A study of defects in single crystal CVD diamond
EPR measurements have been carried out on a range of differently doped samples, and amongst the many systems observed, two previously unreported defects have been identified. They both incorporate hydrogen and are the first defects to be positively identified to contain hydrogen in the diamond lattice. The two defects have been identified as the negatively charged nitrogen-vacancy-hydrogen centre (NVH-), and the negatively charged vacancy-hydrogen centre (VH-). The NVH- centre has been identified as having trigonal (C3v) symmetry and an overall electron spin of S = ½ . The spin Hamiltonian parameters have been determined and explained in terms of the proposed model of the defect. The hydrogen atom of the defect is located in the vacancy of the nearest-neighbour nitrogen-vacancy defect and appears to be bonded to the nitrogen atom, thus maintaining the observed C3v symmetry. The VH- centre has also been identified as having C3v symmetry, but has an overall electron spin of S = 1. The hydrogen atom is bonded to one of the four carbon atoms surrounding the vacancy and produces a very small hyperfine interaction. This is explained with the aid of the model and by performing an extended dipole calculation between the hydrogen atom and the unpaired electron probability density localised on the three equivalent carbon neighbours. No reasonable predictions on this defect could be made from studying the same defect found in silicon. The well-documented NV- defect has also been studied and modified spin Hamiltonian parameters have been determined. They vary significantly from the previously accepted ones and for the first time can explain the accepted model of the defect.