Ambipolar Topological Insulator and High Carrier Mobility in Solution Grown Ultrathin Nanoplates of Sb-Doped Bi₂Se₃

Topological insulators (TIs) are a class of materials that can exhibit robust spin polarizations at the surfaces and have attracted much attention toward spintronic applications. Here, we optimized a solution route to synthesize ultrathin Bi2Se3 and Sb-doped Bi2Se3 nanoplates with a thickness of 6–15 nm and an average lateral size around 5 μm, up to a maximum of 10 μm. Solution chemistry provides high quality nanoplates of TIs with options to manipulate the surface states. We have synthesized Bi2Se3 and Sb-doped Bi2Se3 and characterized single nanoplates. Sb doping is used to suppress the bulk carriers, and an atomic percentage ∼6% of Sb is demonstrated by energy dispersive X-ray spectroscopy (EDS). The 2D electron carrier concentration for Sb-doped Bi2Se3 nanoplates is lowered to 5.5 × 1012 cm–2, reducing the concentration by a factor of 3 compared to the undoped Bi2Se3 nanoplate sample with an average 2D carrier concentration of 16 × 1012 cm–2. At 2 K, the pronounced ambipolar field effect is observed on the low-carrier-density Sb-doped Bi2Se3 nanoplates, further demonstrating the flexible manipulation of carrier type and concentration for these single-crystal nanoplates. Large out-of-plane magnetoresistance is measured, with a gate tunable phase coherence length.