The photovoltaic (PV) effects in Hg1-xCdxTe were mentioned for the first time in 1959 by Lawson et al. The development of Hg1-xCdxTe photodiodes was stimulated initially by their applications as high-speed detectors, mostly for direct and heterodyne detection of 10.6-μm CO2 laser radiation. Later efforts have been dominated by applications for large arrays used in LWIR and MWIR thermal imaging systems. In contrast to photoconductors, photodiodes have a very low power dissipation and can be assembled in 2D arrays containing a very large (<106) number of elements, limited only by existing technologies rather than by heat dissipation issues. Photodiodes are the most promising devices for uncooled operation, and at present, significant efforts are on Auger-suppressed devices and multiple heterojunctions.
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