Photoemission study of the electronic structure of wurtzite GaN(0001) surfaces

The surface electronic structure of wurtzite GaN (0001) (1×1) has been investigated using angle-resolved photoemission spectroscopy. Surfaces were cleaned by repeated cycles of N₂ ion bombardment and annealing in ultra-high vacuum. A well-defined surface state below the top of the valence band is clearly observed. This state is sensitive to the adsorption of both activated H₂ and O₂, and exists in a projected bulk band gap, below the valence band maximum. The state shows no dispersion perpendicular or parallel to the surface. The symmetry of this surface state is even with respect to the mirror planes of the surface and polarization measurements indicate that it is of sp_z character, consistent with a dangling bond state.