Centimeter-Scale CVD Growth of Highly Crystalline Single-Layer MoS2 Film with Spatial Homogeneity and the Visualization of Grain Boundaries

Abstract

MoS₂ monolayer attracts considerable attention due to its semiconducting nature with a direct bandgap which can be tuned by various approaches. Yet a controllable and low-cost method to produce large-scale, high-quality, and uniform MoS₂ monolayer continuous film, which is of crucial importance for practical applications and optical measurements, remains a great challenge. Most previously reported MoS₂ monolayer films had limited crystalline sizes, and the high density of grain boundaries inside the films greatly affected the electrical properties. Herein, we demonstrate that highly crystalline MoS₂ monolayer film with spatial size up to centimeters can be obtained via a facile chemical vapor deposition method with solid-phase precursors. This growth strategy contains selected precursor and controlled diffusion rate, giving rise to the high quality of the film. The well-defined grain boundaries inside the continuous film, which are invisible under an optical microscope, can be clearly detected in photoluminescence mapping and atomic force microscope phase images, with a low density of ∼0.04 μm^-1. Transmission electron microscopy combined with selected area electron diffraction measurements further confirm the high structural homogeneity of the MoS₂ monolayer film with large crystalline sizes. Electrical measurements show uniform and promising performance of the transistors made from the MoS₂ monolayer film. The carrier mobility remains high at large channel lengths. This work opens a new pathway toward electronic and optical applications, and fundamental growth mechanism as well, of the MoS₂ monolayer.

Keywords: chemical vapor deposition; continuous film; grain boundary; grain size; high crystallinity; molybdenum disulfide.