Effect of vacuum annealing on the properties of transparent conductive AZO thin films prepared by DC magnetron sputtering

Using highly conductive Al doped ZnO (AZO) ceramic target, (001)-oriented transparent conductive AZO (Al doped ZnO) thin films are prepared by dc planar magnetron sputtering deposition on glass sheet substrates. The structural, electrical, and optical properties of the films (deposited at room temperature and annealed at different temperatures in vacuum) are characterized with various techniques. The experimental results show that electrical resistivity of the as-grown films (not intentionally heated) can be decreased to 10-4 Ω cm level with post-deposition annealing at 400°C for 2 h in vacuum pressure of 10-5 Torr. AZO thin films deposited at room temperature (RT) and subsequently annealed at 450°C for 2 h in vacuum have nano-crystalline structure with even crystal size distribution. With the increase of annealing temperature, the (002) preferred orientation of AZO thin film grows, the carrier concentration of AZO thin film increases, and the absorption edge in the transmission spectrum shifts toward the shorter wavelength side (blue shift). The oxygen vacancies have played an important role in the improvement of electrical conductivity of these AZO thin films with the vacuum annealing process.