Charge transfer efficiency (CTE) in the WFC3/UVIS CCDs

2.0 Introduction Charge transfer efficiency (CTE) is a measure of how effectively the CCD moves charge from one pixel to another during the chip readout; a perfect device transferring all of the charge without any losses would have a CTE of 100%. In practice, defects in the silicon matrix trap charge and release it at a later time, on scales of microseconds to seconds. The traps can be intrinsic to the device, i.e., introduced during the manufacturing process, or develop over time as the result of radiation damage. Devices in low-earth orbit are particularly susceptible to accumulating damage, in large part due to regular passes through the South Atlantic Anomaly, where the Earth’s Van Allen belts come closest to the Earth and generate regions of higher radiation rates.