LaFeOxNy perovskite thin films: Nitrogen location and its effect on morphological, optical and structural properties

This paper reports on the first study of the chemical, optical, and structural properties of lanthanum ferrite oxynitride thin films deposited by reactive magnetron sputtering. The thin films were deposited in an Ar/O ₂/N ₂ mixture as reactive plasma, from two elemental La and Fe targets, at a room and high temperature (25 and 800 °C). The films deposited at room temperature are amorphous and have been flash annealed to crystallize the perovskite. The oxynitride properties were investigated and compared to the oxide films deposited in Ar/O ₂ gas mixture. All the oxide and oxynitride films present an orthorhombic structure. However, the nitrogen doping is limited to 1–1.5% and leads to the lattice expansion (4%), the bandgap narrowing, a lower electrical resistivity in range [25–350 °C], and a modification of Infrared and Raman spectra. Electron Energy Loss Spectroscopy measurements clearly show the presence of two nitrogen sites with an “active” intra-granular nitrogen associated to a variation of the physical properties.