Sputtering characteristics, crystal structures, and transparent conductive properties of TiO N films deposited on α-Al2O3(0 0 0 1) and glass substrates

Abstract Adding N 2 gas during reactive sputtering of a Ti target prevented the target surface from being severely poisoned by oxygen atoms and sustained a high deposition rate for titanium oxynitride films under metal-mode-like sputtering conditions. With progress in the degree of oxidization, films deposited onto a glass substrate varied from TiO 1− x N x having a face-centered cubic (fcc) structure to TiO 2− x N x having an anatase structure. Titanium oxynitride films deposited on an Al 2 O 3 (0 0 0 1) substrate were epitaxial with major orientations toward the (1 1 1) and (2 0 0) directions for fcc-TiO 1− x N x and (1 1 2) for anatase-TiO 2− x N x . Intermediately oxidized films between TiO 1− x N x and TiO 2− x N x were amorphous on the glass substrate but crystallized into a Magneli phase, Ti n O(N) 2 n −1 , on the Al 2 O 3 (0 0 0 1) substrate. Partially substituting oxygen in TiO 2 with nitrogen as well as continuously irradiating the growing film surface with a Xe plasma stream preferentially formed anatase rather than rutile. However, the occupation of anion sites with enough oxygen rather than nitrogen was the required condition for anatase crystals to form. The transparent conductive properties of epitaxial TiO 2− x N x films on Al 2 O 3 (0 0 0 1) were superior to those of microcrystalline films on the glass substrate. Since resistivity and optical transmittance of TiO x N y films vary continuously with changing N 2 flow rate, their transparent conductive properties can be controlled more easily than TiO x . Nb 5+ ions could be doped as donors in TiO 2− x N x anatase crystals.