In this study, zinc oxide films were deposited by an ion-beam sputter deposition in various oxygen partial pressures at room temperature. The films changed the structures from amorphous to polycrystalline with increasing the oxygen partial pressure ( ). The optimal was found at Torr because the film prepared at the oxygen partial pressure had the lowest resistivity and the highest transparence in the visible light region. The lowest resistivity results from a great number of oxygen vacancy sites formed on the polycrystalline surface as exposed to the atmosphere. Moreover, the film has the highest XRD peak intensity, smallest FWHM diffraction peak, smallest -spacing, and smallest biaxial stress. 1. Introduction ZnO has a hexagonal wurtzite structure with a wide direct band gap of about 3.4？eV. It is naturally an n-type semiconductor due to its deviation from stoichiometry as the presence of oxygen vacancies or zinc interstitials [1]. It is important to fabricate an optimal ZnO film for development of optoelectronic devices due to its high transparence in the visible light region and its low resistivity [2]. In the previous studies of Ti, Zr, Si, and Al metallic oxide films prepared by ion-beam sputter deposition (IBSD) [3], the oxygen partial pressure ( ) can affect their deposition rates, optical properties, and surface morphologies. Depositing at each optimal , the metallic oxide films have higher transparence, higher refractive indices, lower extinction coefficients, and lower surface roughness. They are all amorphous structures and nonconductive films [4]. In this study, an optimal for zinc metallic target was also found. However, the as-deposited zinc oxide film is polycrystalline structure and has conductive property due to free electron carrier, which induces the optical band gap shift by the Burstein-Moss (BM) effect [5] and band-gap-narrowing (BGN) effect [6]. The BM effect is the blue-shift phenomenon of the band edge where the Fermi level merges into the conduction band with the increase of the carrier concentration. Yet, the BGN effect is a red-shift phenomenon of the band edge because the electron-electron repulsive interaction and the localization of the electron wave function is weakened by the screening of the potential in the high carrier concentration [7]. Apparently, the band gap shift is affected by the combination of the BM and BGN effects as increasing carrier concentrations. Sakai et al. have also investigated that the carrier concentration strongly affects the optical band gap resulting from the oxygen vacancies controlled by the
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