Deposition of epitaxial Ga2O3 and (AlxGa1-x)2O3 thin films by ion beam sputtering: a systematic study

离子束溅射是一种沉积技术，它为控制溅射和沉积过程以及研究它们之间的相互关系提供了独特的机会。非晶态、单原子和二元氧化物薄膜的离子束溅射沉积(IBSD)过程已经得到了广泛的研究。在其他方面，它可以表明，该过程提供了一种内在的离子辅助，可以用来调整几个薄膜的性质。在本提案中，这些研究将扩展到两个目标：(I)研究复杂的二元和三元薄膜材料，以及(Ii)研究IBSD工艺参数与技术相关材料的晶体结构和质量之间的关系。调查的对象将是氧化镓(Ga_2O_3)和铝镓氧化物([Al_xGa_1−x]_2O_3)。这些材料因其有趣的特性而引起高度的技术兴趣，例如宽禁带和高击穿场强，这使得它们能够用于例如超高功率电子设备。为了充分开发Ga2O3膜和(AlxGa1−x)2O3膜的潜力，需要高的结晶质量，而这只有通过更好地从根本上了解和控制沉积过程才能实现。其他小组证明，对于不同的单原子和二元材料，IBSD能够生长出高结晶质量的外延薄膜。然而，这些研究忽略了例如先前确定的主要工艺参数之一，即溅射几何形状。因此，需要进行一项全面而深入的系统研究，以揭示离子束溅射沉积Ga2O3膜和(AlxGa1−x)2O3膜的全部潜力。本项目旨在通过研究工艺参数(溅射几何形状、离子种类、离子能量、氧分压、衬底温度、衬底材料)、二次粒子、溅射粒子和分散粒子的性质以及薄膜之间的基本关系，来全面、系统地研究离子束溅射沉积Ga2O3膜和(AlxGa1TiOx2O3膜)薄膜。目的是提高我们对如何利用离子束溅射的独特特性实现薄膜的外延和高结晶质量(更大的颗粒，更低的晶格缺陷)的理解。对于所选择的材料体系，中等能量的成膜物种对生长过程及其调节的贡献是特别感兴趣的。

Ion beam sputtering is a deposition technique, which provides unique opportunities to control the sputtering and deposition processes, and to study the correlations between them. Previous comprehensive investigations of the ion beam sputter deposition (IBSD) process were carried out for amorphous monoatomic and binary oxide films. Among others, it could be shown that the process provides an intrinsic ion-assist, which can be used to tune several thin film properties. In the present proposal, these investigations will be extended with two objectives: (i) study of complex binary and ternary film materials, and (ii) study of relations between IBSD process parameters and crystalline structure and quality of technologically relevant material. The subject of the investigation will be gallium oxide (Ga2O3) and aluminum gallium oxide ([AlxGa1−x]2O3). These materials are of high technological interest because of their interesting properties, such as a wide bandgap and a high breakdown field strength, which enable their use, for instance, in ultra-high-power electronics. To fully exploit the potential of Ga2O3 and (AlxGa1−x)2O3 thin films, high crystalline quality is needed, which can be achieved only through a better fundamental understanding and control of the deposition process. Other groups demonstrated for different monoatomic and binary materials that IBSD is capable to grow epitaxial films with high crystalline quality. However, these studies disregarded, for instance, one of the previously identified major process parameters, namely the sputtering geometry. Therefore, a comprehensive and extended systematic study is needed to reveal the full potential of IBSD with regard to the proposed objectives.The present project aims for a comprehensive, systematic study of ion beam sputter deposition of Ga2O3 and (AlxGa1−x)2O3 films by investigating the fundamental correlations between process parameters (sputtering geometry, ion species, ion energy, partial oxygen pressure, substrate temperature, substrate material), properties of secondary, sputtered and scattered particle species, and thin films. The goal is to improve our understanding of how to achieve epitaxy and high crystalline quality (larger grains, a lower density of lattice defects) of the films by utilizing the unique features of ion beam sputtering. The contributions of moderately energetic film-forming species to the growth process and its tuning are of particular interest for the selected material systems.