The vacancy-hydrogen defects in diamond: a computational study

Hydrogen is grown into CVD diamond and occurs in point defects also involving a lattice vacancy, V. Complexes involving V, H and nitrogen, or silicon have been identified by experiment, and in some cases the microscopic structure has been identified with the use of quantum-chemical simulations. In this study, we present the results of density functional simulations of the primitive vacancy-hydrogen defect in diamond. We find that the symmetry of the VH defect is C_3v, with the H atom strongly bonded to one of the four C radicals that are formed when the vacancy is created. The defect is expected to occur in both the neutral and negatively charged forms, with the possibility of both positive and −2 charge states. For VH⁰, S = 3/2 and S = 1/2 spin states are found to be indistinguishable in energy, with the quartet not expected to yield sharp optical transitions, unlike the doublet. VH⁻¹ in the S = 1 ground-state is predicted to have an optical transition that is broadly similar to that of NV⁻ (S = 1), although it is important to note that the non-degenerate band involved in the transitions arises from a different origin in VH⁻¹ as there are no lone-pairs present in this case. We have also made predictions for the CH stretch mode frequencies, noting a general trend with charge state. Combinations of optical spectroscopy, paramagnetic resonance and vibrational mode spectroscopy are therefore required to fully experimentally resolve VH in its various charge and spin states.