Preparation and atomic structure of reconstructed (0001) InGaN surfaces

The preparation and surface structure of high quality group-III-polar (0001) InGaN layers grown by metal-organic vapor phase epitaxy have been investigated. In order to obtain a clean and well-ordered surface we studied the preparation by annealing at various temperatures under ultra high vacuum and nitrogen-rich conditions in nitrogen-plasma. We show that different InGaN surface reconstructions such as (1×1), (1 + 1/6), (2×2), and (√(3)×√(3))R30° can be obtained as observed by low energy electron diffraction. Dependent on the annealing temperature and nitrogen supply these surfaces exhibit significant differences in stoichiometry and morphology as determined by Auger electron spectroscopy and atomic force microscopy measurements. The (1×1), (2×2), and (√(3)×√(3))R30° superstructures are terminated by single group-III-adatoms, whereas the (1 + 1/6) exhibits a incommensurate overlayer of group-III-atoms. We show that the (2×2) and (√(3)×√(3))R30° an In depletion in the first group-III layer and In or Ga adatoms in ontop position. Strain-relaxation is suggested to explain this structure formation.