We have used pulsed-slow-positron-beam-based positron lifetime spectroscopy to investigate the nature of acceptors and charge states of vacancy-type defects in low-energy proton-implanted 6H-SiC(H). We can infer from the temperature dependence of the lifetime spectra that neutral and negatively charged vacancy clusters exist in the track region. Depending on annealing, they give rise to positron lifetimes of 257±2, 281±4, and 345±2 ps, respectively. The 281 ps cluster likely has an ionization level near the middle of the band gap. By comparison with theory, the 257 and 280 ps are identified as (VC-VSi)2 and (VC-VSi)3 clusters, respectively. In addition, other acceptors of ionic type act as strong trapping centers at low temperature (T< 150 K). Neutral monovacancy-like complexes are also detected with a lifetime of 160±2 after 900 °C annealing. © 2001 American Institute of Physics.