Effect of O/N content on the phase, morphology, and optical properties of titanium oxynitride thin films

Phase formation, morphology, and optical properties of Ti(O,N) thin films with varied oxygen-to- nitrogen ration content were investigated. The films were deposited by magnetron sputtering at 500 °C on Si(100) and c-plane sapphire substrate. A competition between a NaCl B1 structure TiN1−xOx, a rhombohedral structure Ti2(O1−yNy)3, and an anatase structure Ti(O1−zNz)2 phase was observed. While the N-rich films were composed of a NaCl B1 TiN1−xOx phase, an increase of oxygen in the films yields the growth of rhombohedral Ti2(O1-yNy)3 phase and the oxygen-rich films are comprised of a mixture of the rhombohedral Ti2(O1−yNy)3 phase and anatase Ti(O1−zNz)2 phase. The optical properties of the films were correlated to the phase composition and the observation of abrupt changes in terms of refractive index and absorption coefficient. The oxide film became relatively transparent in the visible range while the addition of nitrogen into films increases the absorption. The oxygen rich-samples have bandgap values below 3.75 eV, which is higher than the value for pure TiO2, and lower than the optical bandgap of pure TiN. The optical properties characterizations revealed the possibility of adjusting the band gap and the absorption coefficient depending on the N-content, because of the phases constituting the films combined with anionic substitution.