Aluminum-doped zinc oxide (ZnO:Al) thin films deposited on glass substrates by chemical spray starting from zinc pentanedionate and aluminum chloride

Aluminum-doped zinc oxide thin films (ZnO:Al) were deposited on sodalime glass substrates by the chemical spray technique, starting from zinc pentanedionate and aluminum chloride. The effect of the substrate temperature on the structural, morphological, optical, and electrical properties was studied. A constant [Al]/[Zn] = 3 at.% ratio was used. As the substrate temperature increases, the electrical resistance decreases, reaching a minimum value, in the order of 3 × 10^-2 Ω cm, for as-grown films deposited at 475 °C. The Hall mobility and carrier concentration for these films were around 0.6 cm²/(V s), and 3.42 × 10²⁰ cm ^-3, respectively. Further decrease in the resistivity, in the order of 1.5 × 10^-2 Ω cm, was observed after a heat treatment in vacuum, during 1 h, at 400 °C. All the samples were polycrystalline, with a variation in the preferential growth. Samples deposited at 450 °C show a (0 0 2) preferential growth whereas films deposited at higher temperatures present a significant contribution of other planes. As the substrate temperature increases, the morphology shows slight changes, since the grain size increases. The transmittance in the visible region (400-700 nm) is high, typically of 85% at 550 nm, and band gap values oscillated around 3.3 eV. These results show that zinc pentanedionate can be a good candidate for the manufacturing of transparent conductive ZnO:Al thin films.