Identification of a Three-Site Defect in Semi-Insulating 4H-SiC

Using electron paramagnetic resonance (EPR), we observe a defect that increases significantly with annealing temperature. This spin S = 1 defect is characterized by g _x ≈ g _y ≈ g _z = 2.0056 and a fine structure splitting D ∼ 100 G whose principal axis lies in a plane perpendicular to the c-axis. Also resolved are several hyperfine interactions with the low abundance ²⁹Si and ¹³C neighboring nuclei. A careful analysis of the intensity of these hyperfine lines allows a precise determination of the identity and the quantity of interacting nuclei. This center is diamagnetic in the ground state but can be excited into a paramagnetic triplet state by sub-bandgap light. We identify this new defect as a three-site vacancy involving V _C-V _Si-V _C. The angular dependence of the ¹³C hyperfine interaction supports the proposed model. These may be the simplest of a family of more complex and extended defects that play a role in the semi-insulating (SI) character of SiC.