Controlled Growth of Bilayer-MoS2 Films and MoS2-Based Field-Effect Transistor (FET) Performance Optimization

The effect of hydrogen flow on MoS2 film synthesis via chemical vapor deposition is studied systematically. Large-sized monolayer- and bilayer-MoS2 triangles can be synthesized controllably at given temperatures. Optical microscopy, Raman spectroscopy, photoluminescence spectroscopy, and atomic force microscopy are used to characterize the number of layers, purity, and uniformity of the MoS2 triangle films. Moreover, the back-gated field-effect transistors (FETs) based on the monolayer- and bilayer-MoS2 channels are fabricated using traditional micro-nanoprocessing technology. Electrical behaviors are investigated and the bilayer-MoS2 FETs show preferable performance with high mobility (approximate to 21 cm(2) V-1 s(-1)), on-current (approximate to 22 mu A mu m(-1)), and a small degradation in the on/off ratio (1.1 x 10(7)). Finally, the semiconductive phase MoS2 (2H-MoS2) is transformed to a metallic phase (1T-MoS2) to reduce the resistance in metal-MoS2 contact. The FET device with 1T-MoS2 contact enhances mobility (approximate to 45 cm(2) V-1 s(-1)) and on-current (approximate to 50 mu A mu m(-1)) compared with the 2H-MoS2 FETs. This work sheds light on the synthesis of variable-layer MoS2 films and paves the way for further development regarding MoS2 film-based devices.