Influence of stoichiometry on the structural and optical properties of erbium silicate

Er-doped materials attract a considerable attention for the development of luminescent systems for Si-based microphotonics, since Er ions can emit photons at 1.54 mum. The Er concentration that can be inserted in solid hosts is however limited to about 1020 at/cm3 due to low Er solid solubility; this limits the number of emitting centers. An alternative approach which could overcome this limit is represented by erbium compounds and, in particular by erbium silicate. It has been previously demonstrated that this material contains 1022 optically active Er ions/cm3 and this could allow to obtain high-gain coefficient. High temperature annealing treatments have been demonstrated to be effective for the optimization of optical emission from this compound, but the thermal budget which can be provided to this system is limited by the fact that rare earth silicates can chemically react with silicon. Therefore the synthesis of silicate thin films exhibiting an efficient optical emission, such as to be used for the fabrication of active optical devices integrated in silicon, requires an accurate control of their structural properties. We report a detailed study of the properties of Er silicate thin films as a function of the stoichiometry and of the annealing conditions. A strong correlation between the structural and optical properties has been demonstrated.