Morphology dependent surface properties of nanostructured GaN films grown by molecular beam epitaxy

The effect of film morphology on its surface chemistry and band structure has been analyzed for gallium nitride epitaxial films grown by molecular beam epitaxy. The film morphology has been studied using scanning electron microscopy and atomic force microscopy, and the bandstructure, defect and emission properties have been studied by X ray photoelectron spectroscopy and cathodoluminescence spectroscopy. It was found that the highly porous GaN nanowall network shows the highest relative conductivity and does not have defect related luminescence. The flatter films were more resistive and showed yellow luminescence, due to Ga vacancies. GaN nanowall network exhibited a Fermi level pinning at (1.8 $\pm$ 0.2) eV above valence band maximum, suggesting the presence of a Ga adlayer on the surface of GaN nanowall network. Ar ion sputtering was found to preferentially sputter N atoms leading to surface metallization.