Uniform epitaxy and controllable iron doping of centimeter-size bilayer tungsten disulfide with unidirectional alignment

Bilayer transition-metal dichalcogenides (TMDCs) are promising channel materials for state-of-the-art transistors, due to their smaller bandgap, higher carrier mobility, and better electrostatic control than those of the monolayer counterparts. Epitaxial growth and controllable doping of wafer-scale bilayer TMDCs single crystals are two pivotal tasks to meet the practical applications of high-performance electronic devices. Despite considerable efforts have been made, addressing such fundamental issues simultaneously has yet to be realized. Here we design an ingenious Fe-assisted epitaxial strategy to synthesize centimeter-size uniform bilayer tungsten disulfide (WS₂) with unidirectional alignment on industry-compatible c-plane sapphire. The introduction of Fe promotes the formation of parallel steps on sapphire surfaces to induce the edge-nucleation of unidirectionally aligned bilayer WS₂ and the evolution of centimeter-size uniform films. The ionic liquid gated transistors with ultrahigh electron mobility (169 cm²·V⁻¹·s⁻¹) and remarkable on/off current ratio (10⁸) are constructed based on the centimeter-size bilayer Fe-WS₂, due to the reduction of Schottky barrier width induced by Fe doping. This work provides a simple and general approach for synthesizing and doping of wafer-scale bilayer TMDCs, which should accelerate the further device downscaling to extend Moore’s law.