Dynamic Observation and Theoretical Analysis of Initial O2 Molecule Adsorption on Polar and m-Plane Surfaces of GaN

The initial adsorption behavior of different GaN surfaces (the polar Ga-face (+c) and N-face (-c) and the nonpolar (10 (1) over bar0) (m)-plane) under O-2 molecule beam irradiation was studied by continuous real-time monitoring of the O 1s core X-ray photoelectron spectra generated under synchrotron radiation. The adsorption of O-2 molecules on these crystal planes was also modeled by density functional molecular dynamics calculations. The results predict that triplet O-2 either dissociates or chemisorbs at the bridge position on the +c GaN surface. On the other hand, the O-2 molecule on the N-terminated -c GaN surface only undergoes dissociative chemisorption. On the m-GaN surface, although the dissociation of O-2 is dominant, the bond length and angle were found to fluctuate from those of O-2 molecules adsorbed on the polar surfaces. These theoretical results for the oxygen-binding states on GaN surfaces are consistent with the obtained O 1s spectra under O-2 beam irradiation. The computational model including both the surface spin and polarity of GaN is useful for understanding the interface between GaN and oxide layers in metal-oxide electronic devices because it can successfully explain the adsorption behavior of GaN surfaces.