Herding photons: Correction algorithm for the brighter-fatter effect in the JWST-MIRI Si:As detectors

The Mid-InfraRed Instrument (MIRI) uses three Si:As impurity band conduction (IBC) detectors. These detectors make use of an arsenic-doped infrared-active layer to excite photo-electrons and an electric potential applied across the layer guide them to the pixels. The electric potential depletes the layer of electron-hole pairs. As charge accumulates this region shrinks, resulting in more photo-electrons recombining and not reaching the pixels, which produces non-linear voltage integration ramps. On top of this, the spatial and spectral information may be blurred by up to 20% due to charge migration, depending on the contrast between pixels. This ’Brighter-Fatter Effect’ (BFE) has been observed in detectors for optical and near-infrared wavelengths as well, though it manifests differently in the mid-infrared IBC detectors. Since both the non-linearity and BFE are dependent on the amount of charge accumulated, we propose a fitting and correction routine that corrects both simultaneously for all MIRI observing modes.