First principles study of photoelectric properties of (S, Se) co-doped Si

In order to provide more accurate theoretical guidance for improving photoelectric properties of chalcogens doped silicon, the lattice structure, stability, band structure, density of state and optical properties of (S, Se) co-doped silicon are systematically investigated based on the first principles, and the related properties are compared with those of S-doped and Se-doped silicon. The calculated results show that the photoelectric characteristics of S-doped Si and Se-doped Si are extremely similar to each other, with a new impurity band appearing in their bandgap. This new impurity band primarily results from the contributions of the 3s state electrons of S and the 4s state electrons of Se, promoting the absorption of low-energy photons and increasing the optical absorptivity of doped Si in the near infrared region. Compared with monocrystalline silicon, the S-doped Si and Se-doped Si have the optical absorption spectra, each with a new peak at 0.6 eV, which is caused by the transition of electrons from the impurity band to the conduction band. The (S, Se) co-doped Si exhibits good stability at operating temperature, and two impurity bands appear between the valence band and conduction band, which are formed by electrons from the 3s state of S and the 4s state of Se, respectively. The optical absorptivity of (S, Se) co-doped Si is greatly improved in the low energy region compared with that of single doped Si, with a new absorption peak appearing at 0.65 eV, similar to the formation observed in singly doped Si. However, due to the indirect transition process between two impurity energy bands, the absorption peak of (S, Se) co-doped Si is larger in the low energy region. Compared with S-doped silicon and Se-doped silicon with the same concentration, the (S, Se) co-doped Si has optical absorptivity that is significantly improved in the range from 0.81 eV to 1.06 eV. This study provides theoretical guidance for applying the (S, Se) co-doped Si to the field of photoelectron such as infrared photodetectors and solar cells.