The Research On Crystallization And PL Properties Of Si Quantum Dots In Si-O And Si-O-N System

Si/SiO₂ composite films and SiO₂ /Si/SiO₂ sandwich structure were fabricated through alternate-sputtering. Two-step annealing, rapid thermal annealing and furnace annealing, was adopted to form Si quantum dots in Si/SiO₂ composite films, while the furnace annealing was adopted in SiO₂ /Si/SiO₂ sandwich structure. Several Si_OxN_y films were synthesized by reactive-sputtering, and the samples were treated through furnace annealing. The films were observed using TEM, EDS and FTIR were adopted to investigate the structure and bond types of films. The growth mechanisms of nanocrystals in these films were discussed, and the photoluminescence (PL) properties were also measured. After the two-step annealing, the supersaturated Si atoms in SiO₂ segregated in two forms: some were absorbed by the Si cluters; some others gathered into new Si clusters.The deposition rate can affect the segregation and crystallization of Si in the SiO₂ matrix. With the increase in sputtering rate, the number of structure defects and initial clusters which acted as the nucleation centers increased, and then the density of Si nanocrystals increased after the rapid thermal annealing. At the same time, the size distributions of Si nanocrystals varied from monodisperse to irregular to monodisperse due to influence of the Si nucleus centers and the diffusion of Si atoms.The Si columnar nanocrystals were found in the SiO₂ /Si/SiO₂ sandwich structure after annealing. According to the thermodynamic calculation, the nanocrystals are more likely to nucleate at Si/SiO₂ interfaces, and the appearance of Si {1 1 1} plane parallel to the Si/SiO₂ interfaces is the result of energy optimization. The stress and existence of impurity in the Si layer lead to the formation of nanotwins.The loss of nitrogen in the Si_OxN_y films was investigated. The density of nanocrystals increased with the extent of the nitrogen loss during the annealing. According to the composition measurement and Si-N binary phase diagram, the constraint effect of Si_OxN_y matrix was weakened during the losing process of nitrogen, which accelerated the diffusion and crystallization of Si atoms. The PL properties of Si_OxN_y film with nanocrystals can be attributed to the structure defects in the film and quantum confinement effect.