Chemical Substitution and Band Gap Tunability in Chiral Ag ₃ Au(Se,Te) ₂ Solid Solutions

Ag3AuSe2 and Ag3AuTe2 were previously predicted to be narrow direct gap semiconductors with the same chiral structure type. Recent computational studies using the Perdew–Burke–Ernzerhof (PBE) functional highlighted their potential band gap tunability via strain application. For example, Ag3AuSe2 was predicted to exhibit full band closure above 4% tensile strain. In this study, we explored chemical substitution to examine the density functional theory (DFT) predictions by replacing Se2– with larger Te2– anions. We synthesized and characterized the electronic and optical properties of Ag3Au(Se1–xTex)2 solid solutions for x from 0 to 1. Our findings revealed that the lattice constants increase linearly with Te incorporation, reaching 3.6% expansion at 90% Se2– to Te2– substitution. The activation energy and optical band gap of Ag3Au(Se,Te)2 were determined by using electrical resistivity and ultraviolet–visible (UV–vis) diffuse reflectance measurements. The band gap decreased with increasing Te content, although hybrid functionals are necessary to correctly predict the gap. Further computational studies on the band structures of Ag3Au(Se,Te)2 alloys would shed light on the impact of lattice parameter modification via chemical substitution on the band gap tunability.