Point and extended defects in chemical vapour deposited diamond

Homoepitaxially grown single crystal CVD diamond has a dislocation arrangement not seen in natural IIa diamond. Whereas in the latter, dislocations lie on (111) planes along [11̅0] directions, dislocations in CVD diamond lie nearly along the [001] growth axis and are arranged in bundles with almost four fold rotational symmetry. Their large strain is easily seen in birefringence and we model the arrangements in the bundle to account for the singular behaviour of the birefringence when the polarisers are rotated with respect to the crystal. The optical absorption spectrum of brown CVD diamond displays a continuum similar to that found in brown IIa natural diamonds but in addition broad point defect induced bands. We investigate the suggestion that the 2.38 eV (560 nm) peak is related to VNH. We suggest that the breadth of these bands is related to the large structural change when the defect is excited.