Published in J. Vac. Sci Technol. B 24, 2080 (2006).
Oxidized GaN(0001) Surfaces studied by Scanning Tunneling Microscopy and Spectroscopy and by First-Principles Theory
Y. Dong (a), R. M. Feenstra (a), and J. E. Northrup (b)
(a) Dept. Physics, Carnegie Mellon University, Pittsburgh, PA 15213
(b) Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, CA 94304
Oxidized Ga-polar GaN surfaces have been studied both experimentally and theoretically. For in-situ oxidization at 550°C using molecular oxygen, Auger electron spectroscopy indicates a saturation oxygen coverage of 2.1 + / - 0.5 monolayers. For these surfaces scanning tunneling microscopy reveals two surface phases, one with 3rt(3)x3rt(3)-R30° periodicity and the other with disordered 2x periodicity. Scanning tunneling spectroscopy revealed a surface band gap with size close to that of GaN, indicating that any states of the oxide lie predominantly outside of the GaN gap. From first-principles total energy calculations of surface formation energies two models of energetically favorable surfaces structures are developed, with oxygen coverages of 1.25 and 2 monolayers, respectively. Both structures satisfy electron counting and have surface band gaps close in size to that of GaN, in agreement with experiment.
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