STUDY OF OXYGEN-CHEMISORPTION ON THE GAN(0001)-(1X1) SURFACE

Clean, ordered GaN(0001)-(1 X 1) surfaces are prepared by sputtering w ith nitrogen ions followed by annealing in ultrahigh vaccum. The surfa ces are subsequently exposed at room temperature to O-2 and the chemis orption process studied using Auger, valence and core-level photoemiss ion and electron energy loss spectroscopies, low-energy electron diffr action, and work function measurements. Saturation occurs at a coverag e of Theta(ox)=0.4 ML and is accompanied by the removal of surface sla tes near the band edges. The continued presence of a clear (1 x 1) dif fraction pattern, together with other data, indicates a well-defined a dsorption site, but the relative importance of Ga-O and N-O bonding re mains undetermined. The realization that surface states exist near the valence-band maximum has led to a more accurate determination of the surface Fermi-level pinning position, and of dependent quantities, tha n given previously. Clean-surface data are also compared with those fo r surfaces prepared by in situ deposition of Ga metal followed by ther mal desorption. No significant differences are seen, which suggests th at nitrogen-ion sputtering and annealing is suitable for preparing cle an, ordered GaN(0001)-(1 X 1) surfaces. The results for O chemisorptio n on atomically clean surfaces have been applied to evaluating the pas sivation of surfaces prepared by ex situ wet-chemical cleaning. The ha nd bending is found to be similar to 0.5 eV less than on atomically cl ean surfaces.