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

This paper reports on the first study of chemical, optical, and structural properties of lanthanum ferrite oxynitride thin films deposited by reactive magnetron sputtering. Thin films were deposited in a Ar/O₂/N₂ mixture as reactive plasma, from two elemental La and Fe targets, at room and high temperature (25 and 800°C). Films deposited at room temperature are amorphous and have been flash annealed to crystallize the perovskite. Oxynitride properties were investigated and compared to oxide films deposited in Ar/O₂ gas mixture. All oxide and oxynitride films present an orthorhombic structure. However, nitrogen doping limited to 1-1.5% leads to lattice expansion (4%), bandgap narrowing, a lower electrical resistivity in range [25-350°C] , and 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 an enhancement of the physical properties.