Site effect on the impurity levels in4H,6H, and15RSiC

The existence of site-dependent impurity levels caused by inequivalent sites in $4H$, $6H$, and $15R$ SiC has been verified from a study of configuration coordinate phonons. From analyses of donor-acceptor pair and free-to-acceptor luminescence, two kinds of impurity levels of A1, Ga, and B acceptors and N donors substituted cubic-like and hexagonal-like sites are determined. All the impurities in cubic-like sites take deeper levels than those in hexagonal-like sites. Ratios of the ionization energies are approximately constant independent of polytypes and the kind of impurities, 1.0-1.08 for acceptors and 1.55-1.88 for donors, in spite of a wide range of the ionization energies. The origin of the site effect on the impurity level is explained by assuming the existence of a local dielectric constant and a local effective mass. Haynes' rule is found to apply relatively well to N donors in different sites in various polytypes SiC.