Effect of Thermal Donors Induced in Bulk and Variation in P-stop Dose on the No-gain Region Width Measurements of LGADs

To cope up with high pile-up rates during Phase-2 operation of the LHC, the CMS experiment will install a precision Minimum Ionising Particle Timing Detector (MTD), between the tracker and calorimeter, which will have a timing resolution of $\sim$30~ps. The endcap part of the MTD, called the Endcap Timing Layer (ETL), will be based on Low-Gain Avalanche Detector (LGAD) Technology.\\ In this paper, the authors have performed a study on UFSD3.1 LGAD production from Fondazione Bruno Kessler (FBK). The objective of this production was to optimise the interplay between the p-stop dose and the inter-pad terminal strategy. Results show that the nominal no-gain region width value between pads does not affect the breakdown voltage of the sensors at low p-stop doses. A comparative study on the effect of thermal donors induced in the bulk of the sensor was performed by capacitance versus voltage measurements. Further, the property of the sensors were investigated using infra-red (IR) laser, by performing voltage scans and inter-pad profile measurements with gain variation, on changing temperature in Transient Current Technique (TCT). Results show no significant change in the charge collection efficiency and measured no-gain region width values of sensors irrespective of the nature of the bulk.