Unraveling the Mechanism of Interfacial Charge Transfer and Photoresponsivity of WS Quantum Dots/MoS (0D-2D) Heterostructure-Based Transistors.

To assess the efficacy of a mixed-dimensional van der Waals (vdW) heterostructure in modulating the optoelectronic responses of nanodevices, the charge transport properties of the transition-metal dichalcogenide (TMD)-based heterostructure comprising zero-dimensional (0D) WS quantum dots (QDs) and two-dimensional (2D) MoS flakes are critically analyzed. Herein, a facile strategy was materialized in developing an atomically thin phototransistor assembled from mechanically exfoliated MoS and WS QDs synthesized using a one-pot hydrothermal route. The amalgamated photodetectors exhibited a high responsivity of ∼8000 A/W at an incident power of 0.05 nW of white light, surpassing that of the pristine MoS devices. Furthermore, the detectivity of pristine MoS, which was on the order of 10, increased to 10 Jones for the WS QDs/MoS heterostructure photodetector, outperforming other WS-based materials. The quasiparticle band gap and density of states (DOS) are further analyzed to elucidate the photophysics of the WS QD/MoS hybrid assembly. The difference in the work function between MoS and WS QDs gives rise to an electric field across the 0D-2D interface, facilitating effective charge separation and migration and contributing to the enhancement of photoresponsivity. The analysis of optical responses using density functional theory (DFT) revealed stronger absorption and less reflection over a broader spectrum of wavelengths for the heterostructure compared to the pristine materials. The estimated optical conductivity aligns well with the experimentally predicted maximum photoresponsivity under visible light, which is attributed to the high absorbance of 2D MoS. Combining diverse spectroscopic and imaging techniques with quantum simulation provides insights that clarify the pertinence of 0D-2D TMDs in designing phototransistors.