Evidences of inner Se ordering in topological insulator PbBi2Te4-PbBi2Se4-PbSb2Se4 solid solutions

Yuya Hattori,Keiichi Edagawa,Yuki Tokumoto,Koji Kimoto

doi:10.1038/s41598-020-64742-6

Yuya Hattori, Keiichi Edagawa + Show 2 more

Open Access

https://doi.org/10.1038/s41598-020-64742-6

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Abstract

In topological insulators (TIs), carriers originating from non-stoichiometric defects hamper bulk insulation. In (Bi,Sb)2(Te,Se)3 TIs (BSTS TIs), however, Se atoms strongly prefer specific atomic sites in the crystal structure (Se ordering), and this ordering structure suppresses the formation of point defects and contributes to bulk insulation. It has accelerated the understanding of TIs’ surface electron properties and device application. In this study, we select Pb(Bi,Sb)2(Te,Se)4 (Pb-BSTS) TIs, which are reported to have larger bandgap compared to counterpart compound BSTS TIs. The Se ordering geometry was investigated by combining state-of-the-art scanning transmission electron microscopy and powder X-ray diffractometry. We demonstrated the existence of inner Se ordering in PbBi2(Te,Se)4 and also in Pb-BSTS TIs. Quantitative analysis of Se ordering and a qualitative view of atomic non-stoichiometry such as point defects are also presented. Pb-BSTS TIs’ Se ordering structure and their large gap nature has the great potential to achieve more bulk insulation than conventional BSTS TIs.

Highlights

In topological insulators (TIs), carriers originating from non-stoichiometric defects hamper bulk insulation
The powder X-ray diffractometry (pXRD) study revealed that the strong tendency of Se atoms to occupy the inner site, and 90–100% of Se atoms are considered to occupy inner Te/Se(2) site. We discovered that this ordering occurs in Pb(Bi,Sb)2(Te,Se)[4] (Pb-BSTS), which enables the bulk insulation by Fermi level tuning
The phase constitution and composition of the grown crystals were investigated by an electron probe microanalyzer (EPMA)

Summary

Introduction

In topological insulators (TIs), carriers originating from non-stoichiometric defects hamper bulk insulation. In (Bi,Sb)2(Te,Se)[3] TIs (BSTS TIs), Se atoms strongly prefer specific atomic sites in the crystal structure (Se ordering), and this ordering structure suppresses the formation of point defects and contributes to bulk insulation It has accelerated the understanding of TIs’ surface electron properties and device application. In addition to Se ordering, chemical potential tuning by changing Bi/Sb ratio makes it possible to enhance the BSTSs’ bulk insulation to more than 1000 times higher than the non-doped sample[20,21] These efforts allow one to verify the 2D nature of surface states, and to detect its π Berry phase[23] and other important properties such as mobility by transport measurements[18,20,21,24]. To suppress the formation of such point defects and local band-bending, we began to focus on the Se ordering structure

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