The three-dimensional topological insulators with both metallic surface states and insulating bulk states have attracted enormous attention. We report the composition and gate voltage induced tuning of transport properties in chemically synthesized Bi₂(Te_1-xSe_x)₃ nanoribbons. It is found that increasing Se concentration effectively suppresses the bulk carrier transport and induces semiconducting behavior in the temperature dependent resistance of Bi₂(Te_1-xSe_x)₃ nanoribbons when x is greater than ～10%. In Bi₂(Te_1-xSe_x)₃ nanoribbons with x～20%, gate voltage enables ambipolar modulation of resistance (or conductance) in samples with thickness around or larger than 100 nm, indicating significantly enhanced contribution in transport from the gapless surface states.

Composition-tuned temperature-dependent transport in Bi₂(Te_1-xSe_x)₃ nanoribbons. The dependence of resistance on temperature showing the transport property changes from metallic into semiconducting as the concentration of Se increases in Bi₂(Te_1-xSe_x)₃ nanoribbons.

Magneto-conductivity of the device at different gate voltage showing weak antilocalization effect in Bi₂(Te_1-xSe_x)₃ nanoribbon. The symbols are data and solid lines are fits. (d) The fitting parameter α in the weak antilocalization fit vs. gate voltage.