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Performances and reliability tests of AlGaN based focal plane array for deep-UV imaging

Some 2D imagers based on AlGaN materials have been developed in the framework of a CNES founded research program to sustain visible blind imagers devoted to solar physics. We have already presented several prototypes of focal plane arrays extending the range of detection from near UV to deep UV [1, 2]. It consists in an array of 320x256 pixels of Schottky photodiodes with a pitch of 30 μm. AlGaN is grown on a silicon substrate instead of sapphire substrate only transparent down to 200 nm. The use of honeycomb structure has straightened the membrane after hybridization, maintained membrane integrity but decreases the filling factor. After a preliminary study to optimize substrate and AlGaN window layer elimination, 12 focal plane arrays have been fabricated in order to achieve aging and reliability tests based on thermal cycling. Technological analyses such as cross-section, profilometry, microscopy and electrical measurements are presented without showing any ageing effect. We present here the final results with a complete evaluation of quantum efficiency on all the spectral range of interest. A large intrinsic absorption in AlGaN takes place in the 100 nm range where the quantum efficiency decreases down to 1%. Several growth parameters are identified as a key component to avoid cracks in the epitaxial structure and surface electrical traps affecting the quantum efficiency.