TCAD Simulation of the Electrical Performance of the ATLAS18 Strip Sensor for the HL-LHC

To cope with the increased occupancy and radiation dose expected at the High-Luminosity LHC, the ATLAS experiment will replace its current Inner Detector with the Inner Tracker (ITk), consisting of silicon-based pixel and strip sub-detectors. The strip detector will consist of n+-in-p sensors fabricated by Hamamatsu Photonics, with 300 mu m signal-generation thickness and approximately 75 mu m strip pitch. To guide the operation of these sensors in the ITk, it is desirable to understand the basic mechanisms underlying their performance, including the effects of the radiation fluence (up to 1.6 x 1015 1-MeV neq/cm2) expected during operation. To this end, we have used Sentaurus TCAD to develop a 2D simulation of the ITk large-format strip sensor, based on detailed optical and electrical measurements of the sensors and of test devices fabricated on the same wafers. Current-voltage and capacitance-voltage behaviour is reproduced in the simulation by implementing charge trapping due to defects in the silicon, and the dependence of sensor behaviour on the location of these defects is investigated. Defect parameters are obtained using existing frameworks, such as the Perugia model of surface and bulk radiation damage, and through deep-level transient spectroscopy of test devices on the sensor wafers.