Optical absorption in epitaxial PbTe films on BaF2

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Abstract
Results are presented for below‐band‐gap (λ∼5−12 μm) optical‐absorption measurements at 300 and 77 K on epitaxial p‐type PbTe films grown on BaF2. These results indicate a significant reduction in the absorption previously reported on PbTe epitaxial films on NaCl substrates. A few samples show an additional absorption suggestive of impurity effects. He4 ion‐backscatter spectra of these films show a surface contamination of chlorine. The results of room‐temperature optical‐absorption measurements on less contaminated samples agree reasonably well with bulk sample behavior. In low‐carrier‐concentration films (p < 1017 cm−3) impurity effects appear to eliminate any temperature dependence of the absorption. The presence of the surface contamination does not affect the dc transport or refractive‐index properties.