The influence of precursor type, deposition time and doping concentration on the morphological, optical and electrical characteristics of ZnO and ZnO:Al thin films and nanostructures deposited by ultrasonic spray pyrolysis at 400 degrees C on glass substrates was investigated. A deposition period of 30 min resulted in compact, uniform samples with thickness of 30 and 45 nm, and growth rates in the order of 1 and 1.5 nm/min for the Zn acetate and Zn nitrate precursors, respectively. The as-grown films showed good adhesion and excellent optical transmission. Moreover, films grown using Zn acetate precursor exhibited considerably low resistivity, being 14 Omega.cm for a deposition time of 30 min. Surface roughness was observed to increase with deposition time, while Al doping up to 5% reduced the resistivity down to 4 Omega.cm without affecting the optical transmission of the films. Finally, films grown using Zn nitrate were observed to exhibit better photoconductivity than those grown with Zn acetate. (C) 2013 Elsevier B.V. All rights reserved.