Strategy for Preparing Al-Doped ZnO Thin Film with High Mobility and High Stability

Ideal Al-doped ZnO (AZO) thin films should have high carrier mobility and carrier concentration, as well as high thermal and chemical stability. To achieve these properties, ZnO should be heavily doped with Al and perfectly crystallized. Through analyzing the possible valence state of the elements and local lattice structures of AZO films during the gas-phase deposition process, we find that the current gas-phase deposition method may encounter an intrinsic obstacle that heavy doping of Al, high thermal stability, and high mobility (perfect crystallinity) cannot be achieved simultaneously. However, based on the understanding that an AZO thin film prepared in oxidizing atmosphere is actually accompanied with a high concentration of zinc vacancy, we propose a strategy to obtain an AZO film with ideal characteristics. Under an oxidizing atmosphere, a heavily doped AZO film with a high concentration of zinc vacancy is prepared using a gas-phase deposition method. Then a zinc vapor annealing treatment is employed to improve the crystallinity and conductivity of the film by filling the zinc vacancies with zinc atoms. The prepared AZO films possess the highest mobility (36.8 cm2 V−1 s−1) ever reported. Moreover, the films also show remarkable stability in carrier concentration, mobility, and resistivity under damp heat treatment (85 °C) over months.