Effect of O2/Ar flow ratio on Ga and Al co-doped ZnO thin films by rf sputtering for optoelectronic device fabrication

Abstract

Ga and Al co-doped ZnO thin films were prepared on glass substrates by radio frequency magnetron sputtering and the effect of O2/Ar flow ratio on their physical properties was investigated. The films exhibited a hexagonal wurtzite structure with a predominant (002) peak intensity and their crystallinity improved with O2/Ar flow ratio. Raman spectroscopy confirmed the films’ wurtzite structure and revealed a decrease in residual tensile stress and charge carrier concentration with increasing O2/Ar flow ratio. Low surface roughness resulted in high optical transmittances around 85–90% in the visible region. The Urbach energy decreased with increasing O2/Ar flow ratio indicating a reduction in structural disorders. This was consistent with Raman spectroscopy and X-ray diffraction analysis. The least electrical resistivity (2.6×101 Ωcm) and highest figure of merit (8.8×10−6Ω−1) for films prepared with oxygen admittance were obtained at 0.667 O2/Ar flow ratio, indicating their suitability in optoelectronic device fabrication.