Uniform nucleation and epitaxy of bilayer molybdenum disulfide on sapphire

Two-dimensional transition-metal dichalcogenides (TMDs) are of interest for beyond-silicon electronics^1,2. It has been suggested that bilayer TMDs, which combine good electrostatic control, smaller bandgap and higher mobility than monolayers, could potentially provide improvements in the energy-delay product of transistors^3-5. However, despite advances in the growth of monolayer TMDs^6-14, the controlled epitaxial growth of multilayers remains a challenge¹⁵. Here we report the uniform nucleation (>99%) of bilayer molybdenum disulfide (MoS₂) on c-plane sapphire. In particular, we engineer the atomic terrace height on c-plane sapphire to enable an edge-nucleation mechanism and the coalescence of MoS₂ domains into continuous, centimetre-scale films. Fabricated field-effect transistor (FET) devices based on bilayer MoS₂ channels show substantial improvements in mobility (up to 122.6 cm² V^-1 s^-1) and variation compared with FETs based on monolayer films. Furthermore, short-channel FETs exhibit an on-state current of 1.27 mA μm^-1, which exceeds the 2028 roadmap target for high-performance FETs¹⁶.