Interstitial hydrogen and enhanced dissociation of C-H complexes in GaAs

Local-density-functional-based ab initio calculations are used to investigate hydrogen and carbon-hydrogen defects in GaAs. The equilibrium structure for both the C-H and C-${\mathrm{H}}^{\mathrm{-}}$ complexes are shown to be similar, with the hydrogen located at a C-Ga bond-centered site. The dissociation of these complexes is investigated and it is found that the energy barrier of 1.84 eV for the process C-H → ${\mathrm{C}}^{\mathrm{-}}$ + ${\mathrm{H}}^{+}$ is substantially lowered to 0.88 eV in the presence of an electron resonantly bound to the defect. This is in good quantitative agreement with recent experiments. Isolated interstitial hydrogen is found to lie at a Ga-As bond-centered site for both ${\mathrm{H}}^{+}$ and ${\mathrm{H}}^0$ and at an antibonding site relative to a Ga atom for ${\mathrm{H}}^{\mathrm{-}}$. It is also found that the stable form of the hydrogen dimer is a ${\mathrm{H}}_2$ molecule, the dissociation energy of which is 1.64 eV, and that interstitial hydrogen is a negative-U defect. Finally, a mechanism for minority-carrier-induced device degradation is proposed. © 1996 The American Physical Society.