.043, indicating that k increased nearly tenfold with Al doping. For all thin films, the maximum refractive index (n) was also observed at 300 nm, and the n values decreased with increasing wavelength. At 300 nm, the refractive index of the pure ZnO film was 1.124, while the values for 2.5%, 5%, 7.5% and 10% Al-doped ZnO films were 1.338, 1.322, 1.328 and 1.333, respectively. Additionally, the optical conductivity (σ), real dielectric constant (ϵr), imaginary dielectric constant (ϵi), and dielectric loss (ϵi/ϵr) of the films were determined. All these parameters decreased with increasing wavelength but increased compared to the pure ZnO film. The maximum values were obtained for the 2.5% Al-doped ZnO thin film.