Spontaneous formation of indium-rich nanostructures on InGaN(0001) surfaces

InGaN(0001) surfaces prepared by molecular beam epitaxy have been studied u sing scanning tunneling microscopy and first-principles total energy calcul ations. Nanometer-size surface structures are observed consisting of either vacancy islands or ordered vacancy rows. The spontaneous formation of thes e structures is shown to be driven by significant strain in the surface lay ers and by the relative weakness of the In-N bond compared to Ga-N. Theory indicates that In will preferentially bind at the edges and interior of the structures, thereby giving rise to an inhomogeneous In distribution at the surface.