Importance of charge capture in inter-phase regions during readout of charge-coupled devices

TL;DR

This paper demonstrates that charge trapping in inter-phase regions during CCD readout is significant and must be considered, challenging previous assumptions of negligible trapping due to rapid charge transfer.

Contribution

The study combines advanced electron density simulations with trap pumping data to reveal the importance of inter-phase charge trapping in CCDs, impacting future readout and radiation damage analysis.

Findings

Charge trapping during transfer is necessary to explain experimental data.

Simulation and trap pumping data show non-negligible trapping in inter-phase regions.

Results influence trap pumping methods and CCD readout optimization.

Abstract

The current understanding of charge transfer dynamics in Charge-Coupled Devices (CCDs) is that charge is moved so quickly from one phase to the next in a clocking sequence and with a density so low that trapping of charge in the inter-phase regions is negligible. However, new simulation capabilities developed at the Centre for Electronic Imaging, that includes direct input of electron density simulations, has made it possible to investigate this assumption further. As part of the radiation testing campaign of the Euclid CCD273 devices, data has been obtained using the trap pumping method, that can be used to identify and characterise single defects CCDs. Combining this data with simulations, we find that trapping during the transfer of charge between phases is indeed necessary in order to explain the results of the data analysis. This result could influence not only trap pumping theory and how trap pumping should be performed, but also how a radiation damaged CCD is read out in the most optimal way.