Besides their importance for quantum information processing, NV defects are crucial agents for the diffusion and aggregation of nitrogen in diamond. In the absence of transition metals, it is thought that the first stage of nitrogen aggregation, where close neighbour nitrogen pairs are formed, is mediated by NV defects. Here we use density functional theory to explore the barriers to NV diffusion. We conclude that the barrier is around 5 eV when there is a ready source of vacancies and that this barrier is weakly dependent on pressure.

We present experimental data relating to the slow stage of the illumination-induced or electron-injectioninduced generation, in crystalline p-type silicon, of the carrier-recombination center believed to be the defect complex ͑B s O 2i ͒ + formed by diffusion of oxygen interstitial dimers O 2i ++ to substitutional boron atoms B s − and, taking account of those data, we consider a detailed theoretical model for the kinetics of the diffusion reaction. The model proposes that the generation rate of the ͑B s O 2i ͒ + defects is controlled by the capture of a majority-carrier hole by the dimer following the capture of a minority-carrier electron and by the Coulomb attraction of the O 2i ++ to the B s − atom, and leads to predictions for the defect generation rate that are in excellent quantitative agreement with experiment.

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The formation mechanism and properties of the boron-oxygen center responsible for the degradation of Czochralski-grown Si(B) solar cells during operation is investigated using density functional calculations. We find that boron traps an oxygen dimer to form a bistable defect with a donor level in the upper half of the band gap. The activation energy for its dissociation is found to be 1.2 eV. The formation of the defect from mobile oxygen dimers, which are shown to migrate by a Bourgoin mechanism under minority carrier injection, has a calculated activation energy of 0.3 eV. These energies and the dependence of the generation rate of the recombination center on boron concentration are in good agreement with observations.

The description of the diffusion mechanism of O 2i in the caption of Fig. (3) contained an error in the original article. It should have read: ''A configuration-coordinate diagram for the oxygen dimer. Arrows show the proposed thermally assisted Bourgoin diffusion mechanism with a thermal barrier of 0.3 eV. O sq 2i at A first captures a photogenerated or injected electron and, after overcoming a 0.2 eV barrier, changes its configuration to O st 2i . It then traps a hole becoming O st 2i , and executes a diffusion jump to O sq 2iat B after overcoming a thermal barrier of 0.3 eV.'' This mechanism was described correctly in the main text.