Top gating of epitaxial (Bi_{1-x}Sb_x)2Te3 topological insulator thin films

TL;DR

This paper presents a method to fabricate highly efficient top gates on epitaxial (Bi_{1-x}Sb_x)2Te3 topological insulator thin films, enabling effective tuning of surface carriers without degrading film quality, and demonstrates decoupled surface transport.

Contribution

The authors develop a fabrication technique combining in situ Al2O3 capping and low-temperature SiN_x dielectric layers to achieve high-quality top gating on topological insulator films.

Findings

Top gates can efficiently tune carriers from n- to p-type.

Magnetotransport shows decoupled surface conduction across gate voltages.

The method preserves film quality during fabrication.

Abstract

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 (Bi_{1-x}Sb_x)2Te3 topological insulator thin films without degrading the film quality. By combining an in situ deposited Al2O3 capping layer and a SiN_x 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.