Silicon sensors for HL-LHC tracking detectors

It is foreseen to significantly increase the luminosity of the LHC by upgrading towards the HL-LHC (High Luminosity LHC) in 2021 in order to harvest the maximum physics potential. After the upgrade, unprecedented levels of radiation will require the experiments to upgrade their tracking detectors to withstand hadron fluences equivalent to over $10^{16} \ 1 \rm{MeV}$ neutrons per cm$^2$. Within the RD50 Collaboration, a massive R&D; program is underway to develop silicon sensors with sufficient radiation tolerance. Recent defect characterization and Edge-TCT measurement results improved the understanding of irradiated detector performance. RD50 results show that sensors with n-side readout, easiest made with p-type silicon, have a superior radiation hardness due to the high overlap of electric and weighting field after irradiation, larger contribution of electrons to the total signal and finally due to charge multiplication which may enhance the collected charge at high bias voltages in this type of detector. A further area of activity is the development of advanced sensor types like 3D silicon and thin pixel detectors designed for the extreme radiation levels expected for the inner layers.