【作者】 张波；

【导师】 吴建生； 董显平；

【作者基本信息】 上海交通大学 ， 材料学， 2009， 博士

【摘要】 自从二十世纪九十年代以来,平面显示技术的进步促进了光电薄膜的发展。由于具有较高的载流子浓度和较宽的光学禁带,透明导电氧化物薄膜展示了较好的光电性能,比如低电阻率和高可见光透过率。其中,ITO(Sn掺杂In2O3)薄膜因其具有较好的光电性能而广泛应用于透明电极。但是ITO薄膜的化学和热不稳定性以及低表面能限制了ITO薄膜的应用,同时其光电性能也需要进一步改善,提高ITO薄膜的综合性能是当前研究的一个重要方向。本论文利用磁控溅射制备了基于氧化铟的多元组分氧化物薄膜。同时,利用第一性原理计算了电子能带结构。ITO薄膜的性能主要依赖于其氧化态以及掺杂的浓度,载流子浓度可以通过掺杂进行调节,掺杂施主原子的取代可以提供自由电子而提高载流子浓度。在本文中,锆和钽可作为掺杂施主原子而实现有效的取代,从而释放出自由电子提高薄膜的导电性。掺杂锆和钽离子的半径低于铟离子,可以实现有限固溶体。为了实现高价金属元素的有效掺杂,采用了包含直流和射频功率的双靶溅射系统,共溅射过程中分别采用了ITO靶,Zr靶和Ta2O5靶。利用磁控溅射在玻璃基底上沉积了ITO,ITO:Zr和ITO:Ta薄膜,研究了不同实验参数对薄膜光电性能的影响。结果表明,高价金属元素掺杂促进ITO薄膜晶化的同时,导致了(400)晶面择优取向的形成。低温沉积的ITO:Zr和ITO:Ta薄膜比ITO薄膜展示了较好的光电性能,Zr、Ta掺杂使得室温沉积ITO薄膜的效益指数分别由0.003×10-3Ω-1上升到了0.15×10-3Ω-1和0.88×10-3Ω-1。提高基底温度可以显著提高薄膜的光电性能;过量的氧流量会恶化薄膜的透明性;适当的退火处理使薄膜的光电性能得到改善,过高温度空气中退火处理却降低了薄膜的电学性能。透射谱表明各参数的变化引起了明显的“Burstin-Moss”效应,通过直接跃迁的模型研究了光学禁带的变化。共溅射法制备的ITO:Zr和ITO:Ta薄膜比ITO薄膜展示了较好的光电性能和较宽的光学禁带。在相同制备条件下,ITO:Ta薄膜的电阻略低于ITO:Zr薄膜,但ITO:Ta薄膜的可见光透过率高于ITO:Zr薄膜。采用第一性原理计算了基于氧化铟的透明导电氧化物的电子能带结构。能带结构中的价带顶和导带底对光电性能有重要影响。计算时采用了各掺杂原子取代晶格中更稳定的In1位置,可以发现:价带顶主要源于O 2p和In 4d态的贡献,导带底主要源于In 5s和Sn 5s态(以及Zr 4d,Ta 5d)的贡献。掺杂原子的掺入引起了费米能级以及导带底和价带顶的偏移,这是高价掺杂材料本征光电性能改善的原因所在。根据处于特定介质环境中ITO薄膜的相对电阻变化和表面分析,掺杂ITO薄膜显示了较好的化学稳定性和热稳定性。除了晶体结构的影响之外,稳定性较好的氧化锆和氧化钽也提高了薄膜的化学稳定性和热稳定性。基于薄膜表面接触角的测量,计算了薄膜的表面能和极性度,实验数据和计算结果表明,掺杂使得薄膜的接触角减小,表面能增大,表面极性度增加。薄膜的表面状态和在靠近费米能级处引入d轨道的活性高价原子的存在是促进表面能提高的主要原因。更多还原

【Abstract】 Since 1990s, the rapid development of panel displays promotes the progress of optical-electrical films. Due to high carrier concentration and wide optical band gap, transparent conductive oxide films exhibit outstanding optical and electrical properties such as low resistivity and high transmittance in the visible range. ITO (Sn doped In2O3) films possess the better optical and electrical properties, which make them have wide applications as the transparent electrodes. But some critical factors, such as chemical and thermal instability and lower surface energy, limit the wider application of ITO films, and optical-electrical properties also should be further improved. The improvement of over-all properties of ITO films is one of the key points. In this paper, In2O3-based multi-component oxides films were deposited by magnetron sputtering.The first-principles calculations regarding electronic band structure are performed. The characteristics of ITO films strongly depend on its oxidation state and the content of impurities. Carrier concentration can be modified by the dopant activation state, which is due to a donor atom to substitute the lattice site and produce some free electrons to increase carrier concentration. In this study, zirconium and tantalum are regarded as the donor, which replaces indium in the In2O3 matrix. As a result, some free electrons are released to contribute the electrical conductivity. The ionic radius of Zr4+ or Ta5+ is lower than that of In3+, which implies that a limited solid solution can be formed. In order to realize the effective doping of high valence metal elements, the dual sputtering sources with two targets, including a DC power and a RF power, were used for co-sputtering with an ITO target and a Zr target or Ta2O5 target.ITO, ITO:Zr and ITO:Ta films were deposited on glass substrates by magnetron sputtering. Electrical and optical properties of the films at different experiment parameters were contrastively studied. The results show that the doping of high-valence metal element favors a better crystalline structure for ITO films and leads to the formation of the (400) plane preferred orientateon. ITO:Zr and ITO:Ta films show better electrical and optical properties at low substrate temperature than ITO films. The dopings of Zr and Ta improve the figure of merit of ITO films deposited at room temperature from 0.003×10-3Ω-1 to 0.15×10-3Ω-1 and 0.88×10-3Ω-1. The increase in substrate temperature remarkably improves the electrical and optical properties. The excessive oxygen can worsen the optical properties of the films. Better optical-electrical properties of the films can be achieved after the proper annealing treatment, but the atmosphere annealing treatment with overhigh temperature can worsen the electrical property. Obvious“Burstin-Moss”effect can be revealed by transmittance spectra with different parameters, and the direct transition models show the change of optical band gap of the films. ITO:Zr and ITO:Ta films prepared by co-sputtering reveal better optical-electrical properties and higher optical band gap than that of ITO films. Under the same parameters, ITO:Ta films show lower conductivity but higher transmission in the visual region than that of ITO:Zr films.The first-principles calculations were performed for In2O3-based transparent conductive oxides. The characters of the highest valence states and lowest conduction band are the key characteristics of the band structure responsible for its optical-electrical properties. When Sn, Zr or Ta is introduced into the lattice, it prefers to occupy the less distorted In1 site of In2O3. It is found that the tops of the valence states of those materials are mainly formed by O 2p states and In 4d states. The bottoms of the conduction bands are due to In 5s states hybridized with Sn 5s states (and Zr 4d or Ta 5d). The introduction of Zr or Ta into ITO stimulates the shifts of the Fermi level, conduction band bottom and valence band top, which is related with the improvement in eigen electrical and optical properties observed in the high-valence metal element doped materials.According to the result of the relative resistance change of ITO films in the special medium environments and the analysis of the film surface, the doping films show better chemical and thermal stability than that of ITO films. Besides the influence of crystal structure, the better stability of zirconium oxide and tantalum oxide can improve the chemical and thermal stability of ITO films. Based on the measurements of the contact angles, the surface energy and surface polarity of the films were calculated. The experimental data and calculated results show that the doping decreases contact angle, increases surface energy and enhances surface polarity. The surface condition and the present of active high-valence atom with d-orbital states close to Fermi lever are the main contributions to improve the surface energy.更多还原