Ga-terminated β-GaN(001) surface reconstructions studied by scanning tunneling microscopy

The reconstruction and topography of the β-GaN(001) surface are investigated with scanning tunneling microscopy on GaN/GaAs(001) layers grown by molecular beam epitaxy. Two Ga-terminated reconstructions are observed: a (2 × 2)- and a novel (√10×√10)R18.4°. The experimental results of filled and empty state STM images are in good agreement with a simulation based on structure models that include a dimerization of the surface Ga atoms. The formation of the unique (√10×√10)R18.4° is related to the high ionicity of GaN and to steric reasons, not allowing a full Ga coverage of the surface.