Influence Of Substrate Temperature And Gd Doping On The Structure And Properties Of HfO₂Thin Films

HfO2films with different substrate temperature and HfGdO films with different Gd content are successfully prepared by RF magnetron reactive sputtering. The [Gd]/[Gd+Hf] atomic ratio (between0-72%) of HfGdO films are adjusted by changing the number of Gd target pieces. The structure, composition, surface morphology and optical property of both HfO2films and HfGdO films are characterized by electron probe microscope, x-ray diffraction, atomic force microscope, ultraviolet-visible spectrophotometer and photoluminescence spectroscopy, respectively. The results show that both substrate temperature and Gd content have important influence on structure, surface morphology and property of HfO2based films. For HfO2films the surface roughness gradually reduces with the increase of substrate temperature. The analytical result of multifractal spectra from surface morphology shows that the values of△a gradually reduce, indicating a well distribution of the film surface elevation with the increasing of substrate temperature. All of HfO2films deposited at room temperature are monoclinic phase. Grains are preferentially oriented to (-111). The average grain size increases with the increasing of substrate temperature and has a large effect on the lattice expansion. The optical band gap value of HfO2films deposited at various temperatures is5.72eV (RT),5.76eV (200℃),5.68eV (400℃) and5.73eV (600℃), respectively. For HfGdO films the change of structure with the increasing of Gd Content is HfO2(monoclinic phase) to Gd2Hf207(cubic phase, Gd:22%-38%) to(GdHf)2O3(cubic phase, Gd:56%-72%). Tetragonal phase of the HfO2film is separated from the38%Gd-Gd2HfO7film and phase separation phenomenon is observed from the72%Gd-(GdHf)2O3film after800℃annealing. With the increase of Gd content, the thicknesses of HfGdO films gradually increase, while the surface roughness and optical band gap of HfGdO films gradually reduces.