Abstract
The rise of atomically thin materials has the potential to enable a paradigm shift in modern technologies by introducing multi-functional materials in the semiconductor industry. To date the growth of high quality atomically thin semiconductors (e.g. WS2) is one of the most pressing challenges to unleash the potential of these materials and the growth of mono- or bi-layers with high crystal quality is yet to see its full realization. Here, we show that the novel use of molecular precursors in the controlled synthesis of mono- and bi-layer WS2 leads to superior material quality compared to the widely used direct sulfidization of WO3-based precursors. Record high room temperature charge carrier mobility up to 52 cm2/Vs and ultra-sharp photoluminescence linewidth of just 36 meV over submillimeter areas demonstrate that the quality of this material supersedes also that of naturally occurring materials. By exploiting surface diffusion kinetics of W and S species adsorbed onto a substrate, a deterministic layer thickness control has also been achieved promoting the design of scalable synthesis routes.
Highlights
Thin layers of metal group VI disulfides and diselenides (MoS2, WS2, WSe2, MoSe2,) are being extensively investigated as they present unconventional optoelectronic properties compared to commonly used low-dimensional semiconductors[1,2]
One of the most promising transition metal dichalcogenides (TMDCs) is WS2 owing to light emission in the monolayer form at ~2 eV and the low level of toxicity of growth processes
Any envisioned application relies on materials with high crystal and optical quality extended over wafer-size areas
Summary
Thin layers of metal group VI disulfides and diselenides (MoS2, WS2, WSe2, MoSe2,) are being extensively investigated as they present unconventional optoelectronic properties compared to commonly used low-dimensional semiconductors[1,2]. Monolayer sulfides and selenides show strong light absorption from the visible to the near IR range[1,5,6], valley polarization[7,8], second-harmonic generation[9], tightly bound excitons[10] and strong spin-orbit interaction[11,12]. These properties arise from their intrinsic two-dimensional nature inherently free from dangling bonds and their particular d-orbitals configuration[3,13]. The growth is enabled by molecular precursors, which lead to a complete sulfidization of W and formation of WS2 with lower number of defects compared to the traditionally used direct sulfidization of WO3
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