Deep-level characterization of N-doped ZnO films prepared by reactive magnetron sputtering

We report on band gap states in N-doped ZnO (ZnO:N) films that were deposited on indium tin oxide/quartz substrates by reactive magnetron sputtering. Colored ZnO:N samples showed enhanced polycrystalline with increasing N-doping concentration, as determined by x-ray diffraction patterns. Deep-level optical spectroscopy measurements revealed three characteristic deep levels located at ∼0.98, ∼1.20, and ∼2.21eV below the conduction band. In particular, the pronounced 2.21eV band is newly introduced by the N doping and behaves as part of the valence band, resulting in band gap narrowing of ZnO. Therefore, this deep level is probably one origin of visible-light sensitivity in ZnO:N.