On the density-of-states effective mass and charge-carrier mobility in heteroepitaxial films of bismuth telluride and Bi$_{0.5}$Sb$_{1.5}$Te$_{3}$ solid solution

It is shown that the Seebeck coefficient $\alpha$, the power factor $\alpha^{2}\sigma$, and the density-of-states effective mass $m/m_0$ in heteroepitaxial films of Bi$_{0.5}$Sb$_{1.5}$Te$_{3}$ solid solution are higher than the corresponding characteristics of bulk thermoelectric materials. The elevated values and weak temperature dependences of these parameters lead to a rise in the parameter proportional to the effective mass, the charge-carrier mobility, and the figure of merit. The character of change in $\alpha$, $\alpha^{2}\sigma$, and $m/m_0$ is determined by the peculiarities of the mechanism of charge-carrier scattering, the anisotropy of the constant-energy surface, and the possible influence of topological surface states of Dirac fermions in the films.