Extensive photoluminescence, electron spin resonance, and optically-detected magnetic resonance experiments were carried out on epitaxial layers which had been grown onto sapphire and 6H-SiC substrates. Both undoped and Mg-doped films were investigated. Electron spin resonance studies of undoped samples revealed a sharp resonance which was attributed to effective-mass donors. Optically-detected magnetic resonance which was found in the broad 2.2eV emission band from the same undoped layers exhibited the same effective-mass donor resonance, and a feature which was attributed to a deep-donor state. The optically-detected magnetic resonance which was found for shallow-donor shallow-acceptor recombination from undoped samples revealed evidence only for a very weak shallow-donor resonance. The weakness of the latter signal, and the absence of an effective-mass acceptor resonance of this emission was attributed to the involvement of spin-thermalized holes in the recombination and to the effect of random strain fields in these films, respectively. The same 2 donor resonances, and a Mg-related quasi deep-acceptor resonance, were found by means of optically-detected magnetic resonance experiments on heavily Mg-doped samples. The results provided strong evidence, in the case of p-type films, for compensation via a native defect mechanism which had been predicted for wide band-gap semiconductors such as GaN.

E.R.Glaser: Materials Science Forum, 1995, 196-201, 9-16