Ab initio density functional theory study of non-polar (10(1)over-bar0), (11(2)over-bar0) and semipolar {20(2)over-bar1} GaN surfaces

The atomic structures of non-polar GaN(10 (1) over bar0) (11 (2) over bar0) and semipolar GaN(20 (2) over bar1), (20 (2) over bar(1) over bar) surfaces were studied using ab initio calculations within density functional theory. The bulk-like truncated (1 x 1) structure with buckled Ga-N or Ga-Ga dimers was found stable on the non-polar GaN (10 (1) over bar0) surface in agreement with previous works. Ga-N heterodimers were found energetically stable on the GaN(11 (2) over bar0)-(1 x 1) surface. The formation of vacancies and substitution site defects was found unfavorable for non-polar GaN surfaces. Semipolar GaN {20 (2) over bar1}-(1 x 1) surface unit cells consist of non-polar {10 (1) over bar0} and semipolar {10 (1) over bar1} nano-facets. The {10 (1) over bar1} nano-facets consist of two-fold coordinated atoms, which form N-N dimers within a (2 x 1) surface unit cell on a GaN (20 (2) over bar1) surface. Dimers are not formed on the GaN (20 (2) over bar(1) over bar) surface. The stability of the surfaces with single {10 (1) over bar0} or {10 (1) over bar1} nano-facets was analyzed. A single non-polar {10 (1) over bar0}-(1 x 1) nano-facet was found stable on the GaN (20 (2) over bar1) surface, but unstable on the GaN (20 (2) over bar(1) over bar) surface. A single {10 (1) over bar1} nano-facet was found unstable. Semipolar GaN surfaces with (20 (2) over bar1) and (20 (2) over bar(1) over bar) polarity can be stabilized with a Ga overlayer at Ga-rich experimental conditions. (C) 2014 AIP Publishing LLC.