Al-doped ZnO (ZnO:Al) films were deposited at different substrate temperatures and H-2/(H-2+Ar) flow ratios by rf magnetron sputtering. The (002) preferred orientation is observed in all the deposited films; stress is decreased and crystallinity is improved for the films deposited at RT but they have no obvious change for the films deposited at 100-300 degrees C with increase in H-2 ratio. With increasing H-2 ratio, carrier concentration and mobility obviously increase for the films deposited at RT and 100 degrees C, and they slightly increase for the films deposited at 200 degrees C but they are almost unchanged for the films deposited at 300 degrees C. The results imply that the hydrogen is doped into ZnO lattice to form interstitial hydrogen (H-i), which is unstable above 200 degrees C. The average transmittance of the films in visible region is above 80%, and it can be increased due to the hydrogen doping. The energy gap (E-g) of the films is mainly controlled by the carrier concentration, but it is also related to the crystallite size and stress for ZnO:Al films deposited at RT. The carrier transport mechanism and E-g as a function of carrier concentration in ZnO:Al films are also discussed. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.022206jes] All rights reserved.