Study On Bandgap Regulation And Light Transmittance Properties Of TiO₂ Thin Films

Titanium dioxide is a typical wide band gap semiconductor and widely used as an optical film due to its advantages of corrosion resistance,non-toxicity,environmental protection,high refractive index,ultraviolet light absorption,hydrophilicity and low cost.However,the application of titanium dioxide film is also limited by its wide band gap.Therefore,this thesis focuses on the limitation of visible light absorption of titanium dioxide and enhances the visible light absorption of titanium dioxide films through elemental doping and multi-layer film.The nano-titanium dioxide thin films,multilayer composite films and doped films were prepared by RF magnetron sputtering and element doping was performed by co-sputtering to modify the band gap and light transmittance properties.Firstly,the graphite target was used as carbon doping source and was co-sputtered with TiO₂ceramic target to prepare C doped TiO₂ films.The influence of nitrogen flow on the band gap of the films during sputtering was studied.It was found that the bandgap of C doped TiO₂ thin films was effectively reduced by 0.38 ev compared with the undoped thin films.When nitrogen was introduced into sputtering,the valence state of Ti element in the films decreased,and the binding energy was shifted to the low binding energy.The crystal structure was more disordered and the grain was refined,which resulted in a decrease in the surface roughness of the films from 1.744 nm to 1.218 nm.With the decrease of the roughness,the transmittance of the films increased significantly compared with C doped TiO₂ films,and the band gap also increased from 3.29 e V to 3.55 e V.Cu metal target was used as doping source,and co-sputtered with TiO₂ ceramic target,and the influence of Cu target power,annealing time and temperature on the film properties was studied.It was found that when the sputtering power of Cu target increased,the transmittance of the Cu doped TiO₂ films decreased,and the increase of the doping amount of Cu also reduced the band gap.When the sputtering power of Cu target was 20 W,the bandgap was 2.8 ev and the average transmittance was 75%.With the increase of annealing temperature,the characteristic peak at 140 cm^-1 in Raman spectrum increased first and then decreased.When the temperature was 550?,the characteristic peak of anatase weakend,and part of anatase transformed into rutile.When the annealing temperature was500?,the band gap of the films decreased to 2.7 e V,and the average transmittance in the visible region was 75%.The samples were annealed at 500?at different times,with the increase of annealing time,the bandgap of the film decreased.Finally,Cu₂O thin films and Cu₂O/TiO₂ double layer thin films were prepared by reactive sputtering,and the influence of Cu target power and sputtering time on the properties of Cu₂O thin films and the properties of the double layer thin films were studied.The analysis showed that when the Cu target power was 60 W,the sputtering time was 15 min and the argon-oxygen ratio was 39:1,the Cu₂O thin films with better visible light transmittance,better crystallinity and narrow band gap were obtained.Then,the order of the double layer films was adjusted,and it was found that when TiO₂ film layer was the outermost layer,the transmittance of the double layer films increased by 6%,and the absorption edge showed blue shift.