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

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 ofm andmdnearx= 0.8 are evident and important for the application of these substances.