Pb-doped p -type Bi2Se3 thin films via interfacial engineering

Due to the high density of native defects, the prototypical topological insulator (TI), ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$, is naturally $n$-type. Although ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ can be converted into $p$-type by substituting $2+$ ions for Bi, only light elements such as Ca have so far been 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, which is the heaviest $2+$ ion, located right next to Bi in the Periodic Table, is the most ideal $p$-type dopant for ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$. However, Pb-doping has so far failed to achieve $p$-type ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ not only in thin films but also in bulk crystals. Here, by utilizing an interface engineering scheme, we have achieved the first Pb-doped $p$-type ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ thin films. Furthermore, at heavy Pb-doping, the mobility turns out to be substantially higher than that of Ca-doped samples, suggesting that Pb is a less disruptive dopant than Ca. The availability of Pb-doped $p$-type ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ films will provide opportunities to study a Fermi-level tunable TI system while preserving the SOC strength.