Study Of The Fabrication And Properties Of ZnO Films

ZnO nanostructure films have been attracting considerable attentions owing to their excellent optical and electrical properties as well as promising applications in optoelectronic devices. For example:the Al-doped ZnO (AZO) nanopaticle film is a kind of transparent conductive oxide (TCO) films which can be used as a transparent electrode of solar cells or a window layer of flat-panel displays and other optoelectronic devices due to its high visible transmittance and low resistivity; ZnO nanorod film has been widely used in new solar cells, piezoelectric conversion and gas sensors. The sol-gel method and chemical bath deposition method are usually used to synthesis AZO nanopaticle films and ZnO nanorod films, respectively. These methods can be carried out in soft environments and lower energy consumption. However, there are still some problems that need to be solved.Our works focus on the study of ZnO nanostructure films by sol-gel method and chemical bath deposition method, the AZO transparent conductive films and ZnO nanorod films are synthesized. The influence of the process conditions on the structural, morphological, optical and electrical properties of ZnO films are investigated by XRD, SEM, TEM, XPS, UV-VIS spectrophotometer and standard four-point probe method, respectively. The main findings are listed as follows:The first part:The preparation of AZO films by sol-gel method1. The heating rate during the high temperature annealing process plays a significant role in improving the structure and properties of AZO films. The AZO film with nanorod structure is obtained with the heating rate of50℃/min and the crystal quality of the corresponding film is improved obviously. According to the XRD analysis, we consider that the nanorod structure is caused by the rapid heating process, which leads to a faster crystal growth along the C-axis.2. The AZO nanorods can provide a faster conduction pathway for charge transport due to the high crystal quality and thus enhance the conductivity of the film significantly. The average transmittance of the AZO nanorod film in the visible-light range is larger than85%, which meets the requirement of TCO applications. After the reduction treatment, the conductivity of the AZO nanorod film is further improved, and a minimum resistivity of1.4×10-3Ω·cm is obtained. According to the XPS analysis, the decrease of the resistivity after the reduction treatment is attributed to the increase of oxygen vacancies which can offer more conduction electrons. The second part:The preparation of ZnO nanorod films by chemical bath deposition method1. The perpendicular ZnO nanorod films are prepared by the chemical bath deposition method and the substrates are activated only by simple potassium permanganate solution treatment. The length of the nanorod reaches2.5μm and the aspect ratio is more than10. The deposition can be carried out on a wide variety of substrates including glass, Si and PET.2. The influences of pH value, MEA concentration and temperature on the morphological and structural of ZnO films are obvious. The main reason is the difference of the supersaturation in deposition baths, which leads to different mechanisms of nucleation and crystal growth. When the pH value is11.04, the MEA concentration is1.6M, the temperature is90℃, the resultant ZnO films show a regular hexagon shape. The most growth process involves the orientated attachment mechanism and2D nucleation. The TEM and XRD results confirm that ZnO nanorods grow along the C-axis and have a single crystal structure.The ZnO films with excellent nanostructure are prepared by wet chemical methods in our works. AZO nanorod film is obtained by sol-gel method with a rapid heating rate. The AZO nanorods can enhance the conductivity of the film significantly due to the high crystal quality. This approach to the preparation of AZO nanorods by a simple rapid annealing process may be helpful for the development of sol-gel-derived TCO films. The ZnO nanorod film is prepared by chemical bath deposition method and the substrate is activated only by simple potassium permanganate solution treatment. The perpendicular ZnO nanorod with a single crystal structure is synthesized by controlling the supersaturation in deposition bath. This work provides a simple way to prepare the good quality ZnO nanorod films.