Abstract: Density functional theory (DFT) based on the pseudo-potential plane wave basis set was used to investigate the electronic structures and optical properties of CuAlX₂ (X=S, Se, Te) crystals with a chalcopyrite structure. The results indicate that these compounds have a similar band structure and the bandgap decreases from S to Te. Except for the static birefringence, which is just opposite to a change in the bandgap, the static dielectric constant, refractive index and second harmonic generation (SHG) coefficient d₃₆ of this series of compounds increased from S to Te. The SHG response of the three semiconductors can be attributed to transitions from the occupied bands near the top of the valence band to the unoccupied bands that are contributed to by the p states of the Al and X atoms. Among the three crystals, the optical properties of the CuAlTe₂ crystal are better than those of CuAlS₂ and CuAlSe₂ crystals except that the corresponding static birefringence is too small.

Key words: Density functional theory, Electronic structure, Optical property, Second harmonic generation, Chalcopyrite