Oxygen sensitivity of erbium-doped AlN films probed by site selective spectroscopy

Abstract In the aim of better understand the influence of oxygen on the luminescent properties of Er:AlN films, two samples synthesized by radiofrequency reactive magnetron sputtering, have been analysed by site-selective spectroscopy around 1.55 μm and compared to a reference aluminosilicate sample. The erbium content in the films was estimated to 3.3 at.% and oxygen content ranges from 6.2 at.% to 58.6 at.% (determination by EPMA). Line narrowing study was performed for values 6.2 at.% and 22.5 at.%. Both films were annealed at 1075 K for 1 h. Site-selective spectroscopy was carried out using a Ti:sapphire laser light with typical linewidth of 2 GHz tuned around 980 nm as the excitation source. The samples were cooled down to 1.5 K in a liquid-helium bath cryostat and their 4 I 13/2 ↔ 4 I 15/2 luminescence was detected using a high-sensitivity germanium-cooled detector. It appears that the site distribution of the Er:AlN samples is not continuous as in classical aluminosilicate glass but presents a rupture that suggests the existence of two kinds of sites for erbium: oxygen site and nitrogen site. These observations can easily be interpreted within the framework of the nephelauxetic effect that explains a shift of the site distribution to the longer wavelengths with an increase of boundings bonding covalency.