Electron spin coherence of silicon vacancies in proton- irradiated 4H-SiC

We report T-2 spin coherence times for electronic states localized in Si vacancies in 4H-SiC. Our spin coherence study included two SiC samples that were irradiated with 2MeV protons at different fluences (10(13) and 10(14) cm(-2)) in order to create samples with unique defect concentrations. Using optically detected magnetic resonance and spin echo, the coherence times for each sample were measured across a range of temperatures from 8 to 295 K. All echo experiments were done at a magnetic field strength of 0.371 T and a microwave frequency of 10.49 GHz. The longest coherence times were obtained at 8 K, being 270 +/- 61 mu s for the 10(13) cm(-2) proton-irradiated sample and 104 +/- 17 mu s for the 10(14) cm(-2) sample. The coherence times for both samples displayed unusual temperature dependencies; in particular, they decreased with temperature until 60 K, then increased until 160 K, then decreased again. This increase between 60 and 160 K is tentatively attributed to a motional Jahn-Teller effect. The consistently longer lifetimes for the 10(13) cm(-2) sample suggest that a significant source of the spin dephasing can be attributed to dipole-dipole interactions between Si vacancies or with other defects produced by the proton irradiation. The lack of a simple exponential decay for our 10(14) cm(-2) sample indicates an inhomogeneous distribution of defect spins.