Electron-positron momentum distributions associated with isolated silicon vacancies in 3C-SiC

Two-dimensional angular correlation of annihilation radiation (2D-ACAR) and coincidence Doppler broadening (CDB) of annihilation radiation measurements have been performed on electron-irradiated n-type 3C-SiC in which isolated silicon vacancies are responsible for positron trapping. After irradiation, the intensity of the CDB spectrum increased and decreased in low- and high-momentum regions, respectively. These features were explained by a theoretical calculation considering silicon vacancies. The central region of the 2D-ACAR spectra became isotropic after irradiation, while the overall anisotropies extending within the Jones zone were conserved suggesting that isolated silicon vacancies have tetrahedral symmetry, as expected from a previous electron spin resonance study.