Overview of p-on-n planar IRFPAs at DEFIR

Abstract

In this paper, we report on results obtained both at CEA/LETI and SOFRADIR on p-on-n Infra-Red Focal Plane Arrays (IR FPAs) from the Short-Wave (SW) to the Very-Long-Wave (VLW) spectral range. For many years, p-on-n arsenicion implanted planar technology has been developed and improved within the framework of the joint laboratory DEFIR, a collaborative effort bringing together the expertise of both teams. Compared to n-on-p architecture, p-on-n technology allows to lower dark current density and series resistance by means of respectively long-lifetime minority carriers (hole) and high-mobility majority carriers (electrons). As a consequence, p-on-n photodiodes are well-adapted for very large FPAs operating either at high temperature or very low flux. The Mid-Wave (MW) and Long-Wave (LW) spectral ranges have been firstly addressed with TV/4 FPAs, 30 μm pitch, principally for defence and security applications. Our results showed state-of-the-art detector performances, consistent with “Rule 07” model, a relevant indicator of the p-on-n technology maturity. The subsequent developments of p-on-n imagers have produced more compact, less energy consuming systems, with a substantial resolution enhancement. In this way, MW and LW FPAs, TV format, with 15 μm pixel pitch have been designed. First results obtained in MW (λc=5.3 μm @80 K) for High Operating Temperature (HOT) applications have showed highly promising Electro-Optical (EO) performances. Space applications are another exciting but challenging domains where p-on-n is a good candidate. In this way, imagers dedicated to low-flux detection have first been realized as TV/4 FPAs, with 15μm pitch in the SW spectral range (2 μm). The dark currents obtained are coherent with those published in the literature. Finally, TV/4 arrays, 30 μm pixel pitch, have been manufactured for the very long wave spectral range. For this detection range, the quality of material and reliability of technology are the most critical. The measured dark current fits “Rule 07” well, with homogeneous imagers. In conclusion, DEFIR team have developed, improved and characterized p-on-n IR FPAs from SW to VLW spectral range. In all spectral ranges, we have demonstrated state-of-the-art results, which highlight the quality of material and viability of our p-on-n technology. This technology, currently industrialized by SOFRADIR, opens new ways for next generation of imagers.