Effects of hydrogen content in sputtering ambient on ZnO:Al electrical properties

ZnO-based transparent conducting oxide (TCO) thin films have received increased attention recently because of their potential to reduce production costs compared to those of the prevalent TCO indium tin oxide (ITO). Undoped ZnO and ZnO:Al (0.1, 0.2, 0.5, 1, and 2 wt% Al2O3) polycrystalline films were deposited by RF magnetron sputtering. Controlled incorporation of H2 and O2 in the Ar sputtering ambient was investigated. Though optimal substrate temperature was found to be 200 °C for films grown in 100% Ar, the addition of H2 permits improved electrical performance for room-temperature depositions. Temperature-dependent Hall data suggest that ionized impurity and acoustic phonon scattering dominate at high and intermediate carrier concentration levels, respectively, with evidence of temperature-activated transport at the lowest levels. Lightly doped ZnO:Al demonstrates reduced infrared absorption compared to the standard 2 wt%-doped ZnO:Al, which may be beneficial to device performance.