| Transparent conductive oxide films are extensively used in soler cells, plan displays, sensors and some other fields, their average transmittance in visible range is usually more than 80% and resistivity lower than 10-3Ω·cm. Tin-doped indium oxide (ITO) is being most widely used as a TCO due to its lower resistivity (～10-4Ω·cm) and high transmittance (>85%) in visible range. However, the severe shortage of indium and high cost have become the shackles of ITO films for further application and development. Therefore, looking for a new transparent conductive film to substitute ITO is imperative. Recently, Al-doped ZnO (AZO) film has been actively investigated as an alternative for ITO film because of its excellent photoelectric properties and many other advantages, including abundance in natural resources, low cost, non-toxicity, high thermal and chemical stability.In this paper, AZO films were deposited on normal glasses using radio frequency (RF) magnetron sputtering. The effects of sputtering power, work pressure, bias voltage and secondary magnetic filed on the morphology, crystalline structure and photoelectric properties of AZO films were investigated by X-ray diffraction(XRD), Scanning electron microscope (SEM), atomic force microscope (AFM), four-point probe and UV/vis spectrophotometer. The result showed that:1. The AZO films showed a wurtzite hexagonal structure and preferred orientation along (002).The grain size, surface roughness as well as the diffraction intensity of peak (002) decreased with the increase of sputtering power. The film growth mode at low sputtering power was layer-by-layer mode and then turned to island mode at high sputtering power. The film resistance decreased with the increase of the sputtering power, and achieved a minimum value of 30 Ω/D at 150 W. Films deposited with low sputtering power always owned high transmittance in visible range, the optical band gap got wider slowly as the sputtering power increasing.2. The grain size was small but uniform at low sputtering pressure and got larger as the sputtering pressure increasing. The surface roughness increased first and decreased as the sputtering pressure increased from 0.5 Pa to 2.5 Pa. The intensity of peak (002) increased with sputtering power when it was not exceed 2.0 Pa, which dedicated that increasing the sputtering pressure could speed up the growth of grain. The films acquired a high transmittance which was affected by the film thickness, crystalline degree and surface morphology in visible at 0.5 Pa and 2.0 Pa. The crystalline structure got worse and the growth speed slowed down when the sputtering pressure was too high. The minimum film resistance was 26.59 Ω/□ at 2.0 Pa.3. A varied bias voltage was applied to the substrate that leaded to the surface more compact and homogeneous without abnormal big particles. The grain size as well as the surface roughness increased as the bias voltage increasing. The films had a greater apparent pyramid structure and extremely high transmittance duo to the bias voltage was employed. Bias voltage did not change the preferred orientation of the film growth but also accelerated the growth of the film along other direction. The extremely high bias voltage caused a resputtering which had a negative influence on the film growth.4. An secondary magnetic filed was employed in the conventional magnetron sputtering system. The results show that the secondary magnetic field is responsible for increasing the deposition rate from 13.04 nm/min to 19.93 nm/min. It is found that films prepared in the presence of the secondary magnetic field are well textured with a higher degree of c-axis preferred orientation and exhibit a compact and homogeneous morphology with fewer defects on the surface. As a result of good crystal quality and compact structure, the AZO films achieve a superior conductivity with a lowest sheet resistance of 12.88Ω/□. The average transmittance of all films is over 85% in the visible range of 400～800 nm. The wider band gap in AZO films grown using the secondary magnetic field makes a larger blue shift of the absorbance edge. |
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