Hydrogen-nitrogen complexes in GaPyN1-y alloys

The properties of N–H complexes in the GaP0.97N0.03 alloy have been investigated by DFT-LDA theoretical methods. The achieved results closely parallel and confirm those previously found in the case of the GaAs0.97N0.03 alloy. In particular, they show that a same N–H2*(a) complex neutralizes the N effects on the GaP band structure as it does in the case of GaAsN. However, these results do not explain the different evolution of the optical properties recently observed in GaPN and GaAsN upon hydrogenation. We have investigated, therefore, the formation mechanism of the N–H2*(a) complex. On the ground of the achieved results, we propose that H+ ions diffusing in the GaP (GaAs) lattice form a novel N–H2*2+ complex involving two H+ ions bonded to the N atom, which then transforms into the N–H2*(a) one. Thus, the formation of the latter complex depends on the characteristics of the H+ diffusion in the GaP and GaAs lattices. In this concern, we have estimated that the bonds formed by H+ ions in GaP are stronger than those formed in GaAs, thus inducing a slower motion of these ions in GaP with respect to GaAs. This may affect the hydrogenation procedure and causes a slower formation of the N–H2*(a) complexes and a slower and gradual neutralization of the N effects in GaPN which can account for the different behavior of GaPN and GaAsN upon hydrogenation.