Improved luminescence properties of MoS2 monolayers grown via MOCVD: role of pretreatment and growth parameters

Fabrication of transition metal dichalcogenides (TMDCs) via metalorganic chemical vapor deposition (MOCVD) represents one of the most attractive routes to large-scale 2D material layers. Although good homogeneity and electrical conductance have been reported recently, the relation between growth parameters and photoluminescence (PL) intensity-one of the most important parameters for optoelectronic applications-has not yet been discussed for MOCVD TMDCs. In this work, MoS2 is grown via MOCVD on sapphire (0001) substrates using molybdenum hexacarbonyl (Mo(CO)(6), MCO) and di-tert-butyl sulphide as precursor materials. A prebake step under H-2 atmosphere combined with a reduced MCO precursor flow increases the crystal grain size by one order of magnitude and strongly enhances PL intensity with a clear correlation to the grain size. A decrease of the linewidth of both Raman resonances and PL spectra down to full width at half maxima of 3.2 cm(-1) for the E-2g Raman mode and 60 meV for the overall PL spectrum indicate a reduced defect density at optimized growth conditions.