Evidence for vacancy-interstitial pairs in Ib-type diamond

Diamonds containing nitrogen in different forms have been irradiated by $3\text{–}\mathrm{MeV}$ electrons or ${}^{60}\mathrm{Co}$ gamma photons and characterized by optical absorption (OA) and electron spin resonance (ESR). An unusually low production rate of vacancies $\left(V\right)$ and interstitials $\left(I\right)$ was observed in gamma-irradiated Ib-type diamonds (those containing isolated nitrogen) and pure IIa-type diamonds as compared to Ia diamonds (containing nitrogen clusters). Postirradiation annealing at temperatures above $300°\mathrm{C}$ strongly increased the $V$ and $I$ concentrations in Ib diamond, but not in IIa diamond. These results are explained as gamma irradiation of diamond predominantly produces $V\text{–}I$ complexes instead of individual $V$ and $I$ defects. Strong effect of charge state on $V\text{–}I$ recombination is revealed: In Ib diamond, $V\text{–}I$ complexes are negatively charged and dissociate upon annealing. On the contrary, $V\text{–}I$ pairs are neutral in IIa diamond, and they annihilate during irradiation. The OA, ESR, and positron annihilation signatures of the $V^{-}\text{–}I$ pairs are identified.

Figure 1

Isochronal $\left(1\mathrm{h}\right)$ annealing curves for dominant defects in electron- (a) and gamma- (b) irradiated Ib-type diamond. Both absolute and relative intensities are arbitrary.