X-ray photoelectron spectroscopy measurement of n-ZnO/p-NiO heterostructure valence-band offset

Valence-band offset (VBO) of n-ZnO/p-NiO heterojunction has been investigated by x-ray photoelectron spectroscopy. Core levels of Zn 2p and Ni 2p were used to align the VBO of n-ZnO/p-NiO heterojunction. It was found that n-ZnO/p-NiO heterojunction has a type-II band alignment and its VBO is determined to be 2.60 +/- 0.20 eV, and conduction-band offset is deduced to be 2.93 +/- 0.20 eV. The experimental VBO value is in good agreement with the calculated value based on the electron affinity of ZnO and NiO.