Lateral Diffusion Estimation in Fully Depleted Thick CCD Using Flat Field Image Analysis
In thick fully depleted CCDs charge carrier transport from the back window to the gates is accompanied by charge diffusion. Lateral diffusion smooths out density variations of the incoming photon flux by redistributing charges spatially. This creates short range positive correlations in recorded amplitudes. Pixel-to-pixel amplitude variations can also be caused by pixel size and quantum efficiency variations. Pixel size variations result in short range negative correlations. Our study shows that the characteristic diffusion width can be extracted from flat field data. The study was performed on fully depleted, thick CCDs produced in a technology study for the Large Synoptic Survey Telescope (LSST). Data were taken in the laboratory at bias voltages between -5 and -40 V. To increase statistical accuracy, images taken in identical conditions were co-added after base line subtraction and master files were produced. A flat field image simulator was developed for statistical comparison of simulated and measured images. Results on diffusion, pixel response variations, data features, analysis and modeling techniques are presented and discussed.