Charge collection efficiency in back-illuminated Charge-Coupled Devices

TL;DR

This paper introduces a new X-ray based method to measure charge collection efficiency in back-illuminated CCDs, highlighting the importance of backside processing for low-energy detection in dark matter and neutrino experiments.

Contribution

It presents a novel technique for characterizing charge collection efficiency in fully-depleted back-illuminated CCDs, emphasizing the impact of backside processing on detector performance.

Findings

Backside processing significantly improves charge collection near threshold.

Recombination layers of a few microns distort low energy spectra.

Partial charge collection regions can be reduced to less than 1 micrometer.

Abstract

Low noise CCDs fully-depleted up to 675 micrometers have been identified as a unique tool for Dark Matter searches and low energy neutrino physics. The charge collection efficiency (CCE) for these detectors is a critical parameter for the performance of future experiments. We present here a new technique to characterize CCE in back-illuminated CCDs based on soft X-rays. This technique is used to characterize two different detector designs. The results demonstrate the importance of the backside processing for detection near threshold, showing that a recombination layer of a few microns significantly distorts the low energy spectrum. The studies demonstrate that the region of partial charge collection can be reduced to less than 1 micrometer thickness with adequate backside processing.