We investigated the electrical and structural properties of aluminum (AI) and boron (B) implanted 4H-SiC by using secondary ion mass spectroscopy (SIMS), low temperature photoluminescence (LTPL), Hall effect measurement and positron annihilation spectroscopy. A strong diffusion was observed for B-implanted samples toward both the inside and the surface by post-annealing at 1700 degreesC but not for Al-implanted samples. We could see the luminescence at 4272 Angstrom, which was independent of the dopant species and annealing temperatures, originating in the defect, so-called D-1 center, introduced by the implantation and post-annealing process. For Al implantation, a temperature of 1550 degreesC was enough for the electrical activation of the accepters from the result of Hall effect measurement. The positron lifetime for both Al and B as-implanted samples (216ps) was in good agreement with the theoretical lifetime of positron localized at a Si-C di-vacancy (214ps). The positron lifetime of post-annealed samples (148, 147, 149ps) located between that of the virgin sample (144ps) and the theoretical lifetime of positron localized at a C vacancy (153ps). We supposed that a defect type of di-interstitial or di-vacancy is dominant for post-annealed samples.