Quantitative analysis on the influence of Nb substitutional doping on electronic and thermal properties of n-type Cu_0.008Bi₂Te_2.7Se_0.3 alloys

Cation substitutional doping has been shown to be an effective method to modify both the electronic and thermal transport in p-type (Bi,Sb)₂Te₃-based thermoelectric alloys. However, there are not many studies that have attempted a quantitative analysis on the influence of cation substitution on the electronic and thermal properties of n-type Bi₂(Te,Se)₃-based alloys. In this work, we report a comprehensive analysis of the influence of substitutional Nb doping on the electrical and thermal conductivity in n-type Cu_0.008Bi₂Te_2.7Se_0.3 alloys. First, we found that Nb doping increases the carrier concentration of both the electrons and holes, whereas the weighted mobility of the electrons and holes is only slightly modified based on a single parabolic band model. As a result, the bipolar thermal conductivity was increased as the Nb was doped. Next, the contribution of point defect scattering by the Nb substitution on the thermal conductivity of the lattice was quantitatively analyzed using a Debye-Callaway model, and it was concluded that the influence of cation substitutional doping in n-type Bi₂(Te,Se)₃ is as effective as that in p-type (Bi,Sb)₂Te₃.