Silicon for High-Luminosity Tracking Detectors -Recent RD50 Results

Abstract

In order to harvest the maximum physics potential of the CERN Large Hadron Collider (LHC), it is foreseen to significantly increase the LHC luminosity by upgrading the LHC towards the HL-LHC (High Luminosity LHC) [1] . Especially the final upgrade (Phase-II Upgrade) foreseen beyond 2020 will mean unprecedented radiation levels. Due to the radiation damage limitations of the silicon sensors presently used, the physics experiments will require new tracking detectors for HL-LHC operation. All-silicon central trackers are being studied in ATLAS, CMS and LHCb, with extremely radiation hard silicon sensors to be used for the innermost layers. Within the CERN RD50 Collaboration, a massive R&D programme is underway across experimental boundaries to develop silicon sensors with sufficient radiation tolerance. One research topic is to gain a deeper understanding of the connection between the macroscopic sensor properties such as radiation-induced increase of leakage current, doping concentration and trapping, and the microscopic properties at the defect level. A further area of activity is the development of advanced sensor types like 3D silicon detectors designed for the extreme radiation levels expected for the vertexing layers at the HL-LHC. Results from irradiation with a mix of different particle types as expected for the sLHC are also given. Recent observations of charge multiplication effects in heavily irradiated detectors at very high bias voltages point towards a new way to achieve sizeable signals after high fluences. Results for several detector technologies and silicon materials at radiation levels corresponding to HL-LHC fluences are presented in this article, demonstrating the availabilty of silicon detectors with sufficient radiation hardness for the different radii of tracking systems in the LHC detector upgrades.