The Mid-Infrared Instrument for the<i>James Webb Space Telescope</i>, VII: The MIRI Detectors

Abstract

The MIRI Si:As IBC detector arrays extend the heritage technology from the\nSpitzer IRAC arrays to a 1024 x 1024 pixel format. We provide a short\ndiscussion of the principles of operation, design, and performance of the\nindividual MIRI detectors, in support of a description of their operation in\narrays provided in an accompanying paper (Ressler et al. (2015)). We then\ndescribe modeling of their response. We find that electron diffusion is an\nimportant component of their performance, although it was omitted in previous\nmodels. Our new model will let us optimize the bias voltage while avoiding\navalanche gain. It also predicts the fraction of the IR-active layer that is\ndepleted (and thus contributes to the quantum efficiency) as signal is\naccumulated on the array amplifier. Another set of models accurately predicts\nthe nonlinearity of the detector-amplifier unit and has guided determination of\nthe corrections for nonlinearity. Finally, we discuss how diffraction at the\ninterpixel gaps and total internal reflection can produce the extended\ncross-like artifacts around images with these arrays at short wavelengths, ~ 5\nmicrons. The modeling of the behavior of these devices is helping optimize how\nwe operate them and also providing inputs to the development of the data\npipeline.\n