Preparation of N-doped ZnO thin films was attempted using various co-doping methods. A ZnO:Ga (Ga 2 O 3 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 Ω cm and carrier density from 10 1 7 to 10 2 0 cm - 3 .