The role of He and H on the structural evolution of He- and H-irradiated 6H-SiC

The behavior of irradiated H and He ions in the 6H-SiC lattice was rather different. H irradiated with low fluence at RT, blisters were formed after annealing at 1100°C, while at high irradiation fluence no blister cavities were observed due to the formation of an amorphous layer. At an irradiation temperature of 450 and 900°C, amorphization of 6H-SiC did not occur and hydrogen-containing microcracks grew laterally below the surface. Thus blisters appeared on the surface of the samples irradiated at 900°C even without annealing. For He irradiation, regardless of the fluence and irradiation temperature, blisters did not form. The presented results are well supported by density functional theory calculations. The coalescence between two small bubbles is an exothermic process when the H₂-bubbles contain an unpaired hydrogen and endothermic process when the H₂-bubbles contain paired H atoms, but it is energetically cheap. On the other hand, activation of the coalescence of He bubbles is endothermic and energetically very expensive.