Towards an optimum coupling between Er ions and Si-based sensitizers for integrated active photonics
Résumé
Series of Er-doped Si-rich silicon oxide layers were studied with the aim of optimizing the coupling between Er ions and the Si-based sensitizers. The layers were grown at substrate temperature between 400 and 600 °C by the cosputtering of three confocal targets: Si, SiO2, and Er2O3. The influence of Si excess (5–15 at. %) and annealing temperature (500–1100 °C) was examined for two concentrations of Er ions (3.5x1020 and ~1021 cm−3). We report the first observation of significant Er photoluminescence (PL) from as-grown samples excited by a nonresonant 476 nm line, with a lifetime in the range of 1.3–4 ms. This suggests the occurrence of an indirect excitation of Er through Si-based entities formed during the deposition. A notable improvement was observed for both Er PL intensity and lifetime after annealing at 600 °C. This temperature is lower than that required for phase separation, suggesting the formation of “atomic scale” sensitizers (Si agglomerates, for example) considered in recent work. For high Er doping (~1021 cm−3), an optimum Er PL was obtained for the sample grown at 500 °C, annealed at 600 °C, and containing ~13 at. % of Si excess. This high PL should correspond to an optimum fraction of coupled Er for this series, which was roughly estimated to about 11% of the total Er content for an excitation photon flux of few 1019 ph cm−2 s−1. For the moderately Er-doped series (3.5x1020 cm−3) grown at 500 °C, the optimum Er PL was found for the samples containing about 9 at. % silicon and annealed in the 600–900 °C range. The time decay reached a value as high as 9 ms for low Si excess (<6 at. %) and 6–7.5 ms for high values of Si excess. The fraction of Er ions coupled to sensitizers was similarly estimated for the best sample of this series and found to be as high as 22% of the total Er content.