A study of the effect of oxygen flow rate on the energy band gap of the c-axis-oriented ZnO and Zn_(0.95)Cu_(0.05)O films, deposited on glass substrates by RF magnetron sputtering, is reported. An increase of the oxygen flow rate (partial pressure) during deposition results in an increase in the band gap (Eg) of Zn_(0.95)Cu_(0.05)O films from 2.80 to 3.10 eV. The maximum observed enhancement is 10.5%. For the same oxygen flow rate (partial pressure), the band gap of a Zn_(0.95)Cu _(0.05)O film is found to be lower than that of ZnO as predicted by Ferhat et al (2009 Appl. Phys. Lett. 94 142502). A correlation has been observed between the residual strain and the band gap of doped and undoped ZnO films.
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