InGaN(0001) surface reconstructions

Surfaces of the InGaN alloy system are hardly understood in terms of their atomic structure. In order to reveal the principal mechanisms for the formation of surface reconstructions the preparation of such surfaces for measurements in ultra-high vacuum (UHV) is crucial. The preparation and surface structure of high quality group-III-polar (0001) InGaN layers grown by metal-organic vapor phase epitaxy have been investigated. We show that different InGaN surface reconstructions such as (1 x 1), (1+1/6), (2 x 2) and (√(3) x √(3))R30 circle can be obtained by annealing at various temperatures under ultra-high vacuum and nitrogen-rich conditions as observed by low energy electron diffraction. Depending 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. We show that the (2 x 2) and (√(3) x √(3))R30 circle are explained by indium-adatoms and a related In depletion in the first group-III layer underneath whereas the (1+1/6) exhibits a discommensurate overlayer of group-III-atoms. Strain-relaxation is suggested to explain this structure formation.