Development and analysis of MOCVD growth processes for binary and ternary 2D Transition Metal Dichalcogenides (TMDC)

近年来，二维材料，特别是过渡金属二卤化物(TMDC)在基础研究和新器件概念的开发中的重要性与日俱增。已经发表了许多有趣的结果，通常是基于剥离的材料或通过大多数不可缩放的方法沉积的材料。然而，对于实际应用，开发与工业相关的、可扩展的制造工艺，如金属-有机化学气相沉积(MOCVD)是强制性的，特别是在2D-2D异质结构变得越来越重要的情况下。在我们项目的第一阶段，我们展示了由MOCVD生长的单一异质结构，并将其嵌入到光电探测器中，与由单一2D材料制备的器件相比，显示出显著增强的响应性。在后续项目中，我们的目标是在第一个资助期取得的可喜成果的基础上，系统地将工作扩展到基于可伸缩2D材料的更复杂的双异质结构。这些在目前的文献中几乎没有被探索过，它们提供了迷人的应用前景，以及获得更多深入了解2D材料异质结构的物理的机会。该项目的目的是利用MOCVD技术，通过调节电导和价带偏移量，制备大面积、均匀的二维TMDC量子膜异质结构，并对其结构和光学性质进行分析。通过将合适的量子膜和势垒材料相结合，我们将调整能带偏移量，以定位量子膜中的电子或空穴(或两者)。这一目标应通过分三步走的项目计划来实现。首先，必须优化各层的横向生长，以实现受控的全单层覆盖。主要的挑战，特别是在涉及异质结构的情况下，是保持TMDC的逐层生长，目前TMDC受到寄生的双层和三层成核的阻碍。在下一阶段，将实现由两种不同材料组成的单一异质结。利用光电子能谱、时间积分和时间分辨光谱分析了能带偏移量及其对载流子分布的影响。在最后一步中，我们将开发类量子井型对称双异质结。通过与单一异质结的比较，分析了激子态的预期变化以及与环境的相互作用。通过选择不同的材料，我们想要研究是否只能实现II型或甚至I型类双异质结。

In recent years, 2D materials, in particular transition metal dichalcogenides (TMDC), have gained steadily growing importance in fundamental research and in the development of novel device concepts. Many interesting results have been published, often based on exfoliated material or on materials that have been deposited by mostly non-scalable methods. For practical use, however, the development of industrially relevant, scalable manufacturing processes like metal-organic chemical vapor phase deposition (MOCVD) is mandatory, especially as 2D-2D heterostructures are becoming increasingly important. During the first phase of our project, single heterostructures grown by MOCVD were demonstrated and embedded into photodetectors showing significantly enhanced responsivity as compared to devices prepared from a single 2D material. In the follow-up project, we aim to build upon our promising results from the first funding period and systematically extend the work to more complex double heterostructures based on scalable 2D materials. These are virtually unexplored in literature at the moment and offer fascinating application prospects as well as the opportunity to gain more insight into the physics of 2D-material heterostructures. The aims of the project are to develop large-area and homogeneous 2D TMDC quantum film heterostructures via MOCVD with specifically adjusted conduction and valence band offsets, and to analyze their structural and optical properties. By combining appropriate quantum film and barrier materials, we will tune the band offsets to localize either electrons or holes (or both) within the quantum film. This goal shall be achieved via a three-step project plan. First, the lateral growth of individual layers has to be optimized so that controlled full monolayer coverage is achieved. The main challenge, in particular when heterostructures are involved, is preserving layer-by-layer growth of the TMDC, which is currently hampered by parasitic bilayer and trilayer nucleation. In the next stage, single heterostructures consisting of two different materials will be realized. The band offsets and their impact on the charge carrier distribution will be analyzed by photoelectron spectroscopy and by using time-integrated and time-resolved optical spectroscopy, respectively. In the last step, we will develop quantum-well-like symmetric double heterostructures. The expected changes in the excitonic states and the modified interaction with the environment will be analyzed in comparison with single heterostructures. By choosing different materials, we want to investigate whether only type II- or even type I-like double heterostructures can be realized.