Silica Film And Its Light-emitting Properties Of Nanocrystalline Silicon Mosaic

To improve the light emission of silicon is the foundation for the development of silicon-based optoelectronic device and the realization of silicon-based optoelectronic integration. To build the nanostructure is an important method for the enhancement of silicon luminescence. Si nanocrystals embedded in a SiO₂ matrix (Si-NCs/SiO₂) are considered as one of the most promising Si based light-emitting materials due to their appreciable and stable light emission as well as their robust structure. In this thesis, the fabrication, structure and photoluminescence (PL) properties of Si-NCs/SiO2 are studied.We fabricated Si-NCs/SiO₂ by reactive pulsed laser deposition with subsequent thermal annealing in an inert nitrogen atmosphere. Strong PL was observed at room temperature from Si nanocrystals with an average diameter of about 5 nm at 325-nm light excitation. Raman spectroscopy, Fourier transform infrared spectroscopy, and optical transmission measurements were used to characterize the deposited films prior to and after annealing. Effects of the oxygen pressure and annealing temperature on the PL properties as well as the structure were discussed in detail. We find that samples deposited in 0.7Pa O₂ after annealing at 1100℃have the maximum intensity ofPL.By time- and space-resolved spectroscopy, we investigated the deposition process and the dynamics of laser ablation plasma, including its generation, expanding, propagation as well as its interaction with O₂ ambient. From the Silicon plasma evolution in vacuum and in the O₂ ambient we find that plasma expands freely in vacuum and its density and illumination gradually decrease with the time. However, Si plasma plume is limited by background oxygen and expands more slowly compared with that in the vacuum. The collision between the laser ablated Si plasma and O₂ leads to the excitation of the active oxygen atom, which makes great contribution to the successful deposition of SiO_x films with high oxygen content.In our research, we tried to fabricate Si-NCs/SiO₂ by a novel method which is coablation of the Si and SiO₂ targets simultaneously by two laser beams with subsequent thermal annealing in an inert nitrogen atmosphere. In the film deposition process, two laser ablated plasmas expand to the substrate and form into Si nano particles embedded in a SiO₂ matrix. During the thermal annealing Si nano particles realize crystallization and transform to Si-NCs/SiO₂ with significant PL. Compared with pulsed laser ablation of pure Si in a reactive oxygen gaseous environment and subsequent thermal annealing, the quality of Si nanocrystals has been improved.