Thermal and Optical Energy Gaps in Pb0.93Sn0.07Te and Pb0.85Sn0.15Te

The optical absorption edge (indirect energy gap) was determined for Pb0.93Sn0.07Te and Pb0.85Sn0.15Te in the temperature range from 80° to 520°K. The variation of Eg with temperature indicated that two valence bands were operative. Below 300°K, linear variation of bandgap with temperature was observed yielding values of dEg/dT of 3.0−3.4×10−4 and 2.9−3.3×10−4 eV/°K for the Sn0.07 and Sn0.15 alloys, respectively. Above 400°K, dEg/dT was zero for both. The 0°K extrapolated values of Eg were 0.162 and 0.113 eV for the low-temperature range and about 0.28 and 0.24 eV for the high-temperature range, for Sn0.07 and Sn0.15, respectively. Electrical resistivity data obtained in the intrinsic range (above 500°K) yield thermal energy gaps of 0.30 and 0.23 eV for Sn0.07 and Sn0.15, respectively. A proposed band model for SnTe based on the compositional dependence of the energy gaps is presented.