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Lead selenide layers were obtained by thermal evaporation in vacuum on thermally oxidized silicon. As-deposited layers present no response to infrared radiation and an activation procedure is mandatory. The sensitization process described in this work consists of a thermal treatment developed in two different stages: The first step in an iodine and oxygen rich atmosphere at 220 °C, and the second one at a higher temperature (450 °C) on air. After this treatment, the developed photodetectors show high sensitivity to medium wavelength infrared radiation at room temperature. We have analyzed the structural, compositional, electrical, and morphological changes of the films occurred during the activation process. After processing many films, we conclude that iodine plays a key role in the PbSe sensitization. This halogen behaves as a transport agent during the PbSe recrystallization process, and promotes a fast growth of PbSe microcrystals. Oxygen is trapped into the PbSe lattice during the recrystallization process, as it happens in chemically deposited PbSe films. The introduction of halogens in the PbSe sensitization procedure is a highly efficient technique for the incorporation of oxygen to the semiconductor lattice in electrically active positions.

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The existing technology for uncooled MWIR photon detectors based on polycrystalline lead salts is stigmatized for being a 50-year-old technology. It has been traditionally relegated to single-element detectors and relatively small linear arrays due to the limitations imposed by its standard manufacture process based on a chemical bath deposition technique (CBD) developed more than 40 years ago. Recently, an innovative method for processing detectors, based on a vapour phase deposition (VPD) technique, has allowed manufacturing the first 2D array of polycrystalline PbSe with good electro optical characteristics. The new method of processing PbSe is an all silicon technology and it is compatible with standard CMOS circuitry. In addition to its affordability, VPD PbSe constitutes a perfect candidate to fill the existing gap in the photonic and uncooled IR imaging detectors sensitive to the MWIR photons. The perspectives opened are numerous and very important, converting the old PbSe detector in a serious alternative to others uncooled technologies in the low cost IR detection market. The number of potential applications is huge, some of them with high commercial impact such as personal IR imagers, enhanced vision systems for automotive applications and other not less important in the security/defence domain such as sensors for active protection systems (APS) or low cost seekers.Despite the fact, unanimously accepted, that uncooled will dominate the majority of the future IR detection applications, today, thermal detectors are the unique plausible alternative. There is plenty of room for photonic uncooled and complementary alternatives are needed. This work allocates polycrystalline PbSe in the current panorama of the uncooled IR detectors, underlining its potentiality in two areas of interest, i.e., very low cost imaging IR detectors and MWIR fast uncooled detectors for security and defence applications. The new method of processing again converts PbSe into an emerging technology.

We report the manufacture of an uncooled infrared detector with its natural spectral response modified as design. Thanks to a technology to process uncooled polycrystalline PbSe sensors, we have integrated a filter and a PbSe detector monolithically. Our processing is based on thermal deposition of a thin PbSe layer followed by a specific thermal treatment in an iodine-rich atmosphere that turns PbSe into an infrared sensitive material. Using this technique, we are able to process uncooled medium-wave infrared detectors directly on the last layer of an interference filter. After this achievement, polycrystalline PbSe detectors will be smarter, more reliable, and exhibit better characteristics than their direct competitors (near room-temperature cadmium mercury telluride, InAsSb, etc.). Standard photolithography, interference filter deposition, and dry etching techniques are fully compatible with this polycrystalline PbSe processing. These are essential facts in order to obtain reduced filter and detector sizes (multicolor arrays). The technology described in this work is useful in the field of low cost infrared detection.