Defects in electron irradiated boron-doped diamonds investigated by positron annihilation and optical absorption

Synthetic boron-doped single-crystal diamonds were irradiated by a pulsed electron beam at 2.2 MeV to various accumulated fluences from 0.7 × 10¹⁸ to 10 × 10¹⁸ e^- cm^-2. The samples were then subjected to isochronal annealing up to 1260 °C and characterized by positron annihilation (PA) and optical absorption (OA) spectroscopies after each annealing step. PA combined with in situ monochromatic illumination gave an estimate for the positive/neutral energy level in the band gap for the monovacancy as ~0.6 eV above the valence band-edge. From the analysis of PA and OA results, a dominant OA line at 0.552 eV was associated with a neutral boron-interstitial complex, and the annealing temperature of the positive monovacancy was deduced as ~700 °C.