Polytype-Dependent Vacancy Annealing Studied by Positron Annihilation

In this research we investigated the dependence of annealing behavior of vacancy defects on SiC polytype using positron annihilation spectroscopy. We found that vacancy defects in 3C SiC induced by electron irradiation and multiple-He implantation are annealed below 1100DGC while those in hexagonal SiC above 1200DGC. The amount of residual vacancy defects due to post-electron-irradiation annealing at 1000DGC increases as hexagonality. From two-dimensional angular correlation of annihilation radiation (2D-ACAR) measurements, it was confirmed that the positron annihilation center in electron-irradiated 3C SiC should be silicon vacancies with tetrahedral symmetry. Silicon vacancies should be constituents in vacancy defects responsible for positron trapping in electron-irradiated hexagonal SiC. However, 2D-ACAR experiment shows that the local symmetry is different from that for silicon vacancies in 3C SiC.