The stability of Mg-incorporated GaN surfaces with semipolar ( 101 1 1 1) orientation is investigated by performing first-principles pseudopotential calculations. Several Mg-incorporated surfaces, in which a single Mg atom is substituted for the topmost Ga atom, can be formed when the surfaces include step edges in the [0 1 100] direction. This implies that on the stepped surfaces Mg atoms can be easily incorporated into electrically active substitutional lattice sites, leading to high hole concentrations. The calculated results provide a possible explanation for experimentally observed high hole concentrations in Mg-doped semipolar ( 101 1 1 1) GaN on vicinal (100) MgAl 2 O 4 substrates miscut in the h011i direction.

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We report a systematic and comprehensive investigation of reconstructions of semipolar GaN( 101 1 1 1) and InN(10 1 1 1 1) surfaces by firstprinciples total-energy calculations. The surface formation energy indicates that there are several reconstructions depending on the growth conditions: The 1Â2 surface consisting of a single Ga-Ga dimer and Ga vacancies is stable under N-rich conditions, whereas metallic reconstructions are favorable under Ga-rich (In-rich) conditions. We also characterize atomic structures of semipolar surfaces under realistic growth conditions using surface phase diagrams. For InN, the analysis of density of states predicts charge accumulations on semipolar surfaces.

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