Reducing the Persistent Photoconductivity Effect in Zinc Oxide by Sequential Surface Ultraviolet Ozone and Annealing Treatments

We developed a method to reduce the persistent photoconductivity (PPC) effect of zinc oxide (ZnO) thin film transistors (TFTs) by sequential surface treatment, which includes preannealing/ultraviolet ozone/postannealing (PUP) treatments. Preannealing treatment improves the surface uniformity of the film and eliminates the residual solvent and contaminant molecules without affecting the zinc–oxygen bonds. The ultraviolet ozone (UVO) treatment reduces the oxygen vacancy and increases the amount of metal hydroxide groups on the surface of ZnO by converting adsorbed O 2 – on the ZnO and atmospheric oxygen to highly chemisorbed OH – . Postannealing treatment improves the film quality by making the film densely and inducing zinc–oxygen bonding in the ZnO film. Therefore, the negative threshold voltage shift decreased upon visible light irradiation of the PUP ZnO TFT. The treatment also improve…