Extensive research has been conducted on the negative differential resistance (NDR) behavior in various electronic applications. Theoretical simulations suggest that defects in monolayer 2D materials could impact the NDR phenomenon. In this study, we experimentally validated this theoretical prediction using straightforward fabrication methods on monolayer MoS2. To create MoS2 transistors with a specific amount of sulfur vacancy, we employed techniques such as KOH solution treatment, electron beam irradiation, and chemical vapor deposition (CVD) using low sulfur supply. Through comprehensive analysis of the devices' electrical characteristics and spectroscopic examination, we successfully observed the NDR in the defective monolayer MoS2 field-effect transistors (FETs) with approximately 5% sulfur vacancy, as confirmed by x-ray photoelectron spectroscopy (XPS). Moreover, this NDR effect remains stable and can be controlled by the gate electric field or light intensity at room temperature. This discovery suggests that the NDR effect in monolayer MoS2 transistors holds promising potential for future electronic applications.
The effects of the peculiar in-plane lattice vibrations in monolayer molybdenum disulfide (MoS2) are oftentimes ignored in the analysis of the material’s lattice behaviors due to the lack of variation of polarization for the excitation light. In this work, we have observed variations in the relative intensity of the two most dominant Raman peaks of MoS2 via polarized micro-Raman spectroscopy using elliptically polarized incident light. The asymmetry of the incident excitation light gives an additional degree of freedom affecting the relationship between the x- (E12gx) and y- (E12gy) components of the material’s in-plane lattice vibrations. Different ratio of the magnitudes for E12gx and E12gy in the lattice vibrations can be induced by changing the polarization state of the incident light. This work investigates the material’s unexplored fundamental phonon property which may enlighten past and future studies involving phonon behaviors.
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