Valence-band structure of the polar ZnO surfaces studied by angle-resolved photoelectron spectroscopy

Abstract

Valence-band structures of the polar ZnO surfaces, i.e., ZnO(0001)-Zn and $\text{ZnO}(000\overline{1})\text{-O}$, have been investigated by angle-resolved photoelectron spectroscopy utilizing synchrotron radiation. On the $(1\ifmmode\times\else\texttimes\fi{}1)$ O-terminated surface, surface-localized states forming dispersing bands with a $(1\ifmmode\times\else\texttimes\fi{}1)$ periodicity are identified at the upper portion of the valence-band region. The energetic position of these states and the fact that their photoemission intensities are sensitive to gas adsorption suggest that there is a contribution from the $\text{O}\text{ }2p$ dangling-bond orbital of the surface O atoms. Comparing the valence-band structure of the $(000\overline{1})\text{-O}$ surface with that of the (0001)-Zn surface, a deviation of the electronic structure in the near surface region from that in the bulk is found to be larger on (0001)-Zn than on $(000\overline{1})\text{-O}$. The role of the step structures, which exist on both polar surfaces but with much higher density on the (0001)-Zn surface, in the modification of the electronic structure is discussed.