Effect of annealing on Ge-doped SiO₂ thin films

Thermal annealing effects on optical and structural properties of Ge-doped SiO₂ thin films prepared by the chemical vapor deposition and flame hydrolysis deposition methods were investigated. The thin film prepared by the former method showed inhomogeneous Ge distribution, and Ge oxygen-deficient centers were observed. When it was thermally annealed at temperatures higher than 800°C, the Ge distribution became uniform. The concentration of oxygen deficient centers was found to decrease with the thermal annealing in an O₂ atmosphere, while it increased with the thermal annealing at 1000°C in N₂. This suggests that improvement of the film quality can be achieved by thermal annealing. On the other hand, neither inhomogeneity of Ge distribution nor the appearance of oxygen deficient centers was observed in the film prepared by the latter method, and its film quality was scarcely affected by the thermal annealing.