Concentration of Er3+ ions contributing to 1.5-μm emission in Si/Si:Er nanolayers

We have investigated the percentage of Er3+ ions which contribute to the low temperature 1.5-μm photoluminescence in Si/Si:Er nanolayer structures grown by sublimation molecular beam epitaxy. In a structure optimized for preferential formation of the Er-1 center with ultranarrow emission lines, we find that emission saturates when approximately 2% of all the Er dopants recombine radiatively upon optical excitation. In a structure where the silicon spacer thickness has been optimized for the maximum (broadband) emission intensity relative to Er contents, we show that in saturation approximately 15% of Er dopants contribute photons. At the same time, from the initial growth of emission intensity on excitation flux at low power, we estimate the maximum percentage of Er ions attaining optical activity. These limits of optical activity of Er in Si/Si:Er nanolayer structures are determined as 25% and 48% for Er-1 and total emission, respectively. In the context of this high level of optical activity, potential of Si/Si:Er nanolayer structures for realization of optical amplification at low temperatures is pointed out