ABSTRACT
During the 1950s, IR detectors were built using single-element-cooled lead salt detectors, primarily for anti-air-missile seekers. Usually lead salt detectors were polycrystalline and were produced by vacuum evaporation and chemical deposition from a solution, followed by a post-growth sensitization process. –e £rst extrinsic photoconductive detectors were reported in the early 1950s a«er the discovery of the transistor, which stimulated a considerable improvement in the growth and material puri£cation techniques. Since the techniques for controlled impurity introduction became available for germanium at an earlier date, the £rst high-performance extrinsic detectors were based on the use of germanium. –e extrinsic
8.1 Introduction ......................................................................................191 8.2 Narrow-Gap Semiconductor Materials .........................................193
