Nitrogen solubility and induced defect complexes in epitaxial GaAs:N.

Thermodynamic calculation suggests that the formation of bulk GaN pins N chemical potential mu(N)< or =mu(max)(N), 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(max)(N) considerably from equilibrium mu(max)(N) 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 degrees C in agreement with experiments. The dominant defects at high N concentration are qualitatively different from those at low [N].