Amorphization and recrystallization of ion implanted Si nanocrystals probed through their luminescence properties

In this paper the amorphization of Si nanocrystals (nc) by ion beam irradiation and the subsequent recrystallization are investigated in detail. The luminescence properties of Si nanocrystals embedded within a SiO2 matrix are used as a probe of the damaging effects generated by high-energy ion beam irradiation. Samples have been irradiated with 2 MeV Si+ ions at different doses, in the range between 1 x 10(9) and 1 X 10(16) cm(-2). By increasing the ion dose, the nc-related photoluminescence (PL) strongly decreases after a critical dose value. It is shown that the lifetime quenching alone cannot quantitatively explain the much stronger PL drop, but the total number of emitting centers has to diminish too. Moreover, we studied the recovery of the amorphized Si nc by performing thermal annealings. It is demonstrated that the recovery of the PL properties of completely amorphized Si nc is characterized by a single activation energy, whose value is 3.4 eV. Actually, this energy is associated to the transition between the amorphous and the crystalline phases of each Si grain. The recrystallization kinetics of Si nanostructures is demonstrated to be very different from that of a bulk system.