Improvement of Electrical Transport Performance of BiSbTeSe₂ by Elemental Doping

A topological insulator with large bulk-insulating behavior and high electron mobility of the surface state is needed urgently, not only because it would be a good platform for studying topological surface states but also because it is a prerequisite for potential future applications. In this work, we demonstrated that tin (Sn) or indium (In) dopants could be introduced into a BiSbTeSe₂ single crystal. The impacts of the dopants on the bulk-insulating property and electron mobility of the surface state were systematically investigated by electrical transport measurements. The doped single crystals had the same crystal structure as the pristine BiSbTeSe₂, no impure phase was observed, and all elements were distributed homogeneously. The electrical transport measurements illustrated that slight Sn doping could improve the performance of BiSbTeSe₂ a lot, as the longitudinal resistivity (ρ_xx), bulk carrier density (n_b), and electron mobility of the surface state (μ_s) reached about 11 Ωcm, 7.40 × 10¹⁴ cm^-3, and 6930 cm²/(Vs), respectively. By comparison, indium doping could also improve the performance of BiSbTeSe₂ with ρ_xx, n_b, and μ_s up to about 13 Ωcm, 1.29 × 10¹⁵ cm^-3, and 4500 cm²/(Vs), respectively. Our findings suggest that Sn- or indium-doped BiSbTeSe₂ crystals should be good platforms for studying novel topological properties, as well as promising candidates for low-dissipation electron transport, spin electronics, and quantum computing.