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

Abstract

The optical absorption edge (indirect energy gap) was determined for Pb_0.93Sn_0.07Te and Pb_0.85Sn_0.15Te in the temperature range from 80° to 520°K. The variation of E_g with temperature indicated that two valence bands were operative. Below 300°K, linear variation of bandgap with temperature was observed yielding values of dE_g/dT of 3.0−3.4×10⁻⁴ and 2.9−3.3×10⁻⁴ eV/°K for the Sn_0.07 and Sn_0.15 alloys, respectively. Above 400°K, dE_g/dT was zero for both. The 0°K extrapolated values of E_g 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 Sn_0.07 and Sn_0.15, respectively. Electrical resistivity data obtained in the intrinsic range (above 500°K) yield thermal energy gaps of 0.30 and 0.23 eV for Sn_0.07 and Sn_0.15, respectively. A proposed band model for SnTe based on the compositional dependence of the energy gaps is presented.