INTERSTITIAL HYDROGEN AND ENHANCED DISSOCIATION OF C-H COMPLEXES IN GAAS

Local-density-functional-based ab initio calculations are used to inve stigate hydrogen and carbon-hydrogen defects in GaAs. The equilibrium structure for both the C-H and C-H- complexes are shown to be similar, with the hydrogen located at a C-Ga bond-centered site. The dissociat ion of these complexes is investigated and it is found that the energy barrier of 1.84 eV for the process C-H --> C- + H+ is substantially l owered to 0.88 eV in the presence of an electron resonantly bound to t he defect. This is in good quantitative agreement with recent experime nts. Isolated interstitial hydrogen is found to lie at a Ga-As bond-ce ntered site for both H+ and H-0 and at an antibonding site relative to a Ga atom for H-. It is also found that the stable form of the hydrog en dimer is a H-2 molecule, the dissociation energy of which is 1.64 e V, and that interstitial hydrogen is a negative-U defect. Finally, a m echanism for minority-carrier-induced device degradation is proposed.