Effect of annealing processing on morphology, spectroscopy studies, Urbach disordering energy, and WDD dispersion parameters in Cu-Al doped zinc oxide films

Abstract

In this article, a mosaic target made of ZnO and Al-Cu atoms were used for fabricating of the Cu-Al doped zinc oxide films (CAZO films) using RF magnetron co-sputtering. The CAZO films were deposited in room temperature on glass substrates with the sputtering gases O₂ and Ar in proportion of 30%. Then, films were annealed at different temperatures of 400, 500, and 600 °C in a electrical furnace with Ar atmosphere. Atomic Force Microscopy images showed that the size of nanoparticles in films annealed at 600 °C have maximum value about of 18.8 nm. Atomic Force Microscopy data shown that the films annealed at 600 °C were rougher and they were about of 4.68 nm. Transmittance T(λ) and reflectance R(λ) measurements in the wavelength range (300–2500 nm) were used to calculate the absorption coefficient α (λ), the refractive index n(λ), the optical dispersion parameters according to Wemple and Didomenico, and the optical band gap of films. The optical band gap has been estimated and confirmed by five different methods. It can be seen that with increasing annealing temperature the optical band gap of films were decreased. Films annealed at 400°C have more disordered. It is found that the as films annealed at 500°C have minimum values of the dispersion energy E_d and the oscillator strength fin about of 0.57 eV and 2.42 (eV)², respectively. The as deposited films have minimum values of oscillator length strength S₀ in about of 5.5 μm⁻².

Graphical Abstract

Keywords:

• Nanoparticles size
• annealing processing
• CAZO films
• optical band gap
• the single oscillator model