Substitutional oxygen-nitrogen pair in diamond

Nitrogen is the most important defect in diamond forming a series of aggregates that are used to characterize different types of diamond. Aggregation of substitutional N and O are investigated using detailed ab initio plane-wave calculational procedures. Different charge states of the N-N substitutional pair (the A center) are considered as well as states of an adjacent O-N substitutional pair. Both are suggested to be stable defects, and in charged negative form the [N-O] defect can lead to shallow defect levels. There is substantial local lattice distortion due to a strong repulsion between ions and this leads to shortened C-N bonds, on which there is a related buildup of charge relative to that on a normal C-C bond, and this is responsible for the shallow levels. Possibly such a defect could even lead to efficient electron emission in a very highly nitrogen doped diamond.