thin films via interfacial engineering*

Due to high density of native defects, the topological insulator (TI), Bi₂Se₃, is naturally n-type. Although Bi₂Se₃ can be converted into p-type by substituting 2+ ions for Bi, only light elements such as Ca have been so far effective as the compensation dopant. Considering that strong spin-orbit coupling (SOC) is essential for the topological surface states, a light element is undesirable as a dopant, because it weakens the strength of SOC. In this sense, Pb, the heaviest 2+ ion located right next to Bi in the periodic table, is the most ideal p-type dopant for Bi₂Se₃. However, Pb-doping has not achieved p-type Bi₂Se₃ both in thin films and bulk crystals. Here, by utilizing an interface engineering, we achieved the first Pb-doped p-type Bi₂Se₃ thin films. Furthermore, at heavy Pb-doping, the mobility is substantially higher than that of Ca-doped samples, indicating that Pb is a less disruptive dopant than Ca. With this SOC-preserving counter-doping, it is now possible to fabricate Bi₂Se₃ with tunable Fermi levels without compromising their topological properties. [1]

[1] J. Moon, et al, Phys. Rev. Materials 4, 024203 (2020)