V. A. Kutasov

Galvanomagnetic and thermoelectric properties of p-Bi2−xSbxTe3−ySey solid solutions at low temperatures (<220 K)

The galvanomagnetic and thermoelectric properties of p-Bi2−xSbxTe3−ySey solid solutions (x≤1.2, y≤0.09) are studied for various carrier concentrations. The degeneracy parameter βd governing the scattering processes in solid solutions was calculated in terms of the many-valley energy spectrum model. The data on the degeneracy parameter and the Seebeck coefficient α were used to calculate the effective scattering parameter reff and the reduced Fermi level η. The parameter reff was found to depend on the carrier concentration in the materials studied. The temperature dependences of the effective density-of-states mass m/m0 and mobility μ0 in samples with various carrier concentrations were determined.

Thermoelectric figure-of-merit in p-type bismuth- and antimony-chalcogenide-based solid solutions above room temperature

The specific features of the variation in the thermoelectric figure-of merit Z for p-type bismuth- and antimony-chalcogenide-based solid solutions p-(Bi,Sb)2(Te,Se)3 have been analyzed with allowance made for the data amassed in the investigation of thermoelectric and galvanomagnetic properties. It has been shown that, in the samples with optimum carrier concentrations, the increase in Z in the multicomponent p-Bi2 − xSbxTe3 − ySey composition (x = 1.3, y = 0.06) in the temperature range 300–370 K is mediated by the high carrier mobility and the low lattice thermal conductivity. The higher effective mass of the density of states and the larger slope of the temperature dependence of the mobility as compared to the other compositions bring about an increase in Z in the p-Bi2 − xSbxTe3 solid solution for x = 1.6 in the temperature range 370–550 K. The increase in the figure-of merit reached in the compositions under study stems also from the increasing contraction of constant-energy ellipsoids along the binary and bisector directions and from the change in the angle θ between the principal axes of the ellipsoids and the crystallographic axes.

Carrier mobility in nonstoichiometric n-Bi2Te3−xSex solid solutions

A study has been made of the thermoelectric and galvanomagnetic properties of n-Bi2Te3−xSex solid solutions (x=0.3 and 0.36) in the temperature range 80–300 K. The lowest carrier concentrations, (0.8–1)×1018 cm−3, were obtained by displacing the solid solution from the stoichiometric to a Te-rich composition. At such carrier concentrations, the second subband in the conduction band of n-Bi2Te3−xSex is not filled, which results in a growth of mobility because of the absence of interband scattering, and brings about an increase of thermoelectric efficiency in the 80–120-K range.

Surface states of charge carriers in epitaxial films of the topological insulator Bi2Te3

The galvanomagnetic properties of p-type bismuth telluride heteroepitaxial films grown by the hot wall epitaxy method on oriented muscovite mica substrates have been investigated. Quantum oscillations of the magnetoresistance associated with surface electronic states in three-dimensional topological insulators have been studied in strong magnetic fields ranging from 6 to 14 T at low temperatures. The cyclotron effective mass, charge carrier mobility, and parameters of the Fermi surface have been determined based on the results of analyzing the magnetoresistance oscillations. The dependences of the cross-sectional area of the Fermi surface S(kF), the wave vector kF, and the surface concentration of charge carriers ns on the frequency of magnetoresistance oscillations in p-type Bi2Te3 heteroepitaxial films have been obtained. The experimentally observed shift of the Landau level index is consistent with the value of the Berry phase, which is characteristic of topological surface states of Dirac fermions in the films. The properties of topological surface states of charge carriers in p-type Bi2Te3 films obtained by analyzing the magnetoresistance oscillations significantly expand fields of practical application and stimulate the investigation of transport properties of chalcogenide films.

Thermoelectric properties of p-Bi2 − xSbxTe3 solid solutions under pressure

This paper reports on a study of the Seebeck coefficient and power factor κ of p-Bi2 − xSbxTe3 solid solutions with different contents of antimony atoms in the bismuth sublattice for x = 0, 1.4, 1.5, and 1.6 under variation of pressure of up to 15 GPa. The magnitude of κ has been found to grow nonmonotonically within the pressure region of 2–4 GPa. The effective mass of the density of states m/m0 and the mobility μ0 have been calculated with due account of degeneracy within the parabolic model of the energy spectrum assuming isotropic charge carrier scattering. It has been shown that application of pressure brings about a decrease of the effective mass m/m0 and an increase of carrier mobility. The power factor κ of the p-Bi0.6Sb1.4Te3 composition exhibits at the pressure P ≈ 4 GPa the largest increase of the power factor κ as a result of a weak decrease of the effective mass m/m0 and an increase of carrier mobility as compared to the other solid solution compositions. The specific feature of the variation of the power factor κ with a change of the pressure in bismuth telluride near P ≈ 3 GPa, which is accompanied by formation of a knee in the m/m0 vs. P dependence, can be assigned to an electronic topological transition.

Effective mass and mobility of carriers in p-Bi2−xSbxTe3−ySey solid solutions at temperatures below 300 K

AbstractThe temperature dependences of the Seebeck coefficient α and of the electrical conductivity σ of p-Bi2−xSbxTe3−ySey solid solutions were studied under atomic substitution on the cation (1 ≤ x ≤ 1.5) and anion (0.04 ≤ y ≤ 0.09) bismuth and antimony telluride sublattices within the temperature interval 80–340 K. The effect of variation in the solid-solution composition on the average effective density-of-states mass (m/m0) and carrier mobility (μ0, calculated with due account of degeneracy) was studied under the assumption that carrier scattering is isotropic and that the relaxation time can be approximated by a power-law function

Band gap and type of optical transitions at the interband absorption edge in solid solutions based on bismuth telluride

\tau = a\mathop {E^{eff} }\limits^r

Multicomponent n-(Bi,Sb)2(Te,Se,S)3 solid solutions with different atomic substitutions in the Bi and Te sublattices

, where reff is an effective scattering parameter. It is shown that variations in the pattern of the m/m0 and μ0 temperature dependences produced in the temperature region under study by properly varying the number of substituted atoms in the solid solutions may favor an increase in thermoelectric efficiency.