Monolayer molybdenum disulfide (MoS) is an atomically thin, direct bandgap semiconductor crystal potentially capable of miniaturizing optoelectronic devices to an atomic scale. However, the development of 2D MoS-based optoelectronic devices depends upon the existence of a high optical quality and large-area monolayer MoS synthesis technique. To address this need, we present a thermal vapor sulfurization (TVS) technique that uses powder MoS as a sulfur vapor source. The technique reduces and stabilizes the flow of sulfur vapor, enabling monolayer wafer-scale MoSgrowth. MoS thickness is also controlled with great precision; we demonstrate the ability to synthesize MoS sheets between 1 and 4 layers thick, while also showing the ability to create films with average thickness intermediate between integer layer numbers. The films exhibit wafer-scale coverage and uniformity, with electrical quality varying depending on the final thickness of the grown MoS. The direct bandgap of grown monolayer MoS is analyzed using internal and external photoluminescence quantum efficiency. The photoluminescence quantum efficiency is shown to be competitive with untreated exfoliated MoS monolayer crystals. The ability to consistently grow wafer-scale monolayer MoS with high optical quality makes this technique a valuable tool for the development of 2D optoelectronic devices such as photovoltaics, detectors, and light emitters.
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