Photoconductivity flipping in pure and plasmon-activated 2-dimensional graphene and MoS2 based hybrid photodetectors

Digvijay Singh Tomar^1*, Surojit Chattopadhyay¹

¹Institute of Biophotonics, National Yang Ming Chiao Tung University, Taipei, Taiwan

* Presenter:Digvijay Singh Tomar, email:dyrllr@gmail.com

This work focuses on the performance of photodetectors (PDs) constructed using single-layer graphene on a SiO2/Si substrate. The fabrication process entails thermal evaporation of silver electrodes onto the substrate, succeeded by the deposition of MoS2 and gold nanorods (AuNRs). These PDs exhibit a positive photoresponsivity (R), which is enhanced with the incorporation of chemically exfoliated MoS2. However, the introduction of plasmonic AuNRs into the MoS2/graphene PDs reverses the photoconductivity to negative. This negative photoresponse is attributed to increased dark current in a complex conductive network and reduced photocurrent due to electron capture by the AuNRs within the AuNRs/MoS2/graphene PDs. The dynamic photoresponses are elucidated through a model based on carrier transport within individual components. The graphene PD device, known for its moderate speed, achieves a peak R of 2 × 104 A W−1 at 808 nm. The incorporation of exfoliated MoS2 nanoflakes slightly improves the R to ∼3 × 104 A W−1 but at the expense of a slower response time, which increases from ∼90 ms to 558 ms. The introduction of AuNRs reduces the response time to 20.5 ms in the AuNRs/MoS2/graphene PDs but also induces a distinct negative photoresponse due to the increased dark current. This study proposes a unified mechanism to elucidate the observed positive and negative photoresponses in these hybrid PDs.

Keywords: Graphene, MoS2, Goldnanorods, Photodetector, Negative photoconductivity