First-principles calculations of2×2reconstructions of GaN(0001) surfaces involving N, Al, Ga, In, and As atoms

The ab initio studies presented here employed a pseudopotential-plane-wave method in order to obtain the\udminimum-energy configurations of various 22 GaN0001 surfaces involving N, Al, Ga, In, and As atoms.\udComparison of the various possible reconstructions allows predictions to be made regarding the most energetically\udfavorable configurations. Such comparisons depend on the value of the effective chemical potential of\udeach atomic species, which can be related directly to experimental growth conditions. The most stable structure\udas a function of chemical potentials is determined. Based on these results we have characterized the effect of\udN in the adlayer surface and the stability dependence with number of substitutions as a function of the model\udemployed and the possible surfactant character of some of the added atoms. Surface phase diagrams as a\udfunction of the chemical potential have been calculated to show the phase transition between the different\udreconstructions