Uncooled operation of IR photodetectors

The ultimate performance of long wavelength infrared photodetectors operating at high temperatures is likely to be limited by the noise due to the statistical nature of thermal generation of charge carriers in narrow band gap semiconductors. Additional obstacles to achieve theoretical performance in practical devices arise from weak absorption of infrared radiation, short diffusion length of charge carriers in narrow gap semiconductors and other reasons. Various ways to improve performance of uncooled photodetector such as the reduction of thermal generation rate by proper selection of the semiconductor material, its doping and suppression of thermal generation by the non-equilibrium mode of operation are considered. Another possibility is the reduction of physical volume of a detector. This can be done by reducing a detector physical area and its thickness with appropriate means to preserve the device field of view and a quantum efficiency. The advanced architectures of uncooled Hg1-xCdxTe IR photoconductors, photoelectromagnetic and photovoltaic detector are described. The devices require heterostructures with complex band gap and doping profiles and can be grown by the low temperature epitaxial techniques. The most promising device for uncooled detection is heterojunction photodiode integrated with optical concentrator. The progress in technology of photodetectors will eventually lead to perfect and fast detection of long wavelength radiation without cooling.