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solar blind detectors based on AlGaN grown on sapphire

Jean-Yves Duboz 1Nicolas GRANDJEAN 2Franck Omnes 1Jean Luc Reverchon 3Mauro Mosca 3

1. Centre de Recherche sur l'Hétéro-Epitaxie et ses Applications (CRHEA-CNRS), Rue Bernard Grégory, Valbonne 06560, France
2. Centre de Recherche sur l'Hétéro-Epitaxie et ses Applications (CRHEA-CNRS), Rue Bernard Grégory, Parc Sophia-Antipolis, Valbonne 06560, France
3. Thales Research and Technology (TRT), Orsay 91404, France


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 and Metal Organic Chemical Vapor Deposition (with different processes but similar results). 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. The effect of internal photoemission will be discussed. 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. Schottky diode AlGaN solar blind detectors exhibit a larger dark current due to parasitic leakage currents on the mesa edges. Some limitations in the charge collection were observed, due to the difficulty to get a highly conductive AlGaN with 65% Al and also due to the internal piezoelectric field. As a result, the performance of Schottky diodes, although comparable with published values, remains for the time being, slightly below the one obtained in MSM detectors. Preliminary results obtained in MSM detector arrays illuminated from the back side will possibly be given.


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Presentation: invited oral at E-MRS Fall Meeting 2004, Symposium C, by Jean-Yves Duboz
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-04-22 10:31
Revised:   2009-06-08 12:55