Nitrogen (N) is the most promising p-type dopant for zinc oxide (ZnO) with wurtzite structure. The substitution of N atoms for partial replacement of O atoms in wurtzite structure is predicted to cause the slight change in bonding state. We have synthesized ZnO and N-doped ZnO thin films by utilizing a pulsed laser deposition method. Compared with the ultraviolet-visible spectrum of the ZnO thin film, since the absorption edge of the N-doped ZnO thin film denoted a clear redshift, the band gap shrank for the incorporation of N atoms. The band-gap shrinkage of the N-doped ZnO thin film was considered to be due to the existence of Zn-N bond having smaller ionicity than Zn-O bond. Additionally, from the results of Fourier transform infrared measurements, the absorption peaks of the ZnO and N-doped ZnO thin films emerged at 415 and 408 +/- 2 cm(-1), respectively, and were attributed to transverse optical phonon of E-1 mode. The reduction in phonon frequency of approximately 7 cm(-1) can be induced by the complex factors consisting of not only the decrease in reduced mass and interionic distance but also the increase in covalency. (c) 2007 American Vacuum Society.