Effect of oxygen partial pressure on the Fermi level of ZnO1−x films fabricated by pulsed laser deposition

We investigated the influence of oxygen deficiency on the Fermi level (EF) of ZnO thin film prepared by pulsed laser deposition (PLD). For this purpose, we adopted in situ x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. The oxygen deficiency was effectively controlled by varying the oxygen partial pressure [P(O2)] during the PLD. The EF shifted by +0.6 eV as the P(O2) decreased from 10 to 3.3 Pa. This shift indicates a significant change in the energy balance in the oxygen-deficient ZnO films. This fact suggests that the very large change in the resistivity of ZnO thin films resulting from the oxygen deficiency could be attributed to the EF shift rather than grain boundary formation in the ZnO film.