Concept of Double Peak electric field distribution in the development of radiation hard silicon detectors

The concept of Double Peak (DP) electric field distribution is considered for the analysis of operational characteristics of irradiated silicon detectors. The key point of the model is trapping of equilibrium carriers to the midgap energy levels of radiation-induced defects, which leads to a non-uniform distribution of space charge concentration with positively and negatively charged regions adjacent to the p+ and n+ contacts, respectively. In our new development of the DP model we consider a non-depleted base region in between the space charge regions as a high resistivity bulk, which operates as a drift region with a non-negligible electric field. Electric field characteristics of detectors processed from n-type MCZ Si wafers using various technological procedures, and irradiated by 1 MeV neutrons and 24 GeV/c protons, have been compared. Electric field profiles have been reconstructed from DP pulse response of heavily irradiated detectors and calculated by the simulation of DP electric field distribution caused by carrier trapping. It is shown that detectors from n-type MCZ Si irradiated by 24 GeV/c protons do not show typical space charge sign inversion up to the irradiation fluence of about 2.2×1015 p/cm2 and the region with a positive charge dominates over a negatively charged region.