Defect levels and types of point defects in high-purity and vanadium-doped semi-insulating 4H–SiC

Electron paramagnetic resonance (EPR) spectroscopy and photo-induced EPR are used to examine the point defects in vanadium-doped 4H–SiC and high-purity semi-insulating (HPSI) 4H–SiC grown by physical vapor transport. Both types of samples often exhibit a 1.1-eV activation energy, Ea, as extracted from the temperature-dependent Hall/resistivity measurements; however, different defects are related to the same Ea in each case. In the vanadium-doped wafers, the EPR data reveal both V4+ and V3+ in the same sample; thus, the 1.1-eV Hall activation energy is tentatively interpreted as the V3+∕4+ acceptor level. However, this conclusion cannot be confirmed because additional defects complicate the photoresponse of vanadium. The carbon vacancy, which is detected in all the HPSI wafers, exhibits a range of photothresholds similar to the various values measured for Ea. The photo-EPR and temperature-dependent Hall/resistivity measurements made before and after a 1600°C anneal suggest that several different types of nonuniformly distributed defects participate in compensation of the HPSI material and that annealing selectively removes those with different defect levels.