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，以提高性能并使下一代透明导电氧化物(TCO)薄膜得以开发。氧化铟锡(ITO)是目前大多数工业应用中选择的TCO，但它有许多限制，如中等电导率(2,000-4,000 S/厘米)，相对较低的功函数和在蓝绿光谱区域的一些光吸收。此外，铟的价格很高，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更大规模生产构成了重大挑战。因此，开发具有更好的光学和电学性能的不含铟的替代TCO材料是至关重要的。ITO的替代物包括掺杂的氧化锌(ZnO：Al，ZnO：Ga，ZnO：SnO2)和掺杂的SnO2(SnO2：Sb，SnO2：F，ZnO-SnO2)，其中许多已经以体相的形式进行了研究。然而，这些材料中的一些作为薄膜的研究是有限的，对于许多应用来说，薄膜是必需的。化学气相沉积(CVD)是制备大规模薄膜的理想方法，因为它可以获得具有良好的均匀性和成分控制、大面积生长和阶跃覆盖的薄膜。然而，对于成功的CVD过程，挥发性前体是必需的，对于常压CVD来说，它最好是液体或低金属固体，或者对于基于液体的(气雾剂辅助)CVD来说，它是高度溶解的。目前TCO材料的前驱体，特别是铟和锌，仍然存在化学不稳定、生长过程中重复性差以及薄膜生长的蒸气压力和反应性较差的问题。这项工作旨在开发基于金属酮亚胺的高挥发性和可溶性的前体。使用酮亚胺配体的优点包括：-可以在高产率下形成反应性络合物-可以在单体物种被分离时形成络合物-可以通过调节连接在氮原子上的基团来提高金属络合物的热稳定性-由于络合物的高化学反应活性可以增强金属前驱体和衬底表面之间的表面反应。我们有能力使用一种新的组合气溶胶辅助(AA)CVD反应器来制备基于溶液的薄膜，也可以使用组合APCVD反应器来制备梯度成分的薄膜。这种新的反应器可以在一次CVD实验中在一块平板上制造多达400种不同的化合物。这一点很重要，因为它将使我们能够快速筛选合成空间，为TCO应用程序制作理想和优化的合成。这种结合的方法将使我们能够研究不同的组合，并朝着实现下一代总拥有成本材料的方向迈进。

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.