Title: Overcoming the Manufacturing Barrier in 2D TMD Based Technologies via Multi-wafer Vertical Showerhead MOCVD with In Situ Process Monitoring

Program: Materials Science and Engineering PhD

Committee Chair: Dave Estrada

Committee: Dave Estrada, Dmitri Tenne, Brian Jaques, Michael Snure, Albert Liao

Abstract: Two-dimensional transition metal dichalcogenides (TMDs) are promising candidates for next-generation scaled electronic and optoelectronic devices due to their atomic thickness, direct bandgaps, and compatibility with heterogeneous integration. Despite continuous advances in monolayer synthesis, the transition of 2D TMDs from laboratory scale demonstrations to practical technologies has yet to occur. Achieving wafer-scale uniformity and a high degree of crystalline control remains a challenge on industrial deposition platforms. At the same time, exerting control over the material properties of the 2D layer for device engineering is not compatible with the methods used in legacy semiconductor technologies. A key unresolved challenge is the development of scalable MOCVD processes that simultaneously achieve single-crystal monolayer growth in a system capable of enabling deterministic control of electronic device parameters. In this work it is demonstrated that wafer-scale TMD monolayers can be synthesized in an industry-relevant multi-wafer MOCVD system through a novel epitaxy mechanism, and that intrinsic electronic properties can be engineered via compositionally controlled TMD alloys to directly modulate transistor threshold voltage. By leveraging a hydride precursor and precise reactor conditions, the sapphire substrate and TMD overlayer are made to co-evolve toward a thermodynamically favorable configuration, producing epitaxially aligned, single-crystal MoS2 monolayers with reduced defect density and improved electrical performance. This modular process is then translated to other members of the TMD family. Finally, applying this technique to binary TMD alloys enables systematic tuning of the optical bandgap and corresponding threshold voltage from negative to positive values, demonstrating direct coupling between composition and device behavior. These results provide a method for scalable synthesis and device-level engineering within an industrially compatible MOCVD platform without the need for boutique substrate preparation or ex-situ processing, removing barriers to the integration of 2D semiconductors into high-volume semiconductor manufacturing. This approach represents incremental progress toward the maturation of 2D material-based technologies.