Thermodynamic calculation suggests that the formation of bulk GaN pins N chemical potential ${\mu }_{\mathrm{N}}\le {\mu }_{\mathrm{N}}^{\max }$, resulting in low equilibrium N solubility [N] in bulk GaAs:N. In epitaxial growth, however, a fully relaxed GaN phase cannot form prior to the spontaneous formation of a N-rich layer on the surface. First-principles total-energy calculations show that in the epitaxial regime one can increase ${\mu }_{\mathrm{N}}^{\max }$ considerably from equilibrium ${\mu }_{\mathrm{N}}^{\max }$ without triggering the spontaneous formation of such a N-rich layer. This enhances [N] by 8 orders of magnitude to about $4\%$ at $T=650\mathrm{}°\mathrm{C}$ in agreement with experiments. The dominant defects at high N concentration are qualitatively different from those at low [N].

• Received 1 March 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.1789