Effects of thermal annealing on photoluminescence of Si⁺/C⁺ implanted SiO₂ films

The mechanisms of photoluminescence (PL) originating from Si⁺/C⁺ implanted SiO₂ are still unclear and need to be clarified. Thus, the purpose of this study is to thoroughly investigate the effects of ion implantation and post-annealing temperature on microstructures and PL characteristics of the Si⁺/C⁺ implanted SiO₂ films. A comparative analysis was also conducted to clarify the different optical properties between the Si⁺ and Si⁺/C⁺ implanted SiO₂ films. In this study, thermally-grown SiO₂ films on Si substrates were used as the matrix materials. The Si⁺ ions and C⁺ ions were separately implanted into the SiO₂ films at room temperature. After ion implantation, the post-annealing treatments were carried out using the furnace annealing (FA) method at various temperatures (600-1100°C) for 1 h in a N₂ ambient. The PL characteristics of the implanted SiO₂ films were analyzed using a fluorescence spectrophotometer. The results revealed that the distinct PL peaks were observed at approximately 310, 450 and 650 nm in the Si⁺-implanted SiO₂ films, which can be attributed to the defects, the so-called oxygen deficiency centers (ODCs) and non-bridging oxygen hole centers (NBOHCs), in the materials. In contrast to the Si⁺ ion implantation, the SiO₂ films which were sequentially implanted with Si⁺ and C⁺ ions and annealed at 1100°C can emit white light corresponding to the PL peaks located at around 420, 520 and 720 nm, those can be assigned to the Si-C bonding, C-C graphite-like structure (sp²), and Si nanocrystals, respectively. Moreover, a correlation between the optical properties, microstructures, and bonding configurations of the Si⁺/C⁺ implanted SiO₂ films was also established in this study.