Magnetotransport and ARPES studies of the topological insulators Sb2Te3 and Bi2Te3 grown by MOCVD on large-area Si substrates

L Locatelli,P Tsipas,A Kumar,R Mantovan,E Longo,A Dimoulas

doi:10.1038/s41598-022-07496-7

Abstract

Recently, the topological insulators (TIs) antimony telluride (Sb2Te3) and bismuth telluride (Bi2Te3) are attracting high interest for applications based on spin-charge interconversion mechanisms. Aiming to make a step toward the technology transfer, it is of major importance to achieve and investigate epitaxial quality-TIs on large area Si-based substrates. In view of that, we report here magnetotransport and angle-resolved photoemission spectroscopy (ARPES) studies on Sb2Te3 and Bi2Te3 thin films grown by metal organic chemical vapor deposition (MOCVD) on top of 4″ Si(111) substrates. Clear weak antilocalization (WAL) effects are observed in both TIs, proving the existence of quantum transport mechanism, and the data are successfully interpreted in the framework of the Hikami–Larkin–Nagaoka model. Further, by dedicated magnetotransport experiments, it has been confirmed that the investigated WAL originates from two-dimensional (2D) topological states. ARPES has been performed ex-situ, and in both TIs the gapless Dirac cones have been observed and attributed to the topological surface states. Combining the proofs of the existence of quantum 2D transport as deduced from the analysis of the magnetoconductance curve with the direct observation of the Dirac-like band structure revealed by the ARPES spectra, it is possible to unambiguously confirm the topological nature of our Sb2Te3 and Bi2Te3 thin films. The results obtained on thin films grown by MOCVD on 4’’ Si(111) substrate mark an important step towards the technology transfer of the topological insulators studied in this work.

Highlights

The Bi2Se3, Bi2Te3, and S b2Te3 chalcogenides are in the focus of interest as three-dimensional (3D) topological insulators (TIs), due to the well-documented existence of topologically-protected surface states (TSS)[1–4]
We reported about the metal organic chemical vapor deposition (MOCVD) growth of epitaxial quality S b2Te3 and B i2Te3 on top of 4′′ Si(111) substrates[18,19], and the integration of Sb2Te3 with ferromagnetic thin films[20,21], further demonstrating a high spin-to-charge (S2C) c onversion[22,23]
The main technical issue concerns the typical narrowness of the chalcogenide-based TIs band[1,27] and the unintentional doping provided by the presence of defects or by slight stoichiometric variations

Summary

Introduction

The Bi2Se3, Bi2Te3, and S b2Te3 chalcogenides are in the focus of interest as three-dimensional (3D) topological insulators (TIs), due to the well-documented existence of topologically-protected surface states (TSS)[1–4] These conductive states are protected by the symmetry of the crystal, exhibiting a very high electronic mobility. It is important to highlight that the observation of WAL is a condition which is necessary, but not sufficient, to prove the existence of TSS This effect arises in good conductors where the electronic wave function maintains its phase coherence over a distance that is much larger than the electronic mean free path (MFP)[25], and this is not a prerogative of TIs. the two conditions needed to observe the WAL effect are verified in bulk conductive materials whose lattice is composed by heavy elements, which by means of an intense Spin–Orbit Interaction (SOI) are responsible for the spin conservation over several elastic scattering events[25,26]. Our work demonstrates the potential of MOCVD technique for fabricating functional TIs over large-area Si substrates, providing a substantial contribution to their possible practical uses

Methods

Results

Conclusion