The rapid cadence of MOSFET scaling is stimulating the development of new technologies and accelerating the introduction of new semiconducting materials as silicon alternative. In this context, transition metal dichalcogenides (TMDs) with a unique layered structure have attracted tremendous interest in recent years mainly motivated by the characteristic 2D nature together with distinctive and tunable optoelectronic properties which make them appealing for a wide variety of applications. Their ultra-thin body nature, in particular, is expected to provide superior immunity to short channel effects therefore extending the potential to scale transistors down to the few-nanometer-scale. [1-4] Another key feature of 2D materials is the absence of surface dangling bonds. The latter property has the potential to eliminate lattice mismatch constraints thus paving the way for hybrid integration of TMDs into artificial heterostructures with sharp interfaces and designed band alignment. As researchers explore the physics and applications of layered semiconductors, it is now becoming important to find a wafer-scale path towards technology implementation and integration of these novel materials.

In this context, it has been recently demonstrated that metal-organic chemical vapor deposition (MOCVD) can be used to manufacture large area 2D semiconductor materials. [5]. The goal of this work is to unravel some of the fundamental aspects of film formation and provide a pathway towards a layer-controlled, wafer-scale synthesis of TMD films. More in details, we will provide insights on the different growth mechanisms of TMD films on amorphous and crystalline templates. In this framework, we will discuss the key aspects to enable and control a real van der Waals epitaxy of TMD films. The target, of course, is to achieve unidirectional and high quality monocrystalline domains by forcing an epitaxial relationship between the 2D film and the underlying substrate. In-depth structural AFM, XPS, TEM analyses along with Raman, Photoluminescence and lifetime measurements are used in our study. In order to establish a direct link between electrical performance and material quality, FET devices using our layers are also fabricated. A careful link between the structural analyses and the electrical results is made in order to asses material quality and offer a step further on the understanding of 2D TMDs for nanoelectronics.

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2. R. Ganatra and Q. Zhang, ACS Nano, 8, 4074 (2014).
3. A. Nourbakhsh et al. Nano Lett., 16 7798 (2016).
4. A. Nourbakhsh et al. Nanoscale, 18, 6122 (2017).
5. K. Kang et al. Nature volume 520, 656 (2015)