Al-doped zinc oxide (ZnO:Al) films were prepared on float glass substrates by in-line reactive mid-frequency (MF) magnetron sputtering from a Zn-Al metallic target (Al 2 wt%). The influences of working gas pressure and substrate temperature on the crystallization behaviours as well as on the electrical and optical properties of the films were investigated. The films prepared at substrate temperature from 100 C to 200 degreesC exhibit columnar structure, having high carrier concentration, high Hall mobility and good conductivity. The crystallinity of the films was improved and the columnar film growth became more dominant as the working gas pressure increased. The grains of the film prepared at a working gas pressure of 970 mPa and a substrate temperature of 170 degreesC are facetted on the film surface and the grain columns are grown through the entire film. Optical transmittance up to 87% in the visible range and electrical resistivity as low as 2.86 x 10(-4) Omega cm were obtained under these optimal deposition conditions. (C) 2002 Elsevier Science B.V. All rights reserved.