Enhanced Electron Interactions on Hydrogen Adsorbed ZnO Surface

Zinc oxide (ZnO) is a wide band- gap semiconductor (3.37 eV), and is widely used as a catalyst, a chemical sensor, and a variety of electronic and photonic devices. Recent studies have revealed that a two-dimensional electron gas (2DEG) is formed on a hydrogen adsorbed ZnO(10$\bar{1}$0) surface. However, a precise structure of the 2DEG on a ZnO surface is still uncertain. We have investigated the electronic states using angle-resolved photoemission spectroscopy (ARPES), and found the clear incoherent states associated with the coherent metallic peaks near the Fermi-level, giving direct evidence of many-body interactions inherent to 2D metallic states. The incoherent states are enhanced by the hydrogen adsorptions. Thus, we suggest that the incoherent peaks are originated from electron-phonon and electron-electrons interactions enhanced by the electron doping on the surface.