Coherent and dislocated three-dimensional islands ofInxGa1−xNself-assembled on GaN(0001) during molecular-beam epitaxy

Abstract

Molecular-beam epitaxy of ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ alloy on GaN(0001) is investigated by scanning tunneling microscopy. The Stranski-Krastanov mode of growth of the alloy is followed, where the newly nucleated three-dimensional islands are initially coherent to the underlying GaN and the wetting layer, but then become dislocated when grown bigger than about $20\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in the lateral dimension. Two types of islands show different shapes, where the coherent ones are cone shaped and the dislocated ones are pillar like, having flat-tops. Within a certain range of material coverage, the surface contains both coherent and dislocated islands, showing an overall bimodal island-size distribution. The continued deposition on such surfaces leads to the pronounced growth of dislocated islands, whereas the sizes of the coherent islands change very little.