Valence-band offset of p-NiO/n-ZnO heterojunction measured by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy was used to measure the valence-band offset (VBO) of the NiO/ZnO heterojunction grown on quartz substrate by radio frequency (RF) magnetron sputtering. Core levels of Ni 2p and Zn 2p were used to align the VBO of p-NiO/n-ZnO heterojunction. The valence-band offset (ΔEV) is determined to be 1.47 eV. According to the band gap of 3.7 eV for NiO and 3.37 eV for ZnO, the conduction-band offset (ΔEC) in the structure was calculated to be 1.8 eV, and it has a type-II band alignment. ► We measured the ΔEV of NiO/ZnO heterojunction which use NiO as the epitaxial layer. ► The NiO/ZnO heterojunction has a type-II band alignment with ΔEV of 1.47 eV. ► The ΔEV of NiO/ZnO at different growth sequence of ZnO and NiO layers are different.