Abstract
Scalable chemical vapor deposition (CVD) of two-dimensional semiconducting materials such as MoS2 and WS2 is a key technology for the application of these materials in real devices. In this work, we demonstrate the growth behavior of WS2 crystals from gaseous precursors, i.e. H2S and WF6, under alkali-metal-free conditions. The WS2 crystal growth exhibits layer-by-layer growth, and its behaviors, such as nucleation and lateral growth, are a thermally activated process: the temperature-dependent grain size and density are well fitted by the Arrhenius equation. The obtained WS2 crystal shows quality comparable to that obtained from metal oxides: the WS2 film shows sharp photoluminescence with a peak width of 54 meV and n-type field-effect transistor operation. Optimizing the growth conditions enabled us to obtain WS2 crystals with a grain size of ∼1.5 μm, which is the largest size ever reported for a transition-metal dichalcogenide grown by gas-source CVD without an alkali-metal promotor.
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