Theoretical investigation on the promotion of second harmonic generation from chalcopyrite family A(I)GaS(2) to A(II)Ga(2)S(4)

The chalcopyrite structure is a rich source for the exploration of new IR materials. However, not all of the compounds with a chalcopyrite-type structure exhibit satisfactory optical properties, which may originate from their different microstructure features. In this work, we selected four classical chalcopyrite materials, A(I)GaS(2) (A(I) = Ag, Cu) with normal structures and A(II)Ga(2)S(4) (A(II) = Zn, Hg) with defect structures, to study their electronic structures, optical properties including the contribution of ions and ion groups to their band gaps, SHG responses and birefringences by the first-principles method. The results uncover that the different band gaps are mainly caused by the d orbitals of A* (A* = A(I), A(II))-site atoms and dp hybridizations between the A*-site and S atoms. In addition, the more powerful covalent bonds of A(II)–S and Ga–S in the A(II)Ga(2)S(4) lead to the larger SHG responses of ZnGa(2)S(4) and HgGa(2)S(4). For the birefringences, the sizes of the A*-site atoms make sense, namely larger size will lead to higher distortion of tetrahedra, then result in large birefringences. All the above analyses conclude that the A*-site atoms in the chalcopyrite structures play a modulation role in determining the optical properties.