The status of the middle (3-8 µm) and long (8-16 µm) wavelength Hg1-¬xCdxTe infrared detectors is reviewed with special emphasis on the uncooled operation niche, the Polish specialization in the field.
The devices are based on multilayer Hg1 xCdxTe heterostructures with complex band gap and doping profiles. Modified isothermal vapor phase epitaxy (ISOVPE) has been used for many years for research and commercial fabrication of photoconductive, photoelectromagnetic and photovoltaic devices. At present, the fabrication of IR devices relies on a low temperature epitaxial technique, namely metalorganic vapor phase deposition (MOCVD).
Photoconductive and photoelectromagnetic detectors are still in production. The devices are gradually replaced with flicker noise free photovoltaic devices which offer inherent advantages of no electric or magnetic bias, no heat load. The PV devices could offer high performance and very fast response. Actually, the uncooled long wavelength devices of conventional design suffer from two issues; namely low quantum efficiency and very low junction resistance. It 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.
The present fabrication program includes devices which are optimized for any wavelength within a wide spectral range 1 16 µm and operation in the 200-300 K temperature range. Special solutions have been applied to improve speed of response leading to picoseconds range response times.
The devices have found increasingly widespread civilian (pyrometry, thermography, gas analysis based on conventional, laser and Fourier transform spectroscopy, free space high transfer rate optical communications, laser technology, test and science equipment) and military (night vision, laser range finder, threat warning devices, gun sights, smart munitions) applications. The elimination of cooling will lead to a significant reduction in cost, logistical supply, and an increase in the mean time between failures.