Optical and Electrical Properties and Band Structure of GeTe and SnTe

We describe first our measurements of the variation with carrier concentration of the susceptibility mass and the absorption edge, in a range of hole concentrations of 1×${10}^{20}$ to 2×${10}^{21}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The susceptibility mass for holes varies from 0.075 to $0.51m_0$ for the lowest and highest carrier concentrations, respectively. These properties, and similar published data for SnTe, together with the Fermi energies and energy gaps obtained from tunneling experiments, have been interpreted using a band structure obtained by applying the k·p perturbation approach at the $L$ point of a face-centered cubic zone. We have assumed a coupling scheme such that there is strong transverse coupling across the energy gap while the longitudinal coupling is between the principal conduction band and the second valence band. The energy separations for the second valence bands required in both materials are 0.5 and 0.34 eV for GeTe and SnTe, respectively. As a prerequisite to a meaningful interpretation of the measured quantities versus carrier concentration, we have calculated the ratio of the actual carrier concentration to the Hall concentration $\frac{1}{R_{0}e}$. We have made numerous computer calculations and have obtained a set of band parameters for these materials based on the best fit for a wide variety of experimental results.