Influence of annealing on the Er luminescence in Si-rich SiO2 layers co-implanted with Er ions

The impact of rapid thermal annealing (RTA) in producing samples by sequential implantation of Si and Er ions into a 200 nm SiO2 layer combined with different annealing cycles as well as the corresponding room-temperature visible and infrared photoluminescence (PL) have been studied. The Er-related PL intensity at 1533 nm for the samples prepared by implanting Si with subsequent annealing, followed by Er implantation and final annealing (type-I) was found to be stronger than the one produced similarly but without the first annealing step (type-II). In fact, the 1533 nm peak intensity in the optimized RTA processed sample is comparable to the PL yield of the furnace-annealed sample. Moreover, the excitation wavelength (405 nm) was found to be suitable for exciting the Si=O related point defects in the SiO2 layer, and can provide a PL band with a maximum at ~580 nm. While this band was further intensified in presence of Si nanocrystals (Si NCs), it became weaker by introducing additional Er3+ ions with a concomitant rise of the 1533 nm Er PL, confirming the visible range pumping of Er3+. The detailed spectral analyses suggest that the 580 nm band is the result of the excitation/deexcitation mechanism in molecule like states in Si=O or the Si=O state mediated recombination of carriers in Si NCs according to the model proposed by Wolkin et al. [Phys. Rev. Lett. 82, 197 (1999)]. The samples were further characterized by transmission electron microscopy and Fourier-transform infrared-spectroscopy. The time resolved PL measurements and a modelling by rate equations were also performed to determine and justify the energy migration mechanism from Si NC to the neighbouring Er3+.