Wafer-Scale Epitaxy of 2D Transition Metal Dichalcogenides on Sapphire – An Enabling Technology for Large Area Devices

Monolayer and few-layer semiconducting transition metal dichalcogenides (TMDs), exemplified by materials like MoS₂and WSe₂&lt;span style="font-size:10.8333px"&gt; &lt;/span&gt;have garnered increasing interest for next generation gate-all-around nanosheet devices and heterogeneous integration with silicon CMOS technology. The interest in TMDs arises from their ultra-thin body nature, however, realization of high-performance devices requires advances in TMD synthesis to provide wafer-scale films that can be readily integrated into devices via either direct growth or layer transfer methods.<br/>Our work has focused on the development of metalorganic chemical vapor deposition (MOCVD) as a manufacturing-compatible approach for wafer-scale semiconducting TMDs. The TMDs are grown epitaxially on c-plane sapphire by MOCVD at elevated temperatures (&gt;800 °C) to obtain high crystal quality. Pre-annealing the sapphire surface in H₂S or H₂Se modifies the nucleation behavior of the TMDs on sapphire which is attributed to passivation of dangling bonds on the sapphire surface. Passivation of step terraces can drive nucleation to occur preferentially at step edges on sapphire leading to unidirectional domains and a significant reduction in mirror twin defects. In situ spectroscopic ellipsometry is demonstrated to be an effective real time monitor of TMD growth even at the sub-monolayer level which can be exploited to track surface coverage as a function of time under varying growth conditions. The ability to precisely control and modulate precursor flux during growth is used to synthesize in-plane heterostructures that enable localized exciton confinement and emission. Applications for wafer-scale TMD monolayers in nanoelectronics, sensing and photonics will be discussed.