As a high refractive index material, silicon is widely used for infrared thin-film coatings. However, the absorption of silicon films is relatively high, especially in the near infrared region with wavelengths less than 1.8µm. In this paper, we investigated the effect of post-deposition annealing on the microstructure and optical properties of silicon films. Silicon films were deposited by electron beam evaporation and then annealed in air within the temperature range from 200 to 600 °C. The films were characterized by X-ray diffraction(XRD), Raman spectroscopy, electronic-spin resonance(ESR), and optical transmittance measurement, respectively. The optical constants of the films were obtained by the simulation of transmission spectra. It was found that all the silicon films maintained amorphous in microstructure, but, with the increase of temperature, the amorphous network order was improved on both short-range and medium-range scales. When samples being annealed at 400°C, the defect density decreased to the minimum, about one fifth of the as-deposited samples. Meanwhile, extinction coefficient also fell to the minimum, and then increased by rising the annealing temperature further. These results showed that post-deposition annealing could reduce optical absorption of silicon films remarkably in the near infrared region, so as to improve the optical performance of the silicon films.
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