In 2001 the Large Hadron Collider (LHC) and High Luminosity Large Hadron Collider (HL-LHC) were facing the challenging construction of experiments that have to withstand radiation levels never dealt with before in a particle detector. The innermost tracking layers, closest to the beam, are expected to reach an instantaneous luminosity of 7.5 × 10$^{34}$ cm$^{−2}$s$^{−1}$, being the result of 200 simultaneous proton-proton interactions per bunch crossing, and fluence levels of 2×10$^{16}$ n$_{eq}$/cm$^2$. The LHC experiments’ upgrades utilize silicon for the tracking detection layers, which have to withstand a huge amount of radiation at the end of the experiment lifetime without losing the detectors’ performance. Therefore, in 2001, there was a need to study the precise damage that those detectors were going to receive, as well as to simulate, understand and mitigate the radiation effects in the silicon detectors.

RD50 is a CERN-based collaboration that started in 2002. The collaboration is dedicated to study radiation-hard semiconductor devices for very high luminosity colliders. The collaboration is finishing its activity by the end of 2023 with 65 institutes and more than 400 members, leaving more than 20 years of radiation damage studies and leading the development of new technologies for radiation-hard semiconductor devices, as well as detector technologies and 4D detectors. The collaboration is organized into four research areas: material characterisation, detector characterisation, new detectors and full detector systems.

During 20 years, different silicon detector layouts and materials have been extensively studied before and after irradiation. The trap centres created inside the silicon have been parametrized, which provided valuable information for the implementation of radiation effects for simulation software tools. There have been strategies to mitigate the radiation damage, as well as new measurement techniques to study the electric field inside the sensor bulk. Silicon detector concepts, including monolithic, 3D and LGAD detectors, have been thoroughly investigated for use inside the HL-LHC. As a result, 3D detectors were installed inside the ATLAS IBL layer, and LGADs are being introduced in the timing detectors of the CMS and ATLAS Phase-II upgrades.

This text aims to summarise more than 20 years of RD50 results as well as some current research.