We present a combined analysis using cross-sectional transmission electron microscopy (X-TEM) and Raman
spectroscopy to study the early formation dynamics of Si-nanocrystals, formed in SiO2 thin films after Si+ implantation
and rapid thermal processing (RTP). We obtained values for the diffusion coefficient of Si in thermally grown SiO2 and
the activation energy to precipitate formation in the first 100 seconds of high temperature annealing. These values
indicate that the formation of Si-nanocrystals in implanted oxides proceeds much more efficiently than purely via a self
diffusion process. We propose that the nanocrystal formation is assisted by the presence of both oxygen vacancies and
SiO molecular species, presumably generated by the ion irradiation. Microscopy images reveal the ensemble nanocrystal
population to be most accurately represented by a lognormal distribution function with characteristic values for the mean
particle diameter, d and variance, σ. The evolution of the silicon nanocrystals with annealing was also investigated by
measuring the Raman scattering signal associated with the TO phonon mode arising from Si-Si bonds in Si-rich oxides
grown on transparent (Al2O3) substrates. This greatly simplifies the experimental observation of the Raman spectra from
Si-nanocrystals as compared to previous studies of nanocrystals in oxide films on silicon substrates.
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.
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