Surface morphological and compositional changes of GaN films induced by swift heavy-ion irradiations

Wurtzite GaN films irradiated at room temperature with 308 MeV Xe-129(35+) or 230 MeV Pb-208(27+) ions have been studied by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The three-dimensional AFM images showed that swellings of the GaN films were caused by the ion irradiations at very low fluences. In comparison with the Xe ions, the Pb ions led to a much more pronounced swelling. The XPS results indicated that after the Xe and Pb irradiations, the contents of Ga and N dangling bonds in the GaN increased, and the contents of Ga-O and N-O bonds in the surface layer also increased. In the case of the Pb irradiation, a peak associated with the defect of interstitial N was detected in the N 1s core-level spectrum, implying the formation of N-2 bubbles close to the GaN surface. However, no homonuclear Ga-Ga bond was found according to the related Ga 3d spectrum. The dramatic experimental results are discussed and the distinct difference of irradiation damages in GaN induced individually by the Xe and Pb ions is analyzed.