Dimer-vacancy reconstructions of the GaN and ZnO(10(1)over-bar1) surfaces: Density functional theory calculations

Reconstructed structures of the GaN and ZnO(10 (1) over bar1) anion semipolar surfaces were studied using density functional theory calculations. The twofold-coordinated anion atoms on the unreconstructed surfaces form anion dimers with reduced surface hole density. The residual holes on the dimerized surfaces are additionally compensated by formation of a dimer vacancy (DV) in every four 2 x 1 cells on GaN(10 (1) over bar1) and in two 2 x 1 cells on ZnO(10 (1) over bar1). The electrostatically stable 4 x 2 DV reconstruction on the GaN(10 (1) over bar1) surface is found to be more stable than the previously suggested structures, and the 2 x 2 DV reconstruction on the ZnO(10 (1) over bar1) surface explains the transmission electron microscopy observations.