Uncooled infrared photodetectors in Poland

The history and present status of the middle and long wavelength Hg1-xCdxTe infrared detectors in Poland are reviewed. Research and development efforts in Poland were concentrated mostly on uncooled market niche. Technology of the infrared photodetectors has been developed by several research groups. The devices are based on mercury-based variable band gal) semiconductor alloys. Modified isothermal vapour phase epitaxy (ISOVPE) has been used for many years for research and commercial fabrication of photoconductive, photoelectromagnetic and other devices. Bulk growth and liquid phase epitaxy was also used. At present, the fabrication of IR devices relies on low temperature epitaxial technique, namely metalorganic vapour phase deposition (MOCVD), frequently in combination with the ISOVPE. Photoconductive and photoelectromagnetic detectors are still in production. The devices are gradually replaced with photovoltaic devices which offer inherent advantages of no electric or magnetic bias, no heat load and no flicker noise. Potentially, the PV devices could offer high performance and very fast response. At present, the uncooled long wavelength devices of conventional design suffer-from two issues; namely low quantum efficiency and very low junction resistance. lt makes them useless for practical applications. The problems have been solved with advanced 3D band gap engineered architecture, multiple cell heterojunction devices connected in series, monolithic integration of the detectors with microoptics and other improvements. Present fabrication program includes devices which are optimized for operation at any wavelength within a wide spectral range 1-15 mu m and 200-300 K temperature range. Special solutions have been applied to improve speed of response. Some devices show picoseconds range response time. The devices have found numerous civilian and military applications.