The influence of indium concentrations on electrical properties of In-N co-doped ZnO thin films has been studied. Based on Hall-effect measurements and analyses, impurity scattering is the dominant mechanism determining the diminished mobility in ZnO with higher In concentration. X-ray photoelectron spectroscopy reveals that the presence of In enhances the solubility of N with the formation of In-N and Zn-N bonds. The optimal properties, namely resistivity of 16.1 Omega cm and Hall mobility of 1.13 cm(2) V-1 s(-1), are obtained at an indium concentration of 0.14 at.%. The diffraction angle of co-doped ZnO is closest to that of un-doped ZnO. (c) 2006 Elsevier B.V. All rights reserved.