Implications of a thinned CCD QE model

A thinned CCD QE model derived by Morley Blouke provided more than an estimation of quantum efficiency. The derivation of the model also produced charge flux equations in the direction normal to the imaging surface. First, these equations were converted into velocity expressions and subsequently into velocity profiles along the normal axis. Such profiles are excellent tools for visualizing the charge collection dynamics as a function of device structure. Profile by-products include dark layer thickness and speed of response (collection). The latter characteristic essentially constrains transverse charge spread. A simple random walk model was created in order to evaluate the extent of this spread in terms of radial rms distances. This distance is a measure of point resolution and is expressed as a function of CCD design and incident wavelength. The theoretical radius of charge spread from a point source ranges from about 3 micrometers for near-IR to about 20 micrometers for near-UV light. This article also discusses justifications for the model, although the final justification must wait for funding of experimental work.