Study of irradiation effects in Silicon carbide irradiated by neutrons at the low temperature region

The neutron irradiation effects on the 4H- and 6H-Silicon carbide (SiC) crystals have been investigated by electron spin resonance (ESR), optical and electrical properties measurements. The neutron irradiations were carried out using the low-temperature irradiation loop facility (LTL) of the KUR and the electron linac (KURRI-LINAC) at the Kyoto University Research Reactor Institute, and the fast source reactor (YAYOI) at the Nuclear Engineering Research Laboratory, Faculty of Engineering, University of Tokyo. The irradiation temperature effect for the production rate of the 780nm absorption band in neutron-irradiated SiC crystals was investigated. The results show that its production rate at 15K is lower than that at 360K, which is opposite to the generally observed tendency for the production rate of the Frenkel defects in ceramics such as MgO and Al2O3. Optical absorption and ESR spectra of fast neutron irradiated 4H-SiC crystals were measured at liquid nitrogen temperature (LNT). A broad absorption band was observed at about 780nm, and two zero-phonon lines (ZPL's) were found at 858.8nm and 899.5nm in 4H-SiC. A ESR spectrum labeled T1 center was observed in fast neutron irradiated 4H-SiC. These point defects are annealed out around 1500K. The origin of the 780nm band and T1 center were tentatively attributed to an electron-trapped silicon vacancy. The resistivity of SiC irradiated by neutrons increased with fast neutron fluence. It seems that the increase of resistivity can be explained by the decreases of the carrier density. (author)