Reconstructions and electronic structure of (11-22) and (11-2-2) semipolar AlN surfaces

Τhe energetics, atomic geometry, and electronic structure of semipolar (112¯2) and (112¯2¯) AlN surfaces are investigated employing first principles calculations. For metal-rich growth conditions, metallic reconstructions are favoured on both polarity surfaces. For N rich to moderate Al rich conditions, the (112¯2) planes promote semiconducting reconstructions having 2 × 2 or c(2 × 2) periodicity. In contrast, under the particular range of the Al chemical potential the (112¯2¯) surfaces stabilize reconstructions with excess metal and it is only at the extreme N rich limit that the semiconducting c(2 × 2) N adatom structure prevails. The present study reveals that the reconstructed (112¯2) surfaces do not contain steps in contrast to (112¯2¯) where surface steps are inherent for N rich to moderate metal rich growth conditions and may result in intrinsic step-flow growth and/or growth of parasitic semipolar orientations.