MOVPE growth and characterization of (AlxGa1-x)2O3 thin films for high power devices

β型氧化镓（β-Ga 2 O3）为高功率应用提供了优于当前关键技术的前景，因为预测β-Ga 2 O3具有相当强的电击穿场。此外，与其他有前途的材料相比，它提供了潜在的低成本和大衬底尺寸的制备与可控的n型掺杂的大块晶体。高功率器件的性能直接取决于击穿电场的三次方以及载流子的迁移率。将铝掺入β-Ga 2 O3中可以调节带隙，从而调节击穿场。因此，需要合适的材料生长方法，从而产生具有优化的带隙和不妥协的材料性质的高质量二元氧化物薄膜。在这个项目中，我们提出了一种基于金属有机气相外延（MOVPE）的β-（AlxGa 1-x）2 O3（AlGaO）薄膜在晶格匹配的（100）取向的β-Ga 2 O3上，能够在高于800°C的温度下生长，并增强铝在β-Ga 2 O3中的溶解度。为此，我们将首先生长体铝掺杂的β-Ga 2 O3单晶，其表现出与目标AlGaO膜的最小晶格失配。随后，MOVPE将在这些衬底上准同质外延生长高质量的AlGaO薄膜，这要归功于复杂材料表征的详细见解。我们协调一致，系统地使用原子力，电子和光电子显微镜，原位X射线和电子衍射，光谱椭圆偏振仪以及光电子能谱技术将有助于揭示AlGaO薄膜的生长模式，形态，成分以及结构，电子，电学和光学性质。具体而言，我们将确定Al分布的限制因素及其在不发生相分离的情况下最大可能地掺入β-Ga 2 O3中。然后，我们将探索在AlGaO系统中进行带隙和应变工程的可能性，研究AlGaO在β-Ga 2 O3系统上的表面形貌以及界面，并进行电学和结构分析以了解缺陷形成的过程和杂质的作用。我们的战略有三个方面：（1）制备可外延的掺铝（高达15%）的块状β-Ga 2 O 3晶体（直径2 cm至2英寸），作为随后准同质外延生长AlGaO薄层的衬底，并表征所获得的薄膜，以（2）优化生长和（3）评估与应用相关的性质。特别是，该项目的重点是制备和表征的外延AlGaO与最大的铝掺入导致最高可能增加的带隙和击穿场。

Beta-type gallium oxide (β-Ga2O3) provides promising perspectives for high-power applications outperforming current key technology because for β-Ga2O3 a considerably stronger electrical breakdown field is predicted. In addition, it offers potentially low cost and large substrate size preparation from bulk crystals with controllable n-type doping in comparison to other promising materials. The performance of high-power devices directly depends on the breakdown field to the power of three as well as on the mobility of the charge carriers. The incorporation of aluminum into β-Ga2O3 allows tuning the band gap and consequently the breakdown field. Therefore, a suitable material growth method is required resulting in high-quality binary oxide thin films with optimized band gap and uncompromised materials properties.Hence, in this project we propose to develop a novel approach based on metal-organic vapor phase epitaxy (MOVPE) of β-(AlxGa1-x)2O3 (AlGaO) thin films on lattice-matched (100)-oriented β-Ga2O3 enabling the growth at temperatures above 800°C with an enhanced solubility of aluminum in β-Ga2O3. For this purpose, we will initially grow bulk aluminum-doped β-Ga2O3 single crystals exhibiting a minimal lattice mismatch with the targeted AlGaO films. Subsequently, the quasi-homoepitaxial growth of high-quality AlGaO thin films on these substrates by MOVPE will be engineered and optimized thanks to the detailed insights from sophisticated materials characterization. Our concerted, systematic use of atomic force, electron, and photoemission microscopy, in situ x-ray and electron diffraction, spectroscopic ellipsometry as well as photoelectron spectroscopy techniques will facilitate to unravel the growth mode, morphology, composition as well as the structural, electronic, electrical, and optical properties of the AlGaO thin films.Specifically, we will determine the limiting factors for Al distribution and its maximally possible incorporation into β-Ga2O3 without phase separation. Then, we will explore the possibilities for band gap and strain engineering in the AlGaO system, investigate the surface morphology as well as the interface of the AlGaO on β-Ga2O3 system, and perform electrical and structural analysis to understand the process of defect formation and the role of impurities. Our strategy is threefold: (1) preparation of epitaxy-ready aluminum-doped (up to 15%) bulk β-Ga2O3 crystals (2 cm to 2 inches in diameter) as substrates for the subsequent quasi-homoepitaxial growth of AlGaO thin layers and characterization of the obtained films to (2) optimize the growth and to (3) evaluate the application-relevant properties. Particularly, the project focuses on the preparation and characterization of epitaxial AlGaO with maximum aluminum incorporation resulting in the highest possible increase of the bandgap and the breakdown field.