TiO₂-based Transparent Conductive Films By Magnetron Sputtering:Fabrication And Photoelectric Properties

Compared with the traditional transparent conductive oxide material,doped TiO₂shows the characteristics of chemical stability,abundant reserves and environmental friendliness,which has important application prospect in the field of optoelectronic devices such as flat panel display,solar cell and touch screen.In this work,Ta-doped TiO₂（TaTO）films,Nb/Ta co-doped TiO₂（NTTO）films and NTTO/Cu/NTTO（TCT）multilayer composite films have been fabricated by magnetron sputtering.The effects of substrate temperature,sputtering power,film thickness and other process conditions on the structure,morphology,composition and photoelectric properties of the films were investigated.Also,the effects of crystal structure and carrier transport mechanism on the electrical properties of TiO₂-based transparent conductive films were discussed.The main contents of this thesis are listed as follows:（1）Polycrystalline anatase TaTO films were fabricted on quartz substrates by RF magnetron sputtering,followed by vacuum annealing.The effects of substrate temperature（room temperature?350°C）on the structure and photoelectric properties of the films were studied.The results show that Ti and Ta are mainly existed in the form of Ti⁴⁺and Ta⁵⁺,and most of the Ta⁵⁺ions successfully replace the Ti⁴⁺ions.The surface of the film has uniform nanoparticle characteristics and low surface roughness.The average transmittance in the visible region exceeds 73%,and the value of optical band gap is between 3.4 and3.51 eV.When the substrate temperature is 150°C,the TaTO film with resistivity of7.7?10^-4?cm,carrier concentration of 1.1?10²¹ cm^-3,and Hall mobility of 7.4 cm² V^-1 s^-1is obtained.（2）The effects of sputtering powers and film thicknesses on the photoelectric properties of NTTO films were investigated.It is found that when the power increases from 150 to 210 W,the grain size and density of the film increase gradually,and the substitution rate of Nb⁵⁺and Ta⁵⁺to Ti⁴⁺increases significantly.The carrier concentration and Hall mobility are also improved.The average transmittance in the visible region of the films is more than 82%.With the increasing of the film thickness,the crystallinity of the sample is gradually improved as well as the electrical properties,and the optical band gap becomes narrower.Under the optimized deposition conditions,the NTTO film with a resistivity of?10^-4?cm and an average visible light transmittance of over 80%can be obtained in the experiment.（3）NTTO/Cu/NTTO multilayer composite films with different Cu layer thicknesses were grown by RF and DC alternately sputtering.The results show that the thicker the Cu layer,the stronger the inhibition of the crystallinity of the upper NTTO film.By changing the thickness of the Cu layer,the electrical and optical properties of the composite film can be controlled.When the thickness of the Cu layer is about 16 nm,the average transmittance is close to 80%in the visible region.The resistivity is as low as 7.8?10^-5?cm and the quality factor(F_OM)is about 3.0?10^-2?^-1.The low resistivity in our experiment is close to the best values reported by others.（4）Based on the experimental data,the relationship between the crystal structure and electrical properties of TiO₂-based films was discussed.Furthermore,the physical mechanisam of carrier concentration and its transport were analyzed.The results show that the increase in the interplanar spacing d₁₀₁ can be attributed to the increase in carrier concentration.The effect of grain boundary scattering on carrier transport in TiO₂-based films is dominant over all other scattering.