Atom superposition and electron delocalization molecular orbital calculations were made of the interactions of interstitial H with substitutional B and N in diamond. Nearest-neighbor and next-nearest-neighbor C atoms were relaxed in geometry depending on the cluster size, XC34H36 or XC70H60, respectively, where X = B or N and the H atoms saturate the surface dangling radical orbitals of the models. A small Jahn-Teller distortion occurred for interstitial B, a shallow acceptor which, in the B- state, sits in a tetrahedral lattice site. For interstitial N distortions were large, with a long C-N distance which stabilizes a σ* orbital that would otherwise be in the conduction band. This orbital has one electron in it and has its greatest amplitude on C; the bonding counterpart has its greatest amplitude on N and was similar to the N lone-pair orbital in amines. The calculations indicate that N was a deep donor and N+ relaxes to the tetrahedral lattice site. Interstitial H was a mid-band-gap donor and was possibly also an acceptor with a high 1.9eV calculated activation energy barrier to migration. Interstitial H+ was expected to be very mobile, with a migration barrier of 0.1eV. H- was predicted to be relatively immobile with an activation barrier for migration of 2.5eV. The mobility of bond-inserted H around B in BH pairs should be high, with a calculated activation energy of 0.13eV, but for N the comparable process has an activation energy of 2.50eV. In NH pairs the interstitial H has formed a bond with the radical orbital on the C, so donation would be from the lone-pair orbital on N, which lay deep in the band gap; hence, the donor property was passivated.

Migration of Interstitial H in Diamond and Its Pairing with Substitutional B and N: Molecular Orbital Theory. Mehandru, S.P., Anderson, A.B.: Journal of Materials Research, 1994, 9[2], 383-95