Deterioration and recovery in the resistivity of Al-doped ZnO films prepared by the plasma sputtering

A hot-cathode plasma sputtering technique was used for fabricating the highly transparent and conducting aluminum-doped zinc oxide (AZO) films on glass substrates from a disk-shaped AZO (Al₂O₃: 2 wt.%) target. Under particular conditions where the target voltage was V_T = −200 V and the plasma excitation pressure was P_S = 1.5 × 10⁻³ Torr, the lowest resistivity of 4.2 × 10⁻⁴ Ω cm was obtained at 400 nm, and this was associated with a carrier density of 8.7 × 10²⁰ cm⁻³ and a Hall mobility of 17 cm²/V s. From the annealing experiment of the AZO films in the oxygen and nitrogen gases of the atmospheric pressure it was revealed that both the oxygen vacancies and the grain boundaries in the polycrystalline AZO film played an important role in the electrical properties of the film.