High-Mobility Ambipolar Magnetotransport in Topological Insulator Bi2Se3 Nanoribbons

Gunta Kunakova,Floriana Lombardi,Donats Erts,Matteo Salvato,Jana Andzane,Xavier Palermo,Thilo Bauch

doi:10.1103/physrevapplied.16.024038

Abstract

Nanoribbons of topological insulators (TIs) have been suggested for a variety of applications exploiting the properties of the topologically protected surface Dirac states. In these proposals it is crucial to achieve a high tunability of the Fermi energy, through the Dirac point while preserving a high mobility of the involved carriers. Tunable transport in TI nanoribbons has been achieved by chemical doping of the materials so to reduce the bulk carriers' concentration, however at the expense of the mobility of the surface Dirac electrons, which is substantially reduced. Here we study bare ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ nanoribbons transferred on a variety of oxide substrates and demonstrate that the use of a large relative permittivity ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_{3}$ substrate enables the Fermi energy to be tuned through the Dirac point and an ambipolar field effect to be obtained. Through magnetotransport and Hall conductance measurements, performed on single ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ nanoribbons, we demonstrate that electron and hole carriers are exclusively high-mobility Dirac electrons, without any bulk contribution. The use of ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_{3}$ allows therefore an easy field effect gating in TI nanostructures providing an ideal platform to take advantage of the properties of topological surface states.

Highlights

Topological-insulator (TI) nanoribbons are considered promising candidates for a variety of applications, which can take advantage from the high surface-to-volume ratio and the reduced number of electronic transport modes
We study bare Bi2Se3 nanoribbons transferred on a variety of oxide substrates and demonstrate that the use of a large relative permittivity SrTiO3 substrate enables the Fermi energy to be tuned through the Dirac point and an ambipolar field effect to be obtained
In particular we show that the use of SrTiO3 (STO) enables us (a) to completely deplete the interface accumulation layer by back gating through the substrate, (b) to tune the Fermi surface through the Dirac point, and (c) to obtain an ambipolar field effect; here the electrons and holes exclusively belong to the Dirac bands from the top and bottom surface of the nanoribbon

Summary

INTRODUCTION

Topological-insulator (TI) nanoribbons are considered promising candidates for a variety of applications, which can take advantage from the high surface-to-volume ratio and the reduced number of electronic transport modes. High mobility is instrumental for applications, so doping does not appear a viable strategy to take full advantage of the Dirac electron physics Another critical issue, affecting TI nanoribbon devices, is the unavoidable presence of an oxide layer around the external surface [13,14], which may lead to the formation of an extra twodimensional (2D) gas once they are transferred on oxide dielectric substrates. We have recently demonstrated that in the case for Bi2Se3 nanoribbons transferred on a SiO2/Si substrate a 2D accumulation layer, with a high carrier density up to 2 × 1013 cm−2, is formed at the interface with the SiO2 [18,19] This makes it difficult to tune the Fermi level close to the Dirac point due to the relatively low dielectric

Published by the American Physical Society

EXPERIMENTAL RESULTS AND DISCUSSION

First sstcaarnt

EF s

METHODS