Dependence of zinc oxide thin film properties on filtered vacuum arc deposition parameters

Abstract

The micro-properties (structure and composition) and macro-properties (electrical and optical properties) of zinc oxide thin films deposited on glass substrates using a filtered vacuum arc deposition system were investigated as a function of oxygen pressure (0.37–0.5 Pa) and arc current (100–300 A). The films were polycrystalline and the crystal plane orientation varied with the oxygen pressure and arc current, tending to be aligned parallel to the c-axis. The sizes of the crystallite grains were 10–35 nm. The films were found to be compressively stressed, with stress in the range of −2.5–0 GPa. The stress in any sample decreased as a function of arc current; however, its dependence on the pressure also depended on the applied arc current. The compressive stress in samples deposited with arc current in the range 100–150 A, decreased with the pressure from −2.5 to −1.5 GPa (0.37–0.5 Pa), whereas it increased with the oxygen pressure in samples deposited with arc current ranging from 200–300 A. The compressive stress in all samples deposited with the highest oxygen pressure (0.51 Pa) was in a relatively narrow range of −2.1 to −1.7 GPa.Film composition, determined by x-ray photoelectron spectroscopy, depended weakly on the deposition parameters. All samples had zinc excess, with a typical oxygen to zinc atomic concentration ratio of 0.7–0.8. Film thickness, in the range of 80–780 nm, depended linearly on both the deposition parameters.The electrical resistivity (ρ) of the films was in the range of (1–5) × 10−4 Ωm, depending weakly on the deposition parameters. The electrical resistivity of the films with larger grain size was higher than that of films with smaller grains, whereas it increased with film stress. The optical transmission of the films, expressed by the extinction coefficient, depended strongly on both the deposition parameters (arc current and oxygen pressure). The lowest extinction was obtained with films deposited with higher pressure (P ⩽ 0.5 Pa) and lower arc current (I ⩾ 200 A). The lowest extinction coefficient was ∼4 × 10−4 nm−1 in the visible and the near-IR range of the spectrum. Films with larger grain size and lower stress had a relatively larger extinction coefficient (∼8 × 10−3 nm−1).