NEXAFS and XPS study of GaN formation on ion-bombarded GaAs surfaces

Interaction of low-energy nitrogen ions (0.3–2 keV N2+) with GaAs (100) surfaces has been studied by X-ray photoemission spectroscopy (XPS) around N 1s and Ga 3d core-levels and near-edge X-ray absorption fine structure (NEXAFS) around the N K-edge, using synchrotron radiation. At the lowest bombardment energy, nitrogen forms bonds with both Ga and As, while Ga-N bonds form preferentially at higher energies. Thermal annealing at temperatures above 350 °C promotes formation of GaN on the surface, but it is insufficient to remove disorder introduced by ion implantation. We have identified nitrogen interstitials and anti-sites in NEXAFS spectra, while interstitial molecular nitrogen provides a clear signature in both XPS and NEXAFS. The close similarity between NEXAFS spectra from thin GaN films and ion-bombarded GaAs samples supports our proposition about formation of thin GaN films on ion-bombarded GaAs.