First-principles local density functional calculations were used to investigate H and C-H defects. The equilibrium structures for C-H and C-H- complexes were shown to be similar; with the H located at a C-Ga bond-centered site. The dissociation of these complexes was investigated and it was found that the energy barrier of 1.84eV for the C-H  C- + H+ process was lowered to 0.88eV in the presence of an electron which was resonantly bound to the defect. This result was in good quantitative agreement with recent experimental data. Isolated interstitial H was found to lie at a Ga-As bond-centered site, for both H+ and H0 and at an anti-bonding site, relative to a Ga atom, for H-. It was also found that the stable form of the H dimer was a H2 molecule. The dissociation energy of the latter was 1.64eV. The interstitial H was a negative-U defect.

Interstitial Hydrogen and Enhanced Dissociation of C-H Complexes in GaAs. S.J.Breuer, R.Jones, P.R.Briddon, S.Oberg: Physical Review B, 1996, 53[24], 16289-96