Gold Nanorod-Activated Graphene/MoS2 Nanosheet-Based Photodetectors for Bidirectional Photoconductance

Graphene and its nanohybrid photodetectors (PDs) offer unique interfacial and synergistic properties in contrast to conventional semiconductor-based PDs. In this work, we compare the performance of identically fabricated PDs based on pure chemical vapor deposition-grown monolayer graphene, demonstrating a positive photoresponse, that exhibits a gain in photoresponsivity (R) with the addition of two-dimensional MoS2 (chemically exfoliated). However, further addition of plasmonic gold nanorods (AuNRs), on the MoS2/graphene PD, results in the flipping of the photoconductivity to negative. The negative photoresponse is explained by an increased dark current via the complex conductive network model and a lower photocurrent due to the photogenerated electron capture by the AuNRs in the AuNRs/MoS2/graphene PD. The contrasting shape and nature of the dynamic photoresponses are modeled using theoretical fitting and explained based on carrier transport in individual components. The highest R in the moderately fast graphene PD device is similar to 2 x 10(4)A W-1 under 808 nm which could be slightly improved to similar to 3 x 10(4)A W-1 by introducing MoS2 nanoflakes, albeit at the cost of the response time which slows down from similar to 90 ms (in the former) to 558 ms in the latter. The introduction of AuNRs did speed up the response time in the AuNRs/MoS2/graphene PD to 20.5 ms but produced a strikingly different negative photoresponse attributed to a higher dark current in the material. We proposed a single mechanism to explain the positive and negative photoresponses reported so far for the hybrid PDs.