Spectroscopic ellipsometry study of Co-doped TiO2 films

Co-doped TiO 2 films were characterized by spectroscopic ellipsometry to determine their thickness, deposition rate and optical properties as function of substrate temperature and background gas composition. To fit the data we used a combination of a single Tauc-Lorentz oscillator with the Drude free electron model to take in account the free electrons present in the film. The Co doping and the addition of H 2 to the gas phase during film growth cause the formation of a titanium oxide which containsfree electrons that absorb the energy of the red part of the spectrum, causing k to increase The n of the films at 1.5 eV is about 2.3 eV. The fittigs also show that the n of films decreases and k increases at the surface. This can be related to a segregation of Co to the surface which in some cases, of high substrate temperature and high H 2 flow during deposition, can lead to an even higher concentration of free electrons at the surface.