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 challenge 15 . Here we report the uniform nucleation (>99%) of bilayer molybdenum disulfide (MoS 2 ) 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 MoS 2 domains into continuous, centimetre-scale films. Fabricated field-effect transistor (FET) devices based on bilayer MoS 2 channels show substantial improvements in mobility (up to 122.6 cm 2  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 FETs 16 .