Space charge sign inversion investigation in n-type MCz silicon diodes irradiated by 24 GeV/c and 26MeV protons and reactor neutrons

Magnetic Czochralski (MCz) silicon is currently being considered as a promising material for the development of radiation tolerant detectors for future high luminosity HEP experiments. Silicon wafers grown by the MCz method have been processed by ITC-IRST (Trento, Italy) with a layout designed by the SMART collaboration. The diodes produced with n-type MCz material have undergone various irradiation campaigns, using 24 GeV/c   (SPS-CERN) protons, 26MeV (FZK-Karlsruhe) protons and reactor neutrons (JSI-Ljubljana), with fluences up to 10161016 1 MeV equivalent neutrons (neq)cm-2. This paper investigates space charge sign inversion effects after these irradiation levels. Samples have been characterized by reverse current and capacitance measurements before and after irradiation, and by Transient Current Technique (TCT) after irradiation. Results of the study of depletion voltage as a function of fluence and of TCT signal shapes show that Space Charge Sign Inversion has already occurred in the devices at a fluence of 4.2×1014neqcm-2 after 26 MeV proton irradiation, and at 5×1014neqcm-2 after neutron irradiation.