Persistance and dark current characterization on HgCdTe short wave infrared imagers for astronomy at CEA and Lynred

Linked by ESA’s Astronomy Large Format Array for the near-infrared ("ALFA-N") technology development program, CEA and Lynred aim at setting up the fabrication of very large IR focal plane arrays (FPA) for astronomy needs. Prior to this project, dark current and image persistence are under investigation for achieving the high level of performance needed by astronomers. During previous characterization of this kind of detector, the FPA appeared particularly sensitive to ROIC electro-luminescence, preventing to observe fainter effects such as persistence. With the mitigation of the glow, the first measurements showed that dark current was dominated by persistence instead of classical diffusion, Auger or ShockleyRead-Hall mechanisms. We propose a dedicated test protocol in order to electrically characterize persistence and an empirical modelling tool to describe it in terms of amplitude and characteristic time constant. The first step consists in removing the residual persistence, allowing to characterize the intrinsic photodiode’s dark current, down to 0.03e-/s at 90K on four tested devices. From this reference, the persistence contribution is dramatically minimized and experimental conditions are reproducible, enabling further investigation on persistence to be carried out. Applied on detectors manufactured in the CEA-LETI clean rooms, this protocol aims at a better understanding of the phenomenon. Using an array containing different diode flavours (ie variations in the technological parameters such as diode geometry, passivation…), the characterization scheme described above should bring information about technological contributions on persistence.