The micro-structural changes and electrical activation behavior of P, N, and P/N coimplanted 4H-SiC were investigated. It was shown that a dopant that substitutes for C-lattice site generates less micro-structural defects and leads to lower electrical activations as compare to a dopant that substitutes for Si-lattice site in SiC. First principles calculations were performed to understand the observed anomalous behavior of n-type dopants. Lower activation for N dopant was attributed to the dopant interactions that result in the large ionization energy shift and to the presence of excess C atoms in the SiC lattice. In addition, the residual C vacancy defect that acts as a shallow donor are considered to account for the observed higher activation of P dopant.