Measuring the impact of CCD gate width on the brighter-fatter effect

The brighter-fatter effect is a well known phenomenon in thick, back illuminated CCDs, causing asymmetric increase in the observed size of point sources via correlated charge collection with higher signal levels. Over recent years, the effect of various operating parameters (such as the back bias applied) on the size of measured correlations has been well established. Less well studied is the consequence of changing the effective collection gate width of the CCD, which is of limited accessibility to experiment though several values are available in 3 or 4 phase devices. In this proceeding we present collection gate width experiments using both flat field and spot projection illuminations on a thick back illuminated device as used for the LSST project. We report on the size of the variation of measured correlations with gate width as compared with backside bias voltage, and find that gate width constitutes a small but significant contribution. In light of these results, we give comment on device optimisation when minimising correlated charge collection effects is desired.