A Method to Simulate the Observed Surface Properties of Proton Irradiated Silicon Strip Sensors

During the scheduled high luminosity upgrade of the LHC, the world's largest particle physics accelerator at CERN, the position sensitive silicon detectors installed in the vertex and tracking part of the CMS experiment will face a more intense radiation environment than the present system was designed for. To upgrade the tracker to the required performance level, extensive measurements and simulation studies have already been carried out. \\ A defect model of Synopsys Sentaurus TCAD simulation package for the bulk properties of proton irradiated devices has been producing simulations closely matching to measurements of silicon strip detectors. However, the model does not provide the expected behavior due to the fluence increased surface damage. The solution requires an approach that does not affect the accurate bulk properties produced by the proton model, but only adds to it the required radiation induced properties close to the surface. These include the observed position dependency of the strip detector's charge collection efficiency (CCE). \\ In this paper a procedure to find a defect model that reproduces the correct CCE loss, along with other surface properties of a strip detector up to a fluence $1.5\times10^{15}$ 1 MeV $\textrm{n}_{\textrm{\tiny eq}}\textrm{cm}^{-2}$ ($\Phi_{\textrm{\tiny eq}}$), will be presented. When applied to CCE loss measurements at different fluences, this method may provide means for the parametrization of the accumulation of oxide charge at the SiO$_2$/Si interface as a function of dose.