Kohn-Luttinger Interference Effect for Donors in4HSiC

The different ionization energies for the donor nitrogen at inequivalent sites in SiC polytypes cannot be explained by a central-cell correction. An alternative mechanism is suggested, the Kohn-Luttinger interference effect. This results in donor-electron density differences, not at the donor atoms, but at some of the near neighbors. Using reported values of the coordinates of the 12 conduction-band minima in $4H$ SiC, the relative donor-electron density is calculated for neighbors of the two nonequivalent donor sites. On a silicon plane where significant neighborhood differences can occur, the interference effect favors one site over the other by a factor of 3 in relative electron density. The importance of a small Bohr radius is discussed, as well as the application to other SiC polytypes.