Preparation of N-doped ZnO thin films was attempted using various co-doping methods. A ZnO:Ga (Ga2O3, of 5 wt.%) target was ablated in NO gas by pulsed laser deposition (PLD). In addition, a nitrogen ion gun and an ECR nitrogen plasma source were used as post-N-doping treatment of undoped ZnO films. Optical emission from elemental Zn I, Ga I and O I, as well as from N-2 molecules, was identified in the plasma plume. The structural, optical and electrical properties of these synthesized films were investigated. All films show n-type conduction, with resistivity in the range 10(-3)-10(-2) Omega cm and carrier density from 10(17) to 10(20) cm(-3). (C) 2003 Elsevier Science B.V. All rights reserved.