Polycrystalline ZnO thin films with a preferred orientation were successfully grown by metal organic chemical vapor deposition at temperatures <= 300 degrees C. By injecting additional Ar gas through a by-pass line, good quality ZnO films were grown at low temperature. The ZnO films grown at substrate temperatures < 200 degrees C showed a porous microstructure whereas a dense undoped ZnO film showing a high conductivity and no Zn phases was grown at 210 degrees C. The ZnO film grown at low temperatures by MOCVD showed improved emission properties compared with the films grown by sputtering. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.