Acceptor levels of the carbon vacancy in 4H-SiC: combining Laplace deep level transient spectroscopy with density functional modeling

We provide direct evidence that the broad Z1/2 peak, commonly observed by conventional DLTS in as-grown and athigh concentrations in radiation damaged 4H-SiC, has two components, namely Z1 and Z2, with activation energies for electron emission of 0.59 and 0.67 eV, respectively. We assign these components to Z=1/2 →Z−1/2 +e− → Z01/2+2e−transition sequences from negative-U ordered acceptor levels of carbon vacancy (VC) defects at hexagonal/pseudo-cubic sites, respectively. By employing short filling pulses at lower temperatures, we were able to characterize the first acceptor level of VC on both sub-lattice sites. Activation energies for electron emission of 0.48 and 0.41 eV were determined for Z1(−/0) and Z2(−/0) transitions, respectively. Based on trap filling kinetics and capture barrier calculations, we investigated the two-step transitions from neutral to doubly negatively charged Z1 and Z2. Positions of the first and second acceptor levels of VC at both lattice sites, as well as (=/0) occupancy levels were derived from the analysis of the emission and capture data.