Electronic structure and properties of Cd₄As₂Br₃ and Cd₄Sb₂I₃, analogues of CdSe and CdTe

Substitution of aliovalent anions in metal oxides and chalcogenides significantly affects the electronic structure and properties of the materials. Thus, substitution of P^3- and Cl^- in CdS decreases the band gap and favorably influences the photocatalytic activity. Complete substitution of a trivalent (A^3-) and a monovalent (B^-) anions in a cadmium chalcogenides, CdX, should give rise to a material of the composition Cd A_0.5B_0.5 or Cd₂AB, but a compound with the composition Cd₄P₂Cl₃ (or Cd₂PCl_1.5) is obtained in the case of CdS. We have investigated the analogous compounds, Cd₄As₂Br₃ and Cd₄Sb₂I₃, wherein the anions in CdSe and CdTe are substituted by As, Br and Sb, I respectively. These compounds are direct band gap semiconductors with a band gap of 1.8–1.9 eV and a photoluminescence band in the visible region. First-principles calculations show both Cd₄As₂Br₃ and Cd₄Sb₂I₃ to be direct band gap semiconductors. The arsenic bromide is predicted to be photochemically more active for HER than the antimony iodide.