Characterization of proton-induced damage in thick, p-channel skipper-CCDs

In this work, we characterize the radiation-induced damage in two thick, p-channel skipper-CCDs irradiated unbiased and at room temperature with 217-MeV protons. We evaluate the overall performance of the sensors and demonstrate their single-electron/single-photon sensitivity after receiving a fluence on the order of 10$^{10}$~protons/cm$^2$. Using the pocket-pumping technique, we quantify and characterize the proton-induced defects from displacement damage. We report an overall trap density of 0.134~traps/pixel for a displacement damage dose of $2.3\times10^7$~MeV/g. Three main proton-induced trap species were identified, V$_2$, C$_i$O$_i$ and V$_n$O$_m$, and their characteristic trap energies and cross sections were extracted. We found that while divacancies are the most common proton-induced defects, C$_i$O$_i$ defects have a greater impact on charge integrity at typical operating temperatures because their emission-time constants are comparable or larger than typical readout times. To estimate ionization damage, we measure the characteristic output transistor curves. We found no threshold voltage shifts after irradiation. Our results highlight the potential of skipper-CCDs for applications requiring high-radiation tolerance and can be used to find the operating conditions in which effects of radiation-induced damage are mitigated.