We report on the epitaxial growth of titanium oxynitride (TiOxNy) films on α-Al2O3 (0001) substrates by using a pulsed-laser deposition technique and their optical properties. Using TiN as a solid source, N content (y) in the films was tuned by changing the partial pressure of O2 gas. The crystalline phase was found to evolve up to y ≈ 0.4 either from rock-salt type or from rutile-type structures. The optical absorption spectra of the films had two distinct components in regions of 0.44-2.4 eV and 2.4-6 eV, which arise from d-d and charge-transfer transitions, respectively. The former transition decreased with decreasing y and vanished at y ≈ 0.26, where a fundamental absorption edge due to the latter transition was found to be 2.4 eV. The results demonstrate a range of anion compositions in the TiOxNy being suitable for visible-light harvesting applications.
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