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 GaNs0001d 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 1/2 to 3/4 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 2x2 reconstruction of the GaNs0001d: Mg surface is proposed. (C) 2005 American Institute of Physics.