Uncooled mid-infrared lead salt photodetectors prepared by physical vapor deposition: revealing the generation and evolution mechanisms of photosensitization

Uncooled mid-wave infrared photodetectors feature room-temperature operation, high performance, low power consumption, and small size (meeting SWaP³ standards), making them promising candidates for next-generation infrared detectors. Although there have been numerous reports in recent years on the study of their photo-sensitization mechanisms, a complete understanding of the photo-sensitization process has yet to be established. Here, a temporal mapping of the photo-sensitization process of uncooled PbSe photodetectors is constructed, revealing the evolution mechanism of photo-sensitization and uncovering the transition from a porous grain structure to a core–shell structure. Photosensitization occurs within the range of 11 min < t < 52 min, with the optimal sensitization time being approximately t = 40 min. The mechanism for enhanced photosensitivity is attributed to the formation of pn junction core–shell structures in the grains, which facilitate the separation of photogenerated carriers. The decrease in free carrier concentration caused by sensitization is responsible for the increase in total noise voltage. Density functional theory calculations indicate that iodination and oxidation introduce deep acceptor levels at −0.273 eV below the Fermi level, which can extend carrier lifetime through trap effects. This work provides new insights into the device physics of uncooled mid-wave infrared photodetectors.