A study of substitutional nitrogen impurities in chemical vapor deposited diamond

The behavior of substitutional N impurities in chemical vapor deposited diamond is examined theoretically in order to explain recent channeling experiments indicating a dominant onsite incorporation of N. The calculations are based on a combination of density-functional methods at various levels of approximation applied to supercell and cluster models. Neutral charge N impurities in the presence of highly defective carbon regions, such as dangling bonds, strained bonds, and partially developed rr bonds are studied. We find a perfectly general argument concerning the position of the substitutional N atom in relation to the position of the Fermi level, E-f: if E-f lies above the A(1) level associated with the onsite substitutional N atom, off-site motion in the (111) direction is observed. Conversely, when E-f falls below A(1), N doping charge is transferred to the available deeper lying states. Suitable receptor states include surface dangling bonds, surface reconstruction rr bonds, and bulk defects states such as grain boundaries and vacancies. (C) 1998 American Institute of Physics.