Ionization Energies of Phosphorus Donors in 6H-SiC

6H-SiC was doped with phosphorus (P) donors by neutron transmutation. IR transmission spectra were taken in the temperature range from 6 K to 300 K. A great number of absorption lines is observed at temperatures below 140 K; these lines are attributed to transitions of the donor electron between ground states and bound excited states of P-related donors. Based on Faulkner's theory, three series of effective-mass-like states (P1, P2, P3) could be identified. The corresponding ground state energies are: E(P1) = EC - 91.5 meV, E(P2) = EC - 81.8 meV, E(P3) = EC - 73.5 meV.