【作者】 马勇；

【导师】 王万录；

【作者基本信息】 重庆大学 ， 凝聚态物理， 2004， 博士

【摘要】 氧化锌(ZnO)是一种宽带隙(室温下3.3eV)Ⅱ-Ⅵ族化合物半导体, 激子结合能为60meV,具有六方纤锌矿结构,其空间群为P63mc。晶格常数,。ZnO薄膜具有良好的透明导电性、压电性、光电性、气敏性、压敏性、且易于与多种半导体材料实现集成化。由于这些优异的性质,使其具有广泛的用途和许多潜在用途,如表面声波器件、平面光波导,?透明电极,紫外光探测器、压电器件、压敏器件、紫外发光器件、气敏传感器等。近年来,对其研究和开发在国内外科学界及工业部门引起了极大的关注和兴趣。ZnO薄膜的制备的主要方法有:磁控溅射、金属有机化学气相沉积、脉冲激光沉积、分子束外延、电子束蒸发沉积、喷雾热分解、溶胶-凝胶法、薄膜氧化法等。各种方法各有优缺点。根据需要制备相应的高质量的薄膜是ZnO薄膜应用的关键,同时制备成本也是必须考虑的重要因素。通常认为理想的ZnO薄膜具有高的c轴择优取向。真空蒸发制膜的方法设备简单普及、易操作、适合工业化生产并能得到大面积均匀的薄膜材料。我们采用真空蒸发沉积Zn膜,然后热氧化Zn膜制备出c轴择优定向好的ZnO薄膜。热氧化蒸发Zn膜制备ZnO的条件被优化。讨论了薄膜的择优定向生长过程、特点及影响因素。磁控溅射在最佳条件下可以得到均匀、致密、有良好的c轴取向性和可见光波段透明性好等优点的薄膜,使得它成为在ZnO制备中研究最多并且最广泛使用的方法。我们采用DC反应磁控溅射制备了ZnO和ZAO薄膜。讨论了磁控溅射ZnO薄膜的原理、影响ZnO薄膜质量的因素。用SEM表征ZnO薄膜的形貌和微结构,用TEM表征ZnO纳米微粒的形态,用XDR分析ZnO微粒和薄膜的晶体结构,用紫外-可见光双光束分光光度计测量ZnO薄膜的透射谱,用四探针仪和Hall效应测试仪测量薄膜的电阻率、载流子浓度和Hall迁移率,用自制的气敏效应测试装置测试ZnO气敏元件的气敏性质。 研究ZnO和ZAO薄膜的光学性质是它们的应用和及制备条件优化的重要课题。讨论了光学常数之间的关系,仅采用透射谱确定了所制备ZnO和ZAO薄膜的厚度、折射率、消光系数、吸收系数和能带隙宽度。ZAO薄膜由于具有丰富的地球储量致使其成本低廉,而且无毒,并具有可同ITO比拟的光学、电学性质,已经成为ITO薄膜最佳替代候选者。拓宽氧分压工艺窗口,精确控制氧流量以及薄膜的均匀分布是实现ZAO薄膜商业化生产的值得探讨的课题。从实验上得到了c轴择优定向生长与氧流量之间的关系,得到了很好的柱状生长的纳米ZAO薄膜。给出了所制备的ZAO薄膜电阻率、载流子浓度和Hall迁移率、透射率、晶粒尺寸<WP=6>和晶格常数随氧分压变化的关系曲线。分析了所有这些量随氧分压变化的原因,研究了ZAO薄膜的方块电阻空间分布,微结构和表面形貌,为优化制备条件分析提供依据。从理论上分析了薄膜的厚度和表面平整度对薄膜电导的影响,说明薄膜越薄,电阻越大;表面平整可以在一定程度上改善薄膜的电导,分析了影响薄膜电导的因素。为了有助于开发和研究ZAO薄膜,研究了ITO薄膜的光学性质和电学性质及其应用,它的分析方法和结论对ZAO 薄膜是类似的。ZnO作为一种重要的气敏材料,其ZnO物理化学性质稳定,对可燃性气体具有敏感性,但工作温度偏高(400-500℃)、灵敏度较差。为了改善ZnO气敏元件的性能而采用纳米ZnO材料为原料制作纳米ZnO气敏元件是当前烧结体气敏元件改进的重要方向。我们制作了纳米ZnO气敏元件,测量了其气体灵敏度,研究了灵敏度与退火温度之间的关系,结果表明,不退火的元件灵敏度很高,但不稳定,退火后的元件稳定,但灵敏度下降,这反应了晶粒尺寸效应。纳米ZnO气敏元件的工作温度大大下降。从理论上研究了纳米ZnO气敏元件的气敏效应机理,提出了减少小纳米晶气体传感器的晶界数量也许是改进小纳米晶气体传感器的一种新方法,同时指出,尽管晶界电阻也许比颈部电阻小得多,但不能被忽略。为了理解吸附和催化过程,对空间电荷层的一个详细的描述是必要的。ZnO的空间电荷层经常被测试,这些实验基于耗尽层模型。采用耗尽层模型得到的空间电荷区的势垒电压分布和著名的Schottky关系表示的表面势垒高度简单,但电荷分布对电荷空间分布因子中温度的依赖没有体现。我们分析了ZnO表面势垒模型,讨论了温度对势垒高度的影响,给出了低势垒情况下势垒高度的计算公式,指出这时温度对势垒高度和空间电荷区宽度的影响是重要的。而这些影响在耗尽层模型中不存在。更多还原

【Abstract】 ZnO is a II-VI compound semiconductor with a wide direct bandgap of 3.3 eV at room temperature, exciton binding energy of 60meV, and a hexagonal wurtzite structure of space group P63mc. Its lattice parameters are and . Due to their excellent physical and chemical properties, ZnO films have many realized and potential applications such as surface acoustic wave devices , planar optical waveguides, transparent electrodes, ultraviolet photodetectors, piezoelectric devices, varistors, gas sensors, UV/violet/blue-LEDs (light emitting diodes) and –LDs (laser diodes), etc. And they can be integrated with some materials readily. In recent years, the researches and developments of ZnO films have attracted great attention and interest from researchers and the industry. To achieve the requirements of different applications, many techniques, such as molecular beam epitaxy, magnetron sputtering, metalorganic chemical vapor deposition , and pulsed laser deposition, spray pyrolysis, sol-gel process, reactive deposition and thermal oxidation of Zn films have been used to deposit ZnO films. Each of these techniques has its merits and demerits. The key to the application of ZnO films is high quality for the purpose, and the cost must be considered. In this work, the films were prepared using both thermal evaporation and DC reactive magnetron sputtering techniques. For various applications, highly preferred c-axis orientation of ZnO films is usually important. Thermal evaporation is the easiest deposition technique and applicable to industrial production. Films with a small or large-area coating can be obtained by the method. Zn films were deposited by thermal evaporation technique and then ZnO films with highly preferred c-axis orientation were prepared through thermal oxidation of the metallic Zn films. The thermal evaporation and oxidation were optimized. The process, characteristic and influence elements for preferred orientational growth of the films were discussed. Uniform and compact ZnO films with the highly preferred c-axis orientation and the high transmittance in visible region can be prepared by magnetron sputtering under optimized condition. It is the most investigated and widely used method. The magnetron sputtering principle and influence of deposition conditions on film quality and surface are discussed. The surface morphology and microstructure of the films were characterized by SEM and the morphology of the nano-ZnO particle by TEM. The crystallographic <WP=8>structure of the films and the particles was analyzed with XRD. The optical transmittance of the films was recorded using ultra-violet-visible double beam spectrophotometer. The electrical resistivity, carrier concentration and Hall mobility of the films were measured using four probe instrument and Hall effect instrument. The gas sensing effects were measured using self-made gas sensing effect apparatus.The studies on optical property of ZnO and ZAO films are an important topic for their application and for preparation conditions to be optimized. The relation between optical constants was discussed. The refractive index, the extinction coefficient, the absorption coefficient, the optical energy gap and the thickness of the films were calculated from transmittance spectrum. ZAO film, which has comparable electrical and optical properties to the ITO, are emerging as a potential substitute for ITO films due to its cheap and abundant raw material, nontoxic feature, cost-effective, easy fabrication and good stability. Widening oxygen partial pressure region and controlling film uniformity are important for commercial production. The influence of oxygen flow rate on preferred c-axis orientation of ZAO films was given. The ZAO film with columnar growth parallel to c-axis orientation was obtained. The effects of oxygen flow rate on the resistivity, the carrier concentration, the Hall mobility, the transmittance, the grain size and the lattice constants of ZAO films was determined, whose mechanisms were analyzed. The dependences of the spatial distribution of更多还原