It was recalled that N was the most important defect in diamond, in that it formed a series of aggregates that were used to characterize different types of diamond. The aggregation of substitutional N and O were investigated by using detailed ab initio plane-wave calculation procedures. Various charge states of the N-N substitutional pair (A center) were considered, as well as the states of an adjacent O-N substitutional pair. Both were suggested to be stable defects and, in charged negative form, the [N-O] defect could lead to shallow defect levels. There was substantial local lattice distortion due to a strong repulsion between ions, and this led to shortened C-N bonds, upon which there was a related build-up of charge relative to that on a normal C-C bond. This was responsible for the shallow levels. Such a defect could even lead to efficient electron emission in a very highly N-doped diamond.

Substitutional Oxygen-Nitrogen Pair in Diamond. J.E.Lowther: Physical Review B, 2003, 67[11], 115206 (5pp)