Electronic structure and properties of Cd 4 As 2 Br 3 and Cd 4 Sb 2 I 3 , 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 P3- and Cl- in CdS decreases the band gap and favorably influences the photocatalytic activity. Complete substitution of a trivalent (A3-) and a monovalent (B-) anions in a cadmium chalcogenides, CdX, should give rise to a material of the composition Cd A0.5B0.5 or Cd2AB, but a compound with the composition Cd4P2Cl3 (or Cd2PCl1.5) 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 1.8–1.9eV 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.