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

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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.