| Transparent conducting oxides (TCOs) have been used widely in a range of areas, especially in the flat panel displays, the touch screen of smart phones, tablet computers, solar cells and energy-efficient glass. The indium tin oxide (ITO)is the dominant TCO material, because of excellent optical and electrical performance, but it has poor mechanical properties, and the scarcity of resources and toxic materials. Nb-doped titanium dioxide (NTO) film is a new kind of TCO film, which has a high transmittance, low resistivity characteristics, and stable performance, and the most important advantage is that the raw materials is abundant in nature, and environmentally friendly.In this work, a novel method was used to prepare the transparent conductive oxide films: High Target Utilisation Sputtering (HiTUS), of which the advantages is rapidly sputtering deposition, dense and uniform of the film, and good reproducibility. The NTO films deposited through the way of reactive sputtering used this coating system with high-energy plasma beam bombardment alloy target at a start vacuum of2.0×10-3Pa. During the sputtering deposition process,the plasma emission power was1500W, the argon flow was88sccm, oxygen gas flow rate was between0~7sccm, and bias power applied to the target acceleration was600W. During sputtering the current was0.8~1.0A, and the working pressure was4.7×10-1Pa~5.0×10-1Pa. We have calculated NTO film using the first-principle theory before, about the composition and defects of film, so we chose6%Nb target to do the deposition.The property of film samples were investigated: the profilometer was used to measure the thickness of the NTO film. The UV-Vis spectrophotometer was used to study the optical properties of the film. The high-resolution X-ray diffraction (XRD) was used to study the crystallographic analysis of NTO films. The field emission scanning electron microscope (FESEM) was used to observe the surface morphology of films. The Hall Effect System was used to accurately characterize the electrical properties of films. X-ray photoelectron spectroscopy (XPS) was used to characterize the variation of the valence of elements in the film surface and find out the reason of the changes of carrier concentration in the internal structure and the law of electron transfer.In the sputtering deposition process the optical and electrical properties of films samples was significantly affected by the different flow rate of oxygen. As the oxygen flow is increased,the visible light transmittance of films was significantly improved, up to90%or more. However, the conductive properties of the film were significantly reduced when the oxygen flow rate increased. When the oxygen flow was6sccm the sheet resistance of the film was up to2M/sq. The film resistance was very large, almost insulation when the corresponding oxygen flow was7sccm. After500℃heating the performance of thin film samples has changed a lot, light transmission properties and conductivity of the film significantly increased. After optimization of the parameters, we found that there was a critical value of oxygen flow between6.4sccm and6.6sccm. After heating the film treated at500℃, the light transmittance of the film was above90%, the resistivity of films was as low as9.4×10-4cm.We also studied on the crystallization characteristics, microscopic morphology and energy gap of the film samples before and after hearting, to further understand the deep-seated causes of internal defects and changes in the electrical transport properties of thin films. After heat treatment, the structural defects in the film decrease, forming a more perfect periodic potential field, eliminating the carrier traps, and greatly reduces the movement of the carrier scattering effects, the electrical properties of the films were significantly improved. |
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