Charge Collection in Silicon Imaging Sensors

Weatherill, Daniel Philip (2016). Charge Collection in Silicon Imaging Sensors. PhD thesis The Open University.



The subject of this thesis is the analysis of instrumental effects caused by the interaction between collected signal charge and electric fields within precision CCD imaging sensors typically used for astronomy. These phenomena cause aberrations in the measured spatial distribution of subsequently collected signal, which may present a major error for upcoming astronomy projects which rely heavily on accurately determining shapes of compact sources. Examples are the Large Synoptic Survey Telescope and the Euclid space telescope. The size of dynamic collection effects may be subtly affected by the operating conditions and design parameters of the device. Dynamic charge collection effects differ in origin from many other errors introduced by imaging detectors in that they are attributable to changes in the confinement of charge carriers during the collection phase of operation, rather than the readout phase. The fact that the exact aberration implied by dynamic charge collection effects depends exactly on the incident light field’s spatial distribution also makes them comparatively difficult to correct for.

A method of physically modelling charge collection within the detector using analytical solutions to Poisson’s equation is described, which is shown to qualitatively reproduce many features of measured dynamic charge collection effects. Since the model is derived from device physics, it differs in approach in a complementary way from previous efforts which are empirically based. Experimental charge collection measurements from two different CCDs both affected by dynamic collection effects are presented, and shown in large part to be consistent with the predictions from the theoretical model.

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