Abstract
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), Bi(2)Te(3). Because of their extreme thinness, the Bi(2)Te(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 10(3) 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 Bi(2)Te(3) channel, demonstrating that the liquid gating is an effective way to modulate the electronic states of TIs.
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