Evaluation of 4H-SiC sensor performances for thermal neutron flux measurements

Silicon Carbide (SiC) based neutron sensors present very interesting properties for neutron flux measurements: selectivity between neutron and gamma radiations, response linearity, radiation and temperature hardness, … In 2021, CEA, AMU (Aix-Marseille University), within the framework of their joint laboratory LIMMEX, and FRAMATOME started a study to explore 4H-SiC diodes as possible thermal neutron detectors by using 10 B converter. Following a first exploratory measurement campaign of boron implanted 4H-SiC p-n diode sensors performed in 2021 in the Slovenian TRIGA reactor facility (Jožef Stefan Institute), new diodes have been manufactured with the aim of improving their thermal neutron sensitivity: larger surface (about 1 cm 2 ) and a 1 μm thick layer of B4C coating. These diodes have been irradiated in the same reactor in March 2023. A degradation of diode responses was observed as neutron fluence becomes significant. Investigations of the possible phenomena at the origin of the observed degradation of detector performances raise suspicions of defects induced linked to 10 B(n, α) 7 Li reaction product impacts which deposit their whole energy in the diode depleted area. A literature review confirmed this hypothesis. A model, based exclusively on carbon vacancies concentration, was proposed to simulate degradation of detector performances. It gives a good estimate of the typical fluence of reaction products that leads to a loss of counting rate (about 10 9 particles.cm -2 ).