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.