Highly Thermal-Stable and Transparent Conductive Au-Based Thin Films through Al Doping

Improving the wetting and thermal stability of thin metal films on the oxide substrates is essential to developing ultrathin, low-loss, and thermally stable metal films used for electronic and optoelectronic devices. Here, it is found that the wetting and thermal stability of thin Au films on the oxide substrates can be simultaneously improved by doping a small amount of Al (about 8 at. %) into Au. The Au(Al) film obtained full coverage on the ZnO substrate at a significantly low film thickness of 6 nm. Such Au(Al)/ZnO film with a 6 nm-thick Au(Al) layer exhibits low electrical resistivity (4.19 × 10^–7 Ω·m) and high optical transmittance (84% at λ = 550 nm). The surface morphology, surface roughness, and electrical conductivity of the Au(Al)/ZnO film with a 15 nm-thick Au(Al) layer remain practically unchanged upon annealing at temperatures as high as 500 °C. Quantitative thermodynamic calculations reveal that the significant improvement in the wetting and thermal stability of the Au(Al)/ZnO film originates fundamentally from the Al-induced decrease in the Gibbs energies of the Au(Al)|ZnO interface and the Au(Al) surface. These findings thus shed light on the development of transparent conductive metal films for high-temperature electronic and optoelectronic devices.