The improved efficiency of aluminum doping in ZnO (AZO) thin films grown by atomic layer deposition was demonstrated by controlling the number of surface reaction sites for trimethylalumium (TMA). Prolonged purge time (120 s) for deionized water used as an oxidant decreased the number of hydroxyl groups on the surface via dehydration reaction, resulting in the reduced chemisorption of TMA. The enhanced doping efficiency by sparse distribution of Al dopants was demonstrated by the increased carrier concentration from similar to 4 x 10(20) to similar to 6 x 10(20) cm(-3) for the same Al doping cycle ratio. A comparison was made among the AZO films formed by using the control and modified recipes, focusing on their electrical, structural, and optical properties. (C) 2014 Elsevier B.V. All rights reserved.