Light-tight skipper-CCDs for X-ray detection in space

TL;DR

This paper introduces a light-tight aluminum shielding method for skipper-CCDs, effectively suppressing optical backgrounds in space X-ray detection without compromising X-ray efficiency, validated through experiments and simulations.

Contribution

The study demonstrates that thin aluminum layers effectively block optical light while maintaining X-ray detection efficiency in skipper-CCDs for space applications.

Findings

50 and 100 nm aluminum layers suppress >99.6% of optical light.

No loss in X-ray detection efficiency at 5.9 and 6.4 keV with these coatings.

Simulations confirm effectiveness over broader energy ranges.

Abstract

Skipper Charge-Coupled Devices (skipper-CCDs) are pixelated silicon detectors with deep sub-electron resolution. Their radiation hardness and capability to reconstruct energy deposits with unprecedented precision make them a promising technology for space-based X-ray astronomy. In this scenario, optical and near-infrared photons may saturate the sensor, distorting the reconstructed signal. We present a light-tight shield for skipper-CCDs to suppress optical backgrounds while preserving X-ray detection efficiency. We deposited thin aluminum layers on the CCD surface using an e-beam evaporator and evaluated their blinding performance across wavelengths from 650 to 1000 nm using a monochromator, as well as the X-ray transmission using an $^{55}$Fe source. We find that 50 and 100 nm layers provide >99.6% light suppression, with no efficiency loss for 5.9 and 6.4 keV X-rays. In addition, we used Geant4 simulations to extend these results to a broader energy range and quantify the efficiency loss for different aluminum thicknesses. Results show that thin aluminum coatings are an effective, low-cost solution for optical suppression in skipper-CCDs intended for X-ray detection and space instrumentation.