Abstract: Energy band structure and optical properties of cubic Ca2Si and P(Al)-doped Ca2Si have been calculated by density functional theory of the first-principles pseudo potential wave method.The results show that the energy band of cubic Ca2Si is a direct semiconductor with the band gap of 0.55483 eV.The valance bands are mainly compose of Si 3p and Ca 3d 4s, the conduction bands mainly composed of Ca 3d 4s and Si 3p, the static dielectric function is 11.92474, the refractive index is 3.45322.The P-doped cubic Ca2Si is an n-type direct semiconductor with the band gap of 0.42808 eV.The valance bands are mainly compose of Si 3p, P 3p and Ca 3d 4s, the conduction bands mainly composed of Ca 3d, P 3p 3s and Si 3p, the static dielectric function is 7.92698, the refractive index is 2.81549.The Al-doped cubic Ca2Si is an n-type with the band gap of 0.26317 eV.The valance bands are mainly compose of Si 3p, Al 3p and Ca 3d, the conduction bands mainly compose of Ca 3d 4s, Al 3p 3s and Si 3p, the static dielectric function is 17.02409, the refractive index is 4.12603.The reflectivity are decrease and the absorption are increase by P(Al)-doped.The electronic structure and optical properties of Ca2Si is effectively modulate by doped, the results offer theoretical data for the experimental study of the cubic Ca2Si.

Key words: Energy band structure and optical properties of cubic Ca2Si and P(Al)-doped Ca2Si have been calculated by density functional theory of the first-principles pseudo potential wave method.The results show that the energy band of cubic Ca2Si is a direct semiconductor with the band gap of 0.55483 eV.The valance bands are mainly compose of Si 3p and Ca 3d 4s, the conduction bands mainly composed of Ca 3d 4s and Si 3p, the static dielectric function is 11.92474, the refractive index is 3.45322.The P-doped cubic Ca2Si is an n-type direct semiconductor with the band gap of 0.42808 eV.The valance bands are mainly compose of Si 3p, P 3p and Ca 3d 4s, the conduction bands mainly composed of Ca 3d, P 3p 3s and Si 3p, the static dielectric function is 7.92698, the refractive index is 2.81549.The Al-doped cubic Ca2Si is an n-type with the band gap of 0.26317 eV.The valance bands are mainly compose of Si 3p, Al 3p and Ca 3d, the conduction bands mainly compose of Ca 3d 4s, Al 3p 3s and Si 3p, the static dielectric function is 17.02409, the refractive index is 4.12603.The reflectivity are decrease and the absorption are increase by P(Al)-doped.The electronic structure and optical properties of Ca2Si is effectively modulate by doped, the results offer theoretical data for the experimental study of the cubic Ca2Si.