Fermi level tuning and a large activation gap achieved in the topological insulator Bi2Te2Se by Sn doping

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 x 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 0.004, the Fermi level is lowered into the bulk forbidden gap and the crystals present a resistivity considerably larger than 1 cm 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 μm thickness.

Transport properties of topological insulators: Band bending, bulk metal-to-insulator transition, and weak anti-localization

“…[14,[18][19][20][21][22][23][24][25][26][27][28][29]. On the other hand, in the bulk limit shown in (g) at t = 1000 nm, Δ(t) is zero over most of the range of N BD and n SD .…”

Anomalous composition dependence of the superconductivity in In-doped SnTe

“…At very low concentrations, this state would be relatively localized, and would pin the Fermi energy to the gap, acting as a carrier concentration buffer, much like Sn does in Sn:Bi 2 Te 2 Se. [37][38][39] V. CONCLUSION Our study of a broad range of compositions in the superconducting Sn 1−x In x Te system shows that Indium doped SnTe cannot be thought of as a simple hole doped semiconductor over its full superconducting composition range. The nature of the superconductivity and the carrier type change as a function of Indium doping, going from overall p-type to overall n-type and from a weakly coupled to a strongly coupled superconductor.…”

Topological Insulator Materials

“…The second route to improve the insulating property of Bi 2 Te 2 Se is to employ Sn doping to the Bi site. 109) Using both routes, it has been shown to be possible to achieve surface-dominated transport in bulk single crystals. 108,109) The discovery of tetradymite TI materials demonstrated that elucidating the parity eigenvalues based on ab initio band calculations is a practical and powerful strategy for making predictions for new TI materials.…”

“…109) Using both routes, it has been shown to be possible to achieve surface-dominated transport in bulk single crystals. 108,109) The discovery of tetradymite TI materials demonstrated that elucidating the parity eigenvalues based on ab initio band calculations is a practical and powerful strategy for making predictions for new TI materials. In fact, the next TI material discovered after Bi 2 Se 3 and Bi 2 Te 3 was TlBiSe 2 , and its discovery, [110][111][112] done in 2010, was also led by theoretical predictions.…”

“…It was Xiong et al who first switched to correctly using the minima in xx for the LL fan diagram analysis, 105) and some of the recent works performed reliable analyses and unambiguously demonstrated the Dirac nature of the surface state through determination of the Berry phase. 105,109,172,173) In addition, to determine the Berry phase from the LL fan diagram in a most reliable way, one should fix the slope of the linear fitting by using the frequency F obtained from the Fourier analysis of the data; this way, the intercept on the N-index axis is obtained with little ambiguity. 109,173) An example of the LL fan diagram obtained for an MBE-grown Bi 2 Se 3 film is shown in Fig.…”