Precursor Chemistry and the CVD of Transparent Conducting Oxides

该项目将涉及替代前体和沉积技术的研究，以提高性能并开发下一代透明导电氧化物（TCO）薄膜。氧化铟锡（ITO）是目前大多数工业应用的TCO选择，但它有许多局限性，例如适度的电导率（2000-4000 S/cm）、相对较低的功函数和蓝绿色光谱区域中的一些光学吸收。此外，铟是昂贵的，因为它的供应相对短缺，这对下一代光伏技术和平板显示器的大规模生产提出了重大挑战。因此，开发具有改进的光学和电学性质的不含铟的替代TCO材料至关重要。ITO的替代物包括掺杂的ZnO（ZnO：Al、ZnO：Ga、ZnO：SnO 2）和掺杂的SnO 2（SnO 2：Sb、SnO 2：F、ZnO-SnO 2），并且这些中的许多已经以它们的本体形式被研究。然而，这些材料中的一些作为薄膜的研究是有限的，并且对于许多应用来说，需要薄膜。制备用于大规模应用的薄膜的理想方法是化学气相沉积（CVD），因为可以实现具有良好均匀性和成分控制、大面积生长和台阶覆盖的薄膜。然而，对于成功的CVD工艺，挥发性前体是必需的，对于大气压CVD，挥发性前体优选为液体或低熔点固体，或者对于基于液体（气溶胶辅助）的CVD，挥发性前体是高度可溶的。TCO材料的当前前体，特别是铟和锌，仍然遭受化学不稳定性、生长过程中的差的再现性以及对于膜生长而言不太有利的蒸气压和反应性。本工作旨在开发基于金属酮亚胺盐的高挥发性和可溶性前体。使用酮亚胺配体的优点包括：-可以以高产率形成反应性络合物-当单体物质被分离时可以形成具有高蒸气压的络合物-可以通过调节连接到氮原子上的基团来增加金属络合物的热稳定性-由于络合物的高化学反应性，可以增强金属前体和衬底表面之间的表面反应。我们有能力放下薄膜使用一个新的组合气溶胶辅助（AA）CVD反应器的解决方案为基础，也组合APCVD反应器，使薄膜的梯度组成。这种新的反应器可以在一个CVD实验中在一个平板上制作多达400种不同的成分。这一点很重要，因为它将使我们能够快速筛选组合空间，为TCO应用提供理想和优化的组合。这种组合方法将使我们能够研究不同的组合，并实现下一代TCO材料。

This project will involve the investigation of alternative precursors and deposition technologies in order to improve performance and enable next generation transparent conducting oxide (TCO) films to be developed. Indium tin oxide (ITO) is the current TCO of choice for most industrial applications but it has many limitations, such as modest conductivity (2000-4000 S/cm), a relatively low work function and some optical absorption in the blue-green spectral region. In addition, indium is expensive since it is in relatively short supply, which presents a significant challenge for larger-scale production of next generation photovolatic technologies and flat panel displays. It is therefore crucial to develop alternative TCO materials with no indium with improved optical and electrical properties. Alternatives to ITO include doped ZnO (ZnO:Al, ZnO:Ga, ZnO:SnO2) and doped SnO2 (SnO2:Sb, SnO2:F, ZnO-SnO2) and many of these have been investigated in their bulk form. However, studies of some of these materials as thin films is limited and for many of the applications thin films are required. An ideal method for preparing thin fims for large scale applications is chemical vapour deposition (CVD) given that films with good uniformity and compositional control, large area growth and step coverage can be achieved. However, for a successful CVD process, a volatile precursor is necessary which is prefereably a liquid or low metling solid for atmospheric pressure CVD or highly soluble for liquid based (aerosol assisted) CVD. Current precursors to TCO materials, particularly indium and zinc still suffer from chemical instability, poor reproducibility in the growth process and less than favourable vapour pressures and reactivity for film growth. This work aims to develop highly volatile and soluble precursors based on metal ketoiminates. The advantages of using the ketoiminate ligand include:- reactive complexes can be formed in high yield- complexes with a hign vapour pressure can be formed as monomeric species are isolated- thermal stability of the metal complexes can be increased by tuning the groups attached to the nitrogen atoms- the surface reaction between the metal precursor and the surface of the substrate can be enhanced due to the high chemical reactivity of the complexes.TCO materials to be investigated include doped-ZnO and doped-SnO2. We have the ability to lay down thin films using a new combinatorial aerosol-assisted (AA)CVD reactor for solution based and also a combinatorial APCVD reactor to make films of graded composition. This new reactor enables upto 400 different compositions to be made on a single plate in one CVD experiment. This is important as it will enable us to rapidly screen composition space make idealised and optimised compositions for TCO applications. This combined approach will enable us to investigate different combinations and go towards achieving the next generation TCO materials.