Annealing Effects of Zn Seed Layers on Optical and Structural Properties of ZnO Thin Films grown on Polyimide Substrates

ZnO thin films were grown on Zn-deposited polyimide (PI) substrates using the sol-gel spin-coating method. The Zn seed layers were annealed at 200, 300, and 400 ℃. The annealing effects of the Zn seed layer on the structural and optical properties of the ZnO thin films were investigated for the first time. By adjusting the annealing temperature of the Zn seed layers, we achieved a significant enhancement in the crystallinity of the ZnO thin films. The ZnO thin film grown on a non-annealed Zn seed layer had a yellow/orange emission, whereas those grown on annealed ones had a green emission as well as lower defect-related deep-level emissions. The narrowest full width at half maximum of the near-band-edge emission was observed for the ZnO thin films grown on the Zn seed layers annealed at 200 and 300 ℃. We found that the structural and optical properties of the ZnO thin films grown on the Zn seed layer annealed at 400 ℃ were deteriorated, which could be attributed to considerable changes in the characteristics of the PI substrate at the annealing temperature of 400 ℃.