A study of the silicon divacancy defect in the LSST E2V CCD250 using the single trap pumping method

Charge-coupled devices (CCDs) currently constitute the standard detector for precision astronomical telescopes such as the Large Synoptic Survey Telescope (LSST) due to their high linearity, sensitivity and dynamic range. Charge transfer properties can however be degraded by the presence of defect levels in the silicon band-gap, which can act as trapping centers for signal charge. The technique of single trap-pumping can be used as a tool to probe the underlying properties of relevant defect levels and potentially mitigate against their effects. In this paper we present a single trap-pumping study of the LSST E2V CCD250 across a temperature range of -30 degrees to -110 degrees, a much larger range than previously studied using this approach. The predominant defect level of relevance for CCDs appearing at these temperatures is shown to be the single-acceptor level of the silicon divacancy. Using experimental data and a basic Monte-Carlo model of the trap-pumping process we examine the defect level properties, with an attempt made to account for both the capture and emission of signal charge.