In this paper recent developments made by the French Atomic Energies and Alternative Energies Commission (CEA) at the Electronics and Information Technology Laboratory (LETI) on the fabrication of planar p-on-n HgCdTe photodiodes are reported. Results obtained on long-wavelength infrared (LWIR) liquid-phase epitaxy (LPE) and mid-and short-wavelength infrared (MWIR/SWIR) molecular beam epitaxy (MBE) have been previously published. For these photodiodes, p-type doping is obtained by arsenic implantation followed by diffusion and activation under Hg-overpressure annealing. The active layer is n-type doped by indium incorporation during growth. Control of the p-on-n junctions is one of the key points of this technology, requiring good knowledge of the arsenic implantation and diffusion and the evolution of implantation-induced defects. Concerning implantation, the impact of dose (from 2 9 10 14 at./cm 2 to 2 9 10 15 at./cm 2 ) and energy (from 50 keV to 500 keV) on As profiles is considered. The profiles after implantation are modeled using Pearson IV moments. Realistic descriptions of arsenic distributions are obtained, and the evolution of moments with implantation conditions is fitted. In addition, implantation damage is examined by transmission electron microscopy (TEM) and the evolution of defects is studied depending on implantation conditions and Hg-overpressure annealing. Previous results obtained on 30-lm-pitch LPE LWIR and MBE MWIR/SWIR showed state-of-the-art detector performance. Since these first results, progress has been made to decrease the pixel pitch to 15 lm and increase the focal-plane array (FPA) format. In this way, 640 9 512 LPE LWIR FPAs have been processed and characterized. In addition we report results obtained on our first p-on-n very long-wavelength infrared (VLWIR) photodiode fabricated at CEA-LETI with k c = 13.35 lm at 50 K. These latest results demonstrate the viability of our technology and materials.

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This paper presents a new HgCdTe-based heterostructure to perform quantum infrared detection. The structure is based on the unipolar barrier concept, introduced by White in the 1980s for HgCdTe. The driving concept is the use of a large gap barrier layer to impede the flow of majority carriers (electrons on the conduction band in the case of n-type material) while facilitating the transport of minority (photo) carriers (holes on the valence band). The issue encountered here is the formation of a small potential barrier on the valence band, blocking photocarriers and therefore killing the quantum efficiency. The idea is to optimize the structure with an asymmetric barrier: abrupt on the contact side to efficiently block the majority carriers, and gradual on the absorption layer side to plane down the remaining potential barrier for the collected photocarriers. The concept has been studied by finite element modeling simulation and showed promising results. An optimal design has been identified in the middle wave band and molecular beam epitaxy layers have been grown then processed. First experimental characterization of the electrooptical properties of such structures showed promising features: 60% quantum efficiency and low turn-on voltage have been measured on single pixels.