Thermodynamic calculations suggested that the formation of bulk GaN fixed the N chemical potential so as to result in a low equilibrium N solubility in bulk N-doped GaAs. However, in the case of epitaxial growth no fully-relaxed GaN phase could form ahead of the spontaneous formation of a N-rich layer at the surface. First-principles total-energy calculations showed that, in the epitaxial regime, the maximum N activity could be considerably increased from the equilibrium value; without triggering the spontaneous formation of a N-rich layer. This enhanced the N concentration, by 8 orders of magnitude, to about 4% 650C; in agreement with experiment. The predominant defects at high N concentrations were qualitatively different from those which existed at low N concentrations. Split N interstitials predominated at high N concentrations.

Nitrogen Solubility and Induced Defect Complexes in Epitaxial GaAs:N. S.B.Zhang, S.H.Wei: Physical Review Letters, 2001, 86[9], 1789-92