Diffusion Control on the Van der Waals Surface of Monolayers for Uniform Bi-Layer MoS₂ Growth

2D MoS₂ has gained attention for the post-silicon material owing to its atomically thin nature and dangling bond-free surface. The bi-layer MoS₂ is considered a promising material for electronic devices due to its better electrical properties than monolayer MoS₂. However, the uniform growth of bi-layer MoS₂ is still challenging. Herein, the uniform growth of bi-layer MoS₂ is demonstrated using gas-phase alkali metal-assisted metal–organic chemical vapor deposition (GAA-MOCVD). Thanks to enhanced metal reactant diffusion length in GAA-MOCVD, the uniform growth of bi-layer MoS₂ film is achieved even at fast nucleation kinetics for a shorter growth time compared to previously reported MOCVD. The bi-layer MoS₂ field-effect transistors (FETs) show superior electrical properties such as sheet conductance and electron mobility than monolayer MoS₂ FETs. The electron mobility of bi-layer MoS₂ FETs with bismuth contacts reaches a maximum of 92.35 cm² V⁻¹ s⁻¹. Using the partially grown epitaxial bi-layer (PGEB) MoS₂, it is demonstrated that a photodetector showed a near-infrared photoresponse with a low dark current that is advantageous for both monolayer and bi-layer applications. The potential expansion of the growth technique to layer-by-layer growth can result in boosted performance across a wide spectrum of electronic and optoelectronic devices employing MoS₂.