Ternary Lead Chalcogenide Alloys for Mid-Infrared Detectors

We demonstrate thin films of PbSe 1− x S x and PbSe 1− x Te x lead chalcogenide ternary alloys as infrared detectors. The films were deposited on single crystal BaF 2 substrates using physical vapor deposition. Detectivity in the wavelength range from 1 μ m to 5 μ m was measured at −40°C, and all films showed photoresponse signals more than an order of magnitude larger than their noise. The detectivity spectra were used to assess the tunability of the band gap from mixing the lead chalcogenide binaries. The PbSe 1− x S x system showed tunability that followed Vegard’s law, while the PbSe 1− x Te x system showed tunability with a bowing parameter of −0.096 eV. Comparisons to measurements from the literature taken at room temperature suggest that the bowing parameter decreases with decreasing temperature, and the band gap temperature coefficient with respect to composition also shows bowing.