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.

The electrical degradation of 4H–SiC PiN diodes has recently attracted much interest and is a critical material problem for high power applications. The degradation is caused by stacking faults observed as an increased forward voltage drop after forward injection operation. In this article we have combined electrical, optical, and structural techniques to study the formation and growth of the stacking faults causing degradation. We will show three different sources causing two different types of stacking fault properties.

The structure of stacking faults formed in forward-biased 4H- and 6H-SiC p–n− diodes was determined using conventional and high-resolution transmission electron microscopy. Typical fault densities were between 103 and 104 cm−1. All observed faults were isolated single-layer Shockley faults bound by partial dislocations with Burgers vector of a/3〈1–100〉-type.

Morphological defects and elementary screw dislocations in 4H–SiC were studied by high voltage Ni Schottky diodes. Micropipes were found to severely limit the performance of 4H–SiC power devices, whereas carrot-like defects did not influence the value of breakdown voltage. The screw dislocation density as determined by x-ray topography analysis under the active area of the diode was also found to directly affect the breakdown voltage. Only diodes with low density of screw dislocations and free from micropipes could block 2 kV or higher.

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Detailed information about the electronic structure of the lowest-lying excited states and the ground state of the neutral silicon vacancy in 4H and 6H SiC has been obtained by high-resolution photoluminescence ͑PL͒, PL excitation ͑PLE͒, and Zeeman spectroscopy of both PL and PLE. The excited states and the ground states involved in the characteristic luminescence of the defect with no-phonon ͑NP͒ lines at 1.438 and 1.352 eV in 4H SiC and 1.433, 1.398, and 1.368 eV in 6H SiC are shown to be singlets. The orbital degeneracy of the excited states is lifted by the crystal field for the highest-lying NP lines corresponding to one of the inequivalent lattice sites in both polytypes, leading to the appearance of hot lines at slightly higher energies. Polarization studies of the NP lines show a different behavior for the inequivalent sites. A comparison of this behavior in the two polytypes together with parameters from spin resonance studies provides useful hints for the assignment of the no-phonon lines to the inequivalent sites. In strained samples an additional fine structure of the NP lines can be resolved. This splitting may be due to strain variations in the samples.

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