Two-dimensional (2D) materials offer a route to sustain semiconductor device scaling beyond the limits of silicon, providing atomically thin, dangling-bond-free channels and a versatile platform for further device scaling and the heterogeneous integration of electronic and optoelectronic functions. The principal bottleneck to their adoption, however, is the lack of a manufacturing route that simultaneously delivers wafer-scale area and high crystal quality: synthesis methods that produce the highest-quality crystals are difficult to scale, while scalable methods yield polycrystalline films whose grain boundaries degrade the device performance.

This dissertation develops synthesis methods that address this quality-scalability trade-off, progressing from the improvement of chemical vapor deposition (CVD), the most scalable route for 2D materials, to an alternative growth method that combines melt-based crystal quality with thin-film thickness control. First, a patterned, promoter-assisted CVD method is demonstrated in which lithographically defined metal oxide seeds and a mixed sodium chloride-sodium cholate promoter solution enable the growth of monolayer and bilayer WS₂, WSe₂, and MoSe₂ at controlled locations, with flake sizes on the order of 100 μm. Field-effect transistors fabricated from the as-grown bilayer flakes exhibit carrier mobilities up to ~36 cm² V⁻¹ s⁻¹ and on/off ratios exceeding 10⁵. To extend salt-assisted CVD toward silicon manufacturing, in which mobile alkali ions are prohibited, foundry-compatible growth promoters are screened against the eutectic-formation and precursor-retention functions of sodium. MgCl₂ is identified as a candidate promoter that reproduces both roles and supports chalcogenation to MoS₂, and substrate-driven retention on sapphire is established as a complementary route. Finally, a hot-press melt-cool method is introduced for the growth of trigonal selenium (t-Se) thin films, in which mechanical confinement at 178 MPa suppresses dewetting of the molten film while van der Waals substrates select the horizontal chain orientation suited to planar transistors. The method yields films with single-crystal domains on the order of 10² μm, the largest reported for a thin-film t-Se to the best of our knowledge, from which a back-gated field-effect transistor with a 70 nm-thick channel exhibits a p-type behavior with an on/off ratio on the order of 10³. Collectively, this dissertation advances 2D material synthesis from the optimization of the most established scalable route to the demonstration of an alternative crystallization pathway, toward the combination of crystal quality, thickness control, and scalability required for wafer-scale 2D electronics.