Influence of Ag doping on structural, optical, and photoluminescence properties of nanostructured AZO films by sol-gel technique

The effects of Ag doping on the structural, electrical, optical, and photoluminescence properties of sol-gel derived Al rich zinc oxide (Ag-AZO) films are studied. The Al/Zn atomic ratio was constant (∼20%) in all the films, whereas the Ag/Zn atomic ratio varied from 0% to 3%. All the films were highly transparent in the 400-1200 nm wavelength range. The XRD results and surface morphologies of the films confirmed that the grain size increased with Ag doping. The optical band gap (E_g) of the Ag-AZO film first decreased to a value of ∼3.31 eV for a 1% Ag/Zn atomic ratio from a value of ∼3.69 for undoped AZO film. For higher values (beyond a 1% Ag/Zn atomic ratio) of Ag doping, the values of E_g started to increase and finally attained a value of ∼3.66 eV for an Ag/Zn 3% atomic ratio. The photoluminescence (PL) studies showed that the relative PL intensity of the Ag-AZO films in blue (I_B) and green (I_G) regions increased with Ag doping. The PL positions of these peaks were blue shifted with increased Ag content up to an Ag/Zn atomic ratio of 3%. The increase in I _B and I_G is due to the charge difference between Ag ⁺ and Zn²⁺, whereas shifting of the PL positions is due to the size of Ag⁺ and Zn²⁺ ions.