Bi ₂ Te _3−x Se _x series studied by resistivity and thermopower

Abstract

-We study the detailed temperature and composition dependence of the resistivity, ρ(T ), and thermopower, S(T ), for a series of layered bismuth chalcogenides Bi2Te3−xSex, and report the stoichiometry dependence of the optical band gap. In the resistivity of the most compensated member, Bi2Te2.1Se0.9, we find a low-temperature plateau whose onset temperature correlates with the high-temperature activation energy. For the whole series S(T ) can be described by a simple model for an extrinsic semiconductor. By substituting Se for Te, the Fermi level is tuned from the valence band into the conduction band. The maximum values of S(T ), bulk band gap as well the activation energy in the resistivity are found for x ≈ 0.9.

Optical properties of Bi2Te2Se at ambient and high pressures

“…The measurement of thermopower on a sample from the same batch showed that the charge carriers in the sample are electrons. 35…”

Charge puddles in a completely compensated topological insulator

“…compositional gradient [1] or lightly doped Bi 1.9 Tl 0.1 Te 3 samples (28 mΩcm) [17]. However, they are lower than those obtained for heavy chemical doping in the Bi 2 -Te x 3 Se x system (1-20 Ωcm for = x 0.9 1 -) [5,10,12]. It should be noted that although Bi 2 Te 2 Se has the same crystal structure as Bi 2 Te 3 and is commonly referred to as chemically doped Bi 2 Te 3 , the electronic structures of the two compounds are in fact quite different, particularly near the band edges.…”

“…Since it does not seem realistic that insulating Bi-based bulk TI samples can be achieved by reducing only the defect density [9], it is necessary to compensate the carriers already present to push the Fermi level inside the bandgap. In Bi 2 Te 3 , compensation can be realized either by chemical doping, e.g., Bi 2 -Te x 3 Se x [5][6][7]10], or as recently proposed, by doping using irradiation-induced defects [11]. Irradiations performed on Bi 2 Te 3 at room temperature showed that the created defects act as electron donors and can thus be used to change the conduction from p-to n-type.…”

Two-band model interpretation of the p- to n-transition in ternary tetradymite topological insulators

“…The aforementioned interaction of the n-type defects with the p-type ones leads to the inaccurate determination of carrier concentration derived from volume-averaged (i.e. integral) techniques such as Seebeck coefficient measurements [15,[29][30][31]. In contrast to electrical transport methods, the NMR lineshape and T 1 measurements allow for a site-specific characterization of the electronic band structure [14] due to their proportionality to the effective mass and the carrier density.…”