Modeling Nonlinear Dark Current Behavior in CCDs

A model explaining nonlinear time dependence of pixels in charge-coupled device (CCD) pixels is presented. The model describes the movement of the pixel's depletion edge based on varying quantities of signal charge. Dynamic depletion edges will affect dark current collected by pixels with impurities located in the region of movement of the edge. The model attempts to address nonlinear behavior of dark current with respect to exposure time well below the saturation level seen in some CCD imagers. Modeling an imager by giving pixels varying number of impurities and depths of those impurities, assuming a uniform distribution, leads to characteristic behavior observed in the imagers.