Room temperature free carrier concentrations exceeding 1×1018 cm−1 have been achieved with 1000 °C implants into 4H–SiC using N and Al (1×1017 cm−3 using B). A decrease in resistivity is observed for annealing temperatures above ∼ 1300, ∼ 1500, and ∼ 1750 °C for N, Al, and B, respectively. Rutherford backscattering spectroscopy measurements indicate almost complete recrystallization for N-implanted samples and partial recrystallization on the silicon, but not the carbon, sublattice for B- and Al-implanted samples. An implant and species related step formation is also observed. Only boron is observed to diffuse appreciably. A crystal stoichiometry and Fermi level dependent model is proposed to explain the activation results. © 1998 American Institute of Physics.