Fermi level tuning and a large activation gap achieved in the topological insulator Bi_{2}Te_{2}Se by Sn doping

TL;DR

This study demonstrates that Sn doping in Bi2Te2Se effectively shifts the Fermi level into the bulk gap, significantly increasing resistivity and enabling surface-dominated transport, with potential implications for topological insulator applications.

Contribution

It provides a detailed analysis of how Sn acts as an acceptor in Bi2Te2Se, tuning the Fermi level into the gap and revealing large activation energies and surface conduction in doped samples.

Findings

Fermi level shifted into the bulk gap with Sn doping

Resistivity increased to over 1 Ohm·cm at low temperatures

Surface-dominated transport observed via Shubnikov-de Haas oscillations

Abstract

We report the effect of Sn doping on the transport properties of the topological insulator Bi_{2}Te_{2}Se studied in a series of Bi_{2-x}Sn_{x}Te_{2}Se crystals with 0 \leq x \leq 0.02. The undoped stoichiometric compound (x = 0) shows an n-type metallic behavior with its Fermi level pinned to the conduction band. In the doped compound, it is found that Sn acts as an acceptor and leads to a downshift of the Fermi level. For x \geq 0.004, the Fermi level is lowered into the bulk forbidden gap and the crystals present a resistivity considerably larger than 1 Ohmcm at low temperatures. In those crystals, the high-temperature transport properties are essentially governed by thermally-activated carriers whose activation energy is 95-125 meV, which probably signifies the formation of a Sn-related impurity band. In addition, the surface conductance directly obtained from the Shubnikov-de Haas oscillations indicates that a surface-dominated transport can be achieved in samples with several um thickness.