Fabrication and optical properties of Er-doped multilayers Si-rich SiO2/SiO2: size control, optimum Er–Si coupling and interaction distance monitoring

Abstract

Abstract The conditions governing the optimization of the coupling rate between the Si nanoclusters (Si-NCs) and the Er ions within a silicon oxide (SO) matrix, in terms of size, density and distribution of the Si-NCs and, more particularly, of the characteristic Er–carrier interaction distance, are investigated for single and multilayers (MLs) obtained by reactive magnetron sputtering. The maximum density of the sensitizers Si-NCs was grown in a Si-rich silicon oxide (SRSO) layer for 50% of hydrogen in the plasma upon annealing at about 900 °C. The Er photoluminescence (PL), or the amount of optically active Er ions, was thus enhanced by about one order of magnitude with respect to the standard conditions. The impact of the size of Si-NC and of that of its separating distance from the neighboring Er ions on the efficiency of the energy transfer process were examined through studies performed on two configurations of MLs: SRSO:Er/SO (ML-A) and SRSO/SO:Er (ML-B). The comparison of the PL spectra obtained from both configurations shows that the Er emission at 1.54 μm is a few tens of times higher for ML-A than for ML-B, because of the closer proximity between the Er ions and the Si-NCs formed within the former configuration. By varying the thickness of the SRSO:Er sublayer for the ML-A, which limits the size of the growing Si-NCs, the energy transfer process from Si-NC to Er becomes less efficient (and probably absent) when the size of Si nanograin reaches and exceeds 5 nm. On the other hand, the increase of the SO:Er thickness for ML-B reveals that the Er PL increases and then saturates for an optimum value of the Er–NC spacing. The PL behavior has been reproduced by an exponentially decreasing Er–carrier interaction with a characteristic interaction distance found dependent on the nature of the sensitizers: about 0.4 ± 0.1 nm for amorphous Si-NC and near 2.6 ± 0.4 nm for Si nanocrystal.