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

Abstract

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-Si₄ 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 1000°C. Nevertheless, characteristic nanocrystal photoluminescence was observed only after annealing at 1100°C. 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.