Enhanced responsivity of a graphene/Si-based heterostructure broadband photodetector by introducing a WS2 interfacial layer

Photodetectors based on two-dimensional/three-dimensional (2D/3D) semiconducting heterostructures have attracted tremendous attention in recent years due to their novel performance. Here, we found that the photodetection performance of the graphene (Gr)/Si 2D/3D heterostructure can be very broadly enhanced by introducing an optimized ultrathin WS2 film prepared by sulfidation as an interfacial layer. The fabricated Gr/WS2(10.9 nm)/Si photodetector shows a wide spectralresponse from 400 to 1800 nm with a maximum photoresponsivity of 8.96 x 10(4) A W-1 and photodetectivity of 8.86 x 10(11) Jones at 690 nm, which are more than three orders of magnitude higher than that of the Gr/Si photodetector. Such a high photoresponsivity can be attributed to the strong photogain induced by the hole trap states that exist in the WS2 film. With the increase in the WS2 film thickness, the photoresponsivity increases firstly owing to the increase of hole trap states, and then decreases due to the decrease in light transmittance through WS2. The device also shows a high responsivity of 0.735 A W-1 at 1550 nm by forming type-II interlayer excitation. Our results indicate that 2D transition metal dichalcogenides (TMDCs) could be a good candidate functioning as an interfacial layer for high performance Gr/Si photodetectors, which provide a facile way for enhancing the photodetection performance of van der Waals 2D/3D heterostructure photodetectors.