Hydrogen-assisted Epitaxial Monolayer Growth of MoSe2 on sapphire

초록

Monolayer Transitional metal chalcogenides(TMDs) have been a focus due to their direct bandgap, photoluminescence(PL) emissions, and its potential for application for electronic devices. The chemical vapor deposition(CVD) method is has been widely used to synthesize TMDs monolayer. We have prepared MoSe2 mono- or few-layers on c-plane sapphire wafer under variable flow rate of H2. Synthesized MoSe2 have been investigated with SEM, Raman and PL analysis. SEM images show the coverage of MoSe2 are increased as increasing hydrogen flow rate or growth time. Raman peak intensity in MoSe2 under higher H2 flow rate is stronger, also exhibit a bigger FWHM. PL peaks are observed around 800 nm, corresponding with A-excition emission of monolayer MoSe2. According to the result, MoSe2 grows larger and faster under the existence of hydrogen than the absence of hydrogen. As the reduction of MoO3, Mo precursor, for generating nuclei and growth of MoSe2 is promoted under hydrogen condition. To synthesize epitaxial monolayer MoSe2 on sapphire, no H2 flows at early nucleation step and H￢2 flows at the latter growth step. This strategy provides the growth of epitaxial MoSe2 monolayer due to slow nucleation rate under no hydrogen condition at the nucleation step.