Efficient luminescence centers in H- and D-implanted 6H SiC

The luminescence center formed in SiC by H implantation and annealing is an H atom bonded to a C atom at a Si vacancy. It has high radiative efficiency at low temperatures because of the absence of Auger recombination. This model is derived from an annealing study and by an analysis of the three components of the phonon spectrum, (i) a 370-meV CH bond-stretching mode, (ii) two Si-vacancy localized modes, and (iii) many momentum-conserving modes. The change of frequency of these components on substituting D for H is large for (i), small for (ii), and zero for (iii). Inequivalent sites in $6H$ SiC permit three axial and three nonaxial centers, and five of the six expected spectra were observed. The site dependence of the polarization of localized-mode lines indicates a breakdown of the effective-mass approximation at the defect, for the polarization of momentum-conserving phonon lines is site independent. The H and D spectra are contrasted with the spectrum of the donor N. At 1.3 °K very nearly all the luminescence is due to the nonaxial centers, for recombination from the ground states of axial centers is spin forbidden. Thermally excited states were observed at various temperatures up to 26 °K. H and D luminescence was observed in $15R$ and $4H$ polytypes, but not in $3C. It is suggested that the usual defect is formed in3C$ SiC but does not bind an exciton.