Influence of radiation damage on diffusion of fission products in silicon carbide

Abstract

The influence of irradiation induced damage on the transport of implanted species in poly and single crystalline silicon carbide is investigated. For this purpose published diffusion results of strontium, silver, iodine and cesium are compared with the associated evolution of defect profiles determined by α-particle channelling in a backscattering geometry. Strong diffusion takes place in the amorphized surface layer of room temperature implanted 6H-SiC during annealing at 1100 °C, which drops below the detection limit of 10 -21 m 2 s -1 as soon as re-crystallization is completed. Diffusion in samples implanted above the critical amorphization temperature is only observed when simultaneously a significant reduction of defect density occurs. No diffusion into the undamaged bulk is detected at temperatures up to 1500 °C. The observed diffusion behaviour is explained by a defect related trapping and release mechanism. Normal grain boundary diffusion of silver and iodine occurs in CVD-SiC.

Diffusion of fission products and radiation damage in SiC

“…This lack of diffusion continued even after swift heavy ion bombardment annealing. In agreement with this, Friedland et al [102,134,135,286] also found that vacuum annealing at 1000°C resulted in no broadening (i.e. no diffusion) of the RBS peak of room temperature implanted iodine in 6H-SiC in commercially obtained CVD polycrystalline 3C-SiC.…”

“…In contrast to the room temperature implanted samples, samples implanted at 600°C exhibited significantly less diffusion [102,134,286]. There was only diffusion in the initial stages of annealing due to defects introduced in the crystalline substrate during the ion bombardment process.…”

“…Alternatively, at lower temperatures the diffusion is grain boundary limited until the volume diffusion starts to dominate the diffusion process at higher temperatures. The conflicting results by Friedland et al [135,286] might also be due to this double mechanism. …”

“…Friedland et al [102,134,286] measured iodine diffusion in two different polycrystalline 3C-SiC substrates, viz. a commercially obtained CVD polycrystalline 3C-SiC with a columnar structure, and polycrystalline 3C-SiC grown in the South African PBMR CVD reactor with a random polycrystalline structure.…”

Cs diffusion in SiC high-energy grain boundaries

“…measurements, where the diffusion of Cs in single crystalline (sc-SiC) 6H-SiC 8,9 and polycrystalline (pc-SiC) chemical vapor deposition (CVD)-SiC 8,9 were investigated using an ion implantation, followed by heating tests. These surrogate attempts can help understanding the release mechanism of FPs, however this method is known to create several complications.…”