Pb-doped p-type Bi$_2$Se$_3$ thin films via interfacial engineering

TL;DR

This paper reports the first successful fabrication of Pb-doped p-type Bi$_2$Se$_3$ thin films using interface engineering, preserving strong spin-orbit coupling and achieving higher mobility than Ca-doped counterparts.

Contribution

It introduces a novel interface engineering method to achieve p-type Pb-doped Bi$_2$Se$_3$ thin films, overcoming previous doping challenges while maintaining topological properties.

Findings

First Pb-doped p-type Bi$_2$Se$_3$ thin films created.

Pb doping results in higher mobility than Ca doping.

Doping allows tunable Fermi levels without losing topological features.

Abstract

Due to high density of native defects, the prototypical topological insulator (TI), Bi$_2$Se$_3$, is naturally n-type. Although Bi$_2$Se$_3$ 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, which is the heaviest 2+ ion, located right next to Bi in the periodic table, is the most ideal p-type dopant for Bi$_2$Se$_3$. However, Pb-doping has so far failed to achieve p-type Bi$_2$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 Bi$_2$Se$_3$ thin films. Furthermore, at heavy Pb-doping, the mobility turns out to be substantially higher than that of Ca-doped samples, indicating that Pb is a less disruptive dopant than Ca. With this SOC-preserving counter-doping scheme, it is now possible to fabricate Bi$_2$Se$_3$ samples with tunable Fermi levels without compromising their topological properties.