In this study, the influence of the oxygen/argon (O-2/Ar) flow ratio on aluminum-doped zinc oxide (ZAO) films using a Zn1.22Al0.02O1.25 target was investigated systematically. Different samples were obtained by changing the O-2/Ar flow ratio from 0.11 to 3. The grain size first decreased and then increased as the O-2/Ar flow ratio increased, reaching a minimum size of 8.53 nm at a flow ratio of 1. All films showed different average transmittances above 400 nm because of different surface structures and film thicknesses; the thickness of films varied from 261 to 897 nm. Moreover, the ZAO films exhibited different optical bandgaps between 3.22 eV and 3.31 eV. The resistivity first increased from 2.1 x 10(-4) Omega cm to 350 x 10(-4) Omega cm and then decreased to 220 x 10(-4) Omega cm with increasing O-2/Ar flow ratio. Both the carrier concentration and Hall mobility first decreased from 5.6 x 10(20) cm(-3) to 0.3 x 10(20) cm(-3) and from 3.9 cm(2)/Vs to 0.6 cm(2)/Vs, respectively, and then increased to 0.9 x 10(20) cm(-3) and 1.1 cm(2)/Vs, respectively, with increasing O-2/Ar flow ratio. (C) 2014 Elsevier B.V. All rights reserved.