High quality ZnO films have been obtained by utilizing buffer layers fabricated via nitrogen mediated crystallization (NMC), where sputtering method is employed for preparation of both buffer layers and ZnO films. The crystal grain size of ZnO:Al (AZO) films with NMC-buffer layers is about 3 times larger than that of conventional films, which is considered to be due to the low nuclei density of NMC-buffer layers. As a result, the resistivity of AZO films drastically reduces from 4.76 mΩ·cm for the conventional films to 0.48 mΩ·cm for our films when the total film thickness is 20 nm. The NMC buffer layers also improve the spatial distribution of the resistivity, which indicates that the crystallinity at the initial stage of deposition govern the properties of AZO films. Furthermore, we have succeeded in epitaxial growth of ZnO films, whose FWHM of the rocking curve of (002) peak is as narrow as 0.061°, on c-plane sapphire substrates by using the NMC method. From these results, we conclude that our method described here is full of promise for fabrication of ZnO-based materials.