Effect of Atomic Layer Deposition Temperature on the Growth Orientation, Morphology, and Electrical, Optical, and Band-Structural Properties of ZnO and Fluorine-Doped ZnO Thin Films

The deposition temperature has a significant effect on the growth and physicochemical properties of ZnO thin films. However, changes within a low temperature range have not yet been fully investigated. In this study, ZnO and fluorine-doped (F-doped) ZnO (ZnO:F) thin films were synthesized on glass substrates by atomic layer deposition, and the effect of deposition temperature (80-160 °C) on the crystallization behavior and electrical, optical, and band-structural properties of the thin films were analyzed. During deposition, a constant fluorine concentration was maintained in the anionic pulse gas by employing a 200:1 (v/v) mixing ratio of deionized water to hydrofluoric acid. We found that c-axis growth was preferred with ZnO thin films, while a-axis growth was preferred for ZnO:F thin films. An enhancement in the carrier concentration was also observed in both thin films with increase in the deposition temperature. In addition, the optical transmittance of ZnO:F thin films was slightly higher than that of ZnO thin films, and this transmittance decreased with increasing deposition temperature. More significantly, F-doping led to a larger optical band gap in ZnO:F thin films than in ZnO thin films due to an increase in the carrier concentration with F-doping.