Transition metal dichalcogenides (TMDs) form a compelling class of 2D materials with potential applications in optoelectronics, flexible electronics, chemical sensing and quantum technologies. At the monolayer limit, the semiconducting TMDs (e.g., MX2 where M = Mo/W and X = S/Se) exhibit direct band gaps within the visible range, large exciton binding energies and valley polarization. Current research on TMD monolayers is often carried out using flakes exfoliated from bulk crystals which is a limiting factor for device fabrication. Our research is aimed at the development of an epitaxial growth technology for TMDs based on metalorganic chemical vapor deposition (MOCVD). The high growth temperatures (&gt;700oC) and chalcogen/metal precursor ratios (&gt;10,000) attainable in an MOCVD environment are advantageous for promoting metal surface diffusion needed for epitaxy while maintaining growth stoichiometry. Our studies employ metal hexacarbonyls and hydrides (H2S, H2Se) as precursors in an H2 carrier gas. A multi-step precursor modulation growth method was developed to independently control nucleation density and the lateral growth rate of monolayer domains on the substrate for growth on 2” diameter sapphire substrates. Using this approach, uniform, coalesced monolayer and few-layer films of WS2, MoS2, WSe2 and MoSe2 were obtained on 2” sapphire at growth rates on the order of 0.02-0.1 monolayer/min. The films are epitaxially oriented with respect to the sapphire as determined by in-plane x-ray diffraction and exhibit intense room temperature photoluminescence with negligible defect-related emission at 80K. The field effect mobility in MoS2 and WS2 monolayers, as measured at room temperature in back-gated devices that employ a 50 nm Al2O3 dielectric, is in the range of 20-30 cm2/Vs. Van der Waals epitaxy of TMDs on hBN and TMD monolayers has also been investigated. In the case of WSe2 epitaxy on hBN, single atom B and N vacancies in the hBN can trap metal atoms and thereby serve as nucleation sites for the WSe2 domains. The vacancy-assisted nucleation also imparts directionality to the WSe2 domains which results in a significant decrease in inversion domains in the films. Epitaxial growth of vertical TMD heterostructures will also be discussed.

Epitaxial growth of transition metal dichalcogenide monolayers by metalorganic chemical vapor deposition

Macromolecular Chemistry: The Second Century

[Author Benefits](https://scimeetings.acs.org/?utm_source=pubs_content_marketing&utm_medium=website&utm_campaign=0320_MCF_NPI_Launch_Spring_Homepage&ref=pubs_content_marketing)

[How to use SciMeetings](https://storage.googleapis.com/dl.morressier.com/acs/SciMeetings-ACSSpring2020-HowToGuide_M3020-Final.pdf)

[Frequently Asked Questions](https://storage.googleapis.com/dl.morressier.com/acs/SciMtng_ACSNMSp2020_FAQ_M3120_Final.pdf)

ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.