EPR AND ENDOR INVESTIGATIONS OF SHALLOW IMPURITIES IN SIC POLYTYPES

Investigations of nitrogen donors in 6H-, 4H- and SC-SIG using convent ional election paramagnetic resonance (EPR), electron nuclear double r esonance (ENDOR) and optical detection of EPR and ENDOR as well as opt ical absorption and emission spectroscopy are reviewed and critically discussed. An attempt is presented to interpret the experimentally fou nd large differences in hyperfine interactions of the N-14 nuclei on t he various inequivalent sites in the different polytypes of SiC in ter ms of valley-orbit splittings and ''central-cell corrections'' in the framework of the effective mass theory (EMT). P-doping by neutron tran smutation iri 6H-SiC resulted in various P-related EPR spectra previou sly associated with shallow P donors and P-vacancy complexes. In analo gy to the new interpretation of the N donor spectra in various polytyp es, it is proposed that all P-related spectra found hitherto in 6H-SiC are due to isolated P donors in ground and excited EMT states. A deta iled discussion is presented of the electronic structure of B acceptor s, as determined by EPR and in particular by ENDOR investigations: The B atom itself has only very little unpaired hole density, while the h ole resides mainly on a neighbouring relaxed C atom B acceptors have a rather ''deep'' character and pronounced dynamical properties. P, dis cussion of the present understanding of the so-called deep B centre (D centre) is also given. In contrast to B, the Al acceptor behaves as e xpected from the effective mass theory. It shows, however, tyro optica l absorption bands identified by optical detection of EPR which are re lated to an ionization transition to the valence band and another tran sition, probably to a V impurity.