Effects of hydrogen ambient and film thickness on ZnO:Al properties

Undoped ZnO and ZnO:Al (0.1, 0.2, 0.5, 1.0, and 2.0wt.% Al2O3) films were deposited by rf magnetron sputtering. Controlled incorporation of H2 in the Ar sputtering ambient for films grown at substrate temperatures up to 200°C results in mobilities exceeding 50cm2V−1s−1 when using targets containing 0.1 and 0.2wt.% Al2O3. Temperature-dependent Hall measurements show evidence of phonon scattering as the dominant scattering mechanism in these lightly Al-doped films, while ionized impurity scattering appears increasingly dominant at higher doping levels. A combination of compositional and structural analysis shows that hydrogen expands the ZnO lattice normal to the plane of the substrate and desorbs from ZnO at ∼250°C according to temperature-programmed desorption and annealing experiments.