Ion induced compositional changes and nanodroplet formation on GaN surface

Low energy argon ion bombardment of different fluence onto a GaN film grown on Al 2 O 3 (0 0 0 1) surface induces interesting compositional and morphological modifications. While atomic force microscopy (AFM) studies reveal the formation of a circular flat islands, Energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) core-level and valence-band spectra confirm that these nanodroplets consist of pure Ga. Detailed XPS studies suggest breaking of Ga N bond, that releases Ga to diffuse on the surface and nucleate at the threading dislocation sites, defined by the interfacial surface free energy. The formation of droplet pattern formation is discussed in the light of the existing theories on ion induced surface modification.