Nitrogen substitutions in GaAs(001) surfaces: Density-functional supercell calculations of the surface stability

Abstract

The structures and energies of various probable reconstruction patterns of the GaAs(001) surface with restricted nitrogen substitution on arsenic positions are calculated using periodic supercells and the density-functional method. In dependence on chemical potentials of arsenic and nitrogen the most stable structures and compositions of the surface are obtained: Under extreme As-rich conditions the N-free c(4 × 4) reconstruction is the preferred arrangement. Under Ga-rich conditions the ζ(4 × 2) reconstruction builds in variously high N-substituted structures (especially parallel coupled (GaN)n chains), which can lead to a GaN phase (phase separation). In the transition region between the Ga- and As-rich limits the α2(2 × 4) but also the β2(2 × 4) reconstruction form structures with restricted nitrogen substitution. The high stability of restricted substitutions predestinates the region between the Ga- and As-rich conditions for the growth of GaAsN alloys. The blueshift of the band gap during the annealing of the grown bulk can be explained by the transformation of the grown (GaN)n chains, which are also formed in this region (in the β(2 × 4) reconstruction), to the thermodynamically most stable bulk structures. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.