Band gap narrowing of ZnO:N films by varying rf sputtering power in O2∕N2 mixtures

Band gap narrowing of N-incorporated ZnO (ZnO:N) was achieved by reactive rf magnetron sputtering in O2∕N2 mixture ambient. ZnO:N films with various band gaps were realized by varying N concentration, which was controlled successfully by varying the rf powers. When rf power was increased to 200W, the ZnO:N films exhibited optical band gaps similar to that of Zn3N2 films. Calculations based on first-principles density-functional theory revealed that the band gap narrowing is caused by the mixing of shallower N 2p states with the valence band of ZnO.