Principal Investigator Jing Kong
Two-dimensional transition metal dichalcogenides (2-D TMDs) have shown great promise to be an ideal candidate for post-silicon technology. Their atomic thicknesses and large carrier effective masses can offer excellent electrostatic gate control, a reduced source-to-drain leakage current, and a higher on-current in the ballistic regime, potentially enabling ultra-scaled devices, tunnel field-effect transistors, and ballistic transistors. However, the intricacy and diversity of the structural defects in 2-D TMDs significantly affect their electrical and optical properties, in either beneficial or detrimental ways. In the case of monolayer MoS2, several challenging issues including Femi level pinning at metal/MoS2 interface, unintentional n-type doping, and carrier scatterings, non-radiative excitonic recombinations, etc., have been attributed to a considerable amount of sulfur vacancy in monolayer MoS2.
On the other hand, specific types of defects, if controlled carefully, also offers the access to engineer the nature of monolayer MoS2, such as channel polarity modification for realization of low-power MoS2– based CMOS integrated circuits, exciton reservoirs to prolong the excitonic lifetime for high-performance optoelectronic and photonic devices.
This work explores the correlation between the domain geometries and the presence of different types of defects in monolayer MoS2 synthesized by chemical vapor deposition through transport and spectroscopy measurements. We show that the shapes of MoS2 domain can modulate the photoluminescence intensity and work function of MoS2 monolayers and the threshold voltage in the MoS2 field-effect transistors. Based on a two-defect-state model, the geometry-modulated behavior can be explained. This work not only offers a strategy to engineer the nature of MoS2 from the synthesis perspective, but also pave a path to realize low-power MoS2 CMOS integrated circuits.