Valence band structure of the ZnO(1 0 1¯ 0) surface studied by angle-resolved photoemission spectroscopy

The electronic band structure of the ZnO ( 1 0 1 ¯ 0 ) surface has been studied by angle-resolved photoemission spectroscopy utilizing synchrotron radiation. Photon-energy-dependent measurements and K- and O2-adsorption studies revealed that the O 2p dangling-bond state exists at 3.7 eV below the Fermi level at the Γ ¯ point. Polarization-dependent measurements show that the state has dominant contribution of the O 2px orbital (x is parallel to the ( 1 2 ¯ 1 0 ) direction) at the Γ ¯ point. It is found that the O 2p dangling-bond band lies within the projected bulk bands along the Γ X ¯ and Γ X ` ¯ axes in the surface Brillouin zone. This result settles a controversial issue on the energetic position of the O 2p dangling-bond band, which has been in dispute among theoretical studies. The dispersion widths are found to be 0.8 and 0.5 eV along the Γ X ¯ and Γ X ` ¯ directions, respectively.