Project ID: CERN/05

Duration: 1.01.2020- 31.12.2021

Project title: Defect engineered p-type silicon sensors for LHC upgrade /DEPSIS

Project objectives:

The proposed project is embedded as part of the RD50 efforts, in the subgroup Defect and Material Characterization. The director of the present project is the leader of the NIMP team involved in the CERN-RD50 collaboration and the convener of this research line within the RD50 collaboration. The general objective of the project is to improve the radiation hardness of different types of silicon sensors to be used for ATLAS and CMS Strip Tracker upgrade (pads, LGAD and HVCMOS) built on p-type defect engineered Si. In p-type silicon (Boron doped) the most obvious change observed in the electrical performance is the loss of the doping during irradiation, an effect known as the “acceptor removal” process. Thought the cause for “acceptor removal” is mainly due to the formation of B_iO_i trapping centre, the project addresses a defect engineering approach, consisting in the intentionally addition of Carbon impurity in the bulk of Boron doped Si. The aim is to change the usual defect formation path during irradiation, by slowing down this way the Boron removal while creating other Carbon containing defects with much lower impact on the electrical characteristics of the sensors at their operation temperature. The project will thus focus on the detection, analyses and modelling of the defect generation and kinetics in irradiated Boron doped and Carbon co-doped/implanted silicon. The specific investigation techniques that will be employed (Deep Level Transient Spectroscopy, Thermally Stimulated Current and Thermally Dielectric Relaxation Current methods, High Resolution Transmission Electron Microscopy, I-V and C-V electrical characterization) will deliver defect input parameters regarding the defect generation and kinetics in the presence of different types and amounts of impurities,  needed for developing theoretical models able to calculate (numerically and in some cases even analytically) and predict the impact of the detected radiation induced defects on the electrical properties of Si sensors with respect to impurities content and operation scenario. The ultimate goal of the project is to provide a comprehensive knowledge of radiation induced defects and their generation mechanisms, which will be finally used to improve the radiation hardness of pad, LGAD and HVCMOS devices. Based on these defect engineering studies, viable theoretical models describing and predicting the generation and evolution of the defects in the presence of intentionally added impurities will be achievable. This way it will be possible to develop during the project the strategy for optimizing the doping and the impurity content, which would finally reveal the required performance of each of the envisaged p-type silicon sensors. The studies will start with an already fabricated set of defect engineered pads, LGADs and HVCMOS sensors. At the middle of the 2^nd project year, optimized defect engineered p-type sensors will be produced within the RD50 collaboration, based on the project results obtained until then. It is expected that the new run of experiments on optimized sensors, performed during the last year of the project, will fully validate the predictions evolved from modelling & experimental results performed before. If this will not be the case, further improvements, based on correcting the previous developed models and provide new optimization solutions will be considered beyond the present project.

Stages/Activities (Year)

I. Investigation of acceptor removal process in irradiated p-type sensors (2020)

I.1        Analyses of impurity content in different types of Si sensors

I.2        Analysis of electrically active defects by means of DLTS and TSC/TDRC methods and of the radiation induced changes in the device electrical characteristics

I.3        Microstructural characterization of the irradiated sensors, annealing at 80C

I.4        Modeling of the experimentally observed defect generation and kinetics at 80 C

II. Radiation hard defect engineered p-type silicon (2021)

II.1      defect annealing studies at high temperatures (between 150 and 350 C)

II.2      validity tests for optimized defect engineered sensors

II.3      In-situ microstructural characterization of the irradiated sensors during heat treatment 150-250C

II.4      Modeling of the experimentally observed defect generation and kinetics