Electric-Susceptibility Mass of Free Holes in SnTe

Abstract

The electric-susceptibility mass $m_s$ of free carriers was determined at 300, 80, and 10 °K for $p$-type SnTe having carrier concentrations ranging from 3.6 × ${10}^{19}$ to 1.2 × ${10}^{21}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The values were determined from an analysis of the normal reflectivity of the material in the infrared region. The observed carrier concentration and temperature dependences of $m_s$ were used to test valence-band models recently proposed for SnTe by (i) Koehler, (ii) Rogers, and (iii) Tsu, Howard, and Esaki. In addition, a simple Cohen-type model was evaluated. It is demonstrated that none of these models provides a completely satisfactory description of our experimental results. The temperature dependence of $m_s$ is shown to be anomalous with regard to its relationship to the temperature dependence of the forbidden energy gap. On the basis of our results, it is concluded that the valence-band structure of SnTe is considerably more complex than indicated by the models we have considered.