Highly Suppressed Dark Current and Fast Photoresponse from Au Nanoparticle-Embedded, Si/Au/WS2 Quantum-Dot-Based, Self-Biased Schottky Photodetectors

Two-dimensional semiconductor-based heterojunction photodetectors with ultralow dark current and fast photoresponse are highly desirable for cutting-edge optoelectronic applications. Herein, we study the role of embedded plasmonic Au nanoparticles (NPs) in the photoresponse characteristics of heterojunction photodetectors (PDs) consisting of n-type WS2 quantum dots (QDs) decorated on a p-type Si substrate. The Si/WS2 photodetector without the Au NPs has a fast response/recovery time of ∼55.1/139.8 μs and a photocurrent-to-dark current ratio (Ion/Ioff) of ∼227. By integrating the Au NPs sandwiched between the Si/WS2 QD junctions, the device showed outstanding photodetection performance compared to the Si/WS2 PD. The Si/Au/WS2 Schottky heterojunction device exhibits an astounding Ion/Ioff ratio of ∼1.3 × 105 due to the decrease in the dark current by about 2 orders of magnitude as well as an increase in photocurrent by about 1 order of magnitude and significantly faster rise/fall times of ∼4.4/43.5 μs. The underlying mechanism behind the ultralow dark current and high on/off ratio is investigated in detail. The faster photoresponse is attributed to hot electron transfer as well as carrier tunneling from Au NPs to WS2 QDs. The peak responsivity and detectivity of the fabricated Si/Au/WS2 detector are estimated at ∼276 A/W and ∼4.3 × 1013 Jones, respectively, at an applied bias of 5 V and under 405 nm illumination. Notably, both the devices function as self-powered PDs. Moreover, the Au NP-incorporated hybrid system exhibits an ∼6-fold enhancement in the photoluminescence (PL) as compared to bare WS2 QDs owing to the surface plasmon resonance. We use a theoretical model to calculate the field enhancement factor in the vicinity of WS2 QDs due to the Au NPs and show that the experimental data match very well with the theoretical value at the chosen excitation wavelength. These results indicate that integrating plasmonic nanoparticles with the Si/WS2 QD PD holds great potential for applications in future high-performance optoelectronic devices.