Plasmon induced thermoelectric effect in graphene

Vincenzo Giannini,Xiaofei Xiao,Lesley F. Cohen,Nicholas A. Güsken,Stefan A. Maier,Nicola C. G. Black,Rupert F. Oulton,Adam M. Gilbertson,Viktoryia Shautsova,Themistoklis Sidiropoulos

doi:10.1038/s41467-018-07508-z

Abstract

Graphene has emerged as a promising material for optoelectronics due to its potential for ultrafast and broad-band photodetection. The photoresponse of graphene junctions is characterized by two competing photocurrent generation mechanisms: a conventional photovoltaic effect and a more dominant hot-carrier-assisted photothermoelectric (PTE) effect. The PTE effect is understood to rely on variations in the Seebeck coefficient through the graphene doping profile. A second PTE effect can occur across a homogeneous graphene channel in the presence of an electronic temperature gradient. Here, we study the latter effect facilitated by strongly localised plasmonic heating of graphene carriers in the presence of nanostructured electrical contacts resulting in electronic temperatures of the order of 2000 K. At certain conditions, the plasmon-induced PTE photocurrent contribution can be isolated. In this regime, the device effectively operates as a sensitive electronic thermometer and as such represents an enabling technology for development of hot carrier based plasmonic devices.

Highlights

Graphene has emerged as a promising material for optoelectronics due to its potential for ultrafast and broad-band photodetection
We report an additional but distinct PTE contribution, where a global electronic temperature difference is established across the device channel (ΔTech) itself, which we will refer to as the PTE channel (PTE-ch) effect to distinguish it from the known PTE-j effect
While the temperature profile is sensitive to the input parameters in the model, the results suggest that the carrier temperature at the nonplasmonic contact T0 remains at Tbath ~ 300 K for a wide range of cooling lengths of 0.2–1 μm, which are typical values for graphene observed at room temperature[22,23]

Summary

Introduction

Graphene has emerged as a promising material for optoelectronics due to its potential for ultrafast and broad-band photodetection. The dependence of the PTE-j current on ΔS results in multiple photocurrent sign reversals over a gate voltage sweep due to the nonmonotonic dependence of S1,2 on EF (Fig. 1b for the case of the graphene–metal junction) This is distinct from the PV effect, in which the photovoltage, VPV is related to ΔEF and a single sign change is observed at the flat-band point (Fig. 1b top panel), allowing the PTE-j effect to be identified. The electronic temperature gradient across the channel may, in principle, be present when only one side of the metal–graphene–metal device is illuminated Studies of these graphene photodetectors to date have typically reported carrier temperature increases of just a few degrees Kelvin or less[5,15] so that the contribution from VPTE-ch was negligible compared to VPV or VPTE-j

Methods

Results

Conclusion