Vacancy defects in as-polished and in high-fluence H⁺-implanted 6H-SiC detected by slow positron annihilation spectroscopy

The vacancy defects in near surface region are investigated in n-type 6H-SiC after polishing or low-energy-proton implantation using slow-positron-beam-based positron annihilation spectroscopy. Measuring the momentum distribution of annihilating electron-positron pairs by Doppler broadening spectroscopy we detect an about 100 nm thick vacancy-defects layer under the surface of mechanically polished wafers. No damaged layer is detected after mechano-chemical finishing. Measuring positron lifetime as a function of temperature, we show that neutral and negatively-charged vacancy clusters exist in the track region of low-energy proton-implanted 6H-SiC(H). Depending on annealing, they give rise to positron lifetimes of 257 ± 2 ps, 281 ± 4 ps and 345 ± 2 ps, respectively. By comparison with theory, the 257 ps and 280 ps are attributed to (V_C-V_Si) ₂ and (V_C-V_Si)₃ clusters, respectively. The (V_C-V_Si)₃ cluster has likely an ionization level near the middle of the bandgap.