Stacking monolayers at will: A scalable device optimization strategy for two-dimensional semiconductors

In comparison to monolayer (1L), multilayer (ML) two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) exhibit more application potential for electronic and optoelectronic devices due to their improved current carrying capability, higher mobility, and broader spectral response. However, the investigation of devices based on wafer-scale ML-TMDs is still restricted by the synthesis of uniform and high-quality ML films. In this work, we propose a strategy of stacking MoS2 monolayers via a vacuum transfer method, by which one could obtain wafer-scale high-quality MoS2 films with the desired number of layers at will. The optical characteristics of these stacked ML-MoS2 films (> 2L) indicate a weak interlayer coupling. The stacked ML-MoS2 phototransistors show improved optoelectrical performances and a broader spectral response (approximately 300-1,000 nm) than that of 1 L-MoS2. Additionally, the dual-gate ML-MoS2 transistors enable enhanced electrostatic control over the stacked ML-MoS2 channel, and the 3L and 4L thicknesses exhibit the optimal device performances according to the turning point of the current on/off ratio and the subthreshold swing.