Surface reconstruction and magnesium incorporation on semipolar GaN(1(1)over-bar01) surfaces

Reconstructions and Mg incorporation on GaN surfaces in semipolar (1 (1) over bar 01) orientation are systematically investigated by performing first-principles pseudopotential calculations. The calculated surface phase diagrams demonstrate that there are several reconstructions depending on the growth conditions. When the pressure of H-2 is low, the surface consisting of Ga-Ga dimers is stabilized under N-rich conditions whereas metallic reconstructions are favorable under Ga-rich conditions. The H-terminated surface is stabilized over the wide range of growth conditions when the pressure of H-2 is high. We also reveal that several Mg-incorporated surfaces, in which one Mg atom substitutes for one of the topmost Ga atoms, can be formed under growth conditions. Under growth condition of metal-organic vapor-phase epitaxy, the H-terminated surface with Ga-Ga dimers and substitutional Mg is found to be stable for GaN(1 (1) over bar 01) surface, whereas the H-terminated surface without Mg can be formed for GaN(0001) surface. The orientation dependence in the stability of Mg incorporated surfaces provides a possible explanation for high Mg concentrations on semipolar GaN(1 (1) over bar 01) surface.