Correlation of oxygen vacancy variations to band gap changes in epitaxial ZnO thin films

The modulation of oxygen vacancies in ZnO epilayers and its effect on optical band gap have been investigated. The evolution of band gap is correlated with the oxygen vacancy variations induced by readily varying reactive oxygen partial pressure. The oxygen vacancy increased with the decreased oxygen partial pressure, accompanied with a red shift of absorption band edge and of ultraviolet emission peak. The optical band gap was roughly linear dependent on reactive oxygen partial pressure. The band gap narrowing is attributed to the overlap of the nonlocalized oxygen vacancy states with valence band. (C) 2013 AIP Publishing LLC.