High purity silicon carbide (SiC) materials are of interest from high-power high temperature applications across recent photo-voltaic cells to hosting solid state quantum bits, where the tight control of electrically, optically, and magnetically active point defects is pivotal in these areas. 4H- and 6H-SiC substrates are grown at high temperatures and the incorporation of transition metal impurities is common. In unintentionally Nb-doped 4H- and 6H-SiC substrates grown by high-temperature chemical vapor deposition, an electron paramagnetic resonance (EPR) spectrum with C 1h symmetry and a clear hyperfine (hf) structure consisting of ten equal intensity hf lines was observed. The hf structure can be identified as due to the interaction between the electron spin S 1/2 and the nuclear spin of 93Nb. Additional hf structures due to the interaction with three Si neighbors were also detected. In 4H-SiC, a considerable spin density of ∼37.4 was found on three Si neighbors, suggesting the defect to be a complex between Nb and a nearby carbon vacancy (V C). Calculations of the 93Nb and 29Si hf constants of the neutral Nb on Si site, Nb Si 0, and the Nb-vacancy defect, Nb SiV C 0, support previous reported results that Nb preferentially forms an asymmetric split-vacancy (ASV) defect. In both 4H- and 6H-SiC, only one Nb-related EPR spectrum has been observed, supporting the prediction from calculations that the hexagonal-hexagonal defect configuration of the ASV complex is more stable than others.
ASJC Scopus subject areas
- Physics and Astronomy(all)