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

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Abstract
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.