Identifying the physical mechanisms of polycrystalline lead salt photoconductors

Abstract

Polycrystalline infrared lead salt detectors exhibit exceptionally high sensitivity near room temperature and, as such, are ubiquitous in commercial instruments such as spectrometers and flame detectors. The underlying physical mechanism behind this remarkable performance has been the subject of speculation for many years. In this treatise, data from work performed at BAE Systems and St. John's Optical Systems and from the published literature are analyzed to identify common mechanisms that contribute to the photoconductivity of polycrystalline lead salt detectors from a multitude of material deposition and process technologies, and it was concluded that much of the behavior can be attributed to surface-related phenomenon. Physical models are proposed to explain the observations. Finally, there is a brief description of measurements related to noise in these complex structures, indicating the importance of ohmic contacts, but the observed low frequency spectral noise density remains a mystery.