Irradiation temperature dependence of production efficiency of defects induced in neutron-irradiated silicon carbides

Production efficiency of vacancy-type defects induced in neutron-irradiated silicon carbide single crystals (4H and 6H SiC) is observed as a function of irradiation temperature. The crystals were irradiated at several temperatures (20, 50, 100, 150, 200 and 370 K) using the low temperature irradiation-loop facility of Kyoto University Reactor. In the irradiated crystals, a broad absorption band at 780 nm was observed. The origin of the 780 nm band was attributed to the Si vacancy defect (VSi-type center) because it has similar annealing behavior as a paramagnetic center consisting of a Si vacancy that was identified by electron spin resonance (ESR) measurement. The defect concentration of the VSi-type centers was estimated using the Smakula formula from the absorption intensity of the 780 nm band. The production efficiency of the VSi-type center in SiC crystals irradiated at several temperatures has a maximum at about 200 K. The characterization of the irradiation temperature dependence of the VSi-type center is extremely different from that of MgO or Al2O3which has a steep negative gradient from 20 to 400 K.