Ultrathin (Bi 1-x Sb x ) 2 Se 3 Field Effect Transistor with Large ON/OFF Ratio.

Ultrathin three-dimensional topological insulator films are promising for use in field effect devices. (Bi1-x Sbx )2 Se3 ultrathin films were fabricated on SrTiO3 substrate, where large resistance changes of ∼25 000% could be achieved using the back gate voltage. We suggest that the large ON/OFF ratio was caused by the combined effect of Sb-doping and the reduction of film thickness down to the ultrathin regime. The crossover of different quantum transport under an electric field may form the basis for topological insulators (TI)-based spin transistors with large ON/OFF ratios in the future.