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Solar blind detectors are key devices for applications where a small ultraviolet signal must be detected with a large solar background. In order to fabricate array that can be read by a hybridized Si read out circuit, we developed devices that can be illuminated from the back side. AlGaN heterostructures, with an active region with 43% Al and a window layer with 63% Al were grown on sapphire by Molecular Beam Epitaxy. Metal-Semiconductor-Metal (MSM) and Schottky diode detectors have been fabricated. Photoresponse spectra were recorded and show solar blind characteristics with cut off wavelengths in the range of 270-290 nm. The visible and near UV rejection ratio reaches 5 decades and the cut off slope is 4 nm per decade, which is the current state of the art for solar blind detectors, and is intrinsically limited by internal photoemission as will be discussed. Optical solutions have been implemented in order to increase by one or two orders of magnitude the rejection ratio. In MSM detectors, we reached state of the art detectivities. For a band width of 50 Hz, the detectivity D equals 4E14 /W corresponding to a noise equivalent power NEP=2.5 fW. This corresponds to a photon flux of 500/s per pixel which is among the best values ever reported in AlGaN solar blind detectors. Similar detectivities are also obtained in Schottky diode detectors. Linear arrays have been fabricated and characterized, with a good uniformity as will be shown. Solar blind images have been recorded and will be presented. Two dimensional arrays have also been fabricated based on AlGaN heterostructures hybridized on a silicon read out circuit. First results and images will possibly be presented. |