Photoluminescence of Nitrogen-Exciton Complexes in6HSiC

The photoluminescence of N-doped $6H$ SiC reveals two distinct edge emission spectra, a consequence of the existence of two kinds of nitrogen-exciton complexes. This paper describes the recombination radiation of excitons bound to nitrogen ions, complementing the previously reported recombination radiation of excitons bound to neutral nitrogen. By combining data from the two spectra, we are able to estimate ionization energies of 0.17, 0.20, and 0.23 eV, for the three inequivalent nitrogen donors. Several phonon energies can be determined, and these are compared with known phonon energies in $6H$ SiC. A 90-meV phonon apparently represents a localized vibrational mode. Quenching of edge emission in impure samples is observed, and attributed to exciton hopping. Thermally excited states of the nitrogen-exciton complexes appear to be due to the valley-orbit splitting associated with a sixfold conduction-band degeneracy. A splitting of some of the states is attributed to the Jahn-Teller effect.