Defects of the interlayer surface and thermoelectric properties in layered films of $n$-Bi$_{2}$Te$_{2.7}$Se$_{0.15}$S$_{0.15}$ topological insulators

In layered films of $n$-Bi$_{2}$Te$_{2.7}$Se$_{0.15}$S$_{0.15}$ topological insulators optimized for temperatures below room temperature, morphology of the interlayer (0001) surface and thermoelectric properties are studied. On profiles of the (0001) surface, neutral impurity defects (appearing when Te atoms are substituted by Se and S atoms) and donor antisite defects of tellurium at places of bismuth which have an effect on thermoelectric properties are identified. The mean value of thermoelectric efficiency in $n$-Bi$_{2}$Te$_{2.7}$Se$_{0.15}$S$_{0.15}$ films increases to $\langle Z\rangle\approx3.0\times10^{-3}$ K$^{-1}$ in the range of 80–215 K, while in a bulk solid solution в интервале 80–215 K, в то время как в объемном твердом растворе $\langle Z\rangle\approx 2.0\times10^{-3}$ K$^{-1}$. The increase in thermoelectric efficiency in the films is related to enhancement of the energy dependence of the relaxation time due to the increase in the scattering effective parameter $r_{\operatorname{eff}}$. It is shown than the Seebeck coefficient, density-of-state effective mass $m/m_0$, and material parameter proportional to the power factor increase, while the lattice thermal conductivity $\kappa_L$ and electronic thermal conductivity $\kappa_e$ decrease, which determines an increase in thermoelectric efficiency.