This study analyzes the optical properties of TiO₂ films grown via atomic layer deposition (ALD) using Tetrakis(dimethylamino)titanium with oxidizing agents such as H₂O, H₂O₂, O₃, and O₂-plasma. TiO₂-H₂O exhibited Ti³⁺ states and oxygen vacancies characteristic of black TiO₂, enhancing visible-NIR light absorption. This effect increased with more ALD cycles due to the surface memory effect, leading to a decreased growth rate. In contrast, films grown with H₂O₂, O₃, and O₂-plasma are more stoichiometric, has fewer defects, and show no visible-NIR absorption due to the absence of Ti³⁺. TiO₂ films deposited with H₂O also show increased surface roughness and hydrophobicity, while films grown with other oxidizing agents exhibited higher roughness but decreased hydrophobicity. Ellipsometry and UV–vis spectroscopy confirmed that TiO₂ films grown with H₂O has an increased refractive index and extinction coefficient in the visible range, along with a bandgap widening due to the Moss-Burstein effect. Conversely, films grown with other oxidizing agents showed a decreased bandgap with increasing thickness and an increased refractive index but a zero extinction coefficient below the bandgap. Mid-IR ellipsometry measurements revealed the dielectric response, highlighting the critical role of the oxidizing agent in tailoring the properties of TiO₂ films for energy and environmental applications.