Tungsten diselenide (WSe<sub>2</sub>) is an interesting two dimensional (2D) transitional metal dichalcogenide (TMDC) with a high quantum yield in photoluminescence (PL), a strong spin-orbit coupling and tunable transport properties. One way to increase photon absorption in WSe<sub>2</sub> is to combine WSe<sub>2</sub> with other excitonic nanomaterials such as Quantum dots (QDs) from which photogenerated excitons can be transferred onto the TMDCs via non-radiative energy transfer. Such characteristics prove highly effective in the utilization of QDs toward enhancing the optical responsivity of 2D material-based photo-FET devices. In this study, we fabricated WSe<sub>2</sub> based photodetector and showed that its photoconduction property was improved by incorporation of Au-QDs. Monolayer WSe<sub>2</sub> was synthesized on SiO<sub>2</sub>/Si by low pressure chemical vapor deposition method at a growth temperature of ~ 850°C. Thereafter, Au-QDs (~15 nm) were drop casted onto WSe<sub>2</sub> followed by vacuum annealing. PL spectroscopy showed enhancement in excitonic A-peak intensity by an order of 2-fold in the region where Au QD was incorporated. E-beam lithography was used to fabricate the back gated photo transistor followed by Au/Ti deposition by E-beam evaporation. The device was illuminated with a red laser source (660 nm) to study its optoelectronic properties. The photoresponsivity was found to improve by a factor of ~102 with the incorporation of Au QDs in 1L WSe<sub>2</sub>. Our results demonstrate the viability of this hybrid structure for commercial photodetector and light harvesting applications.
Broadband photodetection is crucial for various defense and scientific applications such as biomedical imaging, communications, and environmental and spectral monitoring. In recent years, transition metal dichalcogenide semiconductors, from the two-dimensional layered materials family, have attracted special attention for their application in photodetection due to their outstanding optoelectronic properties and large optical absorbance for their atomically thin thicknesses. Here, we present a CVD-synthesized MoS<sub>2</sub> phototransistor with Au/Ti contacts enhanced by Au nanoparticles via surface nanoplasmonics. From electronic and optoelectronic characterizations, intrinsic device parameters were extracted and analyzed including the field-effect mobility of 37.4 cm<sup>2</sup>V<sup>-1</sup>s<sup>-1</sup>, a high ON/OFF ratio of 10<sup>6</sup>. Next, the optoelectronic characterization was carried out before and after Au nanoparticles using a tunable laser with a wavelength absorption range from 400 nm to 1100 nm under vacuum conditions. The spectral photoresponse was improved from a cutoff wavelength of ~ 975 nm before the Au nanoparticles to a broadband spectral detection with a minimum standard deviation of 0.56 μA at from near-ultraviolet to near-infrared and a maximum photocurrent of 7.61 μA at an incident optical power density of ~ 2 μWcm<sup>-2</sup>. In addition, the photocurrent has been increased 5-fold after decorating the MoS<sub>2</sub> photodetector with Au nanoparticles. The improvement of the light-matter interaction of MoS<sub>2</sub> nanosheet, described before, is attributed to the localized surface plasmon in gold nanoparticles.