Surface-state-dominated transport in quantum wells of topological crystalline insulator SnTe near the two-dimensional limit

Topological crystalline insulator (TCI) is a crystalline-symmetry-protected topological phase that has been found in IV–VI family compounds. Transport studies on the characteristic surface states of TCIs, the key to realizing the predicted quantum effects and electronic applications, are hindered by the difficulty in obtaining high-quality ultrathin TCI films on insulating and lattice-matched substrates. Here, with molecular beam epitaxy, we have grown Pb1−xEuxTe/SnTe/Pb1−xEuxTe quantum wells on CdTe(111) substrates, enclosing SnTe thin films between insulating and nearly lattice-matched barrier layers. By introducing Bi dopants in PbEuTe barrier layers, we have realized tuning the Fermi level from bulk valence band to bulk conduction band of SnTe. With such quantum wells, a systematic thickness- and chemical potential-dependent study on the transport properties of SnTe films near the two-dimensional limit (from 3 to 20 nm) has been carried out. In 10 nm thick SnTe quantum wells, enhanced electron mobility up to ∼2640 cm2/V s has been observed when Fermi level is tuned in bulk gap and above the charge neutral point near the valence band maximum, which is highly consistent with electron-type surface states of cation-terminated SnTe(111) surfaces. These results pave the road for exploring exotic quantum effects and developing new electronic devices with ultrathin TCI films.