Enhanced rare earth luminescence in silicon nanocrystals

Efficient luminescence from rare earths ions embedded within silicon nanocrystals is reported. Samples were prepared either by high dose Si implantation into Si dioxide or by plasma enhanced chemical vapor deposition of sub-stoichiometric Si-rich oxides. In both cases nanocrystals were formed by Si precipitation and phase separation induced by high temperature annealing. Erbium was then introduced in SiO2 samples containing the nanocrystals by ion implantation. Luminescence measurements showed that the Er signal at 1.54 mu m is two orders of magnitude higher in the sample containing the nanocrystals with respect to pure SiO2. Moreover, this enhanced luminescence is observed also for other rare earths (namely Yb, Tm and Nd). Excitation spectroscopy demonstrated that excitation within the nanocrystals occurs via an efficient carrier-mediated process. Indeed, with increasing rare earth luminescence the intrinsic nanocrystal luminescence is seen to decrease. Furthermore, the non-radiative processes usually limiting Er luminescence in Si, are shown to be almost absent within the nanocrystals. The implications of these results are discussed.