Comparisons are made between the carrier concentrations, ionization energies, and electron mobilities in 4H-SiC samples implanted with similar doses of nitrogen or phosphorus, and annealed at 1300 degreesC or 1700 degreesC for 10 min in argon. Ionization energies of 53 meV and 93 meV are measured from phosphorus-implanted 4H-SiC, and are assigned to the hexagonal and cubic lattice positions in 4H-SiC, respectively. The corresponding ionization energies for nitrogen-implanted 4H-SiC are 42 meV and 84 meV, respectively. Phosphorus is not activated to the same extent that nitrogen is, and the carrier concentrations are about a factor of five lower for phosphorus-implanted 4H-SiC annealed at 1300 degreesC than for nitrogen-implanted 4H-SiC annealed at the same temperature. A higher mobility measured from phosphorus-implanted 4H-SiC is observed, but is not sufficiently high to offset the lower carrier concentration of this material. For the doses considered in this study, the resistivity of nitrogen-implanted 4H-SiC is lower than the resistivity of phosphorus-implanted 4H-SiC following anneals at either 1300 degreesC or 1700 degreesC.