Paramagnetic defects in silicon carbide crystals irradiated with gamma-ray quanta

The results of the first observations of paramagnetic defects in SiC crystals irradiated with gamma-ray quanta are reported. Three types of defects, designated as γ1, γ2, and γ3, were detected in irradiated 4H-SiC:Al and 6H-SiC:Al crystals using electron spin resonance (ESR) measurements. All these centers have almost the same parameters of the spin-related Hamiltonian with S=1/2 and feature an appreciable anisotropy of the g-factors. The γ1 centers are almost coaxial with the local z-axis oriented approximately along one of the directions of the Si-C bond that does not coincide with the c-axis. The γ2 and γ3 centers have a lower symmetry, although the orientation along the above bonds is clearly pronounced. The values of the largest g-factor (gz) decreases in the sequence from γ1 to γ3. The γ1 signal can be detected at temperatures of 3.5–15 K; the γ2 and γ3 signals are detectable at temperatures of 10–35 and 18–50 K, respectively. The hyperfine interaction of an unpaired electron in the γ1 center with a nucleus of the 29Si isotope is detected for certain orientations of the crystal. The γ1, γ2, and γ3 centers cease to exist at a temperature of 160°C; it is concluded that the ESR signals of these centers are related to defects in the C sublattice. It is assumed that the γ1, γ2, and γ3 centers have a common origin and are related to the low-temperature (γ1) and high-temperature (γ2 and γ3) modifications of the same center. The models of a defect in the form of either a carbon vacancy or a complex incorporating an Al impurity atom and a C atom that occupies the silicon site or interstice are discussed.