Large-Area Synthesis of 2D Transition Metal Dichalcogenides Using Plasma-Enhanced Atomic Layer Deposition

2D materials have been the focus of intense research in the last decade due to their unique physical properties. This presentation will highlight our recent progress on the large-area synthesis of two-dimensional transition metal chalcogenides for nanoelectronics using plasma-enhanced atomic layer deposition (PEALD). In particular, we demonstrate wafer-scale deposition of polycrystalline MoS2 thin films at very low temperatures down to 100 °C using PEALD. ALD is a scalable, semiconductor industry compatible gas-phase method producing uniform, high-quality thin films with accurately controlled thickness. Our PEALD process is based on self-limiting, alternating surface reactions of a metalorganic molybdenum precursor Mo(NtBu)2(NMe2)2 and mixed H2S/H2/Ar plasma. We have identified the critical role of hydrogen during the plasma step in controlling the composition and properties of molybdenum sulfide films. By increasing the H2/H2S ratio, we are able to deposit polycrystalline MoS2 films at temperatures as low as 100 °C. To the best of our knowledge, this represents the lowest temperature for crystalline MoS2 films prepared by any chemical gas-phase method.[1]<br/>ALD-grown 2D films typically exhibit a high density of out-of-plane 3D structures in addition to 2D horizontal layers. While the out-of-plane 3D structures are ideal for catalysis applications, the presence of such 3D structures can hinder charge transport, which hampers device applications. In this presentation I will show how we used mechanistic insight obtained by HRTEM to tune the shape and density of the 3D structures during plasma-enhanced ALD. The obtained morphology control was further confirmed by electrical measurements.[2]<br/>Earlier [3] we have shown that ALD is an excellent technique to make MoxW1-xS2 alloys with precise control over the alloy composition. Here, I will focus on how (plasma-enhanced) atomic layer deposition can aid in synthesizing p-doped 2DTMCs with precise control over the doping concentration, which is an asset for 2D TMD based device applications.<br/><br/>[1] M. Mattinen <i>et al., Chem. Mater</i>. (2022), <b>34</b>, 5104<br/>[2] S. Balasubramanyam<i> et al. ACS Appl. Mater. Interfaces </i>(2020), <b>12</b>, 3873<br/>[3] J. J. P. M. Schulpen <i>et al.</i> <i> 2D Mater.</i> (2022), <b>9,</b> 025016