Liquid-gated ambipolar transport in ultrathin films of a topological insulator Bi₂Te₃

Using ionic-liquid (IL) gating in electric-double-layer transistors (EDLTs), we investigate field-effect electrical transport properties of ultrathin epitaxial films of a topological insulator (TI), Bi₂Te ₃. Because of their extreme thinness, the Bi₂Te ₃ films show a band gap opening and resulting semiconducting transport properties. Near room temperature, an obvious ambipolar transistor operation with an ON-OFF ratio close to 10³ was observed in the transfer characteristics of liquid-gated EDLTs and further confirmed by a sign change of the Hall coefficients. Modulation of the electronic states and a phase transition from a semiconducting conduction (dR_xx/dT < 0) to a metallic transport (dR_xx/dT > 0) were observed in the temperature-dependent resistance of the ultrathin Bi₂Te₃ channel, demonstrating that the liquid gating is an effective way to modulate the electronic states of TIs.