Transparent Conducting Zinc Oxide Thin Films Doped with Aluminum and Molybdenum

Undoped ZnO, ZnO:Al (0.5, 1, and 2 wt % Al2 O3), and ZnO:Mo (2 wt % Mo) films were deposited by radio-frequency magnetron sputtering. Optimal deposition temperature was found to be ∼200 °C for all films. Electron mobilities of 48 cm2 V-1 s-1 were achieved for undoped ZnO films using a sputtering gas with H2 Ar ratio of 0.3%; corresponding carrier concentrations were ∼3× 1019 cm-3. A target incorporating 0.5 wt % Al2 O3 in ZnO yielded films with mobility of 36 cm2 V-1 s-1 and carrier concentration of 3.4× 1020 cm-3. These films present comparable conductivity and lower free-carrier absorption than films grown from a target containing 2 wt % Al2 O3. Mo was found to be an n -type dopant of ZnO, though electrical and optical properties were inferior to those of ZnO:Al. Temperature-dependent Hall measurements of ZnO:Al films show evidence of a different scattering mechanism than ZnO:Mo films.