Opposite Hydrogen Behaviors in GaAsN and InAsN Alloys: Band Gap Opening Versus Donor Doping

Experiments suggest that atomic H neutralizes the effects of N (i.e., it recovers the host energy gap) without inducing any band-filling effect (i.e., without behaving as a shallow donor) in the GaAsN alloy, while the vice versa is true in the InAsN one. Moreover, theoretical results on H in GaAsN contradict some experiments. These facts motivated the present study, where the role of N-H complexes has been investigated by performing density functional theory-Heyd-Scuseria-Emzerhof calculations. Present results confirm and explain the H properties; N neutralization is certain only in GaAsN, while H behaves as a shallow donor only in InAsN. They also show that, despite an identical geometry, single-H complexes neutralize the N effects in GaAsN, not in InAsN. This result is accounted for by a simple model showing that: (i) band gap recovery is directly related to a recovery of the atomic charge of the Ga/In cations neighboring the N atom in a N-H complex and (ii) a larger extent of charge recovery is found for the Ga cations with respect to the In ones, consistently with an electronegativity larger for Ga than for In. Remarkably, the same reason is at the ground of the different H behavior, deep versus shallow, in the two GaAsN and InAsN alloys.