Electronic properties of phases in the quasi-binary Bi2Se3–Bi2S3 system

Abstract

We explored the properties of the quasi-binary Bi₂Se₃–Bi₂S₃ system over a wide compositional range. X-ray diffraction analysis demonstrates that rhombohedral crystals can be synthesized within the solid solution interval 0–22 mol% Bi₂S₃, while at 33 mol% Bi₂S₃ only orthorhombic crystals are obtained. Core level photoemission spectroscopy reveals the presence of Bi³⁺, Se²⁻ and S²⁻ species and the absence of metallic species, thus indicating that S incorporation into Bi₂Se₃ proceeds prevalently through the substitution of Se with S. Spin- and angle-resolved photoemission spectroscopy shows that topological surface states develop on the surfaces of the Bi₂Se_3−yS_y (y ≤0.66) rhombohedral crystals, in close analogy with the prototypical case of Bi₂Se₃, while the orthorhombic crystals with higher S content turn out to be trivial semiconductors. Our results connect unambiguously the phase diagram and electronic properties of the Bi₂Se₃–Bi₂S₃ system.