Effects of crystallization on the optical properties of ZnO nano-pillar thin films by sol-gel method

ZnO nano-pillars were prepared on the silica glass by the sol-gel method. The films were crystallized at various crystallized temperatures (600 °C, 650 °C and 700 °C) for 1 h under a pure oxygen atmosphere. The ZnO films had hexagonal structures and preferred a c-axis orientation of (002). Due to the diffused zinc atoms recombining with oxygen atoms at higher temperatures (≥650 °C), the ZnO nano-pillars grew continually from the ZnO grains or the ZnO grain boundaries. When increasing the crystallizing temperature, the quality of ZnO crystallization not only improved, but the ZnO nano-pillars also grew significantly and their length was around 30–150 nm. Notably, a severe decomposition reaction reduced the total volume of crystallization matrix (residual ZnO thin films and increased ZnO nano-pillars). The nano-pillar-thin film of 650 °C not only possessed a better crystallization, but also had the efficacy of nano-pillars that enhanced the optical characteristics. In addition, 5 at.% indium-doped ZnO was also synthesized and then compared with un-doped ZnO to clarify the contribution of indium dopants.