<title>Monolithic IR sensor arrays in heteroepitaxial narrow-gap lead chalcogenides on Si for the SWIR, MWIR, and LWIR range</title>

Abstract

The heteroepitaxy of narrow gap semiconductor (NGS) layers on Si substrates is described, and the fabrication of photovoltaic IR-sensor arrays in the NGS layers is explained. Lead chalcogenides are grown and employed to facilitate the fabrication of NGS material. Stacked intermediate CaF2-BaF2 bilayers are employed to overcome the lattice and thermal expansion mismatches, thereby attaining epitaxy in the NGS layers. Linear sensor arrays were built on Si substrates with cutoff wavelengths ranging from 3 to more than 12 microns. Performance testing shows that the sensitivity of the most effective PbTe on Si sensors equals that of Hg(1-x)Cd(x)Te, with possible improvement. The compositional homogeneity of NGS material is shown to be less critical with lead salts. The efficacious shielding of charges resulting from defects, a consequence of the high permittivity of lead salts, is shown to allow the development of more fault-tolerant IR sensors. The slower response time indicated in photovoltaic IR focal plane arrays for thermal imaging applications is shown to be insignificant.