Nanoscale evidence of erbium clustering in Er-doped silicon-rich silica
Résumé
Photoluminescence spectroscopy and atom probe tomography were used to explore the optical activity and microstructure of Er 3+-doped Si-rich SiO 2 thin films fabricated by radio-frequency magnetron sputtering. The effect of post-fabrication annealing treatment on the properties of the films was investigated. The evolution of the nanoscale structure upon an annealing treatment was found to control the interrelation between the radiative recombination of the carriers via Si clusters and via 4f shell transitions in Er 3+ ions. The most efficient 1.53-μm Er 3+ photoluminescence was observed from the films submitted to low-temperature treatment ranging from 600°C to 900°C. An annealing treatment at 1,100°C, used often to form Si nanocrystallites, favors an intense emission in visible spectral range with the maximum peak at about 740 nm. Along with this, a drastic decrease of 1.53-μm Er 3+ photoluminescence emission was detected. The atom probe results demonstrated that the clustering of Er 3+ ions upon such high-temperature annealing treatment was the main reason. The diffusion parameters of Si and Er 3+ ions as well as a chemical composition of different clusters were also obtained. The films annealed at 1,100°C contain pure spherical Si nanocrystallites, ErSi 3 O 6 clusters, and free Er 3+ ions embedded in SiO 2 host. The mean size and the density of Si nanocrystallites were found to be 1.3 ± 0.3 nm and (3.1 ± 0.2) × 10 18 Si nanocrystallites·cm −3 , respectively. The density of ErSi 3 O 6 clusters was estimated to be (2.0 ± 0.2) × 10 18 clusters·cm −3 , keeping about 30% of the total Er 3+ amount. These Er-rich clusters had a mean radius of about 1.5 nm and demonstrated preferable formation in the vicinity of Si nanocrystallites.
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