Incorporation effect of Y2O3 on the structure and optical properties of HfO2 thin films

HfO2 thin films doped with different concentration of Y2O3 have been prepared on fused silica at substrate temperature of 160 °C using electron beam evaporation technique. The influence of doping ratio on the structure and optical properties was studied in this work. Several characterization techniques including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscope (SEM), ellipsometer and spectrophotometer were used for the study of microstructure and optical properties of the films. From the results of XPS analysis, it is found that core level peak positions of Hf 4f and O 1s shift to lower binding energy, which was attributed to the structure change of the HfO2 films after Y doping. The XRD and SEM results demonstrate that the concentration of Y2O3 affects a lot on the crystallization of Y2O3 doped HfO2 (YDH) films. Cubic phase of the films appears as the doping ratio of Y2O3 is over 8 mol% without any post annealing process. At the meantime, the optical band gap of the film is broadened with doping ratio of Y2O3 increasing. An inverse correlation between band gap energy (Eg) and refractive index (n) of the films is also found in our work.

► HfO2 films with five different doping ratios of Y2O3 were prepared on fused silica. ► Cubic YDH films were obtained at relatively low temperature of 160 °C. ► Core levels of Hf 4f and O 1s shifted to lower energy with doping ratio increasing. ► Optical band gap (Eg) of the films broadened gradually with doping ratio increasing. ► An inverse correlation between Eg and refractive index of films was found.