Observation of a three-site defect in SI 4H-SiC

High temperature anneals were used to study the evolution of native defects in semi-insulating 4H-SiC grown by PVT or HTCVD methods. The samples were annealed in an argon atmosphere for 30 min at temperatures from 1400$^{o}$C to 2100$^{o}$C. Using electron paramagnetic resonance (EPR), we observe a defect that is tentatively identified as V$_{C}$-C$_{Si}$-V$_{C}$. This spin S=1 defect is characterized by g$_{\vert \vert }$=2.0029; g$_{\bot }$=2.0038, a fine structure splitting D$\sim $96G, and several hyperfine interactions with the low abundant Si (A$\sim $5.5G) and C (A$\sim $30G) neighboring nuclei. This center is diamagnetic in the ground state but can be excited into a paramagnetic triplet state by sub-bandgap light. The EPR intensity of this center increases significantly with annealing. This defect could result during annealing by the movement of an adjoining C atom onto the V$_{Si}$ site of the divacancy (V$_{C}$--V$_{Si})$ whose intensity decreases. This may be the simplest of a family of more complex defects that play a role in the SI character. A search for optical signatures associated with this defect from 0.7-3.2 eV PL studies will also be discussed.