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 degrees 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 degrees 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 degrees 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.