Measurement of wurtzite ZnO/rutile TiO2 heterojunction band offsets by x-ray photoelectron spectroscopy

The valence-band offset of the wurtzite ZnO/rutile TiO2 heterojunction was directly determined by x-ray photoelectron spectroscopy. The wurtzite ZnO (0001) layer was grown on commercial rutile (101) TiO2 by metal-organic chemical-vapor deposition. The results show that the valence-band offset is 0.14 +/- 0.05 eV, which agrees well with previous results by other methods. Therefore, the conduction-band offset is deduced from their known band-gap energy values to be 0.45 +/- 0.05 eV, which indicates a type-II band alignment for the ZnO/TiO2 heterojunction.