Advances in MOCVD growth of epitaxial 2D transition metal dichalcogenides

Metalorganic chemical vapor deposition (MOCVD) has emerged as a promising technique for wafer-scale synthesis of 2D transition metal dichalcogenides (TMDs) for device applications. Two general approaches have been pursued: direct growth on oxide-covered substrates at BEOL-compatible temperatures or high temperature epitaxy on single crystal substrates followed by layer transfer. Our work has focused on the later approach with the goal of achieving wafer-scale single crystal TMD films that can be transferred and integrated at BEOL conditions. These efforts are illustrated for epitaxial growth of MoS₂ and WSe₂ on 50 mm diameter c-plane sapphire using metal hexacarbonyls and hydride chalcogen sources in a H₂ carrier gas. The epitaxial orientation of the TMD is found to be strongly dependent on the pre-growth annealing ambient (H₂ vs H₂S/H₂Se) and the growth temperature which can be tuned to minimize inversion domains and high angle grain boundaries which negatively impact field-effect mobility. Spectroscopic ellipsometry is demonstrated as a promising in situ monitoring tool for TMD growth, enabling real time measurements of monolayer and bilayer surface coverage as well as insights into the epitaxial growth process.