Optical spectroscopy of Er doped Si-nanocrystals on sapphire substrates fabricated by ion implantation into SiO₂

We present the results of an optical investigation of a series of Er doped silicon nanocrystal (Si-NC) samples which were fabricated via ion implantation into SiO₂ on sapphire substrates, followed by a range of rapid thermal processing. The photoluminescence spectra of the Si-NC emission revealed an increase in luminescence intensity and a red-shift of the peak wavelength as a function of annealing conditions. We attribute the former effect to the reduction of implantation induced defects with increasing annealing temperature/duration. Measurements of the rate of decay of photoluminescence intensity at room temperature show a corresponding increase in the carrier lifetimes which is also an indication of a reduced contribution from non-radiative centers. The red-shift of the peak Si-NC intensity is ascribed to an increasing mean Si-NC size as a function of the annealing conditions. Also presented is an estimation of the relative Er sensitization which reveals that the smallest Si-NC size distribution leads to the greatest sensitization ratio. Further investigation in the form of excitation spectroscopy was used to show that Er ions are sensitized not only by energy transfer from the Si-NCs, but also, crucially, from defect states in the SiO₂.