Optical properties of anatase TiO2 thin films prepared by aqueous sol–gel process at low temperature

TiO2 thin films were spin-coated on Si (100) substrates via an aqueous sol–gel route using Ti(OBun)4 and H2O2 as starting materials, and were annealed in air at different temperatures up to 550 °C for 1 h. X-Ray diffractometry indicates that crystallization into anatase started at 350 °C. The 350 °C-annealed films were further characterized by Auger electron spectroscopy, X-ray photoelectron spectroscopy, and variable angle spectroscopic ellipsometry. The results show that homogeneous, carbon-free TiO2 films with high refractive index (n=2.3 at 550 nm) were successfully obtained under an annealing temperature as low as 350 °C. The indirect and direct optical absorption bandgaps of the anatase film are estimated as 3.23 and 3.80 eV, respectively.