Monolithic infrared sensor arrays with 3-12 μm cut-off in heteroepitaxial narrow gap lead chalcogenides on silicon substrates

The authors describe heteroepitaxy of narrow gap semiconductor (NGS) layers on Si-substrates, and fabrication of photovoltaic IR=sensor arrays in the NGS layers. They use lead chalcogenides (PbS, PbTe, Pb_1-xEu_xSe and Pb_1-xSn_xSe) as NGS material for sensor integration. The high permittivity of lead salts yields much more fault tolerant devices due to the effective shielding of charges resulting from defects. Epitaxy of the NGS layers is achieved by using stacked intermediate CaF₂-BaF₂ bilayers to overcome the large lattice and thermal expansion mismatch. The authors have fabricated linear sensor arrays on Si-substrates with cut-off wavelengths ranging from 3 μm (with PbS and Pb_1-xEu_xSe) and 5.5 μm (PbTe) up to >12 μm (Pb_1-xSn_xSe). The sensitivities of the best PbTe Si sensors are as high as those of MCT with comparable cut-off wavelengths