We report on 4H-SiC samples implanted with Al, Al and C or Al and Si. Annealing was done using (BN)AlN caps. Sheet resistance measurements suggest that, at low annealing temperatures, implanted C facilitates the incorporation of Al into Si sites while Si impedes it. For annealing temperatures above 1600degreesC, the activation energy for these reactions is no longer the rate determining step and co-implantation has little effect. Optical measurements show that the peak near 3.0 eV, associated with free electrons recombining with an Al-bound hole, decreases as the annealing temperature increases. This suggests that defects are trapping out the hole. This can explain the lower mobility, lower electrical activation and our inability to detect the EPR peak associated with Al-Si in these heavily implanted samples. Finally, RBS and TEM measurements suggest that these defects are extended residual defects that nucleate and grow, as opposed to being annealed out, and that they could be stacking faults.