According to optical theory, the extinction coefficient is an optical constant representing the magnitude of light absorption. The refractive index of silicon is n, the extinction coefficient is k, and the reflectivity is R. The photon energy E is represented by these parameters. Accordingly, silicon has a high reflectance of more than 35% for visible light. Obviously, the reason why silicon has metallic luster is because it has a high refractive index. Solar cells suppress reflection and improve efficiency by integrating refractive index

So why is the refractive index of silicon high? The refractive index has a large relationship with the dielectric constant, and the square of the refractive index is equal to the dielectric constant. On the one hand, the dielectric constant is proportional to the reciprocal of the E-square of the constant gap. Therefore, silicon has a much larger refractive index than silicon with a large band gap (Zn0, etc.).

Silicon has a metallic luster not because of free electrons but because of its high point refractive index.

The refractive index of a semiconductor has a tendency to become larger as the band gap decreases.