Short-period PbTe/Pb1−xSnxTe/CaTe (x = 0.36, 0.48) superlattices were prepared on a KCl (100) substrate and their interband optical absorption was measured. The superlattice indicated strong absorption of more than 2500 cm−1, corresponding to the electron transition from the first valence subband in the PbSnTe layer to the conduction subband in the PbTe layer, which can give enough optical gain for laser operation under inversion population. The absorption coefficient increased with lowering of temperature in the wavelength region from 7 to more than 20 μm. The enhancement of the absorption coefficient was explained by the enhancement of the overlap of wave functions and the two-dimensional density of states in the type-II superlattice retaining a large value even with reduced band gap. The conduction-band offset of the PbTe/Pb0.64Sn0.36Te type-II heterojunction was estimated to be 120 meV.

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