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

Abstract

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 (I on/I off) 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 I on/I off 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.

Ultrafast and Ultrabroadband UV–vis-NIR Photosensitivity under Reverse and Self-Bias Conditions by n+-ZnO/n-Si Isotype Heterojunction with >1 kHz Bandwidth

“…Sublinear photocurrent increase indicates the presence of traps and recombination centers which is quite expected for such a heterojunction. 53,54 As we have observed from Figure 3b the photocurrent at 0 V is not zero which indicates that the n + -ZnO/n-Si heterojunction can also detect optical signal without any external bias (power saving mode). Under the self-powered condition, the photocurrent spectrum has been measured and the photocurrent and responsivity spectrum presented in Figure 9a, clearly demonstrate that the device has a broadband photoresponse from UV to NIR under the self-bias condition with the highest R λ values of 12.7 mA/W at 870 nm.…”

“…As the value of α lies between 0.5 to 0.7, the photocurrent increases sublinearly with the illumination intensity for all wavelengths. Sublinear photocurrent increase indicates the presence of traps and recombination centers which is quite expected for such a heterojunction. , …”

Fast detection of Staphylococcus aureus using thiol-functionalized WS2 quantum dots and Bi2O2Se nanosheets hybrid through a fluorescence recovery mechanism

“…To check the attachment of the aptamers to the WS2 QDs, we have acquired the core level spectra corresponding to phosphorus 2p from the WS 2 QDs and WS 2 QDs/Aptamer , respectively, and this is associated with the W 4+ oxidation state, which confirms the semiconducting 2H-phase of the WS 2 QDs. 70 Along with the semiconducting 2H-phase, we have observed two low energy peaks at 32.2 eV and 34.4 eV, corresponding to the metallic 1T-phase. 71 In addition, we observed two high energy peaks at 36.0 eV and 38.2 eV, corresponding to the 6 + oxidation state of tungsten, indicating the presence of surface oxidized WS 2 QDs.…”

A fully printed ultrafast Si/WS2 quantum dot photodetector with very high responsivity over the UV to near-infrared region

“…An elegant and insightful way to understand the superior photodetection mechanism in a heterojunction photodetector is through a band diagram that illustrates the relative positions of the Fermi levels of two materials, in this case, n-WS 2 and p-Si, 24 as shown in Fig. 7a.…”

“…However, QDs exhibit poor carrier transport compared to conventional semiconductors, which significantly reduces the effectiveness and performance of photodetectors. But heterostructures and composites based on WS 2 quantum dots have demonstrated excellent photodetection performance 23,24 compared to the pristine material, thus providing an avenue to overcome the shortcomings of QDs.…”