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The first results on photoconductivity in Hg1-xCdxTe were reported by Lawson et al. in 1959. Ten years later, in 1969, Bartlett et al. reported background limited performance of photoconductors operated at 77 K in the 8â14-μm LWIR spectral region. The advances in material preparation and detector technology have led to devices approaching the theoretical limits of responsivity over wide ranges of temperature and background (see Refs. 3â6). The simple n-type Hg1âxCdxTe photo-conductor is a mature product that has been in production for over 10 years. The largest market was for 60-, 120-, and 180-element units in the âcommon moduleâ military thermal imaging viewers. Photoconductivity was the most common mode of operation of 3â5-μm and 8â14-μm Hg1âxCdxTe photodetectors for many years.
In 1974, Elliott reported a major advance in IR detectors in which the detection, time delay, and integration functions in serial scan thermal imaging systems were performed within a simple three-lead filament photoconductor, known by the acronym SPRITE (Signal PRocessing In The Element).
The further development of photoconductors is connected with the elimination of the deleterious effect of sweep-out by the application of accumulated or heterojunction contacts. Heterojuction passivation has been used to improve stability. The operation of 8â14-μm photodetectors has been extended to ambient temperatures. The means applied to improve the performance of photoconductors operated without cryogenic cooling include the optimized p-type doping, the use of optical immersion and optical resonant cavities. Elliott and other British scientists introduced Auger-suppressed excluded photoconductors.
The research activity on photoconductors has been significantly reduced in the last decade on reflecting maturity of the devices. At the same time, Hg1âxCdxTe photodetectors are still manufactured in large quantities and used in many important applications.
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