Top gating of epitaxial (Bi₁−xSbx)₂Te₃ topological insulator thin films

The tunability of the chemical potential for a wide range encompassing the Dirac point is important for many future devices based on topological insulators. Here, we report a method to fabricate highly efficient top gates on epitaxially grown (Bi₁−xSbx)₂Te₃ topological insulator thin films without degrading the film quality. By combining an in situ deposited Al₂O₃ capping layer and a SiNx dielectric layer deposited at low temperature, we were able to protect the films from degradation during the fabrication processes. We demonstrate that by using this top gate, the carriers in the top surface can be efficiently tuned from n- to p-type. We also show that magnetotransport properties give evidence for decoupled transport through top and bottom surfaces for the entire range of gate voltage, which is only possible in truly bulk-insulating samples.