Local and lattice relaxation in hydrogenated GaAsyN1_y alloys

The introduction of a few percent of N in GaAsN has striking effects on the band gap of the host GaAs. A recent experimental and theoretical study has shown that small percents of N induce also a lattice contraction of GaAs. Moreover, hydrogenation of these GaAsN alloys restores both the electronic and structural properties of the N-free semiconductor. In the present study, the effects of hydrogen on the lattice structure of GaAsN have been investigated by first-principles theoretical methods. In particular, attention has been focused on the relationships between the local relaxations induced by the formation of N-H complexes and the lattice relaxations of the hydrogenated GaAsN. The achieved results show that, in addition to the local relaxations, the characteristic of the chemical bonding in the N-H complexes must be taken into account in order to explain the effects of H on the lattice structure. They also account for the surprising fact that N-H2* complexes neutralize the lattice contractions caused by the presence of N, whereas monohydrogen complexes do not.