Recrystallization of hexagonal silicon carbide after gold ion irradiation and thermal annealing
Résumé
Silicon carbide (SiC) single crystals with the 6H polytype structure were irradiated with 4.0-MeV Au ions at room temperature (RT) for increasing fluences ranging from 1 x 10(12) to 2 x 10(15)cm(-2), corresponding to irradiation doses from ~0.03 to 5.3 displacements per atom (dpa). The damage build-up was studied by micro-Raman spectroscopy that shows a progressive amorphization by the decrease and broadening of 6H-SiC lattice phonon peaks and the related growth of bands assigned to Si-Si and C-C homonuclear bonds. A saturation of the lattice damage fraction deduced from Raman spectra is found for ~0.8 dpa (i.e. ion fluence of 3 x 10(14)cm(-2)). This process is accompanied by an increase and saturation of the out-of-plane expansion (also for ~0.8 dpa), deduced from the step height at the sample surface, as measured by phase-shift interferometry. Isochronal thermal annealing experiments were then performed on partially amorphous (from 30 to 90%) and fully amorphous samples for temperatures from 200 degrees C up to 1500 degrees C under vacuum. Damage recovery and densification take place at the same annealing stage with an onset temperature of ~200 degrees C. Almost complete 6H polytype regrowth is found for partially amorphous samples (for doses lower than 0.8 dpa) at 1000 degrees C, whereas a residual damage and swelling remain for larger doses. In the latter case, these unrelaxed internal stresses give rise to an exfoliation process for higher annealing temperatures.