This study reports on the dependence on Ga concentration of the electrical and optical properties of ZnO films doped at a N concentration of 10(18) cm(-3). For Ga concentrations below 0.5 mol %, the N concentration was kept at 10(18) cm(-3). However, as the Ga concentration increased to 5 mol %, the N concentration suddenly increased from 10(18) to 10(19) cm(-3). Furthermore, the donor-acceptor pair emission and yellow luminescence in N single-doped ZnO films were suppressed significantly by doping with Ga at a concentration of 0.1 mol %. However, doping with Ga concentrations above 0.5 mol % resulted in increased red luminescence originating from deep levels generated through the excessive incorporation of Ga atoms. An evaluation of the crystalline quality and electrical properties indicated that the Ga atoms located on the Zn sites changed largely from shallow donor sources to compensating defects trapping electrons at Ga concentrations in the 0.5 to 5 mol % range. These results suggested that the increased N concentration and the enhancement of ultraviolet (UV) emission could be attributed to the role played by the Ga atoms located on the Zn sites in the N single-doped ZnO films. (C) 2003 The Electrochemical Society.