Glass-assisted CVD growth of large-area MoS2, WS2 and MoSe2 monolayers on Si/SiO2 substrate

In the last few years, there has been much effort to overcome the challenge of growing large-area transition metal dichalcogenide (TMDC) monolayers with a high-coverage to allow for their wide-usage in practical devices and applications. In this study, we investigate effects of two different glass lamellas on the formation of different monolayer TMDCs, namely MoS2, WS2 and MoSe2 for the CVD process in a horizontal growth configuration. Our approach is different from the widely used techniques of placing the substrate on the top the precursors (face-down configuration, generally causing non-uniform growth) or growing monolayers directly on glass lamellas which generally requires transfer step of the flakes if relevant devices will be fabricated on Si/SiO2 substrates. We confirm that rather than the glass surface effect, the glass lamellas ingredients enable the formation of monolayer TMDCs. Moreover, the repeatability problem of growing large-size monolayer flakes with uniform distribution and high coverage is successfully surpassed. For a comparison of ingredient compositions, two different glass lamellas (Glass-1 and 2) are used where the amount of Na and other ingredients are different. Our results show that although the uniformity and flake sizes change with the composition of the glass lamellas, MoS2, WS2 and MoSe2 monolayer flakes have been grown successfully for both of the glass lamella types. Thus, the catalytic effect of using a glass lamella in the CVD process is verified for three different TMDCs. Our monolayer TMDCs also show long-term stability where no-crack formation is observed since their initial growth, which is more than a year.