Computational study of GaAs1−xNx and GaN1−yAsy alloys and arsenic impurities in GaN

Abstract

We have studied the structural and electronic properties of As-richGaAs1−xNx andN-rich GaN1−yAsy alloys in a large composition range using first-principles methods. We have systematicallyinvestigated the effect of the impurity atom configuration near both GaAs and GaN sidesof the concentration range on the total energies, lattice constants and bandgaps. The N(As) atoms, replacing substitutionally As (N) atoms in GaAs (GaN), cause thesurrounding Ga atoms to relax inwards (outwards), making the Ga–N (Ga–As) bondlength about 15% shorter (longer) than the corresponding Ga–As (Ga–N) bondlength in GaAs (GaN). The total energies of the relaxed alloy supercells and thebandgaps experience large fluctuations within different configurations and thesefluctuations grow stronger if the impurity concentration is increased. Substituting Asatoms with N in GaAs induces modifications near the conduction band minimum,while substituting N atoms with As in GaN modifies the states near the valenceband maximum. Both lead to bandgap reduction, which is at first rapid but laterslows down. The relative size of the fluctuations is much larger in the case ofGaAs1−xNx alloys. We have also looked into the question of which substitutional site (Ga or N)As occupies in GaN. We find that under Ga-rich conditions arsenic prefers thesubstitutional N site over the Ga site within a large range of Fermi level values.