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

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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.