The evolution of the fraction of Er ions sensitized by Si nanostructures in silicon-rich silicon oxide thin films

Photoluminescence (PL) and time-resolved PL experiments as a function of the elaboration process are performed on Er-doped silicon-rich silicon oxide (SRO:Er) thin films grown under NH3 atmosphere. These PL measurements of the Er3+ emission at 1.54 µm under non-resonant pumping with the Er f–f transitions are obtained for different Er3+ concentrations, ranging from 0.05 to 1.4 at.%, and various post-growth annealing temperatures of the layers. High resolution transmission electron microscopy (HRTEM) and energy-filtered TEM (EFTEM) analysis show a high density of Si nanostructures composed of amorphous and crystalline nanoclusters varying from 2.7 × 1018 to 1018 cm−3 as a function of the post-growth annealing temperature. Measurements of PL lifetime and effective Er excitation cross section for all the samples under non-resonant optical excitation with the Er3+ atomic energy levels show that the number of Er3+ ions sensitized by the silicon-rich matrix decreases as the annealing temperature is increased from 500 to 1050 °C. The origin of this effect is attributed to the reduction of the density of sensitizers for Er ions in the SRO matrix when the annealing temperature increases. Finally, extended x-ray absorption fine-structure spectroscopy (EXAFS) shows a strong correlation between the number of emitters and the mean local order around the erbium ions.