We report on an irradiation-induced photoluminescence ͑PL͒ band in 4H and 6H SiC and the corresponding optically detected magnetic resonance ͑ODMR͒ signals from this band. The deep PL band has the same number of no-phonon lines as there are inequivalent sites in the respective polytype. These lines are at 1352 and 1438 meV in the case of 4H and at 1366, 1398, and 1433 meV in the case of 6H. The intensity of the PL lines is reduced after a short anneal at 750°C. ODMR measurements with above-band-gap excitation show that two spin-triplet (Sϭ1) states with a weak axial character are detected via each PL line in these bands. One of these two triplet states can be selectively excited with the excitation energy of the corresponding PL line. These triplet signals can therefore be detected separately and only then can the well documented and characteristic hyperfine interaction of the silicon vacancy in SiC be resolved. Considering the correlation between the irradiation dose and the signal strength, the well established annealing temperature and the characteristic hyperfine pattern, we suggest that this PL band is related to the isolated silicon vacancy in 4H and 6H SiC. The spin state (Sϭ1) implies a charge state of the vacancy with an even number of electrons. By combining the knowledge from complementary electron-spin resonance measurements and theoretical calculations we hold the neutral charge state for the strongest candidate.

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We have studied intrinsic and impurity related defects in silicon carbide (SiC) epilayers grown with fast epitaxy using chemical vapor deposition in a vertical hot-wall reactor. Using capacitance transient techniques, we have detected low concentrations of electron traps (denoted as Z1/2, EH6/7 and titanium) and hole traps (denoted as HS1 and shallow boron) in the n-type 4H–SiC epilayers. The concentration of intrinsic defects (Z1/2, EH6/7, and HS1 centers) increases with increasing growth temperature. The incorporation of shallow boron (B) decreases at higher growth temperatures, whereas the titanium (Ti) concentration is not sensitive to the growth temperature. The concentration of shallow B and Ti increases with increasing C/Si ratio. The concentration of the EH6/7 and the HS1 centers however, decreases with increasing C/Si ratio. We have also tested graphite susceptors with TaC or SiC coating and observed that the purity of the susceptor material plays a critical role in reducing the background impurity incorporation. The correlation with the carrier lifetime of these epilayers indicates that the EH6/7 and the Z1/2 centers may be the lifetime limiting defects in the investigated epilayers.

Ab initio supercell calculations have been carried out to investigate clusters of carbon interstitials in 3C-and 4H-SiC. Based on the calculated formation energies, the complex formation of carbon interstitials or their aggregation to carbon antisites is energetically favored in SiC. The electronic and vibronic properties of the carbon interstitials and their aggregates depends strongly on the polytype. Using the calculated hyperfine constants and local vibrational modes of carbon clusters the possible relation to known carbon-related centers will be discussed.

Carbon vacancies ͑V C ͒ are typical intrinsic defects in silicon carbides ͑SiC͒ and so far have been observed only in the form of positively charged states in p-type or semi-insulating SiC. Here, we present electronparamagnetic-resonance ͑EPR͒ and photoinduced EPR ͑photo-EPR͒ observations of their negatively charged state ͑V C − ͒ in n-type 4H-SiC. This EPR center ͑called HEI1͒ is characterized by an electron spin of 1 / 2 in a Si-Si antibonding state of V C. First-principles calculations confirm that the HEI1 center arises from V C − at hexagonal sites. The HEI1 spectrum shows a transition between C 1h and C 3v symmetries due to a fast reorientation effect reflected in the nature of this defect. The photo-EPR data suggest that V C 2− is the dominant form of V C when the Fermi level lies 1.1 eV below the conduction band.