Hydrogen-induced metallization on the ZnO(0001) surface

The formation of hydrogen overlayers on the Zn-terminated $\mathrm{ZnO}(0001)$ surface has been reexamined by angle-resolved photoemission spectroscopy (ARPES). While low-energy electron diffraction patterns display the same (1 \ifmmode\times\else\texttimes\fi{} 1) symmetry for different surface preparations, the electronic structure feature close to the Fermi level shows the formation of electron pockets, compatible with hydrogen-induced metallic states. Using ARPES and density functional theory (DFT) calculations, we show that hydrogen adspecies can also lead to metallization of this zinc-oxide surface in a similar manner as observed previously on $\mathrm{ZnO}(10\overline{1}0)$ and O-terminated $\mathrm{ZnO}(000\overline{1})$. Importantly, our DFT calculations indicate that these electron pockets are formed by $sp$ hybridized states and therefore the angular distribution of the emitted photoelectron is significantly suppressed at the normal emission.