Investigation of the Valence Band Structure of Thermoelectric (Bi1−xSbx)2Te3Single Crystals

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Abstract
Using combined optical‐spectroscopic and transport investigations it is succeeded for the first time to determine all relevant valence band data for the whole series of mixed crystals (Bi1−xSbx)2Te3(0 ≦x≦ 1). The reflectivity of polarized infrared light including its anisotropy is measured in the wave number range of 300 to 4000 cm−‐1. In addition to the spectra the Hall coefficients ϱ123and ϱ312, the electrical conductivity σ ⟂c, and the Seebeck coefficientS⟂care also given. In term of a six‐valley band model and scattering by acoustical phonons all experimental data are consistently described. The main axis massesm, the ellipsoid tilt angle ϑ, the effective density‐of‐states massmd, and the susceptibility massesm,∥care calculated in dependence on composition, also the Fermi levelEF, the carrier densityp, the mobility μ ⟂c, the high frequency dielectric constant ϵ∞⟂,∥c, and the relaxation time τopt. For the first time the structure factors in the Hall coefficients are given. In the plotm(x) the distinct maxima ofmandmdnearx= 0.8 are evident and important for the application of these substances.