Silicon nanocrystal formation upon annealing of SiO2 layers implanted with Si ions

The formation of silicon nanocrystals in SiO2 layers implanted with Si ions was investigated by Raman scattering, X-ray photoelectron spectroscopy, and photoluminescence. The excess Si concentration was varied between 3 and 14 at. %. It was found that Si clusters are formed immediately after implantation. As the temperature of the subsequent annealing was raised, the segregation of Si accompanied by the formation of Si-Si-4 bonds was enhanced but the scattering by clusters was reduced. This effect is attributed to the transformation of loosely packed clusters into compact, separate-phase nanoscale Si precipitates, with the Raman peak observed at 490 cm(-1) being related to surface scattering. The process of Si segregation was completed at 1000degreesC. Nevertheless, characteristic nanocrystal photoluminescence was observed only after annealing at 1100degreesC. Simultaneously, scattering in the range 495-520 cm(-1), typical of nanocrystals, appeared; however, the surface-related peak at 490 cm(-1) persisted. It is argued that nanocrystals are composed of an inside region and a surface layer, which is responsible for their increased formation temperature. (C) 2002 MAIK Nauka/Interperiodica.