Heteroepitaxial PbTe-Si and (Pb, Sn)Se-Si structures for monolithic 3-5 µm and 8-12 µm infrared sensor arrays

Epitaxial layers of narrow gap PbTe and (Pb,Sn) Se have been grown on Si substrates, and used for the first time to fabricate intrinsic photovoltaic IR-sensors on Si for the 3-5µm and 8-12µm range. The narrow gap semiconductors were grown on the BaF2side of a graded (Ca,Ba)F2buffer film which served to overcome the large lattice mismatch (up to 19%) to the Si. The backside illuminated IR-devices revealed resistance area products at 87K of up to 4Ωcm²for PbTe (cut -off wavelength 5.8µm), and up to 0.5Ωcm²for (Pb,Sn) Se with 9.7 µm cut-off. These values come close to or exceed the photon noise limit (for 295K background radiation, 180° FOV, 50% quantum efficiency). The results open up the possibility to construct large monolithic IR-FPA´s (focal plane arrays) with IR-sensors in the narrow gap semiconductor and signal processing in the Si.