Raman scattering, emission and crystalline phase evolutions in Nd-doped Si-rich HfO₂:N films

The impact of the evolution of crystalline phases with thermal annealing on the Raman scattering and emission spectra of the Nd-doped HfO₂ films enriched with Si- and N- is reported. Films were grown on Si substrates by radio frequency magnetron sputtering of the composed target of Nd₂O₃, Si and HfO₂ in argon-nitrogen reactive plasma. The films were annealed at T_A = 800–1100 °C for t_A = 15 min in a nitrogen atmosphere to stimulate a phase transformation process. The as-deposited and annealed films have been investigated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Raman scattering and photoluminescence (PL) techniques. The as-deposited and annealed films were found to have the fine-grained structure. The monoclinic phase was revealed after film annealing at 950 °C, which transforms into the tetragonal phase after annealing at 1100 °C. The PL study detected a broad PL band in the visible spectral range caused by the emission of host defects and Nd ions. The typical emission of Nd³⁺ ions was also observed in the infrared range (from 800 to 1400 nm). The peculiarities of Raman scattering and PL spectra, their modification with crystalline phase transformation, and the PL excitation mechanism in the films studied are analyzed and discussed. The use of argon-nitrogen plasma allows the manufacture of films with a fine grain structure that can also be of interest for optical waveguide applications.