High quality ZnO thin films with a c-axis-orientated wurtize structure have been grown on a Si(100) substrate by plasma enhanced chemical vapor deposition using a zinc organic source [Zn(C2H5)(2)] and carbon dioxide (CO2) gas mixture at low temperature, The dependence of ZnO thin-film quality on the gas flow rate ratio of Zn(C2H5)(2) to CO2 (GFRRZC) is studied-by x-ray diffraction (XRD), optical transmission spectra (OTS), and photoluminescence spectra (PL). The optical properties show that the GFRRZC has an obvious effect on the band gap of ZnO films. The relationship between the quality of the ZnO thin films and the substrate temperatures is also studied by XRD and PL spectra. The XRD spectra show that the full width at half maximum (FWHM) of the diffraction peak at 34.42degrees of (0002) oriented ZnO is 0.25degrees at the optimized condition, indicating the formation of high quality ZnO films. The PL spectra show a strong excitonic emission at about 3.26 eV without the emission around 2.5 eV related to deep-level defects, implying the formation of the stoichiometric ZnO thin films. The smallest FWHM of the PL spectrum of a ZnO thin film is 111 meV at room temperature.