**3.4 The operational mechanism**

In order to study the potential mechanism of our fabricated photodetector, we simulated the electric field distribution of Au decorated MoS2 using finite element method in the infrared region. We assumed that the Au NPs with a gap of 6 nm and a diameter of 5 nm under illumination of a linearly polarized plane wave with an electric field amplitude of 1 Vm<sup>−</sup><sup>1</sup> for the simulated model. And the thicknesses of MoS2 sheet and incident laser wavelength were 6 and 980 nm, respectively. **Figure 10a**, **b** shows the cross-section of the simulated electric field distribution of Au NPs decorated MoS2. Benefiting from the LSPR effect excited by the Au NPs, when the diameter matched to the incident wavelengths, the intensities of electric field at interfaces of air/Au/MoS2, up to ~3.96 × 105 V/m, are obviously higher than other districts. In comparison, interfaces of air/MoS2 show a poor intensity of electric field, only about 6.72 × 104 V/m. This tendency can be also observed in the recent researches of Au NPs guided MoS2 sheets for photo-detection [30]. We further experimentally proved the absorption by using UV-visible-NIR spectroscopy analysis. **Figure 10c** shows the absorption spectrum of bare MoS2 sheet Au NPs decorated MoS2. The normalized absorptance plots indicate that the Au NPs/MoS2 is obviously enhanced than that of bare MoS2 ranging from 700 to 1600 nm.

The above results and discussion clearly unveil the introduction of Au NPs plays a key role in enhancing the light matter interactions of MoS2 with infrared wavelengths. The significantly improved sensitivity of the fabricated photodetector could be attributed to the LSPR effect, shown in **Figure 10d**, induced by the periodically aligned Au NPs, resulting in obvious improvement of local electric field. When the incident infrared wavelengths highly confined by the deposited Au NPs, the local electric field at the interface of Au/MoS2 is greatly improved by the surface plasmon waves. Firstly, the Au surface plasmons effectively excite a

#### **Figure 10.**

*Cross-section of the simulated electric field distribution for (a) Au NPs/MoS2 sensing layer and (b) air/ Au/MoS2 interfaces. (c) Absorptance plots of bare MoS2 sheet and Au NPs decorated MoS2 using sputtering method. The solid and dashed lines correspond to the experimental and fitted results, respectively. (d) Schematic representation for the operational mechanism of the fabricated Au NPs/MoS2 device [23].*

**91**

*Simple Preparations for Plasmon-Enhanced Photodetectors*

coupling effect at the interface of Au/MoS2 for absorbing photons, yielding a much more photo-induced carriers to improve the photo sensing [30, 31]. Moreover, the additional local electric field generated by the LSPR effect of Au NPs accelerates the photogenerated carriers to separate for producing photocurrent [32, 33]. This facile method, tuning Au NPs by sputtering method to excite LSPR effect for fabricating the unique device structure, is expected to be practical applications in other 2D materials such as WS2 and MoSe2 [34–36], thus offers a new route on a variety of

High performance photodetectors are very important in a lot of applications. We have successfully developed two simple methods to prepare plasmon-enhanced photodetectors. (i) Au nanoparticles (Au NPs) solution were directly spun coated onto the WS2-based photodetectors. The performance has been enhanced by the LSPR of Au NPs, and reached an excellent high responsivity of 1050 A/W at the wavelength of 590 nm. (ii) Au NPs were deposited on MoS2 by magnetron sputtering. The spectral response of pure MoS2 was located in visible light and which was extended to near-infrared region (700–1600 nm) by Au NPs. Further, the responsivity reaching up to 64 mA/W when the incident light is 980 nm. These photodetectors achieved excellent responsivity and response speed. The results not only promote the development of high-performance photodetectors, but also provide a

simplified method for the fabrication of other hybrid structure devices.

The project was supported by grants from the National Basic Research Program

of China (No. 2015CB351905), the National Key Research and Development Program of China (No. 2016YFA 0302300, No. 2016YFA0200400), the National

Natural Science Foundation of China (No. 61306105).

The authors declare no conflict of interest.

*DOI: http://dx.doi.org/10.5772/intechopen.89251*

high-performance optoelectronic devices.

**4. Conclusion**

**Acknowledgements**

**Conflict of interest**

*Simple Preparations for Plasmon-Enhanced Photodetectors DOI: http://dx.doi.org/10.5772/intechopen.89251*

coupling effect at the interface of Au/MoS2 for absorbing photons, yielding a much more photo-induced carriers to improve the photo sensing [30, 31]. Moreover, the additional local electric field generated by the LSPR effect of Au NPs accelerates the photogenerated carriers to separate for producing photocurrent [32, 33]. This facile method, tuning Au NPs by sputtering method to excite LSPR effect for fabricating the unique device structure, is expected to be practical applications in other 2D materials such as WS2 and MoSe2 [34–36], thus offers a new route on a variety of high-performance optoelectronic devices.
