Thermal and optical energy gaps in PbTe

R. N. Tauber, A. A. Machonis, I. B. Cadoff

The optical absorption edge (indirect energy gap) for PbTe was determined in the temperature range of 80°-520°K. It was found that dEg/dT had a value of 4.1×10-4 eV/°K in the temperature range from 80°-350°K, while above 400°K, dEg/dT was approximately zero. The low-temperature linear portion extrapolated to 0.19 eV at 0°K while the high-temperature portion extrapolated to 0.36 eV. This behavior is explained by a two-valence band model, one active at low temperatures, the other in the high temperature range. A thermal energy gap of approximately 0.36eV was obtained from the temperature variation of resistivity and Hall coefficient in the intrinsic range, 500°-900°K. This value agrees with the high temperature optical data extrapolated to 0°K, thus correlating the optical and thermal energy gaps. © 1967 The American Institute of Physics.

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Materials
Curve 1
Temperature K: 298 Wavelength Range, μm: 4.1-5.2 Geometry θ' θ'': ~0°-0° Composition (weight percent), Specifications, and Remarks: Single crystal; equilibrium Pb-rich PbTe at 1193 K and later corrected, both surfaces lapped on 400 paper and polished on a micro-cloth using 0.3 μm Linde Gamma AB; one surface mounted on an optically flat T-12 crystal (τ = 0.80) by plastic, using crystal clear finger, thickness of PbTe 145 μm; surfaces showed no scratches under x10 magnification.
Curve 2
Temperature K: 298 Wavelength Range, μm: 4.1-5.2 Geometry θ' θ'': ~0°-0° Composition (weight percent), Specifications, and Remarks: Similar to the above specimen and conditions except 346 μm thick.
Curve 3
Temperature K: 298 Wavelength Range, μm: 4.1-5.2 Geometry θ' θ'': ~0°-0° Composition (weight percent), Specifications, and Remarks: Similar to the above specimen and conditions except 474 μm thick.
Curve 4
Temperature K: 298 Wavelength Range, μm: 4.1-5.2 Geometry θ' θ'': ~0°-0° Composition (weight percent), Specifications, and Remarks: Similar to the above specimen and conditions except 593 μm thick.