Micrometer-scale WS₂ atomic layers grown by alkali metal free gas-source chemical vapor deposition with H₂S and WF₆ precursors

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. (author)