Annealing impact on emission and phase varying of Nd-doped Si-rich-HfO₂ films prepared by RF magnetron sputtering

HfO₂ films doped with Nd and Si atoms were produced by RF magnetron sputtering in argon plasma atmosphere. The effect of annealing treatment on the morphology, crystal structure and light emission of the films was investigated by means of the scanning electronic microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). The thermal treatment was performed in the temperature range of T_A = 800–1100 °C in horizontal furnace with continuous nitrogen flow. For annealed Si–HfO₂:Nd films, the SEM study revealed the formation of the grains with the mean size of about 20–60 nm that show the tendency to enlarge with the T_A rise. Besides, the phase separation was observed and tetragonal HfO₂ and SiO₂ phases were detected by the XRD method for the films annealed at T_A > 950 °C. The PL study revealed that both Nd³⁺ ions and host defects contribute to PL emission whereas their relative contribution depends on the T_A and on the crystal phase of host matrix. The highest PL intensity of Nd³⁺ ions via 4f inner electronic shell levels was detected for T_A = 950 °C. The variation of PL intensity of Nd³⁺ ions was correlated with the change of PL intensity of the band caused by the host defects. These latter participate in the energy transfer towards Nd³⁺ ions. This statement was confirmed by XPS data, as well as by the shape of PL spectra. It was shown that the bright emission via Nd³⁺ ions can be achieved for those located in the tetragonal HfO₂ matrix.