Annealing and doping effects on structure and optical properties of sol–gel derived ZrO2 thin films

ZrO2 and rare earth elements doped ZrO2 thin films were prepared by sol–gel method using zirconium n-propoxide as the precursor, with rapid thermal annealing (RTA) and conventional furnace annealing (CFA). Crystalline structure of ZrO2 films was analyzed by X-ray diffraction. The high-temperature tetragonal phase was observed at room temperature. The effects of rare earth elements doping and different heat treatment processing on the structure and optical properties were observed and discussed. The temperature of transformation from tetragonal to monoclinic of rapid thermal annealed films (∼750 °C) is higher than that of conventional furnace annealed films (∼450 °C), while in rare earth elements doped films, no monoclinic is observed even at 850 °C. Refractive index of ZrO2 films was measured by prism coupling. The refractive indices were found to vary as functions of annealing temperature, annealing technique and doping elements. RTA and rare earth elements doping were found to increase the refractive index of ZrO2 films.