Effect of magnesium on the structure and growth of GaN(0001)

First-principles total energy calculations were performed to determine the effect of Mg on the structure and growth of the GaN(0001) surface. The relative stabilities of possible Mg-rich reconstructions were determined with respect to those of the clean surface. In very Mg-rich conditions it is proposed that the surface structure comprises 12to34 ML of Mg substituting for Ga in the top layer. The stability of these structures reduces the range of Ga chemical potentials for which the Ga-bilayer is stable and therefore provides an explanation for why the window for smooth growth of GaN is narrowed when Mg is present. A structural model for the 2×2 reconstruction of the GaN(0001):Mg surface is proposed.